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THE DIGESTIVE SYSTEM

AND HUMAN NUTRITION



THE DIGESTIVE SYSTEM



WHAT IS DIGESTION?

process by which food and drink are broken down into

their smallest parts so the body can use them to build

and nourish cells and to provide energy.

involves mixing food with digestive juices, moving it

through the digestive tract, and breaking down large

molecules of food into smaller molecules. Digestion

begins in the mouth, when you chew and swallow, and

is completed in the small intestine.



DIGESTIVE

S YSTEM

a complex series of organs and glands

that processes food

body system tasked to break the food

down into smaller molecules that it can

process and, excrete waste.



made up of the digestive tract: a series of

hollow organs joined in a long, twisting

tube from the mouth to the anus and

other organsOrgans that make up the digestive tract

are the mouth, esophagus, stomach,

small intestine, large intestine,

rectum, and anus.



THE DIGESTIVE

PROCESS, PARTS AND FUNCTIONS



SWALLOWING



mouth: The digestive process begins in

the mouth. Food is partly broken down by

the process of chewing and by the chemical

action of salivary enzymes; these enzymes

are produced by the salivary glands and

break down starches into smaller

molecules.



The pharynx facilitates the passage of the food bolus

into the esophagus. The pharynx is designed to direct

the food bolus in this direction. After the moistened

food bolus is moved to the back of the mouth by the

tongue, an involuntary swallowing reflex is triggered

which prevents food from entering the respiratory

tract



The tongue closes off the mouth,

the soft palate blocks the nose,

and the larynx rises such that the

epiglottis closes off the trachea.

Food then moves from the pharynx

into the esophagus.



esophagus: After being chewed and swallowed, the

food enters the esophagus. The esophagus is a long

tube that runs from the mouth to the stomach. It

uses rhythmic, wave-like muscle movements to force

food from the throat into the stomach. This muscle

movement gives us the ability to eat or drink even

when we're upside-down.



At the junction of the esophagus and stomach,

there is a ring-like muscle, called the lower

esophageal sphincter, closing the passage between

the two organs



NUTRIENTS

Carbohydrates spend the least amount of time in the

stomach, while protein stays in the stomach longer,

and fats the longest.



Carbohydrates: The carbohydrates are broken into

simpler molecules by enzymes in the saliva, in juice

produced by the pancreas, and in the lining of the

small intestine.



Starch: First, an enzyme in the saliva and

pancreatic juice breaks the starch into molecules

called maltose. Then an enzyme in the lining of the

small intestine splits the maltose into glucose

molecules that can be absorbed into the blood.

Glucose is carried through the bloodstream to theliver, where it is stored or used to provide

energy for the work of the body.



Sugar: An enzyme in the lining of the small

intestine digests sucrose, also known as table

sugar, into glucose and fructose, which are

absorbed through the intestine into the blood. Milk

contains another type of sugar, lactose, which is

changed into absorbable molecules by anotherenzyme in the intestinal lining.



Fiber: moves through the digestive tract without

being broken down by enzymes. Many foods

contain both soluble and insoluble fiber. Soluble

fiber dissolves easily in water and takes on a soft,

gel-like texture in the intestines. Insoluble fiber, on

the other hand, passes essentially unchangedthrough the intestines.



Protein: Foods such as meat, eggs, and beans consist of

giant molecules of protein that must be digested by

enzymes before they can be used to build and repair

body tissues. An enzyme in the juice of the stomach starts

the digestion of swallowed protein. Then in the small intestine,

several enzymes from the pancreatic juice and the lining of

the intestine complete the breakdown of huge protein

molecules into small molecules called amino acids. These

small molecules can be absorbed through the small intestine

into the blood and then be carried to all parts of the body to

build the walls and other parts of cells.



6. Fats: Fat molecules are a rich source of energy for the

body. The first step in digestion of a fat is to dissolve it into the

watery content of the intestine. The bile acids produced by theliver dissolve fat into tiny droplets and allow pancreatic and

intestinal enzymes to break the large fat molecules into

smaller ones. Some of these small molecules are fatty acids

and cholesterol. The bile acids combine with the fatty acids

and cholesterol and help these molecules move into the cells

of the mucosa. In these cells the small molecules are formed

back into large ones, most of which pass into vessels called

lymphatics near the intestine. These small vessels carry the

reformed fat to the veins of the chest, and the blood carries

the fat to storage depots in different parts of the body.



Vitamins. Fat-soluble vitamins (A,D, E, K) are

stored in the liver and fatty tissue of the body,

whereas water-soluble vitamins (B and C) are not

easily stored and excess amounts are flushed out

in the urine.



The digested nutrients are absorbed

through the intestinal walls and

transported throughout the body.



DIGESTIVE SYSTEM OF

OTHER ANIMALS Animals, for the most part, ingest their food as large,

complex molecules that must be broken down into

smaller molecules that can then be distributed

throughout the body of every cell.



Single-celled organisms can directly take in

nutrients from their outside environment.

