L118: Kidney 3 Flashcards
(33 cards)
The primary function of the kidneys is to filter blood however, what else do they regulate?
- Fluid and electrolytes: blood volume ~ blood pressure;
- Acid-base blood balance;
- Calcium and vitamin D metabolism;
- Erythropoietin.
What is the series of events upon excess fluid levels?
- Excess fluid;
- Elevated blood volume;
- Elevated blood pressure;
- Large volume of dilute urine;
- Reduced blood pressure.
What is the series of events upon reduced fluid levels?
- Reduced fluid;
- Reduced blood volume;
- Reduced blood pressure;
- Small volume of conc. urine;
- Elevated BP.
What is glomerular filtration rate (GFR)?
The rate at which blood is filtered through the glomerulus into the Bowman’s capsule
What are the three main factors that influence GFR?
- Hydrostatic pressure;
- Osmotic pressure;
- Blood pressure.
What is the main driver of hydrostatic pressure in the glomerulus?
The afferent arteriole is larger than the efferent arteriole
How do the kidneys estimate GFR?
Blood pressure
If blood pressure increases, and the kidneys are unable to adjust (CKD) the GFR, GFR will…
increase
An increase in GFR leads to…
less time to reabsorb sodium and more sodium entering the DCT
What is the juxta-glomerulus apparatus (JGA) and what is its purpose?
- Connects the glomerulus with the DCT;
- Measures the [Na+] of the filtrate;
- Adjusts the diameter of the afferent arteriole.
What is the macula densa?
- A component of the JGA;
- An area of closely packed specialised cells;
- Detect the [Na+].
What are juxtaglomerular cells?
- A component of the JGA;
- Modified smooth muscle cells around the afferent arteriole (some on efferent);
- Synthesise, store and secrete the enzyme, renin;
- Adjust the diameter of the arterioles.
How do macula densa cells respond to an increase in blood pressure and why?
- Increased BP;
- Increased glomerular hydrostatic pressure;
- Increasder GFR;
- Increased Na+ in filtrate;
- Detected by macula densa;
- Macula densa release adenosine.
What does the release of adenosine from macula densa cells cause?
- Paracrine signal to juxtaglomerular cells;
- Juxtaglomerular cells constrict afferent arteriole;
- Tubular-glomerular feedback.
How does the constriction of the afferent arteriole lead to restored homeostasis?
- Reduces glomerular hydrostatic pressure (less blood can flow in);
- Reduced GFR;
- Homeostasis restored.
How do macula densa cells respond to a decrease in blood pressure and why?
- Decreased BP;
- Decreased glomerular hydrostatic pressure;
- Decreasd GFR;
- Decreased Na+ in filtrate;
- Detected by macula densa;
- Macula densa release prostaglandins.
What does the release of prostaglandins from macula densa cells cause?
- Paracrine signal to juxtaglomerular cells;
- Juxtaglomerular cells release renin;
- Activates renin-angiotensin system.
Why is the renin-angiotensin system necessary to restore homeostasis?
The afferent arteriole is already relaxed (dilated) so further relaxation would not have an effect
How does RAAS restore blood pressure?
(Through rapid vasoconstriction!)
- Angiotensinogen is released into circulation (from liver);
- Renin (enzyme from kidneys) converts angiotensinogen into angiotensin I;
- Angiontensin converting enzyme converts angiotensin I into angiotensin II;
- Angiotensin II is a potent vasoconstrictor - rapidly increases BP.
How does RAAS restore blood volume?
(via action of aldosterone and ADH!)
- Angiotensin II is detected by:
- The adrenal medulla - aldosterone;
- Hypothalamus - ADH.
In RAAS, where is aldosterone released from?
The adrenal medulla
In RAAS, where is ADH released from?
The hypothalamus
What hormone counteracts RAAS?
ANP: atrial natriuretic peptide
How does ANP counteract RAAS?
- Acts to reduce blood pressure;
- Works to reduce plasma volume through excretion of Na+ and water;
- i.e. the opposite of RAAS, which works to increase plasma volume and resulting BP.
