GIT 2 Flashcards
Immune functions of the Gut
Protect against microbial pathogens
Permit immunologic tolerance to both the potentially immunologic dietary substances and normal bacterial flora
Non-immunologic defenses
Gastric acid secretion
Intestinal mucin
Peristalsis
Epithelial cell permeability barrier
Roles of GI Tract
Digestion and absorption of dietary calories and nutrients
Maintenance of overall fluid and electrolyte balance
Excretion of waste materials
Immune functions
Non immunologic defenses
Secreted by I cells in duodenum and jejunum
Targets pancreas and gallbladder
Inc enzyme secretion
Inc contraction
Cholecystokinin
Secreted by K cells in duodenum and jejunum
Targets pancreas
Exocrine: dec fluid absorption
Endocrine: inc insulin release
Gastric-Inhibitory Peptide
Secreted by G cells, antrum of stomach
Targets parietal cells in body of stomach
Inc H secretion
Gastrin
Secreted by vagal nerve endings
Targets G cells in antrum of stomach
Inc gastrin release
Gastrin-Releasing Peptide
Secreted by alpha cells of pancreatic islets of Langerhans
Targets liver
Inc glycogenolysis
Glucagon
Secretes endocrine cells in upper GI tract
Targets esophgeal sphincter, stomach, duodenum
Inc smooth muscle contraction
Motilin
Secreted by endocrine cells, wide-spread in GI tract
Targets intestinal smooth muscle
Vasoactive stimulation of histamine release
Neurotensin
Secreted by endocrine cells in ileum and colon
Targets stomach and pancreas
Dec vagally mediated acid secretion
Peptide YY
Secreted by S cells in small intestine
Targets pancreas and stomach
Inc HCO3 and fluid secretion by pancreatic ducts
Dec gastric acid secretion
Secretin
Secreted by D cells of stomach and duodenum
D cells of pancreatic islets
Targets stomach, intestines, pancreas
Dec gastrin release
Inc fluid absorption/secretion
Inc smooth muscle contraction
Somatostatin
Secreted by enteric neurons
Targets enteric neurons and liver
Neurotransmitter
Substance P
Targets small intestines
Pancreas
Dec smooth-muscle relaxation
Vasoactive intestinal peptide
Innervation of GI tract:
Enteric nervous system
Parasympathetic nervous system
Sympathetic nervous system
Primary neural control of GI function
Enteric nervous system
Submucosal plexus
Myenteric plexus
Between muscle layers of proximal esophagus to rectum
Myenteric Auerbach’s Plexuses
Motor effect
Inc tonic contraction
Inc intensity of rhythmic contraction
Inc velocity of excitatory waves
Myenteric Auerbach’s Plexuses
Submucosa of intestines only
Regulates the secretory activities of glandular, endocrine, and epithelial cell
Meissner’s Submucosal Plexuses
Parasympathetic NS of GIT
Vagus N
Pelvic N
Splenic flexure to anus
Cholinergic (Ach)
Terminates in the enteric plexuses
Pelvic Nerves
Stimulated motor and secretory activities
Parasympathetic Nervous System
Inhibits motor activity of muscularis externa
Induces contraction of muscularis mucosae
Induces contraction of some sphincters
Inhibits secretory functions of the GI tract
Vasoconstriction of some GI blood vessels
Sympathetic NS
Functions of GI Motility
Segmental contraction
Propulsive contraction
Allows the stomach and large intestines to act as reservoirs
Segmental contractions
Non propulsive
Mixing and churning - digestion and absorption of nutrients
Propagated movement of food in a caudal direction
Results in elimination of nonabsorbed material
Propulsive contraction
Electrical and mechanical properties of GIT
Rhythmic contraction
Tonic contraction
RMP of GI Smooth Muscle
-40 to -80 mV
Slow waves are produced by the
interstitial cells of Cajal
AP of GI smooth muscle
More prolonged than skeletal
Precise
Modulation of intestinal smooth muscle contraction is dependent on
L type Ca2+
Predominant excitatory neurotransmitter
Acetylcholine
Inhibitory neurotransmitter
VIP
NO
Specialized circular muscles that separate segments of the GI tract
Function as barriers maintaining positive resting pressure that serve to separate two adjacent organs
GI sphincters
Stimuli proximal to sphincter
Sphincteric relaxation
Stimuli distal to sphincter
Sphincter contraction
Esophagus
and Anus histology
Stratified squamous non keratinized
Stomach
Small and large intestines
Rectum
Histology
Simple columnar
Anus histology
Stratified squamous non keratinized
Skin histology
Straified squamous keratinized
Absorption GIT Stomach SI LI
Simple columnar
Most common cancer of esophagus
Squamous Cel Ca
Metaplasia
SSQ
Simple columnar
Adenocarcinoma
Barret’s esophagus
Simple columnar + Glands
Adenocarcinoma
Vagal nerve receptors
Cholinergic receptor
Located between the circular and longitudinal smooth muscle layers
Responsible for motility
Myenteric Auerbach’s Plexus
Cells in the gastric epithelium secreting histamin
Enterochromaffin like cells
Released from enteric neurons, mucosal mast cells and specialized EECs called enterochromaffin cells
Serotonin
5 hydroxytryptamine
AA precursor of serotonin
Tryptophan
Precursor of tryptophan
Niacin
Triad of pellagra
Diarrhea
Dermatitis
Dementia
Death
Where is 5HT localized?
