GI: Physiology of GIT Flashcards
Function of the GI tract
Injestion, secretion, mixing, digestion, absorption and excretion
Layers of the GI tract (out to in)
Mucosa (epithelium, NAV), submucosa (loose CT), muscularis (circular and longitudinal), serosa (peritoneum)
What are villi used for
Absorption
What are crypts used for
Secretion. ECF released into lumen, water follows. (Fluid derived from plasma)
What is involved in the coordination if GI tract?
Nervous system, local (physical stretch or chemical), hormone
Difference between enteric nervous system and ANS
- Enteric, short reflexes, communications in the gut.
- Enteric signals go up to CNS and become ANS. (long reflexes)
Stomach motility stimulation and inhibition
Stimulated by stomach distension and peptides
Inhibited by dudodenal lumen, high peptides, high pressure, high osmolarity, low pH and high fat
Process of stomach motility/ contractions
Meal-> acetylcholine + gastrin -> High threshold -> stomach contracts
Slow wave contractions (3-4mins)
- Cephalic phase (seeing food)
Release gastrin. Chief cells to pepsinogen and parietal cells to HCL.
Phases of gut secretions
Cephalic phase, gastric phase, intestinal phase
- Gastric phase (food in stomach)
Through stretch receptors. Gastrin release, peptides stimulate gastrin release.
Parietal cell secretions
Secretes HCl.
Stimulation: Vagus, Gastric, Histamine
Inhibition: Somatostatin + Low pH
Alkaline tide
HCO3- by pancreas into duodenum to neutralize stomach H+ from stomach.
What is the pancreatic mucus secretion used for
Protective layer against stomach acids
How are the sphincters of the of the GIT controlled?
Controlled by enteric NS/ stretch (except external anal sphincter) and regulated by stretch. Found between each organ.
Causes of vomiting (3)
Physiology, drugs and chemicals (through chemical trigger zone) and pathology
Stages of vomiting (6)
- Postural adaptation
- Saliva stimulated (protect against acidity)
- Respiratory (inspiration inhibited), glottis closed, larynx raised, increased SP
- Diaphragm + abdominal muscles contract
- High intragastric pressure, retching
- Lower oesophageal sphincter relaxes, gastric contents expelled.
- Intestinal phase (What is secreted?)
Parietal cell secretions and mucus secretions
What controls salivary secretion?
Complete neural control
What comprises enteric NS? (2 nerve plexuses)
- Myenteric plexus (sensory, found btw and regulates muscles)
- Submucosal plexus (regulates mucosal gland secretions)
Gastrin
Stimulation of HCl production and supports growth of mucosa. (distal stomach)
Secretin
Stimulates production of bicarbonate by pancreas and Brunner’s glands. (duodenum)
Cholecystokinin (CCK)
Stimulates enzyme production in pancreas and gall bladder by contraction. (duodenum)
Gastric inhibitory polypeptide (GIP)
Reduces HCl production and stomach emptying. Stimulates insulin release. (Proximal small bowel)
Somatostatin
Reduces acid secretion, gastric motility and stomach emptying. (intestines and pancreas)
Leptin
Stimulates satiety
Ghrelin
Stimulates feeding centre
Peptide YY (PYY)
Stimulates satiety, inhibits eating.
Small intestine function
Secretes fluid, mucus and HCO3- (from Brunner’s glands)
S.intestine motility (2)
- Segmentation: Alternating contractions, squeezing back and forth to mix
- Peristalsis: Initiated at a point, contraction of circular muscles on oral side and relaxing on aboral side.
Control of s.intestine motility
- Local distension, enteric peristalsis
- Extrinsic: parasymp increase, sympathetic decreases
Standing- gradient osmosis (how water is absorbed)
- Dependent on Na+
- Pump Na/Cl into lateral space between cells. Water follows
- Pressure build and pushed out into tissue
L. intestine function
- Absorbs remaining water and Na, vitamins produced by commensal bacteria, eliminates metabolic waste, etc.
What happens in the rumen? (Carb and proteins) (2)
- Anaerobic bacteria fermenting carbs into short chain fatty acids
- Microbes use ammonia (by-product) for protein. Flushed through, protein from dead bacteria
Reticuloruminal motility
2nd rumenal wave
- Antiperistalsis and eructation voided through nares
Primary ruminal contractions
- Rumen fill = strength of mixing
- Peristaltic to reticulum
Secondary ruminal contractions
- Eructation of gas
- Anti-peristaltic and follows half of primary ruminal contractions
What do the Short chain fatty acids become? (Ruminant digestion)
Acetate > Proprionate > Butyrate (and ketone bodies)
Acetate, proprionate or butyrate; which one directly produces glucose
Propionate
Lactation ketosis
Ketone bodies replace glucose due to high energy demand and low oxaloacetates in Krebbs.
- Acetyl-CoAs diverted to produce ketone bodies
- Very acidic conditions
Grain overload
- High fermentation rate, acidic rumen, high lactate, lactophiles thrive
- High rumen osmolarity, low BP and dehydration
- Renal and respiratory comprimise + metabolic acidosis.
Uses of saliva (ruminant)
- pH buffer
- plant wetting agent
- anti-frothing proteins (to prevent bloat)
Salivary glands (4)
Parotid, mandibular, zygomatic and sublingual
Control of saliva
Parotid and sublingual nerve + food :)
Chemical compound that provides energy when there isn’t enough glucose (result of ketosis)
B-hydroxybutyrate
