Chapter 18 - Renal Function Flashcards
name main functions of urinary system
regulate plasma ionic composition, regulate plasma volume and blood pressure, regulate plasma osmolarity, regulate plasma pH (through HCO3, H+), remove metabolic waste products and foregin substances (urea, uric acid, drugs), and kidneys ultimately control v olume and composition of all body fluids
describe kidneys as endocrine organs
secrete erythropoietin, secrete renin, turns vitamin D into its active form, gluconeogenesis takes place in them
describe basic function of: kidneys, ureters, bladder, and urethra
Kidneys - form urine, ureters - transport urine from kidneys to bladder, bladder - stores urine, urethra - excretes urine from bladder to outside of body
describe macroscopic appearance of kidneys
paired, and bean shaped. approximate size of fist (115-170 grams), retroperitoneal
what is a nephron
the functional unit of the kidney. there are 1 X 10^6 in each kidney. composed of renal corpuscle and renal tubules
describe renal corpuscle
the glomerulus is a capillary network for filtration, while the bowman’s capsule receives the filtrate and provides inflow to renal tubules
describe renal tubules
consists of proximal convoluted tubule, loop of Henle (descending limb, thin ascending limb, and thick ascending limb), distal convoluted tubule, and collecting duct
compare cortical vs juxtamedullary nephrons
cortical nephrons are the majority (80-85%) and have a short loop on Henle. juxtamedullary nephron has a long loop of Henle that extends deep into medulla, it is responsible for maintaining medullary osmotic gradient, and produces concentrated urine. both types of nephrons produce urine
describe the juxtaglomerular apparatus
contains macula densa cells in the wall of the distal tubule (sense Na content in tubular fluid). and contains juxtaglomerular cells (granular cells) in the wall of afferent arteriole (secrete renin). juxtaglomerular apparatus is important in regulating blood volume and blood pressure
describe blood supply to kidneys
renal artery enters each kidney at hilus, kidneys receive 20% of cardiac output at rest (CO at rest = 5L Kidneys receive 1L/min). renal vein exits from each kidney at hilus
describe basic renal exchange process
- glomerular filtration: from glomerulus to bowman’s capsule 2. reabsorption: from tubules to peritubular capillaries 3. secretion: from peritubular capillaries to tubules. finished urine is excreted from tubules out of the body
describe GFR
glomerular filtration rate is the bulk flow of protein-free plasma from glomerular capillaries into bowman’s capsule. normal GFR is 125ml/min or 180L/day
describe the filtration barrier
glomerular filtrate must cross three barriers to enter bowman’s capsule: capillary endothelial layer, basement membrane, and epithelial layer of bowman’s capsule.
name the four starling forces
glomerular capillary hydrostatic pressure, bowman’s capsule osmotic pressure, bowman’s capsule hydrostatic pressure, and glomerular capillary osmotic pressure
describe starling forces favoring filtration
glomerular capillary hydrostatic pressure (60 mm Hg high due to resistance of efferent arteriole) and bowman’s capsule osmotic pressure (0mm Hg low due to lack of protein in filtrate)
describe starling forces opposing filtration
bowman’s capsule hydrostatic pressure (15 mm Hg relatively high due to large volume of filtrate in closed space) and glomerular osmotic pressure (29 mm Hg higher than in systemic capillaries due to plasma proteins in smaller volume of plasma)
describe glomerular filtration pressure
(Pgc + osmoticbc) - (Pbc - osmoticgc) = 16 mm Hg. combination of starling forces favors net filtration, there is always net filtration at glomerulus
compare filtration pressure and GFR to systemic capillary filtration pressure and rate
GF pressure is 16 mm Hg and GFR is 180L/day while systemic filtration pressure is 2 mm Hg and filtration rate is 20L/day
describe filtration fraction
filtration fraction = GFR/renal plasma flow. normal renal plasma flow is 625mL/min. normal GFR is 125ml/min. so normal filtration fraction is 125/625 = 20%
how much plasma is leaving /min in the efferent arteriole
500mL/min because of the 125 mL/min of filtrate
describe filtered load
filtered load is the quantity of a solute that is filtered per unit time. this involves solutes that are freely filterable. it depends on concentration of solute and GFR. filtered load = GFR X Px (plasma concentration)
give an example of filtered load
filtered load of glucose: GFR = 125mL/min plasma [glucose] = 100mg/dL = 1mg/mL so filtered load of glucose is 125ml/min X 1mg/mL = 125mg/min
how much of GFR is excreted as urine
180L fluid filtered/day and only 1.5L of urine excreted/day (<1%) so >99% of filtered fluid is reabsorbed. GFR is highly regulated: intrinsic mechanism is autoregulation and it is also under extrensic control
describe effect of mean arterial pressure on GFR
GFR is regulated independently from MAP. GFR is kept relatively constant over wide range of MAP due to intrinsic regulation
describe myogenic regulation of GFR
smooth muscle in wall of afferent arteriole contracts in a response to stretch
describe tubuloglomerular feedback
macula densa cells secrete paracrine factors in response to an increase in flow of fluid past them. smooth muscles of arterioles contract in response to these paracrines
describe extrinsic control of GFR and renal vascular resistance during fluid loss due to hemorrhage or sweating
MAP falls below normal levels as a result of hemorrhage or heavy sweating. intrinsic mechanisms are not able to prevent GFR from changing
what is reabsorption
movement of solutes from tubules into peritubular capillaries (returned to blood). most occurs in proximal tubules and most is not regulated
where does solute reabsorption take place
mainly in proximal convoluted tubules but some occurs in distal convoluted tubules.
