13 digestive system

Prof.Sunil Chavan Prin.K.M.Kundnani Pharmacy
Polytechnic
DIGESTIVE SYSTEM
NUTRIENTS—FOOD—LARGE
MOLECULES
CARBOHYDRATES, LIPIDS,
PROTEINS, VITAMINS, MINERALS
BREAKDOWN
SMALL ABSORBABLE MOLECULES
Organs involved in breakdown of food are
collectively known as Digestive System

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Hard palate
Tongue
Soft palate
Oropharynx
Larynx
Diaphragm
Appendix
Rectum
Organs of Digestive System
Alimentary tract
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Rectum &
Anal canal
Accessory organs
3 pairs of salivary glands
Pancreas
Liver & bile duct
Gall bladder

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DFIGESTIVE PROCESS
1. INGESTION: Taking food & liquid into
mouth
2. SECRETION: Cells within GIT &
accessory digestive organs secret about
7 liters of water, acid, buffers, enzymes
into lumen of tract, each day.
3. MIXING & PROPULSION: Alternating
contractions & relaxations of smooth
muscle in the walls of GIT; Mix food &
secretion and propel them toward anus.

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4. DIGESTION: Mechanical Digestion:
• Teeth with aid of tongue cut & grind food
before it is swallowed
• Smooth muscles of stomach & small
intestine churn food
Chemical Digestion:
• Digestive enzymes produced by salivary
glands, tongue, stomach, pancreas &
small intestine carbohydrate, lipid,
protein molecules split into smaller
molecules. Vitamins, Ions, Cholesterol &
Water absorbed without digestion

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5.ABSORPTION:
• Entrance of products of digestion into
epithelial cells lining lumen of GIT
• Absorbed substances pass into Blood or
Lymph
6.DEFECATION:
• Indigestible substances, bacteria, cell
removed from lining of GIT, unabsorbed
digestive material leave the body through
anus
• Feces: Eliminated material

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Basic structure of Alimentary Canal
Muscle Layer

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Walls of Alimentary Tract
• Four layers of tissue:
1. Adventitia /Serosa or outer covering
2. Muscle layer (muscularis)
3. Submucosa
4. Mucosa-lining
Adventitia /Serosa or outer covering
• in the abdomen the organs are covered
by a serous membrane the
PERITONEUM

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Peritoneum: largest serous membrane
Lesser omentum
Greater omentum
Mesentery
Consist of a layer of
Simple Sqamous
epithelium, supported
By areolar conn. Tissue
Parietal - Lines walls
of abdominopelvic
cavity
Visceral – covers
organs in cavity,
forms serosa

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Muscularis:
• Mouth, pharynx, superior & middle parts of
esophagus contains skeletal muscle: produces
voluntary swallowing
• Skeletal muscle also forms external anal
sphincter, it allows voluntary control of
defecation
• Rest of tract contains smooth muscle in 2
sheets: inner sheet of Circular fibers & outer
sheet of Longitudinal fibers
• Involuntary contractions of smooth muscle help
break down food, mix it with digestive secretions
& propel it along tract
• Between layers plexus of neurons: Myentric or
Auerbach

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Submucosa:
• Consists of areolar connective tissue
• It binds mucosa to muscularis
• Contains many blood vessels & lymphatic
vessels, receive absorbed food material
• Contains extensive network of neurons:
submucosal plexus or of Meissner’s
plexus

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Mucosa:
Consists of three layers of tissue:
• mucous membrane formed by columnar
epithelium is the innermost layer and has three
main functions: protection, secretion and
absorption
• lamina propria consisting of loose connective
tissue, which supports the blood vessels that
nourish the inner epithelial layer, and varying
amounts of lymphoid tissue that has a protective
function
• muscularis mucosa, a thin outer layer of
smooth muscle that provides involutions of the
mucosa layer, e.g. gastric glands, villi.

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Nerve Supply
• The parasympathetic supply: provided by one pair of
cranial nerves, the vagus nerves.
• Stimulation causes smooth muscle contraction and the
secretion of digestive juices. The most distal part of the
tract is supplied by sacral nerves.
• The sympathetic supply: provided by thoracolumbar
outflow. These form plexuses in the thorax, abdomen
and pelvis, from which nerves pass to the organs of the
alimentary tract. Their action is to reduce smooth muscle
contraction and glandular secretion.
• The myenteric or Auerbach's plexus, influences
peristalsis.
• The submucosal or Meissner's plexus influences
secretion from mucous membrane and secretory glands.

