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BIOS4001 - Renal System > Nephron Structure and Function, Juxtaglomerular Complex > Flashcards

Nephron Structure and Function, Juxtaglomerular Complex Flashcards

1
Q

What is the renal corpuscle?

A

The renal corpuscle is the filtration unit of the nephron in the kidney.

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2
Q

What is the renal corpuscle composed of?

A
  • glomerulus
  • Bowman’s Capsule
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3
Q

What happens in the renal corpuscle of the nephron?

A

Filtration

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4
Q

What is the function of the proximal convoluted tubule in waste excretion?

A
  • reabsorption of water, ions, and nutrients
  • secretion of drugs and toxins, as well as H+
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5
Q

What happens in the nephron loop during waste excretion?

A
  • descending limb of the nephron loop reabsorbs water
  • ascending limb reabsorbs ions e.g. Na+ & Cl-
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6
Q

What is the function of the distal convoluted tubule in waste excretion?

A

Regulated reabsorption and secretion

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7
Q

What is the function of the collecting duct in waste excretion?

A

Regulates the reabsorption of water and ions, such as Na+, Cl-, K+, H+, and HCO3-

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8
Q

What does the papillary duct deliver?

A

The papillary duct delivers urine to the minor calyx

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9
Q

Summarise the function of the tubules of the tubular portion in the Nephron

A

Renal corpuscle = filtration
Proximal Convoluted Tubule (PCT) = Reabsorption and Secretion
Loop of Henle = Reabsorption
Distal Convoluted Tubule (DCT) = Reabsorption and Secretion
Collecting duct = Reabsorption
(slide 12)

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10
Q

What is the glomerulus?

A

A ball of narrow capillaries that is the filtering part of the renal corpuscle in the kidney.

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11
Q

How many loops does the glomerulus have, and in how many lobes is it found?

A

The glomerulus has 20-30 loops and is found in approximately 5 lobes

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12
Q

How is the glomerulus fed?

A

The glomerulus is fed by the afferent arteriole

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13
Q

What is the pressure like in the glomerulus?

A

The pressure in the glomerulus is high

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14
Q

What is Bowman’s capsule?

A

Bowman’s capsule is a cup-shaped structure that surrounds the glomerulus in the renal corpuscle

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15
Q

Where does the glomerulus feed into?

A

The glomerulus feeds into the efferent arteriole

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16
Q

Where is the renal corpuscle located?

A

The kidney

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17
Q

What is the cellular structure of the glomerulus?

A

The glomerulus has:
- a fenestrated endothelium
- surrounded by a basement membrane
- podocytes
(slide 23 & 25)

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18
Q

What is fenestrated endothelium?

A

A type of endothelium that has fenestrations (pores or openings), which filters molecules based on their size

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19
Q

What are the characteristics of the fenestrated endothelium?

A
  • squamous endothelial cells
  • modified capillary endothelium
  • fenestrations
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20
Q

What is squamous?

A

Squamous refers to a flat and scale-like shape of cells or tissues

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21
Q

What is modified capillary endothelium?

A

A type of endothelium found in the glomerulus
- has fenestrations that allow for the filtration of small molecules & fluids

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22
Q

What is the basement membrane?

A

The basement membrane is a thin layer of extracellular matrix

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23
Q

What does the basement membrane contain?

A

Contains heparin sulphate, collagen, laminin, and other proteins (negatively charged)

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24
Q

What are podocytes?

A

Podocytes are modified epithelial cells that form the cellular structure of the glomerulus in the kidney.
(slide 24)

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25
Q

What is the function of podocytes in the glomerulus?

A

Podocytes form foot processes that
- create filtration slits; allows for filtration of blood in kidney
- provide strength to cellular structure of glomerulus
(slide 24)

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26
Q

What are mesangial cells?

A

Cells located in the glomerulus of the kidney that have three main functions: they are structural, contractile, and phagocytic.

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27
Q

What is the Glomerular Filtration Membrane?

A

A specialized filter in the kidney that is responsible for filtering blood to form urine

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28
Q

What does the Glomerular Filtration Membrane allow to pass from the blood into the kidneys?

A
  • water
  • electrolytes
  • glucose
  • amino acids
  • fatty acids
  • vitamins
  • urea
  • uric acid
  • creatinine
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29
Q

What doesn’t the Glomerular Filtration Membrane allow to pass from the blood into the kidneys?

A
  • blood cells
  • plasma proteins
  • large anions
  • protein-bound minerals & hormones
  • most molecules > 8 nm in diamete
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30
Q

What is the function of the Basement Membrane in the Glomerular Filtration Membrane?

A

Filters molecules based on their size and charge
- negatively charged, so allows positively charged molecules to pass through more easily

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31
Q

What is the effective pore size of the Glomerular Filtration Membrane?

