THE HUMAN DIGESTIVE SYSTEM

Food passes through the digestive tube in the following order

Oral cavity pharynx esophagus

(mouth) (throat) (gullet)

Stomach small large

intestine intestine

Rectum anus

HUMAN DIGESTIVE SYSTEM

• Liver, pancreas and salivary glands lie outside of the digestive tract and they are called as accessory organs.

• Food is never found within the alimentary canal itself.

• These organs aid digestion by the secretion of digestive fluids.

THE MOUTH AND PHARYNX

• Mechanical breakdown and chemical digestion occur.

• Chunks of food are bitten of with the teeth and ground into pieces small enough to swallow

• The tongue moves and shapes the food mass in the mouth

• Saliva is secreted into the mouth by three pairs of salivary glands

TYPES OF SALIVA

Thin, watery secretion that wets the food

Thicker, mucuous secretion that acts as a lubricant and causes the food particles to stick together to form a food mass (bolus)

• Saliva also contains a digestive enzyme called salivary amylase . (This enzyme breaks down starch, which is a polysacharide, into maltose, which is a disaccharide.)

• When the food has been chewed sufficiently , it is pushed by the tongue to the back of the throat, or pharynx. This starts the automatic swallowing reflex, which forces the food into the esophagus, the tube leading to the stomach.

• To prevent food and liquids from entering the larynx, it is automatically closed off during swallowing by a flap of tissue called epiglottis.

• At the same time, breathing stops momentarily and passageways to the nose, ears and mouth are blocked

THE ESOPHAGUS

• The esophagus is a tube through which food passes from pharynx to the stomach.

• Beginning in the esophagus, the movement of food down the digestive tube is aided by alternate waves of relaxation and contraction in the muscular walls of the alimentary canal. This is called peristalsis.

@

• Where the esophagus opens into the stomach , there is a ring of muscle called sphincter. There are two sphincters to isolate the stomach.

THE ESOPHAGUS

Cardiac sphincter

is located between the esophagus and the stomach

Pyloric sphincter

is located between the stomach and the intestine

• When the wave of peristalsis reaches the sphincter, it relaxes and opens, and the food (bolus) enters the stomach.

• During vomitting, a wave of peristalsis passes upward -reverse peristalsis- causing the cardiac sphincter to open, and the contents of the stomach to be “thrown up”

THE STOMACH

• The stomach is thick-walled muscular sac.

• Food is stored temporarily in the stomach.

• Mechanical breakdown and the partial digestion of protein occur.

• Churning of the stomach causes mechanical break down and helps the mixing of the food with its secretions.

GLANDS OF THE STOMACH

Pyloric glands

•Secretes mucus

•Mucus protects the lining of the stomach from being digested

Gastric glands

•Secretes gastric juice(pH 1.5 to 2.5)

GASTRIC JUICE

HCl •HCl kills the bacteria that are swallowed with food

•Activates pepsinogen

Pepsinogen

• Inactive form of pepsin and activated by HCl

•Breaks down large protein molecules into shorter chains of a.a called polypeptides.

In stomach:

Gastric Gland Pyloric Gland

Gastric juice = Hydrochloric acid + Pepsinogen + Mucus

HCl Pepsin Mucus

- kills most bacteria that

enter with food

- activates pepsinogen

Pepsinogen HCl Pepsin

- starts digestion of

proteins (breaks down

large protein

molecules into smaller

polypeptide chains)

- protects the lining of

stomach from HCl and

pepsin

GLANDS OF THE STOMACH

Control of Gastric Juice Secretion

thought/ sight/ smell/ taste of food

food in stomach

(touching the wall of stomach)

food in stomach gastrin (hormone) blood (stretching the wall of stomach)

gastric juice is secreted

GLANDS OF THE STOMACH

The breakdown of starch by salivary amylase which begins in the mouth, continues for some time after the food mass reaches the stomach. Gradually however, the low pH of the acid in the stomach inactivates this enzyme and starch breakdown.

THE STOMACH

There are three mechanisms involved in stimulating the flow of gastric juice.

1. The thought, sight, smell or taste of food stimulates the brain to send messages to the gastric glands, causing them to secrete moderate amounts of gastric juice

THE STOMACH

THE STOMACH2. Food touching the lining of the stomach stimulates the secretion of moderate amounts gastric juice.

