HCP 4 Flashcards
G-cells of the stomach are stimulated by what?
gastric distention
amino acids
vagus nerve stimulation
elevated gastric pH
G cells of the stomach secrete what and where?
Gastrin into the blood
What does gastrin do?
binds to enterochromaffin like (ECL) cells -> release histamine -> histamine binds to H2 receptor of parietal cell -> increased secretion of H+ via H-K exchange
Can also bind to CCKb receptor of parietal cell -> increase H+ secretion
Describe bristol stool type 1
Separate hard lumps, like nuts (hard to pass)
Describe bristol stool type 2
Sausage-shaped but lumpy
Describe bristol stool type 3
like a sausage but with cracks on it’s surface
Describe bristol stool type 4
like a sausage or snake, smooth and soft
Describe bristol stool type 5
soft blobs with clear cut edges (passed easily)
Describe bristol stool type 6
fluffy pieces with ragged edges, mushy stool
Describe bristol stool type 7
watery, no solid pieces, entirely liquid
What is the composition of stool?
75% water and 25% solid matter
Of solid matter (30% bacteria, 10-20% fat, 10-20% inorganic matter, 2-3% protein, 30% undigested roughage from food a dried constituents of digestive juices-bile pigment and sloughed epithelial cells)
What vitamins do normal gut flora produce?
vit K, vit B12, thiamine, riboflavin
What is the most abundant bacteria in normal gut flora?
Bacteroides, abundance of gram-negative bacilli
Mechanism of acquired lactase deficiency
Enteric viral or bacterial infections or unknown ➡ caused by down-regulation of lactase gene expression (common among Native American, African American, and Chinese populations) ➡ decreased lactase (a dissacharidase) on apical membrane of brush-border enterocyte epithelia ➡ decreased catabolism of lactose containing dietary intake ➡ decreased conversion to glucose and galactose ➡ decreased transport of glucose and galactose on apical membrane of brush border into enterocyte via SGLT1 ➡ increased luminal lactose ➡ increased luminal osmolarity ➡ increased water movement from plasma to lumen d/t excessive osmotic forces in intestinal lumen ➡ explosive diarrhea, watery frothy stools
What are unique features of large intestine wall that the small intestine does not have?
Taenia coli (mental taenia, mesocolic taenia, free taenia) Haustra Omental appendices Absence of villi Has a larger diameter than SI
The ascending and transverse colon are supplied by what artery?
superior mesenteric (ileocolic, right colic, middle colic)
The descending and sigmoid colon are supplied by what artery?
Inferior mesenteric (left colic, sigmoid arteries, superior sigmoid artery)
Celiac sprue is a result of
Environmental- ingestion of gluten products (wheat, barley, rye)
Genetic- HLA-DQ2 and/or HLA-DQ8, polymorphisms in CTLA4
Immune response- Enterocyte response to gliadin and gliadin sensitive T cells
What can IgA anti-gliadin antibodies do that is pathological?
lgA anti-gliadin antibodies ➡ cross-react with reticulin ➡ decreased tethering of epidermal basement membrane to superficial dermis ➡ injury and inflammation ➡ produce a subepidermal blister ➡ dermatitis herpetiformis
When does the ascending colon become the transverse colon?
at the hepatic flexure (AKA right colic flexure)
When does the transverse colon become the descending colon?
at the splenic flexure (AKA left colic flexure)
Where is the appendix located?
posteromedial to cecum
Small intestines becomes large intestine where?
ileocecal junction
What are omental appendices?
small fatty tags attached to subserous layer along the omental taenia
What are haustra?
pouches or sacculations of the colon wall between tania
formed by contraction of taenia coli
What are taenia coli?
distinct bands of longitudinal muscle that run the entire length of the colon in 3 different bands (incomplete meaning does not surround the entire colon)
Where is the mesocolic taenia attached?
where transverse and sigmoid mesocolon attach
Where is the omental taenia attached?
where the greater omental appendices attach
Where is the free taenia attached?
no mesocolon or mental appendices attached (it’s free)
What are colonocytes?
columnar absorptive cells ➡ located in LI mucosa ➡ irregular microvilli and dilated intracellular spaces ➡ for active fluid reabsorption
What are the 5 types of diarrhea?
secretory, osmotic, increase motility, malabsorptive, exudative
Diarrhea defined as
an increase in stool mass, frequency, or fluidity greater than 200mL per day
4 main layers of the stomach
- Mucosa (lamina propria and muscularis mucosae
- Submucosa
- Muscularis Externa
- Serosa
Where are rugae found? are they permanent?
