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Digestive System HUMAN ANATOMY AND PHYSIOLOGY-II COLORED Notes 2nd Semester B.Pharmacy Lecture Notes,BP201T Human Anatomy and Physiology II,BPharmacy,Handwritten Notes,Important Exam Notes,BPharm 2nd Semester,

Digestive System HUMAN ANATOMY AND PHYSIOLOGY-II COLORED Notes

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Digestive System HUMAN ANATOMY AND PHYSIOLOGY-II COLORED Notes

BP201T HUMAN ANATOMY AND PHYSIOLOGY-II (Digestive System COLORED Notes)

BP201T (Digestive System)

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Digestive system
 The organs involved in breakdown of the food are collectively known as the digestive
system.
 It contributes to homeostasis by breaking down food into forms that can be absorbed
and used by body cells.
 It also absorbs vitamins, minerals, water, and eliminates indigestible substances and
water from the body.
Anatomy and Physiology of Digestive system
1. Gastro intestinal tract (alimentary canal)
 Tube that extends from mouth to anus (9m).
Includes:
 Oral cavity
 Pharynx
 Esophagus
 Stomach
 Small intestine
 Large intestine
 Rectum
 Anus
2. Accessory digestive system
 Teeth
 Tongue
 Salivary glands
 Liver
 Gall bladder
 Pancreas
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i. Oral cavity
 First part of GIT
 Mucous membrane epithelium
2 incisor cutting
1 canine tearing
2 premolar crushing
3 molar grinding
ii. Tongue
Front and back of tongue, papillae, taste.
Function of tongue
 Chewing(mastication)
 Swallowing(deglutition
 Taste
 Speech
iii. Pharynx
 Part of throat that located behind the mouth and nasal cavity and above the esophagus
and larynx.
 Receives the food from mouth.
 Expel the food towards the stomach through esophagus.
Three parts of pharynx
1. Nasopharynx  Respiratory function
2. Oropharynx
3. Hypopharynx (laryngopharynx)
iv. Esophagus or Oesophagus
 Food pipe
 Muscular tube connecting throat with stomach.
 It runs behind the windpipe(trachea) and heart and in front of the spine.
 Length  25 cm
 Diameter  2 cm
 2 spincture it is a circular muscle that maintains constriction of natural passage or
orifice. It helps to prevent reflux of acidic stomach content.
 Epiglottis  it is like a switch that close off when we are swallowing the food
 Epiglottis prevents the entry of ingested food into respiratory tract and allows it to
pass into stomach through esophagus.
Respiratory function
+
Digestive function
Help to propel food
(mascular contraction)
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Stages of deglutition (swallowing)
1. Voluntary stage
 Ingested food (bolus) passed through oropharynx by upward/downward movement of
tongue.
2. Pharyngeal stage
 Involuntary passage of bolus through pharynx to esophagus.
 Stimulates ⏟

present in brain to give signal to move uvula.
 It will close off nasopharynx.
3. Esophageal stage
 Involuntary passage of bolus through esophagus to stomach.
NOTE:
 For solid food, the time to pass bolus from mouth to stomach is 4-8 sec
 For liquid or semi-solid it is 1 sec.
v. Stomach
 Muscular organ
 Located on left side of the upper abdomen.
 Food Receives from esophagus through muscular valve called lower esophageal spincture.
 A pouch like organ that stores a food (for 2-4 hr) with some mechanical and chemical
digestion process.
 2 spincture at both ends.
 It releases proteases (protein digesting enzyme such as pepsin) and HCl, which kills the
bacteria and provides acidic pH for protease to work.
 Gastric juice digestive fluid that contains HCL, KCL and NaCl
 This Acidic environment plays an important role in digestion through activating
digestive enzymes.
 Four parts of stomach: Cardia, Fundus, Body and Pylorus
Gastric secretory cells
1. Chief cells secrete pepsinogen.
2. Parietal cells  secrete HCL and intrinsic factor (which helps in
absorption of vitamin B12 in the intestine).
3. Goblet cells secrete mucous and alkaline substances to help neutralize
HCL in the gastric juice also to form a protective layer of mucus.
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vi. Small intestine
 Most of the absorption takes place in this part of GIT
 Length3-5 cm
The small intestine divided into 3 structural parts:
1) The duodenum
 ‘’C’’ shaped, short structure ranging from 20 cm to 25 cm in length.
