Ch 26 Urinary System Objectives Identify and describe

Ch 26: Urinary System Objectives Identify and describe the components of the urinary system and their function Describe the (histological) organization of the nephron Identify the blood vessels that supply blood to the nephrons Describe the blood flow through and around the nephron

Functions of Urinary System (Kidneys): ● Regulate fluid balance (fluid volume) of the body ● Excrete organic waste products and conserve nutrients, etc Stabilize p. H Regulate ion concentrations in the blood

Kidney Location Lateral to vertebral column high on body wall, under floating ribs in retro-peritoneal position

Surface Anatomy Size of bar of soap Bean shaped Hilus – indentation Three layers Renal fascia – fibrous tunic Adipose capsule – protects kidney Renal capsule – anchors kidney to body wall, continuous with peritoneum

Sectional Anatomy Cortex: outer layer, light reddish brow, granular appearance (due to many capillaries) Medulla: darker striped appearance (due to tubules) Subdivided into distinct renal pyramids, terminating with a papilla. Separated by renal columns from the cortex. Fig 26 -3

Urine collection: Ducts within each renal papilla release urine into minor calyx major calyx renal pelvis ureter

Renal Circulation Renal Artery Segmental arteries Interlobar arteries Arcuate arteries Interlobular arteries Afferent arterioles Glomerulus Efferent arterioles Peritubular capillaries Renal Vein Segmental veins Interlobar veins Arcuate veins Interlobular veins Venules Fig 26 -4

Functional unit: Nephron (>mio/kidney) Renal corpuscle: Fig 26 -8 » Glomerulus » Bowman’s capsule Tubular passageways with associated blood vessels: » » PCT LOH DCT CD Fig 26 -6

Filtration: Passage across Three Barriers Fig 26 -8 Capillary endothelium Fenestrated What gets through? Basement membrane Glomerular epithelium (= visceral layer of Bowman’s capsule) slit pores between pedicels of podocyte

Two Types of Nephrons Cortical nephrons (85%) shorter, mostly in cortex of kidney, produce "standard" urine Juxtamedullary nephrons (15%), "juxta-next-to" the medulla - responsive to ADH, can concentrate urine

Juxtaglomerular Apparatus Macula densa + Juxtaglomerular cells (smooth muscle fibers from afferent arteriole) = Juxtaglomerular Apparatus = Endocrine system structure (renin and EPO)

Urine Transport, Storage, and Elimination Trace drop of urine from kidneys to outside world Lining of these parts? Nephroptosis (= floating kidneys) Nephrolithiasis

Nephrolithiasis Occurs when urine becomes too concentrated and substances crystalize. Symptoms arise when stones begin to move down ureter causing intense pain. Kidney stones may form in the pelvis or calyces of the kidney or in the ureter.

Anatomy of Urinary Bladder Retroperitoneal, behind pubis Internal folds - rugae - permit expansion (max. holding capacity ~ 1 L) Trigone - area at base delineated by openings of ureters and urethra - without muscle Internal urethral sphincter - involuntary sphincter Histology 1. transitional epithelium 2. detrusor muscle – smooth muscle Fig 26. 10

Urethra External urethral sphincters – voluntary at pelvic floor Female - short – from base of bladder to vestibule Male 1. prostatic urethra – from base of bladder through prostate gland 2. membranous urethra – between prostate gland & base of penis 3. penile (spongy) urethra – traverses penis to orifice

Male versus Female UTIs (esp. E. coli)

The End Manneken Pis Fountain Brussels, 1619 Kidneys may sustain 90% loss of nephrons and still not show apparent symptoms!!! 2 -4 % of population only have 1 kidney!