M1 Renal Physiology

Question 1

Very general kidney functions:

Answer 1

Excretion of metabolic waste products and foreign chemicals
Regulation of water and electrolyte balances
Regulation of body fluid osmolality and electrolyte concentrations
Regulation of arterial pressure
Regulation of acid-base balance
Secretion, metabolism, and excretion of hormones
Gluconeogenesis

Question 2

`What is the central physiologic role of the kidneys?

Answer 2

control the volume and composition of the body fluids

Question 3

What is total body water?

Answer 3

60% of total body weight

Question 4

How much to total body water is ICF and ECF?

Answer 4

2/3 is ICF

1/3 is ECF

Question 5

What is the barrier between the ICF and ECF?

Answer 5

cell membrane

Question 6

What are the major ions of the ECF?

Answer 6

Na+ and Cl- and HCO3-

Question 7

What are the major ions of the ICF?

Answer 7

K+ and PO4- and protein

Question 8

What is the concentration of osmotically active particles in total solution and is expressed in terms of mOsm/liter of water?

Answer 8

Osmolarity

Question 9

What is the average osmolarity of the ECF and ICF?

Answer 9

osmolarity of the ECF and ICF averages 280-300 mOsm/liter - identical in nearly all body fluids

Question 10

What is expressed in terms of mOsm/kg of solvent?

Answer 10

Osmolality

Question 11

In relatively dilute solutions, such as those found in the body, how do osmolality and osmolarity relate to each other?

Answer 11

osmolality ≈ osmolarity

Question 12

What are the 4 kidney processes that determine composition of the urine?

Answer 12

1. filtration
2. reabsorption
3. secretion
4. excretion

Question 13

What is the glomerular filtrate?

Answer 13

ultrafiltrate of plasma containing the same concentration of most salts and organic substances found in plasma

Question 14

What physical forces cause filtration by glomerular capillaries?

Answer 14

starling forces:
glomerular hydrostatic pressure
glomerular colloid osmotic pressure
bowman’s capsule pressure

Question 15

What is the equation for GFR?

Answer 15

GFR = Kf x [ (PGC +πBS) - (πGC + PBS)]

Kf = Ultrafiltration Coefficient- the product of the hydraulic permeability (Lp)and the surface area (SA) of the glomerular capillary membranes
PGC= Glomerular Capillary Hydrostatic Pressure
πGC= Glomerular Capillary Oncotic Pressure
PBS= Bowman’s Space Hydrostatic Pressure
πBS= Bowman's Space Oncotic Pressure

Question 16

Over what range of BP can autoregulation help regulate kidney blood flow best?

Answer 16

80-160 mmHg

Question 17

What are the two mechanisms of autoregulation?

Answer 17

myogenic and tubuloglomerular feedback

Question 18

What is the myogenic mechanism?

Answer 18

Intrinsic property of blood vessels. Stretch of vascular smooth muscle, as experienced during an increase in arterial pressure, elicits contraction which elevates vascular resistance and maintain blood flow (and GFR) constant

Question 19

What is tubuloglomerular feedback?

Answer 19

Autoregulatory mechanism unique to the kidney. In response to an elevation of perfusion pressure, increased fluid is filtered leading to increased delivery of NaCl to the macula densa. This increased delivery elicits an increase in vascular resistance.

Question 20

What hormones can decrease GFR?

Answer 20

Norepinephrine, Epinephrine, Endothelin—decreases GFR

Angiotensin II—no change or decreases GFR

Question 21

What hormones can increase GFR?

Answer 21

Endothelial derived nitric oxide and Prostaglandins

Question 22

The filtration barrier consists of what three layers?

Answer 22

capillary wall, basement membrane, and podocytes

Question 23

What are the characteristics of capillary wall for filtration?

Answer 23

capillary wall is 700 Å fenestrated, freely permeable to small molecules and negatively charged glycoproteins in surface

Question 24

What are the characteristics of basement membrane for filtration?

Answer 24

porous matrix of extracellular proteins including type IV collagen, laminin, fibronectin and other neg. charged proteins

Question 25

What are the characteristics of podocytes for filtration?

Answer 25

processes and slit pores-40x140 Å long finger-like processes with neg. charged proteins

Question 26

Two general traits of the filtration barrier are what?

Answer 26

size-selective: more permeable to small molecules | charge-selective: more permeable to positively charged molecules (proteins generally are negatively charged)

Question 27

What are the two proteins that make up the slit diaphragm between podocytes?

Answer 27

nephrin (N) and P-cadherin (P-C)

Question 28

What happens in the THIN Descending loop of Henle?

Answer 28

reabsorption of water secondary to cortical medullary osmotic gradient

Question 29

What happens in the THIN Ascending loop of Henle?

Answer 29

Impermeable to water. Passive reabsorption of sodium, dilution of tubular fluid. Permeable to urea, urea is secreted.

Question 30

What happens in the THICK ascending loop of Henle?

Answer 30

Reabsorbs 25% of filtered Na+ by the Na/K/Cl transporter Lumen positive potential drives paracellular reabsorption of sodium, potassium, magnesium and calcium. Impermeable to water, dilutes tubular fluid

Question 31

What kind of diuretics act on the Na/K/Cl transporter in the THICK ascending loop of Henle?

Answer 31

loop diuretics - furosemide - ethacrynic acid - bumetanide

Question 32

What happens in the early distal tubule?

Answer 32

Reabsorbs Na+, Cl-, Ca++ and Mg++ Not permeable to water. Thiazide-sensitive segment act on Na/Cl symporter.

Question 33

What happens in the principal cells of the late distal tubule and cortical collecting duct?

Answer 33

Reabsorbs Na+, secretes K+ regulated by Aldosterone. Water permeability regulated by ADH. Reabsorption of sodium and secretion of potassium blocked by K-sparing diuretics

Question 34

What type of sodium channels are on the apical membrane of principal cells?

Answer 34

ENaC (epithelial sodium channel)

Question 35

What happens in the medullary collecting duct?

Answer 35

Reabsorbs Na+. ADH-stimulated water reabsorption. Urea reabsorption

Question 36

How does aldosterone affect tubular reabsorption?

Answer 36

- Acts in principal cells of late distal tubule and collecting duct - increases Na+ reabsorption, increases K+ secretion

Question 37

How does angiotensin II affect tubular reabsorption?

Answer 37

- acts primarily in the proximal tubule | - increases Na+ and water reabsorption, increases H+ secretion

Question 38

How does antidiuretic hormone (ADH aka vasopressin) affect tubular reabsorption?

Answer 38

- acts in principal cells of late distal tubule and collecting duct, inner medullary collecting duct - increases water reabsorption

Question 39

How does atrial natriuretic peptide (ANP or ANF) affect tubular reabsorption?

Answer 39

- acts in distal tubule and collecting duct | - decreases Na+ reabsorption

Question 40

How does parathyroid hormone (PTH) affect tubular reabsorption?

Answer 40

- in proximal tubule decreases PO4--- reabsorption | - in thick ascending loop of Henle and distal tubule increases Ca++ reabsorption