30 The Human Body - Savvas

32043_7TX_Bio_Ch30.pdf

The Human Body

The systems of the body enable these swimmers to

move through the water. 858

THE TELLTALE SAMPLE

On the first day of summer football practice,

all players were required to have a physical.

Each student was handed a plastic cup and

directed to the rest room. "Please provide me with a sample," the physician requested. Most of the athletes had no idea how much could be learned about their health and behavior from a urine sample. Immediately after handing over their samples, Philip and Seth were sent home and told to drink plenty of water before their next practice and to submit new samples then. The next day, Andrew was told to see his family physician because he could have diabetes. Several days later, another student was dropped from the team for violating the school's antidrug policy. How was all of this information gained from a urine sample? Look for clues throughout the chapter to help you discover what can be learned about the body by simply examining what leaves it. Then, solve the mystery.

Never Stop Exploring Your World.

Finding the solution to the Telltale Sample mystery is only the beginning. Take a video field trip with the ecogeeks of

Untamed Science to see where this mystery leads.

TEKS F O C U S O N 10A

Texas Essential Knowledge and Skills

READINESS TEKS: 4C Compare the structures of viruses to cells, describe viral reproduction, and describe the role of viruses in causing diseases such as human immunodeficiency virus (HIV) and influenza. 10A Describe the interactions that occur among systems that perform the functions of regulation, nutrient absorption, reproduction, and defense from injury or illness in animals. SUPPORTING TEKS: 10C Analyze the levels of organization in biological systems and relate the levels to each other and to the whole system.

11A Describe the role of internal feedback mechanisms in the maintenance of

homeostasis.

The Human Body 859

Organization of the

Human Body

Key Questions

How is the human body

organized?

What is homeostasis?

Vocabulary

epithelial tissue connective tissue nervous tissue muscle tissue homeostasis feedback inhibition

Taking Notes

Preview Visuals Examine

Figure 30 -2. For each system,

describe how you think it interacts with at least one other system.

Organization of the Body

How is the human body organized?

Every cell in the human body is both an independent unit and an interdependent part of a larger community - the entire organism. To complete a successful play, a player at �rst base has to use her eyes to watch the ball and use her brain to �gure out how to position her body. With the support of her bones, muscles move her body to �rst base. Meanwhile, the player's lungs absorb oxygen, which her blood carries to cells for use during cellular respiration. Her brain monitors the location of the ball and sends signals that guide her glove hand to make the catch. How can so many individual cells and parts work together so e�ciently? One way to answer this question is to study the organiza- tion of the human body. ?e levels of organization in the body include cells, tissues, organs, and organ systems. At each level of organization, these parts of the body work together to carry out the major body functions. Cells A cell is the basic unit of structure and function in living things. As you learned in Chapter 7, individual cells in multicellular organisms tend to be specialized. Specialized cells, such as bone cells, blood cells, and muscle cells, are uniquely suited to perform a particular function. Tissues A group of cells that perform a single function is called a tissue. �ere are four basic types of tissue in the human body - epithelial, connective, nervous, and muscle. Figure 30-1 shows examples of each type of tissue.

THINK ABOUT IT ?e batter slaps a ground

ball to the shortstop, who �elds it cleanly and throws the ball toward your position - �rst base. In a single motion, you extend your glove hand, catch the ball, and extend your foot to touch the edge of the base.

An easy out, a routine play. But think

about how many systems of your body are involved in making this type of "routine" play. How do they all work together? 30.1

In this lesson you will learn about the organization of the human body (TEKS 10C) as well as how the systems of the

body work together to maintain homeostasis (TEKS 11A). TEKS 10C 860

FUNCTIONS

LOCA TIONS Epithelial TissueConnective TissueNervous TissueMuscle Tissue

Protection, absorption, and

excretion of materials

Binding of epithelial tissue to

structures, support, and transport of substances

Receiving and transmitting

nerve impulses

Voluntary and involuntary

movements

Skin, lining of digestive

system, certain glands

Under skin, surrounding

organs, blood, bones

Brain, spinal cord, and

nerves

Skeletal muscles, muscles

surrounding digestive tract and blood vessels, the heart

LM 65�LM 280�SEM 295�LM 275�

fi epithelial Tissue �e tissue that lines the interior and exterior body�surfaces is called epithelial tissue. Your skin and the lining of your stomach are both examples of epithelial tissue. fi Connective Tissue A type of tissue that provides support for the body and connects its parts is connective tissue. �is type of tissue includes fat cells, bone cells, and even blood cells. Many connective tissue cells produce collagen, a long, tough �ber-like protein that is the most common protein in the body. Collagen gives tissues strength and resiliency, helping them to keep their shape even under pressure. fi Nervous Tissue Nerve impulses are transmitted throughout the body by nervous tissue. Neurons, the cells that carry these impulses, and glial cells, which surround and protect neurons, are both examples of nervous tissue. fi Muscle Tissue Movements of the body are possible because of muscle tissue. Some muscles are responsible for the movements you control, such as the muscles that move your arms and legs. Some mus- cles are responsible for movements you cannot control, such as the tiny muscles that control the size of the pupil in the eye. Organs A group of di�erent types of tissues that work together to perform a single function or several related functions is called an organ. �e eye is an organ made up of epithelial tissue, nervous tissue, muscle tissue, and connective tissue. As di�erent as these tissues are, they all work together for a single function - sight. Organ Systems An organ system is a group of organs that perform closely related functions. For example, the brain and spinal cord are organs of the nervous system. �e organ systems interact to maintain homeostasis in the body as a whole. �e organ systems, along with their structures and main functions, are shown on the next page.

FIGURE 30 -1 Types of Tissues

The four major types of tissues in the

human body are epithelial tissue, connective tissue, nervous tissue, and muscle tissue. Predict Which organ may not contain all four types of tissue?

