Urinary System - Anatomy PDF

Urinary System- Anatomy Dr. S.M. Ng’andwe Anatomy and Physiology TAU-ZM Objectives At the end of this topic you must be able to: 1. Identify the structures of the urinary system. 2. Describe the organization and functions of the urinary system organs. 3. Describe the physiol...

Urinary System- Anatomy Dr. S.M. Ng’andwe Anatomy and Physiology TAU-ZM Objectives At the end of this topic you must be able to: 1. Identify the structures of the urinary system. 2. Describe the organization and functions of the urinary system organs. 3. Describe the physiology of the urinary system. Introduction In the course of carrying out their specific functions, the cells of all body systems produce waste products. These waste products end up in the bloodstream. The bloodstream is analogous to a river that supplies drinking water to a nearby town. The river water may become polluted with harmful substances. But the town has a water treatment plant that removes these waste products and makes the water safe to drink. The urinary system is the body’s “water treatment plant.” Without it, waste products could accumulate in the blood and kill us. Organs of the Urinary System The organs of the urinary system are the: 1. kidneys 2. ureters 3. urinary bladder 4. urethra Functions of the Urinary System 1. Removal of waste products from the bloodstream e.g. urea, ammonia, bilirubin, creatinine, uric acid, drugs, toxins 2. Regulation of blood volume 3. Regulation of blood pressure 4. Regulation of ion balance/acid-base balance 5. Storage of urine 6. Excretion of urine 7. Regulation of erythrocyte production 8. Conversion of the steroid prohormone vitamin D, initially produced in the epidermis, to the active form ( 1,25- dihydroxyvitamin D3 or calcitriol) Kidney The kidneys are located lateral to the vertebral column between the last thoracic and third lumbar vertebrae on each side. They are retroperitoneal organs. The right kidney is situated inferior to the left kidney. They are kidney-bean-shaped organs. The kidney has a concave medial border called the hilum where vessels, nerves, and the ureter connect to the kidney. The hilum is continuous with an internal space within each kidney called the renal sinus. Kidney The interior of each kidney contains: 1. renal cortex: is the outer layer of the kidney which is granular and reddish-brown in color. 2. renal medulla: is internal to the cortex, and is darker in color. The renal medulla consists of 6–18 distinct conical or triangular structures, called renal pyramids. The apex (tip) of the renal pyramid called the renal papilla projects toward the renal sinus. Each renal papilla projects into a funnel-shaped space called the minor calyx. Several minor calyces merge to form larger spaces called major calyces. Kidney The major calyces merge to form a large, funnel-shaped renal pelvis which collects urine and transports it into the ureter. A human kidney is divided into 8 to 15 renal lobes. Nephron A nephron is the basic structural and functional unit of the kidney. Each nephron consists of two parts: 1. Renal corpuscle - where blood plasma is filtered. 2. Renal tubule - into which the filtered fluid passes. Nephron – renal corpuscle The renal corpuscle consists of two parts: i. Glomerulus – a network of capillaries ii. Bowman’s capsule - double-walled epithelial cup that surrounds the glomerular capillaries. The renal corpuscle has two opposing poles: Vascular pole - where the glomerular afferent and efferent arterioles are found. Tubular pole - where the proximal convoluted tubule attaches to the renal corpuscle. Nephron – renal corpuscle Bowman’s capsule consists of visceral and parietal layers. The visceral layer of the glomerular capsule is composed of specialized cells called podocytes. Podocytes have long processes called pedicels or feet, that wrap around the glomerular capillaries. The pedicels are separated by thin spaces called filtration slits that allow materials from the blood plasma to pass into the capsular space. The filtration slits of the podocytes and the fenestrated glomerulus endothelium collectively make up the filtration membrane of the glomerulus. Renal corpuscles also contain mesangial cells situated between the endothelial cells of adjacent capillaries. Nephron – renal corpuscle Nephron – renal tubule The renal tubule consists of a: 1. proximal convoluted tubule 2. loop of Henle 3. distal convoluted tubule The loop of Henle can be divided into a descending limb and an ascending limb. Each limb contains a thick segment and a thin segment. In each nephron, the final part of the ascending limb of the loop of Henle makes contact with the afferent arteriole serving that renal corpuscle. The cells in this region are closely packed and therefore, called Macula densa. Nephron – renal tubule Nephron – Blood supply Nephron – Blood supply Afferent