Human Anatomy, First Edition McKinley & O'Loughlin

1. Human Anatomy, First EditionMcKinley & O'Loughlin Chapter 27 : Urinary System

2. General Structure and Functions of the Urinary System • General Concept: • Waste products accumulate in blood • Are toxic • Must be removed to maintain homeostasis • Urinary System organs • remove waste products from the blood • then from the body • Major homeostatic system

3. General Structure and Functions of the Urinary System • Organs of the Urinary System: • Kidneys • Ureters • Urinary Bladder • Urethra • Primary organs: kidneys • filter waste products from the bloodstream • convert the filtrate into urine. • The Urinary Tract: • Includes: • ureters • urinary bladder • urethra • Because they transport the urine out of the body.

7. Functions of the Urinary System • Removing waste products from the bloodstream. • Storage of urine. • the urinary bladder is an expandable, muscular sac that can store as much as 1 liter of urine • Excretion of urine. • Blood volume regulation. • the kidneys control the volume of interstitial fluid and blood under the direction of certain hormones • Regulation of erythrocyte production. • as the kidneys filter the blood, they are also indirectly measuring the oxygen level in the blood • Erythropoietin (EPO): hormone produced by kidney • Released if blood oxygen levels fall • Stimulates RBC production in red bone marrow

8. Kidneys: Gross and Sectional Anatomy • Retroperitoneal • Anterior surface covered with peritoneum • Posterior surface against posterior abdominal wall • Superior pole: T-12 • Inferior pole: L-3 • Right kidney ~ 2cm lower than left • Adrenal gland on superior pole

10. Kidneys: Gross and Sectional Anatomy • Hilum: concave medial border • Renal sinus: internal space • Houses blood vessels, lymphatic vessels, nerves • Houses renal pelvis, renal calyces • Also fat

11. Kidneys: Gross and Sectional Anatomy • Surrounding tissues, from deep to superficial: • Fibrous capsule (renal capsule) • Dense irregular CT • Covers outer surface • Perinephric fat (adipose capsule) • Also called perirenal fat • Completely surrounds kidney • Cushioning and insulation • Renal fascia • Dense irregular CT • Anchors kidney to posterior wall and peritoneum • Paranephric fat • Between renal fascia and peritoneum

13. Kidneys: Gross and Sectional Anatomy • Sectioned on a coronal plane: • Renal Cortex • Renal arches • Renal columns • Renal Medulla • Divided into renal pyramids • 8 to 15 per kidney • Base against cortex • Apex called renal papilla

14. Kidneys: Gross and Sectional Anatomy • Minor calyx: • Funnel shaped • Receives renal papilla • 8 to 15 per kidney, one per pyramid • Major calyx • Fusion of minor calyces • 2 to 3 per kidney • Major calyces merge to form renal pelvis • Renal Lobe • Pyramid plus some cortical tissue • 8 to 15 per kidney

17. Blood Supply to the Kidney • About 20 to 25% of cardiac output to kidneys • Path: • Renal artery to segmental arteries to interlobar arteries to arcuate arteries to interlobular arteries to: • Afferent arteriole to glomerulus to efferent arteriole to peritubular capilaries and vasa recta

19. Blood Supply to the Kidney • Blood plasma is filtered across the glomerulus into the glomerular space. • Once the blood plasma is filtered • blood leaves the glomerulus • enters an efferent arteriole. • efferent arteriole is still carrying oxygenated blood • a gas and nutrient exchange with the kidney tissues has not yet occurred.

20. Blood Supply to the Kidney • The efferent arterioles branch into one of two types of capillary networks: • peritubular capillaries • vasa recta • these capillary networks are responsible for the actual exchange of gases and nutrients • Peritubular capillaries: primarily in cortex • Vasa recta: surround the thin tubes that project into the medulla.

21. Blood Supply to the Kidney • Path for veins: • Interlobar veins to arcuate veins to interlobar veins to the renal vein

23. Nephrons • The functional filtration unit in the kidney. • Consists of the following: • Renal corpuscle • Glomerulus • Glomerular capsule (Bowman’s capsule) • Proximal convoluted tubule (PCT) • Nephron loop (loop of Henle) • Ascending loop of Henle • Descending loop of Henle • Distal convoluted tubule (DCT) • collectively called the renal tubule • In both kidneys: approximately 2.5 million nephrons. • Are microscopic: measure about 5 centimeters in length.

24. Nephrons • Cortical Nephrons • Near peripheral edge of cortex • Short nephron loops • Have peritubular capillaries • Juxtamedullary nephrons • Near corticomedullary border • Long nephron loops • Have vasa recta

26. Urine Formation • Three processes • Filtration • Renal corpuscle: forms filtrate • From blood to tubule • Reabsorption • Mostly PCT • Water and salt: rest of nephron • From tubule to blood • Secretion • From blood to tubule

27. Renal Corpuscle • Vascular pole • Afferent and efferent arterioles • Tubular pole • Connects to PCT • Two structures: • Glomerulus and glomerular capsule • Glomerulus • Capillary bed • High pressure • fenestrations

28. Renal Corpuscle • Glomerular Capsule • Parietal layer • Simple squamous epithelium • Visceral layer • Podocytes • Pedicels • Filtration slits • Capsular space (Bowman’s capsule): location of filtrate • Filtration membrane • Fenestrations • Filtration slits

31. Proximal Convoluted Tubule • Begins at tubular pole of the renal corpuscle. • Cells: simple cuboidal epithelium • actively reabsorb from the filtrate: • almost all nutrients (glucose and amino acids) • electrolytes • plasma proteins • Osmosis: reabsorption of 60% to 65% of the water in filtrate. • Have microvilli • Solutes and water: • moved into blood plasma • via the peritubular capillaries.

