Lecture 10 and 11 urinary system
- 1. 1 Lecture 10 When blood sugar (glucose) levels are low, the liver converts amino acids into glucose for energy. Amino acids come from the breakdown of protein in the GI tract. The conversion of amino acids to glucose results in the production of the nitrogenous waste product, ammonia (NH3). Ammonia is extremely toxic to cells, so the liver converts NH3 to the less toxic nitrogenous waste product, urea. The URINARY SYSTEM removes urea and other metabolic waste products, toxins, excess water, and excess electrolytes (salts) from the bloodstream and eliminates them from the body in the form of urine. The process of eliminating metabolic wastes is called excretion. The KIDNEYS are the excretory organs of the urinary system. As the kidneys perform their excretory function, they also regulate blood volume and the chemical makeup of the blood. They continuously maintain the proper balance between water and salts in the blood and they help to maintain the blood pH at 7.35-7.45. Kidneys contribute to homeostasis of body fluids by regulation of blood ionic composition, regulation of pH, , regulation of blood volume, regulation of blood pressure, maintenance of blood osmolarity, producing hormones produced by the kidneys stimulates red blood cell production, regulating blood glucose level, and excreting wastes and foreign substances. The Urinary System
- 2. 2 The urinary system consists of two kidneys, two ureters, one urinary bladder, and one urethra. Urine is excreted from each kidney through its ureter and is stored in the urinary bladder until it is expelled from the body through the urethra. The specialized branch of medicine that deals with structure, function, and diseases of the male and female urinary systems and the male reproductive system is known as nephrology. The branch of surgery related to male and female urinary systems and the male reproductive system is called urology.
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- 4. 4 EXTERNAL ANATOMY Kidneys are kidney bean-shaped and reddish in color. The adult kidney weighs 150 grams, is 10-12 cm (4-5 inches) long, 5.0-7.5 cm (2-3 in.) wide and 2.5 cm (1 in.) thick. The kidneys are located between the posterior abdominal wall and parietal peritoneum (they are retroperitoneal), extending from the level of the T12 vertebra to the level of the L3 vertebra. The kidneys receive some protection from the lower part of the rib cage. The right kidney is slightly lower than left kidney. The lateral surface of each kidney is convex. The medial surface is concave and has an indentation called the HILUS. The ureters, renal blood vessels, lymphatic vessels, and nerves enter or exit the kidney at the hilus. There are 3 layers of supportive tissue surrounding each kidney: 1. RENAL CAPSULE: a transparent dense irregular connective tissue covering the kidney surface. The renal capsule prevents infections in surrounding regions from spreading to the kidneys. It also protects the kidney from physical trauma. 2. ADIPOSE CAPSULE: a mass of adipose tissue outside the renal capsule. The adipose capsule helps hold the kidney in place against the posterior abdominal wall and cushions the kidneys against external blows. 3. RENAL FASCIA: a layer of dense irregular connective tissue outside the adipose capsule that anchors the kidney to the abdominal wall.
- 5. 5 KIDNEY: INTERNAL ANATOMY A frontal section of the kidney reveals 3 distinct regions inside the renal capsule and they are the RENAL CORTEX, RENAL MEDULLA, & RENAL PELVIS. 1. RENAL CORTEX: the outer region just inside the renal capsule; light red in color and granular in appearance. 2. RENAL MEDULLA: deep to the cortex; a darker, reddish brown color. Arranged in cone-shaped regions called RENAL PYRAMIDS, which have a striated appearance. Extensions of the RENAL CORTEX between the renal pyramids are called RENAL COLUMNS. Together, the RENAL CORTEX & MEDULLA form the parenchyma (functional portion) of the kidney where urine is formed. 3. Just inside the hilus is the cavity called the RENAL PELVIS. The renal pelvis collects urine that is formed in the renal cortex and medulla.
- 6. 6 Nephrons • A nephron consists of a renal corpuscle where fluid is filtered, and a renal tubule into which the filtered fluid passes. • Nephrons perform three basic functions: glomerular filtration, tubular reabsorption, and tubular secretion. • A renal tubule consists of a proximal convoluted tubule (PCT), loop of Henle (nephron loop), and distal convoluted tubule (DCT). Distal convoluted tubules of several nephrons drain into to a single collecting duct and many collecting ducts drain into a small number of papillary ducts. • The loop of Henle consists of a descending limb, a thin ascending limb, and a thick ascending limb. • There are two types of nephrons that have differing structure and function. – A cortical nephron usually has its glomerulus in the outer portion of the cortex and a short loop of Henle that penetrates only into the outer region of the medulla – A juxtamedullary nephron usually has its glomerulus deep in the cortex close to the medulla; its long loop of Henle stretches through the medulla and almost reaches the renal papilla.
- 7. 7 In the renal cortex, the ascending limb of the loop of Henle becomes twisted again as the DISTAL CONVOLUTED TUBULE. The distal convoluted tubules of several nephrons empty into each COLLECTING DUCT. The collecting ducts absorb water from the filtrate. Several collecting ducts empty into a PAPILLARY DUCT, which delivers urine to the RENAL PELVIS. The filtrate is processed as it passes through these parts of the nephron. Needed substances, such as water, glucose and electrolytes (salts), are returned to the bloodstream. After the filtrate is processed by the nephron, it is called URINE. Urine contains urea and other metabolic wastes, toxins, excess salts, and excess water, as well as drugs and excess vitamins.
