kumar Clarke Flashcards
what does the pharynx consist of
nasal, oral and laryngeal sections
what is the function of the oesophagus
Muscular tube that connects the pharynx to the stomach just below the diaphragm.
what cells line the oesophagus
stratified squamous epithelium which extends to the squamocolumnar junction where the oesophagus joins the stomach, recognised endoscopically by zig zag line
what reflex mediates swallowing
complex reflex involving a swallowing centre in the dorsal motor nucleus of the vagus in the brainstem
what activates the process of swallowing
once the complex reflex is activated the swallowing centre neurones send pre-programmed discharges of inhibition followed by excitation to the motor nuclei of the cranial nerves. This results in initial relaxation , followed by distill progressive activation of neurones to the oesophageal smooth muscle and LOS
what is primary peristalsis
Primary peristalsis is the peristaltic wave triggered by the swallowing center.
what is secondary peristalsis
Secondary peristalsis refers to peristalsis activated by esophageal distention. This can occur physiologically by food left behind after the primary peristaltic wave has passed, or by refluxed contents from the stomach
what nerves supply the smooth muscle to the thoracic oesophagus and LOS
vagal autonomic motor nerves in the myenteric plexus
what is the function of the stomach
It serves as a reservoir where food can be retained and broken up before being actively expelled into the proximal small intestine
what are the 3 layers of smooth muscle on the stomach
outer longitudinal, inner circular and innermost oblique
what are the 2 sphincters at the stomach
gastro-oesophageal sphincter and the pyloric sphincter
what cells are in the upper 2/3 of the stomach
parietal cells that secrete HCL and chief cells which secrete pepsinogen
what does the antral mucosa secrete
it secretes bicarbonate and contains mucous secreting cells and G cells, which secrete gastrin, stimulating acid production
what is the function of the mucosal barrier
Protects the gastric epithelium from damage by acid and for example alcohol, aspirin, NSAIDs
what factors control acid secretion
- Histamine stimulates Gs protein via the H2 receptors and acts via cyclic adenosine monophosphate (cAMP)
- Prostaglandin E2 (PGE2) activates the Gi protein and inhibits acid secretion.
- Acetylcholine (ACh) acts via the vagus M3 receptors. ACh also acts via the enterochromaffun cell
- Gastrin acts via the cholecystokinin B (CCKBB)- gastrin receptor, increasing the intracellular free calcium, and also via ECL cell stimulating histamine
where does the small intestine extend from and to
from the duodenum to the ileocaecal valve
what are the 3 sections of the small intestine
duodenum, jejunum and ilium
what creates a large surface area in the small intestines
circumferential mucosal folds that bear multiple finger like projections called villi. On the villi the surface area is increased due to microvilli on the luminal side if the epithelial cells (enterocytes)
what are the spaces between the bases of the villi called
Crypts of Leiberkuhn
where are enterocytes formed
They are formed at the bases of the crypts of leiberkhun and migrate towards the tops of the villi where they are shed
what supply blood to most of the small intestine
via branches of the superior mesenteric artery
what does the enteric nervous system control
the functioning of the bowel: it is an independent system that coordinates absorption, secretion, blood flow and motility.
