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6/9/2024 GIT physiology
2nd year Lab & Nutrition
1
The Physiology of the Gastrointestinal
Tract (GIT)
General Objectives
• To describe the structural organization of the
GIT (alimentary canal and accessory glands) and
the different layers of the GIT.
• To describe the functions of the various parts of
the GIT (secretion, digestion, absorption and
motility).
• To describe the composition of different
gastrointestinal secretions and their functions.
• To describe the regulatory mechanisms (nervous
and hormonal) of gastrointestinal function.
6/9/2024 GIT physiology
2nd year Lab & Nutrition
2
I- Introduction to GIT Physiology
Learning Objectives
• Describe the general functions of the GIT.
• Describe the general organization of the GIT.
• Describe the common layers of the digestive tract
wall.
• Describe the nervous and hormonal regulation of
GI function.
• Describe the different movements of the GIT.
6/9/2024 GIT physiology
2nd year Lab & Nutrition
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Functions of the GIT
• Ingestion
• Motility: mixing and propulsion
• Secretion
• Digestion
• Absorption
• Excretion
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2nd year Lab & Nutrition
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Organization of the GIT
• The alimentary canal: mouth, pharynx,
esophagus, stomach, small intestine, large
intestine, rectum and anal canal.
• Associated glands: salivary glands,
pancreas, liver and gall bladder.
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2nd year Lab & Nutrition
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Layers of digestive tract wall
• Mucosa
• Submucosa
• Muscularis externa
• Serosa
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2nd year Lab & Nutrition
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2nd year Lab & Nutrition
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2nd year Lab & Nutrition
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Mucosa
• This layer is concerned with secretion of
both the digestive juices and certain
hormones as well as the absorption of the
various nutrients.
• It contains blood capillaries, lymph vessels
and a layer of smooth muscle called the
muscularis mucosa.
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2nd year Lab & Nutrition
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Submucosa
• This is a dense connective tissue layer that
contains larger blood and lymph vessels as
well as a network of neurons called
submucous or Meissner’s plexus.
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• Muscularis externa: an outer longitudinal
layer and inner circular layer of smooth
muscle. In between myenteric or Aurbach’s
plexus.
• Serosa: an outer fibrous coating
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2nd year Lab & Nutrition
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Control of GI functions
(secretions and motility)
• Nervous
• Hormonal
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2nd year Lab & Nutrition
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Nervous supply to the Gut
Extrinsic
(autonomic)
• Sympathetic (decreases
motor and secretory
activity, contraction of
sphincters)
• Parasympathetic
(stimulatory)
Intrinsic
• Submucous or Meissner’s
plexus (controls secretory
function)
• myenteric or Auerbach’s
plexus (controls motor
activity)
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2nd year Lab & Nutrition
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Hormonal control of GIT function
1. Gastrin (from the stomach): stimulates
gastric motility and secretion.
2. CCK (from small intestines) stimulates
pancreatic enzyme secretion, and gall
bladder contraction. Inhibits gastric
emptying.
3. Secretin (from small intestines): stimulates
pancreatic and biliary bicarbonate secretion.
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2nd year Lab & Nutrition
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Types of movements in the GIT
• Propulsive: move bolus forward.
• Segmentation: mixing in the small intestine.
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2nd year Lab & Nutrition
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II- Mouth, Salivary glands & Esophagus
Learning Objectives
• Name the salivary glands.
• Describe the salivary secretion: volume, pH
and composition.
• Describe the different functions of saliva.
• Describe the regulation of salivary secretions.
• Name functions of esophagus.
• Describe the mechanism of swallowing.
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2nd year Lab & Nutrition
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The Salivary glands
• 3 paired salivary glands made of ducts and
acini that make between 1-1.5 liters/day
with a pH of 6-7
• Parotid glands
• Submandibular or submaxillary glands
• Sublingual glands
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2nd year Lab & Nutrition
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2nd year Lab & Nutrition
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Composition of Saliva
• Mostly water 99.5%
• Ionic content: low in Na+ and Cl-, high in
K+ and HCO3
-
• Enzymes: lingual lipase and -amylase
(ptyalin).