The Human Body 861

Nervous

System

Integumentary

System

Immune/

Lymphatic Systems

Skeletal muscle,

smooth muscle, cardiac muscle

Works with

skeletal system to produce voluntary movement; helps to circulate blood and move food through the digestive system

Heart, blood

vessels, blood

Transports

oxygen, nutrients, and hormones to cells; fights infection; removes cell wastes; helps to regulate body temperature

White blood cells,

thymus, spleen, lymph nodes, lymph vessels

Helps protect

the body from disease; collects fluid lost from blood vessels and returns it to the circulatory system

Skin, hair, nails,

sweat and oil glands

Guards against

infection and injury and ultraviolet radiation from the sun; helps to regulate body temperature

Bones, cartilage,

ligaments, tendons

Supports the

body; protects internal organs; allows movement; stores mineral reserves; contains cells that produce blood cells

Brain,

spinal cord, nerves

Recognizes and

coordinates the body's response to changes in its internal and external environments

Muscular SystemCirculatory

System

Respiratory SystemDigestive SystemExcretory SystemEndocrine SystemReproductive System

Hypothalamus,

pituitary, thyroid, parathyroids, adrenals, pancreas, ovaries (in females), testes (in males)

Controls growth,

development, and metabolism; maintains homeostasis

Testes, epididymis,

vas deferens, urethra, and penis (in males); ovaries, Fallopian tubes, uterus, vagina (in females)

Produces gametes; in

females, nurtures and protects developing embryo

Nose, pharynx, larynx,

trachea, bronchi, bronchioles, lungs

Brings in oxygen needed

for cellular respiration and removes excess carbon dioxide from the body

Mouth, pharynx,

esophagus, stomach, small and large intestines, rectum

Skin, lungs, liver,

kidneys, ureters, urinary bladder, urethra

Eliminates waste

products from the body

Breaks down food;

absorbs nutrients; eliminates wastes

STRUCTURES

FUNCTIONS

STRUCTURES

FUNCTIONS

Skeletal System

HUMAN BODY SYSTEMS

FIGURE 30 - 2 Although each of the organ systems shown here has a different set of functions, they all work together, as a whole, to maintain homeostasis. 862

Thermostat senses

temperature change and turns heating system on or off.

Room temperature

increases.

Room temperature

decreases. ONOFF

BUILDVocabulary

Homeostasis

What is homeostasis?

Some things are easy to observe. When you run or swim or even write the answer to a test question, you can see your body at work. But behind the scenes, your body's systems are working constantly to do something that is di�cult to see and that few people appreciate - maintain ing a controlled, stable internal environment. �is stable environment is called homeostasis, which means "similar standing."

Homeostasis describes the relatively constant

internal physical and chemical conditions that organ- isms maintain despite changes in internal and external environments. Homeostasis may not be obvious, but for a living organ ism, it's literally a matter of life or death. Feedback Inhibition If you've ever watched someone driving a car down a relatively straight road, you may have noticed how the person constantly moves the wheel le� or right, adjusting direction to keep the vehicle in the mid- dle of the lane. In a certain sense, that's how the systems of the body work, too, keeping internal conditions within a certain range, and never allowing them to go too far to one side or the other. ? A Nonliving Example One way to understand homeo stasis is to look at a nonliving system that automatically keeps conditions within a certain range like a home heating system. In most homes, heat is supplied by a furnace that burns oil or natural gas. When the temperature within the house drops below a set point, a thermostat sensor switches the furnace on. Heat produced by the furnace warms the house. When the temperature rises above the set point, the thermostat switches the furnace o�, keeping the tempera- ture within a narrow range. A system like this is said to be controlled by feedback inhibition. Feedback inhibition, or negative feedback, is the process in which a stimulus produces a response that opposes the original stimulus. Figure 30-3 summarizes the feedback inhibition process in a home heating system. When the furnace is switched on, it produces a product (heat) that changes the environment of the house (by raising the air temperature). �is environmental change then "feeds back" to "inhibit" the operation of the furnace. In other words, heat from the furnace eventually raises the temperature high enough to trigger a feedback signal that switches the furnace o�. Systems controlled by feedback inhibition are generally very stable. Online Journal Describe another example of a nonliving system that requires constant adjustment.

Figure 30 - 3 Feedback Inhibition

A home heating system uses a feedback

loop to maintain a stable, comfortable environment within a house.

Interpret Diagrams What is the stimulus

in this feedback loop?

ACADEMIC WORDS The

noun inhibition means "the act of blocking the action of."

Therefore, feedback inhibition

refers to a response that blocks further actions of a stimulus. TEKS 11A

The Human Body 863

Cold environment

causes body temperature to decrease.

Body temperature

increases.

STARTSTOP

Hypothalamus senses temperature

change and sends signals that start or stop heat production.

Hypothalamus senses temperature

change and sends signals that start or stop cooling mechanisms.

Warm environment

and exercise cause body temperature to increase.

Body temperature

decreases.

STARTSTOP

?

A Living Example Could biological systems

achieve homeostasis through feedback inhibition? Absolutely. All that is needed is a system that regu- lates some aspect of the cellular environment and that can respond to feedback from its own activities by switching on or o� as needed. Such mechanisms are very common, not only in the human body, but in all forms of life.

One example is the maintenance of body tempera-

ture. �e body regulates temperature by a mechanism that is remarkably similar to that of a home heating system. You can follow body temperature regulation in Figure 30-4. A part of the brain called the hypo thalamus contains nerve cells that monitor both the temperature of the skin at the surface of the body and the temperature of organs in the body's core. If the nerve cells sense that the core temperature has dropped much below 37°C, the hypothalamus produces chemicals that signal cells throughout the body to speed up their activities. Heat produced by this increase in activity, especially cellular respiration, causes a gradual rise in body temperature, which is detected by nerve cells in the hypothalamus.

Have you ever been so cold that you began to

shiver? If your body temperature drops well below its normal range, the hypothalamus releases chemicals that signal muscles just below the surface of the skin to contract involuntarily - to "shiver." �ese muscle contractions release heat, which helps the body tem- perature to rise toward the normal range. If body temperature rises too far above 37°C, the hypothalamus slows down cellular activities to reduce heat production. �is is one of the reasons you may feel tired and sluggish on a hot day. �e body also responds to high temperatures by producing sweat, which helps to cool the body surface by evaporation.

You will receive a thermometer and three

beakers of water at the following temperatures:

25°C, 35°C, and 40°C. Develop a method to

keep the temperature of the 35°C water within one degree for a period of ��een minutes. You may use the contents of the other two beakers.

Analyze and Conclude

1. Compare and Contrast Compare this experi

ment to what happens in your own body during temperature regulation.

2. Interpret Visuals Make a feedback loop similar

to the ones in Figure 30 - 4 that shows how feedback mechanisms were involved in this activity.

Maintaining Temperature

Figure 30 - 4 Body Temperature Control In the human body, temperature is controlled through various feedback inhibition mechanisms. Infer Why do you think moving around on a cold day helps to keep you warm? TEKS 11A 864

1. a. Review What are the levels of organization in the

human body? b. Explain Describe the function of three organ sys- tems depicted in Figure 30 -2. c. Classify Compare the characteristics of two types of tissues. Identify parts of the body that contain these types of tissues.

