PowerPoint ® Lecture Slides prepared by Janice Meeking, Mount Royal College C H A P T E R Copyright © 2010 Pearson Education, Inc. 25 The Urinary System: Part A

Copyright © 2010 Pearson Education, Inc. Kidney Location and External Anatomy The kidneys lie in a retroperitoneal position in the superior lumbar region The right kidney is lower than the left because it is crowded by the liver The lateral surface is convex; the medial surface is concave Ureters, renal blood vessels, lymphatics, and nerves enter and exit at the hilus

Copyright © 2010 Pearson Education, Inc. Kidney is protected by 3 layers: A fibrous renal fascia – outermost Adipose capsule – cushions and holds in place Renal capsule – fibrous sac - innermost PLAY InterActive Physiology ®: Anatomy Review, page 4

Copyright © 2010 Pearson Education, Inc. Kidney Functions Filter 200 liters of blood daily, allowing toxins, metabolic wastes, and excess ions to leave the body in urine Regulate volume and chemical makeup of the blood Maintain the proper balance between water and salts, and acids and bases Production of rennin to help regulate blood pressure and erythropoietin to stimulate RBC production

Copyright © 2010 Pearson Education, Inc. Internal Anatomy Cortex – the light colored, granular superficial region Medulla – exhibits cone-shaped medullary (renal) pyramids separated by columns The medullary pyramid and its surrounding capsule constitute a lobe Renal pelvis – flat funnel shaped tube lateral to the hilus within the renal sinus Minor and Major calyx – large branches of the renal pelvis Collect urine draining from papillae Empty urine into the pelvis

Copyright © 2010 Pearson Education, Inc. Blood Supply Approximately one-fourth (1200 ml) of systemic cardiac output flows through the kidneys each minute Arterial flow into and venous flow out of the kidneys follow similar paths PLAY InterActive Physiology ®: Anatomy Review, page 5 interlobular

Copyright © 2010 Pearson Education, Inc. Blood vessels in and around the nephron The interlobular artery ascends through the cortex, become the arcuate, and a series of afferent arterioles arise from it It leads to a spherical structure – glumerulus The blood from the glumerulus is carried out by efferent arteriole The capillaries in the glumerulus are found between 2 arteries

Copyright © 2010 Pearson Education, Inc. Blood vessels The efferent arterioles divide to form the peritubular capillaries that surround the tubules of the nephron in the renal cortex blood return from the peritubular capillaries to the cortical radiate veins. Some efferent arterioles give rise to long loop-shape capillaries called vasa recta; these capillaries enter the medulla Vasa recta eventually return blood to arcuate veins

Copyright © 2010 Pearson Education, Inc. Nephrons Each kidney contains over million nephrons – the anatomical units responsible for urine formation. Nephron functions include Production of filtrate Reabsorption of organic nutrients, water and ions Secretion of waste products into tubular fluid

Copyright © 2010 Pearson Education, Inc. Nephron’s parts Consists of 2 parts: The renal corpuscle which is the location of blood filtration It is composed of Bowman’s capsule Glomerulus The renal tubule is the location of filtrate processing into urine It is consists of Proximal convoluted tubule (PCT) Loop of Henle Distal convoluted tubule (DCT)

Copyright © 2010 Pearson Education, Inc. Renal corpuscle – in the cortex Bowman’s capsule is the outer, simple squamous ET wall (parietal layer) Bowman’s space also called "urinary space", is the space lying within Bowman's capsule. The glumerulus is the "little ball" which occupies most of the corpuscle: Glumerular capillaries have an endothelium that is fenestrated The capillaries are wrapped by Podocytes (visceral layer of Bowman’s capsule) the filtration membrane is found between the podocytes and the capillary endothelium. Fluid leaving the glumerular capillaries enter the Bowman’s space and is called filtrate

Copyright © 2010 Pearson Education, Inc. Anatomy of the Glomerular Capsule The external parietal layer is a structural layer (Bauman’s capsule) The visceral layer consists of modified, branching epithelial podocytes Extensions of the octopus-like podocytes terminate in foot processes

Copyright © 2010 Pearson Education, Inc. Glomerular filtration membrane Fluid from capillaries need to pass through 3 barriers to get to the capsular space: Fenestrated endothelium of capillaries with pores that allow the passage of relatively large molecules but not blood cells (pores size – 70-90nm) In addition, endothelial cells have negatively charged glycoproteins on their surface that “deny” entrance of negatively charged molecules Basement membrane – negatively charged proteins that do not allow the passage of large and negatively charged molecules (stop molecules >8nm)

Copyright © 2010 Pearson Education, Inc. Glomerular filtration membrane Filtration slits – form by the pedicles of the podocyes that create filtration slits (slit size 30nm). Filtrate on basis of size and negative charge Water and some solutes pass from blood plasma in the glomerulus capillaries to the capsular space of the nephrone Molecules smaller than 3 nm in diameter (water, sodium, glucose, amino acids, nitrogen wastes) pass freely from blood into capsule

Copyright © 2010 Pearson Education, Inc.

Renal Tubule Proximal convoluted tubule (PCT) – composed of cuboidal cells with numerous microvilli and mitochondria Reabsorbs water and solutes from filtrate and secretes substances into it Loop of Henle – a hairpin-shaped loop of the renal tubule Proximal part is similar to the proximal convoluted tubule Proximal part is followed by the thin segment (simple squamous cells) and the thick segment (cuboidal to columnar cells) Distal convoluted tubule (DCT) – cuboidal cells without microvilli that function more in secretion than reabsorption

Copyright © 2010 Pearson Education, Inc. Nephrons Cortical nephrons – 85% of nephrons; located in the cortex Juxtamedullary nephrons: Are located at the cortex-medulla junction Have loops of Henle that deeply invade the medulla Have extensive thin segments Are involved in the production of concentrated urine

Copyright © 2010 Pearson Education, Inc. Pair of muscular tubes Extend from renal pelvis to the bladder Peristaltic contractions force urine toward the urinary bladder Walls have layers Mucosa consists of transitional epithelium Muscularis of circular & longitudinal muscle layers Adventitia that is composed of loose connective tissue The ureters

Copyright © 2010 Pearson Education, Inc. Hollow, muscular organ Reservoir for the storage of urine Contraction of detrusor muscle voids bladder Internal features include Trigone Neck Internal urethral sphincter – smooth muscle External urethral sphincter – skeletal muscle Ruggae Detrusor (muscularis) is 3 layers of smooth muscle: inner longitudinal, middle circular and outer longitudinal. The urinary bladder

Copyright © 2010 Pearson Education, Inc. Extends from the urinary bladder to the exterior of the body Passes through urogenital diaphragm (external urinary sphincter) Differs in length and function in males and females The urethra

Copyright © 2010 Pearson Education, Inc. Micturition (Voiding or Urination) The act of emptying the bladder Distension of bladder walls initiates spinal reflexes Storing reflex: Stimulate contraction of the external urethral sphincter Inhibit the detrusor muscle and internal sphincter (temporarily) Voiding reflexes: Stimulate the detrusor muscle to contract Inhibit the internal and external sphincters