Gastrointestinal Physiology Flashcards
What are the two types of action potential involved in gastrointestinal motility?
Slow waves - produced by cells of Cajal. Resting membran potential -50mV
Spike potential - occur at -40mV due to calcium influx through the Ca-Na channels
What are the two types of contraction that may occur in the gastrointestinal tract?
What are the main components of the gastrointestinal nervous system, functions and their locations?
- The local nervous systems
a) Myenteric plexus (Auerbach’s plexus) = GI muscle contraction (muscularis), inhibition of sphincters (VIP)
b) Submucosal (Meissener’s plexus) = secretions and blood flow, contraction of submucosal muscle (submucosa) - Autonomic nervous system input
- Sensory neurons
- Direct feedback on the myenteric and submucosal NS as well as feedback to the CNS via the vagus nerve.
What may be vasoactive intestinal peptides role in relation to the myenteric plexus?
Autonomic control of the enteric nervous system
- What nerves give parasympathetic innervation to the GIT?
- What nerves give sympathetic innervation to the GIT?
a) Which neurotransmitter?
GIT Sensory Neurons
- Location of cell bodies
- Functions
- Inputs
- Dorsal root ganglion and enteric nervous system
What are the two types of movement in the GIT?
Segmental contractions
Peristalsis
Which cranial nerves are required for the swallowing reflex?
Vagus and glossopharyngeal.
WHere is the swallowing centre located?
Which cranial nerves are involved in the efferent (motor) control of swallowing?
Trigeminal, vagus, glossopharyngeal,
Describe the nervous innervation of the oesophagus
Efferent (sensory)
- Vagus nerve
Afferent (motor)
- vagus and glossopharyngeal - proximal 1/3
- vagus only - distal 1/3
What are the main factors that will stimulate the duodenum to inhibit gastric emptying?
- Distension of the duodenum
- Irritation of the duodenal mucosa
- Acidity in the chyme
- Osmolality of the chyme
- Nutrient content of the chyme (particularly fats)
Which locally produced hormones stimulate and inhibit gastric empting?
Stimulate
- Gastrin
Inhibit
- CCK (most potent)
- GIP
- Secretin
Gastroenteric reflex
Duodenal stretch results in inhibition of gastric motility
Explain:
1) Peristaltic rush
2) Mucosal movements
- Rapid peristalsis that occurs with SI irritaiton resulting in rapid clearance of the duodenum
- Control of small intestinal villous surface area by contraction of the muscularis mucosae.
Which hormons stimulate and inhibit peristalsis?
Increase
Decrease
- Gastrin
- CCK
- Insulin
- Motilin
- Serotonin
- GIP
- Secretin
What are the events that must occur to allow defecation to occur?
Intrinsic defecation reflex, initiated by the myenteric plexus, inreases peristalsis and relaxes the internal colonic sphincter. The parasympathetic nervous system must also add to the strength of this peristalsis and allow relaxation of the external sphincter.
What is the major alpha amylase present in saliva?
Ptyalin
What is the ionic makeup of saliva?
NaCl = 15meq/L
K = 30meq/L
HCO3 = 50-70meq/L
What is the mechanism by which dilation and blood flow of the salivary glands increases with parasympathetic innervation?
One mechanism may be that increased kallikrein is secreted by the salivary gland which converts alpha-2 globulin into bradykinin which is a potent vasodilator.
Which cells are present within the gastric (oxyntic) glands?
- Parietal (oxyntic cells) - HCl secretion
- Peptic (chief) cells - pepsinogen secretion
- Enterochromaffin-like (ECL) cells - histamine secretion
- Mucus neck cells
- Epithelial cells
Explain the chemical process that results in formation of HCl in the gastric gland.
What are the concentrations of the following after they leave the parietal cell?
a) Hydrogen
b) Chloride
c) Sodium
d) Potassium
a) 155meq/L
b) 173meq/L
c) 3meq/L
d) 15meq/L
What is the end result of the stimulatory factors on the parietal cell that results in increased gastric acid secretion?
H+/K+-ATPase and KCl transporters are incorporated into the parietal cell canalicular membrane
Describe the feedback mechanisms involved in gastric acid secretion (see goodnotes for anwers)
Stimulation
1. Gastrin secretion from G-cells in response to dietary protein from pyloric G cells
2. Gastrin stimulates ECL cells to produce histamine
3. Enteric nervous system can also stimulate ECL cells
Inhibition
1. Reverse enterograstric reflex (myenteric, sympathetic and vagus reflex)
- distension of the SI
- acid in upper intestine
- protein breakdown products
- mucosal irritation
2. Hormonal feedback from acid fat or protein in the SI
- Secretin
- GIP
- SST
At what pH is pepsin active?
Where is gastrin released from and in response to which stimulus?
What hormonal factors will inhibit gastric secretion?
- Secretin
- GIP
- VIP
- SST
All released in response ot acid, fat or protein in the small intestine.
List the main digestive enzymes secreted by the pancreas
a) Protein digestion
b) CHO digestion
c) fat digestion
d) miscellaneous
a - trypsinogen, chymotrypsin, carboxypeptidase
b - amylase
c - lipase, cholesterol esterase, phospholipase
d - trypsin inhibitor, bicarbonate
What is the optimal pH for function of pancreatic enzymes?
7.0
What is the name of the duodenal papilla and its sphincter?
Papilla of vater
Sphincter of Odii
What are the main dietary carbohydrates that mammals can digest, what are they digested into?
Sucrose –>
Lactose
Starches
What are the four main intestinal brush border enzymes involved in carbohydrate digestion?
Maltase
Lactase
Sucrase
alpha-dextrinase
What are the main adaptations that the absorptive surfaces of the small intestine have that allow a huge surface area for absorption?
- Villi and microvilli (latter = the brush border)
- Valvulae conniventes (Kerckring folds) - these are finger like projections that contain lots of villi on them.
What is the concentration of sodium inside the intestinal epithelial cell compared to in the chyme?
Need to double check but I believe that sodium is lower in the luminal fluid and higher in interstitial/cell.
What does sodium re-absorption in the GIT tend to also result in the absorption of?
- Glucose via SGLT-1
- Amino acids
- Hydrogen exchange
Where in the SI is the HCO3/Cl exchanger located?
The ileum (as well as the LI).
Outline the events involved in the pancreatic secretion of HCO3-
What are the main stimuli for the production of the following from the pancreas?
a) Enzyme secretion
b) H20 and HCO3 secretion
a) Vagal input
b) Cholecystokinin, Secretin
What is the main hormone responsible for secretion of bile?
Cholecystokinin (contracts the gallbladder and relaxes the sphincter of Odi)
Secretin (stimulates ductal secretion of NaHCO3-)
What is the bile salt synthesis pathway?
Bombesin
A GI hormone that stimulates secretion of gastrin. It is known as either neuromedin B or gastrin releasing peptide in mammals.
Whice VFA, produced by colonic bacteria, provides an energy source for colonocytes??
Butyrate
