Kidney Flashcards
Descending Loop of Henle: (3)
As filtrate moves down the descending Loop of Henle, concentration of solutes increases in the surrounding
ISF around the nephron tubule.
This portion is permeable to water, so water leads osmosis, and is reabsorbed into the bloodstream.
Filtrate is left concentrated.
Ascending Loop of Henle: (3)
Surrounding fluid becomes dilute
This portion is impermeable to water but permeable to sodium chloride, which diffuses out and is reabsorbed
into the bloodstream, lowering the solute concentration of the filtrate
Filtrate is then diluted
Distal Convoluted Tubule: (2)
Sodium chloride are reabsorbed, and bicarbonate ions are reabsorbed into the blood to balance the pH levels
Drugs and poisons are secreted into the filtrate to be removed from the body
Collecting Duct: (4)
Filtrate enters collecting duct
As it moves down, it passes a region where surrounding fluid has higher solute concentration allowing for
water to leave collecting duct via osmosis.
Urine is now concentrated
Urea also diffuses out of the lower portion of the duct adding to the increase in solute concentration in ISF,
allowing for more water to be reabsorbed
Urine =
water + urea + sodium chloride + hydrogen ions + drugs + poison
Nephron =
Renal Corpuscle + Proximal Tubule + Loop of Henle + Distal Tubule
Counter current System in the kidney and its role in maintaining a medullary osmotic gradient.
Medullary osmotic gradient – counter current multiplier:
- The primary cause of the medullary osmotic gradient is the active transport of solutes
- In the ascending limb of the loop, active transport of Na+ ions drives passive transport of Cl- ions
- Addition of these ions to the ISF of the medulla increases its osmolarity
- Squamous epithelial cells of the descending limb of the loop are permeable to water but
impermeable to most solutes - Water leaves the filtrate in the descending limb of the loop, but the solutes cannot enter, thus
increasing filtrate osmolarity - Due to water movement, new filtrate entering the descending limb becomes more and more
concentrated as it flows to the bottom of the loop - Cuboidal epithelial cells of the ascending limb provide for active reabsorption of Na+ and Cl- ions, but are impermeable to water
- Due to the active reabsorption of solutes along the ascending limb, the filtrate being concentrated in
the loop bottom becomes more and more diluted towards the distal convoluted tubule - The limbs of the loop are close enough that each influences the processes occurring in the other
- Water moves out of the descending limb and produces saltier filtrate toward the loop bottom
- In the ascending limb, the solutes pumped out of the concentrated filtrate increase the medullary
osmotic gradient - More solutes leaving the ascending limb cause more water to leave the descending limb and vice versa
- These processes multiply each other until the dynamic equilibrium is achieved between osmolarity of
fluids in the different limbs of the Loop of Henle and the surrounding medullar space - This mechanism that constantly establishes the osmolarity gradient throughout the renal medulla is
called the counter current multiplier
Medullary osmotic gradient – urea recycling: (6)
- The effect of urea recycling greatly increases the medullary osmotic gradient values to their final
amounts - When filtrate enters the medullary part of the collecting duct, most water has been reabsorbed, leaving
urea relatively concentrated - Collecting duct cells are highly permeable to urea, so urea diffuses into the medulla, this increasing
the interstitial osmolarity - The effect of urea recycling greatly increases the medullary osmotic gradient values to their final
amounts - The rest of the nephron tubules are poorly permeable to urea; therefore, urea is recycled back to the
collecting duct in the medulla - Along with sodium chloride, urea provides a great deal of the solute load in the medulla, producing
much of the medullary osmotic gradient
Medullary osmotic gradient – vasa recta counter current exchange:
- An ordinary capillary carrying blood from the cortex, and through the medulla, would remove the
solutes necessary to generate the medullary osmotic gradient - The shape of the vasa recta follows the limbs of the loop, providing a mechanism to maintain the
gradient - Blood enters the medulla of the kidney with normal osmolarity
- As blood moves into the medulla, highly permeable vasa recta capillaries exchange solutes with ISF
- Blood osmolarity increases
- As the blood moves out of the medulla, up to the cortex, it loses solutes
- Blood osmolarity decreases nearly to the normal value
- The small increase of osmolarity in the blood leaving the vasa recta:
Is the result of the blood colloid osmolarity
Indicates that some water is lost from the body - Tissues are provided with nutrients and oxygen, but solutes that maintain the medulla osmotic
gradient are not transported away from the nephron
Kidneys control blood volume and pressure buy changing water level (removing more or less water)
Hormones involved in kidneys: (4)
Vasopressin
Aldosterone
Renin
Atrial natriuretic peptide
Vasopressin: (4)
- Antidiuretic hormone
- Released in response to low blood volume or high plasma osmolarity
- Cause kidneys to retain water by increasing water permeability of collecting duct
- Increase blood pressure
Aldosterone:
- Causes sodium retention and water retention
Renin: (2)
- Is released in response to low blood pressure
- Releases Angiotensin II which causes:
Vasoconstriction
Releases Vasopressin/Aldosterone
Causes thirst which increases water intake
Atrial natriuretic peptide: (2)
- Decreases blood pressure c
- Causes:
Vasodilation
Increases glomerular filtration
Inhibits release of Renin and Aldosterone
Inhibits sodium reabsorption → Less Na+ back in blood → Less water back in blood
Control blood pH
Bicarbonate ions released in filtrate
Reabsorbed back into blood stream based on pH of blood
- If blood is too ______ more bicarbonate ions reabsorbed
- If blood is too _______ less bicarbonate ions reabsorbed
Collecting ducts also secrete bicarbonate into acidic bloc
acidic
alkaline
RBC formation homeostasis:
- Kidneys secrets erythropoietin (EPO) → a stimulating factor for RBC formation
- When RBC count drops, resulting oxygen deficiency state is detected by kidneys which causes kidneys to
increase EPO production
Calcium homeostasis:
- Low blood calcium causes release of parathyroid hormone (PTH) → also causes kidneys to retain calcium
- This causes kidneys to release calcitriol (active vitamin D)
- Calcitriol promotes absorption of calcium in small intestine and increases reabsorption of calcium in nephrons
How are water levels maintained?
