Human Excretory System

The human body is complex and operates with the help of multiple organ systems like digestive system, circulatory system, respiratory system etc. that work non-stop simultaneously. They ensure a state of steady internal, physical and chemical conditions i.e. homeostasis and viability of the human body. These life processes release waste products into the blood. The excretory system helps in eliminating these waste products that could be toxic to the body by filtering the blood.

Human Urinary System

The body takes nutrients from food and converts them into energy and other by products. After the body has taken the necessary nutrients from food, waste products are left behind in the bowel and in the blood.

The purpose of the URINARY SYSTEM is to eliminate waste from the blood, regulate blood volume and blood pressure, and control the levels of electrolytes and metabolites in it. The organs of the urinary system include the kidneys, ureters, urinary bladder, urethra and urinary opening.

Some Parts of the Kidney:

• Renal artery and Renal Vein: The renal artery supplies the kidney with blood. The renal vein, on the other hand, carries the blood filtered by the kidney.
• Nephrons: The kidneys remove urea from the blood through tiny filtering units called nephrons. Each nephron consists of a cluster of tiny blood capillaries, called a glomerulus, and a small tube called a renal tubule. The blood is filtered across the capillary walls and the filtrate is sent to the renal tubule.

 URETERS: These tubes carry urine from the kidneys to the urinary bladder. Muscles in the ureter walls continuously contract and relax like waves pushing the urine in downward direction, towards the bladder. An obstruction in ureters may lead to fever, kidney infections, sepsis and even death.

URINARY BLADDER: Located in the lower abdomen, urinary bladder is a triangle-shaped, hollow organ held in place by ligaments that are attached to other organs and the pelvic bones. The walls of the bladder can relax and expand in order to store urine, and contract and compress to empty urine through the urethra. A typical healthy adult bladder can store up to 400-600 mL urine.

• Sphincter muscles: These pair of muscles controls the exit of urine from the urinary bladder through the urethra. When either of them contracts, the urethra is sealed shut. When it relaxes, the urethra opens up.
• Nerves in the bladder: The nerves send a signal to the brain and alert a person when it is time to empty the bladder.

URETHRA: This thin tube at the lower opening of the bladder allows urine to pass outside the body. Once the brain receives a signal to empty the bladder, it leads to a chain reaction that includes contraction of the bladder muscles, relaxation of the sphincter muscle followed by opening of the urethra.

URINARY OPENING: It is the opening of the urethra where urine exits the body.

Normal Urine

The normal range of urine production in adult humans is 0.6 to 2.6 L with 6-8 urinations per day. However, it depends on the level of hydration in the person’s body, the person’s size, weight, health, activities, and environmental factors. Normal, healthy urine is a pale straw or transparent yellow in color. Darker yellow or honey-colored urine means that our body needs more water.

Thus, the excretory system is a passive biological system that removes excess, unwanted materials from the body fluids of an organism. Any failure in the excretory system would result in internal chemical disturbances with wastes accumulating in our body leading to damage inside it.

Check Point

1. The skin excretes water and excess salts by ____________.
2. The waste material formed by protein rich diet is __________.
3. The filtration of blood takes place in the nephrons present inside the __________.
4. The walls of the ________ can relax and expand in order to store urine.
5. The two main causes of kidney failure in the United States are Type 2 diabetes and _________.

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