• Mucins
• Lysozymes: proteolytic enzyme
• Immunoglobulin A (IgA)
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2nd year Lab & Nutrition
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Functions of saliva
• Digestive functions:
• Amylase breaks down starch, and lingual lipase breaks down
triglycerides (active in the stomach).
• It dissolves food materials so it can be sensed by taste buds.
• Lubrication:
• Keeps mouth moist and thus facilitates movements of lips and
tongue during speech.
• Moistens food and thus facilitates swallowing.
• Protection:
• Keeps mouth and teeth clean by dissolving and washing food
particles from between the teeth.
• Has an anti-bacterial action.
• Buffers acidic gastric secretions.
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2nd year Lab & Nutrition
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Regulation of Salivary secretion
A) Simple or unconditioned: The presence of food in
the mouth results in reflex secretion of saliva.
• Stimulus: presence of food in the mouth.
• Receptors: taste buds.
• Afferent: nerves from taste buds carry impulses
to salivary centre.
• Centre: salivary centre in medulla oblongata
(in brain stem).
• Efferent: autonomic nerves supplying salivary
glands.
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2nd year Lab & Nutrition
22
B) Conditioned
• An acquired reflex and needs training.
• The centre is in the cerebral cortex.
• The sight, smell, thought of food in the
absence of food in the mouth increase
salivary secretion.
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2nd year Lab & Nutrition
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• Salivary secretions are regulated by nervous
mechanisms only
• Parasympathetic stimulation, produces flow
of watery saliva that is rich in enzymes.
• Sympathetic stimulation produces a much
smaller volume of thick saliva that is rich in
mucus.
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2nd year Lab & Nutrition
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2nd year Lab & Nutrition
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Esophagus
• Function:
– swallowing or deglutition, which is the process
of moving food from the mouth through the
esophagus into the stomach
– No digestion or absorption
– Secretions: mucus
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2nd year Lab & Nutrition
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2nd year Lab & Nutrition
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Swallowing
• Swallowing can be initiated voluntarily but
then it is under reflex control.
Swallowing reflex:
• Receptors: touch receptors in pharynx.
• Afferent: sensory impulses from receptors.
• Centre: swallowing centre in brain stem.
• Efferent: parasympathetic nerves to muscles
of pharynx and esophagus.
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2nd year Lab & Nutrition
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Mechanism of Swallowing
• 3 stages:
– Oral or Voluntary: bolus of food is passed into the
pharynx by upward and backward movement of tongue
against palate. This stimulates the touch receptors that
initiate the swallowing reflex.
– Pharyngeal: involuntary passage of bolus through the
pharynx into esophagus. Respiratory passageways are
closed & respiration is inhibited (protective reflexes).
– Esophageal: involuntary passage of bolus from
esophagus to stomach by peristaltic movements of
esophagus.
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2nd year Lab & Nutrition
29
Protective reflexes during pharyngeal phase
of swallowing:
a) Elevation of the soft palate: closes posterior nasal
openings, thus preventing food reflux into the nasal
cavities.
b) Elevation of the larynx against the epiglottis: closes the
superior laryngeal orifice (glottis), thus preventing food
entrance into the trachea.
c) Approximation of the vocal cords: This also closes the
glottis, but its role is much more important than that of the
epiglottis.
d) Temporary apnea: stoppage of breathing for few seconds
which also prevents food entrance into the trachea.
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2nd year Lab & Nutrition
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2nd year Lab & Nutrition
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2nd year Lab & Nutrition
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2nd year Lab & Nutrition
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III- The Stomach
Learning Objectives
• Describe the gross anatomy and histology of the
stomach.
• Describe the different functions of the stomach.
• Describe the composition of gastric secretion
and the function of each constituent.
• Describe the different mechanisms that regulate
gastric secretions.
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2nd year Lab & Nutrition
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2nd year Lab & Nutrition
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Stomach
Functions of the stomach:
– Motor:
• Storage
• Mixing
• Emptying
– Secretory:
• Exocrine (HCL, mucus, intrinsic factor, pepsinogen)
• Endocrine (Gastrin)
– Digestive (proteins and lipids)
– Absorption: water, ions, alcohol and aspirin
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2nd year Lab & Nutrition
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Gastric secretion
• 3 L/day, highly acidic (pH 1-2).
• Composition and function:
Mucus (from mucus cells): protection
Enzymes (from chief cells): pepsin, lipase:
digestion.
