Renal Physiology

Question 1

what is the nephron?

Answer 1

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)

Question 2

describe nephron vasculature

Answer 2

the efferent arteriole brings blood to the glomerulus. once blood is done with the glomerulus it exits through the afferent arteriole.

Question 3

how do kidneys contribute to osmotic regulation

Answer 3

they manage water and salt excretion and maintain total body water.. regulation of water and ions occurs in the nephrons

Question 4

describe water regulation in humans

Answer 4

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

Question 5

three main transport processes of the nephron

Answer 5

glomerular filtration
tubular reabsorption
tubular secretion
(FRESh)

Question 6

what are the three basic processes of urine formation

Answer 6

glomerular filtration
reabsorption
secretion

Question 7

what is glomerular filtration

Answer 7

blood pressure forces water and solutes across the wall of the glomerular capillaries and into the capsular space

Question 8

what is reabsorption

Answer 8

the removal of water and solutes from the filtrate, and their movement across the tubular epithelium and into the peritubular fluid

Question 9

what is secretion

Answer 9

the transport of solutes from the peritubular fluid, across the tubular epithelium, and into the tubular fluid

Question 10

where do nephrons exist within the kidney?

Answer 10

mostly in the renal cortex, but can stretch down into the medulla

Question 11

describe cortical nephrons

Answer 11

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

Question 12

describe juxtamedullary nephrons

Answer 12

minority of neprhons
long loops of henle, stretch down into the medulla
important in producing concentrated urine (along with vasa recta)

Question 13

where does the neprhon’s papillary duct empty into?

Answer 13

the minor calyx

Question 14

describe the tubular structure of a nephron

Answer 14

(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.

Question 15

describe the variation seen in vertebrate nephrons

Answer 15

structure and dimensions vary, but theres all specialized resorption/secretion regions, and theyre in the same arrangement.

Question 16

what is the renal corpuscle

Answer 16

contains the glomerulus and bowman’s capsule. produces filtrate. afferent arteriole feeds in, efferent feeds out.

Question 17

what is the proximal convoluted tubule

Answer 17

tubule closest to corpuscle.
reabsorption of water, ions and organic nutrients.

Question 18

what is the nephron loop?

Answer 18

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)

Question 19

what is the distal convoluted tubule?

Answer 19

tubule farthest from corpuscle. (in the distance)
secretion of ions, acids, drugs, toxins. variable reabsorption of water, Na+, Ca2+ (under hormonal control)

Question 20

what is the collecting duct

Answer 20

variable reabsorption of water and reabsorption/secretion of Na+, K+, H+, HCO3-

Question 21

what is the papillary duct

Answer 21

delivers urine to minor calyx

Question 22

how does filtration occur at the glomerulus?

Answer 22

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.

Question 23

what is the function of podocytes?

Answer 23

they are around the glomerular capillaries to prevent large proteins from leaving the blood and help with managing filtration

Question 24

describe GFR

Answer 24

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.

Question 25

describe the transport across the proximal convoluted tubule

Answer 25

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

Question 26

describe the transport mechanisms of the loop of henle

Answer 26

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

Question 27

how does the countercurrent work in the loop of henle?

Answer 27

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)

Question 28

describe the transport mechanisms across the distal convoluted tubule

Answer 28

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

Question 29

what is absorbed and secreted at the proximal tubule ?

Answer 29

reabsorbed
Na, Cl, K, Ca, HCO3, water , glucose,, amino acids, vitamins, urea, chlorine

secrete
H

Question 30

what is reabsorbed and secreted at loop of henle?

Answer 30

reabsorbed - descending
water

reabsorbed - ascending
Na, Cl, K, Mg, Ca

secreted
none

Question 31

what is reabsorbed and secreted in the distal tubule?

Answer 31

reabsorbed
Na, Ca, Cl, water

secreted
K H

Question 32

what is reabsorbed and secreted at the collecting duct?

Answer 32

reabsorbed
Na, K, Cl, Ca, HCO3, H, urea, water

secreted
K, H

Question 33

how is urinary function regulated?

Answer 33

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)

Question 34

how do nephrons contribute to acid-base balance?

Answer 34

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.

Question 35

acid-base regulation in air breathers (inputs, outputs, effects?)

Answer 35

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)

Question 36

what determines fluid and solute movement across capillaries?

Answer 36

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