Lecture 28 Kidneys

Question 1

Functions of the Kidneys

Answer 1

1. osmoregulation = water and solute balance (ECF osmolarity -290mOsm and volume total H20
2. ion (electrolyte) balance (Na+, K+, Ca2+, etc.)
3. acid-base regulation (H+, HCO3-)
4. excretion - urea + other soluble waste products
5. endocrine function - erythropoietin

Question 2

Regions

Answer 2

Cortex
medulla
renal pelvis -> ureter

Question 3

Nephron

Answer 3

functional unit of the kidney

Question 4

Renal corpuscle

Answer 4

glomerulus

glomerular (Bowman’s) capsule

Question 5

Renal Tubule

Answer 5

proximal convoluted tubule (PCT)
loop of Henle - descending limb, ascending limb
distal convoluted tubule
collecting duct

Question 6

Blood Supply

Answer 6

glomerulus - afferent arteriole
glomerular capsule- efferent arteriole
renal tubule- peritubular capillaries
PCT - vasa recta

Question 7

cortical nephrons

Answer 7

mostly in cortex, short loops of henle

Question 8

juxtamedullary nephrons

Answer 8

long loops of Henle extend deep into the medulla

Question 9

three primary processes of the Nephron

Answer 9

filtration
reabsorption
secretion

Question 10

Filtration: Glomerulus and Glomerular Capsule

Answer 10

formation of protein-free filtrate

filtrate contains H20 + small to medium sized solutes (ions, glucose, urea, etc.)

Question 11

Filtration membrane

Answer 11

consists of three layers
fenestrated capillaries
basement membrane
filtration slits of podocytes

Question 12

Net filtration pressure

Answer 12

Blood pressure 55mm Hg (in glomerular capillaries)

• C.O.P -30 mm Hg (from plasma proteins in cap.)
• Tissue P -15mm Hg (fluid backpressure in glomerulacap)

=NFP 10 mm Hg

Question 13

Glomerular filtration rate

Answer 13

GFR = 125 mL/min

Question 14

GFR

Answer 14

can be estimated by measuring clearance of a substance that is filtered into the nephron but not reabsorbed or secreted. e.g. inulin, creatinine
GFR= insulin clearance = [inulin]urine X urine flow (mL/min) / [inulin]plasma

Question 15

Reabsorption: PCT

Answer 15

“mass reabsorption” in the PCT, isosmotic with ECF (300 mOsm)
approx. 70% filtered fluid is reabsorbed from the PCT into the ECF (peritbular capillaries)

Question 16

Epithelial Transport in the PCT

Answer 16

transport proteins (pumps, carriers, channels) in apical and basolateral membranes 
microvilli on apical surface face into lumen of tubule (increase surface area)

Question 17

Transport mechanisms

Na+

Answer 17

diffusion through channels in the apical membrane

primary active transport: Na+/K+ ATPase in the basolateral mambrane

Question 18

Transport mechanisms glucose

Answer 18

secondary active transport with Na+ (SGLT) across apical membrane 
facilitated diffusion (GLUT) across basolateral membrane

Question 19

Transport mechanisms amino acids

Answer 19

cotransport with Na+ similar to glucose

Question 20

Transport mechanisms H20

Answer 20

via osmosis, follows movement of solutes

Question 21

Glucose reabsorption in the PCT

Answer 21

normally, all glucose filtered into nephrons is reabsorbed

at very high glucose levels, glucose transporters become saturated

Question 22

transport maximum

Answer 22

maximal rate of glucose reabsorption

Question 23

renal plasma threshold

Answer 23

minimum plasma [glucose] at which glucose appears in urine

Question 24

normal plasma

Answer 24

normal plasma [glucose] 90 mg/dL &laquo_space;renal plasma threshold - 180 mg/dL

Question 25

in diabetes mellitus

Answer 25

high plasma [glucose] > renal plasma threshold -> glucose in urine -> osmotic diuresis

Question 26

Vertical Osmotic Gradient: Loop of Henle

Answer 26

Counteractive multiplier mechanism active transport of NaCl osmotic movement of H20

Question 27

Active transport of NaCl

Answer 27

NaCl pumped out of ascending limb (thick region) | decrease osmolarity of tubular fluid and increase osmolarity of surrounding ECF

Question 28

Osmotic movement of H20

Answer 28

H20 moves out of descending limb due to increase ECF osmolarity differential permeability properties along the loop of Henle: descending limb : permeable to H20, impermeable to NaCl Ascending limb: impermeable to H20, permeable to NaCl (active transport)

Question 29

Countercurrent flow

Answer 29

``` opposite direction of flow in descending and ascending limbs concentrated fluid (1200 mOsm) formed at base of loop and surrounding ECF dilute fluid (100 mOsm) at top of ascending limb enters DCT vasa recta around loop of Henle helps maintain vertical osmotic gradient ```

Question 30

Tubular secretion: PCT and DCT

Answer 30

active transport of ions and waste products (H+, K+, organic acids) into tubules occurs in the PCT and DCT

Question 31

Collecting Duct: Regulated Reabsorption of H20

Answer 31

``` hypotonic fluid (100 mOsm) enters collecting duct (CD) from DCT as CD passes down the medulla, it encounters high osmolarity of surrounding ECF permeability of the CD to H20 is variable and regulated ```

Question 32

Antidiuretic Hormone

Answer 32

(ADH)(vasopressin) secreted by the posterior pituitary gland ADH stimualtes insertion of aquaporins into the membrane of the CD epithelial cells promotes reabsorption of H20 from the CD back into the ECF