Anatomy is the study of the structure of the body. Physiology is the study of the functions of the body.
ORGANIZATION OF THE HUMAN BODY
The human body is organized into cells, tissues, organs, organ systems, and the total
organism.
- Cells are the smallest living unit of body construction.
- A tissue is a grouping of like cells working together. Examples are muscle tissue and nervous tissue.
- An organ is a structure composed of several different tissues performing a particular function. Examples include the lungs and the heart.
- Organ systems are groups of organs which together perform an overall function. Examples are the respiratory system and the digestive system.
- The total organism is the individual human being. You are a total organism
MAJOR COMPONENTS OF A "TYPICAL" ANIMAL CELL
Nucleus. The nucleus plays a central role in the cell. Information is stored in the nucleus and distributed to guide the life processes of the cell. This information is in a chemical form called nucleic acids. Two types of structures found in the nucleus are chromosomes and nucleoli. Chromosomes can be seen clearly only during cell divisions.
Chromosomes are composed of both nucleic acid and protein. Chromosomes contain genes. Genes are the basic units of heredity which are passed from parents to their children. Genes guide the activities of each individual cell.
Cell Membrane. The cell membrane surrounds and separates the cell from its environment. The cell membrane allows certain materials to pass through it as they enter or leave the cell.
Cytoplasm. The semifluid found inside the cell, but outside the nucleus, is called the cytoplasm.
Mitochondria (Plural). Mitochondria are the "powerhouses" of the cell. The mitochondria provide energy wherever it is needed for carrying on the cellular functions.
Endoplasmic Reticulum. The endoplasmic reticulum is a network of membranes, cavities, and canals. The endoplasmic reticulum helps in the transfer of materials from one part of the cell to the other.
Ribosomes. Ribosomes are "protein factories" in the cell. They are composed mainly of nucleic acids which help make proteins according to instructions provided by the genes.
Centrioles. Centrioles help in the process of cell division.
Lysosomes. Lysosomes are membrane-bound spheres which contain enzymes that can digest intracellular structures or bacteria.
The next level is called tissues. Similar cells working together to perform a specific function combine to make up tissues. For example, muscle cells form muscle tissue. A histologist is someone who specializes in the study of tissues. The major tissues types are:
- Epithelial tissue: Epithelial tissue covers external surfaces of the body, line body structures, and forms glands. The skin is an example of an organ that is made up of epithelial tissue. Mucous membrane is also made up of epithelial tissue. It is found lining the digestive, respiratory, reproductive, and urinary tracts.
- Connective tissue: Connective tissue functions to support and shape the body structures and keeps them in place. Tendons and ligaments, blood, bone, cartilage, and fat are examples of connective tissues.
- Muscle tissue: Muscle tissue takes its name from its location in the body; for example, in the heart, it is called cardiac muscle tissue. Within organs, such as the stomach and intestines, it is called skeletal muscle tissue. Muscle cells are not round but long and slender. For this reason, muscle cells are referred to as fibers.
- Nervous tissue: This tissue makes up nerves that conduct electrical impulses throughout the body. The brain, spinal cord, and nerves are made up of nervous tissue.
HYPERTROPHY/HYPERPLASIA
Hypertrophy and hyperplasia are two ways by which the cell mass of the body increases.
With HYPERTROPHY, there is an increase in the size of the individual cells. No new cells are formed. An example is the enlargement of muscles due to exercise by the increased diameter of the individual striated muscle fibers.
With HYPERPLASIA, there is an increase in the total number of cells. An example of abnormal hyperplasia is cancer.
ATROPHY is seen when there is a loss of cellular mass.
