16 - Urinary System

Question 1

What are the structures of the urinary system?

Answer 1

• 2 kidneys
• 2 ureters
• 1 urinary bladder
• 1 urethra

Question 2

What are the functions of the urinary system?

Answer 2

• Regulates:
  
  • blood volume
    
    • blood pressure
  • pH
  • ion concentrations
• Eliminates wastes
  - e.g. urea, uric acid, hormones, drugs

Question 3

Describe the kidneys

Answer 3

• external anatomy:
  - retroperitoneal
  - right lower than left
  - supported & protected by 3 layers of CT:
  a) fibrous capsule
  b) perirenal fat capsule
  c) renal fascia
  - renal hilus (hilum)
  - medial indentation
  - entry point of:
  - renal artery (superior)
  - renal vein (inferior)
  - ureter
  - nerves
  
  • internal anatomy:
    
    • renal cortex (superficial)
    • renal medulla
      
      • contains:
        i) renal pyramids
        - apex of pyramid = renal papilla
        ii) renal columns
        - separate pyramids
        - contain blood vessels

Question 4

What are the two parts of a nephron?

Answer 4

Renal corpuscle

Renal tubules

Question 5

Describe the renal corpuscle

Answer 5

• in cortex
• site of blood filtration (first step in urine formation)
• parts:
  i) glomerulus
  = capillary bed
  ii) Bowman’s capsule
  
  • surrounds glomerulus
  • collects filtrate from glomerulus
    -2 layers
    1) outer = simple squamous epithelium
    2) inner = podocytes ⇒ wrapped around glomerular capillaries
    iii) filtration Membrane
  • consists of:
    
    1. glomerular endothelium (capillaries)
       - simple squamous with pores (= fenestrations)
    2. basement membranes
    3. podocytes (of Bowman’s capsule)
       
       • simple epithelium
       • projections “cling” to glomerulus

Question 6

Describe the renal tubules

Answer 6

• 4 parts:
  i) proximal convoluted tubule (PCT)
• in cortex
  ii) loop of Henle
• descending + ascending limbs
• in medulla
  iii) distal convoluted tubule (DCT)
• in cortex
  iv) collecting ducts
• in cortex & medulla
• connect nephron to ureter (via calyces/renal pelvis)

Question 7

What are the two types of nephrons?

Answer 7

a) Cortical (85%)
- renal corpuscles near kidney surface in cortex
- short loop of Henle in outer medulla
b) Juxtamedullary (15%)
- renal corpuscles in cortex near medulla
- long Loops - penetrate deep into medulla
- allow concentration of urine, depending on need

Question 8

Describe the kidney and nephron blood supply.

Answer 8

aorta
 ↓
renal arteries
 ↓
segmental arteries 
 ↓
interlobar arteries (up columns)
↓
arcuate arteries (medulla/cortex junction)
↓
cortical radiate arteries
↓
afferent arteriole
↓				
glomerulus
↓
		efferent arteriole
		↙		↘	
peritubular capillaries in cortex	vasa recta (capillary) 
				↘		↙						
cortical radiate veins						
↓						
arcuate veins
↓
interlobar veins 
↓
renal vein
↓
inferior vena cava

Question 9

Describe the juxtaglomerular complex

Answer 9

• regulates filtrate formation
• point of contact between end of ascending limb, afferent and efferent arterioles at the renal corpuscle of the same nephron
• parts:
  a) tubular portion
• modified (tall and narrow) ascending limb cells = macula densa
  b) arteriolar portion
• afferent + efferent arteriolar portion = granular (juxtaglomerular) cells
• monitor blood pressure
• modified smooth muscle cells ⇒ contain renin (enzyme + hormone)

Question 10

Describe the ureters

Answer 10

• histology:
  a) mucosa
  
  • transitional epithelium
    b) NO submucosa
  • lamina propria directly connected to muscularis externa
    c) muscularis externa
  • smooth muscle (~ 3 layers)
    d) adventitia/serosa
  • retroperitoneal

Question 11

Describe the urinary bladder

Answer 11

• histology:
  a) mucosa
  
  • transitional epithelium with rugae
    b) NO submucosa
  • lamina propria directly connected to muscularis externa
    c) muscularis externa
    = detrusor muscle – smooth muscle (~ 3 layers)
    d) adventitia/serosa
  • adventitia = anterior, posterior and inferior
  • serosa = superior
• internally:
  
  • triangle formed by opening of 2 ureters (posteriorly) and urethra = trigone
  • lacks rugae (smooth) – allows openings to remain in fixed position

Question 12

Describe the urethra

Answer 12

• histology:
  a) mucosa
  
  • transitional to stratified squamous epithelium
    b) muscularis externa
  • smooth muscle
• 2 sphincters (both surround proximal end of ureter)
  a) internal urethral sphincter (smooth muscle)
  - thickening of detrusor muscle at base of bladder
  b) external urethral sphincter (skeletal muscle)
  - in urogenital diaphragm
• in females – transports urine
• in males – transports urine and semen

Question 13

Describe the movement of filtrate in the urinary system.

Answer 13

Several DCTs
 ↓
collecting ducts (exit at renal papilla- fluid now = urine)
 ↓	
minor calyx
 ↓
major calyx
 ↓
renal pelvis							
 ↓
ureter	
 ↓			
urinary bladder
 ↓
urethra
 ↓
exits body