Multicellular animals, with most of their cells

removed from contact directly with the outside

environment, have developed specialized

structures for obtaining and breaking down theirfood.



Ingestive eaters, the majority of animals, use a mouth

to ingest food. Absorptive feeders, such as tapeworms,

live in a digestive system of another animal and absorb

nutrients from that animal directly through their body

wall. Filter feeders, such as oysters and mussels,

collect small organisms and particles from the

surrounding water. Substrate feeders, such as

earthworms and termites, eat the material (dirt or wood)

they burrow through. Fluid feeders, such as aphids,

pierce the body of a plant or animal and withdraw fluids.

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Two types of animal body plans as well as two

locations for digestion to occur: Sac-like plans are

found in many invertebrates, who have a single

opening for food intake and the discharge of

wastes. Vertebrates, the animal group humans

belong to, use the more efficient tube-within-a-

tube plan with food entering through one opening

(the mouth) and wastes leaving through another

(the anus).

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Where the digestion of the food happens is also

variable: Some animals use intracellular digestion,

where food is taken into cells by phagocytosis withdigestive enzymes being secreted into the phagocytic

vesicles. This type of digestion occurs in sponges,

coelenterates (corals, hydras and their relatives) andmost protozoans. Extracellular digestion occurs in

the opening of a digestive system, with the nutrient

molecules being transferred to the blood or some

other body fluid. This more advanced type of digestion

occurs in chordates, annelids, and crustaceans.



Chemotrophs are organisms (mostly bacteria)

deriving their energy from inorganic chemical

reactions. Phototrophs convert sunlight energy into

sugar or other organic molecules. Heterotrophs eat

to obtain energy from the breakdown of organic

molecules in their food.

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STOMACH



is a muscular sac that lies between theesophagus and the small intestine in the upper

abdomen.

the stomach is not the only part of your digestivesystem that absorbs food but rather is a part of the

digestive system and important for churning food

into a consistency that is easier to digest for therest of your intestines.

http://www.laparoscopic.md/digestion/esophagus

http://www.laparoscopic.md/digestion/intestine

http://www.laparoscopic.md/digestion/intestine

http://www.laparoscopic.md/digestion/esophagus



THE STOMACH’S FUNCTIONS

The stomach is J-shaped and it can expand to

temporarily store food.

Partial digestion of the food takes place here. The

churning action of the stomach muscles physically

breaks down the food.

The stomach releases acids and enzymes for the

chemical breakdown of food. The enzyme pepsin is

responsible for protein breakdown.

The stomach releases food into the small intestine

in a controlled and regulated manner.



Cardia

is the first portion of the stomach and is where food

content passes from the esophagus into the stomach.

The acids and enzymes referred to as the gastric

juices are manufactured in the cardia.

Fundus

stores undigested food and also the gases released

from the chemical digestion of food.



Corpus

is the largest of the four parts that make up the

stomach. And this is where the bulk of the partial

digestion occurs.

Pylorus

is connected to the duodenum or the beginning of the

small intestine. The contents of the stomach move

into the small intestine via the pyloric canal.



THE STOMACH WALL

Mucosa

consists mainly of the gastric glands that secrete the

digestive juices. It is covered by a layer of columnar

epithelial tissue.

Sub-mucosa

consists of dense connective tissue and has blood

vessels, lymphatic vessels, and nerves running through it.

The sub-mucosa supports the mucosa and allows it to

move in a flexible manner during peristalsis.



Peristalsis- is the contraction and relaxation of the

stomach muscles to physically breakdown food

and propel it forward. These contractions are

created by the muscular wall of the stomach which

consists of inner circular and outer longitudinal

smooth muscle.

Serosa

consists of an epithelial layer and connective tissue

which connects to the surrounding organs.



CELL TYPES IN THE STOMACH THAT HELP WITH

DIGESTION

Mucous cells secrete the alkaline mucous for

shielding the epithelium from hydrochloric acid.

Parietal cells, the acid activates release of pepsin

for protein digestion. The acid also kills micro-

organisms swallowed with the food.

Chief cells secrete pepsin.

G cells secrete gastrin which stimulates the

secretion of hydrochloric acid.



LIVER

system is to process the nutrients absorbed from

the small intestine. Bile from the liver secreted into

the small intestine also plays an important role in

digesting fat.

In addition, the liver is the body’s chemical "factory."

It takes the raw materials absorbed by the intestine

and makes all the various chemicals the body

needs to function.

It breaks down and secretes many drugs.



P ANCREAS

secretes digestive enzymes into the duodenum, the

first segment of the small intestine. These enzymes

break down protein, fats, and carbohydrates.

also makes insulin, secreting it directly into the

bloodstream. Insulin is the chief hormone for

metabolizing sugar.



G ALLBLADDER

stores and concentrates bile, and then releases it

into the duodenum to help absorb and digest fats.



SMALL INTESTINE



is about 20 feet long and about an inch in diameter

absorb most of the nutrients from what we eat and

drink

Velvety tissue lines the small intestine, which is

divided into the duodenum, jejunum, and ileum.



