Download Gastro Intestinal System

Gastro Intestinal System
Dr. V.P.C.Rajakruna
MBBS (COLOMBO)
Digestion
• Processing of food
• Types
– Mechanical (physical)
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Chew
Tear
Grind
Mash
Mix
– Chemical
• Catabolic reactions
• Enzymatic hydrolysis
– Carbohydrate
– Protein
– Lipid
• Phases
– Ingestion
– Movement
– Digestion
– Absorption
– Further digestion
Anatomy of GI System
– Structures ( Tubal pathway)
• Mouth - stratified squamous
• Oral Cavity - stratified squamous
• Pharynx - stratified squamous epithelium
• Esophagus - simple-columnar
• Stomach - simple columnar
• Duedenum - simple columnar
• Jejenum- simple columnar
• Ileum - simple columnar
• Cecum - simple columnar
• Ascending colon - simple columnar
• Transverse colon - simple columnar
• Descending colon - simple columnar
• Sigmoid colon- simple columnar
• Rectum - nonkeratinized statified squamous
• Anus- nonkeratinized statified squamous
• Accessory structures
– Not in tube path
– Organs
• Teeth
• Tongue
• Salivary glands
• Liver
• Gall bladder
• Pancreas
Layers of GI System
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Consist of 4 tunics
From the inside out:
Mucosa
Submucosa
Muscularis
Serosa
Mucosa
• Lines the lumen
• Consist of epithelium,a connective tissue
layer called lamina propria and a thin layer
of smooth muscle layer called muscularis
mucosae
• Muscularis mucosae is responsible for the
folding of GI tract
Submucosa
• Highly vascular layer of connective tissue
• Consist of nerve plexus which supply the
autonomic nerves ( Meissner’s plexus)
Muscularis
• Also called muscularis externa
• Consist of inner circular and outer
longitudinal smooth muscle layers
• Responsible for the segmental
contractions and the peristaltic movements
of GI tract
• Mesenteric plexus is situated in between
these two layers ,provide the major nerve
supply to the GI tract
Serosa
• completes the wall of GI tract
• Consist of areolar tissue
The physiological functions of the
GI system
• 1. Motility – movement of food through GI
tract
• Ingestion – taking food in to the mouth
• Mastication – chewing the food and mixing
with saliva
• Deglutition – swallowing food
• Peristalsis – rhythmic wave like
contractions that move food through the GI
tract
• 2. Secretion
• Exocrine – digestive enzymes, HCl,HCO3• Endocrine - hormones
• 3. Digestion
• Break down of food molecules in to
smaller sub units which can absorb
• 4. Absorption
• Passage of digested end products in to
blood or lymph
Oral Cavity
• Mouth or oral cavity
– Vestibule: Space between lips or cheeks and
alveolar processes
– Oral cavity proper
• Lips (labia) and cheeks
• Palate: Oral cavity roof
– Hard and soft
• Palatine tonsils
• Tongue: Involved in speech, taste,
mastication, swallowing
Teeth
• Two sets
– Primary, deciduous,
milk: Childhood
– Permanent or
secondary: Adult (32)
• Types
– Incisors, canine,
premolar and molars
Salivary Glands
• Produce saliva
– Prevents bacterial infection
– Lubrication
– Contains salivary amylase and lipase
• Breaks down starch and lipids
• Three pairs
– Parotid: Largest
– Submandibular
– Sublingual: Smallest
Pharynx
Nasopharynx
Oropharynx: Transmits food normally
Laryngopharynx: Transmits food normally
Esophagus
Transports food from pharynx to stomach
Muscular tube approximately 25cm in length
Located posteriorly to the trachea within the
mediastinum of the thorax
Passes through esophageal hiatus (opening) of
diaphragm and ends at stomach
Sphincters
• Upper
• Lower
Skeletal muscle
Skeletal muscle + smooth muscle
Smooth muscle
Deglutition (Swallowing)
• Three phases
– Voluntary
• Bolus of food moved by tongue from oral cavity
to pharynx
– Pharyngeal
Reflex: Upper esophageal sphincter relaxes,
elevated pharynx opens the esophagus, food
pushed into esophagus
– Esophageal
• Reflex: Epiglottis is tipped posteriorly, larynx
elevated to prevent food from passing into
larynx
• Swallowed food is pushed from one end of
the esophagus to the other along the
intestine by a wave like muscular
contraction called peristalsis
• Peristalsis is produced by a series of
localized reflexes in response to the
distension of the GI tract wall by the food
bolus
• Passing of food bolus along the GI tract
happens due to muscular contractions and
relaxations
Stomach
• Openings
– Gastroesophageal: To esophagus
– Pyloric: To duodenum