how does the enteric nervous system communicate with the central nervous system
via autonomic afferent and efferent pathways but can operate autonomously
what are the 2 main ganglionate plexuses of the enteric nervous system
The myenteric plexus and the submucosal plexus
what are the interstitial cells of Cajal
govern rhythmic contractions in the small intestine
during fasting what sequence of motor events occurs
A distill migrating sequence of motor events, termed the migrating motor complex (MMC) occurs in a cyclical fashion
what is the migrating motor complex in the gut motility
Occurs during fasting and the MMC consists of:
- A period of motor quiescence (phase 1)
- A period of irregular contractile activity (phase 2)
- A short (5-10 min) burst of regular phasic contractions (phase 3)
each MMC lasts for around 30 minutes. In the duodenum, phase 3 is associated with increased production of gastric, pancreatic and biliary secretions. The role of MMC is unclear but phase 3 contractions propel secretions, residual foods and desquamitised cells towards the colon
after a meal what happens to the migrating motor complex
It is disrupted and replaced by irregular contractions. Can last 2-5 hours after feeding. The irregular contractions of the fed pattern gave a mixing function, moving intraluminal contents to and fro and aiding the digestive process
what do gut hormones do
Regulate and integrate the functions of the small bowel and other metabolic activities, including appetite. Their actions are complex and interactive, both with each other and the CNS
what occurs in the small bowel
digestion and absorption of nutrients and ions takes place, as does the regulation of fluid absorption and secretion
what is the role of the gut regulatory protein gastrin
Stimulates acid secretion. Trophic to mucus. This is localised at G cells in gastric antrum and duodenum
what is the role if the gut regulatory protein cholecystokinin
Causes gall bladder contraction and sphincter of oddi relaxation. Trophic effects on duodenum and pancreas. Pancreatic secretion.
what is the role if the gut regulatory protein secretin
stimulates pancreatic bicarbonate secretion in the S cells of the duodenum and jejunum
what is the role if the gut regulatory protein glucagon
in the alpha cells of the pancreas it opposes insulin in blood glucose control
what is the role of the gut regulatory protein vasoactive interstitial polypeptide (VIP)
localised at the enteric nerves it causes interstitial secretion of water and electrolytes. Neurotransmitter. Sphlanchnic vasodilation, stimulates insulin release
what is the role if the gut regulatory protein Glucose dose dependent insulinotropic peptide (GIP)
Localised in the duodenum (K cells), gastric antrum and ileum. Release by intraduodenal glucose causes greater insulin release by islets than i.v glucose
what is the role if the gut regulatory protein glucagon-like peptide-1
localised in the ilium and colon (L cells) . Incretin. Stimulates insulin synthesis. Trophic to islet cells. Inhibits glucagon secretion and gastric emptying. Stimulates growth of enterocytes
what is the role if the gut regulatory protein Glincentin
Localised in L and A cells. It stimulates insulin secretion and gut growth and inhibits gastric secretion
what is the role if the gut regulatory protein growth hormone realising factor
Localised in the small intestine and its main actions are unclear
what is the role if the gut regulatory protein pancreatic polypeptide
localised in the pancreas and inhibits pancreatic and biliary secretion
what is the role if the gut regulatory protein peptide YY
Localised in the ileum and colon (L cells) and inhibits pancreatic exocrine secretion. Slows gastric and small bowel transit. Reduces food intake and appetite
what is the role if the gut regulatory protein neuropeptide Y
Localised in the enteric nerves and stimulates feeding. Regulates interstitial blood flow
what is the role if the gut regulatory protein motilin
Localised in the whole gut and increases gastric emptying and small bowel contraction
what is the role if the gut regulatory protein Ghrelin
Localised in the stomach and stimulates appetite and increases gastric emptying
what is the role if the gut regulatory protein Obestatin
Localised in the stomach and the small intestine andnopposed Ghrelin
what is the role if the gut regulatory protein Oxyntomodulin
Localised in the colon and inhibits appetite
what is the role if the gut regulatory protein gastrin realesing peptide (bombesin)
Localised in the whole gut and pancreas and stimulates pancreatic exocrine secretion and gastric acid secretion
what is the role if the gut regulatory protein Somatostatin
Localised in the stomach and pancreas (D cells)a dn the small and large intestine. Inhibits secretion and action of most hormones
what is the role if the gut regulatory protein Substance P
Localised in enteric nerves and enhances the gastric and acid secretion, smooth muscle contraction
what is the role if the gut regulatory protein Neurotensin
Localised in the ileum and affects gut motility and increases jejunal and ill fluid secretion
