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RENAL > Renal processes > Flashcards

Renal processes Flashcards

1
Q

What are the 3 basic renal processes

A
  1. Glomerular filtration
  2. Tubular reabsorption
  3. Tubular secretion
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2
Q

What does Glomerular filtrate contain?

A

All plasma substances except proteins (in same conc as plasma due to diffusion)

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3
Q

What drives Glomerular filtration?

A

Hydrostatic pressure in glomerular capillaries

opposed by hydrostatic pressure in bowman’s space and osmotic force of proteins in glomerular capillary plasma

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4
Q

How can GFR be
A.Measured?
B.Estimated?

A

A. Inulin clearance

B. Creatinine clearance

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5
Q

How can Renal clearance be estimated?

A

Dividing the mass of a substance er unit tame by the plasma concentration of the subtrance

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6
Q

Give two types of incontience and an explanation of each

A

Incontience - involuntary release of urine
Stress incontience - sneezing, coughing, exercising, often due to loss of support from anterior vagina. very common in older women.
Urge incontience - desire to urinate, often due to irritation to bladder or urethra due to bacterial infection

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7
Q

What are insensible water losses? Give examples.

A

Water loss a person is unaware of - evaporation of skin and the lining of respiratory passageways

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8
Q

What are sensible water losses? Give examples.

A

Water loss that a person is aware of, eg. urine, faeces, sweat

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9
Q

Does the proximal tubular cell have a BB? Why/Why not?

A

Yes proximal tubular cell has a BB due to the microvilli, this increases the SA for reabsorption.

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10
Q

Explain the mechanism of water-sodium coupling in reabsorption

A
  1. Na+ is transported out of the tubular lumen to interstitial fluid
    (due to active transport or Na+ channels across luminl membrane, and then ALWAYS due to Na+/K+ pumps on basolateral membrane)
  2. The removal of solutes from the tubular lumen decreases the local osmolarity
  3. This also increases the local osmolarity of the interstitual fluid
  4. Therefore water moves down the gradient from the lumen to the interstitial fluid
  5. From there, water, Na+ and other solutes (some are cotransported by Na+) move via bulk flow into the peritubular capillaries (pressure grad)
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11
Q

Why do water permeability vary along the tubular segments? What segment has a particularly high permeability?

A

It largely depends on aqua porins

The proximal tubule has a high number of aqua porins and so a high water reabsorption and Na+ reabsorbtion

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12
Q

What type of hormone is vasopressin? Where is it secreted?

A

Vasopressin is also known as antidiuretic protein (ADH), it is a peptide hormone. (acts quickly)
It is secreted by the posterior pituitary gland

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13
Q

Describe the mechanism of vasopressin on the luminal membrane

A
  1. When vasopressin is released into the interstitial fluid it binds to its receptor on the basolateral membrane
  2. This increases the production of cAMP
  3. cAMP activates the protein KINASE (PKA)
  4. Kinase phosphorylates proteins that increase the rate of fusion of vesicles containing AQP2 with luminal membrane
  5. This leads to an increase in the number of AQP2s into the luminal membrane
  6. Therefore there is a greater diffusion of water along the conc grad through the aqua porins into the collecting duct cells
  7. Water then diffuses through the AQP3 and AQP4 channels into the interstitial fluid then into the blood
    (Vasopressin has no affect on AQPs on basolateral membrane)
  8. ACTS ON COLLECTING DUCTS
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14
Q

What is water diuresis?

A

When there is low vasopressin so little reabsorption and therefore increased urine (water not solute) excretion

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15
Q

What causes diabetes insipidus?

A

Diabetes insipidus is caused by a failure of the posterior pituitary gland to relsease vasopressin, or the inability of the kidneys to respond to vasopressin correctly.
Therefore excess water is excreted. (This can be up to 25L/day and may lead to death due to dehydration and high solute osmolarity)

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16
Q

What is osmotic diuresis?

A

Osmotic diuresis is when there is increased urine flow due to increased solute excretion.
For example, a failure of Na+ reabsorption causes an increase in Na+ excretion. This increases water excretion due to Na+/H20 coupling.

