C HAPTER 4 T ISSUE : THE L IVING F ABRIC

E PITHELIAL T ISSUE F EATURES Occurs in the body as a covering or lining or as glandular epithelium Performs several functions Protection Absorption Filtration Excretion Secretion Sensory Reception

S PECIAL C HARACTERISTICS Are continuous sheets that have little space between cells Bound together by desmosomes and tight junctions (chapter 3) Supported by a basement membrane made from underlying connective tissue Are innervated (supplied with nerves) and avascular (few or no blood vessels) Have a high regeneration capacity

C LASSIFICATION OF E PITHELIA o Has a two part name First part indicates the number of layers Second part describes the shape of the cell May be simple (single) or stratified (more than one) Cell shapes may be Squamous (flat), Cuboidal (box like) or Columnar (column shape) o Simple epithelium consists of single layer cells that functions in absorption, secretion and filtration o Simple squamous – located where filtration (exchange of substances) take place o Simple cuboidal – forms the smallest ducts of glands or kidney tubules o Simple columnar – lines the digestive track o Pseudostratified columnar – contains a variety of height cells that sit on basement membrane giving a many layered appearance

Stratified Epithelium is made up of several layers of cells to provide protection Stratified Squamous – the external part of the skin and extends into every body opening Stratified Cuboidal – found mostly in the ducts of larger glands Stratified Columnar – found in the pharynx, male urethra, and lining of some glandular ducts Transitional – forms the lining of hollow organs in the urinary system and is designed to stretch as organ distends

C ONNECTIVE T ISSUE F UNCTION Binding and support Protection Insulation Storing Fuel Transporting Substances in the body

C OMMON C HARACTERISTICS All come from mesenchyme (embryonic tissue) Ranges from avascular to highly vascularized Composed mainly of nonliving extracellular matrix that separates the cells of the tissue

S TRUCTURAL C OMPONENTS The space between the cells contains interstitial fluids, cell adhesion proteins, proteoglycans (heavy glycoprotein) and protein fibers Each connective tissue class has specific fundamental cell types in both immature and mature forms Provide support Collagen Fibers are extremely strong and have high tensile strength ( strength of fiber when stretched or twisted) Elastic Fibers contain elastin allowing them to be stretched and recoiled (returned to original shape) Reticular Fibers are fine collagen based that form networks where connective tissue is in contact with other tissue types

T YPES OF C ONNECTIVE T ISSUE Mesenchyme – forms during early weeks of embryonic development from the mesoderm Loose Connective Tissue Areolar – supports and binds body parts, contains fluids and defends against infection and stores nutrients Adipose (fat) – very vascular, stores nutrients, serves as protection and insulation Dense Connective Tissue – Dense regular – densely packed collagen fibers that all go the same direction basis for tendons and ligaments Dense irregular – densely packed collagen fibers arranged in irregular patterns and found in the dermis Elastic – found in select in locations and are more stretchy than dense connective tissue

Cartilage – lacks nerves and is avascular Hyaline – most abundant and provides firm support will little pliability Elastic – found where strength and stretchability are needed (external ear and epiglottis) Fibrocartilage – found where strong support and pressure suppression is needed (knee and intervertebral discs) Bone – supports and protects body structures due to its hardness Blood – develops in the mesenchyme and consists of blood plasma and proteind

M USCLE T ISSUE Are highly cellular and very vascular Responsible for movement 3 types of muscle tissue Skeletal – attaches to the skeleton and produces voluntary movement Cardiac – is responsible for the involuntary movement of the heart (found only in the heart muscle) Smooth – involuntary muscle found in the walls of hollow organs

N ERVOUS T ISSUE Main component of the nervous system Two types of cells Neurons – specialized cells that generate and conduct electrical impulses Supporting cells – nonconducting cells that support, insulate and protect the neurons

T ISSUE R EPAIR Occurs in two ways Regeneration – damaged cells replaced with same type of cell Fibrosis – replaces damaged cells with fibrous connective tissue Three steps involved Step 1: Inflammation as result of cell damage Step 2: Organization replaces blood clot with granulation tissue, restores blood supply Step 3 : Regeneration and fibrosis Regenerative capacity is dependent on the tissue types

D EVELOPMENTAL A SPECTS OF T ISSUE Embryonic and Fetal development Primary germ layer gives rise to the three layers of tissue: ectoderm, mesoderm and endoderm The primary germ layer will specialize to form the four primary tissues In adults, some tissues will regenerate through the division of mature cells while others will regenerate from stem cells As adults age, the epithelial tissue will thin and the repair processes are less efficient. In older adults the bone, muscle and nerve tissue will undergo atrophy (shrink or get smaller)