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Urinary system > Structural basis of kidney function > Flashcards

Structural basis of kidney function Flashcards

1
Q

What is the importance of the kidneys?

A

Homeostasis

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2
Q

Why does a person drinking too much water have urine infections?

A

The kidney pumps out too much water and when they go to sleep they can’t drink anymore. Then in the morning they have concentrated urine which is more likely to get urine infection.

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3
Q

What are the functions of the kidney?

A
  • filters the blood plasma (G)
  • selective reabsorption (PCT)
  • retention of unwanted contents in urine (LOH)
  • concentration selection (DCT)
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4
Q

How is fluid lost?

A

Through exhalation, urine, sweat and faeces

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5
Q

What is the kidney sensitive to?

A

nerves and hormones

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6
Q

What is the endocrine function of the kidney?

A

Renin, erythropoietin

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7
Q

What happens during the process of filtration?

A

The glomerulus filters the blood and the filtrate only has small molecules

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8
Q

What happens during the process of reabsorption?

A

The materials are reabsorbed in the PCT, these include ions, glucose, amino acids, small proteins and water.

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9
Q

What happens during the creation of the hyperosmotic extracellular fluid?

A

The loop of Henle and vasa recta do this and the countercurrent mechanism is involved.

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10
Q

What are the mechanisms that occur during urine production?

A
  • filtration
  • reabsorption
  • creation of hyperosmotic extracellular fluid
  • adjustment of ion content in urine
  • concentration of urine (CD)
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11
Q

What happens during the adjustment of ion content in the urine?

A

Happens at the collecting duct and DCT - the levels of Na+, K+, H+, NH4+ are adjusted

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12
Q

What is the renal corpuscle?

A

The Bowman’s capsule, glomerulus and podocytes

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13
Q

Blood supply in the renal corpuscle

A

At the vascular pole of the corpuscle from afferent arteriole to efferent creating a high pressure to filter

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14
Q

What does the filtration barrier consist of?

A
  • Fenestrated endothelium
  • Specialiased basement membrane
  • Filtration slots between foot processes of podocytes
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15
Q

Where is filtrate drained from the renal corpuscle?

A

At the urinary polt of the corpuscle to PCT

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16
Q

How is urine concentrated

A

At the collecting duct water moves down its osmotic gradient and can be controlled by vasopressin

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17
Q

Proximal convuluted tubule functions

A
  • Reabsorption of 70% of glomerular filtrate
  • Na+ uptake by basolateral Na+ pump
  • Water and anions follow Na+
  • Glucose uptake by Na+/glucose cotransporter
  • Amino acids by Na+/amino acid co-transporter
  • Protein uptake by endocytosis
18
Q

Proximal convuluted tubule structural features

A
  • Sealed with (fairly water-permeable) tight junctions
  • Surface area increased to maximise rate (at the brush border at apical surface
    interdigitations of lateral membrane)
  • Contains aquaporins
  • Lots of mitochondria
19
Q

What happens in the ascending thick limb and why?

A
  • Na+ and Cl- actively pumped out of tubular fluid
  • Water impermeable tight junctions
  • Membranes lack aquaporins
  • Results in hypo-osmotic tubular fluid, hyper-osmotic extracellular fluid
20
Q

Describe the structure of the descending thin limb

A
  • Passive osmotic equilibrium (aquaporins present)

- Simple squamous epithelium

21
Q

Describe the structure of the ascending thick limb

A
  • High cuboidal epithelium, few microvilli

- prominent mitochondria

22
Q

What is the vasa recta?

A
  • Blood vessels arranged in loop

- Loop structure stabilises hyper-osmotic gradient [Na+]

23
Q

Distal convoluted tubule - features, structure and role

A
  • Cuboidal epithelium, few microvilli
  • Numerous large mitochondria
  • Loops back around to the glomerulus to form the juxtaglomerular apparatus (has macula densa cells)
    Complex lateral membrane interdigitations with Na+ pumps
  • Adjustment of Na+/K+/H+/NH4+ (aldosterone)
24
Q

Where does the CD pass through and what happens?

Where does it drain into?

A
  • Passes through medulla with its hyper-osmotic extracellular fluid
  • Completes ion adjustment
  • Water moves down osmotic gradient to concentrate urine
  • Drains into minor calyx at papilla of medullary pyramid
25
Q

What does the rate of water movement depend on in the CD and what is it controlled by?

A
  • On aquaporin-2 in apical membrane
  • under control of vasopressin
  • Basolateral membrane has aquaporin-3, not under control
26
Q

What is the structure of the collecting duct?

A
  • Duct has simple cuboidal epithelium
  • Cell boundaries don’t interdigitate
  • Has smooth muscle wall (2 layers) for peristalsis
  • Little active pumping so fewer mitochondria
27
Q

Juxtaglomerular Apparatus

A

Macula densa of distal convoluted tubule (detects Na+)

Juxtaglomerular cells of afferent arteriole which can detect pressure and secrete renin (angiotensinogen to angiotensin 1)

28
Q

How can renal stenosis affect blood pressure?

A

renal stenosis - kidney think blood pressure had dcereased and makes renin causing high blood pressure

29
Q

Where do aldosterone and vasopressin act?

A

DCT and CT

30
Q

Which parts of the kidney are in the medulla and cortex?

A

cortex - DCT, PCT, CD and Bowman’s capsule

medulla - loop of Henle

31
Q

What are some parts of the kidney?

A 
cortex
medulla (pyramids)
fibrous capsule
medullary rays
minor calyces 
major calyces
papilla of pyramid
renal sinus
renal pelvis
fat in renal sinus
vessels
32
Q

Where does each lobe drain into?

A

Its own part of the renal pelvis called the minor calyx- they join to form the major calyx which drains into the ureter

33
Q

How does urine get from the nephrons to the urethra?

A

minor calyx, major calyx, centre of pelvis and ureter, bladder, urethra

34
Q

What is the special epithelium of the urinary tract and what is its structure?

A

urothelium

Has 3 layers of epithelial cells

35
Q

What are the features of urothelium?

A
  • 3 layers
  • Urine facing (apical) side has high resistance tight junctions
  • Apical side has thick membrane
    These are important to minimise transepithelial migration
  • Urothelial cells have pleated borders to allow folding and unfolding depending on size of the bladder
36
Q

How does the shape of the bladder and its location change when its full?

A

The empty urinary bladder is a small, muscular, tetrahedral organ lying below the pelvic peritoneum and not rising much above the
top of the pubic symphysis. As it fills with urine, it relaxes and expands upwards into the loose connective tissue between the deep surface of the anterior abdominal wall and the parietal peritoneum.

37
Q

What does vesical mean?

A

structures relating to bladder

38
Q

Which epithelium lines the glomerulus, PCT, loop of Henle (ascending and descending), DCT and CD?

A

Bowman’s capsule - simple squamous

PCT - cuboidal

Loop of Henle ascending - cuboidal

Loop of Henle descending - simple squamous

DCT - cuboidal

CD - cuboidal or columnar

39
Q

Which epithelium do the minor/major calyces and pelvis have?

A

Urinary epithelium

40
Q

What is urothelium or transitional epithelium, its features and where is it found?

A
  • A specialised form of epithelium found only in the urinary tract: parts of kidneys, ureters, bladder, parts of urethra
  • All cells contact basal lamina (but epithelium looks stratified)
  • Properties are resistance to urine, and ability to stretch
  • Cells appear squamous or cuboidal according to degree of stretch
  • Luminal cells are specialised for extremely low permeability

Urinary system (12 decks)

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