2) The jejunum
 Mid-section of the small intestine that connects duodenum to the ileum, it is
about 2.5 m long.
3) The ileum
 Is a final section of small intestine of 3 m long and contains micro villi similar
to the jejunum.
 Paneth cellspresent in intestinal epithelial linings and secret anti-microbial peptide
such as Alpha-defensin.
Functions of small intestine
1) Digestion
 Most of the chemical digestion takes place.
 Many enzymes are secreted by pancreas and liver that are entered into small intestine.
through the duct.
2) Absorption
 Digested food is now able to pass into the blood vessels form the wall of intestine though
either diffusion or active transport.
 Here, the most of the nutrients from ingested food are absorbed.
3) Immunological
 Small intestine supports the body’s immune system.
 By balancing of the various types of inflammatory mediators.
Function of parts of small intestine
a. Duodenum:
 It receives gastric chyme from the stomach, with digestive juices from the
pancreas (digestive enzymes) and the liver (bile).
 The digestive enzymes break down proteins and bile emulsifies fats into
micelles.
b. Jejunum:
 It contains villi that increase its surface area.
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 Products of digestion (sugars, amino acids, and fatty acids) are absorbed
into the bloodstream in jejunum.
c. Ileum:
 It contains villi similar to the jejunum.
 It absorbs mainly vitamin B12 and bile acids, as well as any other
remaining nutrients.
 The ileum joins to the cecum of the large intestine at the ileocecal junction.
vii. Large intestine
 Large bowel or colon (last part of GIT).
 Water is absorbed here and remaining material is stored as feces before being removed
by defecation.
5 sections:
1) The cecum
2) The transverse colon
3) The descending colon
4) The sigmoid colon
5) Rectum
Details of five parts:
1) Cecum:
 The first section of the colon and involved in the digestion.
2) Ascending colon:
 The main function is to remove the water and other key nutrients from waste
material.
 The waste material is pumped upwards toward the transverse colon by
peristalsis.
3) Descending colon:
 Store feces that will be emptied into the rectum.
 The walls of the sigmoid colon are muscular and contract to increase the pressure
inside the coloncausing the stool to move into the rectum.
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Large Intestine
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viii. Liver
 Heaviest organ (1.4 kg)
 Lobes contain hepatocytes.
 Gall bladder: Stores and concentrate bile produced by liver.
 Contains smooth muscle that contract to expel out bile from cystic
duct.
Function of Liver:
 Detoxification
 Metabolism
 Immune system
 Production of cholesterol
 Storage of micronutrients
 Blood sugar balance
 Production of bile
 Protein synthesis
ix. Pancreatic enzyme
 12-15 cm long, 2.5 cm width located at greater curvature of the stomach.
 Pancreas made up of small cluster of glandular epithelial cells called Acini.
 Cells present in Acini secretes pancreatic juice.
 99% of cluster called Acini
 1% of cluster called pancreatic islets also known as ‘’islets of langerhans’’
 Pancreatic juice: clear, colorless, liquid of water salts and several enzymes.
 Pepsin (active)  secreted in form of pepsinogen (inactive).
 Trypsin  Trypsinogen
 Acinar cells secrete Trypsin inhibitor  inhibit trypsin activity
when needed.
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Layers of GIT (4 layers):
1. Mucosa
2. Sub-mucosa
3. Muscularis
4. Serosa
Details:
1) Mucosa
 Mucosa: Inner linings of GIT that composed of:
A. Layer of epithelium
B. Layer Connective tissue (lamina propria)
C. Layer of smooth muscle (muscularis mucosae)
A) Layer of epithelium: formed by 2 types of cells:
 Non-keratinized squamous epithelium cellsprotective role
 Simple columnar epithelium cells  secretion and absorption role
o These cells will get replaced by new cells at every 5 – 7 days.
B) Lamina propria: layer of connective tissue.
 Composed of blood vessels and lymphatic vessels which are the route of nutrients to
get absorbed to reach the other parts of the body.
 This layer protects epithelium and binds it to Muscularis mucosae.
C) Muscularis mucosa: it is a layer of smooth muscle.
2) Sub-mucosa
 Consists of areolar connective tissue that connect mucosa to Muscularis.
