Urinary System Objectives 1. Identify organs belonging to the urinary system 2. Describe the gross and microscopic structures of the kidney 3. Describe the structure and function of the nephron in urine formation

Urinary System Objectives 4. Identify the pattern of blood supply and urine output from the kidneys 5. Describe the function, histology, location and structure of the ureters, urinary bladder and urethra 5. Define and use the correct terminology associated with the urinary system

Urinary System

Urinary System Kidneys Ureters Urinary Bladder Urethra

Kidneys Paired 11 cm x 6 cm x 2.5 cm Retroperitoneal Between T12 and L3, left kidney higher than the right

Kidneys Held in place by two layers of fascia Perirenal fat Renal capsule - fibrous CT Indented region = hilus where vessels enter and exit medially

Kidney Regions

Kidney Regions Cortex - outer, reddish Two layers cortical layer Juxtamedullary

Kidney Regions Medulla – inner Contains renal pyramids Apex of renal pyramid = renal papillae Pyramids separated by renal columns interlobar vessels within the columns

Renal Pyramids

Kidney Regions Minor and major calyces = funnel shaped spaces for urine collection Drain via renal pelvis into ureters

Blood Supply

Kidney Blood Supply Arterial - nutrient, O2 and waste product rich Aorta Renal artery Interlobar artery Arcuate artery Interlobular artery

Kidney Blood Supply Venous - O2, nutrient poor, nitrogenous waste eliminated Interlobular veins Arcuate veins Interlobar veins Renal veins Vena cava

Kidney Blood Supply Microscopic blood supply Afferent arteriole Glomerulus Efferent arteriole Capillary Peritubular capillaries

Microcirculation

Microcirculation

Nephron Nephrons - microscopic units responsible for urine formation 1-3 million per kidney

Nephron Two kinds of nephrons (location) Cortical (80%)- renal corpuscle and majority of loop of Henle in cortex Juxtamedullary (20%) - renal corpuscle near junction of cortex - medulla, long loop of Henle penetrates well into medulla

Nephron Consist of two kinds of tubular components Vascular Tubular

Vascular Nephron Afferent arteriole Glomerulus Efferent arteriole Containing blood Afferent arteriole Glomerulus Efferent arteriole ) .

Tubular Nephron Bowman’s capsule Containing urine components double layered epithelium, visceral & parietal visceral layer formed by podocytes, perforated to allow filtration of plasma

Tubular Nephron Proximal convoluted tubule – PCT Loop of Henle descending limb - Thin loop ascending limb - Thick loop distal convoluted tubule – DCT Collecting tubule

Renal Corpuscle Together glomerulus + Bowman’s capsule = renal corpuscle

Glomerulus

Podocyte

Filtration Mechanism

Filtration Movement of “plasma” from glomerulus into Bowman’s capsule, primarily a function of hydrostatic pressure on blood within glomerulus and “leaky” condition of visceral Bowman’s capsule. Product of this process is a dilute glomerular filtrate, similar to plasma without proteins or formed elements.

Secretion Movement from capillaries into tubule via active transport of materials not filtered or added to filtrate. Secreted products include H+, nitrogenous waste, some drugs, etc.

Reabsorption 99% of H2O filtered is reabsorbed. Movement from tubules into capillaries or vasa recta. 99% of H2O filtered is reabsorbed. Other products reabsorbed include amino acids, glucose, ions, water soluble vitamins.

Reabsorption ~180 liters glomerular filtrate produces per day, 1-2 liters actually becomes urine. ADH stimulates H20 reabsorption, primarily at DCT. Aldosterone stimulates reabsorption of Na+ and indirectly, H20 at the DCT.

Counter-current Exchange Method by which ions are secreted and reabsorbed to allow for concentration of glomerular filtrate

Counter-current Exchange Tubes are “leaky” Tubes pass close together

Counter-current Exchange Flow in opposite directions Ions secreted on one side are reabsorbed on the other Provides surface area, time for H20 reabsorption without loss of essential ions (Na+)

Ureters Exit kidney at renal hilus Retroperitoneal 25-30 cm

Ureters Transport urine from kidney to bladder via peristalsis, gravity, hydrostatic pressure 3 layers (deep to superficial) Tunica mucosa Transitional epithelium Lamina propria Tunica muscularis Longitudinal and circular smooth muscle Tunica adventitia Fibrous CT, continuous with renal capsule

Kidney Stones

Urinary Bladder Functions as urine storage site Variable size and shape dependent on condition Posterior to symphysis pubis, anterior to rectum

Urinary Bladder Held in place by ligaments and peritoneum Lateral umbilical ligaments (remnants of hypogastric arteries of fetus) Middle umbilical ligament

Urinary Bladder Three openings for inferior triangular region = trigone 2 ureters 1 urethra

Urinary Bladder Three layers (deep to superficial) Tunica mucosa Transitional epithelium Submucosa Tunica muscularis Smooth muscle Tunica Adventitia/serosa Peritoneum only on superior aspect Lower 2/3 CT only, attaching bladder to surrounding structures

Micturition Reflex mechanism to allow elimination of urine involves: Internal sphincter - smooth muscle, involuntary External sphincter - skeletal muscle, voluntary

Urethra Male and female differ in structure and function Female For elimination of urine only 4-5 cm

Female Urethra Anterior to vagina Lined with transitional epithelium proximally, becoming squamous distally Smooth muscle Opens at external urethral meatus

Female Urethra

Male Urethra Carries urine and semen (not simultaneously) ~20 cm Three portions (proximal to distal) Prostatic ~3 cm, surrounded by prostate Membranous ~2cm, receives bulbourethral gland secretions Cavernous/penile ~15 cm, surrounded by corpus spongiosum

Male Urethra