Yr1 Regulation GFR, K+ and BP Flashcards Preview

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Flashcards in Yr1 Regulation GFR, K+ and BP Deck (37)
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1

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

2

Why is the regulation of GFR important?
What if too hgih or low?

1. don’t want the GFR to change whenever blood pressure does as would mean whenever do any exercise change filtration NOT GOOD
2. Too high GFR - Too much filtrate, and increased urine production (diuresis). Needed substances pass too quickly thro tubules, insufficient reabsorption = lost in urine
3. Too low GFR - too little filtrate. Reduced flow of filtrate. Certain waste substances may not be excreted

3

What is autoregulation?

1. Maintains GFR during short term and moderate variations in mean arterial pressure by changing resistance of the afferent arteriole
2. All about changing the resistance of the afferent arteriole by 2 mechanisms:

- Tubuloglomerular feedback
- Myogenic response

3. afferent arteriole constricts = GFR decreases
4. afferent arteriole dilates = GFR increases

4

What is the JUXTAMEDULLARY apparatus?
main function

1. The ascending LOH (google says DCT) runs between afferent and efferent blood vessels
2. Adjacent cells of the juxtaglomerular cells (arteriole cells) and macula densa (tubule cells) form the J apparatus
3. main function is to regulate blood pressure and the filtration rate of the glomerulus.

5

What are the 2 mechanisms whereby autoregulation occurs?

1. Tubuloglomerular feedback - measures amount of filtration occuring
2. Myogenic response – blood pressure changes in AA
3. Both mechanisms respond to changes in BP

6

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

7

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

8

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

9

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

10

Aldosterone and K+ conc

1. negative feedback mechanism
2. 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
3. ALDOSTERONE is released in response to HIGH K+
4. If K+ conc goes down in blood, less is released

11

How is systemic blood pressure controlled?

1. Neural regulation BP:
- Baroreceptor reflex = regulated SV, HR, TPR via tone of vasculature
2. Hormonal regulation BP:
- angiotensin 2= long term regulation, regulates stroke volume, regulates TPR via tone of the vasculature

12

Mean arterial pressure =

Pa = CO x TPR
Mean arterial pressure = CO X total peripheral resistance

13

Kidney and the CV system

• Kidney  25% blood volume
2. HUUUGE effect on peripheral resistance and CO
3. Also massively affected by large changes in BP

14

Renin and Kidney

1. RENIN is released from Juxtaglomerulat cells (in AA)
2. Angiotensinogen manufactured in LIVER, released in blood
2. Renin in blood stream converts angiotensinogen to angeiotensin 1 in plasma, once in lungs, enzyme in lungs convert to Angiotensin 2!
3. Sooooo lot of renin means lots of Ag2

15

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

16

What is angiotensin 2's affect on the adrenal cortex

1. SO important
2. Ag2 in blood binds to receptors on adrenal cortex causing release of aldosterone
3. Aldosterone directly controls K+ concentration
4. By stimulating principle cells in CD to secrete more K+ and reabsorb more Na+ and Cl-
5. Water follows Na+ so increases blood volume, therefore pressure
6. a significant drop in BP causes activation RAAS: renin whihc activates angiotensin which causes aldosterone to be released from adrenal gland cortex

17

So what are the types of regulation aldosterone has?

2 types
1. K+
2. BP
Inc plasma [K+]
= adrenal gland empties ALDOSTERONE into blood stream, binds to receptors in principle cells DCT, take more K+ into cell, flows down conc gradient and into urine
Decreased BP activates RAAS:
By stimulating principle cells in CD to secrete more K+ and reabsorb more Na+ and Cl-
5. Water follows Na+ so increases blood volume, therefore pressure

18

Systemic vasoconstriction and angiotensin causes which arteriole to constrict more?

EFFERENT
becuase reduces blood flow
increases hydrostatic pressure in glomerular caps which helps preserve the
glomerular filtration rate!
therefore maintaining filtration pressure:)
LIMITS damaging affect of vasoconstriction
This overrides autoregulation!

19

normal fluid intake?

1. 2ml/kg/hr
2. roughly 50ml/kg/day should be
3. get this through ingestion of liquids, moist foods, metabollic synthesis of water

20

Normal fluid loss?

1ml/kg/hr

21

Types of fluid loss

1. Sensible - what you are aware off e.g. kidneys adn peeing
2. insensible - not aware of e.g. exhalation from lungs, evaporation skin, faeces

22

When is angiotensin 2 released

in response to a fall in BP

23

Systemic effect of decrease BP

1. Arterioles vasoconstrict
2. adrenal cortex secretes aldosterone - stimulates principal cells in CD to secrete more K+ and to reabsorb more Na+ and Cl-. osmotic consequence more Na+ and Cl= is that more water is reabsorbed which increases blood volume thus venous return and SV, i.e aldosterone increases blood pressure
3. Hypothalamus ADH secreted and inc thirst
4. Medulla oblongate refelxes to inc BP

24

Dec in BP effects on GFR

1. dec overall as dec blood flow in afferent arteriole and GFR
2. GFR preserved to a degree as constriction of efferent arteriole helps preserve hydrostatic pressure

25

What happens is BP increases

o Natriuretic peptides DECREASE blood pressure  inc GFR

26

Systemic effects of inc BP

1. Afferent arteriole vasodilates
2. adrenal cortex dec aldosterone secretion
3. hypothalamus dec ADH secretion
4. Medulla oblongata reflexes to dec BP
5. increases GFR

27

Does urine composition change between bladder and collecting duct?

NO except in horses where Glands in the renal pelvis and upper ureter secrete mucus. Equine urine is therefore quite viscous

28

Organisation of excretory passage way innermost to outer

• Mucosa: innermost
o Luminal sheet of transitional epithelium : cells in multiple layers, not lined up. In areas that tend to expand (bladder and uretha)
o Lamina propria = connective tissue lies beneath epithelium
• Sub mucosa
o Not particularly large, unusually merged with lamina propria
• Muscularis Externa
o 2-3 layers smooth muscle (involuntary)
o Inner layer longitudinal, middle circular, outer longitudional
• Adventitia or Serosa

29

Male urethra organsiation

• Mucosa
o Folded longitudinally
o Epithelium varies from TE to stratified squamous at urethral orifice
o Lamina propria
• Sub-mucosa
o Usually merged with lamina propria
• Muscularis Externa
o 2-3 layers of smooth muscle bundles
• Adventitia or Serosa

30

How is urine outflow controlled?

Parasympathetic effect:
1. Contraction of the detrusor (smooth) muscle (outside of bladder, in bladder wall): INVOLUNTARY.
Pelvic nerve, Ach acting on muscarinic receptors

Somatic Motor effect:
2. Inhibition of continuous excitation of External urethral sphincter (striated muscle: VOLUNTARY skeletal)
Pudendal nerve, Via inhibition Ach acting on NICOTINIC receptors
------------------------------
3. Internal urethral sphincter – smooth muscle: INVOLUNTARY. Reduction in alpha adrenergic tone