Essentials of Human Anatomy & Physiology

Anatomy refers to structure while physiology is about function. A complete understanding of human anatomy and physiology requires learning large amounts of complex information that describe every aspect of how the human body sustains life. The essential pieces of information can be categorized into five areas.

Levels of Organization

The body is organized into levels that build upon each other. It begins with the smallest atoms and molecules that control the chemical reactions required for the body to function. The basic structural and functional units in the body---cells---are the next level. Learning how different cells work is key to understanding how organs and systems function. Cells with specific roles come together to create tissues. Two or more different tissues working together form an organ. A group of organs with a common purpose is called a system. For example, the respiratory system includes the nose, pharynx, larynx, trachea, bronchi and lungs.

Support and Movement

The bones in the skeletal system support soft tissues, protect internal organs and create a structure that enables movement. They also store minerals and produce red blood cells in the bone marrow. Three types of muscle---smooth, cardiac, skeletal---are responsible for motion, the production of heat and maintenance of posture. Physiology looks at the chemistry of muscle contraction and the development of different types of bones and muscle.

Systems of Control

The systems that control the body are the nervous system and the endocrine system. The nervous system has two parts: the central nervous system (CNS) and the autonomic nervous system. The CNS includes the brain and spinal cord. This system relays all incoming sensory information to the brain, where it is interpreted and actions or reactions are signaled. The autonomic nervous system controls the smooth muscle, cardiac muscle and glands. Even though it operates automatically (without conscious control), it is regulated by the brain.

The endocrine system includes glands---the pituitary, thyroid, pancreas, adrenals, pineal and gonads---and the hormones they produce. They're responsible for secreting more than 60 hormones that circulate throughout the body, influencing virtually every cell. The pituitary regulates many processes, from growth and reproduction to blood pressure. The pineal controls the sleep/wake cycle. The thyroid gland controls metabolism and maintains a constant level of calcium in the blood. The adrenal glands determine physical reactions related to the "fight-or-flight" response. The pancreas produces the hormones that control blood glucose. The gonads manage all hormones related to reproduction and sexuality.

Maintaining Homeostasis

Homeostasis is a state of balance. Nothing in the body functions properly or remains healthy without homeostasis. For example, cells can't survive without a very delicate balance of fluids inside and outside the cell body. Homeostasis is maintained by the cardiovascular, lymphatic, respiratory, digestive and urinary systems. The heart ensures that blood is circulated throughout the body via veins and arteries. The blood transports oxygen, wastes, nutrients, hormones and enzymes. It also helps regulate body temperature, prevents fluid loss and regulates the water content of cells. The white blood cells protect the body from foreign substances. The lymphatic system drains excess proteins, transports fats and helps develop immunities. Oxygen is supplied and carbon dioxide is released through the respiratory system. The process of breaking down food so that it can be absorbed and used for energy, and eliminating wastes, occurs in the digestive system. The primary function of the urinary system is to control the composition and volume of blood by removing and restoring water.

Reproduction

The final category is reproduction. This system carries the responsibility of taking a single cell, duplicating its genetic material, and nurturing its division and growth until another living human is reproduced.

References

• Principles of Anatomy and Physiology, Gerard Tortora and Bryan Derrickson, 2008