Intrinsic factor & HCL (from parital cells):
Intrinsic factor is important for vit B12
absorption from small intestine.
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2nd year Lab & Nutrition
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2nd year Lab & Nutrition
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Functions of HCL
• Kills ingested bacteria.
• Aids protein digestion (activates pepsinogen
into pepsin).
• Provides the optimum pH for pepsin action.
• Stimulates the secretion of hormones that
promote the flow of bile and pancreatic
juice.
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2nd year Lab & Nutrition
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Regulation of Gastric secretion
3 phases:
• Cephalic
• Gastric
• Intestinal
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2nd year Lab & Nutrition
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Cephalic phase (nervous)
Conditioned:
• stimulus: smell, sight, thought of food
• centre: brain
• efferent: along vagus nerve
Unconditioned:
• stimulus: taste of food
• centre: medulla oblongata
• efferent: along vagus nerve
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2nd year Lab & Nutrition
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Gastric phase
Stimulus: food distending stomach
• Nervous: through vagus: continued gastric
secretion and motility.
• Hormonal: (Gastrin) produces secretion rich
in acid and pepsinogen
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2nd year Lab & Nutrition
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Intestinal phase
Stimulus: food distending duodenum.
• Nervous: inhibits gastric secretion and
motility.
• Hormonal: (secretin and CCK) inhibits
gastrin release, gastric secretion and
motility.
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2nd year Lab & Nutrition
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2nd year Lab & Nutrition
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IV- Exocrine Pancreas
Learning Objectives
• Describe the composition and function of
pancreatic secretions.
• Describe the hormonal and nervous
regulation of pancreatic secretion.
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2nd year Lab & Nutrition
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Composition and function of pancreatic
secretion
• 1.5 L/day, alkaline (pH 8)
• Composition and function:
– Digestive enzymes: peptidases (trypsin and
chymotrypsin), lipases, and amylase.
– Water
– HCO3
-:
• neutralize the gastric acid
• Provides optimum medium for action of pancreatic
enzymes.
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2nd year Lab & Nutrition
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Regulation of pancreatic
secretion
Mainly hormonal:
• Secretin: acid chyme in duodenum stimulates
secretions rich in water and HCO3
- but poor in
enzymes
• CCK: digestive products of proteins and fat in
duodenum stimulates secretions of pancreatic juice
rich in enzymes.
Both hormones are secreted by upper intestinal cells.
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2nd year Lab & Nutrition
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2nd year Lab & Nutrition
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Nervous control of pancreatic
secretion
• Parasympathetic impulses along vagus
nerves stimulate secretion of pancreatic
enzymes.
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2nd year Lab & Nutrition
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V- The Biliary System
Learning Objectives
• List the different functions of the liver.
• Describe the composition of bile and its functions.
• Describe the functions of bile salts.
• Describe the different functions of the gall
bladder.
• Describe the different mechanisms that regulate
bile secretion & gall bladder emptying.
• Describe the types of jaundice according to the
cause.
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2nd year Lab & Nutrition
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The biliary system includes:
• The liver
• The gall bladder
• Associated ducts:
– Hepatic ducts (right, left and common)
– Cystic duct
– Common bile duct
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2nd year Lab & Nutrition
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2nd year Lab & Nutrition
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Functions of liver
• Synthesis & Secretion of bile.
• Metabolic processes (e.g. gluconeogenesis,
glycogenolysis).
• Detoxification and degradation (e.g. drugs and hormones).
• Synthesis of plasma proteins (e.g. albumin and clotting
factors).
• Storage (e.g. iron and Vit B12).
• Activation of vitamin D.
• Removal of bacteria and old RBC.
• Excretion of cholesterol and bilirubin.
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2nd year Lab & Nutrition
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Bile secretion
• Bile is secreted by hepatocytes.
• About 500 ml (250-1200ml) is secreted per
day.
• pH 8
• Enters duodenum during digestion of meals.
• Stored in gall bladder and concentrated
between meals.
