HUMAN BODY The human body is a remarkable structure consisting of cells arranged in an orderly fashion . Cells are grouped together to form tissues ,which are grouped to form organs . Organs work together as organ systems ,
CELLS and TISSUES There are many distinguishable kinds of cells are present in the body , there are only four major types of cells : a – Neurons . b – Muscle cells . c – Epithelial cells. d – Connective tissue cells . This classifications are based on the functional differences .
A - Neurons Neurons or nerve cells are specialized to transmit information in the form of electrical signals. For this purpose, neurons typically possess a number of branches that function either to receive signals from or transmit signals to other cells.
KINDS OF THE Neurons a – Neurons in the eyes : that respond to light b – Neurons in the skin: that respond to touch , receive information from the outside environment and allow us to perceive the world through our senses . c - Neurons in the muscles : that respond to movement . d - Neurons in the glands : that respond to hormones secretion .
b – Muscle cells Muscle cells or muscle fibers are specialized to contract ,thereby generating mechanical force and movement .it found in muscle of the arms , legs , and other body parts whose movements are under voluntary control(skeletal muscle ) . Other muscles not under voluntary control, such as the heart ( cardiac m.) and blood vessels (smooth m.)
C – Epithelial cells Epithelial cells :Are found in tissues called epithelia ,which consist of a continuous, sheetlike layer of cells in combination with a thin underlying layer of noncellular material called a basement membrane . The epithelial layer may be one cell thickor several cells thick.
Epithelial cells vary in shape from short and flattened, and in some cases to tall and oblong in others . In all cases cells are joined closely together to form a barrier, prevents material on one side of the epithelium from mixing freely with material on the other side .
Certain epithelial cells are specialized to transport some material such as inorganic ions ,organic molecules or water from one location to anther e.g. cells in lining of the stomach transport acid into the lumen of the stomach to aid the digestion of food . Cells in the lining of the intestine , which transport nutrients and water from the lumen of the intestine into the bloodstream .
Some epithelial cells form glands ,organs specialized in the synthesis and secretion of a product . . There are tow types of glands .
a- Exocrine glands secrete a product into a duct leading to the external environment e.g. sweat gland and salivary glands types of glands :
Endocrine gland secrete hormones, which are chemicals that communicate a massage to cells of the body ,into the bloodstream. e.g. pituitary & adrenal glands . B –Endocrine glands
d – Connective tissue cells Connective tissue refers to any structure whose primary function is to provide physical suport for other stacture ,to anchor them in place ,or to link them together . e.g. tendons : which anchor muscle to bones. Ligaments : which connect bones together , and the elastic tissue in the skin that gives it its toughness & flexibility . Bones them selves , which provide support for all the body `s structures .
Connective tissue consists of widely scattered cells embedded in a mass of noncellular material called extracellular matrix . The mostimportant constituents of the extracellular matrix are the longe , fibrous proteins elastin &collagen .Blood and lymph also a connective tiusses
ORGANS AND ORGANS SYSTESM When two or more tissues combine to make up structures that perform particular functions ,those structures are called organs . e.g. The heart , is an organ whose primary function is to pump blood , Although composed mostly of muscle tissue , it also contains nervous tissue , epithelial tissue and connective tissue
ORGAN SYSTEMS The various organs are organized into organ systems , collections of organs that work together to perform certain functions . e.g. cardiovascular system , whose function Is to deliver blood to all body`s tiusse . cardiovascular system includes the HEART, BLOOD VESSELS & BLOOD .