4 week 20 Flashcards
what are the 4 key processes of the GI system?
- motility
- digestion
- absorption
- secretion
does food enter the pharynx or esophagus first?
pharynx
mucosa components (3)
- epithelial lining: contains absorptive, exocrine and endocrine cells
- lamina propria: connective tissue with small blood vessels, lymphatic vessels, nerves, lymphoid tissue
- muscularis mucosae: thin smooth muscle for mixing luminal
contents
submucosa components (3)
- thick layer of connective tissue that is distensible and elastic
- contains large blood vessels and lymphatic vessels
- submucosal plexus
muscularis externa components (2)
- smooth muscle: mixing luminal contents and moving it down the digestive tract (inner circular layer: changes diameter, outer longitudinal layer: changes length)
- myenteric plexus
serosa components (3)
- inner layer: connective tissue
- outer layer: epithelial tissue (mesothelium)
- mesothelium is continuous with mesenteries, which are continuous with peritoneum
diff bw upper and lower esophageal sphincters?
- upper = skeletal muscle
- lower = smooth muscle
what are the 4 parts of the stomach?
- fundum
- body
- antrum
- pylorus
functions of the…
a) rugae
b) chief cells
c) parietal cells
d) neck cells
a) ruggae: flatten to accommodate food
b) chief cells: secrete pepsinogen
c) parietal cells: secrete HCl
d) neck cells: secrete mucus
the stomach slowly empties chyme into the ____
small intestine
what are the secretions of the stomach? (5)
- pepsinogen: secreted by chief cells (precursor for pepsin which digests proteins)
- hydrogen ions: secreted by parietal cells (maintain acidity)
- intrinsic factor: secreted by parietal cells (necessary for absorption of vitamin B12)
- mucus: secreted from neck cells and cells on stomach surface (protects the stomach lining)
- gastrin (hormone): secreted from G cells
3 layers of the small intestine?
- duodenum
- jejunum
- ileum
what are villi? lacteals?
- villi: projections in small intestine that increase absorption
- lacteals: projections in villi that allow lymphatic drainage
functions of small intestine? (4)
- digestion of all types of nutrients
- main site of absorption of nutrients
- segmentation (mixes contents) and peristalsis (moving contents towards colon)
- releases hormones that regulate gastrointestinal activity and metabolism
how does food travel through the large intestine?
cecum -> ascending -> transverse -> descending colon
colon functions? (3)
- concentration of wastes into feces
- absorption of water
- storage of feces until defectaion
diff bw internal and external anal spinchter?
- internal = smooth muscle
- external = skeletal muscle
- relaxation of both sphincters necessary for defecation
ACCESSORY GLANDS: products are secreted via ___ into the lumen of the GI tract
ducts
which ions is saliva rich in? (1) what else does saliva contain? (3)
- bicarbonate ions
- mucus, salivary amylase (for carb digestion), lysozyme
PANCREAS: what do the following structures do…
a) duct cells
b) islet cells
c) acinar cells
a) secrete bicarbonate-rich fluid
b) secrete hormones
c) secrete enzymes
where does the pancreatic duct lead to?
to the duodenum (sphincter of oddi is there + controls entry of bile)
what is the pancreatic juice composed of? (4)
- bicarbonate (neutralizes chyme)
- pancreatic amylase and lipases
- proteases
- nucleases
functions of liver? (3)
- removal of old RBC
- secretes bile (bile salts and waste products e.g. bilirubin)
- processes and stores nutrients
describe how bile is made and where it travels (4)
- hepatocytes make bile
- secrete bile into bile canaliculi
- canaliculi drain into bile ducts
- bile ducts drain into common hepatic duct
- materials absorbed in the small intestine and colon travel to ___ first via the hepatic portal vein
- materials in the hepatic portal vein and are taken up by ___ or continue to the rest of the body via the ____.
- liver
- hepatocytes, hepatic vein
what does the gallbladder store?
bile
what carbs are polysaccharides (3)? disaccharides (3)?
- polysaccharides: starch, glycogen, cellulose (fiber)
- disaccharides: sucrose (gl + f), lactose (gl + ga), maltose (gl + gl)
brush border enzymes of the small intestine complete carbohydrate digestion. what are the 5 enzymes?
- dextrinase: limit dextrins → glucose
- glucoamylase: polysaccharides → glucose
- sucrase: sucrose → fructose + glucose
- lactase: lactose → galactose + glucose
- maltase: maltose → 2 glucose
describe how the absorption of monosaccharides occurs in small intestine
- maltase breaks maltose into 2 glucose
- glucose + galactose use sodium symporters (sodium goes down gradient, glucose + galactose go against)
- fructose uses glut 5 transporter (facilitated diffusion) into apical membrane… exits cells into blood via glut 2
- NaK ATPase keeps sodium balance
PROTEASES: what do endopeptidases vs exopeptidases do?
- endo = breaks into two
- exo = breaks one pieces off the end
where are proteases? (3)
- stomach
- pancreas (trypsin, chymotrypsin, carboxypeptidase)
- brush border (aminopeptidase, enterokinase)
protein digestion begins in the stomach. describe this process.
- pepsin starts breaking proteins down (acid cleaves pepsinogen to get pepsin)
- positive feedback loop
amino acid and di- and tripeptide absorption occurs in the ___. how does this occur?
- small intestine
- symporters bring them in
- within the cell, peptidases cleave di and tri into singles
- amino acid transporter transports them out of cells and into blood
- NaK ATPase provides gradient for this to be possible
T or F: lipids mix with stomach or intestinal contents
false
where does most fat digestion occur? how?
- small intestine
- bile salts emulsify fat (breaks fat globules into smaller ones)
- increases the surface area for further digestion by pancreatic lipase
what are bile salts?
- synthesized in liver from cholesterol
- hydrophilic and hydrophobic
how do fatty acids and monoglycerides get into the enterocyte? (2)
- diffuse into cell
- FA transporter
what happens after the fatty acids and monoglycerides get into the enterocyte? (4)
- they synthesize new triglycerides in smooth endoplasmic reticulum
- triglycerides combine with other lipids and proteins in the golgi apparatus to form chylomicrons
- chylomicrons leave the enterocyte via exocytosis and enter the lacteal
- chylomicrons travel via the lymphatics to the blood stream (can then be acted on by lipases, taken up by liver)
what is enterohepatic circulation? (3)
- bile salts initially made by liver
- stored in and released from gallbladder
- travel thru duodenum + ileum + capillaries
- end up in hepatic portal vein and travel back to liver
how are vitamins absorbed?
- fat soluble vitamins (ADEK): absorbed with lipids
- water soluble vitamins: require special transport proteins
- vitamin B12: absorbed in ileum only if bound to intrinsic factor
how are minerals absorbed?
- sodium: transporters, channels (mainly NaK ATPase)
- chloride: passively follows sodium
- potassium: passively absorbed mainly via paracellular route
- bicarbonate: passively absorbed in jejunum, secreted in exchange for chloride ions in ileum and colon
how are calcium and iron absorbed?
- CALCIUM
- mostly via paracellular route (NONREGULATED)
- also have calcium channels directly into cell
- cytosolic calcium levels influenced by calbindin (increases drive for calcium to enter cell) (REGULATED)
- calcium can exit cell via calcium ATPase
- …
- IRON
- transported in via symporter (DMT1)
- when iron is high, hepcidin is released which decreases ferroportin transporters to stop iron absorption
how is water absorbed?
passively (follows absorption of solutes by osmosis mainly via a paracellular route)