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2nd year Lab & Nutrition
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Composition of human bile (gm/dl)
Hepatic Gall bladder
Water 98% 89%
Bile salts 1.1 6
Bilirubin 0.04 0.3
Cholesterol 0.1 0.3-0.9
Fatty acids 0.12 0.3-1.2
Lecithin 0.04 0.3
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2nd year Lab & Nutrition
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Electrolyte content of bile (mmol/L)
Hepatic Gall bladder
Na+
145 130
K+
5 12
Ca2+
5 23
Cl-
100 25
HCO3
-
28 10
pH 8.3 7.3
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2nd year Lab & Nutrition
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Functions of bile
• Bile salts play an important role in fat
digestion and absorption.
• Excretion of waste products (e.g. bilirubin).
• Bicarbonate in bile neutralizes acid in
duodenum.
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2nd year Lab & Nutrition
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Bile salts
• Most important component of the bile.
• They are Na+ and K + salts of bile acids.
• They are derivatives of cholesterol.
• Recycled through the enterohepatic
circulation.
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Function of bile salts
• Emulsify large fat particles into smaller
ones that can be attacked by lipase
(detergent action).
• Help in the transport and absorption of fat
(micellar formation).
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• Prevent precipitation of cholesterol by
keeping them in solution (prevent gall
stones).
• Stimulate bile secretion by liver cells.
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Gall Bladder
• No digestive role.
• Stores bile.
• Concentrates bile.
• Empties during meals.
• Secretes mucus.
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2nd year Lab & Nutrition
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Regulation of bile secretion and gall
bladder emptying
• Chemical:
– Bile salts: most important stimulant of bile
secretion by liver cells.
• Hormonal:
– Secretin: secreted in response to acid chyme,
causes secretion of bile rich in water and HCO3
-
– CCK: secreted in response to fatty acids in
duodenum, causes gall bladder to contract and
sphincter of Oddi to relax.
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• Neural
– Vagal stimulation:
• Increases bile secretion
• Weak contraction of gall bladder
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2nd year Lab & Nutrition
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Jaundice
• Jaundice: yellowish discoloration of the
skin, sclera & mucous membranes due to a
 blood bilirubin level.
Causes:
• Pre-hepatic: due to excess production of
bilirubin e.g. haemolytic anaemia.
• Hepatic: liver disease e.g. hepatitis
• Post-hepatic: obstruction to bile flow e.g.
gall stones.
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2nd year Lab & Nutrition
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VI- Small & Large Intestines
Learning Objectives
• Describe the intestinal juice (volume, pH,
composition, function and its regulation).
• Name the different digestive enzymes and their
substrates.
• Describe the reabsorptive processes of different
substances.
• Describe the different intestinal movements
(motility).
• Describe the different functions of the colon.
• Describe the defecation reflex and its regulation.
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2nd year Lab & Nutrition
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Small intestine
Structure
• Long tube (about 6m) extending from
pyloric sphincter in stomach and joins large
intestine at the ileocecal sphincter
• duodenum (20 cm), jejunum (2.5 m) and
ileum (3.5 m).
• Surface area greatly increased by intestinal
mucosal foldings, villi and microvilli.
• Structure of a villus (see figure).
73
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Small intestine
Function
• Digestion : Enzymes are intracellular
(Disaccharidases and aminopeptidases).
• Absorption: completed in s. intestine, large
surface area (as large as a tennis court area).
(Site where most digestion and absorption
take place).
• Secretion
• Motility
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Digestion
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Absorption
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Exocrine intestinal secretions
• Intestinal juice: alkaline fluid (water and
electrolytes) with few enzymes from
desquamated cells (1000-1500 ml/day).
• HCO3
-: neutralize acid.
• Mucus: protection and lubrication.
• No digestive enzymes.
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2nd year Lab & Nutrition
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Regulation of intestinal secretion
Local: mechanical stimulation of intestinal
mucosa by the presence of chyme.
Nervous: vagal nerve stimulation causes
secretion of intestinal glands.
Hormonal: ? secretin
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2nd year Lab & Nutrition
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Intestinal motility
• Segmentation: ring-like contractions. Mix
chyme and expose it to absorptive surface.
• Peristaltic: a wave of contraction preceded
by relaxation. Propels the gastrointestinal
contents toward the large intestine.
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Large Intestine
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Large intestine
• No digestive function.
• Absorption of water, Na+ and other
minerals.
• Secretion of mucus for lubrication.
• Storage of feces (undigested food).