- Mucosa and submucosa of the stomach
- Not permanent; flatten when stomach fills
What are the 4 main types of secretory epithelial cells of gastric glands?
- Mucous neck cells
- Parietal (oxyntic) cells
- Chief (zymogenic) cells
- Enteroendocrine cells
Describe a resting parietal cell?
Contains tubular vesicles, few microvilli, short intracellular canaliculus
Describe an active parietal cell?
(stimulated to produce HCl), tubular vesicles fuse with cell membrane, form large intracellular canaliculus and microvilli
What stimulates parietal cells to secrete HCl?
- Histamine (H2 receptor)
- Acetylcholine (M3 receptor)
- Gastrin (CCKb receptor)
What stimulates G cells to secrete gastrin?
- Distention of stomach
- Presence of small peptides or amino acids
- Stimulation of vagus nerve (release GRP/Bombesin which binds to receptors on G-cells)
How is histamine secretion stimulated?
-Ach and Gastrin can bind to receptors on Enterochromaffin-like cells to stimulate Histamine release
In the gastric phase (stomach) what are the direct and indirect pathways and what do they cause?
- Direct: distention causes vagus nerve to release Ach
- Indirect: vagus nerve releases GRP which stimulates gastrin release
- Both pathways ultimately cause secretion of HCl from parietal cells
What is the main inhibitor of HCl secretion in the stomach?
Decreased pH of contents of the stomach
What are the direct and indirect pathways of somatostatin?
Direct: binds to receptors on parietal cells and causes inhibition
Indirect: inhibits histamine release from ECL cells and gastrin release from G cells
What are inhibitors of HCl secretion?
- Decreased pH of stomach contents
- Somatostatin
- Prostaglandins
What are the 3 salivary glands?
- Parotid gland
- Sublingual Gland
- Submandibular Galnd
Histologically describe the 3 salivary glands
- Parotid glands-serous acini
- Submandibular glands-mostly serous acini
- Sublingual glands-mucous cells
- What ducts modify saliva?
- What modifications are done?
- Striated ducts
- absorption of NaCl into the cell
- K+ and HCO3- secreted into lumen
- How is saliva secretion controlled?
- What are the stimulators for saliva secretion?
- Which is the main stimulator?
- Exclusively under neuronal control by ANS
- Stimulated by both parasympathetic (Ach) and sympathetic (norepinephrine)
- Parasympathetic is the main stimulator
List some functions of saliva
- Keeps mucous membranes moist
- Lubricates food
- Begin starch digestion
- “intrinsic mouthwash”
- prevents tooth decay
What is the function of myoepithelial cells?
-Found in acini and intercalated ducts; stimulated by neural input to contract; mediate movement of saliva
What are the 3 layers of smooth muscle found in the muscularis and what are their functions?
- Outer longitudinal layer- shortening orad region
- Middle circular layer-decreased luminal radius
- Inner oblique layer- wringing motion; aides in retropulsion
What is the pressure of the pyloric sphincter?
10 mmHg (anatomic sphincter)
What stimulates mucus secretions?
- Vagal stimulation
- Physical and chemical irritation
what stimulates bicarbonate secretion?
- Vagal stimulation
- Prostaglandin E2
- Intraluminal acid (secondary to the other two)
What is the function of the mucus gel layer and bicarbonate secretions?