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17
Q

Define the terms, hypo-osmotic, hyper-osmotic and isoosmotic

A

Hypo-osmotic- When the total solute conc is lower than normal ECF
Hyper-osmotic - total solute conc is higher than normal ECF
Isoosmotic- when total conc is normal

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18
Q

What is obligatory water loss?

A

Obligatory water loss is the minimum water loss needed to excrete 600mosmol of urea, sulfate and other waste products.
Daily excretion/max urinary conc = 0.44L/day

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19
Q

How does medullary interstitial fluid become hyperosmotic?

A
  1. Countercurrent anatomy of Juxtamedullary nephrons in loop of Henle
  2. Reabsorption of NaCl in ascending limb of loops of Henle
  3. Impermeability of water in ascending limb (and water permeability of descending limb)
  4. Trapping of urea in medulla (increases osmolarity)
  5. The hair pins loops of the vasa recta which minimise washout of hyperosmotic medulla
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20
Q

Explain the countercurrent multiplier system of the tubule?

A
  1. The two opposing flows of the descending and ascending limb causes a counter current
  2. The ascending limb transported NaCl out of the tubular lumen - therefore interstitial fluid becomes hyperosmotic.
    (-THICK ascending limb has transporters that cotransport Na+ and Cl-
    -THIN ascending limb uses simple diffusion )
  3. The descending limb is highly permeable to water and does not reabsorb NaCl, therefore water diffuses out till osmolarities of descending limb and interstitial fluid are equal
  4. The interstitial hyper-osmolarity is mantained due to ascending limbs continual pumping due to conc grad
  5. As the fluid goes deeper into the medulla the osmolarity difference is ‘multipied’
  6. The fluid enters distal convoluted tube - NaCl pumped out
  7. Then enters cortical collecting duct, water reabsoption occurs due to diffusion until it becomes isoosmotic to interstitial fluid and pertitubular plasma
  8. VASOPRESSIN affects cortical collecting duct and medually collecting duct so more water is reabsrobed due to more AQPs.

-The loop counter current multiplier causes the interstitial fluid of the medulla to become concentrated, this draws the water out of the collecting ducts concentrating the urine.

21
Q

What happens if Na+ plasma conc decreases?

A
  1. If Na+ plasma conc decreases then ECF plasma falls b/c Na+ is the main solute.
  2. This is detected by baroreceptors such as the carotid sinus (↓ plasma volume, ↓ venous pressure, ↓ venous return, ↓ atrial pressure, ↓ ventricular end-diastolic volume, → ↓ Stroke volume, ↓ CO, ↓ Arteriole Bp.)
  3. This activates sympathetic neurons of the kidney which constricts afferent arterioles, and ↓ GFP which ↓ GFR
  4. Therefore less Na+ and H20 are excreted
22
Q

What type of hormone is aldosterone? Where is it secreted?

A

Aldosterone is a steroid hormone (acts more slowly). It is secreted from the adrenal cortex

23
Q

What does aldosterone do?

A

Aldosterone stimulates Na+ reabsorption by distal and cortical collecting ducts, it induces the synthesis of all channels and pumps in cortical collecting duct
no aldosterone = approx 2% of na+ is excreted
high aldosterone = all na+ reabsorbed

24
Q

Decribe the renin-aldosterone system

A
  1. Renin(enzyme) is secreted by juxtaglomerular apparatuses in afferent arterioles.
  2. Renin catalyses the conversion of angiotensinogen (from the liver) to angiotensin I. (10aa)
  3. ACE then catalyses the conversion of angiotensin I to angiotensin II. (8aa) ACE is found on the luminal surface of pulmonary capillary endothelial cells
  4. Angiotensin II stimulates the secretion of aldosterone from the adrenal cortex, and the constriction of arterioles
  5. Aldosterone means that Na+ (and therefore H20) is retained and not excreted leading to an increase in bp
  6. Aldosterone stimulates Na+ reabsorption by distal and cortical collecting ducts, it induces the synthesis of all channels and pumps in cortical collecting duct
    no aldosterone = approx 2% of na+ is excreted
    high aldosterone = all na+ reabsorbed
  7. Vasoconstriction also leads to an increase in bp
25
Q

What is renin, how does it work, and where is it secreted?

