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xB10W1 > STRUCTURE AND FUNCTION OF THE KIDNEYS > Flashcards

STRUCTURE AND FUNCTION OF THE KIDNEYS Flashcards

1
Q

What are the functions of the urinary system?

A

maintaining water balance, maintaining electrolyte balance, maintaining blood pH, excretion of metabolic waste products, blood glucose regulation, regulates blood pressure, metabolises vitamin d into its active form

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2
Q

does the renal artery or which renal vein contains waste products?

A

the renal artery

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3
Q

what are the 5 main structures of the nephron?

A 
glomerulus in bowman capsule
proximal convoluted tubule
loop of Henle with its ascending and descending parts
distal convoluted tubule
collecting duct
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4
Q

what are the 3 structural parts of the loop of Henle?

A

the thin descending limb, the thin ascending limb and the thick ascending limb

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5
Q

what are the 2 types of nephrons?

A

cortical nephrons

juxtamedullary nephrons

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6
Q

what’s the difference in structure between cortical and juxtamedullary nephrons?

A

cortical nephrons have a shorter nephron loop with the glomerulus further from the cortex-medullary junction than the juxtamedullary nephron

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7
Q

what’s the difference in function between cortical and juxtamedullary nephrons?

A

Cortical nephrons are involved in the excretory and regulatory functions while juxtamedullary nephrons concentrate/dilute urine.

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8
Q

outline the difference between cortical and juxtamedullary nephrons in terms of their capillary beds?

A

the efferent arterioles of the cortical nephron supply peritubular capillaries whilst the efferents of juxtamedullary nephrons supply the vasa recta

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9
Q

outline the histology of the filtration barrier in the nephrons?

A

podocytes in bowman’s capsule, glomerular basement membrane and fenestrated epithelial cells on glomerular capillaries

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10
Q

what are juxtaglomerular cells?

A

smooth muscle cells in the walls of afferent arterioles that secrete renin

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11
Q

what are mesangial cells?

A

specialised cells in the kidneys that contain actin and have an important role in altering blood flow

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12
Q

what are macula dense cells?

A

An area of closely packed specialized cells lining the wall at the point where the thick ascending limb of the Loop of Henle meets the distal convoluted tubule.
they monitor the NaCl going into the DCT

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13
Q

what’s the histology of the proximal convoluted tubule?

A

simple cuboidal epithelial cells with a brush border

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14
Q

what is the histology of the loop of Henle?

A

cuboidal cells

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15
Q

what’s the histology of the distal convoluted tubule?

A

cuboidal cells

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16
Q

what’s the histology of the collecting duct?

A

intercalated cells

principal cells

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17
Q

what are principal cells in the collecting duct responsible for?

A

Na+ reabsorption

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18
Q

what are the intercalated cells in the collecting duct responsible for?

A

acid-base homeostasis

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19
Q

briefly describe the nephron capillary beds?

A

renal artery -> afferent gulumerular arterioles -> glomerular capillaries -> efferent glomerular arterioles -> peritubular capillaries/vasa recta -> renal vein

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20
Q

outline glomerular filtration?

A

hydrostatic pressure pushes components from the afferent artery through the glomerular membrane. Anything that doesnt get pushed into the glomerulus, exits through efferent arterioles

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21
Q

what does the fenestrated epithelium in the glomerulus allow into the PCT?

A

everything in the blood except blood cells

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22
Q

what does the glomerular basement membrane not let into the PCT?

A

plasma proteins

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23
Q

what do podocytes prevent from entering the PCT?

A

macromolecules

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24
Q

why do negatively charger molecules not enter from the blood into the PCT?

A

because podocytes and the basement membrane have an overall negative charge due to presence of proteoglycans, this repels most negative molecules (mostly larger proteins)

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25
Q

what is tubular reabsorption?

A

the movement of solutes and water from the lumen of the renal tubule across into the circulatory system

26
Q

what is tubular secretion?

A

the movement of solutes from the blood into the luminal filtrate directly

27
Q

what does urine contain?

A

water, urea, inorganic salts, creatinine, ammonia, pigmented products of blood breakdown e.g. urochrome

28
Q

how is HCO3- reabsorbed in the proximal convoluted tubule?

A

H+ and HCO3- combine to form H2CO3 which is broken down by carbonic anhydrase 4 into CO2 and H20. these can diffuse into the cell and again form H2CO3. This comes into contact with carbonic anhydrase 2 and forms H+ and HCO3-. HCO3- can then be taken back into the blood alongside Na+ whilst H+ is pumped back into the filtrate through H+ channels

29
Q

how is HCO3- reabsorbed in the loop of Henle?

A

through a HCO3-/Cl- anti port (requires ATP)

30
Q

where is most of the Na+ reabsorbed?

A

in the PCT

31
Q

Where is K+ secreted into the kidney? how?

A

in the collecting duct its exchanged for a Na+

32
Q

what is reabsorbed in the PCT?

A

Na+, glucose, amino acids, vitamins, Cl-, K+, Mg2+, Ca2+, HCO3-, water, lipid-soluble solutes, urea

33
Q

what is reabsorbed in the loop of Henle?

A

water, Na+, Cl-, K+, Ca2+, Mg2+

34
Q

what is reabsorbed in the DCT?

A

Na+, Cl-, Ca2+

35
Q

what is reabsorbed in the collecting duct?

