Anatomy of the Digestive System and Circulatory System

8/2/2019 Anatomy of the Digestive System and Circulatory System

1/17

Anatomy of the Digestive System


2/17

Introduction

Digestion is the process by which food is broken down into smaller pieces so that the

body can use them to build and nourish cells and to provide energy. Digestion involves

the mixing of food, its movement through the digestive tract (also known as

the alimentary canal), and the chemical breakdown of larger molecules into smaller

molecules. Every piece of food we eat has to be broken down into smaller nutrients that

the body can absorb, which is why it takes hours to fully digest food.

The digestive system is made up of the digestive tract. This consists ofa long tube of

organs that runs from the mouth to the anus and includes the

esophagus,stomach,small intestine, andlarge intestine, together with the liver,

gallbladder, and pancreas, which produce important secretions for digestion that drain

into the small intestine.The digestive tract in an adult is about 30 feet long

Mouth and Salivary Glands

Digestion begins in the mouth, where

chemical and mechanical digestion

occurs. Saliva or spit, produced by the

salivary glands (located under

the tongue and near the lower jaw), is

released into the mouth. Saliva begins

to break down the food, moistening it

and making it easier to swallow. A

digestive enzyme (called amylase) in

the saliva begins to break down the

carbohydrates (starches and sugars).

One of the most important functions of

the mouth is chewing. Chewing allows

food to be mashed into a soft mass


3/17

that is easier to swallow and digest later.

Movements by the tongue and the mouth push the food to the back of the throat for it to

be swallowed. A flexible flap called the epiglottis closes over the trachea (windpipe) to

ensure that food enters the esophagus and not the windpipe to prevent choking.

Esophagus

Once food is swallowed, it

enters the esophagus,

a muscular tube that is

about 10 inches long. The

esophagus is located

between the throat and the

stomach. Muscular

wavelike contractions

known as peristalsis push

the food down through the

esophagus to the stomach.

A muscular ring (called

the cardiac sphincter) at the end of the esophagus allows food to enter the stomach,

and, then, it squeezes shut to prevent food and fluid from going back up the esophagus.


4/17

Liver

The liver is the largest glandular organ of the body. It weighs about 3 lb (1.36 kg). It is

reddish brown in color and is divided into four lobes of unequal size and shape. Theliver lies on the right side of the abdominal cavity beneath the diaphragm. Blood is

carried to the liver via two large vessels called the hepatic artery and the portal vein.

The heptic artery carries oxygen-rich blood from the aorta (a major vessel in the heart).

The portal vein carries blood containing digested food from the small intestine. These

blood vessels subdivide in the liver repeatedly, terminating in very small capillaries.

Each capillary leads to a lobule. Liver tissue is composed of thousands of lobules, and

each lobule is made up of hepatic cells, the basic metabolic cells of the liver.

The liver has many functions. Some of the functions are: to produce substances that

break down fats, convert glucose to glycogen, produce urea (the main substance of

urine), make certain amino acids (the building blocks of proteins), filter harmful


5/17

substances from the blood (such as alcohol), storage of vitamins and minerals (vitamins

A, D, K and B12) and maintain a proper level or glucose in the blood. The liver is also

responsible for producing cholesterol. It produces about 80% of the cholesterol in your

body.

Stomach

The stomach is a J-

shaped organ that lies between

the esophagus and the small

intestine in the upper abdomen.

The stomach has 3 main

functions: to store the

swallowed food and liquid; to

mix up the food, liquid, and

digestive juices produced by

the stomach; and to slowly

empty its contents into the

small intestine.

Only a few substances, such as

water and alcohol, can be

absorbed directly from the

stomach. Any other food

substances must undergo the

digestive processes of the

stomach. The stomach's strong

muscular walls mix and churn

the food with acids and enzymes (gastric juice), breaking it into smaller pieces. About 3

quarts of the gastric juice is produced by glands in the stomach every day.

The food is processed into a semi liquid form called chyme. About 4 hours or so after

eating a meal, the chyme is slowly released a little at a time through the pyloric


6/17

sphincter, a thickened muscular ring between the stomach and the first part of the small

intestine called the duodenum.

Small Intestine

Most digestion

and absorption of food

occurs in the small intestine.The small intestine is a

narrow, twisting tube that

occupies most of the lower

abdomen between the

stomach and the beginning

of the large intestine. It

extends about 20 feet in

length. The small intestine

consists of 3 parts: the

duodenum (the C-shaped

part), the jejunum (the coiled

midsection), and

the ileum (the last section).

The small intestine has 2 important functions. First, the digestive process is completed

here by enzymes and other substances made by intestinal cells, the pancreas, and the

liver. Glands in the intestine walls secrete enzymes that breakdown starches and

sugars. The pancreas secretes enzymes into the small intestine that help breakdown

carbohydrates ,fats, and proteins.


