RAT 17 Flashcards
what is the final product that exits the papillary ducts?
urine
what is obligatory water reabsorption?
water is “obliged” by osmosis to follow solutes that have been reabsorbed
what percentage of water reabsorption is due to obligatory water reabsorption?
85%
what is facultative water reabsorption?
adjusted by hormones to meet the body’s needs and maintain fluid homeostasis
what percentage of water reabsorption is due to facultative water reabsorption?
15%
how does an adjustment in water reabsorption impact urine concentration?
the kidneys adjust facultative water reabsorption to produce either dilute or concentrated urine
what is the osmolarity of plasma ?
300 mOsm
what is the osmolarity of filtrate in the renal capsule?
the filtrate that exists the blood and enter the renal tubule initially is iso-osmotic to the plasma at 300 mOsm
what happens to the osmolarity of the filtrate in the descending limb of the nephron loop? why?
becomes much more concentrated (~900 mOsm) because the descending limb is permeable to water but not solutes
what happens to the osmolarity of the filtrate in the ascending limb of the nephron loop? why?
concentration decreases ~100 mOsm because the ascending limb is impermeable to water, water cannot follow the movement of the solutes
where does facultative water reabsorption take place?
the last distal tubule and collecting sytsem
what type of urine is produced if there is little facultative water absorption?
dilute urine (< 300 mOsm)
what type of urine is produced if there is a lot of facultative water reabsorption?
concentrated urine (> 300 mOsm)
where in the nephron loop is the filtrate most concentrated?
at the turn of the nephron loop
where in the nephron loop is the filtrate most dilute?
ascending limb
when would you be likely to produce dilute urine? describe the appearance and volume of the urine.
- when ADH secretion is low
- volume increases, color = clear to light yellow
when would you be likely to produced concentrated urine? describe the appearance and volume of the urine.
- from “turning on” facultative water reabsorption in the principal cells of the later distal tubule and collecting system by the release of ADH
- less volume, color = dark yellow
what type of water reabsorption determines if urine is dilute or concentrated?
facultative water reabsorption
if water moves by osmosis, what is needed in order to produce a concentrated urine?
osmotic gradient
what is the medullary osmotic gradient?
- osmotic gradient within the renal medulla
- interstitial fluid = 300-400 mOsm
- cortex/medulla boarder = ~1200 mOsm
what creates and maintains the medullary osmotic gradient?
countercurrent mechanism (mechanism that involves fluids flowing in opposite directions that exchange material or heat)
what are the three components of the countercurrent mechanism?
- countercurrent multiplier system in the nephron loops of juxtamedullary nephrons
- recycling of urea in the medullary collecting ducts
- countercurrent exchanger in the vasa recta
which types of nephrons are the focus for this section? why?
juxtamedullary nephrons because within is found the countercurrent multiplier, which helps to establish the medullary osmotic gradient
what is the purpose of the countercurrent multiplier?
to help the kidneys conserve water and produce concentrated urine
what does the countercurrent multiplier do?
it pumps large amounts of NaCl into the interstitial fluid of the renal medulla to establish a concentration gradient
how does the countercurrent multiplier do this?
in the descending limb, water leaves so that NaCl is left behind in the filtrate, which can then be pumped out
does each step of the countercurrent multiplier occur in sequence?
no, its more like a pendulum continually swinging in a circle
what is the vasa recta? describe the path that it takes in the kidneys
- a special system of blood flow around the nephron loops of juxtamedullary nephrons to maintain the medullary osmotic gradient
- descend into the renal medulla, follow the hairpin turn, ascend toward the renal cortex
why does chemical digestion vary for each type of nutrient?
because digestive enzymes are specific for a single type of bond in a single type of nutrient
what type of reaction is catalyzed by most digestive enzymes?
hydrolysis reactions
where does carbohydrate digestion begin?
mouth
what is the enzyme that begins carbohydrate digestion and where is it produced?
- salivary amylase
- salivary glands
what reaction does salivary amylase catalyze?
breakdown of long polysaccharides into shorter oligosaccharides
what enzyme continues the process of carbohydrate digestion in the small intestine? where is it produced?
- pancreatic amylase
- pancreas
what reaction does pancreatic amylase catalyze?
reactions that breakdown the remaining polysaccharides into oligosaccharides
where are brush boarder enzymes located?
small intestine
name three brush boarder enzymes
- lactase
- maltase
- sucrase
what reactions do lactase enzymes catalyze?
digestion of the sugar lactose into glucose and galactose
what reaction do maltase and sucrase catalyze?
breakdown of oligosaccharides to disaccharides and monosaccharides
what are the three products of those reactions?
- glucose
- fructose
- galactose
once carbohydrates in the small intestine lumen are broken down into monosaccharides, how are they transported into the enterocyte?
- glucose and galactose are transported across the enterocyte’s apical membrane
- they must move against their concentration gradient
how are they transported out of the enterocyte on the basal side?
by the same facilitated diffusion mechanism
what happens next to the monosaccharides?
diffuse through the ECF and into the capillaries in the villus
what is the enzyme that begins protein digestion and where is it produced?
- pepsin
- chief cells of gastric glands
what reaction does pepsin catalyze?
reaction that digest proteins into smaller polypeptide, oligopeptides, and some free amino acids
where does the remainder of protein digestion occur?
small intestin
what enzymes aid the remainder of protein digestion?
pancreatic and brush boarder enzymes
why are the pancreatic enzymes released in an inactive form?
protect the pancreas from autodigestion