3. When a food mass enters the stomach, it stretches the stomach wall. The streching of the stomach wall, as well as the presence of proteins, caffeine, alcohol and certain other substances, stimulates the lining of the stomach to secrete a hormone called gastrin directly into the blood. Gastrin further stimulates the gastric glands in the stomach to secrete large amounts of gastric juice.

THE STOMACH

•Liquids pass through the stomach in 20 minutes or less.

•Solids on the other hand, must first be reduced to a thin, soupy liquid called chyme

THE SMALL INTESTINE

chyme

pyloric sphincter

duodenum ileumjejenum

6.5 meters in length

2.5 cm in diameter

Most of the digestion takes place

FUNCTIONS OF THE SMALL INTESTINE:

1.Most of the chemical digestion takes place and completed in it

2. It is the site of absorption

It has a number of structural features that increase the surface area for absorbtion.

a) It is very longb) Its lining has many foldsc) The lining is covered with millions of finger-like

projections which are called villid) The epithelial cells that make up the intestinal

lining have brush borders. In the brush borders, the membranes of cells that face into the intestinal opening have tiny projections called microvilli that further increase the surface area of the cells.

THE SMALL INTESTINE

Within each villus , there is a network of blood capillaries and in the center of it there is a lacteal. Fatty acids and glycerol are absorbed into tiny lacteals of the lymphatic system.

• Absorption involves both diffusion and active transport.

• When food is present, the small intestine is in constant motion. This peristaltic movements have four effect:

1. They squeeze chyme through the intestine2. They mix the chyme with the digestive

enzymes3. They break down food particles mechanically4. They speed up absorption of digestive end

products by bringing the intestinal contents into contact with intestinal wall.

THE SMALL INTESTINE

Chyme from the stomach is mixed with

Pancreatic juice

from pancreas

Bile from the liver

Intestinal juice from glands in the wall of the intestine

*** Fluids in the small intestine are generally alkaline

PANCREAS

• Pancreas is located in the abdominal cavity between stomach and duodenum.

• It is both endocrine and exocrine gland.

• It secretes insulin and glucagon form the Islets of Langerhans

• pH of pancreatic juice is 8.5

PANCREATIC JUICE

• When the acidic chyme from the stomach enters the small intestine, it stimulates cells in the intestinal lining to secrete two hormones

SECRETINCHOLECYSTOKININ

Pancreas to secrete pancreatic juice and pancreatic enzymes

stimulates

onto the ampulla of vater in the duodenum part of the small intestine

pass throuh the pancreatic duct

PANCREATIC JUICE

Bicarbonate ions

•Converts the acidic chyme into alkaline solution

•Chyme is neutralised by HCO3-

and turns into alkaline solution.

H+ + HCO3 - H2 CO3

Acid from stomach

Bicarbonate from liver

and pancreas

Alkaline because

medium of intestine is

basic

Enzymes

1. Amylase

2. Proteases

3. Lipase

ENZYMES OF PANCREATIC JUICE

1. Pancreatic Amylase:

Starch + water maltose + dextrinamylase

2. Proteases

Trypsin

Trypsinogen trypsin

(inactive) (active)

chymotrypsinanterokinase

They continue the break down of large protein molecules into amino acids begun in the stomach

Polypeptides + water peptide + amino acids

Trypsin and chymotrypsin

ENZYMES OF PANCREATIC JUICE

3. Lipase

lipid fatty acids + glycerollipase

4 . Nucleases

Nucleic acids nucleotides

Digestion in small intestine

(pancreatic juice)

to secrete hormones

Acidic chyme cells in intestinal lining

Secretin and cholecystokinin

stimulate

Pancreas

to secrete

Pancreatic juice Pancreatic duct

given to

Small intestine

BILE• is secreted from liver• stored and concentrated in gall bladder• has no enzyme • is alkaline• consists of water, ions, cholesterol and bile salts, pigments• it passes from gall bladder to duodenum through the bile

duct• the release of bile from the gall bladder is stimulated by

cholecystokinin hormone.• it aids in the digestion of fats and oils by breaking them up

into tiny droplets. This is called emulsification. It increases the surface area for enzyme action.

