L13 Renal System Flashcards
Define diuresis
The removal of excess water in urine
What do diuretic drugs do?
Promote urine excretion
- formation of dilute urine
What do antidiuretic hormones control?
Controls the permeability of cells in the collecting duct to H2O
How do diuretic drugs work?
They make the collecting duct impermeable to H2O
- no reabsorption from the collecting duct
How does ADH regulate water volume?
- ADH makes the collecting duct permeable to H2O
- H2O is reabsorbed passively driven by the osmotic gradient in the medullary interstitium
- results in concentrated urine and water conservation
Outline the mechanism of ADH
1) ADH bonds to receptors on the basolateral cell surface
2) stimulates adenylyl cyclase to generate cAMP and activate protein kinases
3) increased insertion of aquaporin 2 into apical membrane
4) increased water permeability
5) increased water reabsorption
6) concentrated urine water conservation
What controls ADH release?
Osmoreceptors
What can stimulate increased ADH release?
Decreased blood volume and pressure
Where is ADH produced?
By cells in the supraoptic and paraventricular nuclei of the hypothalamus
Where is ADH stored?
In vesicles in the posterior pituitary gland
What are changes in the plasma osmolarity sensed by?
By osmoreceptors in the hypothalamus
How does osmolarity affect ADH?
Increased osmolarity = increased ADH
Decreased osmolarity = decreased ADH
How is ADH removed?
By the liver and kidneys
How is normal osmolarity restored after water deprivation?
- increased ECF osmolarity
- supraoptic and paraventricular nuclei release ADH from the posterior pituitary
- CD made water permeable
- lateral pre optic area leads to thirst and the person drinks water to get back to normal osmolarity
- water retention by the kidney
How is normal osmolarity restored after excessive fluid ingestion?
- decreased ECF osmolarity
- ADH release is suppressed and the CD is made water permeable via supraoptic and paraventricular nuclei
- water excretion from the kidney
- this suppressed by by the lateral pre optic area
List physiological stimuli for ADH release?
High temperature
Exercise
Pain
Heightened emotions/stress
How is nocturnal enuresis (bed wetting) caused?
There is a delay in development of the normal circadian rhythm of ADH
- increased ADH in adults overnight
What leads to innapropriate secretion of ADH?
Post operative pain
Intracranial disease
Ectopic ADH production - tumours
Pneumonia, TB, pulmonary disease
How does MDMA alter fluid balance?
when MDMA increases fluid in It stimulates
- thirst reflex
- repetitive behaviour
When MDMA decreases fluid out it stimulates
- ADH secretion
What is the overall effect of ADH?
Decreased H2O excretion
Increase in blood volume
What happens when there is a deficiency in ADH?
Diabetes insipidus
What is caused when nephrons no longer respond to ADH?
Nephrogenic diabetes insipidus
How are sodium ions handled by the nephron?
Freely filtered at the glomerulus
- 67% reabsorbed from PCT
None reabsorbed from the thin loop of henle
- 25% reabsorbed from thick ascending limb of LOH
- 5% reabsorbed from DCT
- 3% reabsorbed from collecting duct
- 0.4% of the filtered Na is excreted in dilute urine
How can Na+ reabsorption be increased?
When the renin-angiotensin-aldosterone axis is activated
How is renin release stimulated?
Decreased NaCl at macula dense
Stretch receptors in the afferent arteriole sense decreased BP
Increased renal sympathetic nerve stimulation due to central decreased BP
What is the cellular action of aldosterone?
1) aldosterone binds to the receptor in the cytoplasm
2) initiates transcription
3) increased number of ENaC channels in apical surface
4) increased Na-K pumps
5) Na+ reabsorption where Cl- follows K+ secretion
Where and when is aldosterone synthesised?
A steroid hormone synthesised in the adrenal cortex following stimulation by Angiotensin II
What does aldosterone promote?
Promotes reabsorption of Na+ by principal cells in the last third of the distal convoluted tubule an in the cortical collecting duct
What is the overall effect of aldosterone?
Decreased NaCl and H2O excretion
Increased blood volume
What is the role of Angiotensin II?
Stimulates release of aldosterone from the adrenal cortex
Acts on the brain to create the sensation of thirst
Powerful vasoconstrictor
What does Angiotensin II inhibit?
Inhibits the baroreceptor reflex and increases the release of norepinephrine from the sympathetic postganglionic fibres
What is the overall effect of Angiotensin II?
Decreased NaCl and H2O excretions leads to increased blood volume and pressure
How is atrial natriuretic peptide produced?
By the atria in response to stretch (increased BV/BP)
What does atrial natriuretic peptide regulate?
Regulates the plasma volume and concentration of Na+
What does ANP increase?
Increases renal water and Na+ excretion
- opposite actions to ADH and aldosterone
What does ANP inhibit?
Inhibits thirst
Inhibits ADH, aldosterone and renin release
What is the overall effect of ANP?
Increased NaCl and H2O excretion
Decreased blood volume and pressure
What is nephrolithiasis?
The formation of renal calculi (kidney stones) crystalline structures which are composed of calcium oxalate salts
What causes nephrolithiases?
Due to a higher than normal ion and solute concentration in the filtrate
E.g. dehydration, high fat/salt diets, obesity
Where do crystals form in nephrolithiasis?
Form in the nephron loop, distal tubule and or collecting system
Where do crystals travel?
They pass through the epithelium and can adhere to it
What happens if crystals break off and lodge?
They can lodge in calyces, renal pelvis and ureter
Causes severe pain, blood in urine, sweating, nausea and vomitting
Define urine
Fluid that leaves the collecting duct and flows through the ureter to the bladder
Define bladder
A hollow organ that can expand to hold around 500ml
Has a smooth muscle wall
The neck of the bladder is continuous with the urethra
What are the two rings on sphincter muscles?
Internal - smooth muscle that has normal tone which keeps it contracted
External - skeletal muscle controlled by somatic motor neurones and is kept contracted by tonic stimulation from the CNS
Explain the structure of the bladder at rest
Internal sphincter passively contracted
External sphincter stays contracted
The bladder is in a relaxed filling state
Higher CNS input
Outline the mechanism of micturition
1) stretch receptors fire
2) parasympathetic neurones fire and motor neurons stop firing
3) smooth muscle contracts and the internal sphincter passively pulls open
4) external sphincter relaxes
