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MD 1 > Renal Block > Flashcards

Renal Block Flashcards

1
Q

What are the main functions of the kidney?

A
  1. Make urine
  2. Regulate BP
  3. Regulate RBC production (kidney produces erythropoietin)
  4. Contribute to vitamin D metabolism (kidney needed to activate it)
    [5. Communicate with the CNS]
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2
Q

What is urine mainly composed of?

A

Plasma.

The kidneys filter ~200L of plasma to produce 2 litres of urine

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3
Q

What percentage of cardiac output goes to the kidney?

A

20-25%

Large amount of blood flow = big impact on TPR

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4
Q

What are the healthy ranges of potassium, phosphate, urea, creatinine, bicarbonate, glucose and albumin in urine?

A 
Urea = 300
K = 20-70
PO4 = 20-40
Creatinine = 10
HCO3 = 0
Glucose = 0
Albumin = 0

Reabsorbing more water increases the concentration of waste products in the urine (more concentrated urine)

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5
Q

What are the healthy ranges of potassium, phosphate, urea, creatinine, bicarbonate, glucose and albumin in plasma?

A 
Urea = 10
K = 4
PO4 = 1
Creatinine = 0.01
HCO3 = 25
Glucose = 5
Albumin = 30
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6
Q

Name the main components of a nephron

A
  • Afferent (pre-glomerular) arteriole
  • Efferent (post-glomerular) arteriole
  • Bowman’s capsule containing the glomerulus
  • Proximal (convoluted) tubule
  • Loop of Henle (LoH) - has a descending and ascending limb
  • Distal tubule
  • Collecting duct
  • Peritubular capillaries run parallel to the tubules of the nephron
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7
Q

What percentage of plasma is filtered as it goes through the glomerulus?

A

20%

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8
Q

What are the 4 main events/processes that occur in a nephron?

A
  • Filtration (movement from blood to lumen of tubules)
  • Reabsorption (movement from tubule lumen to blood)
  • Secretion (from blood to tubule lumen)
  • Excretion (from tubule lumen to the external environment; urine)
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9
Q

What are the filtration, reabsorption, secretion, and excretion profiles of water, sodium, potassium, calcium, phosphate, glucose, creatinine and urea?

A
  • Filtration: all are filtered
  • Reabsorption: everything is reabsorbed to an extent, except creatinine
  • Secretion: K+ can also be secreted
  • Excretion (% of filtered):
    Water = 1%
    Na = 0.5%
    K = 10%
    Ca = 2%
    PO4 = 20%
    Glucose = 0% (completely reabsorbed)
    Creatinine = 100% (none reabsorbed)
    Urea = 50%
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10
Q

Briefly describe the main features of a glomerulus

A
  • The glomerulus is enclosed within Bowman’s capsule
  • Inside Bowman’s capsule there is Bowman’s space/lumen of Bowman’s capsule: plasma that is filtered out of the glomerular capillaries enter Bowman’s space and are drained into the proximal tubule
  • Glomeruli have podocytes
  • Macula densa (in close proximity to the glomerulus): dense nuclei that provide feedback to the glomerulus
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11
Q

What are podocytes?

A

Podocytes are specialised epithelial cells that wrap around the glomerular capillaries in Bowman’s space. They have foot processes that surround each capillary.

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12
Q

What is the function of podocytes?

A

Podocytes are important in both the structure and function of glomeruli. Together with endothelial cells of the glomerular capillary loop and the glomerular basement membrane, podocytes form a filtration barrier.
There are filtration slits between the foot processes of podocytes that allow materials to be filtered out into Bowman’s space.

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13
Q

Describe the function of mesangial cells

A

Mesangial cells form branches that support the capillaries (known as the mesangium).
Mesangial cells can contract which reduces surface area (SA) = alters GFR

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14
Q

What are 2 features of the glomerular capillaries that allow efficient filtration?

A
  1. Hydrostatic pressure
  2. They have lots of fenestrations that allow plasma to be filtered, whilst preventing the loss of other substances.
    - the filtration slits provide a protein barrier between podocyte foot processes
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15
Q

Which substances in blood are not normally filtered out?

A
  • RBCs
  • WBCs
  • Platelets
  • Albumin (important to maintain oncotic pressure); loss of albumin due to kidney disease = frothy urine & oedema
  • Globulins
  • Fibrinogen
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16
Q

What is the definition of Glomerular Filtration Rate (GFR)?

A

GFR: the volume of plasma filtered by the glomerulus per unit time

17
Q

What is the filtration fraction?

A

Filtration fraction: the proportion of plasma filtered by the glomerulus

18
Q

What is the most important force that affects GFR?