arterioles supply blood to the glomerulus. Blood leaves the glomerular capillaries, not via venules, but via efferent arterioles. Efferent arterioles branch to form another capillary network, widely distributed in the cortex and medulla. In the cortex, this branched capillary network is closely associated with the convoluted tubules and therefore called Peritubular capillaries. In the medulla, this network of capillaries is closely associated with the loop of Henle and collecting ducts and is called Vasa recta. Nephron – renal tubule The wall of the afferent arteriole (and sometimes the efferent arteriole) contains modified smooth muscle fibers called juxtaglomerular (JG) cells. Together with the macula densa, they constitute the juxtaglomerular apparatus (JGA). The juxtaglomerular apparatus plays an important role in the regulation of blood pressure. The distal convoluted tubule (DCT) begins a short distance past the macula densa. In the last part of the DCT and continuing into the collecting ducts are principal cells, which have receptors for both antidiuretic hormone (ADH) and aldosterone. Nephron – renal tubule Nephron – renal tubule The distal convoluted tubule, the last segment of the nephron, opens into the collecting system, which consists of connecting tubules, collecting ducts, and papillary ducts. Individual connecting tubules connect each nephron to a nearby collecting duct. Each collecting duct receives fluid from many connecting tubules, draining both cortical and juxtamedullary nephrons. Several collecting ducts converge to empty into the larger papillary duct that empties into a minor calyx in the renal pelvis Nephron – renal tubule Ureters The ureters are long, fibromuscular tubes that conduct urine from the kidneys to the urinary bladder. Each tube averages 25 centimeters in length and is retroperitoneal. The ureters originate at the renal pelvis as it exits the hilum of the kidney. They then extend inferiorly to enter the posterolateral wall of the base of the urinary bladder. The wall of the ureter is composed of three concentric tunics, that is mucosa, muscularis & adventitia. The mucosa is formed from transitional epithelium. The middle muscularis consists of two smooth muscle layers: an inner longitudinal layer and an outer circular layer. Ureters Urinary Bladder The urinary bladder is an expandable, muscular container that serves as a reservoir for urine. The bladder is positioned immediately posterior to the pubic symphysis. The urinary bladder is a retroperitoneal organ. Ureters enter the posterolateral wall of the urinary bladder through the oblique ureteral openings. The neck of the bladder is located inferiorly and connected to the urethra. Trigone: triangle formed by imaginary lines connecting the two ureteral openings and the urethral opening. Urinary Bladder The mucosa lines the bladder lumen; it is formed by a transitional epithelium. The muscularis consists of three layers of smooth muscle, collectively called the detrusor muscle. At the neck of the urinary bladder, an involuntary internal urethral sphincter is formed by the smooth muscle that encircles the urethral opening. The adventitia forms the outermost layer the urinary bladder. Urinary Bladder Urethra The urethra is a fibromuscular tube that originates at the neck of the urinary bladder and conducts urine to the exterior of the body. The external urethral sphincter is inferior to the internal urethral sphincter and is formed by skeletal muscle fibers of the urogenital diaphragm. The male and female urethras differ slightly in length and morphology. The female urethra has a single function: to transport urine to the exterior of the body. It is 3 to 5 centimeters long. The male urethra has two functions—urinary and reproductive— because it serves as a passageway for both Urethra It is approximately 18 to 20 centimeters long and is partitioned into three segments: the prostatic urethra, the membranous urethra, and the spongy urethra. Urethra Quiz 1. Which statement is true about the urinary bladder? a) The bladder neck is surrounded by the external urethral sphincter. b)The detrusor muscle contains only two layers of smooth muscle. c) The bladder is lined with transitional epithelium. d)The bladder receives urine from the kidneys via the two urethras. Quiz 2. The apex of a renal pyramid is called the renal a) calyx. b)papilla. c) column. d)capsule.  References Prescribed Books: 1. Zuckerman S. A New System of Anatomy. Oxford Medical Publications. 2. Guyton & Hall- Textbook of Medical Physiology 2016.John E. Hall. 3. Anatomy for students. Richard Drake L, Wayne Vogl A. Elsevier. 4. Medical Physiology. Walter F.Boron, Emile L.Boulpae. Recommended Books: 1. Berne & Levy - Physiology 7/2017. Bruce M. Koeppen. S. 2. Review of Medical Physiology. Kim Barrett E, Susan Barman M. 3. Clinical Anatomy. Richard S. Snell. Wolters Kluwer.