• Bacteria in colon synthesize vitamin K and
a number of B complex vitamins.
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Defecation reflex
• Stimulus: undigested material distending rectum.
• Receptor: stretch receptor in rectum.
• Afferent: sensory to sacral segment of spinal cord
• Centre: sacral segment of spinal cord
• Efferent: parasympathetic nerves to smooth
muscle of rectum and internal anal sphincter.
• External anal sphincter is under voluntary control.
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Defecation reflex
• Causes the internal anal sphincter to relax
and the rectum and sigmoid colon to
contract.
• If external anal sphincter is relaxed
defecation occurs.
• Defecation can be inhibited by voluntary
tightening of external anal sphincter.
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GIT BS.pptx about human body their structure and

  • 1. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 1 The Physiology of the Gastrointestinal Tract (GIT) General Objectives • To describe the structural organization of the GIT (alimentary canal and accessory glands) and the different layers of the GIT. • To describe the functions of the various parts of the GIT (secretion, digestion, absorption and motility). • To describe the composition of different gastrointestinal secretions and their functions. • To describe the regulatory mechanisms (nervous and hormonal) of gastrointestinal function.
  • 2. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 2 I- Introduction to GIT Physiology Learning Objectives • Describe the general functions of the GIT. • Describe the general organization of the GIT. • Describe the common layers of the digestive tract wall. • Describe the nervous and hormonal regulation of GI function. • Describe the different movements of the GIT.
  • 3. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 3 Functions of the GIT • Ingestion • Motility: mixing and propulsion • Secretion • Digestion • Absorption • Excretion
  • 4. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 4 Organization of the GIT • The alimentary canal: mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum and anal canal. • Associated glands: salivary glands, pancreas, liver and gall bladder.
  • 6. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 6 Layers of digestive tract wall • Mucosa • Submucosa • Muscularis externa • Serosa
  • 7. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 7
  • 8. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 8
  • 9. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 9 Mucosa • This layer is concerned with secretion of both the digestive juices and certain hormones as well as the absorption of the various nutrients. • It contains blood capillaries, lymph vessels and a layer of smooth muscle called the muscularis mucosa.
  • 10. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 10 Submucosa • This is a dense connective tissue layer that contains larger blood and lymph vessels as well as a network of neurons called submucous or Meissner’s plexus.
  • 11. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 11 • Muscularis externa: an outer longitudinal layer and inner circular layer of smooth muscle. In between myenteric or Aurbach’s plexus. • Serosa: an outer fibrous coating
  • 12. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 12 Control of GI functions (secretions and motility) • Nervous • Hormonal
  • 13. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 13 Nervous supply to the Gut Extrinsic (autonomic) • Sympathetic (decreases motor and secretory activity, contraction of sphincters) • Parasympathetic (stimulatory) Intrinsic • Submucous or Meissner’s plexus (controls secretory function) • myenteric or Auerbach’s plexus (controls motor activity)
  • 14. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 14 Hormonal control of GIT function 1. Gastrin (from the stomach): stimulates gastric motility and secretion. 2. CCK (from small intestines) stimulates pancreatic enzyme secretion, and gall bladder contraction. Inhibits gastric emptying. 3. Secretin (from small intestines): stimulates pancreatic and biliary bicarbonate secretion.
  • 15. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 15 Types of movements in the GIT • Propulsive: move bolus forward. • Segmentation: mixing in the small intestine.
  • 16. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 16 II- Mouth, Salivary glands & Esophagus Learning Objectives • Name the salivary glands. • Describe the salivary secretion: volume, pH and composition. • Describe the different functions of saliva. • Describe the regulation of salivary secretions. • Name functions of esophagus. • Describe the mechanism of swallowing.
  • 17. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 17 The Salivary glands • 3 paired salivary glands made of ducts and acini that make between 1-1.5 liters/day with a pH of 6-7 • Parotid glands • Submandibular or submaxillary glands • Sublingual glands
  • 18. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 18
  • 19. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 19 Composition of Saliva • Mostly water 99.5% • Ionic content: low in Na+ and Cl-, high in K+ and HCO3 - • Enzymes: lingual lipase and -amylase (ptyalin). • Mucins • Lysozymes: proteolytic enzyme • Immunoglobulin A (IgA)
  • 20. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 20 Functions of saliva • Digestive functions: • Amylase breaks down starch, and lingual lipase breaks down triglycerides (active in the stomach). • It dissolves food materials so it can be sensed by taste buds. • Lubrication: • Keeps mouth moist and thus facilitates movements of lips and tongue during speech. • Moistens food and thus facilitates swallowing. • Protection: • Keeps mouth and teeth clean by dissolving and washing food particles from between the teeth. • Has an anti-bacterial action. • Buffers acidic gastric secretions.
