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PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal College CHAPTER 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 http://www.portfolio.mvm.ed.ac.uk/studentwebs/session5/37/ALBL_kidney.htm Copyright © 2010 Pearson Education, Inc. InterActive Physiology ®: Anatomy Review, page 4 PLAY 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 interlobular PLAY Copyright © 2010 Pearson Education, Inc. InterActive Physiology ®: Anatomy Review, page 5 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. 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. The ureters • 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 Copyright © 2010 Pearson Education, Inc. The urinary bladder • 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. Copyright © 2010 Pearson Education, Inc. The urethra • 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 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 Copyright © 2010 Pearson Education, Inc.