Renal function 2 Flashcards
Describe the location and function of neuronal volume sensores in the heart
Type of receptor, location and function.
Type of receptor- Sensory nerve fibers
Location- Mostly right atrium, lesser extent left
Function- Act as Stretch receptors. When When the venous return increases, they become more stretched and signal to the medulla vasomotor centre about volume of blood returning to the heart per minute.
Describe the location and function of hormonal sensors in the heart
Type of receptor, location and function.
Type of receptor- Specialised muscle cells
Location- right atrium and inferior vena cava
Function- Stretching of these cells is caused by increased preload which can indicate excess blood volume.
Stretch causes release of atrial natriuretic peptide.
Causing increased fluid and sodium loss in urine hence reduction in BP
Muscle cells in ventricles also release BNP. Usually very low but rises when ventricles are over stretched. Also increases sodium excretion
Use of osmoreceptors in BP monitoring
Osmoreceptors- located in the supraoptic and paraventricular nuclei of hypothalamus, monitor osmotic stretch (pressure).
of the blood passing through them. Also obtain information from blood volume receptors via NTS.
Paraventricular and supraoptic nucleus send axons down the pituitary stalk to posterior pituitary.
These axons stimulate
ANTIDIURETIC HORMONE (ADH)secretion
And trigger thirst
Name the two nuclei important for control of water balance? How do the work?
Supraoptic and Paraventricular nuclei located in the hypothalamus.
Detect osmotic pressure of blood which passes through them
Release ADH from posterior pituitary in responce to increased osmolarity. Prevents Na+ and water loss.
Which has the higher osmolarity, renal medulla extracellular fluid or plasma
medulla extracellular fluid
What condition must be met before concentrated urine can be formed?
There needs to be concentrated fluid in renal medulla extracellular space
What is the name of the capillaries which surround the loop of henle? What is there function?
vasa reca
Supply oxygen
Describe the process of urine production
- Fluid flows from the proximal tubule go down into the thin descending loop of Henle, and up into the thick part of the ascending limb.
- The initial (thin) part of the loop has special channels (aquaporins) and this allows water to leave the tubule.
- As the fluid descends in the tubule it becomes more and more concentrated, because it is in equilibrium with the high concentration in the extracellular fluid of the renal medulla.
- Fluid then enters distal tubules then collecting ducts
What is special about the thick part of the ascending loop of henle?
IT IS IMPERMEABLE TO WATER. HERE MEMBRANE PUMPS MOVE SODIUM AND CHLORIDE IONS OUT INTO THE EXTRACELLULAR SPACE BY ACTIVE TRANSPORT.
This maintains the high extracellular fluid concentration in the renal medulla.
How is the high osmolarity of the extracellular medulla maintained?
The thick part of the ascending look of henle containes membrane pumps which move sodium and cl- into the extracellular space of the medulla
What is the potential difference between the lumen and the inside of the cell in the thick ascending loop of henle? How is this created? Why is it created?
PD- 80 mV.
A renal outer medullary potassium channel or ROMK
transports potassium out of the cells into the lumen. This creates a positive voltage (about 10 mV) in the tubular lumen.
The positive potential in lumen enhances inward flow of sodium, chloride & potassium
How is sodium, K+ and Cl- transported from the lumen into the medulla extracellular space?
- Na-K-Cl cotransporter channel NKCC2 in luminal walls of the epithelial cells allows sodium chloride & potassium to move passively together down their concentration gradient into the cells.
Sodium is actively transported out
Cl- moves out with the Na+
into the renal medullary extracellular space (interstitial fluid). K+ is transported back to the lumen using ROMK
Where does ADH actually exert its effect in the kidneys? How does it do so?
The collecting ducts
has aquaporin water channels that are opened by Antidiuretic Hormone (ADH).
Channels open- water reabsorbed into extracellular fluid
Consequently- less urine produced and at a high concentration (same as medullary extracellular fluid)
How is dilute and concentrated urone produced?
Dilute-Absence of ADH no reabsorption of water
Concentrated- Presence of ADH; reabsorption of water via aquaporins at the collecting duct; urine as concentrated as the renal medullary fluid
What is diabetes insipidus and water diuresis
Water diuresis occures when you to drinking too much water; blood becomes dilute; ADH release inhibited: result high volume of dilute urine.
This manifestation is diabetes insipidus
What is diabetes mellitus and osmotic diuresis
osmotic diuresis occures when sugars are not competly rebasorbed into the proximal tubules due to excesses.
Glucose passing into the collecting ducts provides an osmotic force which pulls water into the urine, uposing the force of the medulla.
There for high volumes of sugary urine is produced- this is diabetes mellitus
When you give blood your blood pressure does change, why?
- Neuronal blood pressure control system causes immediate vasoconstriction (sympathetic)
- Slight increase in heart rate
- Increase in peripheral vascular resistance
- Water moves from tissue to blood
5 renin-angiotesin system detects loss of water and reduces urine flow and increases thirst
What is the effect ADH has when it is being secreted and when triggered by the sympathetic nervous system?
- Decreases sodium excretion, less sodium lost in urine = less water lost in urine
- Urine is diluted back to normal
When triggered by sympathetic arousal during fight or flight water is conserved in expectation of blood loss due to trauma
Name all the locations where blood volume is sensed?
Blood volume is sensed by 1.neuronal and hormonal receptors in the atria
- Blood sodium level is sensed by sodium detectors in the kidney
- Blood osmolarity is sensed by osmoreceptors in the hypothalamus
What happens if blood volume is too high but osmolarity and sodium levels are normal?
ADH & renin levels do not change. Stretch receptors in atria increase ANP secretion, allowing more sodium and water to be excreted in urine. Conversely if blood volume is too low, ANP secretion is inhibited.
What happens if blood volume is too high and osmolarity & sodium levels are low
blood is too dilute. Antidiuretic hormone release from the posterior pituitary is inhibited, this causes an increased volume of urine to be excreted. Renin and aldosterone release increases and this retains sodium. Thus water but not sodium is excreted to bring volume and osmolarity back to normal
What happens after haemorrhage when blood volume will be low
osmolarity and sodium will also be low due to water moving into blood from tissues. ADH secretion will be stimulated due to low osmolarity. This reduces water loss in urine. ANP secretion is reduced due to reduced preload. Sodium excretion is inhibited. Renin and aldosterone secretion are increased due to low sodium. Tthis increases sodium retention. Thus both water and sodium are retained in the body. Behavioural thirst is stimulated which will help restore blood volume.
How do loop diuretics work? Name an example of this drug
block the transport of sodium and chloride out of the the loop of Henle. This abolishes the high concentration of solutes in the renal medulla and so prevents the formation of concentrated urine.
Drug-Furosemide
Where in the kidneys is the sight of ADH action?
Collecting ducts
What us the counter current multiplier mechanism?
process of pumping out salt into the extracellular fluid around the loop of Henle
What is the purpose of the countercurrent exchange? What is responsible for establishing this?
Function- preserve the concentration gradient in extracellular fluid ensures adequate oxygen supply to the medulla without washout of the high concentration needed for concentration of urine.
Vasa recta
