Urinary Organs
The kidneys produce urine, and the other urinary organs playa role in elimin~ng urine from the body.
Kidneys
The kidneys are paired organs located near the small of the back in the lumbar region on either side of the vertebral column. They lie in depressions against the deep muscles of the back behind the peritoneum, where they receive some protection from the lower rib cage. Each kidney is usually held in place by connective tissue, called renal fascia. Masses of adipose tissue adhere to each kidney. A sharp blow to the back can dislodge a kidney, which is then called a floating kidney.
Each kidney is a bean-shaped, reddish-brown organ about the size of a fist. It is covered by a tough capsule of fibrous connective tissue, called the renal capsule. A depression (the hilum) on the concave side is where the renal blood vessels and the ureters exit.
When a kidney is sectioned longitudinally, it is possible to detect three regions: (1) an outer granulated layer called the renal cortex; (2) a radially striated, or lined, layer called the renal medulla; and (3) an inner space, or cavity, called the renal pelvis, which is continuous with the ureter.
Microscopically, each kidney is composed of over 1 million nephrons. A nephron makes urine, which is transported through a collecting duct to the renal pelvis. In the medulla, groups of nephrons and collecting ducts are massed in cone shapes called renal pyramids. The collecting ducts in each renal pyramid empty into a calyx of the renal pelvis.
Nephrons A nephron has several parts. The end of the nephron is pushed in on itself to form a cuplike structure called a glomerular (glo-mer'u-ler) capsule (Bowman's capsule). Within this cup is a cluster of capillaries called the glomerulus. The proximal (meaning near the glomerular capsule) convoluted tubule is next. At the end of the proximal convoluted tubule, there is a U-turn called the loop of the nephron (loop of Henle). This leads to the distal (meaning far from the glomerular capsule) convoluted tubule, which enters a collecting duct. Each nephron has its own blood supply, and a peritubular capillary network surrounds the tubules and the loop of the nephron.
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis. Microscopically. they are made up of over 1 million nephrons.
Ureters
The ureters are tubes about 25 centimeters long that convey urine from the kidneys to the bladder. Each descends from the renal pelvis, behind the parietal peritoneum, to enter the bladder posteriorly on the inferior surface.
The wall of a ureter has three layers. The inner layer is a mucosa (mucous membrane), the middle layer consists of smooth muscle, and the outer layer is a fibrous coat of connective tissue. Peristaltic contractions cause urine to enter the bladder even if a person is lying down. Urine enters the bladder in spurts that occur at the rate of one to five per minute.
Urinary Bladder
The urinary bladder stores urine until it can conveniently be expelled from the body. The bladder holds up to 600 milliliters (approximately 1 pint) of urine and becomes overdistended at 750 ml. (You get the urge to void at approximately 250 milliliters, and you become uncomfortable at approximately 500 milliliters. When the bladder becomes overdistended, you may lose the urge to void.) The bladder is located in the pelvic cavity, below the parietal peritoneum and posterior to the symphysis pubis. In the male, the bladder lies anterior to the rectum, seminal vesicles, and vas deferens. In the female, it is anterior to the uterus and upper vagina.
The ureters enter the bladder, and the urethra exits the bladder. A sphincter called the internal urethral sphincter is found at the urethra's exit location.
The wall of the urinary bladder has four layers. A mucosa (mucous membrane) and a submucosa (connective
tissue and elastic fibers) are followed by a coarse bundle of smooth muscle that makes up the detrusor muscle. Finally, the bladder's upper surface has a serous membrane that consists of parietal peritoneum. The rest of the bladder has an outer fibrous connective tissue coat.
Urethra
The urethra is a thin-walled tube that extends from the urinary bladder to an external opening called the external urethral orifice. The urethra has an inner mucosa (mucous membrane), and the wall consists of smooth muscular and connective tissues. As already mentioned, the internal urethral sphincter occurs where the urethra leaves the bladder, and an external urethral sphincter is located where the urethra exits the pelvic cavity.
The urethra differs in length in females and males. In females, the urethra lies ventral to the vagina and is only about 4 centimeters (1. 6 inches) long. The short length of the female urethra and its proximity to the vaginal and anal openings help explain why females are prone to urinary tract infections. In males, the urethra averages 20 centimeters (8 inches) in length when the penis is relaxed. As the male urethra leaves the bladder, it is encircled by the prostate gland.
The genital (reproductive) and urinary systems in females are completely separate, but in males, the two systf'.ms share the urethra. During urination in males, the urethra carries urine; during sexual orgasm, it transports semen. This double function of the urethra does not alter the path of urine.
Urination
Urination, also called micturition (mik"tu-rish'un), occurs in the following manner: When the urinary bladder fills with urine, stretch receptors in the bladder wall transmit impulses to the central nervous system (CNS). Thereafter, parasympathetic impulses leave the sacral portion of the spinal cord and go to the internal urethral sphincter at the base of the bladder. Relaxation of this sphincter follows. However, urination does not take place until the cerebrum sends somatic impulses to an external sphincter located in the urethra. When this sphincter relaxes, micturition takes place. A very painful condition arises when small kidney stones (renal calculi) form and are passed through the urinary tract. Large kidney stones may have to be removed surgically, or, as part of a new treatment, smashed with ultrasonic waves.
Urination (micturition) does not occur until parasympathetic and somatic impulses lead to the relaxation of. respectively, the internal and external urethral sphincters.
