The urinary tract is made up of the kidneys, the ureters, the bladder, and the urethra.
The kidneys are a pair of bean-shaped organs located below the ribs near the middle of the back. They remove waste products from the blood, maintain a balance of electrolytes and other substances in the blood, and produce erythropoietin (hormone that triggers the production of red blood cells in the bone marrow).
Each kidney is composed of about 1 million microscopic "filtering packets" composed of capillaries called glomeruli that remove uremic waste products from the blood and form urine. Each glomerulus connects to a long tube, called a tubule.
Together, the glomerulus and the tubule form a unit called a nephron. Each nephron connects to progressively larger tubular branches, until it reaches a large collection area called the calyx. The calices form the funnel-shaped portion of the upper ureter (renal pelvis).
The ureters are fibromuscular tubes that convey the urine from the renal pelvis to the bladder. Each ureter is approximately 16 inches long and the one leading from the right kidney is slightly shorter than the left. The ureters consist of mucosal, muscular, and fibrous layers. The area where the ureters enter the bladder is called the trigone. Valves in this region prevent the reflux (i.e., backing up) of urine into the kidneys.
The urinary bladder is a hollow, muscular organ that stores urine. It is located behind the pubic bone and sits within and is protected by the pelvis. The bladder is held in place by ligaments (bands of tough, fiberlike tissue) that connect it to the pelvis and to other organs. The narrow, internal opening of the urethra within the bladder is called the bladder neck. Muscles in the bladder neck called sphincters tighten around the urethra to prevent urine from leaking.
When the volume of urine in the bladder reaches a certain capacity, the brain sends impulses to the internal sphincter, causing it to relax and to detrusor muscles, causing them to push downward and expel urine. As the bladder contracts, it expels urine out of the body via the urethra.
The urethra is the tube that passes urine from the bladder out of the body. In women, it is approximately 4 centimeters long. It is composed of smooth muscle fibers, sphincter muscle fibers, a layer of elastic tissue, and collagen tissue and is lined with mucous membrane. The female urethra starts at the bladder neck and exits the body directly in front of the vaginal opening (female reproductive canal).
In men, the urethra is roughly 8 to 9 inches long and extends from the bladder neck to the end of the penis. The male urethra is composed of three parts: prostatic, membranous, and spongy. The prostatic urethra is the widest part of the tube and passes through the prostate gland. It is made up of fibrous tissue, muscle fibers, and tiny glandular openings that connect to the prostate. The membranous urethra is approximately three-quarters of an inch long and lies between the triangular ligaments of the pelvis. The spongy urethra is the longest part and extends through the penis to the glans (tip of the penis). The corpus spongiosum is the lower area of the penis that surrounds and protects the urethra.
Male Reproductive System
The male reproductive system is made up of the penis, testicles, epididymes, vas deferens, prostate, and seminal vesicles.
The internal structure of the penis consists of two cylinder-shaped vascular tissue bodies (corpora cavernosa); the urethra (tube for expelling urine and ejaculate); erectile tissue surrounding the urethra; two main arteries; and several veins and nerves. The longest part of the penis is the shaft, at the end of which is the head, or glans penis. The opening at the tip of the glans, which allows for urination and ejaculation, is the meatus.
The testicles, or testes, are the sperm- and testosterone-producing organs. They are located in a sac at the base of the penis called the scrotum. Each testicle is connected to a small, coiled tube called the epididymis, where sperm are stored for as long as 6 weeks while they mature.
The epididymes are connected to the prostate gland by a pair of tubes called the vas deferens. The vas deferens are part of a larger bundle of tissue, blood vessels, nerves, and lymphatic channels called the spermatic cord.
The prostate is a walnut-sized gland located beneath the bladder and in front of the rectum. It is surrounded by fibrous tissue called the prostate capsule. The urethra (tube that transports urine and semen out of the body) passes through the prostate to the bladder neck. The prostate produces prostate specific antigen (PSA) and prostatic acid phosphatase (an enzyme) that are present in seminal fluid (the milky substance that combines with sperm to form semen).
The seminal vesicles are saclike structures located close to the prostate. They secrete a thick fluid that mixes with seminal fluid produced by the prostate and sperm from the testes to form semen (ejaculate).
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