Chapters

Execratory System

Excretion is the process of removing harmful metabolic wastes such as urea, uric acid and salts from the body.

Parts of excretory system in human beings

  1. A pair of Kidney
  2. A pair of ureters
  3. Urinary bladder
  4. Urethra

Kidney

Kidney is an excretory organ present in the human body. Kidneys act as excretory organs and also control the balance of water and mineral ions in the body. Kidney is divided into two parts namely, external region and internal region. They are a pair of organs located in the back of the abdomen. Each kidney is about 4 or 5 inches long -- about the size of a fist. The kidneys' functions are to filter the blood. All the blood in our bodies passes through the kidneys several times a day. The kidneys remove wastes, control the body's fluid balance, and regulate the balance of electrolytes. As the kidneys filter blood, they create urine, which collects in the kidneys' pelvis funnel-shaped structures that drain down tubes called ureters to the bladder. Each kidney contains around a million units called nephrons, each of which is a microscopic filter for blood. It's possible to lose as much as 90% of kidney function without experiencing any symptoms or problems.

Ureters

The ureter is a tube that carries urine from the kidney to the urinary bladder. There are two ureters, one attached to each kidney. The upper half of the ureter is located in the abdomen and the lower half is located in the pelvic area.  The ureter is about 10 to 12 inches long in the average adult. The tube has thick walls composed of a fibrous, a muscular, and a mucus coat, which are able to contract. 

Urinary bladder

The urinary bladder is a hollow muscular organ that collects urine from the kidneys before disposal by urination. A hollow muscular, and distensible (or elastic) organ, the bladder sits on the pelvic floor. Urine enters the bladder via the ureters and exits via the urethra.

Urethra

It develops a connection between the urinary bladder and the genital organs in human body. It is this canal, through which the transfer of excretory fluids occurs, that is ultimately emptied out of the body. The length of urethra varies greatly in feminine and masculine gender, as in the former, it is much shorter, while in the latter, it is comparatively longer. The body wall is composed of three distinct layers that are continuous with the urinary bladder. As with other organs of the body, urethra is likewise vulnerable to a number of inflammatory, infectious, genetic, and STDs or Sexually Transmitted Diseases.

Its length variation is based on gender differences, i.e. in women, it ranges between 3.5 to 4.0 centimetre, while in males, it varies from 15 to 29 centimetres. This is because, in women, it has to travel only a shorter distance to empty into the region between clitoris and vagina and extends from the internal to the external urethral orifice. In case of men, it has to cover comparatively long distance to reach the end of male genital organ, penis.

Function of Urethra

In women, the urinary tube serves only as a passage for urine from bladder to the region near clitoris and vagina, while in men; it is involved in dual functions that are the transfer of urine out of the body through penile opening as well as the ejaculation of seminal fluid. The process of urination is controlled by both voluntary and involuntary actions where the external urethral sphincter is responsible for the deliberate command over the excretion of urinary fluid. The striated muscle tissue that forms the external voluntarily controlled sphincter is responsible for the effective functioning of this structure.


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