describe barrier for reabsorption
epithelial cells of renal tubules are primary barrier while the endothelial cells of capillaries are only a minor barrier due to capillaries being leaky here
describe Y reabsorption
facilitated diffusion into tubule epithelial cell and active diffusion into capillary endothelial cell
describe X reabsorption
active diffusion into tubule epithelium and facilitated diffusion into capillary endothelium
describe water reabsorption
water reabsorption follows the active reabsorption of solutes from region of lower osmolarity (in tubule) to region of greater osmolarity (in blood plasma)
what is transport maximum
rate of transport when carriers are saturated
what is renal threshold
for a solute that is normally 100% reabsorbed if solute in filtrate saturates carriers, then some solute is excreted in urine thus the renal threshold is the plasma concentration of a solute at which it “spills over” into urine
describe glucose reabsorption
at the apical membrane of tubule epithelium is secondary active transport. at basolateral membrane it is facilitated diffusion
describe renal handling of glucose
plasma [glucose] = 100 mg/dL. filtered load glucose = 125mg/min. transport maximum for glucose reabsorption = 375mg/min. theoretical renal threshold = 300 mg/dL. GFRx renal threshold = transport maximum. actual renal threshold is 160-180 mg/dL and filtered load = 225 mg/min
what happens in untreated diabetes mellitus
blood glucose levels increase, glucose filtered load increases, glucose not reabsorbed will increase osmotic pressure to keep water in renal tubules, glucose and more water excreted in urine, increased urine volume = diuresis
describe secretion
solute moves from peritubular capillaries into tubules, barriers are the same as for reabsorption, transport mechanisms are the same, but in the opposite direction.
name 5 secreted substances
potassium, hydrogen ions, choline (waste), creatinine (waste), and penicillin (foreign substances)
what is regional specialization of renal tubules
specific tubules perform specific functions: proximal tubules - nonregulated reabsorption, distal tubules and collecting ducts - regulated reabsorption and secretion, loop of Henle - water conservation
describe proximal tubules reabsorption
proximal tubule is the mass reabsorber: 70 % sodium and water 100% glucose. brush border provides for large surface area. leaky tight junctions allow paracellular (between cells) transport
describe reabsorption and secretion in distal tubules and collecting ducts
transport is regulated across epithelium. tight junctions limit paracellular transport. tubular cells express receptors for hormones that regulate transport of water and solutes
describe water conservation in loop of Henle
loop of Henle establishes conditions necessary to concentrate urine and thus minimizes water loss
what is equation of amount of substance excreted
amount filtered + amount secreted - amount reabsorbed
what 3 factors does amount excreted depend on
filtered load, secretion rate, and reabsorption rate
describe renal handling of a solute
if amount of solute excreted per minute is less than filtered load then solute was reabsorbed (net reabsorption), if amount of solute excreted per minute is greater than filtered load then solute was secreted (net secretion)
what is clearance
volume of plasma from which a substance has been completely removed by kidneys per unit time (volume of plasma that contains the amount of a substance that has been excreted per unit time)
how is GFR determined in relation to insulin
clearance of substance freely filtered and neither reabsorbed nor secreted = GFR. amount of insulin excreted in urine = amount that was filtered = filtered load. excreation rate = filtered load = GFR x Pi. so clearance = GFR x Pi / Pi = GFR
describe estimate of GFR using clearance of creatinine
this is clinically suitable. creatinine is by-product of muscle metabolism that is produced in body continuously. it is freely filtered and not reabsorbed and only small amount secreted. the clearance estimate of GFr is a little greater than actual GFR: 140ml/min
describe determination of fate of solutes in renal tubules using clearance
if Cx > GFR then substance was secreted. if Cx < GFR, then substance was reabsorbed
describe micturition
micturition is urination. urine forms in renal tubules, fluid drains into renal pelvis and into ureter, ureters lead to bladder, and bladder stores urine until it is excreted
describe pathway of micturition reflex
+ volume of fluid in bladder leads to expansion of wall and activation of stretch receptors. - sympathetic activity relaxes internal urethral sphincter and + parasympathetic activity contracts detrusor muscle leading to opening of internal urethral sphincter. at the same time - somatic motor neuron activity relaxes external urethral sphincter which opens external urethral sphincter. with both sphincters open micturition takes place