 It contains many blood vessels that receive absorbed food molecules.
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3) Muscularis:
 Muscularis layer present in mouth, pharynx and esophagus contains skeletal muscle
that produces voluntary swallowing.
 At anal spincture, it control and regulate defecation process (voluntary control).
 Muscularis consist of two types of muscles:
i. Circular muscle inner sheet
ii. Longitudinal muscle outer sheet
4) Serosa (visceral peritoneum)
 Outer most and superficial layer.
 Contains serous membrane with areolar connective tissue.
Production of HCL in stomach:
 HCl secretes from gastric parietal cells but it is not a constant.
 In fed state – HCl secretion increases (pH-below 3)
 When stomach gets empty / in fasting state HCl secretion decreases (pH 4-6)
HCl production is regulated by 3 ways:
1) Parasympathetic nervous system Ach
2) Hormone produced by G-cells Gastrin
3) Paracrine  Histamine
 Each of above 3 ways will stimulate activity of H+/K+ ATPase pump to increase
secretion = Potentiation
Phases of acid production
1. Cephalic phase of acid production
 Regulated by parasympathetic nervous system (Ach release).
Smell of food, thought of food, chewing of food = increase secretion of HCl by
stimulation of parasympathetic nervous system (40% HCL secreted in this phase).
2. Gastric phase of acid production
 Initiated by mechanical digestion in stomach by arrival of food in antrum.
 Leads to secretion of Gastrin hormone from G-cells of antrum.
 Gastrin acts on fundus and stimulate the parietal cells to activate H+
/K+ ATPase pump.
 60% HCl secretion occurs in this phase.
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 Acetylcholine, Gastrin and Histamine stimulate the parietal cell.
Parasympathetic nervous system regulates 2 regions of stomach:
1. Antrum:
 Increase the secretion of Gastrin.
 Activate parietal cells to increase H+/K+ ATPase pump activity.
 Gastrin acts on ECL (Enterochromaffin cell) to release of Histamine and increase
H+/K+ pump to release HCl.
2. Fundus:
 Stimulation of parietal cells and increase the activity of H+/K+ ATPase pump.
 Increase acid secretion.
 The hydrogen ion concentration in parietal cell secretions is roughly 3 million fold
higher than in blood.
 Note: The ability of the parietal cell to secrete acid is dependent on active transport.
 The key player in acid secretion is a H+/K+ ATPase or "proton pump" located in the
cannalicular membrane.
 Hydrogen ions are generated within the parietal cell from dissociation of water. The
hydroxyl ions formed in this process rapidly combine with carbon dioxide to form
bicarbonate ion, a reaction catalyzed by carbonic anhydrase.
⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗ ⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗

 Bicarbonate is transported out of the basolateral membrane in exchange for chloride.
 The outflow of bicarbonate into blood results in a slight elevation of blood pH known
as the "alkaline tide".
 Chloride and potassium ions are transported into the lumen of the cannaliculus by
conductance channels, and such is necessary for secretion of acid.
 Hydrogen ion is pumped out of the cell, into the lumen, in exchange for potassium
through the action of the proton pump; potassium is thus effectively recycled.
Inhibition of Acid Secretion:
 Strict regulation of HCl secretion is needed; because excess acid can be harmful for
digestive system.
 Acid secretion only needed during feeding state.
 Negative regulation of HCL secretion is mediated by stomach luminal pH.
 During feeding = protein present in chyme are acts as a buffer to make a pH above 3.
 In the fasting / empty stomach = pH falls below 3
 At this pH, D-cells present in antrum region of stomach secreted a hormone called
Somatostatin.
 Somatostatin acts as paracrine.
 Somatostatin pass the signals to G-cells to prevent secretion of gastrin.
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 Somatostatin also initiates activity of enzyme ‘’Secretin’’.
 Secretin is released from duodenum in response to acidic chyme and
inhibits gastrin secretion from G-cells of stomach.
 Ultimately it will make an acidic pH to alkaline and prevents acidity.
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6 steps of digestive system
1. Ingestion
2. Secretion
3. Mixing and propulsion
4. Digestion
5. Absorption
6. Defecation/ Excretion of waste materials
Detail…
1) Ingestion
 Taking food and liquid into mouth.