7/17

The liver produces bile, which is stored in the gallbladder. Bile helps to make fat

molecules (which otherwise are not soluble in water) soluble, so they can be absorbed

by the body. Second, the small intestine absorbs the nutrients from the digestive

process. The inner wall of the small intestine is covered by millions of tiny fingerlike

projections called villi. The villi are covered with even tinier projections called microvilli.

The combination of villi and microvilli increase the surface area of the small intestine

greatly, allowing absorption of nutrients to occur. Undigested material travels next to the

large intestine.

Large Intestine

The large intestine forms

an upside down U over the

coiled small intestine. It

beginsat the lower right-

hand side of the body and

ends on the lower left-hand

side. The large intestine is

about 5-6 feet long. It has

3 parts: the cecum,

the colon, and the rectum.

The cecum is a pouch at

the beginning of the large

intestine. This area allows

food to pass from the small

intestine to the large

intestine. The colon is

where fluids and salts are

absorbed and extends

from the cecum to the


8/17

rectum. The last part of the large intestine is the rectum, which is where feces (waste

material)is stored before leaving the body through the anus.

The main job of the large intestine is to remove water and salts (electrolytes) from the

undigested material and to form solid waste that can be excreted. Bacteria in the large

intestine help to break down the undigested materials. The remaining contents of the

large intestine are moved toward the rectum, where feces are stored until they leave the

body through the anus as a bowel movement.


9/17

Anatomy of the Human Circulatory System

INTRODUCTION


10/17

The circulatory system is responsible for the transport of water and dissolved materials

throughout the body, including oxygen, carbon dioxide, nutrients, and waste. The

circulatory system transports oxygen from the lungs and nutrients from the digestive

tract to every cell in the body, allowing for the continuation of cell metabolism. The

circulatory system also transports the waste products of cell metabolism to the lungs

and kidneys where they can be expelled from the body. Without this important function

toxic substances would quickly build up in the body.


11/17

The human heart is a specialized, four-chambered muscle that maintains the blood flowin the circulatory system. It lies immediately behind the sternum, or breastbone, andbetween the lungs. The apex, or bottom of the heart, is tilted to the left side. At rest, theheart pumps about 59 cc (2 oz) of blood per beat and 5 l (5 qt) per minute. Duringexercise it pumps 120-220 cc (4-7.3 oz) of blood per beat and 20-30 l (21-32 qt) per

minute. The adult human heart is about the size of a fist and weighs about 250-350 gm(9 oz).

The human heart begins beating early in fetal life and continues regular beatingthroughout the life span of the individual. If the heart stops beating for more than 3 or 4minutes permanent brain damage may occur. Blood flow to the heart muscle itself alsodepends on the continued beating of the heart and if this flow is stopped for more than afew minutes, as in a heart attack, the heart muscle may be damaged to such a greatextent that it may be irreversibly stopped.

The heart is made up of two muscle masses. One of these forms the two atria (the

upper chambers) of the heart, and the other forms the two ventricles (the lowerchambers). Both atria contract or relax at the same time, as do both ventricles.

An electrical impulse called an action potential is generated at regular intervals in aspecialized region of the right atrium called the sinoauricular (or sinoatrial, or SA) node.Since the two atria form a single muscular unit, the action potential will spread over theatria. A fraction of a second later, having been triggered by the action potential, theatrial muscle contracts.

The ventricles form a single muscle mass separate from the atria. When the atrial actionpotential reaches the juncture of the atria and the ventricles, the atrioventricular or AV

node (another specialized region for conduction) conducts the impulse. After a slightdelay, the impulse is passed by way of yet another bundle of muscle fibers (the Bundleof His and the Purkinje system.) Contraction of the ventricle quickly follows the onset ofits action potential. From this pattern it can be seen that both atria will contractsimultaneously and that both ventricles will contract simultaneously, with a brief delaybetween the contraction of the two parts of the heart.

The electrical stimulus that leads to contraction of the heart muscle thus originates inthe heart itself, in the sinoatrial node (SA node), which is also known as the heart'spacemaker. This node, which lies just in front of the opening of the superior vena cava,measures no more than a few millimeters. It consists of heart cells that emit regularimpulses. Because of this spontaneous discharge of the sinoatrial node, the heartmuscle is automated. A completely isolated heart can contract on its own as long as itsmetabolic processes remain intact.

The rate at which the cells of the SA node discharge is externally influenced through theautonomic nervous system, which sends nerve branches to the heart. Through theirstimulatory and inhibitory influences they determine the resultant heart rate. In adults atrest this is between 60 and 74 beats a minute. In infants and young children it may be


12/17

between 100 and 120 beats a minute. Tension, exertion, or fever may cause the rate ofthe heart to vary between 55 and 200 beats a minute.

