Anatomy Flashcards
basic anatomy of the digestive tract
mouth esophagus stomach small intestine large intestine rectum anus
where does digestion begin?
in the mouth with alpha amylase in the saliva- breaks down starch into polysaccharides.
what is chewed food called?
bolus! : pushed into the esophagus by swallowing and then moved down the esophagus via peristaltic action.
does digestion occur in the esophogous?
no
how is chyme made?
stomach mixes and stores food reducing it to a semifluid mass called chyme .
important function of the stomach is to start protein digestion with the enzyme pepsin.
what are the four major cell types in the stomach?
- mucous cells
- chief (peptic cells)
- parietal cells
- G cells.
what do the mucous cells do?
line the stomach wall , lubricate the stomach walll so that food can slide along its surface without causing damage and mucous protects the epithelial lining from the acidic env of the stomach.
what do the chief cells do?
are found deep in the exocrine glands. they secrete pepsinogen , which is a zymogen precursor to pepsin. pepsinogen is activated to pepsin by the low pH of the stomach . once activated pepsin begins protein digestion
what do the parietal cells do?
secrete HCL
they also secret intrinsic factor which helps the ileum absorb B12
What do the G cells do?
secret gastrin. gastrin is a peptide hormone which stimulates parietal cells to secrete HCL.
what are the major hormones that affect the secretion of the stomach juices?
acetylcholine- increases the secretion of all cell types
gastrin
histamine
gastrin and histamine mainly increase HCL secretion.
about 90% of the digestion and the absorption occurs in the ?
small intestine.
the SI is divided into 3 parts , from smallest to largest : duodenum, jejunum and ileum.
most of the digestion occurs in which part of the SI?
duodenum
where does most of the absorption occur?
jejunum and ileum.
the SI wall has finger like projections called villi
villi inc the SA allowing for greater digestion and abs .
on the apical surface (lumen side) surface of the cells of each villus are much smaller finger like projections called microvilli
the microvilli inc the SA of the intestinal wall still further.
under the microscope the microvilli appear as a fuzzy covering which is called the brush border. the brush border has membrane bound digestive enzymes.
goblet cells in the intestine are epithelial cells
they secrete mucus to lubricate the intestine and help protect the brush border from mechanical and chemical damage.
the semifluid chyme is squeezed out of the stomach thru the pyloric spinster and into the duodenum. the fluid inside the duodenum has a pH of 6 mainly due to bicarb ion secreted by the pancreas.
pancreas also acts as an exocrine gland releasing enzymes through the pancreatic duct into the duodenum
the major enzymes released by the pancreas are:
trypsin chymotrypsin pancreatic amylase lipase ribunuclease deoxyribonuclease all enzymes are released as zymogens . trypsin is activated by the enzyme enterokinase located in the brush border. activated trypsin then activates other enzymes
trypsin and chymotrypsin do what?
degrade proteins into small polypeptides.
what does pancreatic amylase do?
like salivary amylase, it hydrolyzes polysaccharides into disaccharide and trisaccharides. however the pancreatic amylase is much more powerful.
what does lipase do?
breaks down fat, specifically triglycerides.
where is bile made and stored?
made in the liver and stored in the gall bladder.
the gall bladder releases bile though the cystic duct, which empties into the common bile duct shared with the liver.
what does bile do?
emulsify the fat. this inc the SA of the fat, allowing the lipase to degrade it .
what does bile contain?
bilirubin! - end product of hemoglobin breakdown. much of the bile is reabsorbed by the small intestine and is transported back to the liver.
the large intestine or the colon has 4 parts:
ascending colon, transverse colon , descending colon, sigmoid colon
what are the major function of the large intestine?
water absorption , electrolyte absorption
when this function fails, diarrhea occurs.
the large intestine has Ecoli , what does E coli do?
produces Vitamin K, B12, thiamin and riboflavin
what local peptide hormones are secreted by the small intestine after a meal?
secretin
cholecystokinin
gastric inhibitory peptide
each of these hormones inc blood insulin levels esp in presence of glucose.
what does the gastric inhibitory peptide do?
is released in response to fat and protein digestates in the duodenum and to a lesser extent in response to carbs.
what causes secretin release?
HCL in the stomach!
secretin stimulates sodium bicarb secretion by the pancreas
what causes the release of cholecystokinin?
food in the upper duodenum. especially fat digestates
cholecystokinin causes gallbladder contraction and pancreatic enzyme secretion.
it also decreases the motility of the stomach allowing the duodenum more time to digest fat.
enterokinase does what?
converts trypsinogen to trypsin
what does lactase do?
converts lactose into galactose and glucose.
what does sucrase do?
converts sucrose to fructose and glucose.
can cellulose be digested by humans?
no
how is glucose absorbed?
by secondary active transport down the concentration gradient of sodium. sodium is actively pumped out of the enterocyte on the basolateral side. the low sodium in the enterocyte drags sodium into the cell through a transport protein, but only after glucose has also attatched itself to the protein. as the concentration of the glucose builds inside the cell, it moves out of the cell on the basolateral side via facilitated transport. at high concentrations of lumen plc, glucose builds up in the paracellular space and raises the osmotic pressure there. the aqueous solution of the lumen is dragged into the paracellular space pulling glucose along with it. glucose is abs by this second method only when present in high concentrations
all carbs are absorbed into the bloodstream and carried by the portal vein to the?
liver ! : whose job is to maintain constant glucose level.
in all cells except ___ glucose is transported from high concentration to low concentration via facilitated diffusion
except enterocytes and cells of the renal tubule
when glycogen stores are full, glucose is converted to
fat - long term form of energy storage
where does the conversion of glucose to fat take place?
in the liver and adipocytes and stored in the adipocytes
fat is insoluble in water so requires a carrier ..
which can be a lipoprotein or albumin
what are the 4 types of lipoproteins ?
very low density lipoproteins
intermediate density lipoproteins
low density lipoproteins
high density lipoproteins
all are made from triglycerides, cholesterol , phospholipids and protein.
as the density increases the amount, the amount of triglycerides decrease .
the very low density triglycerides have a lot of triglycerides.
fats are broken down into?
monoglycerides! and then put back together again into triglycerides.
The liver receives blood from?
beds of the intestines, stomach, spleen and pancreas via the hepatic portal vein. this blood is worked upon by the liver. a second blood supply which oxygenates the liver is received through the hepatic artery
all blood recieved by the liver moves through large flattened spaces called hepatic sinusoids and collects in the hepatic vein , which leads to ..?
vena cava
what are the functions of the liver?
blood storage : liver can expand to act as a blood reservoir for the body
blood filtration: kupffer cells phagocytize bacteria picked up from the intestines
carb metabolism
fat metabolism: liver makes bile from cholesterol and coverts carbs and proteins into fat. it oxidizes fatty acids for energy and forms most lipoproteins
protein metabolism: dominates aa, forms urea from ammonia , makes plasma proteins like fibrinogen, prothrombin, albumin, and most globulins and it makes non essential aa.
detoxification: detoxified chemicals are excreted by the liver as part of bile or polarized so the kidney can remove them
erythrocyte destruction : kupffer cells also destroy irregular erythrocytes, but most irregular erythrocytes are destroyed by the spleen
vitamin storage: vitamin A,D B12. liver also stores iron combining it with protein apoferritin to form of ferritin.
what happens when the liver mobilizes fat for energy?
it makes acids called ketone bodies! this often results in condition called ketosis or acidosis.
so know that when the liver moves fat or protein for energy the blood acidity will increase.