2. a. Review What is homeostasis?

b. Explain What are two roles of the liver in maintaining homeostasis? c. Apply Concepts Do you think that feelings of hunger and fullness are an example of feedback inhibition? Explain.

3. Draw a Venn diagram to relate the

four basic levels of organization in the human body. Provide at least three examples for each level of organiza- tion. Hint: Your Venn diagram should have a nesting structure. One set of examples could be skin cells, epithelial tissue, skin, and the integumentary system. The Liver and Homeostasis ?e liver is technically part of the digestive system because it produces bile, which aids in the digestion of fats. However, it is also fair to say that the liver is one of the body's most important organs for homeostasis. For example, when proteins are broken down for energy, ammonia, a toxic by-product, is produced. �e liver quickly converts ammonia to urea, which is much less toxic. �e kidneys, as you will read a bit later, then remove urea from the blood. �e liver also converts many dangerous substances, including some drugs, into compounds that can be removed from the body safely. One of the liver's most important roles involves regulating the level of a substance we take almost for granted as something completely harmless - the simple sugar, glucose. Glucose is obtained from the foods we eat, and cells take glucose from the blood to serve as a source of energy for their everyday activities. Naturally, right a�er a meal, as the body absorbs food molecules, the level of glucose in the blood begins to rise. �at's where the liver comes in. By taking glucose out of the blood, it keeps the level of glucose from rising too much. As the body uses glucose for energy, the liver releases stored glucose to keep the level of the sugar from dropping too low. �e liver's role in keeping blood glucose levels within a certain range is critical. Too little glucose, and the cells of the nervous system will slow down to the point that you may lose consciousness and pass out. On the other hand, too much glucose gradually damages cells in the eyes, kidneys, heart, and even the immune system. Abnormally high levels of glucose are associated with a disease called diabetes. In diabetes, changes occur in either the pancreas or body cells that a�ect the cells' ability to absorb glucose. Diabetes, one of the fastest-growing health problems in the developed world, is the unfortunate result of failure of homeostasis with respect to blood glucose levels.

30.1 Review Key Concepts TEKS 10C, 11A

The Human Body 865

Eects of Digestive Enzymes

E�ect on FoodEnzymeActive Site

Mouth

Stomach

Small intestine

(released from pancreas) Small intestine

Salivary amylase

Pepsin

Pancreatic amylase

Trypsin

Lipase

Maltase, sucrase, lactase

Peptidase

Breaks down starches into disaccharides

Breaks down proteins into large peptides

Continues the breakdown of starches

Continues the breakdown of proteins

Breaks down fats

Breaks down remaining disaccharides into monosaccharides

Breaks down dipeptides into amino acids

FIGURE 30-5 Digestive enzymes

Human Body Systems I

Key Question

What are the structures and functions of the digestive system, excretory system, circulatory system, lymphatic system, and respiratory system?

Taking Notes

Outline Before you read, make

an outline of the major headings in the lesson. As you read, �ll in main ideas and supporting details for each heading. What are the functions of the digestive system? fie need for food presents every animal with at least two challenges - how to obtain it and how to convert that food into molecules the body can use. In humans and many other animals, this is the job of the digestive system. ��e digestive system converts food into small molecules that�can be used by the cells of the body. Food is pro- cessed by the digestive system in four phases - ingestion, digestion, absorption, and elimination. �e �rst step in the process is ingestion, the act of putting food into your mouth. Food in the digestive system is broken down in two ways - by mechanical and chemical digestion. Mechanical digestion is the physical breakdown of large pieces of food into smaller pieces. �ese smaller pieces can be swallowed and accessed by digestive enzymes. During chemical digestion, enzymes break down food into the small molecules the body can use. Some of the enzymes used in digestion are shown in Figure 30-5. Once food has been broken into small molecules, it can be absorbed by cells in the small intestine. From the small intestine, the molecules enter the circulatory system, which transports them throughout the body. �e digestive system can- not digest and absorb all the substances in food that enter the body. Some materials, such as cellulose, travel through the large intestine and are eliminated from the body as feces.

The Digestive System

30.2
TeKS 10A

In this lesson you will learn the structure and function of some human body systems (TeKS 10A) and how they work

together to maintain homeostasis (TeKS 11A). 866

Mouth Teeth tear and grind food

into small pieces. Enzymes in saliva kill some pathogens and start to break down carbohydrates. 1 minute

Esophagus The bolus travels from

the mouth to the stomach via the esophagus. Food is squeezed through by peristalsis. 2-3 seconds

Stomach Muscle contractions

produce a churning motion that breaks up food and forms a liquid mixture called chyme.

Protein digestion begins.

2-4 hours

Small Intestine Chyme is slowly

released into the small intestine.

Bile, which is made in the liver, is

released from the gallbladder into the small intestine and aids in fat digestion. Enzymes from the pan- creas and duodenum complete digestion. Nutrients are absorbed through the small intestine wall.

3-5 hours

Large Intestine The large intestine

absorbs water as undigested material moves through and is eliminated from the body. 10 hours-several days

Epiglottis

Bolus Liver

Pancreas

Gallbladder

The cardiac sphincter

closes after food passes into the stomach.

Glands in the stomach

lining release hydrochloric acid, pepsin, and mucus.

Large intestine

Salivary gland

Pharynx

1 2 3 4 5

SEM 340

THE DIGESTIVE SYSTEM

Figure 30-6 Food travels through many organs

as it is broken down into nutrients your body can use. The time needed for each organ to perform its role varies based on the type of food consumed.

The Human Body 867

Small Intestine

Circular folds

Villi

Epithelial

Capillaries

Vein

Artery

Lymph vessel

Microvilli

Villus

Absorption and Elimination

Once the small intestine has completed the digestive process, it's time to absorb nutrients. Most nutrients from food are absorbed through the walls of the small intestine. �e large intestine absorbs water and several vitamins and prepares waste for elimination from the body. Absorption From the Small Intestine A?er leaving the duodenum, chyme moves along the rest of the small intestine. By this time, most of the chemical digestion has been completed. �e chyme is now a rich mixture of small- and medium-sized nutrient molecules. �e small intestine's folded surface provides an enormous surface area for absorption of nutrients. Its �ngerlike projections, called villi (singular: villus), are covered with tiny projections known as microvilli, which absorb the nutrients. Figure 30-7 illustrates villi and microvilli. Nutrient molecules are then passed into the circulatory system. Sugars and amino acids pass into capillaries, while most fats and fatty acids are absorbed by lymph vessels. By the time chyme leaves the small intestine, most nutrients have been absorbed, leaving only water, cellulose, and other indigestible substances behind. Absorption From the Large Intestine When chyme leaves the small intestine, it enters the large intestine, or colon. �e large intes- tine gets its name due to its diameter, which is greater than the small intestine. �e primary function of the large intestine is to remove water from the material that is le�. Large colonies of bacteria pres- ent in the large intestine produce compounds that the body is able to absorb and use, including vitamin K. Elimination ?e concentrated waste material - feces - that remains a�er most of the water has been removed passes into the rectum and is eliminated from the body through the anus. When something happens that interferes with the removal of water by the large intestine, you usually become aware of it right away. If not enough water is absorbed, a condition known as diarrhea occurs. If too much water is absorbed, constipation occurs.