• Regions
– Cardiac
– Fundus
– Body
– Pyloric
• J shaped
• Most distensible part of the GI tract
• Layers
– Serosa
– Muscularis: Three layers
• Outer longitudinal
• Middle circular
• Inner oblique
– Submucosa
– Mucosa
Special Features
• Rugae: Folds in stomach when empty
• Gastric pits: Openings for gastric glands
• Gastric gland containing cells
• Goblet cells: Mucus
• Parietal cells: Hydrochloric acid and
intrinsic factor
• Chief cells : Pepsinogen
• Enterochromafin like cells: Histamine
• G cells: Gastrin
• D cells: Somatostatin
• The exocrine secretions of the gastric cells
together with large amount of water form
highly acidic solution known as Gastric
juice ( pH = 2 or less than 2 )
Functions of stomach
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Store food
Initiate digestion of protein
Kill bacteria
Move the food into small intestine
Pepsin and HCl secretion
• The parietal cells secrete H+ , at a pH as
low as 0.8, in to the gastric lumen by
active transport against million to one
concentration gradient
• This is done by H+/K+ ATPase pumps,
moving K+ in to the cell cytoplasm from
the gastric lumen while secreting H+ in to
the gastric juice
Functions of gastric juice
• Ingested proteins are denatured at low pH
• Pepsinogen converts in to active pepsin
• Pepsin is more active under acidic
conditions
• Kills bacteria
Digestion and absorption in the
stomach
• Proteins are only partially digested
• Carbohydrates and lipids not digested at
all ( salivary amylase inactivated by acidic
media)
• Absorption???????????
certain drugs
yes
Mechanism of gastric secretion
Smell, taste of food
CNS activation and send the commands to stomach
Increase volume of gastric juice and secretion of
gastrin
Cephalic phase – few minutes
Stimulation of
stretch receptors of
the stomach wall
Increase
Pepsin
production
Stimulation of
chemoreceptors
as pH increases
Increase
of Acid
production
Initiate the digestion
of proteins
Stimulation of
parasympathetic
NS
Stimulation
of Gastrin
production
Increase motility
and initiating
mixing waves
Gastric Phase – 3 to 4 hours
Distension of
duodenum
Stimulation of cholesytokinin, gastric
inhibitory peptide in the presence of
acids, carbohydrates and lipids
Inhibition of gastric acid
and pepsinogen secretion
Reduction of gastric
mortality
Control of food
entering in to
the duodenum
Intestinal phase – take hours
Small Intestine
• Site of greatest amount of digestion and
absorption
• Extends from pyloric sphincter of the stomach
to the ileocecal valve opening into the large
intestine
• Approximately 3m in length
• Longest part of the GIT
• Divisions
– Duodenum – 20-30cm
– Jejunum – 2/5 from the rest
– Ileum – 3/5 from the rest
(Peyer’s patches or lymph nodules)
• Modifications
– Circular folds or plicae circulares, villi,
lacteal, microvilli( increase the surface
area)
• Cells of mucosa
– Absorptive, goblet, granular, endocrine
Small Intestine Secretions
• Mucus
– Protects against digestive enzymes and stomach
acids, allow smooth transmit of food bolus
• Digestive enzymes
– Disaccharidases: Break down disaccharides to
monosaccharides
– Peptidases: Hydrolyze peptide bonds
– Nucleases: Break down nucleic acids
• Duodenal glands
– Stimulated by vagus nerve, secretin, chemical or
tactile irritation of duodenal mucosa
Intestinal contractions and motility
• Peristalsis- much weaker than in the
stomach and esophagus
• Intestinal motility ( the movement of food
bolus or chyme ) is slow
• Segmentation – major contractile activity
• This occur by the smooth muscles of small
intestine
• Smooth muscle of intestine capable of
spontaneous electrical activity and auto
rhythmic contractions
Intestinal Reflexes
• Gastroileal – increased gastric activity
causes increased motility of the ileum and
increased motility of the ileum and
increased movement of chyme through the
ileocecal sphincter
• Ileogastric – distension of the ileum
causes a decrease in gastric motility
• Intestino intestinal – overdistention of one
intestinal segment causes relaxation
through out the rest of the intestine
Functions of Small Intestine
• Mixing: Segmental contraction that occurs
in small intestine
• Secretion: Lubricate, liquefy, digest
• Digestion: Mechanical and chemical
• Absorption: Movement from tract into
circulation or lymph
• Elimination: Waste products removed from
body
What are absorbed?
