Body Structures & Organ Systems

Component	Description	Function
Plasma membrane	Selectively permeable membrane (allows only certain substances through) made of phospholipids and proteins surrounding the entire cell	Separates the internal components of the cell from the surrounding environment Essential to the life of the cell
Cytoplasm	Gel-like fluid filling the inside of the cell that is comprised primarily of water, with electrolytes, metabolic waste products, and nutrients dissolved within it	Contains many suspended organelles, or cell structures Medium for chemical reactions
Nucleus	Large, spherical body near the center of the cell containing genetic material in the form of DNA	Control center of the cell Regulates cell activity Houses genetic material
Nuclear membrane	Double-layered, porous membrane surrounding the nucleus	Protects the nucleus, allowing in only specific materials
Nucleolus	Dark, dense body within the nucleus without an enclosing membrane; most cells contain one to four	Forms RNA and ribosomes
Mitochondria	Elongated, rod-shaped bodies filled with fluid, containing DNA Known as the “power plant” of the cell	Convert nutrients into energy for use by the cell/body; create adenosine triphosphate (ATP)
Ribosomes	Small granules of RNA found in the nucleolus or cytoplasm	Protein synthesis for both internal and external use
Endoplasmic reticulum	Complex connection of membranous fluid-filled, flat sacs and tubular channels Connects the cell membrane to the nucleus membrane, as well as some organelles Comprised of the rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER)	Transports materials throughout the cell RER: Supports the synthesis and transport of proteins SER: Supports the synthesis of some lipid molecules, including steroids
Golgi apparatus	Four to six flat membranous sacs, connected to the endoplasmic reticulum; typically found near the nucleus	“Packaging and shipping plant” of the cell Packages and releases materials secreted by the cell for external use Forms lysosomes for use within the cell
Lysosomes	Sacs surrounded by membranes created by the Golgi apparatus	Digest waste materials including damaged materials found in the cell, old cell components, and materials entering the cell
Cytoskeleton	Comprised of protein microfilaments and microtubules	Maintains the shape and structure of the cell Keeps organelles in place and moves them throughout the cell as needed
Centrioles	Pair of rod-shaped bodies made of microtubules found near the nucleus	Participate in cell reproduction through the distribution of DNA to new cells
Cilia	Short, hair-like microtubules projecting from the cell membrane	Aid in the movement of substances along the surface of the cell
Flagella	Long, hair-like microtubules, projecting from the cell membrane	Move the cell itself, through a whip-like motion

Planes of the Body

Sagittal plane: Divides the body into left and right sides. Midsagittal refers to an equal division of left and right sides, running along the midline of the body.
Transverse plane: Divides the body into upper and lower sections, not necessarily equally
Frontal plane: Also called coronal plane, divides the body into anterior and posterior sections

Body Cavities

Cranial cavity: Within the skull; houses the meninges (brain)
Spinal cavity: Traveling down the midline of the back and formed by the vertebrae, this contains the spinal cord
Thoracic cavity: Within the chest; houses the lungs, heart, and major vessels
Abdominal cavity: Within the abdomen; houses several major organs such as the stomach, liver, gallbladder, and intestines
Pelvic cavity: Inferior to the abdominal cavity; houses the bladder and reproductive organs

Body Quadrants and Regions

The abdomen can be divided into four quadrants or nine regions, either of which is helpful as reference during physical examination of internal organs. Familiarity with each quadrant assists in correctly documenting a patient’s chief complaint pertaining to issues related to the abdomen.