Kristina C. Erasmo, M.D.

URINARY SYSTEM Kidneys (paired) Ureters (paired) Urinary bladder Urethra

Functions of the Urinary System Production of urine – Elimination of metabolic waste products – Fluid and electrolyte balance Production of hormones/enzymes – Renin – Erythropoietin – Calcitriol

KIDNEYS Bean-shaped, reddish-brown organ cm Posterior abdominal wall T12-L3

KIDNEYS Hilus Renal pelvis Major calyx Minor calyx

KIDNEYS Cortex Medulla Medullary pyramids Medullary rays Renal columns Renal lobe

Nephron Functional unit of the kidney Approx. 1.5 million

Nephron Functional unit of the kidney Approx. 1.5 million

Parts of a Nephron Renal corpuscle Renal tubule – Proximal convoluted tubule – Thin and thick limbs of Henle’s loop – Distal convoluted tubule – Collecting tubules and ducts

Renal Corpuscle Located in the cortex (grainy appearance) 200 um diameter Consists of a tuft of capillaries (glomerulus) surrounded by a double-walled epithelial capsule called Bowman’s (glomerular) capsule

Renal Corpuscle Vascular pole – Afferent arteriole enters, efferent arteriole leaves Urinary pole – Where the renal tubule begins

Glomerulus Results from the breakup of an afferent arteriole Drain into a single efferent arteriole Fenestrated capillaries

Glomerulus Mesangial cells Juxtaglomerular cells

Glomerulus Mesangial cells – Stellate-shaped cells – Found in the CT surrounding the glomerular capillaries – Contractile cells, phagocytes

Glomerulus Juxtaglomerular cells – Polyhedral cells – Found in tunica media of afferent arteriole before it enters the vascular pole – Contain secretory granules – Responsible for production of renin

Bowman’s Capsule Visceral layer – Internal, envelops the capillaries of the glomerulus Parietal layer – External, forms the outer limit of the renal corpuscle

Bowman’s Capsule Visceral layer – Internal, envelops the capillaries of the glomerulus Parietal layer – External, forms the outer limit of the renal corpuscle

Bowman’s Capsule Urinary (Bowman’s) space – Between the two layers of Bowman's capsule – Receives the fluid filtered through the capillary wall and the visceral layer

Bowman’s Capsule Visceral layer – Made up of podocytes (cell body + primary processes) – Primary processes give rise to secondary processes (pedicels) that embrace the capillaries of the glomerulus – Filtration slits – small spaces between adjacent processes

Bowman’s Capsule Parietal layer – Simple squamous epithelium – Basal lamina – Thin layer of reticular fibers – Epithelium changes to simple cuboidal or low columnar at level of urinary pole

Filtration Barrier Between the fenestrated endothelial cells of the glomerular capillaries and the podocytes that cover their external surfaces is a thick basement membrane

Filtration Barrier Separates the urinary space and the blood in the capillaries From fusion of basal laminae of capillary and podocyte