ABSORPTION IN THE SMALL

INTESTINE

Figure 30-7 The lining of the small

intestine consists of folds that are covered with tiny projections called villi. Within each villus there is a network of blood capillaries and lymph vessels that absorb and carry away nutrients. TEKS 10A 868

Urine is released

through a tube called the urethra.

The urinary bladder

stores urine until it is released from the body.

Ureters transport urine

from each kidney to the urinary bladder. Skin Lung Liver

Kidneys

TEKS 11A Structures of the Excretory System What is the principal role of the structures of the excretory system? fie chemistry of the human body is a marvelous thing. However, every living system, including the human body, produces chemical waste products, some of which are so toxic that they will cause death if they are not eliminated. Ammonia, one of the most toxic of these waste compounds, is produced when amino acids from proteins are used for energy. Ammonia is converted to a less toxic compound called urea, but it, too, must be elimi- nated from the body. �e process by which these metabolic wastes are eliminated is called excretion.

Excretion is one part of the many processes that

maintain homeostasis. �e excretory system, which includes the skin, lungs, liver, and kidneys, excretes metabolic wastes from the body. fie ureters, urinary blad- der, and urethra are also involved in excretion.

Figure 30-8 shows the major organs of excretion.

The Skin fie skin excretes excess water, salts, and a small amount of urea in sweat. By releasing sweat in very small amounts, this process eliminates wastes even when you may not think you're sweating.

The Lungs fie blood transports carbon dioxide,

a waste product of cellular respiration, from the body cells to the lungs. When you exhale, your lungs excrete carbon dioxide and small amounts of water vapor. The Liver fie liver plays many important roles in excretion. One of its principal activities is the con- version of dangerous nitrogen wastes into less toxic urea. Urea is then transported through the blood to the kidneys for elimination from the body. The Kidneys fie major organs of excretion are the kidneys, a pair of �st-sized organs located on either side of the spinal column near the lower back. �e kidneys remove excess water, urea, and metabolic wastes from the blood. �e kidneys produce and excrete a waste product known as urine. Ureters transport urine from the kidneys to the urinary bladder, where urine is stored until it is released through the urethra.

FIGURE 30-8 The Excretory

System The organs of the excretory

system include the skin, lungs, liver, kidneys, ureters, urinary bladder, and urethra.

The Human Body 869

To ureter

Collecting

duct Vein

Artery

Loop of

Henle

Bowman's

capsule

Glomerulus

Renal artery

Renal vein

Waste-laden blood

enters kidney.

Filtered blood

leaves kidney.

To the bladder

Ureter

Nephron

Renal cortex

Renal medulla

Nephron

Kidney

Capillaries

Tubule

1 2 3

Filtration takes place in the glomerulus, a

dense network of capillaries encased in

Bowman's capsule. Blood pressure forces

much of the �uid from the capillaries into

Bowman's capsule. The result is a �ltrate

containing water, urea, glucose, salts, amino acids, and some vitamins.

Reabsorption Dissolved salts and other

materials are removed from the �ltrate by active transport and reabsorbed by capillaries, causing nearly all of the �ltered water to follow by osmosis. In effect, the kidney �rst throws away nearly everything and then takes back only what the body needs. The loop of Henle conserves water and minimizes the volume of �ltrate.

Urine Excretion The fiuid entering collect-

ing ducts is now known as urine. From the collecting ducts, urine �ows to the ureter of each kidney. The ureters carry urine to the urinary bladder for storage until the urine leaves the body through the urethra.

Each kidney contains nearly a million

individual processing units called nephrons.

These nephrons are where most of the work

of the kidney takes place. Blood puri�cation in the kidneys involves two distinct processes: �ltration and reabsorption.

STruCTure AND FuNCTiON

OF THE KIDNEYS

FIGURE 30-9 Kidneys are made up of nephrons.

Blood enters the nephron, where impurities are

�ltered out and emptied into the collecting duct. Puri�ed blood leaves a nephron through a vein. 870

Calcium

Glucose

Potassium

Sodium

Urea 0.01 0.10 0.02 0.32 0.03

Average Concentration

in Blood (g/mL)

SubstanceAverage Concentration

in Urine (g/mL) 0.02 0.00 0.20 0.60 2.00

Concentrations of Selected Substances

in Blood and Urine TEKS 11A The Kidneys and Homeostasis How do the kidneys help maintain homeostasis? ?e kidneys play an important role in maintaining homeostasis. Besides removing wastes, the kidneys also maintain blood pH and regulate the water content of the blood. ?e kidneys respond directly to the composition of the blood. �ey are also in�uenced by the endocrine system. Disruption of proper kidney function can lead to serious health problems. To a large extent, the activity of the kidneys is controlled by the composition of the blood itself. For example, if you eat salty food, the kidneys will respond to the excess salt in your blood by returning less salt to your blood during reabsorption. If the blood is too acidic, then the kidneys excrete more hydrogen ions in the urine. If your blood glucose levels rise past a certain point, the kidneys will even excrete glucose into the urine. �is is one of the danger signals of diabetes, a disease caused by the body's inability to control the concentration of glucose in the blood. Glands release hormones that also in�uence kidney function. For example, if you have not consumed enough �uids or if you have sweat excessively, your pituitary gland releases antidiuretic hormone (ADH) into your blood. �is hormone causes the kidneys to reabsorb more water and to excrete less water in the urine. If the blood contains excess water, ADH secretion stops and more water is excreted. Did you know that the color of your urine is an indicator of how hydrated you are? A pale yellow color indicates that you are well hydrated because your kidneys are releasing a good amount of water. A darker color indicates that the water level in your blood is low, causing your kidneys to conserve water.

2. Calculate Approximately how many times

more concentrated is urea in urine than in the blood?

3. Infer Recall that urea is a by-product of

amino acid breakdown. How might the urea concentration vary in the blood and urine as the result of high protein diets? Explain.