- Mucus gel layer- acts as a diffusion barrier for gastric secretions
- Bicarbonate- maintain local pH ~7.0; neutralize acid secretions that penetrate the barrier
- Both function to protect the mucosa from autodigestion
What sized particles can get propelled through the pyloric sphincter?
2mm
Describe viscous fingering and HCl secretion
HCl is secreted under pressure from the gastric glands and penetrate the mucus layer through narrow fingers. It does not diffuse back because of the high viscosity of the mucus gel layer
Describe the mucosa of the esophagus?
Nonkeratinized stratified squamous epithelium
Muscle layers of esophagus that contribute to peristalsis?
Outer longitudinal layer and inner circular layer
Describe the parts of the esophagus?
- Cervical part- voluntary skeletal muscle
- Thoracic part- mix of voluntary skeletal muscle and involuntary smooth muscle
- Abdominal part- involuntary smooth muscle
What are the 3 constrictions of the esophagus?
- Cervical constriction
- Thoracic constriction
- Diaphragmatic constriction
What is the Z line of the esophagus?
Where the esophageal mucosa transitions into gastric mucosa
Histology of stomach
Simple columnar epithelia
What is the pressure of the LES?
20 mmHg (physiologic sphincter)
Anatomic features of the LES?
- skeletal fibers of crural portion of diaphragm surround surround esophagus and exert clamp-like action on esophagus
- oblique/sling fibers of stomach create flap valve which helps to close the esophagogastric junction
List teeth type and functions?
8 Incisors- cutting 4 canines- tearing 8 premolars- grinding 12 molars- grinding and crushing Total=32 teeth
composition of enamel?
What is enamel demineralized to?
95% hydroxyappitite
-Soluble calcium and phosphate
Most common organism that initiates dental carries; why?
Streptococcus mutans; able to metabolize sucrose more quickly than other oral bacteria
What is dental plaque biofilm?
adherent dental deposit which forms of tooth surface and composed almost entirely of bacteria derived from normal flora
What anatomical structures of the small intestine ⬆️ its surface area to ⬆️ absorption of nutrients?
1) Plicae circulates: permanent circular folds of mucosa
2) Villi: short, finger-like projections, cover entire mucosa ➡️villi covered with enterocytes (epithelium)
3) Microvilli: form brush-border on apical membrane of enterocytes
Where are the intestinal glands of the small intestine found? What is another name for these glands?
Between villi
Crypts of Lieberkuhn
Histology of small intestine:
Function of goblet cells? Location?
Secrete glycoprotein mucins ➡️ hydrated to form mucus
Interspersed among enterocytes covering villi
Histology of small intestine:
Function of Paneth cells? Location?
Innate immunity: Secrete lysozyme, phospholipase A2, and defensins ➡️ breakdown microorganisms & bacterial cell walls
Base of Crypts of Lieberkuhn (beneath stem cells)
Histology of small intestine:
Function of Enteroendocrine cells? Location?
Contain chemoreceptors, triggered by presence of nutrients ➡️ secrete various peptide hormones ➡️ regulate intestinal motility, secretion of enzymes, HCl, bile
Crypts of Lieberkuhn
What type of cell is primarily found in the duodenum? Function?
Brunner’s (duodenal) glands: secrete alkaline mucus to neutralize acidic chyme from stomach
What type of cell is primarily found in the ileum? Function?
M (microfold) cells: specialized epithelium in ileal mucosa ➡️ have basal membrane invaginations with intraepithelial lymphocytes (IELs) and APCs ➡️ endocytose antigens ➡️ transported to underlying lymphocytes and dendritic cells in Peyer patches
What is the arterial blood supply of the parts of the duodenum?
Celiac trunk: superior and descending parts of duodenum
Superior mesenteric artery: inferior and ascending parts of duodenum
What is the arterial blood supply of the jejunum and ileum?
Superior mesenteric artery ➡️ jejunal and ileal arteries ➡️ arterial arcades ➡️ vasa recta
What are the specialized lymphatic vessels of the small intestine, involved in fat absorption?
