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