• since bile is alkaline, it aids in neutralizing the acidic chyme from stomach.

Digestion in small intestine

(bile from gall bladder)

Bile produced in the liver

Hormone cholecystokinin

stored in the gallbladder

releases bile into the

Bile duct

opens to

Small intestine

Bile is transfered from liver to duodenum through the choledoc duct onto the ampulla of vater

Numerous oil droplets are physically formed as a result of emulsification.

INTESTINAL JUICE

• The wall of the small intestine contain millions of intestinal glands, which secrete intestinal juice.

1. Peptides amino acids

2. Maltose 2 glucose

3. Sucrose glucose+fructose

4. Lactose glucose+galactose

(erepsin)

peptidase

maltase

sucrase

lactase

DIGESTION IN INTESTINE

1.Remaining Polypeptide peptides

2. Peptides amino acids

3. Remaining starch disaccharides

peptidase

(erepsin)

Pancreatic amylase

Trypsin

chymotrypsin

4.Maltose 2 glucose

5.Sucrose glucose+fructose

6.Lactose glucose+galactose

7. Lipids fatty acids+ glycerol

8. Nucleic acids nucleotides

DIGESTION IN INTESTINE

maltase

sucrase

lactase

lipases

nucleases

HORMONE SOURCE TARGET TISSUE

ACTION FACTORS THAT STIMULATE RELEASE

Gastrin Stomach(Mucosa)

Stomach(Gastric

glands)

Stimulates gastric glands to secrete pepsinogen

Presence of food in stomach and certain substances such as caffeine

Secretin Small intestine

(Duodenum mucosa)

Pancreas Signals secretion of sodium bicarbonate

Acidic chyme acting on mucosa of duodenum (small intestine)

Liver Stimulates bile secretion

Cholecytokinins

Small intestine

(Duodenum mucosa)

Pancreas Stimulates release of digestive enzymes

Presence of fatty acids and partially digested proteins in duodenum

(small intestine)

Gallbladder Stimulates emptying of bile

HORMONAL CONTROL OF DIGESTION

LARGE INTESTINE

• Undigested and unabsorbed materials pass from the small intestine through a sphincter into the large intestine.

• No digestion occurs• On the right side of the abdomen, where the small

intestine joins the large intestine, is a small pouch the appendix.(It plays no part in the HDS)

• The appendix becomes infected or inflamed, a condition known as appendicitis

FUNCTIONS OF THE LARGE

1. Reabsorbtion of water form the food mass ¾ of water is reabsorbed.

• If too much water is reabsorbed, constipation results.

• If too little water is reabsorbed , diarrhea results.

2. The absorption of vitamins (vitamin K and Vitamin B) that are produced by bacteria that normally live in the large intestine.

3. The elimination- removal of undigested and indigestible material from the digestive tract.

LARGE INTESTINE

• This material consists of cellulose, bacteria, bile, mucus and worn-out cells from the digestive tract. As this material travels through the intestine, it becomes feces.

• Fecal matter is stored in the rectum and periodically eliminated, through the anus.

Check If Your Feces Are Healthy Dietary fibers and lactobacillus bifidus are essential for a healthy and comfortable life.The best feces are like bananas. They are modestly hard with no strong smell. Feces are like a barometer of your health and beauty. Check the following questions to see if you have a healthy feces or not. 

Do they float?They float..................1 pointThey sink...................2 points

                                                 

How often do you evacuate?Once a day............1 pointNot everyday.......2 points

                  

How hard are they?Like toothpaste.........1 pointHard.............................2 points

                                          

What color are your feces?Yellow.....................1 pointDark brown..........2 points

                                 

How much do they weight? ( 2 pcs of feces a day, each about 2cm in diameter and about 15cm in length )Over 200g.............1 pointBelow 200g...........2 points                                             

Do your feces smell?Not much.................1 pointBad smell................2 points

                          

If you score:7 to 9 points..........You are quite healthy10 to 12 points......Be careful what you eat everyday Take more dietary fibres.13 to 14 points......Warning! If these conditions continue long, you should see a doctor.

                                                            

Like pebbles...2points Like paste....1 point

                                                              

Like banana....1 point Very hard....2 point

                                           

                                    

Liquid....2 point Like mud....2 point