  • 21. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 21 Regulation of Salivary secretion A) Simple or unconditioned: The presence of food in the mouth results in reflex secretion of saliva. • Stimulus: presence of food in the mouth. • Receptors: taste buds. • Afferent: nerves from taste buds carry impulses to salivary centre. • Centre: salivary centre in medulla oblongata (in brain stem). • Efferent: autonomic nerves supplying salivary glands.
  • 22. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 22 B) Conditioned • An acquired reflex and needs training. • The centre is in the cerebral cortex. • The sight, smell, thought of food in the absence of food in the mouth increase salivary secretion.
  • 23. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 23 • Salivary secretions are regulated by nervous mechanisms only • Parasympathetic stimulation, produces flow of watery saliva that is rich in enzymes. • Sympathetic stimulation produces a much smaller volume of thick saliva that is rich in mucus.
  • 24. 6/9/2024 24 GIT physiology 2nd year Lab & Nutrition
  • 25. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 25 Esophagus • Function: – swallowing or deglutition, which is the process of moving food from the mouth through the esophagus into the stomach – No digestion or absorption – Secretions: mucus
  • 26. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 26
  • 27. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 27 Swallowing • Swallowing can be initiated voluntarily but then it is under reflex control. Swallowing reflex: • Receptors: touch receptors in pharynx. • Afferent: sensory impulses from receptors. • Centre: swallowing centre in brain stem. • Efferent: parasympathetic nerves to muscles of pharynx and esophagus.
  • 28. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 28 Mechanism of Swallowing • 3 stages: – Oral or Voluntary: bolus of food is passed into the pharynx by upward and backward movement of tongue against palate. This stimulates the touch receptors that initiate the swallowing reflex. – Pharyngeal: involuntary passage of bolus through the pharynx into esophagus. Respiratory passageways are closed & respiration is inhibited (protective reflexes). – Esophageal: involuntary passage of bolus from esophagus to stomach by peristaltic movements of esophagus.
  • 29. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 29 Protective reflexes during pharyngeal phase of swallowing: a) Elevation of the soft palate: closes posterior nasal openings, thus preventing food reflux into the nasal cavities. b) Elevation of the larynx against the epiglottis: closes the superior laryngeal orifice (glottis), thus preventing food entrance into the trachea. c) Approximation of the vocal cords: This also closes the glottis, but its role is much more important than that of the epiglottis. d) Temporary apnea: stoppage of breathing for few seconds which also prevents food entrance into the trachea.
  • 30. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 30
  • 31. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 31
  • 32. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 32
  • 33. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 33 III- The Stomach Learning Objectives • Describe the gross anatomy and histology of the stomach. • Describe the different functions of the stomach. • Describe the composition of gastric secretion and the function of each constituent. • Describe the different mechanisms that regulate gastric secretions.
  • 35. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 35
  • 37. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 37 Stomach Functions of the stomach: – Motor: • Storage • Mixing • Emptying – Secretory: • Exocrine (HCL, mucus, intrinsic factor, pepsinogen) • Endocrine (Gastrin) – Digestive (proteins and lipids) – Absorption: water, ions, alcohol and aspirin
  • 38. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 38 Gastric secretion • 3 L/day, highly acidic (pH 1-2). • Composition and function: Mucus (from mucus cells): protection Enzymes (from chief cells): pepsin, lipase: digestion. Intrinsic factor & HCL (from parital cells): Intrinsic factor is important for vit B12 absorption from small intestine.
  • 39. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 39
  • 40. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 40 Functions of HCL • Kills ingested bacteria. • Aids protein digestion (activates pepsinogen into pepsin). • Provides the optimum pH for pepsin action. • Stimulates the secretion of hormones that promote the flow of bile and pancreatic juice.