The kidneys produce urine, and the other urinary organs playa role in elimin~ng urine from the body.
Kidneys
The kidneys are paired organs located near the small of the back in the lumbar region on either side of the vertebral column. They lie in depressions against the deep muscles of the back behind the peritoneum, where they receive some protection from the lower rib cage. Each kidney is usually held in place by connective tissue, called renal fascia. Masses of adipose tissue adhere to each kidney. A sharp blow to the back can dislodge a kidney, which is then called a floating kidney.
Each kidney is a bean-shaped, reddish-brown organ about the size of a fist. It is covered by a tough capsule of fibrous connective tissue, called the renal capsule. A depression (the hilum) on the concave side is where the renal blood vessels and the ureters exit.
When a kidney is sectioned longitudinally, it is possible to detect three regions: (1) an outer granulated layer called the renal cortex; (2) a radially striated, or lined, layer called the renal medulla; and (3) an inner space, or cavity, called the renal pelvis, which is continuous with the ureter.
Microscopically, each kidney is composed of over 1 million nephrons. A nephron makes urine, which is transported through a collecting duct to the renal pelvis. In the medulla, groups of nephrons and collecting ducts are massed in cone shapes called renal pyramids. The collecting ducts in each renal pyramid empty into a calyx of the renal pelvis.
Nephrons A nephron has several parts. The end of the nephron is pushed in on itself to form a cuplike structure called a glomerular (glo-mer'u-ler) capsule (Bowman's capsule). Within this cup is a cluster of capillaries called the glomerulus. The proximal (meaning near the glomerular capsule) convoluted tubule is next. At the end of the proximal convoluted tubule, there is a U-turn called the loop of the nephron (loop of Henle). This leads to the distal (meaning far from the glomerular capsule) convoluted tubule, which enters a collecting duct. Each nephron has its own blood supply, and a peritubular capillary network surrounds the tubules and the loop of the nephron.
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis. Microscopically. they are made up of over 1 million nephrons.
Ureters
The ureters are tubes about 25 centimeters long that convey urine from the kidneys to the bladder. Each descends from the renal pelvis, behind the parietal peritoneum, to enter the bladder posteriorly on the inferior surface.
The wall of a ureter has three layers. The inner layer is a mucosa (mucous membrane), the middle layer consists of smooth muscle, and the outer layer is a fibrous coat of connective tissue. Peristaltic contractions cause urine to enter the bladder even if a person is lying down. Urine enters the bladder in spurts that occur at the rate of one to five per minute.
Urinary Bladder
The urinary bladder stores urine until it can conveniently be expelled from the body. The bladder holds up to 600 milliliters (approximately 1 pint) of urine and becomes overdistended at 750 ml. (You get the urge to void at approximately 250 milliliters, and you become uncomfortable at approximately 500 milliliters. When the bladder becomes overdistended, you may lose the urge to void.) The bladder is located in the pelvic cavity, below the parietal peritoneum and posterior to the symphysis pubis. In the male, the bladder lies anterior to the rectum, seminal vesicles, and vas deferens. In the female, it is anterior to the uterus and upper vagina.
The ureters enter the bladder, and the urethra exits the bladder. A sphincter called the internal urethral sphincter is found at the urethra's exit location.
The wall of the urinary bladder has four layers. A mucosa (mucous membrane) and a submucosa (connective
tissue and elastic fibers) are followed by a coarse bundle of smooth muscle that makes up the detrusor muscle. Finally, the bladder's upper surface has a serous membrane that consists of parietal peritoneum. The rest of the bladder has an outer fibrous connective tissue coat.
Urethra
The urethra is a thin-walled tube that extends from the urinary bladder to an external opening called the external urethral orifice. The urethra has an inner mucosa (mucous membrane), and the wall consists of smooth muscular and connective tissues. As already mentioned, the internal urethral sphincter occurs where the urethra leaves the bladder, and an external urethral sphincter is located where the urethra exits the pelvic cavity.
The urethra differs in length in females and males. In females, the urethra lies ventral to the vagina and is only about 4 centimeters (1. 6 inches) long. The short length of the female urethra and its proximity to the vaginal and anal openings help explain why females are prone to urinary tract infections. In males, the urethra averages 20 centimeters (8 inches) in length when the penis is relaxed. As the male urethra leaves the bladder, it is encircled by the prostate gland.
The genital (reproductive) and urinary systems in females are completely separate, but in males, the two systf'.ms share the urethra. During urination in males, the urethra carries urine; during sexual orgasm, it transports semen. This double function of the urethra does not alter the path of urine.
Urination
Urination, also called micturition (mik"tu-rish'un), occurs in the following manner: When the urinary bladder fills with urine, stretch receptors in the bladder wall transmit impulses to the central nervous system (CNS). Thereafter, parasympathetic impulses leave the sacral portion of the spinal cord and go to the internal urethral sphincter at the base of the bladder. Relaxation of this sphincter follows. However, urination does not take place until the cerebrum sends somatic impulses to an external sphincter located in the urethra. When this sphincter relaxes, micturition takes place. A very painful condition arises when small kidney stones (renal calculi) form and are passed through the urinary tract. Large kidney stones may have to be removed surgically, or, as part of a new treatment, smashed with ultrasonic waves.
Urination (micturition) does not occur until parasympathetic and somatic impulses lead to the relaxation of. respectively, the internal and external urethral sphincters.
