9,10 -regulation of kidney func Flashcards
What are starling forces ?
govern the formation of the glomerular filtrate:
o Out (glomerular capillaries → Bowman’s space):
o Hydrostatic pressure in glomerular capillaries (HPgc);
In (Bowman’s space → glomerular capillaries):
o Hydrostatic pressure in the capsular/Bowman’s space (HPcs);
o Oncotic pressure in glomerular capillaries (OP
What is net filtration pressure ?
sum of oppsosing pressures
Hydrostatic pressure
pushes fluid out of a vessel.
* Oncotic pressure pulls fluid
into a tissue/vessel, due to
the presence of proteins.
What affects Glomerulad filtration rate ?
et filtration pressure (NFP) & filtration coefficient determine
Since glomerular capillaries are much more permeable to fluid (than other
capillaries), NFP causes massive filtration of fluid into Bowman’s space
Intrinsic vs Extrinsic mechanism ?
In=control is from within so autoregulation
Ex-outside of tiddue
using nerves or hormones
A
An intrinsic response ?
Myogenic :intrinsic ability of vascular smooth muscle to respond to changes in the blood pressure
in BP: ↑ in renal vessel
diameter (smooth muscle
in arteriole wall stretches:
myogenic hypothesis →
vessel will then contract
/(vaso)constrict → leads
to ↑ vascular resistance,
thus, ↓ RBF (…↓ GFR)
GFR tightly regulation in sodium sensing ?
changes affect sodium in particular ;tubular Na+ is sensed and if needed adjustments are made
he renin-angiotensin-aldosterone system (RAAS) is activated by
low [Na+] in the filtrate entering the distal convoluted tubule:
o Macula densa cells sense this change: are chemoreceptors
(slides 11 & 17) → signal to granular cells, aka juxtaglomerular
(JC) cells, which in turn release renin (a proteolytic enzyme)
What is Angiotensin ?
AT II has 4 principle actions:
1. Stimulates adrenal cortex to secrete aldosterone.
2. Stimulates posterior pituitary to release anti-diuretic
hormone (ADH).
3. Triggers sensation of thirst (targets the hypothalamus).
4. Is a potent vasoconstrictor (↑ total peripheral resistance (TPR), thus ↑ BP).
- Na+ is the major solute in the ECF
What 2 method smaintai blood volume and blood pressure ?
- RAAS system
- ANP
What is Aldosterone ?
Reabsorption of Na+ and secretion of K+ occurs in Principal (P) cells
in the distal convoluted tubule, due to the action of aldosterone.
* K+ movement depends on the potential caused by Na+ movement →
determines the amount of K+ lost in urine
majority of Na+ is reabsorbed in the proximal
convoluted tubule (water too; follows).
Yet ‘fine tuning’ happens in the distal tubule and
collecting ducts.
Anti diuretic hormone ?
ADH secretion promotes the reabsorption of water and increases BP (by increasing blood volume).
* Osmoreceptors (in the hypothalamus) detect changes in osmolarity
(the measure of solute concentration, defined as the # of osmoles per litre
of solution (Osmol/L)).
ADH can concentrate dilute urine ?
1.ADH is secreted when plasma osmolality is >290 mOsmol kg-1
2. Binds to vasopressin V2 receptor(s) on Principal cell basolateral mem.
3. Activates adenylyl cyclase (AC) → cAMP → PKA → fusion of vesicles containing AQP2 with the apical
membrane → water can now enter → urine is concentrated..!
4. When ADH levels fall, AQP2 is removed and recycled.
Diabetes Insipidus ?
Condition caused by the inability of kidneys to conserve water (i.e.
to concentrate urine) when needed.
- Symptoms: characterised by frequent urination (polyuria) and extreme thirst (polydipsia).
- Different to diabetes mellitus; urine does not contains sugar.
* Central (/cranial) diabetes insipidus:
o Caused by a lack of ADH e.g. due to damage of the posterior
pituitary (→ insufficient secretion), surgery, head trauma, etc.
* Nephrogenic diabetes insipidus:
o Kidneys fail/unable to respond to ADH:
o Cause(s): congenital (i.e. genetic) or acquired.
o Lack/loss of functional V2 receptors or AQP2
Why measure renal clearance ?
Problems with kidney function may lead to:
o Loss of nutrients from the body.
o Failure to remove toxins.
o Changes in blood pressure (BP).
o Change/affect drug treatments:
o Many drugs (and their metabolites) are cleared from body via the kidneys.
Clearance and GFR ?
- Freely filtered from the blood capillaries into bowman’s capsule;
- Neither reabsorbed nor secreted by the renal tubules;
- Has no overt effect on renal metabolism…
* …Then the renal clearance of that substance must reflect the GFR.
These criteria are met by the plant polysaccharide inulin, and creatinine (latter is produced at a fairly constant rate in skeletal muscle);
creatinine is typically used in the clinic to estimate GFR
What is the important of checking creatin levels ?
Relatively low levels of creatinine (urea, uric acid) in the plasma.
* If kidneys are not functioning as efficiently, these levels can rise →
could indicate that kidneys are not functioning to their full ability.
* In practice: blood is taken from the patient (so to measure amount
of creatinine in the plasma):
o Higher the levels of creatinine in the plasma, the slower the kidneys are working = low creatinine clearance, CrCl (ml/min
A urinalysis is a urine test. It is used to detect and manage a wide range of disorders; involves
checking appearance, content and concentration of urine
