Physiology Flashcards
Where does carbohydrate digestion start
Mouth
What are the 3 salivary glands
Parotid
Sublingual
Submandibular
Which salivary gland secretes the least amount of saliva
Parotid
Which salivary gland secretes the most amount of saliva
Submandibular
Which salivary gland secretes the most viscous saliva
Sublingual
What other enzyme does the mouth produce
Lingual lipase
Where is the draining of parotid gland located at
upper 2nd molar teeth
List the layers of GI mucosa from outermost to innermost
Serosa Muscularis externa submucosa muscularis mucosae lamina propria epithelium
What does muscularis externa consist of
Circular and longitudinal smooth muscles
Which muscle is next to serosa (outermost muscle)
Longitudinal muscle
What is between the circular and longitudinal muscle layers
Myenteric plexus
What is between the submucosa and circular muscle layers
Submucosal plexus
What does lamina propria contain
Capillaries
Enteric neurones
gut associated lymphoid tissue
What is right underneath the epithelium
Lamina propria
What does submucosa contain
Connective tissue
glands
large blood and lymph vessels
What nervous systems control the GI tract
Enteric nervous system
Parasympathetic and sympathetic nervous systems
Which nervous system is most important at regulating GI tract
Parasympathetic nervous system
Which nerves are included in parasympathetic NS for GI tract
Vagus nerves
Pelvic nerves
What are the effects of sympathetic stimuli
Decreases motility, secretion and blood flow
Causes contraction of sphincters
What are the effects of parasympathetic stimuli
Increases motility
Increases gastric, duodenal, pancreatic secretion
Relaxes sphincters
What are the abdominal prevertebral ganglia that innervates the abdominal, pelvic and perineal organs
Coeliac
superior mesenteric
Inferior mesenteric
What are the neurones of enteric nervous system
sensory
Interneurones
effector
What is the function of interneurones
alter activity of effector neurone
What is special about enteric nervous system and what affects the ENS
Can operate by itself but it is heavily affected by hormones and extrinsic nerves (parasympathetic / sympathetic )
What is the function of muscularis mucosae
Contraction changes the absorptive and secretory area of mucosa
What feature allows smooth muscle in GI tract to depolarise at the same time
Gap junctions
What neurotransmitters do excitatory neurones release
ACh and substance P
What neurotransmitters do inhibitory nervous system release
NO and VIP
What are the pacemaker cells in GI tract called
Interstitial cells of cajal (ICC)
Function of ICC
Continuously generate slow wave of depolarisation to control motility
Do all slow waves cause smooth muscle contraction?
No, because not all slow waves reach threshold
What does the strength of contraction depend on
how long the membrane potential has stayed above threshold
What affects the threshold for contraction
Neuronal, hormonal and mechanical stimuli
How do neuronal, hormonal and mechanical stimuli affect slow waves
Shifts the membrane potential in a depolarising manner, allowing each cell to have different starting MP
Where is the enteric nervous tissue located at
myenteric and submucosae plexus
Describe peristalsis
Rhythmic contractions ; the smooth muscle in front of food bolus relaxes while the smooth muscle behind contracts
Function of gastrin
Stimulate gastric acid secretion
Stimulate pepsinogen and IF secretion
Inhibit migrating motor complex
What triggers the release of gastrin
Distension of stomach
What inhibits the release of gastrin
Low pH
Somatostatin
Function of Secretin
Increase pancreatic and biliary bicarbonate secretion
Decreases gastric acid secretion
What stimulates the release of secretin
In response to presence of fatty acids and H+ in intestinal lumen
Which cells secrete gastrin
G cells in stomach
Which cells secrete secretin
S cells in duodenum
Function of CCK
Inhibit gastric emptying
Stimulate release of pancreatic enzyme
Stimulate relaxation of sphincter of oddi and contraction of gall bladder to release bile
Potentiates action of secretin
What triggers the release of CCK
Monoglycerides, fatty acids, amino acids in intestinal lumen
Which hormone induces satiety
CCK
Resistance in which hormone causes obesity
Leptin
How does leptin resistance cause obesity
It reduces satiety and causes overconsumption of food
Function of GIP
Stimulates the release of insulin
Inhibits gastric emptying
Which cell secretes CCK
I cell in duodenum
Which cell secretes GIP
K cells in duodenum and jejunum
Function of somatostatin
Inhibit gastric acid secretion by binding to receptor on parietal cells hence inhibiting adenylyl cyclase
Inhibits CCK and secretin
Which cell produces somatostatin
D cells in pyloric gland area (stomach)
Where is pyloric gland area
Antrum
Where are G cells located
Pyloric gland
Function of enterochromaffin cells
Release histamine
How does histamine stimulate production of gastric acid
1) histamine binds to H2 receptors on parietal cells
2) activates adenylyl cyclase: ATP converted to cAMP
3) PKA activated by cAMP
4) proton pump on parietal cells are stimulated
Which cell produces gastroferrin and what other hormones does this cell produce
Parietal cell; also secretes intrinsic factors and HCL
Function of gastroferrin
Allows Fe2+ to bind hence allow absorption
Function of intrinsic factors
Bind to vitamin B12, allowing absorption
Signs of vitamin B12 deficiency
Macrolytic
Pernicuous anaemia
Paraesthesia
What activates pepsinogen
HCL, causing pepsinogen -> pepsin
How does the activation of pepsinogen amplifies itself
Pepsinogen activated by HCL -> pepsin
Pepsin activates more pepsinogen
Which cell produces pepsinogen and gastric lipase
Chief cells
Function of GLP-1
Stimulate release of insulin
Decreases appetite
Decrease glucagon secretion
What stimulates the release of GLP-1
glucose and fats
Which cell releases GLP-1
L cells in distal ileum
Function of motilin
Stimulates migrating motor complex
What stimulates the release of motilin
when duodenum and jejunum are empty
Which cells produce motilin
M cells in duodenum and jejunum
What is migrating motor complex
Strong peristaltic contraction to expel small intestine debris / undigested remains through ileocaecal valve to the caceum
What triggers the migrating motor complex
Motilin
Why does Migrating motor complex only occur between meals
To avoid losing nutrients
Describe the mucosa of small intestine
Simple columnar epithelium with microvilli
Villi
With crypts of lieuberkuhn between villi
What cells are at the bottom of crypts of lieuberkuhn
Paneth cells
What cells are at the upper portion of crypts of lieuberkuhn
Stem cells
Function of paneth cells
Produce substances that attack bacteria
Which enzyme activates trypsinogen
Enterokinase in duodenal mucosa
What is in submucosal layer of duodenum
Brunner’s glands
Function of Brunner’s glands
Release alkaline mucous to neutralize the chyme
When is somatostatin released
After meal when pH is low
What are the 3 phases of gastric acid secretion
Cephalic
Gastric
Intestinal
What stimulates cephalic phase
smell, sight, chewing, swallowing
What does somatostatin inhibit
CCK and secretin