A

The effective pore size is approximately 8 nanometers

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32
Q

What is Glomerular Filtration Rate (GFR)?

A

GFR is a measure of the rate at which blood is filtered through the glomerular capillaries in the kidney.

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33
Q

What is Capillary Hydrostatic Pressure (Pc)?

A

Pc is the pressure exerted by the blood within the glomerular capillaries

34
Q

What is Capillary Osmotic Pressure (πc)?

A

πc is the pressure exerted by the proteins in the blood within the glomerular capillaries

35
Q

What is Tubular Hydrostatic Pressure (Pt)?

A

Pt is the pressure within the tubules of the kidney

36
Q

What is Tubular Osmotic Pressure (πt)?

A

πt is the pressure exerted by the solutes within the tubules of the kidney

37
Q

What is the equation for Glomerular Filtration Rate (GFR)?

A

GFR = Kf x net filtration pressure

Kf = kidney permeability constant
net filtration pressure = difference between the forces favoring filtration (Pc & πt) and those opposing filtration (Pt & πc)
(slide 28)

38
Q

What factors determine Kf in the GFR equation?

A
  • membrane permeability
  • filtration area
  • ml min-1 mmHg-1
39
Q

What is the GFR equation including pressure constants?

A

GFR = Kf[(Pc–Pt) – (πt–πc)]

40
Q

What is the average GFR?

A

120ml min-1

41
Q

What is the clinical relevance of GFR and how is it clinically determined?

A

GFR is the best indicator of renal function and is clinically determined by plasma clearance rate

42
Q

What is plasma clearance rate?

A

Rate at which a substance is cleared from plasma

43
Q

What is the formula for the plasma clearance rate (Cx)?

A

Cx = (Ux x V) / Px

44
Q

What do the variables Ux, V, and Px represent in the clearance formula?

A

Cx = clearance of x in ml min-1
Ux = concentration of x in the urine in mg ml-1
V = volume of urine in ml min-1
Px = concentration of x in the plasma in mg ml-1

45
Q

What are the requirements for a substance to be used in the calculation of plasma clearance rate?

A

The substance must be:
- freely filtered by the glomerulus
- not reabsorbed or secreted by the kidney
- not be produced or metabolised by the kidney
- not alter GFR

46
Q

What is the gold standard test for measuring GFR and what substance is used in this test

A

The inulin clearance test, and inulin is the substance used in this test

47
Q

What is inulin?

A

Inulin is a plant polysaccharide that is not secreted or reabsorbed by the kidney

48
Q

How is inulin infused during the inulin clearance test, and what measurements are taken during the test?

A

Inulin is infused at a rate that maintains constant plasma concentrations
- urine inulin concentration and urine flow are measured over time

49
Q

What is the usual clinical test for estimating GFR, and what substance is used in this test?

A

Serum creatinine or 24-hour urine collection

50
Q

What is the substance used in the serum creatinine / 24-hour urine collection?

A

serum creatinine (a muscle metabolite)

51
Q

What are the key features of the cellular structure of the Proximal Convoluted Tubule (PCT)?

A
  • cuboidal epithelium with microvilli brush border for absorption
  • lots of mitochondria
  • highly permeable to water & solutes
    (slide 42)
52
Q

How do the ascending loop (AL) and descending loop (DL) of the loop of Henle differ in permeability?

A
  • DL: passive transport of water leaving
  • thin part of AL: passive reabsorption of NaCl
  • thick part of AL: active reabsorption of only NaCl
53
Q

What does peritubular capillary arrangement depend on?

A

Depends on the nephron type

54
Q

How is the peritubular capillary arrangement in cortical nephrons?

A

The arrangement is the same as other tissues

55
Q

What is the vasa recta?

A

Blood supply that runs in parallel to the loop of Henle and has branches going around it

56
Q

How is the peritubular capillary arrangement in juxtamedullary nephrons?

A

Efferent arteriole leads to the vasa recta

57
Q

What is the counter-current multiplier in the Loop of Henle?

A

It refers to the counter-current flow of filtrate and blood in opposite directions in the Loop of Henle.

58
Q

How does the structure of the Loop of Henle contribute to the counter-current multiplier?

A
  • blood & filtrate want same osmolarity as surrounding medulla
  • vasa recta is permeable to water & NaCl
  • descending limb = permeable to water only
  • thin ascending limb = passive reabsorption of NaCl
  • thick ascending limb = actively reabsorbs NaCl
59
Q

What is the effect of the counter-current multiplier in the Loop of Henle?

A

The water diffuses out of the descending limb
- concentrating the filtrate
- rehydrating the blood

NaCl is moved out of the ascending limb
- concentrating the blood going into the medulla
- making filtrate exiting the loop hypo-osmotic

60
Q

What is the cellular structure of the thin descending limb of the Loop of Henle?

