URINARY SYSTEM I. INTRODUCTION Each kidney is made up of about a million tiny tubules called nephrons. Each nephron individually filters the blood and makes urine and it does the job completely, from start to finish. In order to learn how the kidneys make urine, then, you must first become familiar with the nephron. A large part of the anatomy studied in this lab will be the microscopic structure (histology) of the nephron. II. ANATOMY OF THE URINARY SYSTEM A. Overview of gross anatomy 1. Organs of the urinary system and nearby structures (Fig. 26.2a) These can be seen on the torso models, the male and female pelvises, and the abdominal models. The right kidney is located a little more inferiorly than the left, allowing room for the liver. Kidneys Ureters Bladder Urethra Adrenal glands Renal artery Renal vein 2. The position of the kidneys, ureters, bladder and adrenal glands is retroperitoneal. (Fig. 26.2b). Note that this is a view from inferior looking superiorly These organs lie posterior or inferior to the (membrane). 3. Identify the perirenal fat (renal fat pad), which protects and stabilizes the kidneys. This is shown on the illustration only. 4. Using this illustration, identify the parietal peritoneum, peritoneal cavity, and liver. 41
42 B. Kidney (Fig. 26.3a, b) Use the large kidney models. 1. Renal capsule 2. Cortex 3. Medulla Renal pyramids Renal papilla (tip of the pyramid) Renal columns 4. Urine collection structures Minor calyx (kay-licks; plural is calyces [kay-li-seze]) Major calyx Renal pelvis Ureter 5. Blood vessels of the kidney (Fig. 26.7). Renal artery and vein Segmental artery and vein Interlobar artery and vein Arcuate artery and vein Interlobular artery and vein C. Nephron Use the large kidney models with nephrons for items 1-6 below. 1. Tubular portion (Fig. 26.4) Clear fluid called filtrate is filtered from the renal corpuscle into the proximal convoluted tubule of the nephron. Most of the filtrate is reabsorbed into the blood as it flows along the nephron. What is left becomes the urine, which exits the collecting duct and enters a minor calyx. Renal corpuscle Proximal [convoluted] tubule Thin descending segment of the loop of Henle Thin ascending segment of the loop of Henle Thick ascending segment of the loop of Henle Distal convoluted tubule Collecting duct
43 2. Types of nephrons (Fig. 26.4) Juxtamedullary nephrons (long loops of Henle) Cortical nephrons (short loops of Henle) 3. The renal corpuscle (Fig. 26.5a,b) Bowman's capsule Glomerulus (a capillary bed; the name means tuft ) Afferent arteriole Efferent arteriole Juxtaglomerular apparatus 4. Microanatomy of Bowman s capsule (Fig.26.5b) Parietal layer of Bowman's capsule Visceral layer of Bowman's capsule Podocytes ( foot-cells that form the visceral layer) 5. Filtration membrane (Fig. 26.5d): Capillary endothelium (capillary wall of the glomerulus) Basement membrane of capillary Visceral layer of Bowman's capsule consisting of podocytes 6. Blood vessels of the nephron (Fig. 26.7b) Note that the efferent arteriole branches to form the peritubular capillaries and vasa recta. Notice how these vessels surround the nephron. Afferent arteriole Glomerulus Efferent arteriole Peritubular capillaries Vasa recta D. Urinary bladder (Fig. 26.21) Study the male and female pelvises. 1. Layers of the bladder Mucosa of transitional epithelium Submucosa of connective tissue
44 Muscularis of smooth muscle Serosa (formed from parietal peritoneum; superior surface only) Adventitia (outer connective tissue where serosa is not found) 2. Sphincter muscles (Fig. 26.21) This illustration shows the location of the female external urethral sphincter only. In the male, the internal urethral sphincter is formed by the smooth muscle of the bladder wall that surrounds the urethra s opening into the bladder. The external urethral sphincter is formed by the skeletal muscle of the pelvic floor muscles, inferior to the prostate gland. Ask your instructor to point these structures out on both male and female pelvises. Internal urethral sphincter External urethral sphincter 3. Trigone The floor of the bladder, surrounded by three openings E. Urethra Use the male and female pelvises. Optional notes on the urinary system 1. Staghorn kidney stones are large deposits that take the shape of the renal pelvis, major and minor calyces in which they form. 2. Glomerulonephritis is an autoimmune disease in which the body forms antibodies which attack the glomerulus. 3. Transitional epithelium forms the mucosa of the bladder. It is capable of great stretching without tearing. 4. Urinary tract infections are more common in women than in men because of the shorter length of the urethra in women. Emptying the bladder regularly is one way to reduce the likelihood of bladder infection. The flushing action of the urine washes away bacteria. A stretched bladder has a reduced blood supply to its wall; a good blood flow discourages infection, since blood contains immune factors. 5. The "Kegel" exercise which is taught to women in childbirth classes strengthens the external urethral sphincter. It is done by consciously stopping a stream of urine.
45 Notes and Sketches