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Chapter 4The Human Body

ALABAMA 7TH GRADE SCIENCE STANDARDS COVERED IN THIS CHAPTER INCLUDE:

3 Relate major tissues and organs of the skeletal, circulatory, reproductive,muscular, respiratory, nervous and digestive systems to their functions.

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: • •• •

:.you think of the human body as a team, then the organ

ScINKS systems within it would be the players This team must work

.l.LJI4M;_44cIwI F together in order for the body to maintain homeostasis

ACO65 Let’s review the definition of homeostasis It is the process. of maintaining a constant internal environment, despite

changing environmental conditions. It is how we “regulate ourselves.” Here are afew examples:

. Sweating cools us and helps us maintain a constant internal temperature.

. We drink water to remain hydrated and maintain our body’s water balance.

. We excrete waste products to maintain a clean bloodstream.

To accomplish homeostasis, the combined efforts of cells, organs and organ systemsare required. We won’t look at every part of our “human body team,” but we willexamine several “star players.”

Figure 4.1 The Human Body Team

37

The Human Body

Table 4.1 Overview ofHuman Body Systems

System Major Parts and Organs

Respiratory nose, trachea, bronchial tubes, lungs, alveolus and diaphragm

Circulatory heart, veins, arteries and capillaries

Digestive tongue, teeth, salivary glands, esophagus, stomach, pancreas,liver, gall bladder, small intestine, appendix and large intestine

Skeletal skull, vertebral column, sternum, ribs, humerus, radius, ulna,carpals, metacarpals, phalanges, pelvic girdle, femur, patella,tibia, fibula, tarsals and metatarsals

Immune lymphatic system, spleen, tonsils, thymus, leukocytes and bonemarrow

Lymphatic lymph nodes, tonsils, thymus and spleen

Muscular involuntary (smooth muscles), heart (cardiac muscle) andvoluntary (striated muscles)

Nervous brain (cerebrum, medulla, cerebellum), spinal cord and nervecells

Excretory kidney, blood vessels, bladder, ureter, urethra, skin and sweatglands

Reproductive male: testes, vas deferens, seminal vesicle and penis

female: ovary, oviduct, uterus, cervix and vagina

REsPIRAToRY SYSTEMThe respiratory system allows ourbodies to obtain oxygen from theair. Respiration refers to themovement of air in and out of thelungs. Respiration happens whenwe breathe in (inspiration). Totake a breath, a special musclecalled the diaphragm mustcontract. The diaphragm is a flatmuscle that runs across the bodycavity below the lungs. When thediaphragm contracts, it increases

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38

Chapter 4

the total overall volume of the lungs, causing air to rush into the body. When thediaphragm relaxes, it decreases the volume of the lung cavity, causing air to leave thebody. During inspiration, air enters the nose or mouth, where it passes through thetrachea (a hollow tube made of cartilage), bronchial tubes and into the alveoli. Alveoli

are air sacs rich in blood vessels, where gases exchange between lungs and blood.Oxygen then diffuses into the cells, and carbon dioxide diffuses out of the cells.

When we breathe out, we rid our bodies of carbon dioxide. Breathing out is calledexpiration. To leave the body, air reverses the path it used to enter.

CIRCULATORY SYSTEMThe circulatory system is a transport system for manysubstances, most notably, blood. Blood is essentiallymade up oftwo parts: cells and plasma. Blood plasma

is a yellowish fluid that suspends the cells. It is similarto the broth in chicken noodle soup; it provides a liquidfor the cells and other nutrients. Plasma is about 55%of total blood volume and carries important dissolvedsalts, water, fats and amino acids.

Blood cells can be one ofthree main types: red bloodcells, white blood cells or platelets. Red blood cells

are responsible for transporting oxygen. They containan iron rich protein called hemoglobin, which gives

.

these cells their red color. Red blood cells are the mostcommon type of blood cell. White blood cells attack

________________________

harmful microorganisms (bacteria, viruses or Figure 4.3 Circulatory Systemparasites) and aid in immunity. Platelets are bloodcells that form clots. Platelets, along with white blood cells, stop the bleeding at the siteof a wound and eventually lead to the formation of a scab.

The heart is the pump of the circulatory system. It is a hollow muscular organ locatedbetween the lungs. It has four chambers that perform two primary functions. The heart:

. . collects deoxygenated (without oxygen) blood from the body and pumps it to the

! lungs, and then...