A

Na+, K+, HCO3-, Cl-, water, urea

36
Q

why isnt water reabsorbed in the DCT?

A

because its impermeable due to no aquaporin channels

37
Q

what are the 2 types of natriuretic peptides?

A

atrial natriuretic peptides and B-type natriuretic peptides (ANP and BNP)

38
Q

outline how natriuretic peptides work?

A

cardiomyocytes release ANP when atria are overstretched and BNP when ventricles are overstretched. They dilate afferent arterioles, suppers resorption of Na+ which increases Na+ and water loss into urine, reducing blood volume, decreasing blood pressure and decreasing the stretch and workload of the heart

39
Q

what is myogenic control of glomerular filtration?

A

when smooth muscle cells in afferent and efferent arterioles adapt to systemic BP through constriction and dilation

40
Q

what is tubulo-glomerular feedback?

A

when GFR increases there is not enough time for reabsorption so the concentration of NaCl remains high and macula densa cells respond by releasing vasoconstrictor chemicals to reduce blood flow to the glomerulus and allowing more time for NaCl reabsorption
and vice versa at low NaCl concentrations

41
Q

outline the renin angiotensin aldosterone reflex?

A

a drop in bp causes kidneys to secrete renin which activates angiotensinogen which converts angiotensin 1 to angiotensin 2. angiotensin 2 causes adrenal glands to release aldosterol

41
Q

outline the renin angiotensin aldosterone reflex?

A

a drop in bp causes kidneys to secrete renin which activates angiotensinogen which converts angiotensin 1 to angiotensin 2. angiotensin 2 causes adrenal glands to release aldosterol

42
Q

what’s the effect of aldosterone on the nephrons?

A

nephrons secrete K+, reabsorb Na+ and therefore water. this causes expanded plasma volume which increase bp and inhibits renin release

43
Q

what is the countercurrent mechanism in kidneys?

A

the process of using energy to generate an osmotic gradient that enables you to reabsorb water from the tubular fluid and produce concentrated urine.

44
Q

What are the steps of the counter current mechanism in kidneys?

A

Filtrate enters the nephron loop and is isomotic to blood plasma and cortical interstitial fluid
Water moves out of the filtrate in the descending limb down its osmotic gradient, concentrating the filtrate
Filtrate reaches its highest concentration at the bend of the loop
Na+ and Cl- get pumped out of the filtrate in the ascending loop, increasing interstitial fluid osmolality
Filtrate is at its most dilute as it leaves the loop of henle

45
Q

Outline out ADH/vasopressin regulates urine concentration?

A

If extracellular fluid osmolality increases then Na+ concentration in the plasma increases. This stimulates osmoreceptors in the hypothalamus which stimulates the posterior pituitary to release ADH which increases the expression of aquaporins and therefore increases water reabsorption = decreased, concentrated urine
This negatively feedbacks to the hypothalamus which causes posterior pituitary to stop expressing ADH

46
Q

How can oestrogen affect urine concentration?

A

Estrogen is chemically similar to aldosterone so it enhances NaCl reabsorption and water follows- this is why women retain fluid as their oestrogen levels rise e.g. in pregnancy

47
Q

How does progesterone affect urine concentration?

A

It decreases Na+ reabsorption by blocking the effect aldosterone has on renal tubules by competing for these receptors = diuretic effect

48
Q

Why can glucocorticoids promote oedema?

A

They enhance tubular reabsorption of Na+ so water follows

49
Q

What is the normal pH of blood?

A

7.34-7.38

50
Q

At what blood pH is acidosis and alkalosis?

A

Acidosis - below 7.35

Alkalosis - above 7.45

51
Q

What are the 2 buffer systems for urine?

A

H2PO4- -> H+ + (HPO4)2-

NH4+ -> NH3 + H+

52
Q

What are the 2 ways in which kidneys control pH?

A

By reabsorption of HCO3- and secretion of H+

53
Q

How do kidneys reabsorb HCO3- to regulate pH?

A

H+ comibines with HCO3- to form H2CO3. Carbonic anhydrase 4 converts this to H2O and CO2. CO2 and water can now enter tubule cells and can combine to form H2CO3. Carbonic anhydrase 2 can then split this into H+ and HCO3-. HCO3- then can enter the peritubular capillary via an NCB1 channel (with Na+) whilst H+ is excreted back into the filtrate.

54
Q

At what pH urine does H+ secretion stop?

A

4.5

55
Q

How does the body increase blood pH?

A

Ventilating to excrete more CO2 and kidneys secreting more acid and making more HCO3-

56
Q

How does the body decrease blood pH?

A

Respiratory system ventilates less to trap CO2 and not reabsorbing HCO3-

57
Q

Why are infants more susceptible to acid-base imbalance?

A

Lower lung volume, excessive fluid shift, higher metabolic rate, high water loss rate and inefficiency of kidneys

58
Q

Why are elderly more susceptible to acid-base imbalance?

A

Decrease in total body volume which slows homeostasis

Unresponsive to thirst cues

59
Q

What is renal clearance?

A

The volume of plasma that is cleared of a susbatnce in 1 minute (ml/min)

60
Q

How do you calculate renal clearance?

A

Urine concentration x urine flow rate

Divided by plasma concentration

61
Q

What’s normal glomerular filtration rate?

A

180L of plasma a day

xB10W1 (9 decks)

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