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MOUTH (ORAL CAVITY)
• oral cavity is lined throughout with mucous
membrane, consisting of stratified squamous
epithelium containing small mucus-secreting
glands-Labial, Buccal, Palatal.
• Lips-Fleshy folds, surroundin opening of mouth
• Labial frenulum-a middle fold of mucus
membrane, attaches inner surface of lip to
gingiva
• Vestibule-space bounded by cheek & lips
externally and gums & teeth internally

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• Hard Palate-Anterior portion of roof of mouth,
formed by maxillae & palatine
bones
• Soft Palate- Posterior portion of roof of mouth,
arch shaped muscular portion between
oropharynx & nasopharynx
• Uvala- conical muscular process hanging from
soft palate
• Palatoglossal arch- Anterior muscular fold from
base of uvala on lateral side
• Palatopharyngeal arch- Posterior muscular fold
from base of uvala on lateral side
• Fauces- opening between oral cavity &
oropharynx

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TONGUE
• Forms floor of oral cavity
• Composed of skeletal muscle covered with
mucus membrane
• Lingual frenulum- fold of mucus membrane,
undersurface of tongue attached to floor of
mouth
• Papillae-Projections on dorsal & lateral surfaces
of tongue
• Lingual gland-secrete mucus & watery fluid
containing enzyme Lingual Lipase, acts on
triglycerides

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Functions: Plays important role in
• Mastication
• Formation of bolus
• Deglutition
• Sense of taste
• Speech

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TEETH
• Located in sockets of alveolar process of
Mandible & Maxillae
• Periodontal Ligament-Lines sockets,
consists of fibrous connective tissue, holds
teeth into socket walls

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Structure of Tooth:
• the crown — the part which protrudes from the gum
• the root — the part embedded in the bone
• the neck — the slightly narrowed region where the crown
merges with the root.
• pulp cavity- In the centre of the tooth containing blood
vessels, lymph vessels and nerves, and surrounding
• Dentine- hard ivory-like substance
• Enamel. - Outside the dentine of the crown is a thin layer
of very hard substance.
• The root of the tooth,is covered with a substance
cement, which fixes the tooth in its socket.
• Blood vessels and nerves pass to the tooth through a
small foramen at the apex of each root.
Functions:1.Cutting 2.Grinding

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SALIVARY GLANDS
• 3 pairs of salivary glands:
Parotid
Sublingual
Submandibular
Tongue
Muscles of cheek

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Saliva: Composition
• Chemically saliva is 99.5 % water & 0.5%
solutes
• Solutes: Ions- Na+
, K+
, Cl-
,HCO3
-
& PO4
--
some dissolved gases, organic substances-
urea, uric acid, mucus, immunoglobin A,
lysozyme, and salivary amylase
Function: 1.initiates breakdown of starch. It is
converted into disaccharide maltose,
trisaccharide maltotriose & glucose polymer
alpha dextrin. Enzyme action continues till food
riches stomach. 2.Lubrication of food

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PHARYNX
• The pharynx is divided for descriptive purpose
into three parts, the nasopharynx, oropharynx
and laryngopharynx.
• The nasopharynx is important in respiration.
• The oropharynx and laryngopharynx are
passages common to both the respiratory and
the digestive systems.
• Food passes from the oral cavity into the
pharynx then to the esophagus below.
• When food reaches the pharynx swallowing is
no longer under voluntary control.

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ESOPHAGUS (GULLET)
• A collapsible muscular tube, about 25 cm
long & about 2 cm in diameter
• Lies anterior to vertebral column & behind
trachea
• Begins at inferior end of pharynx, ends
below diaphragm at level of 10th thoracic
vertebra joins the stomach
• Formed by 4 layers:1.Mucosa
2.Submucosa 3. Muscularis-upper:
skeletal middle: skeletal & smooth; lower:
smooth 4.Adventitia

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Muscularis has two sphincters:
Upper or Cricopharyngeal (skeletal)
Lower Esophageal or Cardiac
(smooth)
FUNCTIONS:
-Esophagus secretes mucus
-Propels food into stomach by
peristalsis

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DEGLUTITION OR SWALLOWING
• Process of movement of food from mouth into
stomach
• It is facilitated by secretion of saliva & mucus
• Involves Mouth, Pharynx, Esophagus
• Deglutition occurs in three stages:
1. Voluntary stage -bolus passed into oropharynx
2. Pharyngeal stage -passage of bolus through
pharynx into esophagus
3. Esophageal stage - involuntary passage of
bolus through esophagus into stomach

