kidney function III: regulation of ECF and blood volume Flashcards
What are some causes of increased extracellular fluid (ECF) osmolality?
Water deprivation, solute ingestion, diarrhea.
What happens when ECF osmolality increases?
Osmoreceptors detect the change and initiate responses.
What are the two key osmoreceptor areas in the brain?
Supraoptic & paraventricular nuclei
Lateral preoptic area
What is the function of the supraoptic & paraventricular nuclei?
They stimulate ADH release from the posterior pituitary.
What does ADH do after being released from the posterior pituitary?
It makes the collecting duct (CD) water-permeable, leading to water retention by the kidneys.
What is the function of the lateral preoptic area?
It stimulates thirst, prompting the person to drink water.
How does drinking water and water retention restore balance?
It reduces ECF osmolality, bringing it back to normal (290 mosm/kg).
what process happen in water excretion instead?
opposite of water retention
What can cause a decrease in extracellular fluid (ECF) osmolality?
Excessive fluid ingestion.
What happens when ECF osmolality decreases?
Osmoreceptors detect the change and initiate responses.
What are the two key osmoreceptor areas in the brain?
supraoptic & paraventricular nuclei
Lateral preoptic area
What happens when the supraoptic & paraventricular nuclei detect low osmolality?
ADH release is suppressed, making the collecting duct (CD) water-impermeable.
What is the function of the lateral preoptic area in response to low osmolality?
It suppresses thirst, reducing fluid intake.
How does the kidney respond to suppressed ADH?
It excretes more water, restoring osmolality to normal (290 mosm/kg).
What is osmolality?
The concentration of water in the extracellular fluid (ECF), which is tightly controlled.
What determines the volume of the extracellular fluid (ECF)?
The total quantity of solute, mainly NaCl (sodium chloride)
What is the key factor in ECF volume regulation?
Sodium balance.
How much dietary salt (NaCl) is typically consumed per day?
It varies between 0.05g to 25g per day, with an average of 2.3g/day.
What dictates the volume of the extracellular fluid (ECF)?
The total amount of sodium (NaCl) in the ECF.
What happens when 0.2g NaCl is added to 1L of water?
The concentration increases from 1g/L to 1.2g/L.
How does osmoregulation correct changes in ECF osmolality?
It increases water retention, diluting the concentration back to 1g/L.
What is the final volume after osmoregulation when 1.2g NaCl is present?
1.2L of water is retained to restore normal concentration.
What are the major compartments of body water?
Intracellular water (28L)
Extracellular fluid (ECF) – includes:
Interstitial water (10L)
Plasma (4L)
What are the key solutes in body fluids?
Sodium (Na⁺) – Mostly in ECF
Potassium (K⁺) – Mostly in intracellular fluid
Glucose – Found in small amounts
Why is plasma volume important?
It determines blood pressure in veins, cardiac chambers, and arteries.
What happens if total body sodium is low?
Low plasma volume
Low cardiovascular pressures
What does the body directly control in the vascular system?
The osmolality and volume of the extracellular fluid (ECF).
How does the control of ECF osmolality and volume affect the body?
It affects the osmolality and volume of other compartments in the body.
How is ECF osmolality normally maintained?
At the expense of volume.
What controls water balance (H₂O) in the body?
osmoreceptors.
How do osmoreceptors regulate water balance?
Renal excretion by altering ADH release.
Water intake by altering thirst.
How is sodium excretion in urine determined?
Sodium excreted in urine = Sodium filtered - Sodium reabsorbed.
What are the two main factors that regulate sodium (Na⁺) content in the body?
Glomerular Filtration Rate (GFR)
Sodium Reabsorption
Is there strong evidence for a regulatory “Na⁺ appetite” in humans?
No, there is little evidence for a regulated sodium appetite in humans.
What does glomerular filtration rate (GFR) depend on?
Net filtration pressure
Permeability of filtration interface
Surface area
How is GFR regulated?
By both neural and hormonal input.
What does a higher GFR result in?
Greater excretion of salt and water.
What is Intrinsic Control of GFR?
Internal to the kidney, it protects renal capillaries from hypertensive damage and maintains a healthy GFR.
What is Extrinsic Control of GFR?
External to the kidney, it maintains arterial blood pressure by controlling GFR.
What is the Intrinsic Control of GFR?
It protects renal capillaries from hypertensive damage and maintains a healthy GFR.
How does Intrinsic Control regulate GFR when blood pressure changes?
Afferent arterioles constrict when BP suddenly increases.