The Composition of Urine

?e kidneys are selective ?lters. As blood passes through them, urea, other impurities, and excess salts are removed from the blood. But important substances such as water, protein, and glucose remain in cir- culation. �e collected waste products are excreted in urine. �e concentrations of certain substances in the blood compared to their concentration in urine reveal the important work of the kidneys.

1. Interpret Data Which substances listed have

the highest and lowest concentrations in the blood? Which substances have the highest and lowest concentrations in the urine?

The Human Body 871

Pulmonary Arteries

Carry oxygen-poor

blood to the lungs

LEFT ATRIUM

Accepts oxygen-rich

blood from the lungs Aorta

Carries oxygen-rich

blood from the left ventricle to the body

Superior Vena Cava

Brings oxygen-poor blood

from the upper body to the right atrium

Left Pulmonary Veins

Bring oxygen-rich

blood from the left lung to the left atrium

Right Pulmonary Veins

Bring oxygen-rich

blood from the right lung to the left atrium

Inferior Vena Cava

Brings oxygen-poor blood from

the lower body to the right atrium

LEFT VENTRICLE

Pumps oxygen-rich

blood to the body

Septum

Aortic Valve

Mitral Valve

Tricuspid Valve

RIGHT ATRIUM

Accepts oxygen-poor

blood from the body

RIGHT VENTRICLE

Pumps oxygen-poor

blood to the lungs

Pulmonary Valve

Functions of the Circulatory System

What are the functions of the circulatory system? Some animals are so small that all of their cells are in direct contact with the environment. Di�usion and active transport across cell membranes supply their cells with oxygen and nutrients and remove waste products. �e human body, however, contains millions of cells that are not in direct contact with the external environment. Because of this, humans need a circulatory system. ?e circulatory system transports oxygen, nutrients, and other substances throughout the body, and removes wastes from tissues. Blood is pumped through the body by the heart, a hollow organ composed almost entirely of muscle. An adult's heart contracts on average 72 times a minute, pumping about 70 milliliters of blood with each contraction. As Figure 30-10 shows, the heart is divided into four chambers. A wall called the septum separates the right side of the heart from the le� side. �e septum prevents oxygen-poor and oxygen-rich blood from mixing. On each side of the septum is an upper and lower chamber. Each upper chamber, or atrium (plural: atria), receives blood from the body. Each lower chamber, or ventricle, pumps blood out of the heart.

Figure 30-10 The Heart The

human heart has four chambers: the right atrium, the right ventricle, the left atrium, and the left ventricle.

Valves located between the atria and

ventricles and between the ventricle and vessels leaving the heart prevent blood from �owing backward between heartbeats. 872

ARTERYVEINCAPILLARY

Endothelium

Smooth Muscle

Regulates the

diameter of arteries; only a thin layer present in veins

Connective Tissue

Helps vessels,

especially arteries, expand under pressure and connects them to surrounding tissue

Endothelium

Lines the walls of

all blood vessels

Endothelium

Smooth muscle

Connective tissue

Arteriole

Very small arteries

that deliver blood to capillaries

Venule

Very small vessels

that form when capillaries unite; venules unite and form veins Valve

Superior

vena cava

Inferior

vena cava Aorta

Capillaries of

abdominal organs and legs

Capillaries

of left lung

Capillaries of

head and arms

Pulmonary

artery

Pulmonary

vein

Capillaries

of right lung

Systemic

Pulmonary

Blood leaving the heart passes through the aorta, the �rst of a series of vessels that carries blood through the systemic circulation. As blood �ows through the circulatory system, it moves through three types of blood vessels - arteries, capillaries, and veins. Arteries Arteries are large vessels that carry blood from the heart to the tissues of the body. Except for the pulmonary arteries, all arteries carry oxygen-rich blood. Arteries have thick elastic walls. Capillaries The smallest blood vessels are the capil- laries. Most capillaries are so narrow that blood cells pass through them in single �le. Their thin walls allow oxygen and nutrients to diffuse from blood into tissues, and carbon dioxide and other waste products to move from tissues into blood. Veins After blood passes through the capillaries, it returns to the heart through veins. Many veins are located near and between skeletal muscles. When you move, the contracting skeletal muscles squeeze the veins, pushing blood toward the heart. Many veins contain valves, which ensure blood �ows in one direc- tion through these vessels.

The heart functions as two pumps. One pump

pushes blood to the lungs, while the other pushes blood to the rest of the body.

The right side of the heart pumps oxygen-poor

blood from the heart to the lungs through the pulmonary circulation. In the lungs, carbon dioxide diffuses from the blood, and oxygen is absorbed. Oxygen-rich blood then �ows to the left side of the heart. The left side of the heart pumps oxygen-rich blood to the rest of the body through the systemic circula- tion. Cells absorb much of the oxygen and load the blood with carbon dioxide by the time it returns to the heart.

Blood Vessels

Circulation

The Human Body 873

Platelets Take Action

Platelets clump at the site and release

the clotting factor thromboplastin, which triggers a series of reactions.

Thromboplastin converts the protein

prothrombin into the enzyme thrombin.

Capillary Wall Breaks

A blood vessel is injured

by a cut or scrape.

Clot Forms

Thrombin converts the soluble plasma

protein fibrinogen into insoluble, sticky fibrin filaments, which form the clot.

The clot seals the damaged area and

prevents further loss of blood. 123
Blood In addition to serving as the body's transportation system, components of blood also help regulate body temperature, �ght infections, and produce clots to minimize the loss of body �uids from wounds. Plasma The human body contains 4 to 6 liters of blood. About 55 percent of total blood volume is a �uid called plasma. Plasma is about 90 percent water and 10 percent dissolved gases, salts, nutrients, enzymes, hormones, waste products, plasma proteins, cholesterol, and other compounds. Plasma proteins consist of three types - albumin, globulins, and �brinogen. Albumin and globulins transport substances such as fatty acids, hormones, and vitamins. Albumin also plays an important role in regulating osmotic pressure. Some globulins �ght viral and bacterial infections. Fibrinogen is necessary for blood to clot. Red Blood Cells The most numerous cells in blood are red blood cells, or erythrocytes (eh rith roh syts). The main function of red blood cells is to transport oxygen. They get their crimson color from the iron in hemoglo- bin, a protein that binds oxygen. Red blood cells are produced by cells in the bone marrow. As they mature and �ll with hemoglobin, nuclei and other organelles are forced out. White Blood Cells White blood cells, or leukocytes (loo koh syts), are the "army" of the circulatory system. White blood cells guard against infection, �ght parasites, and attack bacteria. A sudden increase in white blood cells is a sign that the body is �ghting a serious infection. Different types of white blood cells perform different protective functions. For ex- ample, macrophages engulf pathogens. Lymphocytes are involved in the immune response. B lymphocytes produce antibodies that �ght infection and provide immunity. T lymphocytes help �ght tumors and viruses. In a healthy person, white blood cells are outnumbered by red blood cells by almost 1000 to 1. Platelets As you know, a minor cut or scrape may bleed for a bit, but then the bleeding stops. Why? Because blood can clot. Blood clotting is made possible by plasma proteins and cell fragments called platelets. When platelets come in contact with the edges of a broken blood vessel, their surfaces becomes sticky, and they release proteins called clotting fac- tors that start reactions to produce a solid clot.

