GI Physiology - Giovanni Mann Flashcards
Learn about how structure and function relate in GI Systems
4 Key points about the serosa
1) it is the outermost layer of GIT, and is connective tissue 2) covered by visceral peritonium 3) made of loose connective tissue and squamous cells 4) contains blood vessels, lymph and nerves
4 key points about the submucosal layer
1) It is the site of larger blood vessels 2) brings oxygen and nutrients to the cells, removes waste and digestion products 3) Lympatic system helps drain the unwanted substances and UPtake fats 4)Nerve fibres from autonomic NS control reflexes here (e.g smooth muscle contraction)
5 key points about the GIT mucosa
1) Innermost layer of GI Tract 2) Products of digestion pass into capillaries here 3) Thin double layer of smooth muscle present for local movement of products(muscularis mucosa) 4) mucosal layer highly folded to provide large surface area for digestion and absorption 5) goblet cells scattered throughout mucosa
Composition of bile
bile salts, cholesterol, triglycerides, phospholipds, electrolytes
difference between epithelial cells in stomach and parietal cells
epithelial cells line the mucosa, releasing bicarbonates. Parietal cells are in the oxyntic glands, releasing HCl.
ECF can be up regulated to release more histamine when stimulated by
gastrin and acetylcholine stimulus
functional adaptations of the stomach epithelium during HCl secretion
1 - Pepsinogen release to initiate digestion of protein 2 - Surface epithelial cells secrete protective mucus to save us from acid 3 - “intrinsic factor” - a glycoprotein secreted from gastric pits, combines with Vit B12 to aid absorption in the ileum.
Gastric emptying is regulated by
Neural enterogastric reflexes
Goblet Cells. Where are they located, and what is their role?
Scattered throughout the mucosa. Secretes mucus to lubricate and protect the lining of the gut from the acid
histamine from ECF acts on..
H1 receptors on parietal cells, increasing intracellular cAMP. H2 receptor activation on parietal cells will result in expression of the proton pump
how are interstitial cells of cajal connected. What does this allow?
via gap junctions. Allows electrical impulse to be transmitted efficiently + quickly across the whole muscularis
How are proteins absorbed?
Na+ Cotransport
How are vitamins absorbed?
if fat soluble - incorporated into the micelles, moving across epithelium by passive diffusion. If water soluble - abosorbed by passive diffusion or via specific active transport. Exception is B12. Endocytosis through targeting specific receptor sites.
how do CCK and Secretin work together in pancreatic juice stimulation
CCK induces secretion of enzyme rich pancreatic juice, Secretin causes copious secretion of HCO3-
How does bile salts work?
repel lipids preventing them from forming fat globules. smaller globules are formed, but there is an increased surface area for lipase to attack
How does glucose, fructose and galactose enter the body? and where
facilitated diffusion at the level of the microvilli
how does lipids leave the micelle
by collision or incorporation with the lipid barrier. or by non-ionic diffusion.
In the stomach, how are bicarbonates formed?
CO2 and H2O in parietal cells form H2Co3 and then dissociate into bicarbonate ions which are then secreted into the musosal lining of stomach, via the HCO3-/Cl- antiport, to the blood
Name 3 proteolytic enzymes found in pancreatic juice
trypsinogen, chymotrypsinogen, procarboxypeptidase
Name a few enzymes that break down sugars
lactase, glucoamylase, dextrinase
name a principal enzyme that breaks down carbohydrates
a-Amylase
name the two muscle layers necessary for peristalsis. What are they collectively known as?
Circular + Longitudinal smooth muscle. Collectively known as Muscularis Externa
Neurotransmitter(s) responsible for stimulating secretion of hormones?
VIP & Ach. Both are neurotransmitters in myenteric plexus
Oxyntic glands are the sites of:
ECL cells/ Parietal Cells/ Chief Cells
Pancreatic juice contains
bicaronates (to neutralise acidic chyme entering duodenum) Proteolytic enzymes (e.g deoxyribonuclease) Amylase Lipase
Role of Submucosal plexus?
regulates endocrine and exocrine function
Role of the Myenteric plexus?
regulates smooth muscle contraction
State differences between endocrine and exocrine glands
Exocrine: Has Ducts, Secretes Enzymes, controls short term activity, secretion is poured directly @site of action Endocrine: Ductless glands, secretion directly into blood. Secretes Hormones, ad controls long term activity of target organs
State the 5 main layers of the GIT
mucosa, muscularis mucosa, submucosa, muscularis externa, serosa
state the term given to bile conservation
enterohepatic circulation
State the three divisions of the stomach
Cardiac glands, Pyloric glands, Fundus (Oxyntic) glands
Summarise carbs digestion and absorption
begins with amylase and glycoproteins in saliva -> pancreatic enzymes in duodenum break any remaining undigested starch-> brush border enzymes liberate disaccharides and oligosaccharides-> absorbed either by facilitated diffusion or by Na+ co-transport
Summarise protein digestion & absorption
pepsin in stomach cleaves bonds involving tyrosine + phenylalanine -> large polylpeptides broken down by pancreatic enzymes -> Brush border enzymes liberate final amino acid products. -> absorbed by co-transport
The Enteric NS contains two interconnected plexuses
Myenteric Submucosal
The pacemaker sets the…
rate of contraction, but does not initiate contractions or regulate their force.