.collects oxygenated blood from the lungs and pumps it throughout the body.

The respiratory system and circulatory system work closely together, because your body

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needs to take in oxygen and send it to your cells.

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The Human Body

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Capillaries Oxygenated blood has passed through the lungs topick up oxygen, and is ready to travel through the bodyto deliver the oxygen to cells. Oxygenated bloodmoves through the arteries. Arteries are the blood

Capillaries ThsueCells ‘ Vein vessels that carry blood “away” from the heart. Blood. . . vessels are hollow tubes that transport blood. There areFigure 4.4 Capillanes

large vessels, like the aorta which measures roughly2.5 cm, and small vessels, measuring 5 — 10 tm (that’s about 0.0005 cm). Really smallblood vessels are called capillaries. The walls of a capillary are only one cell layerthick. This allows molecules and elements like oxygen, glucose and carbon dioxide topass through. Capillaries are what actually bring the nutrients to individual cells.

Deoxygenated blood has traveled through the body and has already delivered oxygento your cells via the capillaries. Deoxygenated blood travels in blood vessels calledveins. Veins bring blood back to the heart and lungs.

DIGESTIVE SYSTEMThe digestive system breaks down food into smaller pieces that can be used by yourcells. The digestive system is made up of several organs located in your mouth andinside your body. Some important organs involved in digestion include the esophagus,stomach, liver, small intestine and large intestine.

Digestion can happen two ways: mechanically and chemically. Mechanical digestionoccurs when food is physically broken into smaller pieces. Mechanical digestionoccurs when you chew your food, and during movement of the stomach. Chemicaldigestion happens when chemicals inside your body break down food. One example ofchemical digestion is stomach acid dissolving food. The digestive system works withthe circulatory and excretory system to bring nutrients to cells and remove wastes.

The mouth is wherethe digestive systembegins. Food is placedinside the mouth,where your teeth,tongue, saliva and jawmuscles chew it. foodis then swallowed, oringested, down a tubecalled the esophagus.

Digestive Systemesophagus I

gall bladder—

pancreas

small intestines .e::::

large

appendix

Figure 4.5 Digestive System

40

Chapter 4

The esophagus is a tube of smooth muscle tissue that transports food to the stomach.The

stomach is a bag-like organ that receives the large pieces of food from the mouth.The stomach chemically and mechanically breaks down large food pieces into muchsmaller pieces. The stomach has strong acids, a pH of 1 — 2, that chemically break downlarge food particles into much smaller pieces. In fact, acids inside the stomach are so

h strong, if placed on skin they could cause a chemical bum. In the first part of the smallintestine (the duodenum), secretions from the pancreas neutralize stomach acids. Alsoin the duodenum, the liver secretes several chemicals that help break down fats. Thesmall intestine is a hollow, highly folded tube that absorbs nutrients from food as itslowly moves the food to the large intestine. The last organ involved in digestion is thelarge intestine. The main ffinctjons of the large intestine are to absorb water fromindigestible food and absorb vitamins released by bacteria living inside the largeintestine. Another function ofthe large intestine is to compact solid wastes (indigestiblefood, also called feces).

SKELETAL SYSTEMThe skeletal system includes

_________ ________

bones, cartilage, tendons andligaments. The skeletal systemprovides support and structurefor the body. This isaccomplished through the use ofbones. Bones are an organ madeup of hard connective tissues(mostly of calcium phosphate).Skeletal muscle attaches tobones to allow for movement.Bones are also a source ofcalcium for other organs in our Figure 4.6 Skeletal System

bodies. Calcified bone tissuerenews itselfperiodically. When old bone breaks down, calcium and phosphorus move

I into the bloodstream and are able to be used in other ways.(

A place where two bones join is called a joint. Joints allow your skeleton to move.. Tough fibrous tendons attach muscles to bones and allow muscles to “pull” the bones in

different directions. Ligaments are a band of dense, fibrous connective tissues that

I connect one bone to another. Ligaments function to stabilize joints. Cartilage, a tough

connective tissue, is found at mostjoints. Injoints, cartilage softens movement between

)two bones. This allows a smooth, gliding action as the bones move past one another. Inother body organs, like your ear or nose, firm yet flexible cartilage forms the main

Skeletal System

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41

The Human Body

support structure. Cartilage lacks blood vessels resulting in a slow rate of repair, injuryto certain cartilaginous tissues often results in lifelong diseases. This is particularly trueofknee or back cartilage injury.