Blood Clot (SEM 2200)

874

Subclavian

veins

Thymus

Heart

Spleen

Lymph nodes Lymph vessels TEKS 10AThe Lymphatic System What is the function of the lymphatic system? As blood passes through capillaries, some blood cells and components of plasma move through capillary walls and into the �uid between cells. Each day about

3 liters of �uid leaves the blood in this way. Most of

this �uid, known as lymph, is reabsorbed into capil- laries, but not all of it. �e rest goes into the lymphatic system. ?e lymphatic system is a network of vessels, nodes, and organs that collects the lymph that leaves capillaries, "screens" it for microorgan- isms, and returns it to the circulatory system.

Role in Circulation Lymph collects in a system

of lymphatic capillaries that slowly conducts it into larger lymph vessels. Pressure on lymph ves- sels from surrounding skeletal muscles helps move lymph through the system into larger and larger ducts. Lymph vessels have valves, similar to the valves in large veins that prevent lymph from �ow- ing backward. �ese ducts return lymph to the blood through openings in veins just below the shoulders. When injury or disease blocks lymphatic vessels, lymph can accumulate in tissues, causing swelling called edema.

Role in Nutrient Absorption ?e lymphatic

system, shown in Figure 30-11, also plays an impor- tant role in the absorption of nutrients. A system of lymph vessels runs alongside the intestines. �e vessels pick up fats and fat-soluble vitamins from the digestive tract and transport these nutrients into the bloodstream.

Role in Immunity Hundreds of small bean-shaped

enlargements - called lymph nodes - are scattered along lymph vessels throughout the body. Lymph nodes act as �lters, trapping microorganisms, stray cancer cells, and debris. White blood cells inside lymph nodes destroy this cellular "trash." When large numbers of microorganisms are trapped in lymph nodes, the nodes become enlarged. �e thymus and spleen also play important roles in the immune functions of the lymphatic system.

T lymphocytes mature in the thymus before they

can function in the immune system. �e functions of the spleen are similar to those of lymph nodes. However, instead of lymph, blood �ows through the spleen, where it is cleansed of microorganisms and other debris. �e spleen also removes old or dam- aged blood cells and stores platelets.

Figure 30-11 The Lymphatic

System The lymphatic system is

a network of vessels, nodes, and organs that recycles �uids from tissues and plays a role in nutrient absorption and immunity. Infer Why do you think your doctor feels your neck for swollen lymph nodes when you are sick?

The Human Body 875

TEKS 11A

Structures of the Respiratory System

What is the function of the respiratory system? For multicellular organisms, means the process of gas exchange with the environment. ?e respiratory system picks up oxygen from the air we inhale and releases carbon dioxide as we exhale. With each breath, air enters the body through the air passage- ways and �lls the lungs, where gas exchange takes place, passing oxygen to the circulatory system. �e respiratory system consists of the nose, pharynx, larynx, trachea, bronchi, and lungs. You can see these organs in

Figure 30-12.

Air Flow As air enters the respiratory system, it is ?ltered, moist- ened, and warmed. Incoming air is warmed and �ltered in the inner nasal cavity and sinuses. Air then moves from the nose to a cavity at the back of the mouth called the pharynx, or throat, and then into the trachea, or windpipe. A �ap of tissue called the epiglottis covers the entrance to the trachea, ensuring that food or liquid goes into the esophagus instead. Between the pharynx and the trachea is the larynx, which contains two highly elastic folds of tissue known as the vocal cords. Your ability to speak, shout, and sing comes from these tissues. Mucus produced in the trachea traps inhaled particles, which cilia then sweep away from the lungs toward the pharynx. From the trachea, air moves into two large tubes called bronchi (singular: bronchus) leading to the lungs. �ese tubes divide into smaller bronchi, then into even smaller bronchioles. Bronchi and bronchioles are surrounded by smooth muscles that regulate the size of air passageways. �e bronchioles lead to millions of tiny air sacs called alveoli (singular: alveolus). Alveoli are grouped in clusters, like bunches of grapes. A delicate network of capillaries surrounds each alveolus. Gas Exchange and Transport As air enters the alveoli, oxygen dis- solves in their moist surfaces and di�uses across thin capillary walls into the blood. Meanwhile, carbon dioxide di�uses in the opposite direction. When you inhale, a muscle called the diaphragm contracts and �attens, creating a partial vacuum inside the tightly sealed chest cavity. Atmospheric pressure does the rest, �lling the lungs as air rushes into the breathing passages. Di�usion of oxygen from alveoli into capillaries is a passive pro- cess. But hemoglobin in red blood cells actively binds oxygen, increas- ing the blood's oxygen-carrying capacity more than 60 times. Most carbon dioxide enters red blood cells and combines with water, form- ing carbonic acid. �e rest of it dissolves in plasma or binds to hemo- globin and proteins in plasma. Online Journal In your own words, compare and contrast cellular respiration and respiration at the organism level. 876

Bronchiole

Epiglottis

Pharynx

Nose

Larynx

Trachea

Lung

Bronchus

Bronchioles

Capillaries

Pulmonary

vein

Alveoli

Diaphragm

Pulmonary artery

Capillary

O 2

Alveolus

CO 2 1 2

3Lungs Tubes called bronchi

carry air to the lungs, dividing into smaller and smaller passageways that end in alveoli, where gas exchange with the bloodstream takes place. Alveoli are grouped in clusters, like bunches of grapes.

A delicate network of capillar-

ies surrounds each alveolus.

Nose As air enters, the lining of

the nose starts the �ltering process by trapping large particles.

Incoming air is warmed in the

inner nasal cavity and sinuses.

These areas produce mucus that

moistens the air and catches even more dust particles.

Pharynx, Larynx, and Trachea

The pharynx serves as a

passageway for both air and food. Air moves from the pharynx into the trachea, or windpipe.

