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Kidneys and Renal functions > Functional Histology of the Kidney > Flashcards

Functional Histology of the Kidney Flashcards

1
Q

What is the function of the urinary system?

A

To maintain homeostasis of:

  • plasma composition
  • BP
  • RBC content
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2
Q

How is plasma concentration maintained stable?

A

by regulated excretion of water, ions and organic waste products into urine

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3
Q

How is blood pressure maintained?

A

through the enzyme renin via RAAS

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4
Q

How is the RBC content kept stable by the kidneys?

A

through secretion of erythropoietin

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5
Q

How much of the cardiac output do the kidneys receive?

A

Kidneys receive ~25% of cardiac output

Huge renal vessels

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6
Q

How do humans mimic the function of the kidneys for patients with renal failure?

A

Dialysis Machine

Best human engineering can provide, less effective than a kidney

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7
Q

What is the outer protective layer of the kidney called?

A

Capsule

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8
Q

What is the outermost inside layer of the kidney?

A

Cortex

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9
Q

What part of the kidneys are the pyramids structures a part of?

A

The medulla, the tip of each pyramid is the papilla

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10
Q

What is the calyx of the kidney?

A

The inner space where all the urine produced is collected

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11
Q

What are the vessels supplying and draining the kidneys?

A

Renal artery and renal veins

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12
Q

What is the area all the tubes connect to the kidney called?

A

The hilum

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13
Q

What is a nephron?

A

The functional unit of the kidney

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14
Q

What occurs at the nephrons?

A

blood is filtered at the molecular level (dialysis), to produce urine, while retaining cells and large proteins

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15
Q

How many nephrons are present in one human kidney?

A

About 1 million nephrons in each human kidney

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16
Q

What is a nephron composed of?

A 
Bowman’s capsule	
Glomerulus  (blood capillaries) 
Proximal convoluted tubule 
Loop of Henle - thin arm
Loop of Henle - thick arm
Distal convoluted tubule
Collecting tubule (straighter, epithelium)
Collecting duct
Papilla
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17
Q

What does the renal corpuscle refer to?

A

Bowman’s capsule and glomerulus

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18
Q

What is the renal tubule?

A 
Proximal convoluted tubule 
Loop of Henle - thin arm
Loop of Henle - thick arm
Distal convoluted tubule
Collecting tubule (straighter, epithelium)
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19
Q

What is the function of the glomerulus?

A

Site of ultrafiltration (filtration/dialysis of blood through extremely fine molecular filter)

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20
Q

What is the glomerulus?

A

A knot of fenestrated capillaries covered in epithelial cells (podocytes) to allow movement of fluid during ultrafiltration

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21
Q

What are the 3 layers of the glomerular filter?

A
  1. Cytoplasm of capillary endothelial cell
  2. Thick, fused basement membrane
  3. Filtration slit membranes (podocytes)
22
Q

What is the filter cut off size?

A

> 70kDa molecules are retained in the blood. Many proteins, nutrients (e..g sugars) and ions are filtered through

23
Q

Explain the affect of nephrotic syndrome on the structures within a kidney

A

Glomerular basement membranes become damaged and more leaky – so proteins lost in urine (proteinuria).

24
Q

Why may some basement membranes become thickened during nephrotic syndrome?

A

thought to be through deposition of immunoglobulins (autoimmunity)

25
Q

What affect does high blood pressure have on the kidney structure?

A

Some glomeruli destroyed and replaced by masses of clear “hyaline” material

26
Q

What is the function of the renal tubule?

A

Adjusts composition of ultrafiltrate, to recover nutrients, water etc,
and to regulate plasma composition

27
Q

How does the renal tubule reabsorb from the ultrafiltrate?

A

By active transport across membrane into cell:
small molecules: Na+, glucose, amino acids

By pinocytosis: macromolecules, especially proteins.
Broken down in lysosomes & returned to blood.