The Heart Sounds

The closure of the heart valves and the contraction of the heart muscle produce soundsthat can be heard through the thoracic wall by the unaided ear, although they can beheard better when amplified by a stethoscope. The sounds of the heart may berepresented as lubb-dubb-pause-lubb-dubb-pause. The lubb sound indicates theclosing of the valves between the atria and ventricles and the contracting ventricles; thedubb sound indicates the closing of the semilunar valves. In addition, there may also becardiac murmurs, especially when the valves are abnormal. Some heart murmurs,however, may also occur in healthy persons, mainly during rapid or pronounced cardiacaction. The study of heart sounds and murmurs furnishes valuable information tophysicians regarding the condition of the heart muscle and valves.

Coronary Circulation

The coronary arteries supply blood to the heart muscle. These vessels originate fromthe aorta immediately after the aortic valve and branch out through the heart muscle.The coronary veins transport the deoxygenated blood from the heart muscle to the rightatrium. The heart's energy supply is almost completely dependent on these coronaryvessels. When the coronary vessels become blocked, as in arteriosclerosis orhardening of the arteries, blood flow to the cardiac muscle is compromised. This iswhen the common "bypass surgery" is performed where the coronary arteries are"bypassed" by replacing them with, for example, a vein from the leg. A "double bypass"is when two coronary arteries are bypassed. A "triple bypass" is when three are

bypassed, etc.

The Heartbeat

The heart muscle pumps the blood through the body by means of rhythmicalcontractions (systole) and relaxations or dilations (diastole). The heart's left and righthalves work almost synchronously. When the ventricles contract (systole), the valvesbetween the atria and the ventricles close as the result of increasing pressure, and thevalves to the pulmonary artery and the aorta open. When the ventricles become flaccidduring diastole, and the pressure decreases, the reverse process takes place.

The Pulmonary Circulation

From the right atrium the blood passes to the right ventricle through the tricuspid valve,which consists of three flaps (or cusps) of tissue. The tricuspid valve remains openduring diastole, or ventricular filling. When the ventricle contracts, the valve closes,sealing the opening and preventing backflow into the right atrium. Five cords attached tosmall muscles, called papillary muscles, on the ventricles' inner surface prevent thevalves' flaps from being forced backward.


13/17

From the right ventricle blood is pumped through the pulmonary or semilunar valve,which has three half-moon-shaped flaps, into the pulmonary artery. This valve preventsbackflow from the artery into the right ventricle. From the pulmonary artery blood ispumped to the lungs where it releases carbon dioxide and picks up oxygen.

The Systemic Circulation

From the lungs, the blood is returned to the heart through pulmonary veins, two fromeach lung. From the pulmonary veins the blood enters the left atrium and then passesthrough the mitral valve to the left ventricle. As the ventricles contract, the mitral valveprevents backflow of blood into the left atrium, and blood is driven through the aorticvalve into the aorta, the major artery that supplies blood to the entire body. Theaortic valve, like the pulmonary valve, has a semilunar shape.

The aorta has many branches, which carry the blood to various parts of the body. Eachof these branches in turn has branches, and these branches divide, and so on untilthere are literally millions of small blood vessels. The smallest of these on the arterialside of the circulation are called arterioles. They contain a great deal of smooth muscle,

and because of their ability to constrict or dilate, they play a major role in regulatingblood flow through the tissues.

The major artery that supplies blood to the body is the aorta.

The blood passing through the arterioles passes through a bed of minute vesselscalled capillaries, which are a single cell thick. These capillaries are so small that thered blood cells must line up single file to pass through. The exchange of nutrients and


14/17

waste products takes place between the capillary blood and the tissue fluids. Thearterialized blood that enters the capillaries thus becomes venous blood as it passesthrough them.

The capillaries empty the venous blood into collecting tubes called venules, and these

in turn empty into small veins, which empty into larger veins, and so on until finally allthe blood returns to the heart through two large veins, the superior and inferior venacavae. These terminate in the right atrium, and the systemic circulation is complete.

A one-way flow of blood in this system is maintained by valves located, not only in theheart, but in the veins as well. Some veins also have semilunar valves and the pressureof contracting muscles against the veins works with the action of these valves toincrease the venous return to the heart. This is the reason that exercise is so importantfor the circulation.

The Lymphatic System

An often overlooked part of the circulatory system is the lymphatic system. As bloodpasses through the capillaries, some of the fluid diffuses into the surrounding tissues.One function of the lymphatic system is to collect and recycle this fluid (called lymph).Lymph passes from capillaries to lymph vessels and flows through lymph nodes that arelocated along the course of these vessels. Cells of the lymph nodes phagocytize, oringest, impurities such as bacteria, old red blood cells, and toxic and cellular waste.Finally, lymph flows into the thoracic duct, a large vessel that runs parallel to the spinalcolumn, or into the right lymphatic duct, both of which transport the lymph back intoveins of the shoulder areas where is mixes with blood and is returned to the heart. Alllymph vessels contain one-way valves, like the veins, to prevent backflow.