Enterochromaffin cells 90% Platelets: thrombosis CNS 10% Dorsal raphe Ventral raphe Raphe nuclei
Allows GI smooth muscles to perform slow wave contractions and sustained muscle contraction
Intersitital cells of Cajal
Most common location of GIST
Stomach
DOC for GIST
Imatinib
Tumors arising from interstitial cells of Cajal
GIST
Tumor marker in GIST
CD 117 c KIT
Main feature of cephalic phase is
activation of the GI tract in readiness for the meal
Cognitive and include anticipation or thinking about the consumption of food, olfactory input, visual input (seeing or smelling appetizing food when hungry) and auditory input
Sight, smell, thought of food Inc parasympathetic outflow Inc salivary secretion Inc gastric acid secretion Inc galbladder contraction
Relaxation of sphincter of oddi
All these responses enhance ability of GI tract to receive and digest incoming food
Cephalic phase
The only difference of oral phase with cephalic phase is that
Food is in contact with the surface of the GI tract
Subdivides and mixes food with salivary amylase and lingual lipase and with the glycoprotein mucin which lubricates food for chewing and swallowing (degluttition)
Chewing
Cleaves internal alpha 1,4 glycosidic linkage
Activity in stomach is limited by
Alpha salivary amylase
Acid pH
Voluntary behavior and a reflex
To lubricate food
To initiate digestion of starch
To mechanically chop food into smaller pieces
Mastication (chewing)
Bolus of food in mouth -> mastication inhibited -> stretch reflex of jaw muscles -> rebound contraction
Chewing reflex
A rigidly ordered sequence of events that propel food from the mouth to the stomach
Initially voluntary, later, a reflex
Swallowing center:
Medulla and lower pons (CN V, IX, X, XII)
Degluttition (swallowing)
Swallowing center:
Medulla Lower pons (CN V, IX, X, XII)
Elevates the jaw
Closing the mouth
Medial pterygoid
Lowers the jaw
Open Mouth
Lateral pterygoid
Chewing problem
Stroke - swallowing (medulla) ALS Parkinson’s disease Myesthenia Gravia ENT trauma Tetanus
Movement of bolus through pharynx and UES
Pharynx contracts
UES opens
Airway closed
Larynx elevated
Bolus enters esophagus
Bolus in mouth
Tongue thrust up and back
Nasopharynx is closed
Oral phase
Voluntary
Pharyngeal phase
Esophageal phase
Reflex
Has primary peristalsis and secondary peristalsis
Esophageal reflex
18-26 cm hollow muscular tube
Lines with stratified squamous epithelium
No serosa
Esophagus
Upper 1/3 of esophagus
Striated muscle
Voluntary
Middle 1/3 of esophagus
Striated
Smooth
muscle
Lower 1/3 of esophagus
Smooth muscle
Conduit that moves food from the pharynx to the stomach
Esophagus
Prevents entry of air
UES
Prevents the entry of gastric contents
Resting pressure of 20 mmHg
LES
Reduced LES resting pressure
Can lead to esphagitis
GERD
Defect in LES relaxation
Achalasia
A j shaped dilation of the GI tract
Stomach
Stomach motor fxns:
Storage
Formation of chyme
Emptying gastric contents into duodenum
Storage in the stomach happens in the
proximal part
Expulsion of gastric and duodenal contents from the GI tract through the mouth
Vomiting
Vomiting center
Medulla
Vomiting is preceded by
Retching
Small intestine functions
To mix chyme with digestive secretions
To bring chyme into contact with the absorptive surface of the microvilli
To propel chyme toward the colon
Types of SI movement
Segmentation
Peristalsis
Most frequent SI movement
