Physiology Flashcards
Where are G cells located
Antrum of stomach, duodenum
Which cells secrete gastrin
G cells
Function of G cells
Increase:
- gastric H+ secretion
- growth of gastric mucosa
- increase gastric motility
Increased vagal activity releasing gastrin-releasing peptide (GRP) stimulates which cells in the stomach
G cells to secrete gastrin
What decreases gastrin release by G cells?
Decreased pH
Increase in stomach distention or alkalinization will cause release of what regulatory substance
Gastrin from G cells
Peptic ulcers with extremely high levels of gastrin even after administration of secretin indicates that you have what condition?
Zollinger-Ellison syndrome
Conditions that increase gastrin levels
Chronic PPI use - alkalinizes stomach
Chronic atrophic gastritis - H. pylori infection
Zollinger-Ellison syndrome - gastrinoma
Location of D cells in GI tract
Pancreatic islet and GI mucosa
What do D cells secrete?
Somatostatin
What is the function of somatostatin?
Decreases pretty much all types of secretions in stomach
Somatostatin analog used to treat acromegaly, carcinoid syndrome and variceal bleeding
Ocreotide
Stimulates D cells to secrete somatostatin
Acid
Stops D cells from secreting somatostatin
Decreased vagal stimulation
Secrete cholecystokinin
I cells
Secrete somatostatin
D cells
Secrete gastrin
G cells
Location of I cells
Duodenum, jejunum
Stimulates I cells to secrete cholecystokinin
Fatty acids and amino acids
Causes pancreatic secretions, gallbladder contraction, decreases gastric emptying and increases relaxation of sphincter of Oddi
Cholecystokinin
I cells secrete cholecystokinin and produce the following effects
Increased pancreatic secretions, gallbladder contraction, and relaxation of the sphincter of Oddi
Decrease gastric emptying
Acts on neuronal muscarinic pathways to cause pancreatic secretions
Cholecystokinin
Secrete secretin
S cells
Location of S cells
Duodenum
Causes secretion of pancreatic HCO3- and bile and decreases gastric acid secretion
Secretin
S cells secret secretin and produce the following actions
Increase pancreatic bicarb and bile secretion
Decrease gastric acid secretion
Allows pancreatic enzymes to function in the duodenum by neutralizing stomach acids
Bicarb secreted from pancreas
Type of cells found in the duodenum
S, I, K, G, M cells
What do K cells secrete?
Glucose-dependent insulinotropic peptide
Endocrine function of Glucose-dependent insulinotropic peptide
Increase insulin release
Exocrine function of Glucose-dependent insulinotropic peptide
Decrease gastric acid secretion
What increases Endocrine function of Glucose-dependent insulinotropic peptide secretion
Fatty acids, Amino acids, and Glucose (FAG)
Secrete Endocrine function of Glucose-dependent insulinotropic peptide
K cells
Where are K cells located
Duodenum, jejunum
Endocrine function of Glucose-dependent insulinotropic peptide is also known as what?
Gastric inhibitory peptide (GIP)
Which causes a greater increase in insulin release, oral or IV glucose administration
Oral glucose
Produces migrating motor complexes
Motilin
Secretes motilin
Small intestine
Macrolide that is a motilin receptor agonist, used for stimulation of intestinal peristalsis
Erythromycin
What increases release of motilin
Fasting state
Secretes vasoactive intestinal polypeptide (VIP)
Parasympathetic ganglia in sphincters, gallbladder, small intestine
Causes increased intestinal water and electrolyte secretion and relaxation of intestinal smooth muscle and sphincters
VIP
Secretion of this peptide is increased by distention and vagal stimulation and decreased by adrenergic input
VIP
Patient presenting with watery diarrhea, hypokalemia and achlorhydria most likely has what?
VIPoma
Location of VIPoma
Non-alpha and non-beta islet cell tumor of the pancreas
What is typically the cause of achalasia
Increased LES tone from loss of NO
NO loss results in achalasia due to what mechanism
Increased LES tone
Function of NO in the GI tract
Increases smooth muscle relaxation including lower esophageal sphincter (LES)
What cells are located in the stomach?
Parietal cells, Chief cells, Mucosal cells, G cells
Hormone that acts on the stomach by increasing appetite
Ghrelin
What decreases secretion ghrelin?
Food
What increases secretion of ghrelin?
Fasting state
What heritable disease increases ghrelin
Prader-Willi syndrome
What elective procedure decreases ghrelin
Gastric bypass surgery
Required for B12 uptake in terminal ilium
Intrinsic factor
What cells secrete intrinsic factor?
Parietal cells
Where are parietal cells located?
