Page 189 - 84 human physiolofy part-1

The Urinary System

Urethra

The urethra is a muscular tube that connects the bladder with the outside of the body. The
function of the urethra is to remove urine from the body. It measures about 1.5 inches (3.8 cm) in a
woman but up to 8 inches (20 cm) in a man. Because the urethra is so much shorter in a woman it
makes it much easier for a woman to get harmful bacteria in her bladder this is commonly called a
bladder infection or a UTI. The most common bacteria of a UTI is E-coli from the large intestines that
have been excreted in fecal matter. Female urethra

In the human female, the urethra is about 1-2 inches long and opens in the vulva between the
clitoris and the vaginal opening.

Men have a longer urethra than women. This means that women tend to be more susceptible to
infections of the bladder (cystitis) and the urinary tract.

Male urethra

In the human male, the urethra is about 8 inches (20 cm) long and opens at the end of the penis.

The length of a male's urethra, and the fact it contains a number of bends, makes catheterisation
more difficult.

The urethral sphincter is a collective name for the muscles used to control the flow of urine from
the urinary bladder. These muscles surround the urethra, so that when they contract, the urethra is
closed.

• There are two distinct areas of muscle: the internal sphincter, at the bladder neck and
• the external, or distal, sphincter.

Human males have much stronger sphincter muscles than females, meaning that they can retain a
large amount of urine for twice as long, as much as 800mL, i.e. "hold it".

Nephrons

A nephron is the basic structural and functional unit of the kidney. The name nephron comes from
the Greek word (nephros) meaning kidney. Its chief function is to regulate water and soluble substances
by filtering the blood, reabsorbing what is needed and excreting the rest as urine. Nephrons eliminate
wastes from the body, regulate blood volume and pressure, control levels of electrolytes and
metabolites, and regulate blood pH. Its functions are vital to life and are regulated by the endocrine
system by hormones such as antidiuretic hormone, aldosterone, and parathyroid hormone.

Each nephron has its own supply of blood from two capillary regions from the renal artery. Each
nephron is composed of an initial filtering component (the renal corpuscle) and a tubule specialized for
reabsorption and secretion (the renal tubule). The renal corpuscle filters out large solutes from the
blood, delivering water and small solutes to the renal tubule for modification.

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