Lesson XIII Urinary System PDF

Anatomy and Physiology MODULE XIII Urinary System Overview The urinary system is responsible for controlling the electrolyte (ion) and fluid balance of your body. The kidneys filter blood, reabsorb and secrete ions, and produce uri...

Anatomy and Physiology MODULE XIII Urinary System Overview The urinary system is responsible for controlling the electrolyte (ion) and fluid balance of your body. The kidneys filter blood, reabsorb and secrete ions, and produce urine. Without them, fluid and ion imbalance, blood pressure irregularities, and nitrogen waste build-up would cause death in a matter of days. The urinary system consists of two kidneys, bean-shaped organs located in the superior dorsal abdominal cavity, and accessory structures that filter blood and make urine. A ureter is a tube that carries urine from each kidney to the single urinary bladder, located in the inferior ventral pelvic cavity. The urinary bladder is an expandable sac that holds the urine. The urethra is the tubing that transports urine from the bladder to the outside of the body. General Objectives At the end of the course, you should have:  described the anatomic structures and physiologic processes involved in physiologic concepts;  utilized basic anatomical facts and physiologic concepts and principles in the nursing care of individuals;  used an understanding of how human organ systems are interrelated to apply a holistic approach to human health; and synthesized ideas to make connection between knowledge of anatomy and physiology and real-world situations, including healthy lifestyle decisions and homeostatic balance. Learning Objectives After studying this lesson, you should have:  described the internal and external anatomy and physiology of the kidneys,  described the process of urine formation,  discussed the importance of renal blood flow, and  traced the pathway of reabsorption or secretion of vital substances. Discussion The job of the urinary system is to make urine, thereby controlling the body’s fluid and electrolyte (ion) balance, and eliminating waste products. Functions of the Urinary System: 1. Excretion of nitrogenous wastes, drugs and toxins from the body and reabsorb needed substances and return them to the blood. 2. Maintain blood volume and concentration by regulating the proper balance in the blood between salts and water. They regulate the volume of urine produced as well as the concentration of ions in body fluids and blood, so the proper balance of sodium, chloride, potassium, calcium and phosphate ions is maintained. Page 136  Anatomy and Physiology MODULE XIII 3. The kidneys control the proper balance of hydrogen ions in the blood, thus helping to regulate the proper pH levels in the body. 4. The kidneys produce the enzyme renin which helps adjust filtration pressure. 5. The kidneys produce erythropoietin, a hormone that stimulates red blood cell production in red bone marrow. They help regulate concentration of erythrocytes in the blood in cases of hypoxia. 6. The kidneys convert vitamin D to its active form calciferol. It also helps control calcium and phosphorus metabolism. Parts of the Urinary System: 1. Two kidneys 3. Urinary bladder 2. Two ureters 4. Urethra Kidneys – they are paired organs that are reddish in color and they resemble lima beans in shape. They are about the size of a closed fist located just above the waist between the parietal peritoneum and the posterior wall of the abdomen. The right kidney is slightly lower than the left because of the large area occupied by the liver. Hilum – part of the kidney through which the ureter leaves the kidney as well as where blood vessels, nerves and lymph vessels enter and exit the kidney. Renal sinus – a cavity in the kidney consisting of connective tissue and fat. Layers of Tissue Surrounding the Kidney: 1. Renal capsule – innermost layer which acts as a barrier against infection and trauma to the kidney. 2. Adipose capsule – the second layer consisting of fatty tissue that protects the kidney from blows. It also firmly holds the kidney in place in the abdominal cavity. 3. Renal fascia – outermost layer that also anchors the kidney to their surrounding structures and to the abdominal wall. Internal Parts of the Kidney: 1. Cortex – outer area which is reddish in color 2. Medulla – inner area which is reddish-brown in color 3. Renal pyramids – 8-18 striated, triangular structures consisting of straight tubules and blood vessels. 