When you swallow food or

liquid, a �ap of tissue called the epiglottis covers the entrance to the trachea, ensuring that the food or liquid goes into the esophagus. The larynx contains two highly elastic folds of tissue known as the vocal cords. When muscles pull the vocal cords together, the air moving between them causes the cords to vibrate and produce sounds.

THE RESPIRATORY SYSTEM

FIGURE 30-12 Air moves through the

nose, pharynx, larynx, trachea, and bronchi into the lungs.

The Human Body 877

Air inhaled

Air exhaled

Rib cage

rises

Rib cage

lowers

Diaphragm

contracts

Diaphragm

relaxes

InhalationExhalation

Breathing

1. a. Review Explain the function of the digestive

system. b. Apply Concepts What impact do the folds and villi of the small intestine have on absorption?

2. a. Review List the organs involved in excretion.

b. Explain How do the kidneys maintain water balance?

3. a. Review List the structures of the circulatory

system and explain their roles. b. Review Describe the two paths of blood circula- tion through the body. c. Explain Describe the functions of three types of blood vessels in the circulatory system. d. Review List the main function of plasma, red blood cells, white blood cells, and platelets.

4. Describe What is the role of the lymphatic

system?

5. a. Review Explain the function of the respi-

ratory system. b. Review Describe the process of gas exchange in the lungs. c. Review Explain the process of breathing.

30.2 Review Key Concepts

Surprisingly, there are no

muscles in our lungs or con- nected directly to them that participate in breathing. The force that drives air into the lungs comes from ordinary air pressure, the diaphragm, and muscles associated with the ribs. Movements of the diaphragm and rib cage change air pressure in the chest cavity during inhalation and exhalation. You can control your breathing almost any time you want, to blow up a bal- loon or to play a trumpet. But this doesn't mean that breathing is purely volun- tary. Your nervous system has �nal control of your breathing muscles whether you are conscious or not. This is why people who drown have water in their lungs. When they lose consciousness, they "breathe" water into their lungs. Breathing is initiated by the breathing center in the part of the brain stem called the medulla oblongata. Sensory neurons in or near the medulla and in some large blood vessels gather information about carbon dioxide levels in the body and send the information to the breathing center. When stimulated, the breathing center sends nerve impulses that cause the diaphragm and chest muscles to contract, bringing air into the lungs. The higher the blood carbon dioxide level, the stronger the impulses. If the blood carbon dioxide level reaches a critical point, the impulses become so powerful that you cannot keep from breathing.

Breathing and Homeostasis

TEKS 4B, 10A, 11A 878

The cell body contains the nucleus

and much of the cytoplasm.

The axon carries impulses

away from the cell body. Nodes

Nucleus

The myelin sheath is an insulating membrane that surrounds some axons, leaving gaps called nodes that expose the axon membrane. Impulses jump from node to node, traveling faster than they would through an axon without a myelin sheath.

Axon terminals at the end of the axon

transmit information to other nerve cells, glands, or muscles.

Dendrites receive impulses

from other neurons and carry impulses to the cell body.

Human Body Systems II

What are the functions of the nervous system? fie nervous system is our window on the world. �e nervous system collects information about the internal and external envi- ronment, processes that information, and responds to it. All these messages are carried by electrical signals called impulses, through nerve cells called neurons. �e neurons and supporting cells that form the peripheral nervous system collect information about the body's external and internal environment. �e brain and spinal cord form the central nervous system, which processes and creates a response to that information, which is carried to muscles, glands, and other tissues by the peripheral nervous system. �e billions of messages sent through your body at any given moment may tell you to laugh at a joke, or tell you that it's cold outside. �ese messages enable the organs of the body to act together and also to react to external conditions.

Key Questions

What are the structures and functions of the nervous system, skeletal system, integumentary system, endocrine system, and the male and female reproduc- tive systems?

Taking Notes

Outline As you read this lesson,

continue adding to the outline you started in Lesson 30.2.

The Nervous System

30.3

Neurons

Neurons can be classi?ed into three types. Sensory neurons carry impulses from sense organs, such as eyes and ears, to the central nervous system. Motor neurons carry impulses from the central nervous system to muscles and glands. Interneurons process information from sensory neurons and send commands to other interneu- rons or motor neurons. All neurons have certain features in common. These include a cell body, dendrites, an axon, and, in many neurons, a myelin sheath.

In this lesson you will learn the structure and function of the rest of the human body systems (TEKS 10A) and how they

work together to maintain homeostasis (TEKS 11A). 879
Na + K +

Outside of Cell

Cell membrane

Inside of Cell

Sodium-potassium

protein pump

Gated sodium channel

protein (closed)

Gated potassium

channel protein (closed)

ATPATP

ADPADP

Na+ K + Na + ------- -------

Action Potential

At the leading edge of the impulse, gated sodium channels open. Na + ions �ow into the cell, reversing the potential between the cell membrane and its surroundings. This rapidly moving reversal of charge is called an action potential. As the action potential passes, gated potassium channels open, allowing K + ions to �ow out, restoring the resting potential inside the axon.

At rest

Cell bodyAxon

---- -- -++ -----++

Action Potential

---++ -----++ 1 2 3

The Nerve Impulse

Neurons carry information by using specialized pro- teins in their cell membranes to create small electrical currents. But nerve cells do not carry electric currents the way that telephone wires do. To understand how neurons work, we need to examine a neuron at rest (see above). Neurons at rest have an electrical charge of �70 mil- livolts (mV), called the resting potential, between the inside and outside of their cell membranes. This charge is produced by membrane proteins that pump sodium ions (Na + ) out of the cell and potassium ions (K + ) into it. Separate potassium channel proteins make it easier for K + ions than Na + ions to diffuse back across the membrane. Because the pumps create a higher concentration of K + ions inside the cell, positively charged K + ions diffuse out of the cell. The inside of the cell therefore becomes negatively charged compared to the outside. When a neuron receives a large enough stimulus, it this resting potential changes suddenly, producing a nerve impulse called an action potential. The smallest stimulus that can produce an action potential is called a threshold stimulus. Stimuli weaker than threshold will not produce an action potential. Nerve impulses are not created by a �ow of elec- trons down the axon. Instead, each action potential is produced by a sudden reversal of the resting potential. This charge reversal travels down the axon like ripples passing down the surface of a stream. 880

Sensory

neuron Motor neuron

Spinal cord

Interneuron

Effector

(responding muscle)

Sensory

receptors Brain

Spinal cord

The Central Nervous System

The central nervous system, which includes the brain and spinal cord, is contained almost entirely inside the bony structures of the skull and vertebral column. Most infor- mation processing occurs in the major brain regions - cerebrum, cerebellum, and brain stem. Different parts of the brain perform different functions. Sensations from various body areas are "felt" by speci�c brain regions. Commands to muscles originate in other brain areas. The spinal cord, which contains most neurons that enter and leave the brain, links the brain to the rest of the body.