Joints are classified by the type of movement theyallow and the types of tissues they have. The mostcommonly accepted types of joints are fixed, hinge,pivot, gliding and ball-and-socket. Fixedjoints, like inyour skull, do not move but serve to absorb shockwhile protecting sensitive tissues underneath. Hingejoints, like your knee, allow for two directionalnIovement and move like a door hinge. Pivot joints,like your elbow, allow for rotational movement around1 80° axes. Gliding joints, like your wrists, allowslightly more rotational movement than pivot jointsand function as two bones glide past one another. Themovement allowed by this joint type is defined by the

shape ofthe bones involved. A ball-and-socketjoint, like your shoulder, allows the mostfreedom of movement and permits bones to rotate a full 360°. Can you name anotherball-and-socket joint? Right — your hip! Figure 4.7 shows a typical synovial joint, themost common moveablejoint. It is called a synovialjoint because ofthe synovial tissueslocated in and around it. An example of a synovialjoint is your knee.

IMMUNE SYSTEMThe immune system is a collectionof cells and tissues that defend the

Iw4grqwLw human body against invaders. TheABCO8O immune system works with your..... .. dasese .

skm, respiratory system anddigestive system to prevent

disease. It consists of the lymphatic system, spleen,tonsils, thymus and bone marrow. Bone marrow makesleukocytes, white blood cells, which defend againstinfection and disease.

Figure 4.7 Synovial Joint

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Figure 4.8 White Blood Cell

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LYMPHATIC SYSTEM

The lymphatic system is a network of the parts

of the immune system. It consists of lymph

vessels, lymph and lymphoid tissues (i.e.

lymph nodes, tonsils, thymus and spleen).

Lymph vessels transport lymph. Lymph is

composed of tissue fluid and white blood cells.

Tissue fluid is fluid that surrounds cells. It is

made up of water,. small molecules and lymph

cells.

Lymph nodes filter lymph fluid and prevent Figure 4.9 Lymphatic System

foreign particles and microorganisms from

entering the bloodstream. As the lymphatic system fights these invaders, lymph nodes

can become swollen and sore.

The lymphatic system also plays a role in returning fluid to blood. Lymph vessels do not

have a pump (the heart) like arteries do. They operate like veins, relying on muscle

contractions to push fluid throughout the body. Exercise helps keep lymph moving. This

is one reason why people who regularly exercise seem to be sick less often!

MUSCULAR SYSTEM

The muscular system is used to move the body, help circulate blood and move food

through the digestive system. The three types of muscular tissue that accomplish these

tasks are skeletal, cardiac and smooth.

Skeletal muscle tissue is attached to bones by tendons. Skeletal muscles, also called

voluntary muscle, move the body. Voluntary muscle tissues are under the complete

control ofthe organism; you decide when to move your arms and legs. Cardiac muscles

are found only in the heart. These are a type of involuntary muscle. Involuntary

muscles contract automatically. You don’t have to think about making your heart beat;

it just happens! Mother type of involuntary muscle tissue is smooth muscle. Smooth

muscle is found in many organs like the esophagus, stomach and intestines.

Lymphatic System

43

The Human Body

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NERVOUS SYSTEMThe nervous system is the control and communicationnetwork of the body. It detects and responds to stimuliboth inside and outside the body. The five senses (smell,touch, taste, sight and hearing). are controlled by thissystem. A nerve is a bundle of nerve cells or neurons.Neurons carry information from one place to another.

The two main parts of the nervous system are the centralnervous system (CN$) and the peripheral nervoussystem. The central nervous system is made up of thebrain and spinal cord. The CNS is the main control center

. Figure 4.10 Nervous Systemfor the human body. The peripheral nervous systemconsists of all other parts of the nervous system. The peripheral nervous system carriesnerve impulses from the brain and spinal cord to the body and back to the brain. Thenerves that detect heat in your fingers exemplify the peripheral nervous system.