DUODENUM

The C-shaped first part of the small

It protects the duodenal lining from the acidity of the

chyme and raises the luminal pH to the optimum

level for pancreatic enzyme activity

It is also the point of entry for the bile and

pancreatic ducts, which penetrate the full thickness

of the duodenal wall



FUNCTION

receives roughly digested and mixed food from the

stomach and neutralizes the stomach acid.

also receives bile from the galbladder and digestive

enzymes from the pancreas. The combination of

food, bile and enzymes are mixed with mucus and

passed into the jejunum. The intermixed structure

of protein, fats and carbohydrates of food is broken

apart as it passes through the duodenum.



JEJUNUM

The passage that takes place between the

duodenum and jejunum

The jejunum is not only second in order but is also

second in length when talking of the small intestine,

measuring around 8.2 feet.



FUNCTION

The combination of food, bile, enzymes and mucus

passes into the jejunum after exiting the duodenum.

The inner lining of the jejunum and the later section

the ileum are lined with villi, small fingers containing

capillaries that increase the surface area that can

absorb nutrients.



The jejunum absorbs nutrients such as

carbohydrates that have been broken down into

simple sugars, proteins that have been broken

down into amino acids and many vitamins.

Much of this transport is accomplished by an array

of transporter proteins that shuttle the nutrients

from the intestines to the capillaries.



ILEUM

the longest and the lowest part of small intestine,

coming in at eleven and a half feet.

The ileum is slightly paler in color when compared

to the jejunum and mostly absorbs fatty acids and

glycerol, besides glucose and amino acids.



FUNCTION

Water, minerals and salts as well as fats and

remaining nutrients are absorbed by the ileum.

Where much of the initial transport of nutrients was

specific, the ileum takes small amounts of water as

well as the minerals and vitamins floating in it and

shuttles them into the capillaries.

Fats are able to pass directly from the intestines to

the bloodstream.



MICROSCOPIC P ARTS OF SMALL INTESTINE

The membrane that connects all parts of the small

intestine is known as the mesentery. This membrane is

richly supplied by blood vessels in the form of small

capillaries which help in absorption of food.

The internal lining of the small intestine in the ileum

consists of glandular epithelium which is present in the

form of highly convoluted and folded microscopic

structures known as microvilli



L ARGE INTESTINE



The large intestine is the second to last part of the

digestive system—the final stage of the alimentary

canal is the anus —in vertebrate animals. Its

function is to absorb water from the remaining

indigestible food matter, and then to pass useless

waste material from the body.

The large intestine consists of the cecum and

colon. It starts in the right iliac region of the pelvis,

just at or below the right waist, where it is joined to

the bottom end of the small intestine.



From here it continues up the abdomen, then

across the width of the abdominal cavity, and then itturns down, continuing to its endpoint at the anus.

The large intestine is about long, which is about

one-fifth of the whole length of the intestinal canal.

The large intestine takes 32 hours to finish up the

remaining processes of the digestive system. Food

is not broken down any further in this stage

of digestion.



FUNCTION

The large intestine simply absorbs vitamins that are

created by the bacteria inhabiting the colon. It also

absorbs water and compacts feces, and stores fecal

matter in the rectum until eliminated through the anus

and thus is responsible for passing along solid waste.

Cecum The cecum marks the beginning of



Cecum- The cecum marks the beginning of

the large intestine and is basically a big pouch that

receives waste material from the small intestine.

Ascending Colon- The ascending colon runsthrough the abdominal cavity, upwards toward the

transverse colon for approximately eight inches (20

cm).



Transverse Colon- The transverse colon is the large

part of the colon that attaches the ascending colon

to the descending colon by crossing the abdominal

cavity.

Descending Colon- The descending colon traverses

inferiorly along the left abdominal wall to the pelvic

region.



Rectum- The rectum is a short, muscular tube that forms

the lowest portion of the large intestine and connects it

to the anus. Feces collects here until pressure on the

rectal walls cause nerve impulses to pass to the brain,

which then sends messages to the voluntary muscles in

the anus to relax, permitting expulsion.



Appendix- The appendix, also called the (veriform),

is a troublesome pouch attached to the first portionof the large intestine. Digestion takes place almost

continuously in a watery, slushy environment. The

large intestine absorbs water from its inner contentsand stores the rest until it is convenient to dispose

of it. The appendix has no function in modern

humans; however, it is believed to have been part

of the digestive system in our primitive ancestors.



HOW DO THE WASTE MATERIALS MOVE

THROUGHOUT THE LARGE INTESTINE?

Peristalsis is the coordinated contraction of muscle

movement to move food or waste through a tube.

To simplify, food and waste particles are squeezed

through a tube-like structure by a squeezing

motion. Peristalsis takes place in

the esophagus when an individual swallows food. It

also takes place in the colon as it moves solid

waste through the large intestine to be expelled

from the body through the rectum.

the digestive system and human nutrition continue

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