2)Secretion
 Secretion of saliva to mix up food particles
 Secrete various metabolic substances into lumen (water, acid, buffers, and
enzymes).
3)Mixing and propulsion
 Contraction and relaxation of smooth muscles of wall of GIT.
 To mix the food and expel them towards anus.
 GI Motility
4)Digestion
 Breakdown of food particles into smaller molecules
2 types of digestion:
A) Mechanical digestion
B) Chemical digestion
A) Mechanical digestion
 Teeth cut the food and grind before it swallowed.
 Smooth muscles of stomach and intestine  churn the food
 Food molecules will get dissolved and mixed with digestive fluid.
B) Chemical digestion
 Hydrolysis
 ⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗ ⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗⃗
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5) Absorption
 Entrance of digested product and secreted fluids
Epithelial cell linings of lumen of GIT
Absorption
6) Defecation / Excretion of waste material:
 Elimination of indigestible waste products through anus.
 Indigestible substances like: bacteria, lumps of broken cells of GI linings etc.
 Materials that will leave the body through anus into external environment are called
feces.
Digestion of Carbohydrates
 When food is chewed, it is mixed with saliva, which contains the digestive enzyme
ptyalin (α -amylase) secreted mainly by the parotid glands.
 This enzyme hydrolyzes starch into the disaccharide maltose and other small polymers
of glucose.
 Only about 5% of starch is digested because food remains in the mouth only for a
short time.
 At stomach activity of the salivary amylase is blocked by acid of the gastric secretions
( amylase is non-active at pH < 4.0)
 30 to 40 % of the starches will have been hydrolyzed mainly to form maltose at
stomach
 Pancreatic secretion contains a large quantity of α-amylase
 Carbohydrates are almost totally converted into maltose or other very small glucose
polymers before passing beyond the duodenum.
 The enterocytes present in lining the villi of the small intestine contain four
enzymes (lactase, sucrase, maltase, and α-dextrinase), which split the
disaccharides lactose, sucrose, and maltose into their constituent monosaccharides.
 These enzymes are located in the enterocytes covering the intestinal microvilli
brush border:
 Maltasecatalyses the hydrolysis of maltose to 2 moleules of glucose.
 Sucrase catalyses the hydrolysis of sucrose to glucose and fructose
 Lactase catalyses the hydrolysis of lactose to glucose and galactose.
 Absorbed substances go into blood circulation.
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Digestion of carbohydrate
Polysaccharide (Starch and Glycogen)
Salivary amylase
Short branched polysaccharides Disaccharides
Limit dextrins Maltose Lactose Sucrose
α-Dextrinase Maltase Lactase Sucrase
Monosaccharide Monosaccharide
Glucose 2 Glucose 1 Glucose and 1 Glucose and
1 Galactose 1 Fructose
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Digestion of proteins
I. Endopeptidases
 Cleave proteins by hydrolyzing peptide bonds between specific amino acids throughout the
molecule.
 Endopeptidase breaks peptide bonds within the protein molecules.
II. Exopeptidases
 Remove amino acids one at a time from either the amino or carboxyl end of the molecule, again
by the hydrolysis of the peptide bond.
 Exopeptidase cleaves peptide bonds at the terminals of the protein molecules.
 Trypsin, chymotrypsin and elastase secreted by the pancreas into the small intestine.
There are two classes of Exopeptidase:
1. Carboxypeptidases
 Secreted in the pancreatic juice, release amino acids from the free carboxyl terminal of peptides.
2. Aminopeptidases
 Secreted by the intestinal mucosal cells, release amino acids from the amino terminal of peptides.
 Pepsin, the important peptic enzyme of the stomach (active at a pH of 2.0 to 3.0).
 Pepsin can digest collagen fiber.
 Most protein digestion occurs in the upper small intestine, in the duodenum and
jejunum.
 Major proteolytic pancreatic enzymes are: trypsin, chymotrypsin,
carboxypolypeptidase, and proelastase.
 Trypsin and chymotrypsin split protein molecules into small polypeptides.
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Digestion of Fat
 A small amount of triglycerides is digested in the stomach by lingual lipase that is
secreted by lingual glands in the mouth and swallowed with the saliva.
 Physically to break the fat globules into very small sizes so that the water-soluble
digestive enzymes can act on the globule surfaces.