Closely spaced contractions of the circular muscle layer
Effectively mixes chyme with digestive secretions
Segmentation
Progressive contraction of successive secretions of circular smooth muscle
Orthograde direction
Involves only a short length of SI
Peristalsis
The respiratory center in the medulla is inhibited during this phase of swallowing
Pharyngeal
Produces mainly serous secretions
Largest
Parotid gland
Secretes mainly mucus
Sublingual
Produces a mixed secretion
Submandibular gland
Salivary gland that profuce entirely serous ptyalin rich secretion
Parotid
Most common benign salivary gland tumor
Pleomorphic adenoma
Most common malignant salivary gland tumor
Mucoepidermoid tumor
Bursts of intense electrical and contractile activity separated by long quiescent periods
Occurs in the fasting state
From the stomach to the terminal ileum
Repeats every 75-90 mins
Stronger than contractions in the fed state
Housekeeper of small intestine
Migrating myoelectric complex
Cystadenoma lymphomatosum
Limited to parotid gland
Warthin’s tumor
Composition of saliva
Low osmolarity High K Concentration and organic constituents including enzymes (amylase, lipase) Mucin Growth factors
A tubular structure 1.5m in length
The longitudinal muscle layer is concentrated into 3 bands called
Large intestine
Taenia coli
Absorb of fluids and electrolytes and converts the liquid content of ileocecal materials to solid and semi-solid food
Absorb the short chain-fatty acids formed by the catabolism of dietary carbohydrates that are not absorbed in the SI
Serve as reservoir
Large intestine
Salivary secretion is always
Hypotonic
Na, K, HCO3, Ca, Mg, and Cl
Dry mouth (xerostomia) Dry eyes (xeropthalmia) Causes by impaired salivary secretion Congenital or autoimmune process Keratoconjunctivitis sicca
Sjogren’s
Types of movement in large intestine
Segmentation/Haustration
Mass movement
Haustra
Cecum and proximal part of colon
Circular muscle contractions churn the luminal contents and move them in an orad direction
Facilitates absorption of salts and water by the mucosal epithelium
Segmentation/Haustration
1-3x a day
Propulsive movement
Sweeps feces toward the rectum
Mass movement
Length of esophagus in UGI Endoscopy
40cm
Start of esophagus
C6
Cricoid cartilage
Where does esophagus end?
Esophageal opening of diaphragm
T10
Distention of one part of the colon causes a relaxation in other parts of the colon
Colonocolonic reflex
An increase in the motility of proximal and distal colon and the frequency of mass movements after a meal
Gastrocolic reflex
Most common location of cancer in esophagus
Middle 1/3
SCC
If in the lower 1/3 of esophagus
Adenocarcinoma associated with Barett’s esophagus
Presence of acid in duodenum cause release of
Secretin
Other name of CCK
Pancreozymin
Effect of CCK on gallbladder
and sphincter of Oddi
GB contraction
Sphincter of Oddi relaxation
Storage and secretion of GB
Capacity of GB
500 ml
30 ml
Produced by duodenum S cells
Secretion of HCO3
Secretin
Promotes secretion of pancreatic juice
Secretin
K cells of small intestine produce
Glucoinsulinotropic peptide
GIP
Targets beta cells of pancreas
Stimulates insulin secretion
Glucoinsulinotropic Peptide
Regulatory petide released from EEC cells in the gut wall in response to presence of luminal carbohydrate and lipids
Glucagon like peptide 1
Drug: agonist exenatide type 2 DM