Renal System

Question 1

Mechanisms responsible for renal autoregulation

Answer 1

1. myogenic constriction of the afferent arteriole due to the ability of smooth muscle to sense and respond to increase in arteriole pressure
2. the effects of locally produced chemicals on the afferent arterioles by a group of specialized sensor cells known as the macula densa located in the thick portion of ascending limb where it loops back and comes into contact with afferent and efferent arterioles in renal cortex

Question 2

Macula Densa

Answer 2

Located in the thick portion of ascending limb part of the tubulogloberular feedback, release ATP to cause constriction of afferent arteriole to regulate GFR

Question 3

Renal auto regulation

Answer 3

When there is an increase in water and salt through the distal tubule this leads to vasoconstriction of afferent arteriole in response to ATP from macula densa thus lowering the GFR. This is a negative feedback response reducing sodium and water entering the nephron tubule preventing overloaded of the collection duct.

Question 4

Explain the significance of the GFR and how it is regulated by sympathetic nerves.

Answer 4

The GFR is the rate at which waste (creatine) is cleared from blood. The SNS response leads to the vasoconstriction of the afferent arteriole due to the flight or flight reaction or exercise. This helps preserve blood volume and divert blood to the muscles and heart. This decreases the GFR and decreases rate of urine formation to compensate for rapid drop in BP.

Question 5

Glomerular hydrostatic pressures

Answer 5

Pushes fluid out of capillaries into Bowman’s capsule

Question 6

Glomerular Filtration

Answer 6

First step of urine formation

Question 7

Glomerular pores

Answer 7

Endothelial cells of the glomerular capillaries have large pores called fenestrae, thus the glomerular endothelium is said to be fenestrated. Prevent the passage of RBCs, WBCs, and platelets

Question 8

Three layers the fluid in blood plasma can enter before it enters the interior of the glomerular capsule, which serve as selective filters

Answer 8

1. Capillary fenestrae, which ae large enough to allow proteins to pass but are surrounded by charges that may present some barrier to plasma protein
2. Glomerular Basement Membrane- a layer of collagen IV and proteoglycans lying immediate outside the capillary endothelium. This may offer some barrier to plasma proteins. More than five times as thick as the basement membrane of other vessels, and is the structure that most restricts the rate of fluid flow into the capsule lumen.
3. Inner (Visceral) layer of the glomerular capsule. This layer is composed of podocytes which are unique epithelial cells with a bulbous cell body, primary processes extending from the cell body from the primary processes.

Question 9

What passes through all three potential filtration barriers of the glomerulus?

Answer 9

All dissolved plasma solutes pass easily through all three potential filtration barriers to enter the interior of the glomerular capsule. However, plasma proteins are mostly excluded from the filtrate because of their large sizes and net negative charge.

Question 10

Podocytes allow

Answer 10

Cells called podocytes are little globby cells that have feet, that interdigitate around the capillary, so you can see the foot from another one, gaps where intererdigitation is not complete and there are slits. So strange anatomy.
Massive amount of fenestration to allow filtration and then you put barriers to protein movement around it
End result: everything can get through to Bowman’s capsul except proteins and cells

Question 11

Glomerular ultrafiltrate

Answer 11

composed of plasma solutes except proteins

Question 12

Proximal Tubule Reabsorption

Answer 12

Approx 65% of the salt and water in the original glomerular ultrafiltrate is reabsorbed across the proximal tubular fluid. Glucose, sodium, water get reabsorbed through carriers and channels and pumps. Glut transporters transport glucose
Na/K ATP pumps pumps sodium out and K in
amino acids get pumped out

Question 13

Proximal Tubule concentration

Answer 13

300 mOsm, isosmotic with blood

Question 14

Obligatory water loss

Answer 14

=400 mL urine/day

Question 15

Reabosorption that occurs constantly regardlyess of the person’s state of hydration, not Subject to hormonal regulation

Answer 15

Reabsorption through the descending limb of the nephron loop and proximal tubule, as opposed to distal tubule and collecting tube which are subject to hormonal regulation!

Question 16

Glucose reabsorption

Answer 16

Tm= 375 mg/min
Plasma glucose (fasting) is ~100 mg/dl
Fasting rate of glucose filtration is 125 mg/min

Glycosuria (when plasma glucose exceeds 250 mg/dl)

Question 17

Glycosuria

Answer 17

When plasma glucose exceeds 250 mg/dl

Question 18

Glucose in urine

Answer 18

diabetes

Question 19

Renal Clearance and Secretion

Answer 19

Clearing the blood of waste products
Excretion of certain foreign compounds (ie. drugs)- renal clearance via organic anion transporters (OAT) or organic cation transporters (OCT)

Two mechanisms (not mutally exclusive):
Filtered and not reabsorbed
Secreted

Question 20

Examples of molecules that are secreted by OATs or OCTs

Answer 20

Penicillin
Steroids
Bile acids
Metformin
Histamine
Phenobarbitol
Amphetamine
Paraquat
quinine

Question 21

Measurement of GFR

Answer 21

Use a substance that is filtered but not secreted or reabsorbed.
INULIN (produced in artichokes, onion, garlic)- a fructose polymer

Question 22

Calculation of GFR

Answer 22

Use a substance that is filtered but not secreted or reabsorbed.
INULIN (produced in artichokes, onion, garlic)- a fructose polymer

Question 23

Reabsorption in the proximal tubule

Answer 23

~65% of salt and water in the original glomerular ultrafiltrate is reabsorbed across the proximal tubule and returned ot th vascular system.
Fluid is still isoosmotic with the blood =[300 mOsm]
Plasma membranes are freely permeable to water, so taht water and salt are removed in proportionate amounts

Question 24

Water reabsorption

Answer 24

Cannot be actively transported across the tubule wall, only can occur via osmosis following concentration gradient. So this only occurs if the surrounding interstitial fluid is hypertonic (saltier= more solutes)