Chapter 21: The Urinary System © 2013 John Wiley & Sons, Inc. All rights reserved.

The Urinary System Overview of the urinary system Structure of the kidneys Functions of the nephron Transportation, storage, and elimination of urine Aging and the urinary system

Overview of the Urinary System The organs of the urinary system include the kidneys, ureters, urinary bladder, and urethra. After the kidneys filter blood and return most of the water and many solutes to the blood, the remaining water and solutes constitute urine. The kidneys regulate blood ionic composition, blood volume, blood pressure, and blood pH. The kidneys also release calcitriol and erythropoietin and excrete wastes and foreign substances. © 2013 John Wiley & Sons, Inc. All rights reserved.

Organs of the Female Urinary System

© 2013 John Wiley & Sons, Inc. All rights reserved. Organs of the Female Urinary System

© 2013 John Wiley & Sons, Inc. All rights reserved. Anatomy Overview: You must be connected to the internet to run this animation. The Urinary System

Overview of the Urinary System Functions of the Urinary System 1. The kidneys regulate blood volume and composition, help regulate blood pressure and pH, produce two hormones, and excrete wastes. 2. The ureters transport urine from the kidneys to the urinary bladder. 3. The urinary bladder stores urine and expels it into the urethra. 4. The urethra discharges urine from the body. © 2013 John Wiley & Sons, Inc. All rights reserved.

Overview of the Urinary System

© 2013 John Wiley & Sons, Inc. All rights reserved. Overview of the Urinary System

Structure of the Kidneys The kidneys lie on either side of the vertebral column between the peritoneum and the back wall of the abdominal cavity. Each kidney is enclosed in a renal capsule, which is surrounded by adipose tissue. Internally, the kidneys consist of a renal cortex, renal medulla, renal pyramids, renal columns, major and minor calyces, and a renal pelvis. Blood enters the kidney through the renal artery and leaves through the renal vein. The nephron is the functional unit of the kidney. A nephron consists of a renal corpuscle (glomerulus and glomerular [Bowman’s] capsule) and a renal tubule (proximal convoluted tubule, descending limb of the nephron loop, ascending limb of the nephron loop, and distal convoluted tubule). Each nephron also has its own blood supply. The distal convoluted tubules of several nephrons empty into a common collecting duct. © 2013 John Wiley & Sons, Inc. All rights reserved.

Functions of the Nephron Nephrons perform three basic tasks: glomerular filtration, tubular reabsorption, and tubular secretion. Together, the podocytes and glomerular endothelium form a leaky filtration membrane that permits the passage of water and solutes from the blood into the capsular space. Blood cells and most plasma proteins remain in the blood because they are too large to pass through the filtration membrane. The pressure that causes filtration is the blood pressure in the glomerular capillaries. The amount of filtrate that forms in both kidneys every minute is the glomerular filtration rate (GFR). Atrial natriuretic peptide (ANP) increases GFR; sympathetic stimulation decreases GFR. © 2013 John Wiley & Sons, Inc. All rights reserved.

Functions of the Nephron Epithelial cells all along the renal tubules and collecting ducts carry out tubular reabsorption and tubular secretion. Tubular reabsorption retains substances needed by the body, including water, glucose, amino acids, and ions such as sodium (Na + ), potassium (K + ), chloride (Cl - ), bicarbonate (HCO 3 - ), calcium (Ca 2+ ), and magnesium (Mg 2+ ). Angiotensin II enhances reabsorption of Na + and Cl -. Angiotensin II also stimulates the adrenal cortex to release aldosterone, which stimulates the collecting ducts to reabsorb more Na + and Cl - and secrete more K +. Atrial natriuretic peptide (ANP) inhibits reabsorption of Na + (and Cl - and water) by the renal tubules, which reduces blood volume. Most water is reabsorbed by osmosis together with reabsorbed solutes, mainly in the proximal convoluted tubule. Reabsorption of the remaining water is regulated by antidiuretic hormone (ADH) in the last part of the distal convoluted tubule and collecting duct. © 2013 John Wiley & Sons, Inc. All rights reserved.

Functions of the Nephron Tubular secretion discharges chemicals not needed by the body into the urine. Included are excess ions, nitrogenous wastes, hormones, and certain drugs. The kidneys help maintain blood pH by secreting H +. Tubular secretion also helps maintain proper levels of K + in the blood. Table 21.2 describes the physical characteristics of urine that are evaluated in a urinalysis: color, odor, turbidity, pH, and specific gravity. Chemically, normal urine contains about 95 percent water and 5 percent solutes. Table 21.3 lists the abnormal constituents that can be diagnosed through urinalysis, including albumin, glucose, red blood cells, white blood cells, ketone bodies, bilirubin, urobilinogen, casts, and microbes. © 2013 John Wiley & Sons, Inc. All rights reserved.

Functions of the Nephron

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© 2013 John Wiley & Sons, Inc. All rights reserved. Glomerular Filtration

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© 2013 John Wiley & Sons, Inc. All rights reserved. Functions of the Nephron

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© 2013 John Wiley & Sons, Inc. All rights reserved. Filtration, Reabsorption, and Secretion in the Nephrons and Collecting Ducts

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© 2013 John Wiley & Sons, Inc. All rights reserved. Negative Feedback Regulation of Water Reabsorption by ADH

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Transportation, Storage, and Elimination of Urine The ureters transport urine from the renal pelves of the right and left kidneys to the urinary bladder and consist of a mucosa, muscularis, and adventitia. The urinary bladder is posterior to the pubic symphysis. Its function is to store urine prior to micturition. The mucosa of the urinary bladder contains stretchy transitional epithelium. The muscular layer of the wall consists of three layers of smooth muscle together referred to as the detrusor muscle. © 2013 John Wiley & Sons, Inc. All rights reserved.

Transportation, Storage, and Elimination of Urine The urethra is a tube leading from the floor of the urinary bladder to the exterior. Its function is to discharge urine from the body. The micturition reflex discharges urine from the urinary bladder by means of parasympathetic impulses that cause contraction of the detrusor muscle and relaxation of the internal urethral sphincter muscle, and by inhibition of somatic motor neurons to the external urethral sphincter. © 2013 John Wiley & Sons, Inc. All rights reserved.

Aging and the Urinary System With aging, the kidneys shrink in size, have lowered blood flow, and filter less blood. Common problems related to aging include urinary tract infections, increased frequency of urination, urinary retention or incontinence, and renal calculi (kidney stones). © 2013 John Wiley & Sons, Inc. All rights reserved.

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