physiology of GI system

1. GASTRO INTESTINAL
SYSTEM

2.  Ingestion
 Propulsion
 Digestion
 Absorption
 Elimination

3.  This is taking of food into the
alimentary tract that is eating and
drinking

4.  This mixes and moves the contents
along the alimentary tract

5.  This consist of 2 processes
Mechanical Digestion: larger pieces of food get
broken down into smaller pieces while being
prepared for chemical digestion. Mechanical
digestion starts in the mouth and continues in to
the stomach.
Chemical Digestion: several different enzymes
break down macromolecules into smaller
molecules that can be more efficiently
absorbed. Chemical digestion starts with saliva
and continues into the intestines.

6.  This is the process by which digested
food substances pass through the
walls of some organs of the alimentary
canal into the blood for circulation and
use by body cells

7.  Food substances that have been eaten
but cannot be absorbed are excreted
from the alimentary canal as faeces by
the process of defaecation.

9. Tongue plays an important part in
 Chewing (mastication)
 Swallowing (deglutition)
 Speech
 Taste

11.  Mastication or chewing is the process
by which food is crushed and ground by
teeth. It is the first step of digestion.
 During the mastication process, the
food is positioned by the cheek and
tongue between the teeth for grinding.

12.  The muscles of mastication move the jaws to
bring the teeth into intermittent contact,
repeatedly occluding and opening.
 As chewing continues, the food is made
softer and warmer, and the enzymes in saliva
begin to break down carbohydrates in the
food.
 After chewing, the food (now called a bolus)
is swallowed

14.  Swallowing of food happens when the muscles in the
tongue and mouth move the food into pharynx.
 The pharynx, which is the passageway for food and
air, is about five inches (5") long.
 A small flap of skin called the epiglottis closes over
the pharynx to prevent food from entering the
trachea.
 For swallowing a combination of 25 muscles must
all work together at the same time.
 Salivary glands also produce an estimated three liters
of saliva per day.

15.  The tongue is the most important articulator
for speech production. During speech, the
tongue can make amazing range of
movements

17.  The primary function of the
tongue is to provide a mechanism for taste.
Taste buds are located on different areas of the
tongue, but are generally found around the
edges.They are sensitive to
four main tastes: Bitter, Sour,
Salty & Sweet

18.  Chewing and grinding

20.  Chemical digestion of polysaccharides
 Lubrication of food
 Cleaning and lubricating the mouth
 Defence
 taste

21.  Saliva contains enzyme amylase that begins
the breakdown of the complex sugars.
Salivary pH is ranges from 5.8 to 7.4.

22.  Dry food entering into the mouth is
moistened and lubricated by saliva before it
made into bolus ready for swallowing

23.  Adequate flow of saliva is necessary to
cleanse the mouth and keep its tissue soft
and moist. It helps to prevent damage to the
mucous membrane by rough and abrasive
food stuffs.

24.  Lysozyme and immunoglobulin prevent
invading of micro organism

25.  The taste buds are stimulated only by
chemical substances in solution. Dry foods
stimulate the sense of taste only after mixing
with saliva.

26.  Pharynx is a passage way of food from oral
cavity to esophagus.

27.  Formation of bolus
Food is masticated by the teeth and moved
round the mouth by the tongue and muscles
of the cheeks.
saliva makes the food soft and that is bolus
ready for swallowing.

28.  Deglutition or swallowing
this occurs in 3 stages after mastication
 The mouth is closed and voluntary muscles of the
tongue and cheeks push the bolus backwards into
the pharynx
 The muscles of the pharynx are stimulated by a
reflex action initiated in the walls of the
oropharynx and coordinated in the medulla and
lower pons in the brain stem contraction of these
muscles propels the content into esophagus

29.  The presence of the bolus in the pharynx
stimulates a wave of peristalsis which propels
the bolus through the esophagus to the
stomach

30.  Stomach size varies with volume of food it
contains which may be 1.5 litres or more in an
adults. Mixing with gastric juice takes place
here.

31.  About 2 litres of gastric juice are secreted
daily by secretory glands in the mucosa. It
consist of
 Water
 Mineral salts
 Mucus
 HCL
 Pepsinogen

32.  Water further liquefies the food swallowed
 HCL
o Acidifies the food and stops the action of
salivary amylase
o Kills the ingested microbes
o Provides the acid environment needed for
effective digestion by pepsins

33.  Pepsinogen
These activated to pepsins by HCL , they begin
the digestion of proteins, breaking them into
smaller molecules. Pepsin act most
effectively at pH 1.5 to 3.5
 Mucus
It prevents mechanical injury to the stomach
walls by lubricating the contents.

34.  There is always a small quantity of gastric
juice present in the stomach even when it
contain no food.This is known as fasting
juice. Secretion reaches its maximum level
about 1 hour after a meal then declines to the
fasting level after about 4 hours

35.  Cephalic phase
 Gastric phase
 Intestinal phase

36.  Cephalic phase
Flow of juice occurs before food reaches the
stomach and is due to reflex stimulation of
the vagus nerve initiated by the sight, smell
or taste of food

37.  Gastric phase
Stimulated by the presence of food ,the
enteroendocrine cells in the antrum and
duodenum secrete gastrin, a hormone which
passes directly into the circulating blood it
stimulate gastric gland to produce more
gastric juice

38.  Intestinal phase
When the partially digested contents of the
stomach reach the small intestines slow
down of gastric juice secretion occurs with
the help of 2 hormones secretin and
cholecystokinin(CCK)

39.  Temporary storage allowing time for the
digestive enzyme pepsin to act
 Chemical digestion- pepsins convert proteins
to polypeptides
 Limited absorption of water and lipids
 Defence against microbes
 Absorption of iron and vitamins
 Passage of gastric contents into the
duodenum

