Digestive System- Vasanth

8/12/2019 Digestive System- Vasanth

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Digestive system

Introduction

What happens to food after it is eaten?

The body uses various kinds of food for energy and growth. To be used, however,

food must be converted into nutrients that can be carried through the bloodstream and

absorbed by the organism's cells.This conversion process is called digestion.

Digestion takes place in a series of organs that together are called the alimentary

canal,or digestive tract.

In simple invertebrates,such as worms, this may consist of a simple or specialied

tube or duct! food enters at one end and waste is eliminated at the other.


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In humans and other vertebrates, the system is more developed, and consists of a

group of connected organs"the mouth, pharyn#, esophagus, stomach, small and large

intestines, and anus. Through these structures, food is processed via mechanical and

chemical action into usable nutrients and e#pendable waste. $lthough the liver,gallbladder, and pancreasplay a critical role in digestion, they are not part of the

digestive tract itself.

The structure of the digestive system is adapted to diet rather than body sie. Tough

plant materials such as cellulose re%uire longer and more intensive digestion than do

foods such as meat or milk.

Herbivorous &planteating( animals have highly comple# digestive systems. The cow,

for e#ample, has four sections to its stomach. The small and large intestines of all

herbivores, regardless of body sie, have specialied areas that help digest plant fibers

"thus the comple#ity of an elephant's intestines is the same as that in a pygmy goat.

The digestive system of carnivorous&meateating( animals is relatively simple and

considerably shorter than that found in herbivores.

)umans and other animals that eat both plant and animal matter are called

omnivores.Their digestive tracts are not as simple as those of carnivores, nor as

comple# and specialied as in herbivores. *ather, the digestive system of an omnivore

generally contains some characteristics of both herbivores and carnivores.

Process ~digestion:

Where Digestion Begins ~mouth,gullet,epiglottis

Digestion begins in the mouth,where the food is cut and chopped by the

teeth. The tongue helps mi# the food particles with a digestive +uice called

saliva, which is secreted by glands in the mouth. Thorough chewing cuts food

into small pieces that are more easily attacked by saliva, which moistens thefood so it can be swallowed easily. aliva also contains the enyme amylase,

which changes some starches into simple sugars.

-rom the mouth the food is swallowed into the tubelike esophagus, or gullet.

Peristalsis ~~ a wavelike muscular movementof the esophagus walls, forces

food down the esophagus to the stomach. eristalsis takes place throughout the

digestive tract. /nlike swallowing, which is a voluntary muscular action,

peristalsis is involuntary, and is controlled by nerve impulses stimulated by the

tract's contents .


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$s food is swallowed, a flap called the epiglottis closes the windpipe, or

trachea, to prevent choking.

/nder normal circumstances, a person is unaware of the movements of theesophagus, stomach, and most of the intestine.

Work of the Stomach

$t the end of the esophagus there is a muscular valve, or sphincter, through which

food enters the stomach. This esophageal sphincterkeeps food in the stomach from

being forced back into the esophagus.

Peristalsis in the stomachchurns the food and mi#es it with mucus and with gastric

+uices, which contain enymes and hydrochloric acid. These +uices are secreted from

millions of small glands in the lining of the upper stomach walls. The glands pour

about three %uarts of fluid into the stomach daily. )ydrochloric acid maintains the

acidic environment necessary for the stomach enymes, such as pepsin, to function.

The mucus that is secreted protects the stomach wall from being harmed by the acid .

The stomach churns the food into a thick liquid~~ called chyme. $ strong sphincter

muscle in thepyloric region near the bottom of the stomachfurther mashes the chyme

and helps control the rate at which it is passed outof the stomach and into the

duodenum, or upper small intestine. The sphincter also prevents the chyme from

passing back into the stomach. $s the digestive process in the stomach is completed,

all the chyme ispassed into the duodenum.This process continues over a period of

time.

01 to 21 hours for food to travel the length of the digestive tract. Different kinds of

food are held in the stomach for varying lengths of time.