Hypothalamus + Posterior pituitary gland + kidneys maintain water balance in body
Osmoreceptors in hypothalamus monitor water levels
Neurosecretory cells in hypothalamus secrete ADH if
osmoreceptors detect low levels of water/increase in blood osmolarity (more solutes in blood)
The ADH travels down axons and is stored in posterior pituitary until needed
ADH targets kidney’s collecting
ducts to conserve water
How ADH works on collecting duct cells:
Collecting duct cells have ADH receptor proteins on the cell membrane.
When ADH binds to receptor, this stimulates the attachment of aquaporin proteins to the cell membrane, facilitating movement of water from lumen of collecting ducts to the blood stream (reabsorption)
An ADH receptor will receive the ADH hormone, a secondary messenger and protein kinase within the cells activate vesicles containing aquaporin proteins to move to the cell surface and allow for exocytosis to include the aquaporins on the membrane on cell. More aquaporins means that osmosis can take place more readily and more efficiently, thus the amount of water reabsorbed from the collecting ducts increases.
Effect of ADH on balancing of Blood Osmolarity:
Diuretics –. Enhances urine output + increases urine formation: (4)
- Alcohol – ADH inhibitor leading to dehydration (leads to hangover) (this is why the longstanding presence of alcohol in the system can cause a person to suffer a hangover)
- Drugs for hypertension or oedema (e.g.: furosemide or Lasix); Na+ reabsorption inhibitors (and resultant H2O reabsorption)
- Loop diuretics inhibit the medullary gradient formation (make the loop of Henle and the vasa recta inefficient) → kidney will not be able to release concentrated urine but rather diluted urine
- Osmotic diuretics: Substances that are not reabsorbed and this water will remain within the filtrate
(for e.g., high glucose of a diabetic patient)
Antidiuretic hormone disorders: (2)
- Mutation in ADH production or lack of receptors for ADH
- Causes severe dehydration and solute imbalance
- Diabetes insipidus - Hypersecretion of ADH
- Syndrome of inappropriate ADH secretion (SIADH)
- This will cause the body to retain far too much water and as a result the individual will be too hydrated.
Polyuria vs Oliguria vs Anuria
How do kidneys maintain homeostasis?
Aldosterone, renin, ANP (atrial natriuretic peptide) help maintain salt balance in order to control blood volume
Aldosterone: adrenal hormone that regulates sodium excretion
➔ Mechanism used to regulate sodium excretion → increases Na+ reabsorption from distal tubule and
collecting duct
Aldosterone secretion is controlled by the RAAS (renin-angiotensin-aldosterone system)
Juxtaglomerular apparatus (JGA)=
= afferent arteriole + efferent arteriole + distal tubule
What is juxtaglomerular apparatus?
It is a specialised structure made from the afferent
arteriole and the convoluted distal tubule. It is located
near the vascular pole of the Bowman’s capsule and its
main function is to correct changes in blood pressure
within the nephrons of the kidneys.
Mechanism of RAAS system to balance blood pressure and blood volume: (7)
- Blood pressure or blood volume drops
- Sensors in the JGA in the afferent arteriole detect the decrease
- This stimulates renin-secreting cells in afferent arteriole to secrete renin
- Renin causes angiotensinogen (liver) to convert into Angiotensin I
- ACE (angiotensin converting enzyme produced in lungs) converts Angiotensin I to Angiotensin II
- This causes adrenal gland to secrete aldosterone and causes arterioles to constrict causing blood
pressure to increase - Aldosterone increases reabsorption of sodium and hence water, increasing blood volume + blood
pressure
Clinical Application: Renin-Angiotensin System controls blood volume and blood pressure
ACE inhibitors: (2)
- Medication for blood pressure
- These inhibit angiotensin converting enzyme in the lungs (ACE)
Block normal production of Angiotensin II
Aldosterone concentration will decrease
Sodium + water excretion will increase
Blood volume will be slightly reduced
Blood vessels will dilate → lowering blood pressure
Coordinated Regulation of Salt and Water Balance
ADH (triggered by change in blood osmolarity) and RAAS (triggered by change in blood volume or blood
pressure) both increase water reabsorption, but only _____ maintains body fluid _______ (leads to sodium
reabsorption by release of aldosterone) by stimulating Na+ ________.
RAAS
osmolarity
reabsorption
Atrial natriuretic peptide(ANP), opposes the RAAS
- Secreted by atrial _________ of the heart
- Released in response to an increase in blood volume and ______
- inhibits the release of ______…aldosterone… (NaCl reabsorption) —ADH secretion
- lowers blood pressure and volume
myocardium
pressure
renin
_____, ADH, and the RAAS - checks and balances to control blood osmolarity, salt concentration, volume,
and pressure
ANP
Kidney disorders
If kidneys malfunction: (4)
- high blood pressure
- anaemia (too few RBCs)
- vitamin D deficiency
- dangerous fluctuations in blood pH
Disorders of the urinary system:
Causes of renal dysfunction → (3)
obstruction + infection + inflammation
What are the 3 types of kidney disease?