Lacteals
What are the two nerve plexuses of the GI tract? Where is each located?
Submucosal (Meissner’s) plexus: In submucosa
Myenteric (Auerbach’s) plexus: Between the inner circular layer and outer longitudinal layer of the muscularis
What are the anatomical parts of the duodenum?
Head (widest part)
Neck
Body
Tail
What are the two main ducts of the exocrine pancreas? How do they drain into the duodenum?
Main pancreatic duct: drains into duodenum via Ampulla of Vater ➡️ Sphincter of Oddi ➡️ major duodenal papilla
Minor (accessory) pancreatic duct: drains into duodenum via minor duodenal papilla
What is the arterial blood supply of the pancreas?
Pancreatic branches of the splenic artery
Head also supplied by superior & inferior pancreaticoduodenal arteries (branches of gastroduodenal and superior mesenteric arteries)
Describe the histology of the serous cells of the pancreatic acini.
Lack striated ducts
Each acinus has serous cells surrounding a very small lumen
Round basal nuclei
Numerous apical zymogen granules (contains enzymes & zymogens)
Describe the drainage of the pancreatic acini up to the main pancreatic duct.
Each acinus drained by short intercalated duct (simple squamous epithelium, initial portion consists of centroacinar cells) ➡️ intralobular ducts ➡️ interlobular ducts ➡️ joins main pancreatic duct ➡️
What is the volume of pancreatic secretions produce per day?
1.5 liters
What enzymes are secreted by the pancreas (active vs zymogens)?
Active: alpha-amylase, lipase, nucleases
Zymogens: procolipase, trypsinogen, chymotrypsinogen, proelastase, kalliekreinogen, procarboxypeptidase A & B
What makes up the aqueous component of pancreatic secretions? What cells secrete these components?
Na+, Cl-, K+, HCO3-
Centroacinar cells, duct cells
What stimulates enzymatic secretions from acinar cells in pancreas?
a.a., peptides, FAs in duodenum ➡️ stimulates Cholecystokinin (CCK) secretion from I cells ➡️ circulation ➡️ acts on CCKa receptors on acinar cells
Potentiated by Acetylcholine from vagus nerves ➡️ acts on muscarinic M3 receptors on acinar cells
What stimulates aqueous secretions from pancreatic duct cells?
H+ in duodenum ➡️ stimulate secretion of Secretin from S cells ➡️ circulation ➡️ binds to receptors on duct cells
Potentiated by CCK and secretin
What are the anatomical parts of the gallbladder?
Fundus
Body: main part
Neck: S-shaped bend, joins cystic duct
What is the arterial blood supply to the gallbladder by
cystic artery (usually arises from R hepatic artery)
What type of cells line the biliary tree up the common bile duct?
Cholangiocytes
Canals of Hering: simple cuboidal
Interlobular biliary ductules: simple cuboidal or columnar
Hepatic, cystic, common bile ducts: simple columnar
What type of epithelium lines the walls of the gallbladder?
Simple columnar epithelium
What is the length of the sphincter of Oddi?
What is its basal (resting metabolic) pressure?
4-6 mm
5-10 mmHg
What is the size of the bile salt pool in the body?
What is the amount of bile salts excreted in the feces each day?
2.5 g
~600 mg/day
Where in the GI tract is bile salts reabsorbed?
Ileum ➡️ returns to liver via enterohepatic circulation
What are the components of bile?
Bile acids Bile salts Electrolytes Water Phospholipids Cholesterol Bile pigments
What are the two bile acids made from cholesterol? What secondary bile acid is each converted to?
Cholic acid ➡️ deoxycholic acid
Chenodeoxycholic acid ➡️ lithocholic acid
What two amino acids are conjugated to secondary bile acids?
Glycine & taurine
What stimulates the gallbladder to secrete bile?
FAs in duodenum ➡️ stimulate I cells ➡️ secretion of CCK ➡️ circulation ➡️ binds to CCKa receptors on gallbladder
What hormone causes inhibition or slowing down of gastric emptying?
CCK
