Renal System - Renal Regulation of ECF Flashcards
What is aldosterone ?
Is a mineralocorticoid released from the adrenal cortex and directly affects Na+ reabsorption
Aldosterone is released when blood pressure is low (and angiotensin II is formed) and when there is a high potassium concentration in the ECF
It increases Na+,K+and ATPase activity and the expression of preformed epithelial Na+ channels at the cell membrane of tubular cells, primarily at the collecting duct.
What is the renin angiotensin system ?
Renin is released from juxtaglomerular cells in the kidney
Renin release is affected by 3 different stimuli;
Blood pressure - inverse relationship, renin release increases when arterial blood pressure decreases
Na+ entry to distal convoluted tubule - macula densa (modified region of DCT) links the amount of Na+ entering the tubule to renin secretion with renin secretion being inversely proportional to Na+ entry
Sympathetic nerves - renin release can be stimulated via activity of the sympathetic nerves innervating the juxtaglomerular cells
What is atrial natriuretic peptide ?
This peptide is secreted by the atrial myocardium in response to stretch caused by high blood volume
As a result the release of renin and aldosterone is reduced ; and water and Na+ reabsorption is reduced
Dilation of the afferent arteriole in response to atrial natriuretic peptide increases the glomerular filtration rate, and decreases blood volume
Why is it important to control ECF osmolarity ?
Cellular function
Hormonal regulation
Electrolyte and water balance
Kidney maintains extracellular fluid composition by regulating both Na+ and water reabsorption
Kidney does this by tailoring the composition of the urine to what is required by the body at that particular time
What is antidiuretic hormone and the 2 stimuli it produces ?
ADH is manufactured by paraventricular and supraoptic neurones in the hypothalamus, the neurones of which extend into the posterior pituitary
Affects the permeability of DCT, PCT and collecting duct epithelium to water
Baroreceptor stimulus
Osmoreceptor stimulus
Describe the baroreceptor stimulus.
The baroreceptor stimulus is the physiological response triggered by changes in blood pressure or ECF volume.
It works by detecting changes in blood pressure and then projection neurones from medulla oblongata relay signals to the hypothalamic neurones.
When blood pressure increases, baroreceptors decrease sympathetic and increase parasympathetic activity, reducing blood pressure.
Conversely, when blood pressure decreases, they increase sympathetic and decrease parasympathetic activity, raising blood pressure.
The baroreceptor reflex acts as a negative feedback loop, ensuring adequate perfusion of tissues and organs.
Describe the osmoreceptor stimulus.
Neurones within hypothalamus that monitor plasma osmolarity
They shrink with an increase in ECF osmolarity, this causes mechanosensitive ion channels to open and action potentials to be fired.
These signals are then relayed to the ADH manufacturing neurones of the hypothalamus, triggering the release of ADH from the posterior pituitary
At normal plasma osmolarity and volume there is a ‘background’ level of ADH release, therefore ADH levels can be increased or decreased if there is any deviation from normal body fluid composition
