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