Afferent arterioles dilate when BP suddenly decreases.
This keeps capillary pressure and glomerular blood flow constant.
What is the normal BP range where Intrinsic Control maintains GFR?
Between 90-200 mmHg.
What is Autoregulation in GFR control?
The kidney’s ability to maintain constant renal blood flow despite changes in BP.
What is Autoregulation in the kidney?
The ability to control afferent arteriole constriction to regulate glomerular filtration rate (GFR).
What are the mechanisms of autoregulation in the kidney?
Myogenic response
Tubuloglomerular feedback
What is the myogenic response in renal autoregulation?
A mechanism where afferent arterioles constrict in response to increased blood pressure, helping maintain constant glomerular filtration rate (GFR).
What happens to smooth muscle cells in response to increased hydrostatic pressure?
Stretch-activated calcium channels open
Smooth muscle contracts
Afferent arteriole vasoconstricts
GFR remains stable
How does the myogenic response regulate renal blood flow?
By adjusting vascular resistance in the afferent arteriole to maintain stable glomerular capillary pressure.
what is the tubuloglomerular feedback mechanism?
A process where the macula densa detects increased NaCl delivery and signals the afferent arteriole to constrict, reducing glomerular filtration rate (GFR).
What happens when NaCl delivery to the macula densa increases?
- ATP and ADP are released.
- Converted to adenosine.
- Adenosine binds A1 receptors, increasing Ca²⁺ in vascular smooth muscle cells (VSM).
- Vasoconstriction of the afferent arteriole occurs.
- GFR decreases to prevent excessive filtration.
How does adenosine affect the afferent arteriole?
It increases calcium in smooth muscle cells, causing vasoconstriction and a decrease in GFR
What is intrinsic control of GFR (autoregulation)?
A mechanism where the kidney maintains GFR despite changes in arterial pressure.
When is intrinsic control of GFR absent?
When arterial pressure falls below 90 mmHg.
Why is autoregulation not perfect?
Because renal blood flow (RBF) and GFR still fluctuate with arterial pressure.
What is extrinsic control of GFR?
GFR can be altered by neural and hormonal input when extracellular fluid volume (ECFV) is outside the normal range.
Can GFR be controlled by both intrinsic and extrinsic mechanisms?
Yes! Intrinsic autoregulation maintains GFR, but extrinsic factors (e.g., hormones, neural signals) can override it.
What do sensors regulate in sodium reabsorption?
They affect renin or natriuretic peptide secretion.
Name the main sensors involved in sodium reabsorption control.
Macula densa
Intrarenal baroreceptors (granular juxtaglomerular cells)
High-pressure baroreceptors (central arterial tree)
Low-pressure baroreceptors (cardiopulmonary circuit)
Muscle cells of cardiac atria & ventricles
What is the role of renin-angiotensin II-aldosterone in sodium reabsorption?
It stimulates Na⁺ reabsorption.
How does direct pressure on the kidney affect renin?
it stimulates renin release.
How do renal sympathetic nerves regulate sodium reabsorption?
They stimulate renin release.
What is the effect of natriuretic peptides on sodium reabsorption?
They cause natriuresis and inhibit Na⁺ reabsorption.
What is the juxtaglomerular apparatus (JGA)?
A structure in the kidney involved in renin release, consisting of juxtaglomerular cells, macula densa, and extraglomerular mesangial cells.
What are the intrinsic mechanisms controlling renin release?
Tubuloglomerular feedback
Intrarenal baroreceptors
What are the extrinsic mechanisms controlling renin release?
Sympathetic nervous system.
What is the function of the macula densa?
It acts as a sensor that detects NaCl (sodium chloride) levels in the filtrate and regulates renin release.
How does increased NaCl delivery to the macula densa affect renin release?
Increased NaCl → More adenosine (ADO) formation
Adenosine increases calcium (Ca²⁺) in granular cells
Increased calcium inhibits renin release
Result: Reduced GFR due to afferent arteriole vasoconstriction.
What is the key messenger that mediates the macula densa’s effect on renin release?
Adenosine (ADO)—it increases calcium in granular juxtaglomerular cells, inhibiting renin release.
What is the extrinsic control of renin release?
Sympathetic nerves of granular cells receive signals from baroreceptors.
What type of nerve fiber is involved in extrinsic control of renin release?
Sympathetic nerve fiber.
Where are renin-containing cells located?
Granular juxtaglomerular cells.
What anatomical structure includes juxtaglomerular cells and macula densa?
The juxtaglomerular apparatus (JGA).
What causes renin release from the kidney?
