Alimentary Flashcards
(122 cards)
Layers of the gut
Mucosa- epithelium, glands and lamina proper
Submucosa-connective, submucosal plexus
Muscularis-circular and longitudinal
Serosa/Adventita
Oesophagus
Stratified squamous
Upper oesophagus- skeletal muscle
Lower oesophagus- smooth muscle
Oesophageal sphincters
Upper-2 muscles- constrictor pharyngeal medius
-constrictor pharynges inferior- voluntary
Lower- 2 components- internal- circular
External- formed by diaphragm
Change from oesophagus to stomach
Z line
Stratified Squamous to columnar
Swallowing
Originally both spinsters closed
Then both open as food goes to end of pharynx
Then upper sphincter and superior rings contract and inferior rings dilate
Then after food passes through lower sphincter it contracts- pushing it into stomach
Functions of stomach
Digestion
Storage- reservoir until downstream ready
Immunological protection
Stomach wall
Similar structure to rest of GI tract but has extra oblique layer of smooth muscle in circular muscle- aiding grinding motion
Gastric pits
Deep pores in mucosa containing gastric glands that produce HCL, enzyme, zymogens and mucus
Mucous Cells
Produce mucous that protects mucosa from highly acidic substances, since it also contains bicarbonate.
Also protects the layer from enzymatic action
Parietal Cells
Produce HCL, usually in response to gastrin
Causes activation of carbonic anhydrase, in which bicarbonate is exchanged for Cl- and H+ is exchanged for K+ which enters the cell via Na/K pump
Chief Cells
Produce zymogen pepsinogen (prevents breakdown of chief cell)
Which is activated by low pH to pepsin which breaks down dietary proteins
Also produces gastric lipase
G cells
Endocrine cell that produces gastrin in response to vagus innervation, presence of peptides and stomach distention
Travels via blood and causes smooth muscle contraction, acid secretion, pyloric sphincter relaxation
Enterochromaffin like cells
Respond to gastrin and produce histamine which activated HCL production
D cell
Secrete somatostatin which inhibits GI function such as histamine and HCL production
Phases of stomach activity
Cephalic- response to smell and though of food
Vagus causing production of mucus, HCL and pepsin- for short period
Gastric- response to distention of stomach and chemoreceptors
Vagus causing secretions for prolonged periods
Intestinal- response to duodenal stretch and reduced pH in duodenum
I cells- CCK and S- Secretin causing decrease in secretions
But can be stimulated if there’s long peptides in chyme
Sphincters of small intestine
Pyloric sphincter
Ileocaecal valve
Sections of small intestine and function
Duodenum- 0.25m- contians submucosal glands that neutralise acidic chyme
Jejenum- 2.5m- large submucosal folds- plicae circularis- larger than rest of SI folds
Ileum- 3.75m- many peyers patches
Features in small intestine
Villi
Crypts of liebemkuhn
Cells of the small intestine
Enterocytes- tall columnar with microvilli, glycocalyx traps mucus and enzymes
Goblet- used to hydrate contents since a lot is being
absorbed, therefore increase in number further down
Enteroendocrine-G Gastrin,I CCK,S Secretin,D somatostatin
Paneth- immunological cell, near bottom of crypts, contain lysozyme
Motility of small intestine
Peristalsis- aids movement of substances further down GI tract
Segmentation- aids mixing- with enzymes
Migrating motor complex- periodic contractions from stomach to distal end of ileum, during fasted state, in order to cleanse SI of residue food
Digestion and absorption of Carbohydrates
Salivary amylase- breaks down polysaccharides
Pancreatic amylase- also breaks them down to disaccharides
Sucrase, maltase and lactase in small intestine breaks them down to monosaccharides- located one brush border
Glucose and galactose absorbed via secondary active transport by SGLT1 on apical
Fructose absorbed via facilitated diffusion by GLUT5 on apical
All 3 absorbed by facilitated diffusion by GLUT2 on basal
Digestion of Protein
Parietal cells produce HCl which activates pepsin, which breaks down proteins into polypeptides
Pancreas produces Trypsinogen, procarboxypeptidase, chymotrypsinogen. Trypsinogen is activated to trypsin by enterokinase which is produced by duodenal cells. Trypsin further activates the other zymogens to carboxypeptidase and chymotrypsin which breakdown the polypeptides to di/tripeptides
Carboxypeptidase, endopeptidase, dipeptidase and aminopeptidase are located in the brush border which digest to amino acids
Absorption of peptides
Single amino acids are absorbed by secondary active transport via AA/Na symporter
Di/tripeptides can also be transported in via this mechanism
AA are them absorbed by facilitated diffusion on basal membrane but peptides cannot and have to be broken down by cytoplasmic peptidase enzymes first
Digestion of lipids
Linguinal and gastric lipase start to digest triglycerides
Churning of stomach starts to emulsify
Bile enters duodenum and emulsifies fats
Pancreatic lipase breakdown TAG to MAG and fatty acids