A

Renin is an enzyme that catalyses the reaction of angiotensinogin to angiotensin I. It is secreted by juxtaglomerular apparatuses in afferent arterioles of the kidney.
-Stimulates RAAS

26
Q

What causes an increase in renin production?

A
  1. Renal Symp nerves (leads to an increase in plasma bp, and increased na+ reabsorption)
  2. intrarenal baroceptors (detects low plasma bp)
    Juxtaglomerular (JG) cells act as intra renal baroceptors.
    When plasma pressure in the kidney is decreased these cells are stretched less and therefore secrete more renin
  3. Mascula densa - senses the amount of Na+ flowing past, a decrease causes the release of paracrine factors that diffuse to nearby JG cells, activating them and causing renin release.
    (If salt intake is low then less na+ passes mascula densa and renin is released)

It is secreted by juxtaglomerular apparatuses in afferent arterioles of the kidney. (It catalyses reaction of angiotensinogin to angiotensin I, therefore releasing angiotensin II and aldosterone which raises bp)

27
Q

How do ACE inhibitors work? Give an example

A

ACE inhibitors stop the conversion on angiotensin I (10aa) to angiotensin II (8aa). eg, linsinopril

28
Q

How do angiotension II receptor blockers work? Give an example

A

Angiotension II receptors prevent angiotension II from binding the receptors on target organ. eg losartan

29
Q

What does atrial natriuretic peptide (ANP) do? Where is it secreted? How is it stimulated?

A

ANP (or ANF or ANH) acts on several tubular segments to inhibit Na+ reabsorption.
Cells in the cardiac atria synthesize and secrete ANP.
ANP also acts on renal blood vessels, the afferent arteriole is dilated and the efferent is contricted, this creates a higher pressure that ↑ GFR and further ↑ Na+ excretion
ANP can also inhibit aldosterone secretion, inhibiting Na+ reabsorption
ANP is stimulated by an increase in atrial distension (due to high Na+ levels and therefore high plasma volume)

30
Q

Explain osmoreceptor control of vasopressin

A

Osmoreceptors in the hypothalamus measure osmolarity changes

  • Excess water
  • Leads to decreased blood fluid osmolarity
  • Decreased firing of hypothalamic osmoreceptors
  • Decreased vasopressin secretion by the posterior pituitary gland
  • Decreased plasma vasopressin
  • Collecting ducts have less AQPs, and therefore lower permeability
  • Reduced water reabsorption
31
Q

Explain baroreceptor control of vasopressin

A

baroreceptors only respond when a large amount fo water has been lost - eg hemorrhages
-large decrease in plasma volume
-reduced venous, atrial and arterial pressures
-increased cardiovascular baroreceptors firing
-increased vasopressin released from posterior pit
-1. When vasopressin is released into the interstitial fluid it binds to its receptor on the basolateral membrane
2. This increases the production of cAMP
3. cAMP activates the protein KINASE (PKA)
4. Kinase phosphorylates proteins that increase the rate of fusion of vesicles containing AQP2 with luminal membrane
5. This leads to an increase in the number of AQP2s into the luminal membrane
6. Therefore there is a greater diffusion of water along the conc grad through the aqua porins into the collecting duct cells
7. Water then diffuses through the AQP3 and AQP4 channels into the interstitial fluid then into the blood
(Vasopressin has no affect on AQPs on basolateral membrane)

32
Q

Explain the response to the following stimuli

  • ethanol
  • hypoxia
  • nausea
  • sweating
  • thirst
A

-ethanol, inhbits vasopressin release, less reaborption, more water excreted
-hypoxia, alters vasopressin release via afferent input from peripheal arterial chemoreceptors to hypothalamus, (via ascending pathways from medulla oblongata to hypothaalmus)
-nausea, potent stimulus to vasopressin
-sweating, loss of hypoosmotic salt solution
a) increased plasma osmolarity - increased vasopressin - decreased urination
b)decreased plasma volume - increased aldosterone, increased na+ reabsorption
decreased GFR, decreased na+ excretion
-thirst
stimulated by increased plasma osmolarity and decreased ECF volume (stimulates vasopressin release by osmo/baroreceptors)
hypothalmus

33
Q

What is the most abundant ICF ion?

