Functional Organization of the Human Body and Control of the Internal Environment

Vocabulary flashcards covering the functional organization of the human body, cell counts, fluid compartments, homeostasis, and feedback mechanisms.

Physiology

The science that seeks to explain the physical and chemical mechanisms that are responsible for the origin, development, and progression of life.

Human Physiology

The science that attempts to explain the specific characteristics and mechanisms of the human body that make it a living being.

Cell

The basic living unit of the body, which forms aggregates held together by intercellular supporting structures to construct organs.

Red Blood Cells

The most abundant single type of cell in the body, numbering about $25\text{ trillion}$ in each human being, whose primary function is to transport oxygen from the lungs to the tissues.

Total Cell Count of the Human Body

The entire body contains about $100\text{ trillion}$ cells, consisting of about $25\text{ trillion}$ red blood cells and about $75\text{ trillion}$ additional cells of other types.

Adult Body Fluid Composition

About $60\%$ of the adult human body is fluid, mainly a water solution of ions and other substances.

Intracellular Fluid

Fluid located inside the cells, constituting about $\frac{2}{3}$ of the total body fluid.

Extracellular Fluid

Fluid in the spaces outside the cells that makes up about $\frac{1}{3}$ of total body fluid and contains the ions and nutrients needed by cells to maintain life.

Internal Environment (Milieu Intérieur)

Another term for extracellular fluid, denoting the environment in which all body cells live, introduced more than 150 years ago by Claude Bernard.

Claude Bernard

Great 19th-century French physiologist who introduced the term milieu intérieur to refer to the extracellular fluid or internal environment of the body.

Homeostasis

Maintenance of near-constant conditions in the internal environment (extracellular fluid).

Negative Feedback

Feedback that reduces the output of a given system, such as high circulating levels of a hormone reducing further secretion of that hormone.

Positive Feedback

Feedback that increases the output of a system, such as injury resulting in bleeding that causes the release of clotting factors that themselves increase the clotting process.