  • 41. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 41 Regulation of Gastric secretion 3 phases: • Cephalic • Gastric • Intestinal
  • 42. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 42 Cephalic phase (nervous) Conditioned: • stimulus: smell, sight, thought of food • centre: brain • efferent: along vagus nerve Unconditioned: • stimulus: taste of food • centre: medulla oblongata • efferent: along vagus nerve
  • 43. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 43 Gastric phase Stimulus: food distending stomach • Nervous: through vagus: continued gastric secretion and motility. • Hormonal: (Gastrin) produces secretion rich in acid and pepsinogen
  • 44. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 44 Intestinal phase Stimulus: food distending duodenum. • Nervous: inhibits gastric secretion and motility. • Hormonal: (secretin and CCK) inhibits gastrin release, gastric secretion and motility.
  • 45. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 45
  • 46. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 46 IV- Exocrine Pancreas Learning Objectives • Describe the composition and function of pancreatic secretions. • Describe the hormonal and nervous regulation of pancreatic secretion.
  • 47. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 47
  • 48. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 48 Composition and function of pancreatic secretion • 1.5 L/day, alkaline (pH 8) • Composition and function: – Digestive enzymes: peptidases (trypsin and chymotrypsin), lipases, and amylase. – Water – HCO3 -: • neutralize the gastric acid • Provides optimum medium for action of pancreatic enzymes.
  • 49. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 49 Regulation of pancreatic secretion Mainly hormonal: • Secretin: acid chyme in duodenum stimulates secretions rich in water and HCO3 - but poor in enzymes • CCK: digestive products of proteins and fat in duodenum stimulates secretions of pancreatic juice rich in enzymes. Both hormones are secreted by upper intestinal cells.
  • 50. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 50
  • 51. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 51 Nervous control of pancreatic secretion • Parasympathetic impulses along vagus nerves stimulate secretion of pancreatic enzymes.
  • 52. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 52 V- The Biliary System Learning Objectives • List the different functions of the liver. • Describe the composition of bile and its functions. • Describe the functions of bile salts. • Describe the different functions of the gall bladder. • Describe the different mechanisms that regulate bile secretion & gall bladder emptying. • Describe the types of jaundice according to the cause.
  • 53. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 53 The biliary system includes: • The liver • The gall bladder • Associated ducts: – Hepatic ducts (right, left and common) – Cystic duct – Common bile duct
  • 54. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 54
  • 55. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 55 Functions of liver • Synthesis & Secretion of bile. • Metabolic processes (e.g. gluconeogenesis, glycogenolysis). • Detoxification and degradation (e.g. drugs and hormones). • Synthesis of plasma proteins (e.g. albumin and clotting factors). • Storage (e.g. iron and Vit B12). • Activation of vitamin D. • Removal of bacteria and old RBC. • Excretion of cholesterol and bilirubin.
  • 56. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 56 Bile secretion • Bile is secreted by hepatocytes. • About 500 ml (250-1200ml) is secreted per day. • pH 8 • Enters duodenum during digestion of meals. • Stored in gall bladder and concentrated between meals.
  • 57. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 57 Composition of human bile (gm/dl) Hepatic Gall bladder Water 98% 89% Bile salts 1.1 6 Bilirubin 0.04 0.3 Cholesterol 0.1 0.3-0.9 Fatty acids 0.12 0.3-1.2 Lecithin 0.04 0.3
  • 58. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 58 Electrolyte content of bile (mmol/L) Hepatic Gall bladder Na+ 145 130 K+ 5 12 Ca2+ 5 23 Cl- 100 25 HCO3 - 28 10 pH 8.3 7.3
  • 59. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 59 Functions of bile • Bile salts play an important role in fat digestion and absorption. • Excretion of waste products (e.g. bilirubin). • Bicarbonate in bile neutralizes acid in duodenum.
  • 60. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 60 Bile salts • Most important component of the bile. • They are Na+ and K + salts of bile acids. • They are derivatives of cholesterol. • Recycled through the enterohepatic circulation.
  • 61. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 61
  • 62. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 62 Function of bile salts • Emulsify large fat particles into smaller ones that can be attacked by lipase (detergent action). • Help in the transport and absorption of fat (micellar formation).