By passive flux: water, Cl-

28
Q

Describe the structure of the epithelial cells in the proximal convoluted tubule

A
  • Long microvilli; high SA for reabsorption
  • Lytic enzymes on surface; break down macromolecules
  • Pinocytotic vesicles carry macromolecules to lysosomes
  • Many lysosomes; break down + recycle macromolecules
  • Many mitochondria; fuel active transport
    (seen especially near the basolateral sodium pumps)
29
Q

What is the function of the thin loop of henle?

A

Reabsorption of water and salts from filtrate - passive flux across epithelium, by osmosis & concentration gradients

30
Q

Describe the structure of the epithelial cells present in the proximal convoluted tubule

A

Thin squamous epithelium to allow passive fluxes

Have minimum organelles present

31
Q

What are the functions of the distal convoluted tubule?

A

Homeostasis by regulated active transport & exchange of ions
(Na+/K+, H+/HCO3-)

32
Q

Describe the structure of the epithelial cells in the DCT

A

Cuboidal epithelium:
thicker than squamous, to reduce passive fluxes + accommodate organelles
- Few, short microvilli (unlike PCT)
- Many mitochondria; fuel active transport. These are mainly basal + can show as a pale or striped basal area in H&E-stained sections

33
Q

What are the functions of the collecting duct?

A

Transport of urine to ureter.

Water homeostasis: passive reabsorption of water, regulated through epithelial permeability

34
Q

Describe the epithelial cells structure in the collecting duct

A

Cuboidal / columnar epithelium; prevent passive flux of water (and urea etc)
Specialized dense membranes at cell contacts
Function unclear – probably helping prevent passive flux

35
Q

Describe how you’d be able to identify DC cells in light microscopy

A

Cells are paler, smaller and have a smoother lumen

36
Q

Describe the PCT cells seen using a light microscope

A

Bigger tubules and cells with wispy material in lumen (fixed protein)

37
Q

What is the juxtaglomerular apparatus?

A

Where DCT loops back to meet arterioles of same nephron

38
Q

What are the 3 components of the juxtaglomerular apparatus?

A

Macula densa
Juxtaglomerular cells
Lacis cells

39
Q

What is the role of the macula densa?

A

Senses [Na+] in the DCT fluid. Appears to signal to JG cells

40
Q

What is the role of the juxtaglomerular cells?

A

release renin – more so in response to lower [Na+] in DCT. Renin indirectly increases vascular tone and sodium resorption

41
Q

What is the function of the Lacis cells?

A

Function unknown but as it lies between JXG and MD cells; most probably signals between them

42
Q

Describe the structure of the Ureter

A
  • Transitional epithelium in the centre (found only ureters)
  • Connective tissue - middle area; made of collagen
    fibroblasts - supports the ureter
  • Smooth muscle on the outside
  • Adventitia - connective tissue carrying blood vessels and
    nerves
43
Q

What is the transitional epithelium?

A

Special stratified epithelium, only in ureters + bladder
Impermeable to urine
Transitions between shapes; changes appearance on stretching

44
Q

Explain how the transitional epithelium change shape when stretching?

A 
On contraction (empty)
- apical cells are biggest; lots of apical cytoplasm 
On distension (full)
- Basal cells biggest, apical cells are flat
45
Q

Explain the significance of a large apical surface?

A

There are plaques of specialised (urine-resistant) plasma membrane in apical cells of transitional epithelium - specialised to resist toxic substances in urine e.g. acidic v. hypertonic

46
Q

Explain how the apical cells are protected during distension when the bladder is full

A

Impermeable, rigid plaques protect apical cells from toxic urine

47
Q

How are apical cells protected during contraction when the bladder is empty?

A

Rigid plaques invaginated forming pits + vesicles in cells, allowing cells SA to decrease

48
Q

What are the disadvantages of the transitional epithelium?

A
  • Urinary infections are common (esp. in women)
49
Q

Why are urinary infections so common?

A

Transitional epithelium highly impermeable - leukocytes of immune system cannot readily penetrate

50
Q

Why are women at a higher risk of developing urinary infections?

A

Female urethra shorter. More risk of contamination, e.g. from anal region

51
Q

How can we prevent getting a urinary infection?

A

Drinking plenty of water

Kidneys and Renal functions (14 decks)

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