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.
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• 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