  • 63. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 63
  • 64. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 64
  • 65. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 65 • Prevent precipitation of cholesterol by keeping them in solution (prevent gall stones). • Stimulate bile secretion by liver cells.
  • 66. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 66 Gall Bladder • No digestive role. • Stores bile. • Concentrates bile. • Empties during meals. • Secretes mucus.
  • 67. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 67 Regulation of bile secretion and gall bladder emptying • Chemical: – Bile salts: most important stimulant of bile secretion by liver cells. • Hormonal: – Secretin: secreted in response to acid chyme, causes secretion of bile rich in water and HCO3 - – CCK: secreted in response to fatty acids in duodenum, causes gall bladder to contract and sphincter of Oddi to relax.
  • 68. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 68
  • 69. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 69 • Neural – Vagal stimulation: • Increases bile secretion • Weak contraction of gall bladder
  • 70. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 70 Jaundice • Jaundice: yellowish discoloration of the skin, sclera & mucous membranes due to a  blood bilirubin level. Causes: • Pre-hepatic: due to excess production of bilirubin e.g. haemolytic anaemia. • Hepatic: liver disease e.g. hepatitis • Post-hepatic: obstruction to bile flow e.g. gall stones.
  • 71. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 71 VI- Small & Large Intestines Learning Objectives • Describe the intestinal juice (volume, pH, composition, function and its regulation). • Name the different digestive enzymes and their substrates. • Describe the reabsorptive processes of different substances. • Describe the different intestinal movements (motility). • Describe the different functions of the colon. • Describe the defecation reflex and its regulation.
  • 72. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 72 Small intestine Structure • Long tube (about 6m) extending from pyloric sphincter in stomach and joins large intestine at the ileocecal sphincter • duodenum (20 cm), jejunum (2.5 m) and ileum (3.5 m). • Surface area greatly increased by intestinal mucosal foldings, villi and microvilli. • Structure of a villus (see figure).
  • 73. 73
  • 74. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 74
  • 75. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 75
  • 76. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 76
  • 77. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 77 Small intestine Function • Digestion : Enzymes are intracellular (Disaccharidases and aminopeptidases). • Absorption: completed in s. intestine, large surface area (as large as a tennis court area). (Site where most digestion and absorption take place). • Secretion • Motility
  • 78. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 78 Digestion
  • 79. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 79
  • 80. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 80
  • 81. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 81
  • 82. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 82
  • 83. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 83 Absorption
  • 84. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 84
  • 85. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 85
  • 86. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 86 Exocrine intestinal secretions • Intestinal juice: alkaline fluid (water and electrolytes) with few enzymes from desquamated cells (1000-1500 ml/day). • HCO3 -: neutralize acid. • Mucus: protection and lubrication. • No digestive enzymes.
  • 87. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 87 Regulation of intestinal secretion Local: mechanical stimulation of intestinal mucosa by the presence of chyme. Nervous: vagal nerve stimulation causes secretion of intestinal glands. Hormonal: ? secretin
  • 88. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 88 Intestinal motility • Segmentation: ring-like contractions. Mix chyme and expose it to absorptive surface. • Peristaltic: a wave of contraction preceded by relaxation. Propels the gastrointestinal contents toward the large intestine.
  • 89. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 89
  • 90. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 90
  • 91. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 91 Large Intestine
  • 92. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 92
  • 93. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 93 Large intestine • No digestive function. • Absorption of water, Na+ and other minerals. • Secretion of mucus for lubrication. • Storage of feces (undigested food). • Bacteria in colon synthesize vitamin K and a number of B complex vitamins.
  • 94. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 94 Defecation reflex • Stimulus: undigested material distending rectum. • Receptor: stretch receptor in rectum. • Afferent: sensory to sacral segment of spinal cord • Centre: sacral segment of spinal cord • Efferent: parasympathetic nerves to smooth muscle of rectum and internal anal sphincter. • External anal sphincter is under voluntary control.
  • 95. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 95 Defecation reflex • Causes the internal anal sphincter to relax and the rectum and sigmoid colon to contract. • If external anal sphincter is relaxed defecation occurs. • Defecation can be inhibited by voluntary tightening of external anal sphincter.
  • 96. 6/9/2024 GIT physiology 2nd year Lab & Nutrition 96