osmoregulation 4

Question 1

proximal tubule function

Answer 1

• most solute, salt, nutrient, and water reabsorption
• excretion of most toxins
• cells abundant with mitochondria and microvilla, specialized for energy-dependent solute transport

Question 2

loop of henle descending limb function

Answer 2

-water reabsorption

Question 3

loop of henle ascending limb

Answer 3

-solute reabsorption

Question 4

distal tubule

Answer 4

-reabsorption completed for most solutes, plus K+, H+ secretion

Question 5

collecting duct

Answer 5

• drains multiple nephrons
• carries urine to renal pelvis
• final osmotic balance

Question 6

what compounds are filtrated back out after reabsorption?

Answer 6

H+, NH4+, toxins, drugs, K+

Question 7

proximal tubule filtrate

Answer 7

• Na’s active transport out of prox tube cells allows cotransport of nutrients against their gradients out of lumen and into prox tube cells, with water following by osmosis
• 2/3 of water and NaCl are filtered by the proximal tubule; remaining filtrate is relatively high in wastes, low in nutrients, and reduced in volume

Question 8

loop of henle purpose

Answer 8

descending and ascending each differential create a countercurrent multiplier for reabsorption of both water at solutes

• accomplished via descending being permeable only to water, decreasing volume of urine and making it more concentrate (still a net loss of water back into body)
• ascending limb impermeable to water, and the concentrated urine allows reabsorption by diffusion gradient in ascending limb in lower portion, while solutes are actively transported in upper part, resulting in primary urine becoming more dilute

Question 9

countercurrent multiplier of loop of henle

Answer 9

• concentrated urine from water reabsoprtion at the descending limb allows reabsorption of solutes by diffusion gradient on the ascending limb
• this also results in low osmolarity near cortex, and high osmolarity deep in medulla

Question 10

distal tubule process

Answer 10

• hormones control final absorption of electrolytes and water, and final conc of urine in collecting ducts
• leaves mostly urea and other wastes in filtrate

Question 11

distal tubule hormones

Answer 11

• parathyroid hormone
• aldosterone
• vasopressin/ADH

Question 12

aldosterone

Answer 12

increases K+ secretion (Na/K ATPase, K channel; active if Na+ blood levels are low, causes reabsorption of NaCl into tissues, with water following by osmosis, reducing urine volume

Question 13

parathyroid hormone

Answer 13

increases Ca2+ reabsorption

Question 14

vasopressin/adh

Answer 14

-increases water reabsorption during dehydration by activating aquaporin expression

Question 15

struture of distal tubule and collecting duct

Answer 15

principal and intercalated cells, the latter containing microvilli, which maintaion acid-base regulation through excretion of H+ and bicarbonate

Question 16

collecting duct

Answer 16

• drains multiple nephrons
• carries urine to renal pelvis
• final osmotic balance
• further regulation of ion and water balance
• reabsorption of Na+
• K+ absorption or secretion
• pH balance
• urea reabsorption

Question 17

excretion/micturition

Answer 17

• after urine is produced, it leaves kidney and enters urinary bladder via ureters
• urine leaves bladder via urethra; schincters of smooth muscle control flow of urine out of bladder, which are controlled by spinal cord reflex arc

Question 18

hormones affecting kidney function

Answer 18

• steroids from adrenal gland, such as aldosterone, are slow response
• peptide hormones from hypo-pit axis like vasopressin are rapid response

Question 19

dietary factors that affect urine output

Answer 19

• diurectics=stim excretion of water

- antidiuretics=stim water reabsorption

Question 20

glomerular filtration rate

Answer 20

-determined by pressure across glomerular wall
-three forces: glomerular capillary hydrostatic pressure
2. bowman’s capsule hydrostatic pressure
3. oncotic pressure=osmotic pressure due to PROTEIN CONC. in blood
(pg 508)

Question 21

glomerular cap hydrostatic pressure determined by

Answer 21

cardiac output
systemic bp
efferent artery vasoconstriction

Question 22

bowman’s caopusle hydrostatic pressure is caused by

Answer 22

glom cap hydrostatic pressure

Question 23

oncotic pressure caused by

Answer 23

osmotic pressure due to protein conc in blood

Question 24

intrinsic regulators of GFR

Answer 24

1. myogenic regulation
2. tubuloglomerular feedback
3. mesangial control
4. pressure natriuresis

Question 25

myogenic regulation

Answer 25

- constriction/dilation of afferent arteriole via smooth muscle cells: - -as blood flow increases, bp increases, and there is increased hydrostatic gradient - in response afferent arteriole constricts, decreasing GFR, creating a -ve feedback loop to regulate GFR, as pressure is increased to increase GFR when it is lowered

Question 26

tubulorglomerular feedback

Answer 26

- juxtaglomerular apparatus (afferent arteriole); macula densa cells (distal tubule) controls diameter of afferent arteriole - they are positioned sidebyside so dilation/contriction of distal tubule will affect afferent arteriole

Question 27

mesangial control

Answer 27

- special smooth muscle cells regulate blood flow through caps - increased flow causes stretching, which increases permeability of the filter - results in changes in GFR independent of vascular effects

Question 28

pressure natriuresis

Answer 28

- small number of vessels penetrate the medulla of kidney without passing through a glomerulus - when BP increases, pressure of these vessels increases, renal interstitial hydrostatic pressure increases, reducing ability of tubule to recover solutes and water from primary urine, leading to more urine excretion and lowering of bp - thus creates a negative feedback loop on blood pressure and renal arterialpressure/filtration

Question 29

longterm mechanisms of GFR

Answer 29

- baroreceptor activation at SNS decreases MAP causes vasocontriction of aff/eff vessels, decreased GFR and increased recovery of Na+, water conservation and increase blood volume - decreased renal circ=increased peripheral resistance=increased MAP - endocrine hormones also control bf and gfr

Question 30

endocrine hormones involved in blood flow and GFR

Answer 30

angiotensin 2= vasoconstrictor, decreases GFR | -prostoglandin=vasodilator, increases GFR