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Review of GIT Physiology
Prof.Dr.Rashid Mahmood
© Prof.Dr.Rashid Mahmod 2
GIT: A long tube with Accessory glands
© Prof.Dr.Rashid Mahmod 3
Lesson ContentsMouth EsophagusStomachPyloric SphincterSmall intestineIleo-Cecal Valve & SphincterLarge intestineInternal & External Anal SphincterAccessory glands
© Prof.Dr.Rashid Mahmod 4
MouthIngestion of food
MasticationSwallowing
3 Stages i. Voluntary Stage (Movement of Tongue)ii. Pharyngeal Stage (Involuntary) (Swallowing
Reflex)iii. Esophageal Stage (Involuntary)
Khyber Girls Medical College Prof.Dr.Rashid Mahmood Prof.Dr.Rashid Mahmood Prof.Dr.Rashid Mahmood Prof.Dr.Rashid Mahmood Prof.Dr.Rashid Mahmood
5
Mastication (Chewing Reflex)• Components of reflex
1. Stimulus2. Receptors3. Afferent Nerve4. CNS5. Efferent Nerve6. Effector7. Response
• Components of Chewing reflex1. Bolus of Food2. Receptors of Sensory Nerves3. 5th Nerve4. Swallowing Centre5. 5th Nerve6. Muscles of Mastication7. Reflex Inhibition →Rebound Contraction (Stretch Reflex)
Khyber Girls Medical College Prof.Dr.Rashid Mahmood Prof.Dr.Rashid Mahmood Prof.Dr.Rashid Mahmood Prof.Dr.Rashid Mahmood Prof.Dr.Rashid Mahmood
6Swallowing
Oropharyngeal stage of swallowing
Resting
© Prof.Dr.Rashid Mahmod 7
Swallowing (Deglutition) Reflex
1. Stimulus→ Touch2. Receptors→ Tactile3. Afferent Nerve→ 5,94. CNS→ Swallowing Centre (Medulla &
Lower Pons)5. Efferent Nerve→ 5,9,10,126. Effector→ Muscles of Pharynx & Upper
esophagus7. Response → Contraction
© Prof.Dr.Rashid Mahmod 8
Esophagus3rd Stage of swallowing No secretion except mucus, more
marked at upper & lower end PeristalsisUpper and lower esophageal Sphincter
© Prof.Dr.Rashid Mahmod 9
StomachMovements (Motor functions)Secretions Digestion AbsorptionRegulation
© Prof.Dr.Rashid Mahmod 10
Movements (Motor functions) of Stomach
1. Storage• Until food is processed in stomach and intestine
2. Mixing (with gastric secretions)• Unless semifluid mixture: chyme
3. Slow emptying• At a rate suitable for digestion and absorption
in small intestine4. Hunger contractions
© Prof.Dr.Rashid Mahmod 11
Secretions of Stomach
Components1. HCl2. Pepsins3. Gastric Lipase 4. Gastric Amylase5. Mucus6. Intrinsic factor7. Gelatinase
(Liquefies Gelatin)8. Electrolytes9. Water
Phases Cephalic
PhaseGastric PhaseIntestinal
Phase
© Prof.Dr.Rashid Mahmod 12
Digestion in Stomach1. Gastric Lipase (Digestion of lipids)2. Gastric Amylase (Digestion of
carbohydrates)3.Pepsinogen (Digestion of Proteins)
Pepsinogen
Pepsin
HClCauses proteolysis
© Prof.Dr.Rashid Mahmod 13
Absorption in Stomach Water, if the body is dehydrated. Medication, like aspirin. Amino acids.
© Prof.Dr.Rashid Mahmod 14
Regulation of Gastric Functions
Nervous Control Enteric Nervous System Autonomic Nervous System Reflexes:
Entero Gastric Reflex Cephalic Phase of Gastric Secretion
Hormonal Control Gastrin Secretin CCK GIP Motilin
© Prof.Dr.Rashid Mahmod 15
Pyloric SphincterPyloric Pump & Gastric Emptying
1. Gastric factors (Excitatory)
Hormonal control GASTRIN →
Mild to moderate stimulation of gastric movements
Nervous control local Myenteric
reflexes
2. Duodenal factors (Inhibitory)(more powerful)
Nervous control Enterogastric nervous
reflexes Hormonal control
i. Cholecystokinin ii. Secretiniii. GIP
© Prof.Dr.Rashid Mahmod 16
Small IntestineMovementsSecretions Digestion AbsorptionRegulation
© Prof.Dr.Rashid Mahmod 17
Movements of Small Intestine1. Mixing (Segmentation Contractions)2. Propulsive (Peristalsis)
Overlap
3. Movements of Muscularis MucosaFolds
↑ surface area4. Contraction of villi
“milk” the villi↑ lymph flow
© Prof.Dr.Rashid Mahmod 18
Secretion of Small IntestineSecreted Into Intestinal Lumen
EnterokinaseEnterocytes covering the villi contain enzymes
Digestion during absorptionFor digestion of proteins
PeptidasesFor digestion of carbohydrates
Sucrase, maltase, isomaltase, lactaseFor digestion of fats
Intestinal lipase
Hormones Secreted by Small Intestine:
SecretinCCKMotilin
© Prof.Dr.Rashid Mahmod 19
Digestion in Small IntestineFinal Digestion occurs inside the
Enterocytes lining the epithelium of small intestine.