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- 11. 11 BLOOD SUPPLY OF THE KIDNEYS While the body is at rest, the large left and right RENAL ARTERIES deliver about about 1.2 liters of blood through the kidneys every minute. The renal arteries are branches of the ABDOMINAL AORTA. After each renal artery enters a kidney, it branches into numerous small arteries, which carry most of the blood to the renal cortex. The arteries in the renal cortex branch into numerous AFFERENT ARTERIOLES, one for each nephron. Each afferent arteriole, divides to form a capillary tuft called the GLOMERULUS. The glomerulus is surrounded by the glomerular capsule and is specialized for filtration of blood. The glomerular capillaries merge to form the EFFERENT ARTERIOLE, which leads away from the glomerular capsule. The efferent arteriole's diameter is smaller than the afferent arteriole. This raises the blood pressure in the glomerulus, which aids in forcing water and solutes into the glomerular capsule.
- 12. 12 Each efferent arteriole branches into a second capillary network called the PERITUBULAR CAPILLARIES. These capillaries cling closely to the PROXIMAL and DISTAL CONVOLUTED TUBULES of both cortical and juxtamedullary nephrons. The efferent arterioles of juxtamedullary nephrons also branch into the VASA RECTA, capillaries that surround the LOOP OF HENLE in the medulla. The peritubular capillaries and vasa recta are adapted for absorption. They absorb water and needed substances from the filtrate in the nephron, so that much of the water and solutes that the body requires are returned to the bloodstream rather than flushed out in the urine. Toxins and excess water and solutes remain in the filtrate and are eliminated as urine. The peritubular capillaries and vasa recta merge into venules that join veins which empty into the RENAL VEIN. The RENAL VEIN of each kidney leaves the kidney through the hilus. The renal vein of each kidney returns freshly cleansed blood to the INFERIOR VENA CAVA.
- 13. 13 URETERS The URETERS are slender tubes about 25-30 cm (10-12 in) long that convey urine from the kidneys to the urinary bladder. Each ureter runs posterior to the parietal peritoneum (retroperitoneal) from the renal hilus to the level of the urinary bladder. At the urinary bladder, each ureter makes a medial turn toward the bladder and enters the posterior bladder wall at an oblique angle, which prevents backflow of urine from the bladder into the ureters. The inner lining of the ureter wall is MUCOSA that consists of transitional epithelium that stretches as urine passes through. Mucus secreted by the mucosa protects the epithelial cells from coming into contact with the urine, which contains toxins and is slightly acidic. Beneath the mucosa is the MUSCULARIS, which is composed of smooth muscle arranged in longitudinal and circular layers. The muscularis creates peristaltic contractions, similar to those in the GI tract. When the renal pelvis fills with urine, smooth muscle in the renal pelvis wall contracts rhythmically, sending urine into the ureter. Peristalsis propels the urine through the ureter to the urinary bladder.
- 14. 14 URINARY BLADDER The URINARY BLADDER is a hollow muscular organ located in the pelvic cavity posterior to the pubic symphysis. Like the kidneys and ureters, the urinary bladder is retroperitoneal. In males, the urinary bladder lies anterior to the rectum. In females, the bladder is anterior to the vagina and inferior to the uterus. The function of the urinary bladder is the temporary storage of urine. The inner wall of the urinary bladder consists of a MUCOSA made of transitional epithelium, which is able to stretch a great deal. Mucus produced by the bladder mucosa helps protect the wall from urine. Beneath the mucosa is smooth muscle, arranged in longitudinal and circular layers. The smooth muscle in the wall allows the bladder to stretch a great deal.
- 15. 15 When empty, the bladder is 5.0-7.5 cm (2-3 in) long. Its walls are thick and its mucosa is thrown into folds called RUGAE. When urine accumulates in the bladder, it expands and becomes pear-shaped as it rises upward in the pelvic cavity. The transitional epithelium and smooth muscle stretches and thins. This increases the internal volume of the bladder by decreasing the thickness of its wall. A moderately full bladder is about 12.5 cm (5 in) long and holds about 500 ml of urine. The average capacity of the bladder is 700-800 ml. When the volume of urine in the bladder exceeds 200-400 ml, stretch receptors in the bladder transmit nerve impulses to the brain, initiating the conscious desire to urinate.
- 16. 16 URETHRA The URETHRA is a muscular tube that drains urine from the urinary bladder and conveys it out of the body. The INTERNAL URETHRAL SPHINCTER is an involuntary smooth muscle sphincter at the base of urinary bladder, surrounding the opening called the INTERNAL URETHRAL ORIFICE. The EXTERNAL URETHRAL SPHINCTER is a voluntary skeletal muscle sphincter in the UROGENITAL DIAPHRAGM. The urogenital diaphragm is formed by skeletal muscles of the pelvic floor;. In FEMALES, the urethra is 4 cm (1.5 in) long and 6 mm in diameter. It lies posterior to the pubic symphysis and anterior to the vagina. The EXTERNAL URETHRAL ORIFICE lies anterior to the vaginal opening. In MALES , the urethra is 15-20 cm (6-8 in) long. The urethra passes through the PROSTATE GLAND, then through the PENIS to the outside through the EXTERNAL URETHRAL ORIFICE.
- 17. 17 WASTE MANAGEMENT IN OTHER BODY SYSTEMS • One of the many functions of the urinary system is to rid the body of waste materials. • Other organs, tissues and processes contribute to waste management. • Buffers prevent an increase in the acidity of body fluids. • The blood transports wastes. • The liver is the primary site for metabolic recycling. • The lungs excrete CO2. H2O, and heat. • Sweat glands eliminate excess heat, water, and CO2, plus small quantities of salts and urea. • The GI tract eliminates solid, undigested foods, waste, some CO2, H2O, salts and heat.