Yr1 Regulation GFR, K+ and BP Flashcards
What is GFR
Glomerular filtration rate - volume of fluid filtered from the glomerular capillaries into bowman’s space per minute mls/min IT IS A RATE
Why is the regulation of GFR important?
What if too hgih or low?
- don’t want the GFR to change whenever blood pressure does as would mean whenever do any exercise change filtration NOT GOOD
- Too high GFR - Too much filtrate, and increased urine production (diuresis). Needed substances pass too quickly thro tubules, insufficient reabsorption = lost in urine
- Too low GFR - too little filtrate. Reduced flow of filtrate. Certain waste substances may not be excreted
What is autoregulation?
- Maintains GFR during short term and moderate variations in mean arterial pressure by changing resistance of the afferent arteriole
- All about changing the resistance of the afferent arteriole by 2 mechanisms:
- Tubuloglomerular feedback
- Myogenic response
- afferent arteriole constricts = GFR decreases
- afferent arteriole dilates = GFR increases
What is the JUXTAMEDULLARY apparatus?
main function
- The ascending LOH (google says DCT) runs between afferent and efferent blood vessels
- Adjacent cells of the juxtaglomerular cells (arteriole cells) and macula densa (tubule cells) form the J apparatus
- main function is to regulate blood pressure and the filtration rate of the glomerulus.
What are the 2 mechanisms whereby autoregulation occurs?
- Tubuloglomerular feedback - measures amount of filtration occuring
- Myogenic response – blood pressure changes in AA
- Both mechanisms respond to changes in BP
Tubuloglomerular feedback
What cells detect flow?
What happens if detech inc GFR and dec?
- Macula densa cells in LOH, at angle between A and E arterioles, detect flow rate
- if detect increase in GFR - paracrine (local) signal to neighbouring AA to constrict - reduces filtration rate
- Detect decreased GFR - vasodilation in AA to increase GFR
Myogenic response
blood pressure changes in AA
• Contraction of vascular myocytes in afferent arteriole: vasoconstriction
• Relaxation of vascular myocytes in afferent arteriole that follows a reduction in pressure: vasodilation
Talk about K+ homeostasis
K+ not stored in the body
Major component of intracellular fluid in all animals and plants
Urine concentration of K+ is greater than ECF
Concentration of K+ in ECF is relatively low
More potassium may be excreted than was originally filtered
Regulation of secretion is more important than regulation of reabsorption
1. Secretion in DCT
Principle cells in DCT
1. Asymmetric, large amount Na+ and K+ ATPASE driving Na+ gradient
2. Leaky channels on apical side (tubular), allow Na+ and K+ to move down conc gradients
3. Difference to cells in PCT, in DCT regulated by hormone aldosterone
Adrenal Gland
Paired = lie cranial medially in bod
Adrenal gland produces whole range of hormones
3. has distinct functional zones: Medulla, cortex
4. MEdulla secretes hormones like adrenaline and noradrenaline
5. Zona glomerulus (outermost part of cortex) secretes aldosterone
Aldosterone and K+ conc
- negative feedback mechanism
- If [K+] in plasma goes UP = adrenal gland empties ALDOSTERONE into blood stream, binds to receptos n principle cells DCT, take more K+ into cell, flows down conc gradient and into urine
- ALDOSTERONE is released in response to HIGH K+
- If K+ conc goes down in blood, less is released
How is systemic blood pressure controlled?
- Neural regulation BP:
- Baroreceptor reflex = regulated SV, HR, TPR via tone of vasculature - Hormonal regulation BP:
- angiotensin 2= long term regulation, regulates stroke volume, regulates TPR via tone of the vasculature
Mean arterial pressure =
Pa = CO x TPR
Mean arterial pressure = CO X total peripheral resistance
Kidney and the CV system
• Kidney 25% blood volume
- HUUUGE effect on peripheral resistance and CO
- Also massively affected by large changes in BP
Renin and Kidney
- RENIN is released from Juxtaglomerulat cells (in AA)
- Angiotensinogen manufactured in LIVER, released in blood
- Renin in blood stream converts angiotensinogen to angeiotensin 1 in plasma, once in lungs, enzyme in lungs convert to Angiotensin 2!
- Sooooo lot of renin means lots of Ag2
Physiological effects of angiotensin 2
It is released in response to decreased blood pressure over time
Systemic effects:
• Arterioles vasoconstrict
• Total Peripheral Resistance
- CV control system in Medulla O reflexes to inc BP
- Increases CO and TPR this increases BP
- hypothalamus, ADH secretion and inc thirst
- adrenal cortex secreted aldosterone (more K+ in urine)
- proximal tubule
Effects on GFR:
Overall decreases as decreases blood flow in afferent arteriole but GFR is preserved to a degree as constriction of efferent arteriole helps preserve hydrostatic pressure