Histology of the Kidney

Question 1

Anatomical features of the kidney

Answer 1

• capsule surrounds outer cortex of kidney
• under cortex ==> medullary pyramids
  
  • pyramids = collection of nephrons + collecting ducts
• collecting ducts ==> empty at tip of pyramid (papilla) into calyx
• Calices ==> renal pelvis ==> ureter @ hilum
  
  • hilum = central region
  • hilum also = site of entry of renal artery and vein

Question 2

Vasculature/blood flow (renal artery ==> renal vein)

Answer 2

• renal artery ==> interlobar arteries = between medullary pyramids
• ==> arcuate arteries ==> interlobular arteries ==> afferent arterioles ==> glomerular capillaries
• filtration @ glomeruli ==> efferent arterioles
  
  • @ outer cortex ==> capillary plexus @ tubules and extend as vasa recta into medulla
  • @ medulla ==> enter directly into medullary region
• capillaries ==> interlobular veins ==> arcuate veins ==> interlobar veins ==> renal vein

Question 3

Nephron: general characteristics

Answer 3

• basic fxn unit of the kidney
• =renal corpuscules + renal tubules
  
  • corpuscules @ cortex
  • tubule @ extends into medulla
  • loop of Henle = bend of tubule

Question 4

Renal corpuscle characteristics

Answer 4

• =where blood filtration occurs
• =glomerulus (capillary network) + Bowman’s capsule (epithelial capsule)
• glomerulus
  
  • interior = mesangium (mesangial cells)
  • endothelial lining
• Basal lamina = filtration barrier
• Bowman’s capsule
  
  • outer layer = parietal epithelium
  • layer of podocytes = visceral epithelium of Bowman’s capsule
  • begining of urinary space

Question 5

Filtration barrier characteristics

Answer 5

• = fenestrated endothelium + shared basal lamina + filtration slits between podocytes
• filtration = driven by hydrostratic pressure of blood
• fenestrae prevent cellular components from contacting basal lamina, but all other components can pass through

Question 6

Elements of blood that do not readily enter filtrate @ Bowman’s capsule

Answer 6

• large proteins/cellular components
• mlx > 60-70,000 MW in size (albumin, etc.) <== prevented by basal lamina
• negative mlx have more difficult passing through

Question 7

Purpose of mesangial cells

Answer 7

• =connective tissue
• supports glomerular structure
• secrete matrix that is continous w/basal lamina
• mesangial cells = phagocytic ==> maintian filtration lamina

Question 8

Main sections of the tubular portion of nephron

Answer 8

1. proximal convoluted and straight tubule
2. thin descending loop of Henle
3. thin ascending loop of Henle
4. ascending thick loop of Henle
5. distal convoluted tubule
6. collecting tubule

Question 9

Proximal tubule characteristics

Answer 9

• cuboidal epithelium + microvilli brush border on luminal side
• cells @ luminal surface connected by tight jxns
• basolateral side
  
  • extensive folds
  • Na⁺/K⁺ ATPase ++ ==> drives uptake of sodium, glucose, amino acids via facilitated diffusion

Question 10

Loop of Henle general characteristics

Answer 10

• thin descending ==> thin ascending ==> thick ascending
• thin = simple squamous
  
  • maintains osmotic salt gradient in medulla
• thick = cuboidal
  
  • active sodium transport

Question 11

Distal tubule general characteristics

Answer 11

• cuboidal + microvilli
• acid-base regulation
• Na⁺/K⁺ ATPase transporters

Question 12

Collecting tubules/ducts

Answer 12

• cuboidal
• =principal + intercalated cells
  
  • principal = active transporters
  • intercalated = secrete H⁺ + reabsorb bicarbonate (acid-base regulation)
• ADH ==> regulates water permeability/reabsorption by collecting ducts
• ducts join together and drain ==> papillary ducts ==> minor calices

Question 13

Juxtaglomerular complex characteristics

Answer 13

• =specialization of cells @ vascular pole of renal corpuscle
• JG cells = modified smooth muscle cells @ wall of afferent arteriole
  
  • contain renin granules ==> control systemic/local BP w/release