Renal Physiology Flashcards
what is the nephron?
the nephron is the individual tubular structure, functional unit of the kidney. It produces urine- by the time urine leaves the nephron it is fully formed
The main vasculature is the glomerulus (capillary cluster)
describe nephron vasculature
the efferent arteriole brings blood to the glomerulus. once blood is done with the glomerulus it exits through the afferent arteriole.
how do kidneys contribute to osmotic regulation
they manage water and salt excretion and maintain total body water.. regulation of water and ions occurs in the nephrons
describe water regulation in humans
water enters via ingestion and cellular metabolism.
digestive tract has water resorption and secretion. some is excreted in fecal matter
sweating gets rid of some body water
renal tubules filter, secrete and reaborb, and control urine excretion.
to keep input = output, the renal tubules can regulate how much is excreted and how much is kept
three main transport processes of the nephron
glomerular filtration
tubular reabsorption
tubular secretion
(FRESh)
what are the three basic processes of urine formation
glomerular filtration
reabsorption
secretion
what is glomerular filtration
blood pressure forces water and solutes across the wall of the glomerular capillaries and into the capsular space
what is reabsorption
the removal of water and solutes from the filtrate, and their movement across the tubular epithelium and into the peritubular fluid
what is secretion
the transport of solutes from the peritubular fluid, across the tubular epithelium, and into the tubular fluid
where do nephrons exist within the kidney?
mostly in the renal cortex, but can stretch down into the medulla
describe cortical nephrons
majority of the nephrons
exist in the cortex
short loop of henle (makes sense- cortex is thinner)
perform most absorptive and secretory functions of the kidney
describe juxtamedullary nephrons
minority of neprhons
long loops of henle, stretch down into the medulla
important in producing concentrated urine (along with vasa recta)
where does the neprhon’s papillary duct empty into?
the minor calyx
describe the tubular structure of a nephron
(from entering to urine excretion)
the renal corpuscle (With the bowman’s capsule), and then the proximal convoluted, then distal convoluted tubules. empty into collecting duct.
describe the variation seen in vertebrate nephrons
structure and dimensions vary, but theres all specialized resorption/secretion regions, and theyre in the same arrangement.
what is the renal corpuscle
contains the glomerulus and bowman’s capsule. produces filtrate. afferent arteriole feeds in, efferent feeds out.
what is the proximal convoluted tubule
tubule closest to corpuscle.
reabsorption of water, ions and organic nutrients.
what is the nephron loop?
also called loop of henle.
further reabsorption of water in the thin descending limb (you only drink water to stay thin, weight goes down)
and sodium and chloride ions in ascending limb (Salty foods make you fat, your weight goes up)
what is the distal convoluted tubule?
tubule farthest from corpuscle. (in the distance)
secretion of ions, acids, drugs, toxins. variable reabsorption of water, Na+, Ca2+ (under hormonal control)
what is the collecting duct
variable reabsorption of water and reabsorption/secretion of Na+, K+, H+, HCO3-
what is the papillary duct
delivers urine to minor calyx
how does filtration occur at the glomerulus?
blood pressure forces water and solutes across the walls of the glomerular capillaries into capsular space
walls retain blood cells and large macromolecules, liquids and small solutes leak into lumen of bowman’s capsule by getting through the foot processes. they’re very leaky capillaries. mesangial cells control blood pressure and filtration. (between capillaries)
fitrate flows from bowman’s capsule into proximal tubule.
what is the function of podocytes?
they are around the glomerular capillaries to prevent large proteins from leaving the blood and help with managing filtration
describe GFR
glomerular filtration rate is the amount of filtrate the kidneys produce each minute. as filtrate passes through tubules, 99% is absorbed, the rest is excreted as urine.
describe the transport across the proximal convoluted tubule
majority of filtrate volume is reabsorbed into the blood, including organic substrates and Na+/Cl-
Na+ enters the tubular cells via diffusion, co/counter transport. it is then pumped via Na/K pump into peritubular fluid.
cotransporter for glucose and other organic solutes via secondary active transport
solutes like Cl can diffuse
water is osmosis.
H+ secreted
describe the transport mechanisms of the loop of henle
reabsorbs 25% of water, and 20-25% of the Na/Cl ions
K+ leaves
thin descending loop reabsorbs water
thick ascending loop is active Na transport and diffusion of Cl
how does the countercurrent work in the loop of henle?
descending limb is permeable to water. this makes water reabsorption easier, and volume of the primary urine decreases. this makes it more concentrated as it moves along. the thin limb is only permeable to water, because the outside is less concentrated than the inside. (comes in, lots of salt out (bc of activity next to it in ascending limb. so water gets out)
the ascending limb is were ions are reabsorbed, primary urine dilutes.
because the urine entering is more concentrated, the ions leave into the peritubular space along the concentration gradient, which pulls them out and dilutes primary urine.
reabsorbed ions accumulate in interstitial fluid, which helps with this osmotic gradient.
it efficiently reabsorbs water and ions, and maintains a concentration gradient to keep this passive reabsorption of water from tubular fluid into collecting duct area (next to ascending loop. basically ascending loop pulls water out of the tubes next to it just by functioning and pulling salts out)
describe the transport mechanisms across the distal convoluted tubule
reabsorption is not regulated in the proximal, it is in the distal.
reabsorbs a variant amount under antidiuretic hormone stim.
also reabsorbs sodium ions under aldosterone stimulation from adrenal cortex, and Cl- (cotransport)
under direction of calcitonin, Ca2+ is reabsorbed.
K+ leaves
what is absorbed and secreted at the proximal tubule ?
reabsorbed
Na, Cl, K, Ca, HCO3, water , glucose,, amino acids, vitamins, urea, chlorine
secrete
H
what is reabsorbed and secreted at loop of henle?
reabsorbed - descending
water
reabsorbed - ascending
Na, Cl, K, Mg, Ca
secreted
none
what is reabsorbed and secreted in the distal tubule?
reabsorbed
Na, Ca, Cl, water
secreted
K H
what is reabsorbed and secreted at the collecting duct?
reabsorbed
Na, K, Cl, Ca, HCO3, H, urea, water
secreted
K, H
how is urinary function regulated?
hormones affect kidney function
- steroid hormones like aldosterone, slow response
- peptides hormones like antidiuretic hormone (rapid response)
dietary factors also affect urine output
- diuretics: stimulate excretion of water (more secretion)
- antidirectics: reduce excretion of water (more reabsorption) (anti-piss)
how do nephrons contribute to acid-base balance?
acid secretion and bicarbonate reabsorption is an active process (Na/K pump, H pump both need ATP)
H and HCO3 transport is linked to Na and Cl transport (Na/H exchanger, Cl/HCO3 exchanger, Na/HCO3 cotransporter)
CA is expressed in epithelial cells, so CO2 can be source of secreted acid.
acid base regulation of blood and interstitial fluid is very dependent on renal/respiratory systems.
acid-base regulation in air breathers (inputs, outputs, effects?)
too acidic, nervous system depresses, coma. too basic, nervous system is overly excitable and muscles are tetanus-prone.
inputs
diet- proteins and fats have acid
metabolism- CO2, lactic and keto acids
outputs
H+ from kidneys (renal system slowly excretes H+ and HCO3)
CO2 from lungs (respiratory system rapidly changes breathing to alter expiration of CO2)
what determines fluid and solute movement across capillaries?
the pressure across the glomerular wall
3 forces:
- glomerular capillary (blood) hydrostatic pressure
- bowman’s capsule (lumen) hydrostatic pressure
- blood oncotic (osmotic) pressure
oncotic tends to push things into blood, hydrostatic tends to push things into lumen
