Do you know how human organs work?

The trachea, bronchi and alveoli are all parts of the respiratory system.

The uterus is a muscular female organ located in the pelvis. It has a pre-pregnancy size of a pear, but during pregnancy it can stretch to the size of a watermelon.

The pancreas creates and releases insulin into the bloodstream.

The skin is classified as an organ and is the largest organ of the human body. The skin of an average person weighs about 10 pounds and has a surface area of roughly 20 square feet.

The fluid-filled semicircular canals are located in the inner ear and contain hair cells that are activated by movement of fluid within each canal.

As part of the urinary system, kidneys filter blood, balance electrolytes and produce urine.

Ovaries are a pair of small organs in the female pelvic cavity that produce eggs. Each ovary is roughly the size and shape of an almond.

The adrenal glands produce hormones that trigger the "fight or flight" response. These hormones -- adrenaline and noradrenaline -- increase blood pressure, heart rate and oxygen intake and prepare the body for action.

The nervous system includes ganglia and neurons and responds to internal as well as external stimuli.

The thyroid gland regulates metabolism, growth and maturation of the human body.

The bladder is a muscular organ that stores urine before expelling it through the urethra.

In addition to filtering blood, the liver produces cholesterol and important proteins like albumin.

The gall bladder is located under the right lobe of the liver and stores bile for digestion. Bile is a yellow-brown fluid that is excreted into the small intestine to break down fatty foods.

While the spleen does function to filter blood and manage the immune system, humans can live without it. Other organs, such as the liver and lymph nodes, take over the functions of a spleen when it is removed.

The cochlea is a fluid-filled organ that translates sound into nerve impulses which are sent to the brain. Humans have two cochlea. They are snail-shaped caverns in the mastoid bones behind each ear.

At a length of approximately 22 feet, the small intestine is indeed the longest part of the digestive system.

Rod and cone cells are the two photoreceptors of the human eye. Rods are most sensitive to light and dark, shapes and movement. Cones are sensitive to color and fine detail.

The pineal gland is the smallest human organ and it is located near the center of the brain. The pineal gland produces a hormone called melatonin, which affects how humans sleep.

The human heart uses four chambers to circulate blood through the body: the left atrium, right atrium, left ventricle and right ventricle.

The integumentary system, commonly known as skin, is made up of three main layers: the epidermis, dermis and the hypodermis.

The human brain weighs an average of three pounds and is approximately 73 percent water. Brain attention, memory and other cognitive skills are affected by as little as a 2 percent drop in hydration.

The large intestine begins at the cecum and ends at the rectum. The large intestine extracts moisture from food particles and excretes the unusable waste.

The spleen filters out old and damaged red blood cells. The spleen can recycle useful components, such as iron, when the red cells are broken down.

The endocrine system is made up of glands and secretes hormones to regulate a number of body functions.

The stomach is a bean-shaped organ about the size of a fist. Food is swallowed through the esophagus and churned by the stomach before passing on to the small intestine.

An organ is defined as a group of tissues that perform a specific function or group of functions.

Renal agenesis is a condition in which a person is missing a kidney at birth. Most people with renal agenesis experience no symptoms or complications.

The small intestine contains the duodenum, jejunum and ileum. The primary functions of the small intestine are to digest food and absorb nutrients.

The right lung is larger and heavier than the left. The left lung is smaller because of the position of the heart.

Carbon dioxide (not monoxide) and oxygen are exchanged in the lungs. Oxygen is inhaled into the lungs and carbon dioxide is exhaled.