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ESOPHAGEAL STAGE
This stage begins as bolus
enters esophagus
-Presence of bolus stimulates
Peristalsis
-Peristalsis pushes bolus
Forward
PERISTALSIS IS A
PROGRESSION OF
COORDINATED
CONTRACTIONS &
RELAXATIONS OF
CIRCULAR &
LONGITUDINAL
LAYERS OF
MUSCULARISMucus secreted by esophagus
lubricates bolus & reduces friction

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STOMACH
• J shaped enlargement of GIT
R.adrenal
Esophagus

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Situated inferior to diaphragm, in epigastric,
umbilical and left hypochondriac regions
- large folds
of mucosa

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Walls of Stomach- 4 layers with some
modifications
Mucosa:
Columnar
Epithelial cells
Form columns
Of
Secretary Cells-
GASTRIC GLANDS -intrinsic factor & HCl
-pepsinogen & gastric
lipase
-Mucus

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Muscularis-3 layers of smooth muscle. This
arrangement produces mixing waves

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Gastric Juice
• About 2 liters of gastric juice are secreted daily by
special secretary glands in the mucosa
It consists of: water, mineral salts, mucus, hydrochloric
acid, intrinsic factor, inactive enzyme precursors:
pepsinogens
Functions of Gastric Juice:
1.Water-further liquidation of food
2.HCl-a.acidifies food & stops action of salivary amylase b.
Kills microbes c. Provides acid environment for activation
of pepsinogen
3.Pepsinogens Pepsins activated, begins digestion
of proteins
4.Intrinsic factor-binds Vit B12 for absorption
5.Mucus-Prevents mechanical injury to stomach by
lubricating contents

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Secretion of Gastric Juice

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FUNCTIONS OF STOMACH

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PANCREAS
• A pale gland, about 12-15gm long &
2.5cm thick
• Lies posterior to greater curvature of
stomach in epigastric & left
hypochondriac region
Consists of head
body & tail
connected to
duodenum by pancreatic ductic duct

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Exocrine Pancreas:
• consists of a large number of lobules made up of
small alveoli, the walls of which consist of
secretary cells.
• Each lobule is drained by a tiny duct and these
unite eventually to form the pancreatic duct,
opens into the duodenum.
• Just before entering the duodenum the
pancreatic duct joins the common bile duct to
form the hepatopancreatic ampulla.
• The function of the exocrine pancreas is to
produce pancreatic juice containing enzymes
that digest carbohydrates, proteins and fats

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Composition & Function of Pancreatic
Juice:
• Each day pancreas produces 1.2 to 1.5 L
pancreatic juice, clear colourless liquid,
• Consists of: Water, sodium bicarbonate &
enzymes-pancreatic amylase, trypsin,
chymotrypsin, carboxypeptidase, estalase,
pancreatic lipase, ribonuclease,
deoxyribonuclease
• Functions:
1.Sod. Bicarbonate-makes juice alkaline, stops
action of pepsin from stomach, creates pH for
action of digestive enzymes in small intestine

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2. Pancreatic amylase acts on starch converts into
maltose, maltotriose & alpha dextrin
3. Trypsinogen, inactive form, in small intestine,
encounters with Enterokinase, converts into
Trypsin. Trypsinacts on inactive precursors to
produce acive enzymes.
Chymotrypsinogen Chymotrypsin
Procarboxypeptidase Carboxypeptidase
Porelastase Elastase
All these active form act on proteins to produce
peptides & amino acids
4.Pancreatic lipase acts on trigycerides that
previously emulsified with bile salts
5.Nucleases act on RNA & DNA Nucleotides

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LIVER
• Largest gland in the body, weighing
between 1 and 2.3 kg.
Situated in the upper part
of the abdominal cavity
occupying the greater part
of the right hypochondriac
region, part of the
epigastric region and
extending into the left
hypochondriac region

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• Divided into 2 major lobes-a larger right
lobe & smaller left lobe and 2 smaller
lobes-Quadrate lobe & Caudate lobe
• Portal fissure-part of liver on posterior
surface where various structures enter &
leave th gland
Caudate
lobe
Left lobe
Right lobe
Right renal impression

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Structure of liver:
• The lobes of the liver are made up of tiny
lobules just visible to the naked eye.
These lobules are hexagonal in outline
and are formed by cubical-shaped cells,
the hepatocytes, arranged in pairs of
columns radiating from a central vein.