• Absorption of carbohydrates, lipids , amino
acids, calcium and iron occurs primarily in
duodenum and jejunum
• Bile salts, vitamin B12, water and
electrolytes are absorbed primarily in the
ileum
Large Intestine
• Extends from ileocecal valve to anus
• Consists of cecum, colon, rectum, anal
canal
• Movements sluggish
• Cecum
– Blind sac, vermiform appendix attached
• Colon
– Ascending, transverse, descending,
sigmoid
• Rectum
– Straight muscular tube
• Anal canal
– Internal anal sphincter (smooth muscle)
– External anal sphincter (skeletal muscle)
Secretions of Large Intestine
• Mucus provides protection
– Parasympathetic stimulation increases rate of
goblet cell secretion
• Pumps
– Exchange of bicarbonate ions for chloride
ions
– Exchange of sodium ions for hydrogen ions
• Bacterial actions produce gases called
flatus
Movement in Large Intestine
• Mass movements
– Common after meals
• Local reflexes in enteric plexus
– Gastrocolic: Initiated by stomach
– Duodenocolic: Initiated by duodenum
• Defecation reflex
– Distension of the rectal wall by feces
• Defecation
– Usually accompanied by voluntary movements to
expel feces through abdominal cavity pressure
caused by inspiration
Function of Large Intestine
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Little or no digestive function
Absorb water passively
Absorb electrolytes
Absorb several B complex vitamins and
vitamin K
• Resident bacteria in large intestine also
produce significant amount of Vit K and
Folic acid which absorb by large intestine
• Forms, stores and expels feces
Defecation
Liver
• Immediately below the diaphragm in the
abdominal cavity
• Lobes
– Major: Left and right
– Minor: Caudate and quadrate
• Ducts
– Common hepatic
– Cystic
• From gallbladder
– Common bile
• Joins pancreatic duct at hepatopancreatic ampulla
Structure of the Liver
• Hepatocytes
Hepatic plates
Liver Lobules
( Functional Unit of the liver )
• Hepatic plates are separated each other
by large capillary spaces called sinusoids
• Sinusoids are lined by phagocytic kupffer
cells
• Middle of the lobule contains central vein
central vein connects with branches of
hepatic vein and hepatic artery via
sinusoids
• Bile is produced by the hepatocytes and
secreted in to channels called bile
canaliculi, located within each hepatic
plate
Bile canaliculi
Bile duct
Hepatic ducts
( carry bile away from the liver )
Hepatic Portal System
• The products of digestion absorbed in to
the blood capillaries in the intestine do not
directly enters to the general circulation
• These capillaries drain in to the hepatic
portal vein
• It carries this blood in to the capillaries in
the liver
• Then enters to the general circulation
through the hepatic vein that drains the
blood from the liver
• Hepatic artery gives the oxygenated blood
to the liver
Enterohepatic circulation
• In addition to the bile a wide variety of
compounds secreted by the liver in to the bile
ducts
• These products enter to the intestine
• Some are excreted with the feces
• Some are again enter to the blood via the
intestinal absorption
• Via the intestinal capillaries they enter to the
hepatic portal blood
• This recirculation of compounds call
enterohepatic circulation
Functions of the Liver
• Bile production
– Salts emulsify fats, contain pigments as
bilirubin
• Storage
– Glycogen, fat, vitamins, copper and iron
• Nutrient transport
• Detoxification
– Hepatocytes excrete the unwanted
compounds
– Chemical alteration of compounds
– phagocytosis
• Phagocytosis
– Kupffer cells phagocytize dying red and
white blood cells, some bacteria
• Synthesis
– Albumins, fibrinogen, globulins, heparin,
clotting factors
Gallbladder
• Sack like organ attached to the inferior
surface of the liver
• Bile is stored and concentrated
• Stimulated by cholecystokinin and vegal
stimulation in the arrival of chyme to the
intestine
Cystic
• Liver
Bile duct
Hepatic duct
duct
Gall Bladder
Gall
Bladder
Cystic
Duct
Common
Bile Duct
Duodenum
• When
the small intestine is empty of food, the
sphincter of Oddi at the end of common bile duct
closes and bile is forced up to the cystic duct and
then to the gall bladder for storage.
Bile
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Bile acid
Phospholipids
Cholesterol
Bilirubin
Waste products
Electrolytes
Mucin
Pancreas
• Anatomy
– Endocrine
• Pancreatic islets produce insulin and
glucagon
– Exocrine
• Acini produce digestive enzymes
– Regions: Head, body, tail
• Secretions
– Pancreatic juice (exocrine)
• Trypsin – digest protein
• Chymotrypsin - digest protein
• Pancreatic amylase - digest carbohydrates
• Pancreatic lipases – digest lipids
• Enzymes that reduce DNA and ribonucleic acid
• Carboxypeptidase - digest protein
• Bicarbonate ions
Pancreatic juice secretion stimulated by
secretin and cholecystokinin
• Acidic chyme rapidly neutralized by the
alkaline pancreatic juice in the small
intestine
• Vomiting
• Diarrhea
Alkalosis
Acidosis