Urinary System 1

Question 1

What is Tubular reabsorption?

Answer 1

Tubular reabsorption:
returning to blood; renal tubule to peritubular capillaries

Question 2

What is Glomerular filtration?

Answer 2

Glomerular filtration:
leaving blood; glomerulus to capsular space

Question 3

What is Tubular secretion?

Answer 3

Tubular secretion:
leaving blood; peritubular capillaries to renal tubule

Question 4

What is Urinary Excretion?

Answer 4

Urinary excretion:
elimination from the body;
combination of Globular Filtration, Tubular Reabsorption and Tubular Secretion:

Excreted = Filtered + Secreted – Reabsorbed

Question 5

What are the main functions of the Urinary System?

Answer 5

Main functions:
Regulation – water, ions, acidity, blood volume and pressure.

Removal – eliminating waste, foreign substances, excesses

Question 6

What % of Resting Cardiac Output (Q) moves through the Kidneys?

Answer 6

~20% resting Q moving through kidneys (~1 L of 5 L blood volume).

Question 7

What is “Filtrate”?

Answer 7

name for fluids/solutes leaving blood and entering capsular space

Question 8

What is the Principle of Filtration?

Answer 8

Principle of filtration
- use pressure to force fluids/solutes through a membrane, while retaining what is needed
- Creates filtrate

Reported as:
Filtration fraction: percentage (~20%).
Glomerular filtration rate (GFR): volume per unit time (~125 mL/min or ~150 – 180 L/day).

Question 9

What is the Glomerulus?
(mention SA and Pressure)

Answer 9

The glomerulus is a small network of blood vessels in the kidney responsible for filtering waste and excess substances from the blood to form urine.

More efficient filter than other capillary beds (150-180 L/day glomerulus vs. 4 L/day systemic capillary beds):

Capillary membrane:
very large surface area, very permeable (with pores; 45x “leakier” than typical systemic capillary bed).

Glomerulus blood pressure higher (~ 60 mmHg) than typical systemic capillary blood pressure (~15-35 mmHg).

Question 10

GFR

Answer 10

Glomerular Filtration Rate

Question 11

What happens if GFR is too high?

Answer 11

Issues if: GFR too high
Filtrate moves too quickly so not enough time for reabsorption and too much ends up in urinary excretion.

Valuable fluid/solutes lost.

Question 12

What happens when GFR is too low?

Answer 12

GFR too low
Filtrate is nearly all reabsorbed so minimal urinary excretion.
Some waste, foreign substances, and excesses are not adequately eliminated.

Strong link between kidney problems – low GFR.

Question 13

What are the 4 Starling Forces of Glomerular Filtration?

Answer 13

Question 14

Which of the 2 Starling Forces Favour Filtration?

Answer 14

P-GC and π-CS
Blood Hydrostatic Pressure
Fluid Osmotic Pressure

Question 15

Which of the 2 Starling Forces Oppose Filtration?

Answer 15

P-CS and π-GC
Fluid Hydrostatic Pressure
Blood Osmotic Pressure

Question 16

Directions of Starling Forces

Answer 16

Question 17

Net Filtration Pressure

Answer 17

Question 18

Do we want a Positive or Negative NFP?

Answer 18

If healthy, favour filtration entire glomerulus surface area (positive NFP).

Question 19

How can NFP affect GFR?

Answer 19

NFP a strong force affecting GFR:
Higher NFP – higher GFR /
lower NFP – lower GFR.

NFP changes directly affect GFR unless steps are taken to prevent it.

Question 20

What is Renal autoregulation?

Answer 20

Intrinsic mechanisms within kidneys.
Largely operates to try and keep GFR the same despite changes outside the kidney that would alter it.
Homeostasis of GFR

Question 21

What is the 1st autoregulatory mechanism or the Myogenic Mechanism (MM)?

Answer 21

1st autoregulatory mechanism:
Myogenic Mechanism (MM)- Responds in seconds.

Example - Stimulus:
alter blood pressure – alters PGC – alters NFP – alters GFR.

MM Response:
Alter smooth muscle contraction (bloodflow)
- Alters arteriole radius (blood pressure)
- Alters P-GC -> alters NFP -> alters GFR (opposite direction to stimulus).

Question 22

What is the 2nd autoregulatory mechanism or the Tubologlomerular Feedback (TG)?

Answer 22

2nd autoregulatory mechanism – tubuloglomerular feedback (TG)- A little slower to respond than MM.

Example- Stimulus:
alter blood pressure – alters PGC – alters NFP – alters GFR.

TG Response: macula densa of JGA detects altered filtrate because of blood pressure change / JGA alters release of nitric oxide (NO) / alters afferent arteriole radius / alters P-GC / alters NFP / alters GFR (opposite direction to stimulus).

Question 23

make q

Answer 23

Question 24

Myogenic Mechanism

Answer 24