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MCAT Biology Lecture 6

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digestive tract anatomy
mouth, esophagus, stomach, small intestine, large intestine, rectum, anus
subsets of small intestine
duodenum, ileum, jejunum
subsets of large intestine
ascending colon, transverse colon, descending colon, sigmoid colon
mouth
salivary amylase (alpha amylase) breaks down starch chains. Chewing increases surface area of food.
esophagus
moves chewed food (bolus) to stomach via peristaltic action.
chyme
mixture of semifluid mass of food in stomach
cells of exocrine glands of stomach
mucous cells - mucous lines stomach wall to protect from acid, food
chief cells - secrete pepsinogen, activated by low PH
parietal cells - secrete HCl, taking alot of energy
G cells - secrete gastrin, which stimulates parietal cell HCl production
small intestine
villi contain capillary network and lymph vessel called lacteal. Microvilli cover apical side of 'enterocytes', forming brush border--contains digestive enzymes. Goblet cells secrete mucus to lubricate intestine.
bile
released by liver stored in gallbladder. emulsifies fat, physically breaking into small particles.
pancreatic enzymes
trypsin - degrade proteins to small polypeptides
chymotrypsin - same as trypsin
amylase - polysaccharides to di, tri
lipase - degrades fat, triglycerides.
large intestine function
water absorption, electrolyte absorption. E. coli producing vitamins in gut.
random ideas about digestion
food may move too fast through digestive tract... enzymes to counter this. stomach stores for constant level of digestion. gastrointestinal hormones regulate speed for these reasons.
urea
byproduct of gluconeogenesis from proteins
glyconeogenesis
formation of glycogen from nonglucose precusors.
7 functions of the liver
1. blood storage
2. blood filtration, bacteria phagocytized
3. carbohydrate metabolism
4. fat metabolism, synthesizes bile, creates fat.
5. protein metabolism, deaminates AAs, forms urea.
6. detoxification
7. erythrocyte destruction, assists spleen in destroying RBCs
renal corpuscle
consists of
glomerulus: first capillary bed in nephron
Bowman's capsule: where filtrate collects after being forced through fenestrations
net result of proximal tubule
reduce amount of filtrate in nephron while changing the solute composition without changing osmolarity.
distal tubule
reabsorbs Na+, Ca+. secretes K+ H+ HC03-. Lowers filtrate osmolarity. ADH creates more permeable cells, water leaves filtrate making it more concentrated.
juxtaglomerular apparatus
monitors filtrate pressure in distal tubule. secretes renin, which ultimately makes adrenal cortex make aldosterone. aldosterone acts on tubule, creating Na+ absorbtion and K+ secretion proteins.
nephron function details
renal corpuscle - filtration
proximal tubule - reabsorption, secretion
loop of Henle - concentrate solute in medulla
distal tubule - empties into collecting duct
collecting duct - concentrates urine
enterocytes
cells exposed to lumen of intenstine, in villi. Absorb and break down small polymers, di and tri.
glycogenolysis
break down of glycogen into glucose, in liver.
albumin
carrier molecule to move fatty acids through blood, can take up to 30 but usually takes 3 FAs.
result of liver mobilizing fat or protein for energy
blood acidity goes up, metabolizing those elements produces acids.
3 functions of kidney
1. execrete waste products, urea, uric acid, ammonia, phosphate
2. maintain moneostasis of body fluid and solute
3. help control plasma pH
Urine path
kidney outer cortex, kidney inner medulla. Urine created by kidney goes to renal pelvis, emptied into ureter, goes to bladder. Bladder drained by urethra.
nephron
functional unit of kidney
proximal tubule
where reabsorption takes place, glucose, proteins and other solutes leave proximal tubule by 2ndary active transport.
drugs, toxins etc secreted into filtrate by prox tubule.
loop of Henle
dips into medulla, increases solute concentration and osmotic pressure of medulla.
collecting duct
distal tubule empties into CD, which carries it into medulla. IF ADH in medulla, it makes duct permeable to water, so water diffuses into medulla.
ducts empty into renal calyx and finally renal pelvis.
descending loop of Henle vs ascending
permeable to water vs impermeable to water.

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