4. Renal papillae – it formed at the bases of the renal pyramids pointing toward the center of the kidney. 5. Renal columns – cortical substances in between the pyramids 6. Parenchyma of the kidneys – it is made up of the cortex and renal pyramids which consist of millions of collecting tubules called nephrons (functional units of the kidneys) that regulate the composition and volume of blood and form the urine. Page 137  Anatomy and Physiology MODULE XIII 7. Minor calyx – funnel-shaped structure (8-18) surrounding the tip of each renal pyramid that collects urine from the ducts of the pyramids. 8. Major calyx – (2-3) joined minor calyces which further unites forming the large collecting duct called the renal pelvis which is found in the renal sinus. 9. Ureter – a narrowing of the renal pelvis that drains urine out from the kidneys. Urine drains from the tips of the renal pyramids minor calyx major calyx renal pelvis ureters. Nephrons – functional units of the kidneys that is basically a microscopic renal tubule, that functions as a filter. Bowman’s Glomerular Capsule – a double-walled globe where nephrons begin and is located in the cortex of the kidney. Layers of the Bowman’s Capsule: 1. Visceral layer – innermost layer consisting of epithelial cells called podocytes that surrounds a capillary network known as the glomerulus. 2. Parietal layer – outermost layer Renal corpuscle – it is made up by the Bowman’s glomerular capsule and the glomerulus. Endothelial-capsular membrane – it is located in the glomerulus which is the site of filtration of water and solutes from the blood. The filtered fluid now moves to the renal tubule. ✓ Flow of filtered fluid start from the Bowman’s capsule and opens into the first part of the proximal convoluted tubule descending limb of Henle loop of Henle (u-shaped) ascending limb of Henle distal convoluted tubule collecting duct renal pyramids. ✓ Proximal tubule, ascending limb of Henle and the collecting duct – transport molecules and ions across the wall of the nephron. ✓ Descending limb of Henle – highly permeable to water and solutes Page 138  Anatomy and Physiology MODULE XIII Blood and Nerve Supply to the Nephrons ✓ The right and left renal arteries transport 1,200 ml of blood to the kidneys every minute. ✓ Interlobar arteries – branches of right and left renal arteries in the renal columns ✓ Arcuate arteries – branches of the interlobar arteries located between the cortex and the medulla ✓ Afferent arteriole/interlobular arteries – branches of arcuate arteries in the cortex of the kidney ✓ Glomerulus – branches of afferent arteriole that had divided into tangled capillary network. ✓ Efferent arteriole – reunited glomerular capillaries carrying blood away from the glomerular capsule. ✓ Peritubular capillaries – branches of efferent arteriole surrounding the convoluted tubules of the nephron. ✓ Interlobular vein – reunited peritubular capillaries ✓ Arcuate vein – reunited interlobular vein that drains filtered blood at the base of the pyramid ✓ Interlobar veins – it run between the pyramids in the renal columns ✓ Right and left renal veins – reunited interlobar veins that leave the kidney at the hilum. ✓ Renal plexus of the autonomic nervous system – nerve supply to the kidney NEPHRON Urine is formed by three processes in the nephrons: 1. Glomerular filtration – glomerulus filters water and certain dissolved substances from the blood plasma. This process results in increased BP which forces the fluid to filter from the blood. Dissolved substances include: a. Positively charged ions – Na, K, Ca, Mg b. Negatively charged ions – Chloride, Bicarbonate, sulfate, phosphate c. Glucose d. Urea e. Uric acid Page 139  Anatomy and Physiology MODULE XIII Both kidneys filter about 45 gallons of blood plasma per day but only a small portion of the glomerular filtrate leaves the kidney as urine. 2. Tubular reabsorption – substances are transported out of the tubular fluid and back into the blood of the peritubular capillary which occurs throughout the renal tubule but majority of reabsorption occurs in the proximal convoluted tubule. a. Active transport reabsorbs glucose, amino acids, creatine, lactic acid, uric acid, citric acid, ascorbic acid, phosphate, calcium, sulfate, sodium, potassium ions at the ascending limb of Henle b. The process of osmosis rapidly reabsorbs water at the descending limb of Henle, in the collecting duct and in the distal convoluted tubule c. Electrochemical attraction and active transport reabsorbs chloride ions at the ascending limb of Henle and other negatively charged ions ✓ About 95% of water is reabsorbed back into the blood stream. ✓ Vasopressin and aldosterone are two hormones essential to help control tubular reabsorption. 