Lecture 1: Renal Histology

Question 1

What are the functions of the Kidney?

Answer 1

1. Filter blood, to remove waste in urine (purify blood)
2. Regulate water, slat, acid-base balance (pH) (main homeaostatic regulator)
3. Produce hormones/enzymes (epo, renin, vitamin D)
4. Regulate blood pressure (due to its 3x other functions)

Question 2

What are the functions of the Hormones produced by the kidney?

Answer 2

Renin needed to make angiotensin
Erythropoietin needed to make RBC
Involved in the last part of Vitamin D synthesis

Question 3

What is the gross pathway of body fluid?

Answer 3

aorta –> Renal artery –> Renal Vein –>Vena Cava –> ureter –> Bladder –> urethra

Question 4

Nephrons

Answer 4

Functional unit of the kidney
about ~1 million per kidney
"filtering tubules"
Blood filter + tubular epithelium
1. Renal corpuscle (capillary tuft enveloped by the tubule)
2. Proximal --> thin --> distal tubules
Drain into collecting ducts

Question 5

Urethra length

Answer 5

Urethra is shorter in females and longer in males

Question 6

How does the Nephron function in relation to Filtration

Answer 6

Renal Corpuscle conducts filtration
Proximal Tubule reabsorbs 65% of the filtrate volume
Segments after the Proximal tubule fine tune levels of: Salt, pH and/or extract water

Question 7

Glomerulus

Answer 7

= Renal corpuscle = capillary tuft
Surrounded by epithelial cells:
1. Podocytes envelope capillaries
2. Parietal Epithelial cells form the outer layer (squamous epithelium)
- These epithelial cells are continuous at the Vascular Pole

Question 8

Glomerular Filtration Barrier

Answer 8

1. Endothelium
2. Basement Membrane: Physical barrier. Relatively thick layer of Protein/Collagen
3. Podocytes: Secondary Foot Processes/Indigitations that lock in with layers and form slits.
   Restricts Albumin (most abundant protein in plasma), Cells and other large proteins (immune and hormone) so dont lose them in urine

Question 9

Glomerular Capillary Endothelium

Answer 9

1. Fenestrations/holes: allows small cells to filter through. Restricts cells from exiting
2. Negative Glycocalyx Coat: -ve charge formed by proteins with sugars attached. Repels (mainly -ve) plasma proteins, stops them from being filtered in the nephron

Question 10

Glomerular Basement Membrane

Answer 10

Thick
Collagen + -ve Proteoglycans
2x Layers:
1. Less Dense Outer layer: Charge barrier
2. Dense Core: Physical barrier of collagen

Question 11

Glomerular Podocytes

Answer 11

Adhere to glomerular BM
Primary and Secondary Foot processes interdigitate to form Slit membrane: slits linked by a Protein bridge
Function:
Glycocalyx coat (-ve)

Question 12

Affect of Diabetes on the Glomerular Filter

Answer 12

High Blood Pressure + Disease Damaged podocytes –> Mesangial cells find it difficult to hold components together –> Leaky glomerular filter e.g. Podocyte effacement
1. Initially: deposit more matrix for increased structural support
2. Overtime severe deposition of matrix causes scarring of the glomerulus –>
Focal segmental glomerulosclerosis
- Mesangial cell proliferation and ECM deposition (scar)
Can be more spread if disease is far gone
→ constricts capillaries in that region → Cannot filter (compromised) → renal failure of high BP (as blood cannot pass through)

If disease is really far gone then everything is scarred up and nothing works

Question 13

Mesangial Cells

Answer 13

Smooth muscle cells inside glomerulus
Continuous with squamous layer
not part of the direct filtration of the plasma
Functions: (holds structure together)
1. Supportive: linkages to resist expansion and maintain tuft shape
2. Contractile role: maintains tuft shape
3. Produces ECM: maintins structural integrity
Involved in glomerulosclerosis (glomerular scarring)

Question 14

Juxtaglomerular Apparatus composition

Answer 14

1. JG cells: Modified Smooth muscle cells. Black w. white dots in afferent artertiole wall. secretes Renin (the white dots)
2. Macula Densa Cells: TAL wall + sense filtrate’s salt concentration
3. Extraglomerular cells:

Question 15

Juxtaglomerular Apparatus Function

Answer 15

Internal mechanism so kidney can filter at the same rate
Regulatory Functions:
1. High distal Tubular NaCl induced afferent arteriolar vasoconstriction (tubuloglomerular feedback) –> Less blood into filter –> decreased flow
2. Low tubular NaCl induced Renin released –> cleaves angiotensin –> Increase BP and Increased BV

Question 16

Proximal tubular Cells

Answer 16

Features aiding Bulk Reabsorption:

1. Cuboidal epithelium
2. Prominent microvilli brush border (increased apical cell SA for transporters –> increased reabsorption)
3. Pinocytosis: Macromolecule droplet uptake (proteins)
4. Lateral Processes and Infoldings/ Interdigitations: Basolateral cell surface expansions. Increase SA

Question 17

Thin Limb cells

Answer 17

Thin squamous epithelium
Nuclei bulge into the lumen
Function: Loop of Henle Water reabsorption

Question 18

Distal Tubule Cells

Answer 18

1. Cuboidal Epithelium
2. No Brush border (shorter microvilli).
3. No Pinocytosis
4. Lateral Processes and Infoldings/ Interdigitations: Basolateral cell surface expansions. Increase SA
   - relatively decreased absorptive capacity (just fine tuning)

Question 19

Collecting Duct

Answer 19

Cuboidal –> columnar

Final modifier of Urine’s Water, salt and pH

Question 20

Higher organisation of the Kidney

Answer 20

Renal Capsule: Tough fibrous bag
Lobes:
1. Cortex= contains medullary rays
2. Medulla: Medullary pyramids (Conical structures)
- Renal Papilla: apex of M pyramid. Enveloped by calyces.
Renal Pelvis: Dilations of ureter