The tissues of the lymphatic system include the spleen. The spleen serves as areservoir for blood, releasing additional blood into the circulatory system as needed. It isalso involved with destruction of old cells and other substances by phagocytosis. Thelymphatic system is also responsible for collecting nutrients that the digestive systemhas extracted from our foods, and is a very important part of the immune system. Wewill cover the lymphatic system in detail in the lesson on the immune system.


15/17


16/17

The Blood

The blood transports life-supporting food and oxygen to every cell of the body andremoves their waste products. It also helps to maintain body temperature, transportshormones, and fights infections. The brain cells in particular are very dependent on a

constant supply of oxygen. If the circulation to the brain is stopped, death shortlyfollows.

Blood has two main constituents. The cells, or corpuscles, comprise about 45 percent,and the liquid portion, or plasma, in which the cells are suspended comprises 55percent. The blood cells comprise three main types: red blood cells, orerythrocytes;white blood cells, orleukocytes, which in turn are of many different types;and platelets, or thrombocytes. Each type of cell has its own individual functions in thebody. The plasma is a complex colorless solution, about 90 percent water, that carriesdifferent ions and molecules including proteins, enzymes, hormones, nutrients, wastematerials such as urea, and fibrinogen, the protein that aids in clotting.

Red Blood Cells

The red blood cells are tiny, round, biconcave disks, averaging about 7.5 microns(0.003 in) in diameter. A normal-sized man has about 5 l (5.3 qt) of blood in his body,containing more than 25 trillion red cells. Because the normal life span of red cells in thecirculation is only about 120 days, more than 200 billion cells are normally destroyedeach day by the spleen and must be replaced. Red blood cells, as well as most whitecells and platelets, are made by the bone marrow.

The main function of the red blood cells is to transport oxygen from the lungs to the

tissues and to transport carbon dioxide, one of the chief waste products, it to the lungsfor release from the body.

The substance in the red blood cells that is largely responsible for their ability to carryoxygen and carbon dioxide is hemoglobin, the material that gives the cells their redcolor. It is a protein complex comprising many linked amino acids, and occupies almostthe entire volume of a red blood cell. Essential to its structure and function is the mineraliron.

White Blood Cells

The leukocytes, or white blood cells, are of three types; granulocytes, lymphocytes,and monocytes. All are involved in defending the body against foreign organisms.

There are three types of granulocytes: neutrophils, eosinophils, and basophils, withneutrophils the most abundant. Neutrophils seek out bacteria and phagocytize, orengulf, them.


17/17

The lymphocytes' chief function is to migrate into the connective tissue and buildantibodies against bacteria and viruses. Leukocytes are almost colorless, considerablylarger than red cells, have a nucleus, and are much less numerous; only one or twoexist for every 1,000 red cells. The number increases in the presence of infection.

Monocytes, representing only 4 to 8 percent of white cells, attack organisms notdestroyed by granulocytes and leukocytes.

The granulocytes, accounting for about 70 percent of all white blood cells, are formed inthe bone marrow. The lymphocytes on the other hand are produced primarily by thelymphoid tissues of the bodythe spleen and lymph nodes. They are usually smallerthan the granulocytes. Monocytes are believed to originate from lymphocytes. Just asthe oxygen-carrying function of red cells is necessary for our survival, so are normalnumbers of leukocytes, which protect us against infection.

Platelets

Platelets, or thrombocytes, are much smaller than the red blood cells. They are round orbiconcave disks and are normally about 30 to 40 times more numerous than the whiteblood cells. The platelets' primary function is to stop bleeding. When tissue is damaged,the platelets aggregate in clumps to obstruct blood flow.

Plasma

The plasma is more than 90 percent water and contains a large number of substances,many essential to life. Its major solute is a mixture of proteins. The most abundantplasma protein is albumin. The globulins are even larger protein molecules than albumin

and are of many chemical structures and functions. The antibodies, produced bylymphocytes, are globulins and are carried throughout the body, where many of themfight bacteria and viruses.

An important function of plasma is to transport nutrients to the tissues. Glucose, forexample, absorbed from the intestines, constitutes a major source of body energy.Some of the plasma proteins and fats, or lipids, are also used by the tissues for cellgrowth and energy. Minerals essential to body function, although present only in traceamounts, are other important elements of the plasma. The calcium ion, for example, isessential to the building of bone, as is phosphorus. Calcium is also essential to theclotting of blood. Copper is another necessary component of the plasma.

Anatomy of the Digestive System and Circulatory System

Documents

Transcript of Anatomy of the Digestive System and Circulatory System