Complex carbohydrates, such as whole grains and vegetables, are held usually no

more than one to two hours3 refined starches and sugars move from the stomach and

into the small intestine even more %uickly.

Protein foodsare retained for three to five hours, and

fat foodsmay remain in the stomach even longer. This is why eating a heavy dinner

of meat, potatoes, and gravy satisfies hunger longer than one made up entirely of

sweets or greens.


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The stomach, though important, is not considered by physicians to be essential to

life. eople who have had their stomachs completely or partially removed are

fre%uently able to live by taking special foods in small %uantities many times a day.

The small intestine is then able to perform all necessary digestion.

Work of the Small Intestine

In the small intestine, proteins are changed into amino acids fats are changed into

fatty acids and carbohydrates are changed into sugars . These products are soluble

and can be absorbed into the bloodstream through the walls of the small intestine.

The main areas of the small intestine are the duodenum, !e!unum, and ileum. In

humans, the small intestine, which measures from 44 to 45 feet &6.7 to 7.6 meters(

long, is the longest part of the digestive tract.

-ood remains in the small intestine for several hours. Digestion here is aided by

secretions produced by the liver and pancreas, which are connected to the small

intestine by ducts.

The pancreas is one of the most important glands in the body. It secretes pancreatic

+uice, which contains digestive enymes such as trypsin, which helps digest protein

foods3 amylase and maltase, which break down carbohydrates3 and lipase, which

works with bile from the liver to digest fat.

Bile is produced in the liver but stored in the gallbladder, a small hollow organ

located +ust under the liver. 8ile does not contain enymes3 rather, it consists chiefly

of acids, salts, cholesterol, and other substances that work with lipase to break down

fats.

The gallbladder, which is prone to numerous disorders, can be surgically removed

without serious effect.

The liver, however, is essential to life. It has many important functions, such as

removing to#insfrom the body and producing clottingfactors for the blood. The liver

is an important site of metabolism3 proteins and fats are synthesied here, and sugars

are converted to glycogen, which is then stored in the liver until it is needed for

energy.

Working:

$s food is broken down in the small intestine it is further diluted by fluid

secreted by glands in the intestinal wall.


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The lining of the small intestine contains many folds that e#pand its surface

area, allowing increased contact between the wall and food products.

Villi~operation :

The surface area is further increased by thousands of villi, microscopic

fingerlike pro+ections of the intestinal wall. 9utrients pass through the cell

membranes of the villi and are taken into the blood and lymph, which carry

them to the cells, where they are used for energy and growth.

8y the time the diluted food products have traveled the length of the small

intestine, most of their nutrients have been absorbed into the bloodstream.

ome water is absorbed here, though most water is reabsorbed in the large

intestine.

Work of the "arge Intestine

The large intestine is made up of the

ascending colon

transverse colon

descending colon

rectum

anus.

In the large intestine water is reabsorbed through the intestinal wall, converting the

remaining waste into solids that are passed from the body as feces. The colon is

populated by bacteria that digest any remaining food products. These bacteria also

produce folic acid, which prevents anemia, and other vitamins.

#eristalsismoves digested material from the small intestine into the ascending

colon through a sphincter muscle, which prevents their return into the small

intestine.

Peristalsis in the large intestine is much slower than in other parts of the

digestive tract. The large intestine in humans is only about 6 feet &4 meters(

long, yet waste material takes :1 to 41 hours to pass through it.

In the ascending colon, fluids and salts are absorbed.

In the transverse colonmore water is removed from the waste materials until

they are in solid form.

The descending colon is a holding area for solid waste. When the body is

ready to eliminate this material, it moves into the rectum, the last 5 to 6 inches


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&:0 to :5 centimeters( of the descending colon. When enough waste material

accumulates, it is eliminated through the anus"the open end of the rectum"

as feces.

$sphincterat the edge of the anus prevents fecal material from leaving the

body involuntarily.

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Digestive System- Vasanth