Unchanging pressure in a filling stomach is due to
‘reflex-mediated’ relaxation of the stomach muscle plasticity of the visceral smooth muscle
What are Chylomicrons and what are they made from?
Phospholipids, Cholesterol, and Protein (coated on top). The they’re lipoprotein droplets made at SER
What are the key inhibitiors for acid secretion?
Prostaglandins and Somatostatin
what are zymogen granules
granules that contain digestive enzymes made by acinar cells. They adapt with diet
what causes release of bile and what enhances its flow?
presence of fatty rich chyme. Secretin enhances flow of bile from gallbladder.
What cells produce salivary fluid?
Acinar cells - into a duct
What chemical messengers up-regulate acid secretion?
Gastrin, histamine and acetylcholine
what CONTROLS salivary secretion
primarily, the parasympathetic NS
what do cardiac glands do and where found
secrete mucus. found near oesophagus.
what does Ach stimulate on the parietal cell?
muscarinc M3 receptors
What does ECF stand for and what does it contain? What does it lie close to?
Enterichromaffin-like cells contains histamine and lies close to the parietal cells
what does gastrin stimulate?
acid release from PARIETAL cells. release of pepsinogen increase stomach motility
what does the salivary glands do when food enters your mouth? What does saliva even do?
salivary glands secrete electrolytes and proteins (amylase) as a fluid into the oral cavity. Saliva lubricates the food for swallowing, and glycoproteins aid in starch digestion. + CDMC (cleanses, dissolves, mastens food into bolus, contains enzymes)
What glands secrete glycoproteins and what are gylcoproteins for?
Submandibular, Sublingual, Buccal glands aid in starch digestion
What happens without bile?
lipids would be incompletely digested and floats on the surface of chyme. most lipids will pass into the faeces.
what happens, without micelles to absorb fat?
the lipids float above the chyme, inaccessible to the absorptive surfaces of epithelial cells.
what is a peptic ulcer
erosion of small patch of the lining of stomach (gastric ulcer) or duodenum (duodenal ulcer)
what is pepsin’s inactive form and why is it secreted in this inactive state?
Pepsinogen - to prevent self digestion of stomach where it works
What is the role of the Spinsters? What muscle are they made from
made from circular muscle. They help separate one section of the tract from another. Controls speed of contents
What neurotransmitter is responsible for inhibiting contraction?
VIP - Vasoactive Intestinal Peptide
What neurotransmitter is responsible for stimulating contraction?
Acetylcholine
what part of intestine does bile and pancreatic juice enter from
duodenum
what pH does pepsin function optimally at?
1.5-2.5
what pH does salivary amylase operate best at?
6.75-7
What releases Somatostatin (SST), and name location. what receptor does act on and where?
D cells at several locations within the stomach. Acts at SST receptor where it inhibits gastrin release from G Cells, Histamine release from ECL cells in inhibts directly on parietal cell output
what role for CCK have on pancreatic juice stimulation. and what does Vagal stimulation cause?
causes gall bladder to contact and hepatopancreatic sphincter to relax. Vagal stimulation causes weak contractions of gall bladder
What secretes pepsinogen
Chief cells in the oxyntic glands, NOT parietal cells
what sets the contractile rhythm of the stomach? location?
the interstitial waves of cajal in the longitudinal smooth muscle layer
What stimulates saliva
it is set off by taste, smell and touch receptors in mouth, or by chewing.
What’s the name given to the epithelial cells of the small intestine?
Enterocyte!
when there is no digestion, what guards bile release?
Heteropancreatic spincter.
where are lipids digested, and why?
small intestine, because the pancreas is the only significant source of lipase
where does the bicarbonate ions from pancreatic secretion come from?
the epithelial cells lining the pancreatic ducts
where is CCK Released from? What sites of action?
Released from intestinal mucosa. Stimulated by Fat and Amino acid present in chyme. acts at: Bladder (bile release) Pancreas (lipase) Stomach (slowdown)
where is secretin released? and what are its action sites?
released from intestinal mucosa. Enhances flow of bile. At the pancreas, secretin will stimulate release of pancreatic enzymes. At the stomach, it Inhibits pepsinogen release, decreases stomach motility.
where is the bile reabsorbed in SI
ileum!
Where is the Lymphatic system located in GIT? Name some roles
the submucosal layer: -drains excess + unwanted substances -responsible for uptaking fat
Where’s gastrin synthesised? what stimulates it’s release? what does it bind to?
by G cells in the gastric antrum. Stimulated by food (protein). binds at cholecystokinin and gastrin receptors. Its stimulates histamine synthesis by ECL cells.