A

Composed of:
- squamous epithelial cells
- highly permeable to water but not solutes
- connected by tight junctions - prevent movement of solutes between cells

61
Q

What is the cellular structure of the thin ascending limb of the Loop of Henle?

A

Has passive NaCl transporters

62
Q

What is the cellular structure of the thick ascending limb of the Loop of Henle?

A

Made up of:
- cuboidal epithelial cells
- connected by tight junctions
- have a glycoprotein layer
- highly permeable to solutes but not water
- have lots of mitochondria to power the K+/Na+ ATPase that drives NaCl reabsorption

63
Q

What are the key cellular features of the Distal Convoluted Tubule (DCT) in the kidney?

A
  • cuboidal epithelium
  • arranged in a single layer
  • few microvilli - no brush border
  • not as impermeable to water as ascending limb
64
Q

What is the mechanism of water reabsorption in the Collecting Duct of the kidney?

A

Controlled by the following mechanisms:
- filtrate from the distal convoluted tubule is hypo-osmotic
- water diffuses out of the filtrate (tubular fluid) into the salty medulla
- urea reabsorption – helps generate medulla concentration gradient

65
Q

What is the role of hormones in the regulation of water reabsorption in the Collecting Duct of the kidney?

A

The amount of water reabsorbed in the Collecting Duct of the kidney is under hormonal (ADH) control to maintain homeostasis.

66
Q

What are the 2 cell types in the upper collecting duct?

A
  • principal cells
  • intercalated cells
67
Q

What is the cellular structure of the Collecting Duct in the upper cortex and medulla?

A

Principal cells:
- cuboidal cells with short microvilli
- permeability to water that is hormonally regulated

Intercalated cells:
- cuboidal cells with microvilli
- involved in the secretion of H ions for acid-base balance in the body
- lots of mitochondria

68
Q

What is the cellular structure of the Medullary Collecting Duct in the upper cortex and medulla?

A
  • positioned in the renal medulla
  • principal cells
69
Q

What is auto regulation in the context of GFR control?

A

Ability of the kidneys to maintain a constant glomerular filtration rate (GFR) despite fluctuations in blood pressure

70
Q

What is the myogenic mechanism in GFR control?

A

Type of auto regulation that involves smooth muscle cells in the afferent arteriole responding to changes in renal blood vessel pressure.
- BP increases = arteriole constricts to prevent excessive increase in GFR
- BP decreases = the arteriole dilates to maintain GFR

71
Q

What are the baroreceptors involved in the myogenic mechanism of GFR control?

A

Stretch receptors located in the afferent arteriole
- detect changes in BP and send signals to the smooth muscle cells to constrict or dilate the arteriole accordingly
- increased stretch = increased BP

72
Q

What is the tubuloglomerular mechanism in GFR control?

A

Type of auto regulation, macula densa cells sense and respond to changes in nephron tubular flow.
- detects Na & Cl in the distal convoluted tubule
- low Na & Cl absorption = high fluid flow = high pressure
- high Na & Cl absorption = low fluid flow = low pressure

73
Q

What do levels of Na correlate with tubular flow?

A
  • high Na+ = high tubular flow
  • low Na+ = low tubular flow
74
Q

What is the Juxtaglomerular Apparatus?

A

A specialized structure located in the kidney, specifically at the junction of the afferent arteriole and the distal convoluted tubule (DCT)

75
Q

What are the components of the Juxtaglomerular Apparatus?

A

The JGA is composed of three main cell types:
- juxtaglomerular (JG) cells
- macula densa cells
- extraglomerular mesangial cells

76
Q

What are JG cells?

A
  • modified smooth muscle cells
  • located in walls of afferent arteriole
  • ability to constrict or dilate arterioles
  • release of enzyme renin
77
Q

What are macula densa cells?

A
  • modified epithelial cells located in wall of DCT
  • sense NaCl in tubular fluid
  • release paracrine signaling molecules that regulate JG cell function
78
Q

How is blood flow in the glomerulus regulated in response to low GFR?

A

detects:
- baroreceptors sense low arteriole pressure
- macula densa cells sense low Na concentration in DCT (low tubular flow)

action:
- dilate afferent arteriole
- constrict efferent arteriole

79
Q

How is blood flow in the glomerulus regulated in response to high GFR?

A

detects:
- baroreceptors sense high arteriole pressure
- macula densa cells sense high Na in DCT (due to high tubular flow)

action:
- constrict afferent arteriole
- dilate efferent arteriole

80
Q

What are mesangial cells?

A

Contractile cells in the glomerulus:
- provide structural support
- contribute to auto regulation

81
Q

What is the role of smooth muscle cells in the glomerulus?

A

regulating blood flow through the afferent & efferent arterioles

BIOS4001 - Renal System (4 decks)

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