3. Tubular secretion - substances will move from the plasma in the peritubular capillary into the fluid of the renal tubule. ✓ The proximal convoluted tubule actively secretes penicillin, creatinine and histamine. ✓ The entire renal tubule actively secretes hydrogen ions thus helping regulate the pH of the body fluids. ✓ The distal convoluted tubule and the collecting duct secrete potassium ions. Page 140  Anatomy and Physiology MODULE XIII Composition of Urine: Urine is composed of 95% water with urea, uric acid, some amino acids and electrolytes. The daily production of urine is between 0.6 and 2.5 liters per day. Urine production of 56 ml/hour is considered normal; 30 ml an hour indicates possible kidney failure. Ureters – it is basically an extension of the pelvis of a kidney and extends about 23 – 30 cm (10 – 12 inches) down to the urinary bladder. Function: Transport urine from the renal pelvis into the urinary bladder Urinary Bladder – a hollow muscular organ located in the pelvic cavity posterior to the symphysis pubis. The interior of the urinary bladder has three openings. Trigone – a triangular region of the bladder outlined by the three openings that is most commonly infected. Detrusor muscle – layers of smooth muscle inside the urinary bladder Internal urinary sphincter – smooth muscle at the junction of the urinary bladder and urethra which is under involuntary control. External urinary sphincter – skeletal muscle that surrounds the urethra as it leaves the bladder, must relax and urine leaves the bladder. Micturition/urination/voiding – the act of expelling urine from the urinary bladder Average capacity of the urinary bladder – 700- 800 ml but when the amount of urine reaches 200 – 400 ml, stretch receptors in the bladder wall transmit nerve impulses to the lower portion of the spinal cord initiating a conscious desire to expel urine. Urethra – a small thin-walled tube leading from the floor of the urinary bladder to the outside of the body. In females – urethra is 3.8 cm (1.5 inches) long with its opening located between the clitoris and the vaginal opening. In males – urethra is about 20 cms. (8 inches) long located directly below the bladder passing through the prostate gland, then to the urogenital diaphragm and enters the penis. Disorders of the Urinary Bladder 1. Kidney stone/renal calculi – composed of the precipitates of uric acid, magnesium or calcium phosphate or calcium oxalate. 2. Cystitis – an inflammation of the urinary bladder usually caused by bacterial infection. The infection causes a frequent urge to urinate, with an accompanying burning sensation during urination. 3. Gout – a condition caused by high concentration of uric acid in the plasma. Crystals of uric acid get deposited in joints of the hands and feet causing inflammation and great pain. Page 141  Anatomy and Physiology MODULE XIII 4. Glomerulonephritis – an inflammation of the kidneys where the filtration membrane within the renal capsule is infected with bacteria. It can be acute following streptococcal sore throat or scarlet fever, or it can be a chronic condition resulting in kidney failure. 5. Renal failure – it can result from almost any condition that interferes with kidney function. 6. Hematuria – presence of blood in the urine 7. Oliguria – scanty urine output 8. Polyuria – excessive urine output 9. Pyuria – presence of pus in the urine 10. Uremia – presence of urine in the blood RENAL FAILURE Page 142  Anatomy and Physiology MODULE XIII Self-Check Test I. Answer the following. (5 Points each) 1. Describe the internal and external anatomy and physiology of the kidneys. _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ ____________________________________________________________________. 2. Describe the process of urine formation. _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ ____________________________________________________________________. References Books 1. Ankney,J., Colbert, B., and Lee, K. (2007). Principles of anatomy and physiology, an interactive journey: New Jersey: Pearson Education Inc. 2. Rizzo, D. C. (2006). Fundamentals of anatomy and physiology: Michigan: Thomson Delmar Learning 3. Van De Graaf, K., Fox, S. I., and LaFleur, K. (1997). Synopsis of human anatomy and physiology: Chicago: Wm. C. Brown Publishers. Page 143