Stomach
Consequence of autoimmune destruction of parietal cells
Chronic gastritis and pernicious anemia
Cells that secrete gastric acid in the stomach
Parietal cells
Function of gastric acid
Decrease pH and convert pepsinogen to pepsin
What increases gastric acid secretion by parietal cells?
Histamine, ACh, and gastrin
What decreases gastric acid secretion by parietal cells?
Somatostatin, GIP, prostaglandin, secretin
What drugs inhibit prostaglandin synthesis, increasing gastric acid secretion?
NSAIDs
Where are parietal cells located?
In the body of the stomach
Which cells secrete pepsin?
Chief cells
Where are Chief cells located?
In the body of the stomach
What is the function of pepsin
Protein digestion
What causes Chief cells to secrete pepsin?
Vagal stimulation and local acid
Secrete pepsin
Chief cells
Digests protein in stomach
Pepsin
Neutralizes acid
Bicarbonate
Secretes bicarbonate
Mucosal cells and Brunner glands
Where are mucosal cells found?
Stomach, duodenum, salivary glands, pancreas
Where are Brunner glands located?
Duodenum
What causes increased secretion of bicarbonate?
Secretin
Where is bicarbonate trapped in?
Mucus secreted by gastric epithelium
What is the function of mucus secreted by gastric epithelium?
Trap bicarbonate
What is the strongest regulator of gastric acid secretion
Histamine released by ECL cells via gastrin stimulation
In what section of the stomach are the majority of mucus cells found?
Antrum of the stomach
Responsible for starch digestion
Alpha amylase
Responsible for fat digestion
Lipases
Responsible for protein digestion
Proteases
Enzyme secreted in its active form
Alpha amylase
Brush border enzyme found on duodenal and jejunal mucosa that converts trypsinogen to its active form
Enterokinase/enteropeptidase
Function of Enterokinase/enteropeptidase
Convert trypsinogen to trypsin
Function of trypsin
Convert other zymogens to their active form
Proteases that digest protein
Trypsin, chymotrypsin, elastase, carboxypeptidases
Trypsin, chymotrypsin, elastase, carboxypeptidases are secreted as zymogens, inactive proenzymes and are converted to their active enzyme form by which enzyme
Trypsin
Trypsin converting trypsinogen to more trypsin is a type of what regulation
Positive feedback loop
What saccharides are absorbed by enterocytes?
Monosaccharides: glucose, galactose, fructose
Which sodium-glucose transport protein-1 (SGLT1) takes up which to monosaccharides?
Glucose and Galactose
Which transporter is responsible for the uptake of Fructose?
GLUT5
Which transporter is responsible for the uptake of all monosaccharides?
GLUT2
Which sodium-glucose transport protein has Na-dependent transport?
SGLT1
Which glucose transporter works via facilitated diffusion?
GLUT5
What form of iron is absorbed in the duodenum?
Fe2+ (oxidized)
What part of the small intestine absorbs iron?
Duodenum
What part of the GI tract absorbs folate?
Small bowel
Vitamin that requires intrinsic factor for absorption
B12
What part of the small intestine absorbs vitamin B12?
Terminal ileum
Part of the small intestine where bile and salts are absorbed
Terminal ileum
Patient with small bowel disease may be deficient in what nutrients?
Iron, B9 and B12
Unencapsulated lymphoid tissue found in lamina propria and submucosa of ileum
Peyer patches
Function of Peyer patches
Contain M cells that sample and present antigens to immune cells
Cells in Peyer patches that sample and present antigens to immune cells
M cells
Major type of immunoglobulin found in gut epithelium
IgA
B-cells in Peyer patches are stimulated and differentiate to secrete which type of immunoglobulin
IgA
Enzyme that is the rate-limiting step in bile acid synthesis
7alpha-hydroxylase
Responsible for digestion and absorption of lipids and fat-soluble vitamins
Bile
Responsible for cholesterol secretion and is the body’s primary way of eliminating cholesterol
Bile
Provides antimicrobial activity in the GI tract via membrane disruption of pathogens
Bile
Functions of bile
- Digestion and absorption of lipids and fat-soluble vitamins
- Cholesterol excretion
- Antimicrobial activity
What is bile composed of?
Bile salts, phospholipids, cholesterol, bilirubin, water, and ions
Enzyme that heme to biliverdin
Heme oxygenase
Protein that carries bilirubin to liver
Albumin
Bilirubin that is water insoluble
Indirect bilirubin
Function of UDP-glucuronosyl-transferase
Conjugate bilirubin to direct bilirubin
Bilirubin that is water soluble
Direct bilirubin
Form of bilirubin that is excreted in feces and gives stool its brown color
Stercobilin
What happens to the majority of bilirubin
Excreted in feces
Organ where bilirubin is conjugated
Liver
Form of bilirubin that is excreted in urine and gives it its yellow color
Urobilin