Human anatomy is a branch of science that describes the function of each part of the body and how these parts work together. The human body can be divided into the main parts that are visible from the outside such as the head, neck, trunk, and limbs. However, human anatomy is much more complicated than this. The human body is made up of cells, tissues, organs, and organ systems, which all work together to help the body move, think, breathe, stay safe and healthy, and reproduce.
Cells, Tissues, and Organs
The cell is the basic unit of life. Some organisms, like bacteria, have only one cell. The human body, on the other hand, consists of trillions of cells. The cells in the human body are of different types, each with its own purpose. For example, nerve cells send and receive messages while smooth muscle cells form a lining inside organs such as the bladder. The cells in the human body also vary in size. The female reproductive cell, called a gamete, is quite large, but red blood cells that are manufactured in bones are small. Some very tiny cells in the body can only be seen with a microscope.
Groups of cells form tissue. There are four main types of tissue in the human body: muscle tissue, connective tissue, nervous tissue, and epithelial tissue. Muscle tissue helps the body move and comes in two types: skeletal and smooth. Skeletal muscle tissue is voluntary, which means a person can choose to move it. Skeletal tissue can be found in the arms and legs. Smooth muscle tissue is involuntary, which means it moves on its own. Smooth muscle tissue is in the intestines and bladder. Connective tissue protects, supports, and connects various parts of the body. Nervous tissue sends and receives messages to the brain. Epithelial tissue covers the surface of the body. The skin is epithelial tissue.
Each organ in the body is made of tissue and has a specific function. For example, the heart pumps blood throughout the body, and the lungs bring oxygen into the bloodstream.
Organs are grouped together into organ systems, and each has a specific function. Human beings have eleven major organ systems.
Skeletal muscles, but not smooth or cardiac muscles, make up the muscular system, which helps the body move. In most cases, a skeletal muscle is attached to one end of a bone, stretches across a joint, and attaches to another bone. The strongest and largest skeletal muscles are in the back near the spine and enable the body to push and pull heavy objects. While the muscular system works closely with the skeletal system, it is controlled by the nervous system.
The nervous system is responsible for sending and receiving messages to and from the brain. It has two parts: the central nervous system and the peripheral nervous system. The central nervous system consists of the brain, which controls the body’s movements and functions, and the spinal cord. The peripheral nervous system consists of the many nerves that branch off of the spinal cord and extend to all parts of the body.
An adult’s skeletal system contains 206 bones along with tendons, ligaments, and cartilage. The main task of the skeletal system is to protect the organs within the body but it has other functions as well such as enabling movement. The bones produce blood cells, store calcium and phosphorus, and regulate the endocrine gland.
The respiratory system enables breathing through the nose, mouth, throat, lungs, larynx, and trachea. This critical organ system brings much-needed oxygen into the body and releases carbon dioxide.
The organs in the digestive system include the stomach, small intestine, large intestine, liver, gallbladder, and pancreas. The digestive system breaks down food into substances that the body can use and gives it nutrients and energy.
The urinary system, also called the renal system, includes the bladder, kidneys, and urethra. This system filters blood and eliminates waste in the form of urine.
The heart, blood, and blood vessels make up the cardiovascular, or circulatory, system. The heart pumps blood in a continuous loop throughout the body, using the arteries to carry blood away and the veins to transport it back. The blood circulating throughout the body carries oxygen, removes carbon dioxide, and transports nutrients to cells.
The integumentary system protects the body from the environment and aids in temperature regulation. The organs in this system include the skin, which is the largest organ in the body, and the hair and nails.
The endocrine system consists of many glands, including the thyroid and hypothalamus glands. These glands secrete hormones that regulate body functions such as growth and development and metabolism.
The tonsils, adenoids, and spleen are part of the lymphatic system, which serves as the body’s first line of defense against harmful viruses and bacteria.
The reproductive system is the only organ system that is different in males and females. It consists of the organs needed for reproduction. The male reproductive system includes the testicles and the penis. The female reproductive system includes the fallopian tubes, ovaries, and uterus.