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• Between two pairs of columns of cells there are
sinusoids (blood vessels with incomplete walls)
containing a mixture of blood from the tiny
branches of the portal vein and hepatic artery
• This arrangement allows the arterial blood and
portal venous blood (with a high concentration of
nutrients) to mix and come into close contact
with the liver cells. Amongst the cells lining the
sinusoids are hepatic macrophages (Kupffer
cells) whose function is to ingest and destroy
any foreign particles present in the blood flowing
through the liver.

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• One of the functions of the liver is to
secrete bile.
• Bile canaliculi run between the columns of
liver cells. This means that each column of
hepatocytes has a blood sinusoid on one
side and a bile canaliculus on the other.
• The canaliculi join up to form larger bile
canals until eventually they form the right
and left hepatic ducts which drain bile from
the liver.

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Functions of Liver
• Carbohydrate metabolism: Conversion of glucose to
glycogen in the presence of insulin, and converting liver
glycogen back to glucose in the presence of glucagon.
• Fat metabolism: Desaturation of fat, i.e. converts stored
fat to a form in which it can be used by the tissues to
provide energy.
• Protein metabolism. Deamination of amino acids
• removes the nitrogenous portion from the amino acids
not required for the formation of new protein; urea is
formed from this nitrogenous portion which is excreted in
urine.
• breaks down genetic material of worn-out cells of the
body to form uric acid which is excreted in the urine.

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• Breakdown of erythrocytes and defence
against microbes: This is carried out by
phagocytic Kupffer cells (hepatic macrophages)
in the sinusoids.
• Detoxification of drugs and noxious
substances: These include ethanol (alcohol)
and toxins produced by microbes.
• Metabolism of ethanol: This follows
consumption of alcoholic drinks.
• Inactivation of hormones: These include
insulin, glucagon, cortisol, aldosterone, thyroid
and sex hormones.

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• Synthesis of vitamin A from carotene:
Carotene is the provitamin found in some plants,
e.g. carrots and green leaves of vegetables.
• Production of heat: The liver uses a
considerable amount of energy, has a high
metabolic rate and produces a great deal of
heat. It is the main heat-producing organ of the
body.
• Secretion of bile. The hepatocytes synthesise
the constituents of bile from the mixed arterial
and venous blood in the sinusoids. These
include bile salts, bile pigments and cholesterol.

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• Storage: The substances include:
• fat-soluble vitamins: A, D, E, K
• iron, copper
• some water-soluble vitamins, e.g. riboflavin,
niacin, pyridoxine, folic acid and vitamin B12.
Composition of Bile: about 500 ml of bile
secreted by liver daily. It consists of :water,
mineral salts, bile pigment-bil
irubin, cholesterol and bile salts-

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Gall Bladder
• Pear shaped sac, attached to posterior
surface of liver by connective tissue
• Parts :Fundus, Body, Neck
• Composed of 4 layers with some
modification
• Muscularis-Presence of additional layer of
oblique muscle fibers
• Mucosa- simple columnar epithelium
arranged in rugae

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Functions:
• Acts as a reservoir of bile
• Adds mucus to bile
• Concentrates bile
• Ejects bile into
cystic duct by
contraction

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Small Intestine
• The small intestine is continuous with the
stomach at the pyloric sphincter and leads
into the large intestine at the ileocaecal
valve. It is a little over 5 metres long and
lies in the abdominal cavity surrounded by
the large intestine.
• In the small intestine the chemical
digestion of food is completed and most of
the absorption of nutrients takes place.
• The small intestine comprises three main
sections continuous with each other.

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• Duodenum: first about 25 cm long
• Jejunum: middle part about 1m long
• Ileum: terminal part about 2 m ends at
Ileocecal valve
• Composed of 4 layers with some
modifications in Mucosa

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Mucosa
• Epithelium-simple columnar epithelium
that contains may types of cells
• Absorptive cells-digest & absorb nutrients
in small intestinal chyme
• Goblet cells-secrete mucus
• Intestinal Glands:
-Paneth cell secrete lysozyme
-Enteroendocrine cells: S cells secrete
secretin & CCK cells secrete
Cholecystokinin

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Enterocyte
Lacteal
Goblet cells
Capillary nertwork
O
n
e
c
o
m
p
l
e
t
e
v
i
l
l
u
s
One complete Villus

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Special Structural Features
Circular Folds:
• These are folds of Mucosa & Submucosa
about 10 mm long, begin at proximal
portion of duodenum & end at midportion
of ileum
Villi:
• These are fingerlike projection of mucosa,
0.5 – 1 mm long, 20-40/sq.mm
• Vastly increases surfcae area