 This process is called emulsification of the fat, most of the emulsification occurs in the
duodenum under the influence of bile.
 Bile salts and the phospholipid lecithin are extremely important for emulsification of the
fat.
 The most important enzyme for digestion of the triglycerides is pancreatic lipase,
present in enormous quantities in pancreatic juice.
 In addition, the enterocytes of the small intestine contain still more lipase, known as
enteric lipase, but this is usually not needed.
Absorption of Nutrients
 Majority of absorption takes place in the small intestine.
1) Passive diffusion  nutrients move from high concentration to low concentration; no
energy is required.
2) Facilitated diffusion – nutrients move from high concentration to low concentration
with the help of a carrier protein; no energy is required.
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3) Active transport  nutrients move from low concentration to high concentration
with the help of a carrier protein, energy is required.
4) Endocytosis  cell forms a vesicle to surround and engulf nutrients (Phagocytosis
and pinocytosis).
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Movement of GIT
What is GI Tract Motility?????
 Gastrointestinal (GI) motility is defined by the movements of the digestive system,
and the transit of the contents within it.
 Gut motility is the term given to the stretching and contractions of the muscles in the
gastrointestinal (GI) tract.
 The synchronized contraction of these muscles is called peristalsis.
 These movements enable food to progress along the digestive tract while, at the same
time, ensuring the absorption of the important nutrient.
What is Peristalsis????
 Peristalsis is a distinctive pattern of smooth muscle contractions that propels foodstuffs
distally through the esophagus and intestines.
 Segmentation contractions (or movements).
 It is a type of intestinal motility.
 Unlike peristalsis, which predominates in the esophagus, segmentation contractions occur
in the large intestine and small intestine, while predominating in the latter.
 Peristalsis involves one-way motion in the caudal direction, segmentation contractions
move chyme in both directions, which allows greater mixing with the secretions of the
intestines.
 Segmentation involves contractions of the circular muscles in the digestive tract, while
peristalsis involves rhythmic contractions of the longitudinal muscles in the
gastrointestinal tract.
 Unlike peristalsis, segmentation actually can slow progression of chyme through the
system
Movement in Esophagus
 After food is chewed into a bolus, it is swallowed and moved through the esophagus.
 Smooth muscles contract behind the bolus to prevent it from being squeezed back into the
mouth.
 Then rhythmic, unidirectional waves of contractions work to rapidly force the food into
the stomach.
 This process works in one direction only and its sole esophageal function is to move food
from the mouth into the stomach.
 In the esophagus, two types of peristalsis occur:
 A primary peristaltic wave, which occurs when the bolus enters the esophagus during
swallowing.
 It forces the bolus down the esophagus and into the stomach.
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 If bolus gets stuck, stretch receptors in the esophageal lining are stimulated and a
local reflex response causes a secondary peristaltic wave around the bolus,
forcing it further down the esophagus.
 The process of peristalsis is controlled by the medulla oblongata.
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Absorption of Carbohydrate
 The cells in the small intestine have membranes that contain many
transport proteins in order to get the monosaccharides and other nutrients
into the blood where they can be distributed to the rest of the body.
 Fructose is absorbed by facilitated diffusion while glucose and
galactose are actively transported.
 The first organ to receive glucose, fructose, and galactose is the liver.
 The liver takes them up and converts galactose to glucose, breaks fructose
into even smaller carbon-containing units and either stores glucose as
glycogen or exports it back to the blood.
Absorption of proteins
 Active process that need energy
 Energy needed is derived from hydrolysis (from ATP)
 This process occurs in small intestine.
 Absorption of amino acids is rapid in duodenum and jejunum but slow in
ilium.
Absorption of lipid
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Absorption of Fats
 Micelles bring the products of lipid digestion into contact with the
absorptive surface of the intestinal cells.
 Then, fatty acids, monoglycerides, and cholesterol diffuse across the
luminal membrane into the cells.
 In the intestinal cells, the products of lipid digestion are re-esterified to
triglycerides, cholesterol ester, and phospholipids and, with apoproteins,
form chylomicrons.
 Chylomicrons are transported out of the intestinal cells by exocytosis.
 Because chylomicrons are too large to enter the capillaries, they are
transferred to lymph vessels and are added to the bloodstream via the
thoracic duct.


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