M22: Urinary System - Nephron

Question 1

how many nephrons does a kidney have?

Answer 1

~1 million

Question 2

2 parts of the nehpron

Answer 2

1. RENAL CORPUSCLE (site of plasma filtration)
   - GLOMERULUS
   - GLOMERULAR (BOWMAN’S) CAPSULE
2. RENAL TUBULES
   - PROXIMAL CONVOLUTED TUBULE
   - NEPHRON LOOP (LOOP OF HENLE)
   - DISTAL CONVOLUTED TUBULE
   - COLLECTING AND PAPILLARY DUCTS

Question 3

Name of filtrate in renal tubules vs papillary ducts

Answer 3

tubules: TUBULAR FLUID
papillary ducts: URINE

Question 4

Two types of nephrons

Answer 4

1. CORTICAL NEPHRON (80-85%)
   - corpuscle near outer cortex
   - short nephron loop
   - loop has similarly structured ascending and descending loops
   - blood supply to loop via peritubular capillaries (extend into pyramid)
2. JUXTAMEDULLARY NEPHRON (15-20%)
   - corpuscle near medulla in cortex
   - long nephron loop
   - ascending loop has thin (simple squamous) and thick
   - blood supply via peritubular capillaries (cortex) and vasa recta (loop)
   - can produce dilute or concentrated urine

Question 5

flow of fluid through a juxtamedullary nephron

Answer 5

• glomerular capsule
• proximal convoluted tubule
• descending limb of nephron loop
• thin ascending limb
• thick ascending limb
• distal convoluted tubule, drains into collecting duct

Question 6

histology of glomerular (bowman’s) capsule, superficial to deep

Answer 6

PARIETAL LAYER OF GLOMERULAR CAPSULE
- simple squamous
CAPSULAR SPACE
PODOCYTES (visceral layer cells)
- tight to glomerulus
- modified simple squamous - finger like projections (PEDICLES) provide extra layer of protection

Question 7

juxtaglomerular apparatus

Answer 7

Structure where afferent arteriole makes contact with ascending nephron loop, helps regulate BP in kidneys

2 cells:
MACULA DENSA: specialized cells on ascending loop of henle that come in direct contact with afferent arteriole
JUXTAGLOMERULAR CELLS: modified smooth muscle cells on afferent arteriole

• Macula densa detect water, Na+ and Cl- proportions. If proportions too high, body is producing too much filtrate
• signal sent to juxtaglomerular cells to contract afferent arteriole, reduces bloodflow to glomerulus.
• high amounts of water and ions mean too much filtrate

Question 7

mesengial cells

Answer 7

• located in afferent, efferent arterioles and glomerulus
• when contracted, reduce surface area
• can reduce flow of blood and regulate filtrate production

Question 8

3 layers glomerular filtration membrane, deep to superficial

Answer 8

1. FENESTRATION OF GLOMERULAR ENDOTHELIAL CELL
   - allows majority of plasma to be removed, but not blood cells
2. BASAL LAMINA
   - prevents filtration of larger pr-
3. SLIT MEMBRANE BETWEEN PEDICELS
   - prevents filtration of medium sized pr-
   - located between pedicels (finger-like projections on podocytes)

Question 9

cells of proximal convoluted tubule

Answer 9

• simple cuboidal with a brush border microvilli
• creates large surface area to reabsorb things back into blood

Question 10

cells of descending limb and thin ascending limb in nephron loop

Answer 10

• simple squamous
• allows for greater movement of ions and fluids

Question 11

cells of thick ascending limb in nephron loop

Answer 11

simple cuboidal to low columnar

Question 12

cell type of distal convoluted tubule

Answer 12

most of DCT
- simple cuboidal
last part of DCT and collecting duct
- simple cuboidal
- intercalated cells (monitor H+ ions, regulate pH)
- principal cells (hormonally controlled, regulate Na/K levels in blood and renal tubule)