A

K+

34
Q

What is hyperkalemia?

A

Hyperkalemia is high K+ levels
Hypokalemia is reduced K+ levels
(can lead to problems with arrhythmias, skeletal muscle, and action potentials)

35
Q

Explain the relationship between K+ and Na+ reabsorption

A

K+ and Na+ are transported across the basolateral membrane via Na+/K+ATPase molecules, this means that when Na+ is reabsorbed (due to high aldostrone) K+ is secreted into the tubular lumen. However K+ can diffuse back down the membrane./
The cells in the adrenal cortex are sensitive to K+ conc, increased K+ = increased aldosterone = increased secretion of K+ and increased excretion

36
Q

Explain Ca2+ reabsor

A

-60% of Ca is available for filtration, the remainind 40% is protein bound or in complexes with anions
-Decreased Ca levels
-Increased PTH
-Opens Ca channels in distal convoluted tubbule
-Increased Ca reabsorption
low Ca levels also increases the acvitity of 1-hydrolase enzyme activating 25(OH)-D to 1,25(OH)2 which increases calcium and phosphate reabsorption for the GI tract
(60% of Ca reabsorption occurs in the proximal tubule which is not under hormonal control)

37
Q

What is PTH?

A

Parathyroid hormone from the parathyroid gland

38
Q

What are diuretics and how do most of them work?

A

Diuretics are drugs that are used to increased urination
-most act on the tubules to inhibit na+ reabsorption (along with Cl or HC03) and therefore increase excretion, as water is dependent on solutes, and na and water coupling, water reabsorption is also reduced = increased water excretion

39
Q

How do the following diuretics work?

  • loop diuretics eg, furosemide
  • spirondactone
  • Osmotic diuretics eg, mannitol
A
  • loop diuretics eg, furosemide. acts on ascending limb of the loop of Henle to inhibit the cotransportation of NaCl across the luminal membrane
  • spirondactone, blocks action of aldosterone
  • Osmotic diuretics eg, mannitol . water is filtered by not reabsorbed, so water is retained in the urine
40
Q

What is osmolality?

A

Measure of dissolved solute particles per kg of solvent

41
Q

What is osmolarity?

A

Measure of dissolved solute particles per L of solvent

42
Q

What is oncotic pressure?

A

The pressure exerted by proteins (notably albumin) on capillary walls that tends to keep water in the circulatory system

43
Q

What is osmotic pressure

A

The minimum pressure that must be applied to a solution to stop the net flow of water

(in capillaries it acts against the blood pressure, this usually means that water flows out of the capillary at the beginning and then back in nearer the end, when the blood pressure decreases)

44
Q

What is glomerular filtration rate? (GFR)

A

Glomerular filtration rate (GFR) is the volume of fluid filtered from the renal (kidney) glomerular capillaries into the Bowman’s capsule per unit time

(Urine conc * Urine volume) / plasma conc

-GFR dependent on the difference between the higher blood pressure created by vasoconstriction of the input or afferent arteriole versus the lower blood pressure created lesser vasoconstriction of the output or efferent arteriole.

(more or less equal to clearance of creatinine)

45
Q

How can low albumin lead to odema?

A

Low albumin = low ONCOTIC pressure (lower than hydrostatic)
this means water is drawn out of the capillary into cells due to the hydrostatic pressure and then isn’t drawn back in because the oncotic pressure is lower than the hydrostatic pressure

(in normal person water flows out of the capillary at the beginning and then back in nearer the end, when the hydrostatic pressure decreases)

46
Q

What are insensible losses?

A
  • Evaporation, respiratory losses

- Losses you cannot detect or measure

47
Q

What occurs due to angiotensin II?

A
  1. Increased Symp activity
  2. SODIUM REABSORPTION = water coupling
  3. Vasopressin release = water reabsoption
  4. Vasoconstriction = increase in bp
  5. acts on pituitary gland = releases ADH
48
Q

What is the juxtaglomerular apparatus?

A

The juxtaglomerular apparatus consists of three cells:

the macula densa, a part of the distal convoluted tubule of the same nephron
juxtaglomerular cells, which secrete renin
extraglomerular mesangial cells

RENAL (2 decks)

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