Urinary System

Functions of Urinary System 1.Remove wastes from blood 2.Produce/store/excrete urine 3.Regulate blood volume 4.Regulate erythrocyte production – Secretes erythropoeitin (EPO)

Urinary System 1.Kidneys 2.Ureters 3.Urinary bladder 4.Urethra

Kidneys Retroperitoneal Concave medial border = hilum Renal capsule – fibrous outer covering Perinephric fat – cushions kidneys

Regions of the Kidney Outer renal cortex and inner renal medulla renal columns - projections of cortex into medulla – subdivide medulla into renal pyramids – Tip of pyramid = renal papilla

Tubing within the Kidney Each papilla projects into minor calyx Several minor calyces  major calyx Major calyces  renal pelvis Renal pelvis  ureter

Arterial Supply to the Kidney Blood enters kidneys via renal arteries renal arteries  segmental arteries  interlobar arteries  arcuate arteries  interlobular arteries

Arterial Supply to the Kidney interlobular arteries  afferent arterioles Afferent arterioles  glomerulus  plasma filtered  remaining blood enters efferent arteriole

Capillary Supply to the Kidney Efferent arterioles branch into either: 1.Peritubular capillaries – surround PCT and DCT 2.Vasa recta – surround nephron loop

Venous Return from the Kidney Peritubular capillaries and vasa recta  interlobular veins  arcuate veins  interlobar veins  renal vein **NO SEGMENTAL VEINS

Nephrons Nephron = functional filtration unit of kidney ~ 1.25 million nephrons per kidney Form urine through: 1.Filtration – fluid/solute pushed out of blood 2.Tubular reabsorption – fluid/solute pulled back into blood 3.Tubular secretion – additional solute added to urine from blood

Nephron Structure Nephron comprised of: 1.Renal corpuscle 2.Renal tubule

Renal Corpuscle Located in renal cortex Composed of two structures: 1.Glomerulus – a thick tangle of fenestrated capillaries 2.Glomerular (Bowman’s) capsule – epithelial covering around glomerulus

Glomerular Capsule 1.Visceral layer – directly overlies glomerulus – comprised of specialized cells called podocytes Form filtration membrane 2. Parietal layer – forms wall of capsule

Renal Tubule Consists of – Proximal convoluted tubule – Loop of Henle (nephron loop) – Distal convoluted tubule

Proximal Convoluted Tubule Directly connects to GC In renal cortex Lined w/simple cuboidal ET with microvilli – reabsorbs most nutrients and water from filtrate Reabsorbed into peritubular capillaries returned to general circulation

Nephron Loop Projects into medulla 1.Descending limb 2.Ascending limb Reabsorption of water and solutes – Into vasa recta

Distal Convoluted Tubule Found in renal cortex Lined w/simple cuboidal – Short, sparse microvilli K + and H + secreted from peritubular capillaries into DCT DCTs of all nephrons in a pyramid dump into central collecting duct

Juxtaglomerular Apparatus Consists of: – Juxtaglomerular cells: modified smooth m. of afferent arteriole – Macula densa – modified epith. cells in DCT If low blood volume/solute conc., MD stimulates JG cells JG cells release renin Renin  aldosterone  incr. ion conc. and BV  incr. BP

Urinary Tract Composed of: 1.Ureters 2.Urinary bladder Stores urine Lined with transitional epithelium 3.Urethra Urethra ends at opening called external urethral orifice Release of urine controlled by: – Detrusor muscle – smooth muscle in wall of bladder – Internal urethral sphincter – smooth muscle – External urethral sphincter – skeletal muscle

Urinary Bladder Posteroinferior triangular area of bladder = trigone – Defined by two ureteral openings and the urethral opening

Female Urethra Has single function of transporting urine to exterior of body – Short tube

Male Urethra Both urinary and reproductive functions – transports both urine and semen Three segments: 1.Prostatic urethra 2.Membranous urethra 3.Penile urethra Much longer than female urethra

Male vs. Female Urethra