40.  Intestinal juices
About 1500 ml of intestinal juice are secreted
daily by the glands of the small intestine
Consist of
• Water
• Mucus
• Mineral salts
• Enzymes
The pH-7.8 and 8.0

41.  Onward movements of its contents by
peristalsis, which is increased by
parasympathetic stimulation
 Secretion of intestinal juice also increased by
parasympathetic stimulation
 Completion of chemical digestion of
carbohydrates, protein, and fats in the
enterocytes of the villi
 Protection against infection
 Absorption of nutrients
 Secretion of cholecystokinin(CCK) and secretin

42.  When acid chyme (the pulpy acidic fluid which
passes from the stomach to the small intestine,
consisting of gastric juices and partly digested
food.) passes into the small intestine it is mixed
with pancreatic juice, bile, and intestinal juice and
is in contact with the enterocytes of the villi
 Villi are the finger-like projections of the lining of
the small intestine which is specialized in
absorption of nutrients.

43.  In the small intestine digestion of all the
nutrients is completed:
 CHO are broken down to
monosaccharides
 Proteins are broken down to amino acids
 Fats are broken down to fatty acids and
glycerol

46.  Pancreatic juice is secreted by the
exocrine pancreas and enters the
duodenum at the duodenal
papilla. It consist of
• Water
• Mineral salts
• Enzymes(amylase and lipase)
• Inactive enzyme
(trypsinogen,chymotrypsinogen)

47.  The pancreas contains exocrine glands that
produce enzymes important for digestion.
 These enzymes include trypsin and
chymotrypsin to digest proteins;
 amylase for the digestion of carbohydrates
 lipase to break down fats.

48.  The liver regulates most chemical levels in the
blood and excretes a product called bile.
 Bile helps to break down fats, preparing them
for further digestion and absorption.
 All of the blood leaving the stomach and
intestines passes through the liver.
 The liver processes this blood and breaks down,
and creates nutrients for the body to use.
 It also metabolized drugs in the blood into
forms that are easier for the body to use.

49.  Store and release glucose as needed
 Processing of hemoglobin for use of its iron content
(the liver stores iron)
 Conversion of ammonia to urea (urea is one of the
end products of protein metabolism that is excreted
in the urine)
 Clearing the harmful substances from blood

50.  Regulating blood clotting
 Resisting infections by producing immune
factors and removing bacteria from the
bloodstream
 Clearance of bilirubin (if there is a buildup
of bilirubin, the skin and eyes turn yellow)

51. • Bilirubin is made in the body when old red
blood cells are broken down. The breakdown
of old cells is a normal, healthy process. After
circulating in blood, bilirubin then travels to
liver. In the liver, bilirubin is excreted into the
bile duct and stored in gallbladder.
Eventually, the bilirubin is released into the
small intestine as bile to help digest fats and
ultimately excreted with stool.

52.  Indirect (or unconjugated) bilirubin. This form
of bilirubin does not dissolve in water (it is
insoluble). Indirect bilirubin travels through the
bloodstream to the liver, where it is changed into a
soluble form (direct or conjugated).
 Direct (or conjugated) bilirubin. Direct bilirubin
dissolves in water (it is soluble) and is made by the
liver from indirect bilirubin.
 Total bilirubin and direct bilirubin levels are
measured directly in the blood, whereas indirect
bilirubin levels are derived from the total and direct
bilirubin measurements.

53.  Normal Range of Bilirubin
• Direct (also called conjugated) bilirubin: 0
to 0.3 mg/dL
• Total bilirubin: 0.3 to 1.9 mg/dL
• Indirect : 0.3 to 1.2 mg/dl

54.  Composition of bile
Between 500 to 1000 ml of bile secreted by liver
daily. Consist of
• Water
• Mineral salts
• Mucus
• Bile pigments mainly bilirubin
• Bile salts
• cholesterol

55.  Emulsify fats and break it down into small
particles.This is a detergent-like action of bile.
 increases the absorption of fats, and absorption
of the fat-soluble substances, such as
the vitamins A, D, E, and K.
 destroying many of the microbes that may be
present in the food.
 Bile also carries excess cholesterol out of the
body

56.  Reservoir of bile
 Release of stored bile
 Increasing the concentration of bile

57.  The large intestine is primarily responsible for
removing water from the contents of the
intestine and making it ready for removal from
the body.
1. AbsorbWater
Within 24 hours after eating, undigested food
moves from the small intestine into the large. At
this point, most of the digestive process is
complete. One of the primary functions of the
large intestine is to absorb water and prepare
the waste as a solid stool that will be expelled
from the body.

58. 2. AbsorbVitamins
There are a number of beneficial bacteria that normally
live in the large intestine and play an important role in
breaking down undigested sugars and fibers.These
bacteria also create the gas that is composed of
methane, hydrogen sulfide, carbon dioxide and other
gases.This flatus is the foul-smelling result of the
breakdown of the sugars by the bacteria.The
beneficial bacteria produce many vitamins, of which
areVitamin K and Biotin that are absorbed back into
the body.

59. 3. ReduceAcidity and Protect from Infections
The fatty acids that are produced by the bacteria
in the large intestine cause an acidic
environment.The large intestine produces
alkaline solutions that help to reduce the
acidity and balance the pH in the large
intestine.The mucous lining of the large
intestine acts as a protective layer that
prevents harmful bacteria from being
reabsorbed into the body.

60. 4.Elimination
 fecal matter is finally stored in the rectum
and sigmoid colon until it can be eliminated
from the body through the process of
defecation.