Lecture 26- Chapter 25- Urinary System

Question 1

BLANK is the volume of filtrate formed per minute by both kidneys.

Answer 1

Glomerular Filtration Rate

Question 2

What is the goal of local intrinsic controls (renal autoregulation)?

Answer 2

To maintain GFR

Question 3

The glomelular filtration membrane has three layers, what are they?

Answer 3

1. Fenstrated endothelium (facing glomerulus)
2. Basement membrane
3. Foot processes of podocytes with filtration slits

Question 4

What is the purpose of the podocytes that are located on the bowmans capsule?

Answer 4

To block out macromolecules and allow small molecules to pass through into the PCT. Water, glucose, amino acids, nitrogenous wastes are allowed to pass through.

Question 5

Why do plasma proteins remain in blood of the glomerulous capillaries?

Answer 5

To maintain colloid osmotic pressure. If all plasma proteins leave, all water will follow. No water in the capillaries is bad for plasma.

Question 6

How does Glomerular filtration rate affect the systemic blood pressure?

Answer 6

Increased GFR causes increased urine output, which lowers blood pressure and vice versa.
Decreased GFR decreases urine output, which highers blood pressure.

Question 7

What is the goal of **extrinsic **controls?

Answer 7

To maintain systemic blood pressure

Nervous system and endocrine mechanisms are main extrinsic controls

Question 8

Regulation of Glomerular Filtration

What are the two intrinsic mechanisms to regulate GFR?
What are the two extrinsic mechanisms to regulate GFR?

Answer 8

• **Intrinsic Mechanisms: **
  1. Myogenic
  2. Tubuloglomerular
• Extrinsic Mechanisms:
  1. Hormonal (renin-angiotensin-aldosterone)
  2. Neural controls

Question 9

Describe how the myogenic mechanism regulates GFR.

Answer 9

• Low systemic blood pressure means that blood pressure in the afferent arteriole is low, Low afferent arteriole blood pressure means that glomerular filtration rate is low
• Low GFR will decrease the stretch of smooth muscle in walls of afferent arterioles
• This causes the vasodilation of afferent arterioles. This allows for more blood flow and increases GFR

Ask yourself: Is this intrinsic or extrinsic mechanism of regulation?

Opposite is true for this mechanism, meaning that if there is high systemic blood pressure, the reverse will happen. (Increase stretch of smooth muscle, vasoconstriciton, decrease GFR)

Question 10

Describe how the tubuloglomerular mechanism regulates GFR.

Answer 10

• Low systemic blood pressure = Low GFR
• Low GFR means that there is a decrease in filtrate flow and a decrease in NaCl in ascending limb of nephron loop
• This acts on the macula densa cells of the juxtaglomerular complex of kidney
• Macula densa cells cause vasodilation of afferent arterioles, allowing for more blood flow and increases GFR.

Ask yourself: Is this intrinsic or extrinsic mechanism of regulation?

Opposite is true for this mechanism, meaning that if there is high systemic blood pressure, the reverse will happen. (Increase systemic blood pressure = High GFR, Increases filtrate flow and NaCl in ascending limb, Vasoconstriction, decrease GFR)

Question 11

Describe how Hormonal (renin-angiotensin-aldosterone) mechanism regulates systemic blood pressure.

Answer 11

In case of low systemic blood pressure:
* Granular cells of juxtaglomerular complex of kidney cause the release of renin
* Renin causes the formation of angiotensin 2
* Angiotensin 2 cause the vasoconstriction of systemic arterioles which increase peripherial resistance, this increases systemic blood pressure
* Angiotensin 2 causes Aldosterone secretion by adrenal cortex
* Increased Aldosterone = increase of Na+ reabsorption, this makes water follow
* As a result, blood volume is increased
* This increases systemic blood pressure

Question 12

Does an **increase in ADH **cause an increase or decrease of urination?

Answer 12

Decrease.
More ADH = Less Urination

Less ADH = More Urination

Question 13

What is the name of the cells in the nephron that monitor the NaCl levels?

Answer 13

Macula Densa cells

Question 14

What happens to the macromolecules that get stuck in the filtration membrane?

Answer 14

Glomerular mesangial cells will engulf the macromolecules.

Question 15

What is the outward pressure?

This promotes filtrate formation.

Answer 15

Hydrostatic pressure in glomerular capillaries (HP gc)

Question 16

What are the inward pressures?

Answer 16

1. Hydrostatic pressure in capsular space (HP cs)
2. Colloid osmotic pressure in capillaries (OP gc)

Question 17

BLANK quickly reclaims most of the tubular contents and returns them to blood.
* Selective process that allows almost all organic nutrients to be reabsorbed
* Water and Ion reabsorption is hormonally regulated and adjusted

Answer 17

Tubular reabsorption

Includes active and passive reabsorption

Question 18

Na+ is the most abundant cation in the filtrate, we want the majority of it to go back into the blood. How is Na+ crossed from the filtrate back into the interstital space?

This is happening in the PCT.

Answer 18

• Na+ is transported across the basolateral membrane via primary active transport. There are Sodium-Potassium pumps that shoot Na+ across the membrane.
• Na+ will act as a cotransporter and take glucose, amino acids, some ions, and vitamins into the interstital fluid. This is known as secondary active transport.

Question 19

How is water reabsorbed in the PCT?

Answer 19

Through obligatory water reabsorption, this means that aquaporins are always present in the PCT.

Facultative water reabsorption: Aquaporins are inserted in collecting ducts ONLY IF ADH is present.

Question 20

What is the transport maximum(T m) ?

Answer 20

When carriers for a solute are saturated. There is no room for excess solutes. As a result, the remaining gets excreted in urine. (Example: Hyperglycemia leads to high blood glucose levels that exceed the T m, and glucose spills over into urine)

Question 21

What is the function of the PCT?

Answer 21

It is the site of most reabsorption
* All nutrients, such as glucose and amino acids, are reabsorbed
* 65% of Na+ and water reabsorbed
* About half of urea (Later will be secreted into the filtrate)

Question 22

Nephron Loop

The descending limb allows BLANK to leave, but keeps the BLANK inside.

Answer 22

H2O ; solutes (Na+)

Question 23

The ascending limb allows BLANK to leave, but keeps BLANK inside.

Answer 23

Solutes (Na+) ; H2O

Thin segment is passive to Na+ movment. While the thick segment has Sodium-Potassium-Chloride symporters and Sodium-Hydrogen antiporters that transport Na+ into the cell.

Question 24

Reabsorption is hormonally regulated in these areas of the nephron.

Two locations

Answer 24

1. DCT
2. Collecting duct

Question 25

What is the function of ADH on the DCT and collecting ducts?

Answer 25

• ADH released by the posterior pituitary gland
• Causes principal cells of collecting ducts to insert aquaporins in apical membranes, this increases water reabsorption

More ADH = More water reabsorption

Question 26

What is aldosterone’s function in the collecting ducts?

Answer 26

• Targets collecting ducts and DCT
• Promotes Na+ reabsorption (water follows)
• Because of this, little Na+ leaves the body
• Increases blood pressure and decrease K+ levels

Question 27

What is the function of atrial natriuretic peptide?

Answer 27

Reduces blood Na+ resulting in decreased blood volume and blood pressure

Released by cardicac atrial cells if blood volume or pressure is elevated.

Question 28

Overview of Nephron reabsorptions and secretions

Blue = reabsorption ; Green = secretion

Answer 28