Week 11 Flashcards
What is in the tubular GI tract
Mouth, Pharynx, Esophagus, Stomach, Small and large intestines
What happens in the swallowing reflex?
Pushes tongue against the soft palate
Respiration is inhibited (epiglottis blocks airway)
Pushes food into the esophagus
What is peristalsis?
Rhythmic contraction of the esophagus and small intestine moves down the food
3 areas of the small intestine
Duodenum -> Jejunum -> Illeum
Areas of large intestine
Cecum -> Ascending colon -> Transverse colon -> Descending colon -> Sigmoid colon -> Rectum
4 layers of the GI tract
Mucosa
Submucosa
Muscularis
Serosa
What do transport cells secrete
Acids, bicarbonate, absorb nutrients and water/vitamins
What do enteroendocrine cells do
Secrete hormones into the blood
Functions of the goblet and paneth cells
Goblet - Mucous
Paneth - Secretes antimicrobial compounds
What 2 plexuses control the enteric nervous system?
Mytenteric plexus
Submucosal plexus
What does the myenteric plexus do
Regulates motility
What does the submucosal plexus do?
Regulates secretion and absorption
What’s the general format for external stimuli signalling for GI?
- External stimuli such as smell, sight ->
- Efferent signals to the cephalic brain -> Sympathetic/Parasympathetic neurons
- Myenteric and submucosal plexuses ->
- Smooth muscle contractions/Secretory cells ->
- Either changes in contraction, exocrine secretion or endocrine secretions
How does local stimuli change how the GI behaves?
Local stimuli such as pH, stretch feed into interneurons and myenteric/submucosal plexuses -> Smooth muscle -> Changes in secretion, muscle contractions, endocrine secretions
Sympathetic vs Parasympathetic control of the digestive system
Sympathetic -> Inhibit gut movements, constrict sphincters, reduce secretion
Parasympathetic -> Increase gut movements, dilate sphincters, increase secretion
Arteries that supply the GI tract
Stomach: Celiac artery
Small intestine: Superior mesenteric artery
Large intestine: Superior and inferior mesenteric arteries
Veins from the GI tract
Hepatic veins
Hepatic portal veins
Inferior vena cava
Superior and inferior mesenteric vein
What feature of the GI smooth muscle allows contraction as a single unit?
Muscle cells are connected by gap junctions, allowing AP to travel throughout the muscles
How are slow waves in the GI smooth muscle generated?
By the interstitial cells of Cajal, very similar to the AV node of the heart
spontaneous AP produced by pacemaker potential
Heart pacemaker cells vs Interstitial cells of Cajal (what causes depolarisation for cajal?)
Heart : Every potential caused to produce AP, higher freq of AP
Cajal: Not every slow wave will cause AP, depolarisation is due to Ca2+ entry. Lower freq of AP
What causes the depolarization of GI smooth muscle?
- Stretch
- Acetylcholine
- Parasympathetics
What causes the hyperpolarisation of GI smooth muscle?
- Noradrenaline
- Sympathetics
Steps of peristalsis
- Circular muscle contraction behind food
- Longitudinal muscles contract ahead of mass
- Contraction of circular muscle moves food forward
What is the vagovagal reflex?
When stomach is stretched, info is sent to the brain and then adjusts stomach size
What are the segmentation contractions
Concentric contractions along the intestine, where circular muscles contract, and longitudinal muscles relax, mixing food
Function of the ileocecal valve?
To prevent back flow from cecum (large intestine) to the illeum, controls the emptying of small intestine
How is the ileocecal valve opened or closed?
Opened by the distension of ileum and by gastroileal reflex
Closed by the distension of the colon
What controls the large intestine’s motility?
PNS - Increase motility
SNS - decrease motility
How is vomiting initiated?
Stimulation of the vomiting center in the medulla
What do the vagus nerves do during vomiting?
- Enhance salivation
- Relaxes esophagus
- Contracts pylorus
What do the spinal nerves do during vomiting?
- Inspiration
- Contraction of abdominal muscles
What does the phrenic nerve do during vomiting?
Diaphragm descends
How much fluid is secreted into and out from the lumen?
9L for both~
What’s the rugae?
Wrinkles in the stomach, increasing surface area
What are the 2 components in the small intestine that increase the surface area?
- Villi
- Crypts of Lieberkuhn
What are the large bumps of the large intestine called?
Haustra
What are the large bumps of the small intestine called?
Plica
What are the 3 salivary glands?
Parotid
Submandibular
Sublingual
Sympathetic vs Parasympathetic saliva difference
Para: Lots of water (serous) saliva
Sympa: Small amount of thick mucous saliva
Which salivary gland produces the most saliva
Submandibular > Parotid > Sublingual
What do parietal cells release?
HCl, Intrinsic factor
What do chief cells release?
Pepsinogen, Gastic lipase
What do enterochromaffin-like cells release?
Histamine
What do D-cells release?
Somatostatin
What do G cells release?
Gastrin
How can the stomach cells survive? What neutralises the pH?
Bicarbonate is released, allowing pH ~ 7 at cell surface
How do parietal cells secrete Acid?