what is the role if the gut regulatory protein Insulin
Localised in pancreatic beta cells and increases glucose utilisation
what is the role if the gut regulatory protein chromogranins
Localised in the neuroendocrine cells. Precursor for other regulatory peptides that inhibit neuroendocrine secretion
how are carbohydrates broken down and absorbed
Carbohydrates consist of mainly starch that contains numerous glucose units, so it has to be digested into smaller oligo-, di-, monosaccharides which may then be absorbed. Polysaccharide absorption begins in the mouth and is catalysed by salivary amylase, the the majority occurs under the action of pancreatic enzymes in the upper intestine. The products of this (maltose, maltotriose, sucrose and lactose) are further hydrolysed to from glucose, galactose and fructose that then can be transported across enterocytes to the blood
how is dietary protein absorbed in the small intestine
Digested by pancreatic proteolytic enzymes to amino acids and peptides prior to absorption. Protein in the duodenal lumen stimulates the enzymatic concersion of trypsinogen to trypsin and this in tern activates proenzymes, chymotrypsin and elastase. The enzymes break down protein to oligopeptides
how is dietary fat absorbed in the small intestine
fat is emulsified by mechanical action in the stomach. Bile acids and phospholipid enter the duodenum following gall bladder contraction which also act to promote the hydrolysis of of triglycerides in the duodenum by pancreatic lipase to yield fatty acids and monoglycerides. Micelles are formed and trapped in the centre of the micelles are absorbed fatty acids and cholesterol. The lips content of micelles are absorbed. Inside the cell the monoglycerides and fatty acids are re-esterfied to triglycerides
what is the “ileal break”
the delay allows more time for absorption of lipids in the small intestine
how is water and electrolytes absorbed in the small intestine
Absorbed paracellularly (between the enterocytes) down the electrochemical and osmotic gradient. Additional water and electrolytes are absorbed in the ileum and colon, where active sodium transport is not coupled with solute absorption
what are physical defence mechanisms that occurs to prevent colonisation and invasion by pathogens in the small bowel
- The mucus layer
- Continuous shedding of surface epithelial cells
- The physical movement of the luminal contents
- Colonization resistance - the ability of the indigenous microbiota to outcompete pathogens for a survival niche in the gut
what is the innate chemical defence mechanisms that occurs to prevent colonisation and invasion by pathogens in the small bowel
- Enzymes such as lysozyme and phospholipase A2 recreated by Paneth cells at the base of the crypts, help to ensure an infection free environment in the gut, even in the presence of commensal bacteria
- Antimicrobial peptides are recreated from enterocytes and Paneth cells in response to pathogenic bacteria. These include defensives with a potent activity against a broad range of pathogens
- Trefoil peptides have a three loop structure making them highly resistant to digestion. Their actions include stabilisation of mucus, promotion of cell migration to injured areas and promotion of repair
what is the innate immunological defence in response to antigens and pathogens in the small bowel
- Humoral defence - IgA is the principal mucosal antibody and mediates mucosal immunity by agglutinating and neutralising pathogens in the lumen
- B cell sensitisation - Antigens form the lumen of the bowel are transported by M cells and dendritic cells in follicle-associated epithelium. Activated B cells then produce IgA locally and are programmed to home back Ito the lamina propria. They undergo terminal differentiation into plasma cells.
- Cellular defence - T lymphocytes also provide host defence and initiate, activate and regulate adaptive immune responses.
where doe stem large intestine start
at the caecum, on the posterior medial wall of which is the appendix
what are the 4 parts of the colon
ascending, transverse, descending and sigmoid parts, which join to the rectum at the rectosigmoid junction
what supplies the blood supply to the colon
the superior and inferior mesenteric vessels
what innervates the colon
mainly by the enteric nervous system with input from the parasympathetic and sympathetic pathways. Spinal afferent neurones from the dorsal root ganglia innervate the entire colon
what are the main roles of the colon
The absorption of water and electrolytes and the propulsion of contents from the caecum to the anorectal region.
what stimulates absorption in the colon
absorption is stimulated by short chain fatty acids which are produced predominantly in the right colon by the anaerobic metabolism of dietary fibre by bacterial polysaccharide enzyme systems. Colonic contents are mixed aiding absorption
what are the 3 main groups of gut hormones based on their chemical structure
- Gastrin–cholecystokinin family
- Secretin family
- Somatostatin family