A

Hydrostatic pressure in the glomerular capillaries.
The glomerular capillaries have a relatively high pressure (~55 mmHg), allowing efficient filtration (no reabsorption occurs across the glomerulus, only filtraton)

19
Q

What other factors can affect GFR?

A
  • Hydrostatic pressure in the Bowman’s capsule: this isn’t much but can increase if there’s a blockage downstream (e.g. prostate enlargement)
  • Oncotic pressure in the glomerular capillaries: this increases as you go down the capillary
  • Normally there is no oncotic pressure in Bowman’s capsule (no albumin) and thus this does not effect GFR
20
Q

How is the net filtration pressure calculated?

A

Hydrostatic pressure of capillaries (55 mmHg) - colloid osmotic pressure/oncotic pressure (30 mmHg) - hydrostatic pressure of Bowman’s capsule (15 mmHg) = 10 mmHg

Key principles:

  • Hydrostatic pressure of the capillaries pushes fluid out into the Bowman’s space to be filtered
  • Colloid osmotic pressure/oncotic pressure of glomerulus drives fluid into the capillaries
  • Fluid/hydrostatic pressure due to fluid in Bowman’s capsule drives fluid into the glomerular capillaries
21
Q

What happens to GFR when the afferent arteriole dilates?

A

GFR increases because you are getting more blood and high (hydrostatic) pressure

22
Q

What happens to GFR if the efferent arteriole is constricted?

A

GFR increases because blood is banking up inside the glomerulus (increased resistance). More blood inside = increased glomerular hydrostatic pressure
*Ang II constricts the efferent arteriole, more on this later

23
Q

What is autoregulation in the kidney?

A

Autoregulation is the way the kidney maintains stability of flow despite changes in systemic blood pressure.
Autoregulation maintains a nearly constant GFR when MAP is between 80-180 mmHg.

24
Q

How does autoregulation in the kidney work?

A

Via its myogenic response facilitated by tubuloglomerular feedback (messages from the tubules to the glomerulus).

  • The Bowman’s capsule is strategically located beside the macula densa (found in the thick ascending limb of LoH).
  • The macula densa detects how much salt is present in the filtrate (via receps) and sends the appropriate messages to the afferent arteriole. E.g. if it is filtering too much (GFR too high) the macula densa will tell it to constrict the afferent arteriole = GFR restored to normal level
25
Q

What can alter renal excretion?

A
  1. The Renin-Angiotensin-Aldosterone System (RAAS)
  2. The SNS
  3. Atrial Natriuretic Peptide (ANP)
  4. Vasopressin (ADH)
26
Q

Briefly describe the effects of RAAS on nephrons

A
  • Angiotensin II (Ang II) causes efferent arteriole constriction
  • This increases GFR as blood remains in the glomerulus
  • Ang II also acts on the proximal tubule, causing an increase in Na reabsorption
  • Aldosterone acts on the collecting duct to increase sodium reabsorption
  • People with chronically low BP rely on RAAS (specifically Ang II) to maintain their GFR. Administering ACE inhibitors to these people will cause their GFR to plummet
27
Q

Briefly describe the actions of the SNS (noradrenaline) on nephrons

A
  • Noradrenaline acts on the proximal tubule to increase Na reabsorption
  • Noradrenaline acts preferentially on the afferent arteriole (constricts it) to increase TPR in order to maintain BP (it reduces filling of the glomerulus = decreased GFR)
  • Noradrenaline also stimulates granular cells in the afferent arteriole to secrete Renin = activate RAAS = constrict efferent arteriole = increase GFR
  • It causes increased TPR and Na reabsorption
  • If person is in shock, lots of NA is released = constriction or arterioles = the tubules of the cortex will suffer = acute tubular necrosis (reversible if BP/blood flow is restored)
28
Q

What is the juxtaglomerular apparatus?

A

Juxta = next to
JGA = next to the glomerulus
It contains the macula densa, granular cells and extraglomerular mesangial cells
- It senses Na, provides glomerular feedback, and can cause direct release of Renin (separate from tubuloglomerular feedback)

29
Q

What is the function of Atrial Natriuretic Peptide (ANP)?

A

Atrial = heart
Natriuresis = pass urine
- ANP helps maintain ECF/BP
- AN increase in ECF = more blood returns to atrium = more stretch, causes release of ANP which acts on the heart and kidney
In the kidney, ANP:
- increases GFR by dilating the afferent arteriole
- acts on collecting duct to reduce Na reabsorption (more Na, and thus water, excretion = decrease ECF)
*It is essentially the antithesis of RAAS and Noradrenaline

MD 1 (1 decks)

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