The Peripheral Nervous System

The peripheral nervous system contains nerves and associated cells that are not part of the brain or spinal cord, and has two major divisions - sensory and motor. The sensory division consists of receptor cells that gather information, and sensory neurons, which transmit im- pulses from sense organs to the central nervous system. The motor division transmits impulses from the central nervous system to the muscles and glands. These messages are relayed through networks called the somatic nervous system and the autonomic nervous system. Somatic Nervous System The somatic nervous system regulates activities such as movement of skeletal muscles. Some somatic nervous system actions are under voluntary control. When you lift your �nger or wiggle your toes, impulses originating in the brain are carried through the spinal cord to motor neurons, which stimulate muscles. Other somatic nervous system actions occur automatically. If you step on a tack with your bare foot, your leg may recoil before you are aware of the pain. This rapid response (a re�ex) is produced by impulses that travel through a pathway known as a re�ex arc, as shown in the �gure. Information about the injury is also sent to the brain, even though your leg and foot have already moved. Autonomic Nervous System The autonomic nervous system regulates activities that are not under conscious control. For instance, when you start to run, the autonomic nervous system speeds up your heart rate and blood �ow to skeletal muscles, stimulates sweat glands, and slows down contractions of smooth muscles in the digestive system. The autonomic nervous system consists of two equally important parts, the sympathetic nervous system and the parasympathetic nervous system, which usually have opposite effects. For example, the sympathetic nervous system increases heart rate, and the parasympathetic nervous system decreases it. This enables precise control of body systems, in the same way that using both the gas pedal and the brake enables a driver to control the speed of a car. In general, the sympathetic system prepares the body for intense activity - the so-called "�ght or �ight" reaction. The parasympa- thetic system produces the "rest and digest" response.

The Human Body 881

Axial skeleton

Appendicular

skeleton

Growth Plate Growth plates contain

dividing cartilage cells that increase the size of a bone until a person reaches his or her adult height.

Periosteum

Yellow

bone marrow

Periosteum

Blood vessels

Osteocyte

Compact bone

Spongy

bone

Compact Bone Dense

compact bone, found under the periosteum, contains networks of tubes through which blood vessels and nerves travel.

Haversian Canals These

canals contain blood vessels and nerves.

Osteoclasts and osteo-

blasts line the canals.

Spongy Bone The tiny

structures of spongy bone are arranged in such a way that they can support a lot of force.

Red bone marrow is found in

the spaces of spongy bone.

SEM 180�

The Skeletal System

What are the functions of the skeletal system? ?e skeletal system, shown in Figure 30-13, supports and shapes the body like an internal wooden frame supports a house. ?e skel- eton supports the body, protects internal organs, assists movement, stores minerals, and is a site of blood cell formation. Bones also act as rigid rods on which muscles exert force to produce movement. In addition, bones contain reserves of minerals, such as calcium salts. �e 206 bones in the adult human skeleton form the axial skeleton and the appendicular skeleton. �e axial skeleton - the skull, the ver- tebral column, and the rib cage - supports the body's central axis. �e bones of the arms, legs, pelvis, and shoulder area make up the appen- dicular skeleton. Bones Bones are living tissue made up of a solid network of living cells and protein �bers surrounded by deposits of calcium salts. Bones are surrounded by tough connective tissue called periosteum (pehr ee ahs tee um). Beneath the periosteum is a thick layer of compact bone. Nerves and blood vessels run through compact bone in chan- nels called Haversian canals. A less dense tissue known as spongy bone may be found under the compact bone, especially in the ends of long bones. Despite its name, spongy bone is quite strong. Near the ends of bones where force is applied, spongy bone forms latticework structures that resemble sup- porting girders in a bridge. This adds strength without excess mass. Inside many bones are cavities containing one of two types of bone marrow. Yellow marrow consists primar- ily of cells that store fat. Red marrow contains stem cells that produce most types of blood cells.

Figure 30-13 The Skeleton The

human skeleton is divided into the axial skeleton and the appendicular skeleton. 882

Ball-and-Socket Found in the

shoulders and hips, these joints allow for movement in many directions. They are the most freely movable joints.

Hinge These joints permit

back-and-forth motion, like the opening and closing of a door.

They are found in the elbows,

knees, and ankles.

Saddle These joints allow

one bone to slide in two directions. Saddle joints allow a thumb to move across a palm.

Pivot These joints allow

one bone to rotate or turn around another.

Pivot joints allow you

to turn your arm at your elbow and shake your head to say no.

Joints

A place where one or more bones meet each other is called a joint. Joints contain connective tissue that holds bones together and permits bones to move without damaging each other. Joints can be classi�ed as immovable, slightly movable, or freely movable. Immovable Joints Immovable joints, often called �xed joints, allow no movement. The bones at an immovable joint are interlocked and grow to- gether until they are fused. Most bones in the skull meet at immovable joints. Slightly Movable Joints Slightly movable joints permit a small amount of movement. Unlike the bones of immovable joints, the bones of slightly movable joints are separated from each other. The joints between the two bones of the lower leg and the joints between vertebrae are examples of slightly movable joints. Freely Movable Joints Freely movable joints, like the shoulder joint, permit movement in two or more directions. Freely movable joints are grouped ac- cording to the shapes of the surfaces of the adjacent bones. Several types of freely movable joints are shown below.

The Human Body 883

Smooth Muscle

LM 450×

Cardiac Muscle

LM 370×

Skeletal Muscle

LM 275×

Smooth Muscle

LM 450×

Cardiac Muscle

LM 370×

Skeletal Muscle

LM 275×

Smooth Muscle

LM 450×

Cardiac Muscle

LM 370×

Skeletal Muscle

LM 275×

The Muscular System

What are the principal types of muscle tissue? Despite the fantasies of Hollywood horror ?lms, a skeleton cannot move by itself. Muscles generate the force needed to power movement - from a leap in the air to the hint of a smile. ?ere are three di�erent types of muscle tissue that are specialized for di�erent functions: skeletal, smooth, and cardiac muscle. ?e three types of muscles and where they are found in the body are shown in Figure 30-14. Skeletal muscles are usually attached to bones. �ey are responsible for voluntary movements. When viewed under a microscope at high magni�cation, skeletal muscle appears to ha