Urinary System 1 Flashcards
What is Tubular reabsorption?
Tubular reabsorption:
returning to blood; renal tubule to peritubular capillaries
What is Glomerular filtration?
Glomerular filtration:
leaving blood; glomerulus to capsular space
What is Tubular secretion?
Tubular secretion:
leaving blood; peritubular capillaries to renal tubule
What is Urinary Excretion?
Urinary excretion:
elimination from the body;
combination of Globular Filtration, Tubular Reabsorption and Tubular Secretion:
Excreted = Filtered + Secreted – Reabsorbed
What are the main functions of the Urinary System?
Main functions:
Regulation – water, ions, acidity, blood volume and pressure.
Removal – eliminating waste, foreign substances, excesses
What % of Resting Cardiac Output (Q) moves through the Kidneys?
~20% resting Q moving through kidneys (~1 L of 5 L blood volume).
What is “Filtrate”?
name for fluids/solutes leaving blood and entering capsular space
What is the Principle of Filtration?
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).
What is the Glomerulus?
(mention SA and Pressure)
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).
GFR
Glomerular Filtration Rate
What happens if GFR is too high?
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.
What happens when GFR is too low?
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.
What are the 4 Starling Forces of Glomerular Filtration?
Which of the 2 Starling Forces Favour Filtration?
P-GC and π-CS
Blood Hydrostatic Pressure
Fluid Osmotic Pressure
Which of the 2 Starling Forces Oppose Filtration?
P-CS and π-GC
Fluid Hydrostatic Pressure
Blood Osmotic Pressure
Directions of Starling Forces
Net Filtration Pressure
Do we want a Positive or Negative NFP?
If healthy, favour filtration entire glomerulus surface area (positive NFP).
How can NFP affect GFR?
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.
What is Renal autoregulation?
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
What is the 1st autoregulatory mechanism or the Myogenic Mechanism (MM)?
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).
What is the 2nd autoregulatory mechanism or the Tubologlomerular Feedback (TG)?
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).
make q
Myogenic Mechanism