32. Nephron Loop (loop of Henle) • originates at end of proximal convoluted tubule • projects toward and/or into the medulla. • Each loop has two limbs. • descending limb: • from cortex toward and/or into the medulla • ascending limb: • returns back to the renal cortex

35. Distal Convoluted Tubule • begins at the end of the thick ascending limb of the nephron loop • adjacent to the afferent arteriole (important physiologically) • Juxtaglomerular apparatus. • primary function: • Secretion • From blood plasma to filtrate. • secretes ions • potassium (K+) • acid (H+) • Reabsorption of water also occurs: • influenced by two hormones • Aldosterone • antidiuretic hormone (ADH).

36. Collecting Collecting Ducts • Function in a well hydrated person: • transport the tubular fluid into the papillary duct and then into the minor calyx. • Function in a dehydrated person: • water conservation • more-concentrated urine is produced. • ADH can act on the collecting duct epithelium • Cells become permeable to water • Water moves from filtrate into blood plasma • Involves vasa recta.

37. Innervation of the Kidney • innervated by a mass of autonomic nervous system fibers • called the renal plexus. • The renal plexus • accompanies each renal artery • enters the kidney through the hilum.

38. Urinary Tract : Ureters • long, fibromuscular tubes • conduct urine from the kidneys to the urinary bladder. • average 25 centimeters in length • retroperitoneal. • ureters originate at the renal pelvis • extend inferiorly to enter the posterolateral wall of the base of the urinary bladder. • wall is composed of three concentric tunics. • mucosa • muscularis • adventitia.

39. Urinary Tract – Urinary Bladder • The urinary bladder: • expandable, muscular container • serves as a reservoir for urine • positioned immediately superior and posterior to the pubic symphysis. • in females • the urinary bladder is in contact with the uterus posterosuperiorly and with the vagina posteroinferiorly. • in males • it is in contact with the rectum posterosuperiorly and is immediately superior to the prostate gland. • is a retroperitoneal organ. • when empty exhibits an upside-down pyramidal shape. • Filling with urine distends it superiorly until it assumes an oval shape.

40. Urinary Tract – Urinary Bladder • Trigone • posteroinferior triangular area of the urinary bladder wall • formed by imaginary lines • connect the two posterior ureteral openings • and the anterior urethral opening. • The trigone remains immovable as the urinary bladder fills and evacuates. • It functions as a funnel • directs urine into the urethra as the bladder wall contracts • four tunics • mucosa • submucosa • Muscularis: called the detrusor muscle • adventitia. • Internal urethral sphincter (smooth muscle)

44. Micturition (Urination) • The expulsion of urine from the bladder. • Initiated by a complex sequence of events called the micturition reflex. • The bladder is supplied by both parasympathetic and sympathetic nerve fibers of the autonomic nervous system.

45. Urethra • Fibromuscular tube • exits the urinary bladder through the urethral opening • at anteroinferior surface • conducts urine to the exterior of the body. • Tunica mucosa: is a protective mucous membrane • houses clusters of mucin-producing cells called urethral glands. • Tunica muscularis: primarily smooth muscle fibers • help propel urine to the outside of the body. • Two urethral sphincters: • Internal urethral sphincter • restrict the release of urine until the pressure within the urinary bladder is high enough • External urethral sphincter • and voluntary activities needed to release the urine are activated.

46. Urethra • The internal urethral sphincter • involuntary (smooth muscle) • superior sphincter surrounding the neck of the bladder, where the urethra originates. • a circular thickening of the detrusor muscle • controlled by the autonomic nervous system • The external urethral sphincter • inferior to the internal urethral sphincter • formed by skeletal muscle fibers of the urogenital diaphragm. • a voluntary sphincter • controlled by the somatic nervous system • this is the muscle children learn to control when they become “toilet-trained”

47. Female Urethra • Has a single function: • to transport urine from the urinary bladder to the vestibule, an external space immediately internal to the labia minora • 3 to 5 centimeters long, and opens to the outside of the body at the external urethral orifice located in the female perineum.

49. Male Urethra • Urinary and reproductive functions: • passageway for both urine and semen • Approximately 18 to 20 centimeters long. • Partitioned into three segments: • prostatic urethra is approximately 3 to 4 centimeters long and is the most dilatable portion of the urethra • extends through the prostate gland, immediately inferior to the male bladder, where multiple small prostatic ducts enter it • membranous urethra is the shortest and least dilatable portion • extends from the inferior surface of the prostate gland through the urogenital diaphragm • spongy urethra is the longest part (15 centimeters) • encased within a cylinder of erectile tissue in the penis called the corpus spongiosum • extends to the external urethral orifice