Digestion of Carbohydrates
Cellulose: Not digested
Action of Ptylin (Amylase):5% digestion in mouth
15-35% in stomach (before it is inactivated by HCl)
More Powerful
Contd………
Absorbed
Digestion of Proteins
Collagen (Meat)
Digestion of Fats
Lingual Lipase: < 10% digestion (Not important)Enteric Lipase: < 10% digestion (Not important)
Cholesterol Esterase digests Cholesterol Esters
Phospolipase A2 digests Phospolipids
Which is the main enzyme for digestion of fats?
© Prof.Dr.Rashid Mahmod 23
Absorption in Small IntestineFinal Absorption of all nutrients by
enterocytes
Absorption of Carbohydrates
A small fraction as Disaccharides Mainly Monosaccharides
Glucose (80%) Galactose
Sodium Co-Transport Fructose
Facilitated Diffusion Presence of glucose also facilitates reabsorption of Sodium
Absorption of Proteins
Protein molecules : rarely absorbed → antigenic reaction Absorbed as
Tripeptides Bipeptides Amino Acids
Mainly Co-transport with Sodium
Absorption of Fats
Fats
Monoglycerides
Fatty Acids
Bile Micelles
Microvilli
Bile Acids Monoglycerides
Fatty Acids
Bile Acids
Epithelial Cells
New Triglycerides
Chylomicrons
Lymph
Intestinal Lumen
++ +
+
© Prof.Dr.Rashid Mahmod 27
Regulation of Functions of Small Intestine
Nervous ControlEnteric Nervous SystemAutonomic Nervous SystemReflexes
Gastro-EntericGastro-Ileal etc
Hormonal ControlSecretin CCK
Ileocecal valve andIleocecal sphincter
Excitatory factors
Inhibitory factors
© Prof.Dr.Rashid Mahmod 29
Large IntestineMovements SecretionsNo DigestionAbsorptionFormation of FecesOther Functions
Movements of Colon
Mixing Movements (Haustrations) Proximal half
Propulsive Movements (Mass Movements) Distal half
Functions of colon: Absorption Storage of fecal matter
Secretions of Large Intestine:Mucus secretion
Crypts of Lieberkϋhan No villi No enzymes Moderate amount of bicarbonate ions
Absorption in Large Intestine
Proximal Half: Absorbing Colon
Water Electrolytes
Distal Half: Storage Colon
Formation of Feces No villi
Other Functions of Large Intestine
Bacteria Normally present Substances formed as a result of bacterial action:
Vitamin K Vitamin B12 Thiamine Riboflavin Gases (flatus)
CO2
Methane Hydrogen
External & Internal Anal Sphincter:Defecation reflex
Defecation Reflexes
Intrinsic Reflex Parasympathetic Defection reflex
11Prof .Dr. Rashid Mahmood
Defecation
• Rectum is empty most of the time– Weak functional sphincter at juncture between
sigmoid colon & rectum– Sharp angulation
• Feces into rectum → Defecation reflex– Desire for Defecation– Reflex contraction of rectum– Reflex relaxation of anal sphincters
Voluntary/conscious/subconscious involuntary
External Internal Pudendal nerve
© Prof.Dr.Rashid Mahmod 36
Accessory glandsSalivary GlandsPancreasLiver/ Gall Bladder
© Prof.Dr.Rashid Mahmod 37
Salivary Glands: Saliva
1. Digestion i. Salivary Amylase
Secreted by salivary glandsii. Lingual lipase
Secreted by glands on the tongue
2. Articulation3. Moistening of food4. Mastication 5. Water regulation (thirst)6. Taste receptors7. Swallowing 8. Keeps mouth clean9. Neutralization of gastric
acid Relieve of heartburn
10. Protection from bacteriai. Wash away bacteriaii. Wash away the food of
bacteriaiii. Destroy bacteria
11. Tooth Protection1. By neutralizing acid2. By affecting mineral
dissociation equilibrium by means of its calcium phosphate content.
3. Proline-rich proteins protect the tooth enamel and bind toxic tannins
12. Excretion:Urea, Heavy Metals, Drugs etc
PancreasComponents of Pancreatic Secretion1. Exocrine
i. Digestive enzymes Secreted by acinar cells
ii. HCO3- - Secreted by duct cells
2. Endocrinei. Insulinii. Glucagon
Functions of Liver
1. Formation and secretion of bile2. Nutrient and vitamin metabolism3. Inactivation of various substances4. Synthesis of plasma proteins5. Immunity
Functions of Bile
Digestion of fats Emulsification
Large fat particles →small fat particles Absorption of fats Excretion
Bilirubin End product of hemoglobin destruction
Excess cholesterol
Emptying of Gall Bladder
Food in DuodenumMainly Fatty Food
Cholecystokinin
BLOOD
GALL BLADDER
EMPTYING
RELAXATION OF SPHINCTER OF ODDI
duodenum
Vagus nerve
Food in mouth
The EndQuestions? Next:
EOME