Urinary System

Function of Urinary System

excretion of metabolic wastes

elimination of foreign substances

maintenance of extracellular fluid

regulation of body water

regulation of salt

control of acid-base (pH) balance

hormone production (to a lesser extent)

• renin for blood volume
• erythropoietin for RBC development

Kidney Structure

bean shaped with a small depression called the hilum/hilus

• this hilum has the renal artery, renal vein, and ureter

surrounded in a thick capsule

• a series of parallel collagen bundles running in all directions

under capsule is myofibroblasts

• these are contractile to squeeze out contents
• not coordinated pumping system

Within the kidney there is a cortex and medulla

• the cortex is the outer, darker (basophilic staining) portion
• the medulla is the inner lighter (eosinophilic staining) portion

Renal pyramids

• within the medulla there is triangular shaped portions called renal pyramids
• between the pyramids is portions of the cortex called renal columns
• the tips are called papilla
  • has an opening for a duct to allow filtrate to leak out
• at the end of the ducts is the minor calyx
  • these are at every papilla to catch the filtrate that is leaked
  • these converge together to become the major calyx
  • the major calyx converges to the renal pelvis
  • the renal pelvis leaves the kidney as the ureter
• running through the pyramid from cortex to the papilla is a collecting duct
  • this collects filtrate from nephrons
• Portions
  • the widest portion of the pyramid is called the outer stripe
  • the second widest portion is the inner stripe
  • the outer and inner stripe together are called the outer medulla
  • everything below the outer medulla is the inner medulla
• Nephrons
  • about 2 million nephrons per kidney
  • composed of glomerulus and tubules
  • glomerulus is surrounded by Bowman’s Capsule
  • together the glomerulus and Bowman’s capsule is the renal corpuscle
  • renal corpuscle is always in the cortex
  • nephrons closest to the capsule are called subcapsular
  • those a little deeper are called midcortical or superficial
  • those near the medulla are called juxtamedullary
  • the location of the corpuscle determines the length of the loop of Henle in the pyramid
  • The glomerulus is more arteriole than capillary bed
  • fenestrated - can leak similar to capillary
  • highly nucleated and spherical
  • afferent arteriole enters the corpuscle
    • forms the tuff
    • this side is the vascular pole
  • efferent arteriole leaves the corpuscle
    • this is included in the vascular side
  • Podocytes
    • cells wrapped around arteriole
    • many “feet”
    • surround endothelium
    • additional layer of limiting what comes out
  • Bowman’s Corpuscle is simple squamous epithelium
  • catches the filtrate squeezed out of vessels in glomerulus
  • send filtrate to proximal convoluted tubule at urinary pole
  • mesangium
  • supports corpuscle
  • Proximal convoluted tubule
  • reabsorbs about 80% of what was filtered
    • water, salts, sugars, and amino acids
    • simple cuboidal epithelium with extensive microvillar border
    • called brush border
    • will see almost if not all of nuclei
  • transport what was absorbed back to blood
    • basal infoldings with striated lamina
    • lots of mitochondria
  • Loop of Henle
  • our textbook includes
    • straight portion of PCT
    • simple cuboidal epithelium
    • thin descending limb
    • simple squamous epithelium
    • thin ascending limb
    • simple squamous epithelium
  • counter current exchange
    • what produces concentrated (hypertonic) urine
  • entangled by efferent arteriole
  • distal convoluted tubule
  • simple cuboidal epithelium
    • no brush border
  • larger lumen
    • because less large microvilli
  • not all cells will have visible nucleus
  • open lumen where PCT has obscured lumen
  • juxtaglomerular complex
  • macula densa
    • where DCT come close to vascular pole
    • denser portion of DCT
    • sodium sensors
    • if sodium is down, stimulate the juxtaglomerular cells
  • juxtaglomerular cells
    • modified glomerular smooth muscle
    • secretes renin
    • increase sodium
  • collecting duct
  • simple cuboidal epithelium for most of the length
  • simple columnar epithelium closer to papilla
  • mucosa made up of light and dark cells
    • light are sodium transporters
    • outnumber the dark
    • dark are potassium transporters
    • can’t separate light from dark
  • nucleus is more toward base of cell
    • rather than middle as in the loops of Henle
• Flow of filtrate
  • glomerulus
  • proximal convoluted tubule
  • proximal straight tubule
  • loop of Henle
  • distal straight tubule
  • distal convoluted tubule
  • collecting duct (not in nephron)
  • minor calyx (not in nephron)
  • major calyx (not in nephron)
  • renal pelvis (not in nephron)
  • ureter (not in nephron)
  • Medullary ray
  • all nephrons and tubules associated with 1 collecting duct

Ureter

mucosa

• transitional epithelium called urothelium
  • about 5 layers thick
  • umbrella cells
  • allow for stretching

Lumen

• stellate (star-shaped)

Muscularis

• 3 layers of smooth muscle
  • inner longitudinal
  • middle circular
  • outer longitudinal
  • in lower 1/3
• collagen fibers

Bladder

storage of urine

trigone

• imaginary line connecting the 2 ureters and urethra in a triangle

mucosa

• urothelium

muscularis

• detrusor muscle
• ply wood smooth muscle
  • complex orientation of smooth muscle fibers
• includes stress receptors
  • to signal when full
• internal urethral sphincter
  • holds urine bladder until emptying

Urethra

male - 20 cm length

• prostatic urethra (first 3-4 cm)
  • prostate gland sits on both sides of urethra
  • urothelium
• membranous urethra (middle 1 cm)
  • transition point
• penile urethra (last about 15 cm)
  • within penis
  • stratified squamous epithelium
• in transition from prostatic urethra to penile urethra will cross through pseudostratified epithelium

female - 3-5 cm length

• quick transition from urothelium to stratified squamous epithelium

often flattened tube

glands around urethra associated with reproductive organs