The brain is the most important andcomplex human organ. A complete

(Bodysensesorientation, discussion of the brain is beyond thevisualand apaUnipercepUon) scope of this text; however, it isOccipft& LobeVialon)

Cerebellum)Muac)e coordination)

‘ Spinal Cord

Language AreaJudgment. initiation,

abstract thought, speech)IHandukills sensory. reading.writing, numbers)

Temporal Lobe(Hearing, music, understandingspeech menroryfornomverbalevents) .

Brain SternMaintain homeostasis:

a.blood pressureb. heartbeat

Figure 4.11 Parts ofthe Human Brain

important to have a basicunderstanding of how the brainfunctions. It serves as the controlcenter for the entire human body. Itregulates behavior, blood chemistry,mood, growth, heart rate, sleepcycles, reproduction orjust about any

other bodily function you can think of. The brain has a complex network of nerves (atleast 23 billion neurons) that interact closely with the spinal cord and sensory neurons.The brain sends messages down the spinal cord, a long thin bundle of nerves runningthe length of the vertebral column, to different parts of the body. The main function ofthe spinal chord is to transport messages from the brain to the body’s nerves and viceversa. The brain receives information from your senses (eyes, nose, etc.) and processesthis information to cause appropriate action. While your eyes merely perceive the wordson the page, your brain allows you to understand their meaning. Internal body signalsare also perceived by the brain. Changes in blood chemistry, like a buildup of CO2during exercise, are detected by the brain. The brain then sends signals to the rest of thebody to increase both the heart and breathing rate.

44

Chapter 4

EXCRETORY SYSTEM

The excretory system removes wastes from the body. Thelungs and skin release some wastes through respiration andsweating, but the majority of metabolic wastes are removedthrough the urinary tract. The urinary tract consists of thekidneys, ureters, bladder and urethra. The excretory systemremoves wastes from cells in the body.

REPRODUCTiVE SYSTEMReproduction is necessary for the continuation ofa species.Human reproduction involves two parents: a male and a figure 4.12 The Uñnaiy Tract

female. The reproductive system allows humans toreproduce. The organs in the reproductive system are different for males and females.In males, the reproductive system is composed of the testes and the penis. In females,the reproductive system includes the ovaries, uterus, vagina and breasts.

Males have two testes — glands that produce testosterone, the male sex hormone.Upon sexual maturity, the amount of testosterone increases, and sperm are produced inthe testes. Sperm are male sex cells, or gametes, that move via flaggeflum. Males canproduce sperm throughout their lifetime. Sperm leave the body, in semen, through theurethra. The urethra is the opening the head of the penis.

females produce ova, or eggs, which are housed in twoovaries. Upon sexual maturity, one ovum formsapproximately every 28 days, when it is released from theovary and travels along the fallopian tube on its way to theuterus. The uterus is a hollow organ that provides a place forthe embryo (an embryo is a developing baby) to develop.During pregnancy, the uterus more than doubles in size.

If sperm and egg unite, fertilization occurs, resulting in azygote. The zygote develops into a fetus in the uterus until,

g finally, a baby is born. The human female feeds the infant withmilk produced by mammary glands in the breasts.

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female Reproductive System

Figure 4.13 FemaleReproductive System

Activity

Research the different organ systems using textbooks or the Internet. Determinewhich body system (circulatory, digestive, skeletal, respiratory, immune,lymphatic, muscular, nervous, excretory or reproductive) you could live without.

reparedtodefendyourposffionwithevidenceandJorlogical reasoning.

45

The Human Body

CHAPTER 4 REVIEW

1. What is one major function ofthe lymphatic system?

A transporting oxygenated and deoxygenated bloodB providing support and structure for the bodyC transmitting information from the environment to the brainB preventing foreign particles from entering the bloodstream

2. How does the stomach aid in digestion?

A It mechanically breaks down fats.B It chemically and mechanically breaks down foods.C It mechanically breaks down sugars.B It chemically breaks down proteins.

3. The diaphragm contracts to

A force air into the lungs.B force air into and out of the lungs.C move the stomach, assisting in the mechanical breakdown of food.B support the spinal column.

4. What is the main job of the respiratory system?

A delivering carbon monoxide to the important parts of the bodyB pumping blood to the capillariesC taking in oxygen needed for respirationB taking in carbon dioxide and delivering it to the cells

5. What are the main components of the circulatory system?

A bone marrow, ligaments and tendons i

B heart, veins, arteries and capillariesC brain, spinal cord and neurons ,

B stomach, esophagus and small intestine