- Water breaks down to H+ and OH-, H+ is effluxed into lumen
- CA combines CO2 and OH - to form bicarb
- Bicarb is exchanged out for Cl- and effluxed into lumen
Functions of the intrinsic factor
Bind to B12 and ensures its absorption in the ileum
What stimulates the release of gastrin?
Peptides and amino acids
Which region is the G cells mainly located in?
G-cells located in pylori region
Where is the parietal and enterochromaffin-like cell located?
Fundus/Body region
What does gastrin do
- Stimulates release of acid, histamine, pepsinogen and mucous
- Increase stomach motility and mass movement
2 cell types in the pancreas (exocrine)
Acinar
Duct cells
What do acinar cells release
Pancreatic enzymes
What do duct cells release
sodium bicarb and water
How is bicarb synthesized and excreted by the pancreas?
- H2O + CO2 combine to make bicarb and H+ via CA
2.Bicarb is pumped outand exchanged for Cl- from lumen, and H+ is exchanged for sodium - Sodium pumped out by Na+/K+ pump
- Cl- leaks out through the CFTR channel
Why do cystic fibrosis patients need to take digestive enzymes
Thick mucous block the pancreatic ducts, prevents enzymes from reaching the small intestine
What does secretin do?
- Increase release of bicarbonate
- Decrease gastric acid, and emptying
GLP-1 function
- Increase insulin, decrease glucagon, increase B-cell growth
- Decrease gastric acid, and gastric emptying
How are monosaccharides absorbed?
Influx into cell by SGLT (Glucose and galactose) and GLUT5 (Fructose), efflux into blood via GLUT2 for both
Which cell releases pepsinogen?
Chief cells
Which specific amino acids to pepsin digest?
Aromatic - Tryptophan, Tyrosine, Phenylalanine
Endo vs Exo peptidases
Endo peptidases cut internal peptide bonds
Exo peptidases cut terminal peptide bonds
How are zymogens activated in the pancreas?
- Trypsin is activated from Trypsinogen via Enteropeptidase
- Trypsin activates various zymogens into enzymes
3 ways amino acids are absorbed in the small intestine
- Di and Tri peptide cotransport with H+
- Amino acids cotransport with Na+
- Small peptides carried intact via transcytosis
Where does fatty acids digestion start?
In the mouth
Function of bile salts and lecithin
Emulsify fat to increase digestion
What does emulsification do?
Forms micelles
How does fat get absorbed? both monoglycerides and cholesterol
- Monoglycerides and fatty acids diffuse into cell, re-esterification to triglycerides in the smooth ER
- Cholesterol enters through energy dependent transporter (NPC1L1)
What happens in the Golgi for triglycerides?
Transformed to to chylomicrons, and they are absorbed by the lymphatic system
How are fat soluble vitamins absorbed?
Absorbed with fat
How are water soluble vitamins absorbed?
Through a transporter
How is vitamin B12 absorbed?
Absorbed by intrinsic factor and transported into the illium
How is Ca2+ absorbed?
Through calcium channels in apical, and then Ca2+ ATPase in the basolateral
How is Iron absorbed?
Fe2+/H+ cotransporter called DMT-1 in apical side
Fe2+ ferroportin transpoter in the basolateral side
Ways Na+ can get absorbed
Na+ ion channels, Na+/Cl- cotransporter, Na+/H+ exchanger, HCO3-/Cl- exchanger to balance out pH
3 phases of digestion
Cephalic
Gastric
Intestinal
What triggers the cephalic phase?
Coming of food, such as smell or sight of it, causing a parasympathetic stimulation to salivary glands and stomach (through vagus)
What happens in the cephalic phase to the salivary glands?
Saliva production (Watery)
What happens in the cephalic phase to the stomach?
Stimulation of the submucosal plexus, which stimulates Mucous, Chief, Parietal, and G cells
What happens in the cephalic phase in the small intestine?
- Gastrin production via the stomach will cause Bicarb and enzymes to be produced in the pancreas
- Acetylcholine signalling via the vagus nerve will also cause similar effects
- Both are released into the intestines
What are the causes of GERD?
Fatty meal, alcohol, caffeine, chocolate, peppermint, causing CCK release and decrease in gastric motility
What happens in the gastric phase?
Stretch and increased pH will signal more release of HCl, Pepsinogen, Mucus, and G cell (also stimulated by peptides)
What inhibits the gastric phase?
Somatostatin
What causes stomach ulcers?
H.pylori infection
How is a H.pylori infection tested for?
breathing test using a radioactive urea. Urea is converted to bicarb (radioactive) and breathed out in lungs. They test the radioactivity of the breaths to see H.pylori infection
What happens in the intestinal phase?
Presence of lipid and carbs will secrete CCK and GIP, which inhibit stomach function, Secretin released by decreased pH
Mechanism of cholera
Bacteria produces a toxin that permanently activates Gas, thus leading to overproduction of cAMP, leads to inhibit Na+ uptake and enhanced Cl- efflux (leading to even less Na+ uptake)
How to treat cholera?
With oral rehydration solutions and antibiotics, containing glucose so Na+ can uptake, and also bicarbonate if metabolic acidosis
