GIT 2 Flashcards by Denisse Tiangco

Immune functions of the Gut

Protect against microbial pathogens

Permit immunologic tolerance to both the potentially immunologic dietary substances and normal bacterial flora

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Non-immunologic defenses

Gastric acid secretion
Intestinal mucin
Peristalsis
Epithelial cell permeability barrier

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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

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Secreted by I cells in duodenum and jejunum

Targets pancreas and gallbladder

Inc enzyme secretion
Inc contraction

Cholecystokinin

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Secreted by K cells in duodenum and jejunum

Targets pancreas

Exocrine: dec fluid absorption
Endocrine: inc insulin release

Gastric-Inhibitory Peptide

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Secreted by G cells, antrum of stomach

Targets parietal cells in body of stomach

Inc H secretion

Gastrin

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Secreted by vagal nerve endings

Targets G cells in antrum of stomach

Inc gastrin release

Gastrin-Releasing Peptide

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Secreted by alpha cells of pancreatic islets of Langerhans

Targets liver

Inc glycogenolysis

Glucagon

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Secretes endocrine cells in upper GI tract

Targets esophgeal sphincter, stomach, duodenum

Inc smooth muscle contraction

Motilin

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Secreted by endocrine cells, wide-spread in GI tract

Targets intestinal smooth muscle

Vasoactive stimulation of histamine release

Neurotensin

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Secreted by endocrine cells in ileum and colon

Targets stomach and pancreas

Dec vagally mediated acid secretion

Peptide YY

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Secreted by S cells in small intestine

Targets pancreas and stomach

Inc HCO3 and fluid secretion by pancreatic ducts
Dec gastric acid secretion

Secretin

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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

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Secreted by enteric neurons

Targets enteric neurons and liver

Neurotransmitter

Substance P

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Targets small intestines
Pancreas

Dec smooth-muscle relaxation

Vasoactive intestinal peptide

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Innervation of GI tract:

Enteric nervous system
Parasympathetic nervous system
Sympathetic nervous system

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Primary neural control of GI function

Enteric nervous system

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Submucosal plexus

Myenteric plexus

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Between muscle layers of proximal esophagus to rectum

Myenteric Auerbach’s Plexuses

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Motor effect

Inc tonic contraction
Inc intensity of rhythmic contraction
Inc velocity of excitatory waves

Myenteric Auerbach’s Plexuses

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Submucosa of intestines only

Regulates the secretory activities of glandular, endocrine, and epithelial cell

Meissner’s Submucosal Plexuses

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Parasympathetic NS of GIT

Vagus N

Pelvic N

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Splenic flexure to anus
Cholinergic (Ach)
Terminates in the enteric plexuses

Pelvic Nerves

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Stimulated motor and secretory activities

Parasympathetic Nervous System

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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