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Microvilli:
• These are projections of apical membrane
of absorptive cells
• Each microvillus is 1 microm. Long
cylindrical, look like BRUSH-BORDER
• 200 million / sq.mm of intestine
• Contains enzymes that have digestive
functions

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Intestinal Juice
• About 1.5 to 1.8 L/day intestinal juice is
secreted by intestinal glands
• pH is about 7.8 – 8.3
• Composition: Water, mucus, mineral salts
& enzymes-
Peptidases: aimno peptidase,
Dipeptidase, tripeptidase
Sucrase, Maltase, Lactase
Lipase
Enterokinase

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Functions:
• Alkaline juice raises ph of intestinal contents to
between 6.5 – 7.5
• Enterokinase activates pancreaticic peptidases
• Peptidases convert polypeptides into amino
acids
• Lipase completes digestion of emulsified fats to
fatty acids & glycerol
• Sucrase, Maltase, Lactase complete digestion of
carbohydrates
• Mucus protects intestinal wall from injury,
prevents intestinal ulcer
• Water helps in all enzymatic reactions of
digestion

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Functions of Small Intestine
1. Onward movements of its contents by
peristalsis
2. Secretion of intestinal juice
3. Completion of chemical digestion of
carbohydrates, protein and fats in the
enterocytes of the villi
4. Protection against infection by microbes that
have survived the antimicrobial action of the
hydrochloric acid in the stomach, by Lymphatic
nodules
5. Secretion of the hormones cholecystokinin
(CCK) and secretin
6. Absorption of nutrients.

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Chemical Digestion in Small Intestine
• Partly digested carbohydrates, proteins &
fats are completely digested by collective
action of pancreatic juice, bile & intestinal
juice in small intestine
• Digestion of Carbohydrates-
Sucrose Glucose + Fructose
Lactose glucose + G-------
Maltose Glucose + G--------

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Digestion of Proteins-
• Continuation of breakdown of proteins into
peptides by action of pancreatic enzymes.
Peptides are splited by peptidases into
single Amino Acids
Digestion of Lipids-
• Lipid Globules Small Lipid Globules
• Triglycerides Fatty Acids+
Monoglycerides

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Absorption of Nutrients
By two processes:
1. Diffusion- Monosaccharides, amino acids, fatty acids
& glycerol diffuse slowly down their concentration
gradients into absorptive cells
2. Active Transport -Monosaccharides, amino acids,
fatty acids and glycerol may be actively transported
into absorptive cells this is faster than diffusion.
• Monosaccharides and amino acids pass into the
capillaries in the villi and fatty acids and glycerol into
the lacteals.
• Vitamins, mineral salts and water are also absorbed
from the small intestine into the blood capillaries.
• Fat-soluble vitamins are absorbed into the lacteals
along with fatty acids and glycerol. Vitamin B12
combines with intrinsic factor in the stomach and is
absorbed in the terminal ileum.
• Water is absorbed by Osmosis

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Large Intestine
About 1.5 m
1.
2.
3.
4.
5.

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Structure

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• Colon made up of 4 layers of GIT with
modifications in longitudinal muscle layer
• longitudinal muscle do not form a smooth
continuous layer of tissue but are collected into
three bands, called taeniae coli, situated at
regular intervals round the colon. They stop at
the junction of the sigmoid colon and the rectum.
• anal sphincters - thickening of the circular
muscle layer.
• In the submucosal layer there is more lymphoid tissue
than in any other part of the alimentary tract, providing
non-specific defence against invasion by resident and
other microbes.
• Mucosal lining of the colon and the upper region of the
rectum-large numbers of goblet cells secrete mucus.
• The lining membrane of the anus consists of stratified
squamous epithelium continuous with the mucous
membrane lining of the rectum

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Functions
• Absorption: absorption of water
continues until the familiar semisolid
consistency of faeces is achieved.
Mineral salts, vitamins and some drugs
are also absorbed
• Microbial Activity: E.coli, enterobacter
aerogenes help in synthesis of Vit. K &
Folic acid. Gases- CO2,H2 & methane are
released by bacterial fermentation of
unabsorbed nutrients

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• Mass Movement: At fairly long intervals
(about twice an hour) does a wave of
strong peristalsis sweep along the
transverse colon forcing its contents into
the descending and sigmoid colons.
• Defaecation: a mass movement forces
the contents of the sigmoid colon into the
rectum the nerve endings in its walls are
stimulated by stretch. Contraction of the
muscle of the rectum and relaxation of the
internal anal sphincter causes defaecation

13 digestive system

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