↓ sodium delivery to the macula densa
↓ wall tension in the renal afferent arteriole
↑ sympathetic activity in response to low blood pressure
What is a common cause of renin release?
Low blood volume (Hypovolemia).
What is the precursor molecule in the renin-angiotensin system?
Plasma angiotensinogen
What enzyme converts angiotensinogen into angiotensin I?
Renin
What converts angiotensin I into angiotensin II?
Plasma ‘converting enzyme’
What are the effects of angiotensin II?
Stimulates Proximal Tubule Na⁺ Reabsorption
Stimulates ADH Release
Causes Aldosterone Secretion
Causes Thirst
Vasoconstricts Small Arterioles
What is the role of Angiotensin II in sodium reabsorption?
Angiotensin II stimulates proximal tubule Na⁺ reabsorption by binding to AT1 receptors.
What receptor does Angiotensin II bind to for sodium reabsorption?
AT1 (Angiotensin II Type 1 receptor).
What transporters are involved in sodium reabsorption in the proximal tubule?
Na⁺:H⁺ Exchanger (NHE3)
Na⁺:K⁺ ATPase pump
Where does Angiotensin II bind in the brain?
It binds to angiotensin II receptors in the hypothalamus.
What are the two main effects of Angiotensin II binding in the brain?
Stimulates ADH release
Causes thirst
What brain structure contains osmoreceptors that regulate ADH release?
The hypothalamus.
What stimulates the release of aldosterone?
Angiotensin II stimulates aldosterone release from the adrenal cortex.
Where is aldosterone released from?
The zona glomerulosa of the adrenal cortex.
What is the sequence of events leading to aldosterone release?
Renin converts angiotensinogen to angiotensin I.
Angiotensin I is converted to angiotensin II by a converting enzyme.
Angiotensin II stimulates the adrenal cortex to release aldosterone.
What is the effect of aldosterone on sodium reabsorption
Aldosterone increases Na⁺ reabsorption in the distal convoluted tubule (DCT) and collecting duct (CD).
In which parts of the nephron does aldosterone act?
Distal convoluted tubule (DCT) and collecting duct (CD).
What is the role of renin in the renin-angiotensin system?
Renin converts angiotensinogen into angiotensin I.
How is angiotensin II formed?
Angiotensin I is converted to angiotensin II by a plasma ‘converting enzyme’.
What hormone is released by angiotensin II to regulate sodium?
Aldosterone is released from the adrenal cortex.
What is the effect of aldosterone on sodium?
Aldosterone increases sodium reabsorption in the DCT and CD.
How does increased sodium reabsorption affect extracellular fluid (ECF)?
It leads to ECF expansion via osmoregulation
What is the final outcome of this process?
Restoration of blood volume and regulation of blood pressure.
What is the primary function of aldosterone?
Increases sodium (Na⁺) reabsorption in the distal convoluted tubule (DCT) and collecting duct (CD).
Aside from the kidney, where else does aldosterone increase Na⁺ reabsorption?
Sweat glands, salivary glands, and the gut.
How does aldosterone regulate sodium balance?
It promotes Na⁺ retention, helping to maintain blood pressure and extracellular fluid volume.
What receptor does angiotensin II bind to in renal arterioles?
Angiotensin II type 1 (AT1) receptors.
How does angiotensin II affect renal arterioles?
Vasoconstriction of both afferent and efferent arterioles, reducing GFR.
What is the effect of reduced GFR on sodium and water excretion?
Decreased sodium and water excretion, helping to conserve blood volume and pressure.
What receptor does low plasma angiotensin II bind to in the kidney tubules?
Angiotensin II type 2 (AT2) receptors.
What renal process is stimulated by low plasma levels of angiotensin II?
Pressure natriuresis and diuresis.
What triggers the release of natriuretic peptides (NP) in the heart?
Heart stretch due to high blood volume.
Where is A-type Natriuretic Peptide (ANP) secreted from?
Atrial myocardium.
Where is B-type Natriuretic Peptide (BNP) secreted from?
Ventricular myocardium.
What is the natriuretic effect of ANP and BNP?
Inhibits Na⁺ entry into collecting duct cells by blocking epithelial sodium channels (ENaC), inhibits renin and aldosterone release.
How do ANP and BNP act as diuretics?
Inhibit ADH release, reducing water retention.
What are the hypotensive effects of ANP and BNP?
Decrease blood pressure by systemic vasodilation and increase GFR by dilating renal afferent arterioles.
What ion channels are involved in the action of ANP and BNP?
