Renal Physiology

Question 1

What are the vascular, combined vascular/tubular, & tubular components of the nephron?

Answer 1

-Vascular component of the nephron: Afferent arteriole, glomerulus, efferent arteriole, peritubular capillaries
-Combined vascular & tubular component: Juxtaglomerular apparatus
-Tubular components of nephron: Bowman’s capsule, Proximal convoluted tubule, Loop of Henle, Distal convoluted tubule, collecting duct

Question 2

What are the 3 structures that filter blood plasma into filtrate/urine?

Answer 2

-Endothelial fenestrations: pores in the endothelial capillary cells
-Basement membrane
-Filtration slits between the podocyte foot process (inner layer of Bowman’s capsule)

Question 3

What are the factors that move water into and out of the glomerulus?

Answer 3

-Glomerular capillary blood pressure
-Plasma-colloid osmotic pressure
-Bowman’s capsule hydrostatic pressure
-GFR = Glomerular filtration rate

Question 4

What is Kf? What variables are built into Kf?

Answer 4

-Kf= filtration coefficient
-Glomerular surface area for filtration
-Permeability of the glomerular membrane

Question 5

How is capillary blood pressure regulated to maintain a constant GFR?

Answer 5

-Regulating blood flow into glomerular capillaries via changes in the arteriole resistance
-Autoregulation to prevent spontaneous changes in GFR
-GFR changes are directly proportional to arterial pressure
-Kidneys maintain constant GER despite changes in arterial pressure via:
-myogenic mechanism
-tubuloglomerular feedback mechanism
-Juxtaglomerular apparatus
-Granular cells
-Macula densa cells

Question 6

What is the myogenic mechanism with regards to maintaining constant GFR?

Answer 6

-myogenic mechanism
-tubuloglomerular feedback mechanism
-Juxtaglomerular apparatus
-Granular cells
-Macula densa cells

Question 7

Can the macula densa detect changes in GFR? If so, how does it correct the changes to GFR?

Answer 7

-Detects changes in GFR and when the macula densa cells detect the change, they signal granular cells in the wall of the afferent arteriole to release vasoactive chemicals
-These chemicals will either vasodilate or vasoconstrict the arteriole to re-establish normal arteriolar pressure and hence GFR

Question 8

How can the GFR autoregulatory mechanism be harmful to us?

Answer 8

-Pressure would decrease = GFR would decrease
-Auto-regulatory mechanisms would increase GFR by vasodilating the afferent arteriole, leading to “normal” urine excretion
-But if plasma volume had dropped, would we want to excrete a “normal volume of urine (NO!)

Question 9

Describe the extrinsic control mechanism for blood pressure and how does it relate to renal functioning?

Answer 9

1. Plasma loss= decrease in arterial blood pressure
2. Baroreceptor reflex kicks in = increased sympathetic activity
3. Vasoconstriction of arterioles (including afferent arteriole)
4. Decreases glomerular capillary blood pressure
5. Decreases GFR = decreases urine volume = conservation of fluid and salt
6. Increases arterial blood pressure

Question 10

How can Kf be modulated?

Answer 10

-Under physiological conditions: surface area and permeability can be modified via glomerular call contractions

Question 11

What cells serve as pre-capillary sphincters in the glomerulus?

Answer 11

-Mesangial cells hold together tufts of capillaries, they close off sections of capillaries like pre-capillary sphincters in response to sympathetic stimulation
-Podocytes also possess contractile elements

Question 12

How can the permeability of the glomerulus be modulated?

Answer 12

-Podocytes also possess contractile elements
-When contracted the podocytes reduce the number of slit filters available for filtration

Question 13

What reabsorbed molecules rely on sodium reabsorption?

Answer 13

-Glucose, amino acid, H2O, Cl- and urea re-absorption in proximal tubule
-Cl- re-absorption and modulating urine concentration and volume in the loop of henle\
-K+ And H+ secretion and regulation of ECF volume in the distal tubule

Question 14

What secreted molecules rely on sodium reabsorption?

Answer 14

1. Glucose, amino acid, H2O, Cl-, & urea re-absorption in
   the proximal tubule
2. Cl- re-absorption & modulating urine concentration &
   volume in the loop of Henle
3. K+ & H+ secretion & regulation of ECF volume in the
   distal tubule

Question 15

Where is the sodium-potassium ATPase pump located

Answer 15

-Basolateral membrane

Question 16

How is sodium reabsorption regulated (discuss aldosterone & atrial naturetic peptide)?

Answer 16

-A. In the proximal tubule & loop of Henle a constant percentage of Na+ is
reabsorbed all the time
B. If Na+ levels are too low or too high following this transport, Na+
transport in the distal tubules is regulated via hormones
1. Renin-angiotensin-aldosterone system promotes uptake
3. Atrial natriuretic peptide promotes loss

Question 17

How are glucose & amino acids reabsorbed?

Answer 17

-Reabsorbed by a Na+ dependent secondary active transport
-Lumen side possesses co-transport carriers
-Basolateral side possesses facilitated carrier

Question 18

What is Tm?

Answer 18

Tubular Maximum

Question 19

What determines Tm?

Answer 19

-The maximal number of available carriers at a given time
-Once all carriers are bound with their substance (saturated) the rate at which the substrate can be transported will plateau

Question 20

What does parathyroid hormone regulate?

Answer 20

-Can alter Tm and hence the renal threshold to alter re-absorption

Question 21

How are potassium & hydrogen ion secretion related to one another?

Answer 21

-K+ secretion affected by H+ secretion
-The BL membrane pump can exchange either K+ or H+ for Na+ hence levels of secretion of one will affect the other; so when the body fluids are too acidic, H+ will be pumped out in lieu of K+

Question 22

What does the vertical osmotic gradient refer to?

Answer 22

Their exists in the kidney a vertical osmotic gradient extending from the cortex-
medulla junction to the deepest part of the medulla
A vertical osmotic gradient refers to the fact this this area has zones of different
osmolarity stacked on top of one another (see figure 14-27)
This allows the osmolarity of the urine to be adjusted to either expel excess water or
conserve it

Question 23

What parts of the tubule and impermeable vs. permeable to water?

Answer 23

-Descending limb of the loop of Henle is highly permeable to water
-Ascending limb of the loop of Henle is impermeable to water

Question 24

How does ADH make the collecting tubules permeable to water?

Answer 24

Vasopressin (ADH) released by the posterior pituitary will change the permeability
of the collecting tubules so that water can be re-absorbed
ADH reaches the basolateral membrane of the collecting tubules where it binds to
receptors, activating a cAMP second messenger
Increased levels of cAMP stimulate the incorporation of water channels into the apical
(luminal) membrane, which increases its permeability
As the filtrate passes deeper into the medulla more water is re-absorbed as it passes
through the vertical osmotic gradient set up by the loop of Henle
ADH cannot completely halt urine production, due to the need to remove wastes
Urine may be concentrated up to 12X and a minimum of 500 ml must be excreted

Question 25

What can result in renal failure?

Answer 25

-Metabolic acidosis: Inability of the kidneys to secret H+ = depression of the central nervous system
-Potassium retention: leading to altered cardiac and neural excitability
-Anemia: caused by retention of waste products = leading to nausea, vomiting, nervous system abnormalities
-Loss of plasma proteins: leading to edema