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is a group of cells that usually have a common embryonic origin and function to carry out specialized activities.
- covers body surfaces, body cavities, and ducts. It also forms glands. forms coverings and linings through-out the body
- - it is never covered by another tissue so it always has a free surface
protects and supports the body and its organs. Various types of connective tissue bind organs together, store energy reserves as fat, and help provide immunity to disease-causing organisms.
generates the physical force needed to make body structures move and generates body heat.
detects changes in a variety of conditions inside and outside of the boddy and respinds by generating action potentials (nerve impulses) that activate muscular contractions and glandular secretions
Primary germ Layers
- -tissues of the body develop from three primary germ layers
- 1) ectoderm- nervous tissue, epithelial tissue
- 2)endoderm- epithelial tissue
- 3)mesoderm- epithelial tissue, muscular tissue, connective tissue
- are contact points between the plasma membranes of tissue cells.
- -five most important cell junctions- tight junctions, adherens junctions, desmosomes, hemidesmosomes, and gap junctions
Structure: consist of weblike strands transmembrane proteins that fuse the outer surfaces of adjacent plasma membranes together to seal off passageways between adjacent cells
Function: form fluid tight seals between cells
Structure: contain plaque, (a dense layer of proteins on the inside of plasma membranes that attach both to membrane proteins and to microfilaments of the cytoskeleton) transmembrane glycoproteins called cadherins join the cells. Each cadherin inserts into the plaque from the opposite side of the plasma membrane, partially crosses the intercellular space (space between the cells) and connects to cadherins on the opposite side.
Function: anchor cells to one another or to the basement membrane
Structure: contain plaque and transmembrane glycoproteins that extend into the intracellular space between adjacent cells and attach cells to one another. However, the plaque of desmosomes does not attach to microfilaments.
Function: anchor cells to one another
Structure: resemblem desmosomes but they do not link adjacent cells. They look like half of a desmosomes. The transmembrane glycoproteins are integrins not cadherins.
membrane proteins called connexins form tiny fluid-filled tunnels called connexons that connect neighbouring cells.
- Function: permit electrical and chemical signals to pass between cells. cellular communication
- -transfer of waste and nutrients
Structure: Consists of cells arranged in continuous sheets, in either single or multiple layers. because the cells are closely packed and held together by many cell junctions there is little intercellular space between adjacent plasma membranes.
- Functions: selective barriers that limit or aid the transfer of substances into and out fo the body.
- -secretory surfecase that release products produced by the cell onto their face surfaces.
- -protective surfaces that resis the abrasive influence of the environment
Arrangement of cells in layers: Simple epithelium
is a single layer of cells that function in absorption, secretion, diffusion, osmosis, and filtration
Arrangement of cells in layers: Pseudostratified epithelium
appears to have multiple layers of cells becuase the nuclei lie at different levels not all cells reach the apical surface
Arrangement of cells in layers: Stratified epithelium
consists of teo or more layers of cells that protect underlying tissues in locations where there is considerable wear and tear
Cell shapes: Squamous cell
are arranged like floor tiles and are thin, which allows for the rapid passage of substances
Cell shapes: Cubodial cells
are as tall as they are wide and are shaped like cubes or hexagones. They may have microvilli at their apical surfaces and function wither in secretion or absorption
Cell shapes: Columnar cells
are much taller than they are wide, like columns and protect underlying tissues. Their apical surfaces maye have cilia or microvilli and they are often specialized for secretion and absorption
Cell shapes: transitional cells
cells chage shape, from flat to cubodial and back as organs such as the urinary bladder stretch to a larger size and then collapse to a smaller size
Covering and lining Epithelial: Simple squamous epithelium
- Description: Single layer of flat cells: centrally located nucleus
- Location: lines heart, blood vessels, lymphatic vessels, air sacs of lungs, glomerular sapsule of kidneys, and inner surface of the eardrum; forms epithelial layer of serous membranes (mesothelium) such as the peritoneum and pleura
- Function: filtration, diffusion, osmosis and secretion in serous membranes
Covering and lining Epithelial: Simple Cubodial Epithelium
Description: single layer of cube shaped cells; centrally located nucleus
Location: Covers surface of ovary, lines anterior surface of capsule of the lens of the eye, forms the pigmented epithelum at the posterior surface of the eye, lines kidney tubules and smaller ducts of many glands, and makes up the secreting portion of some glands such as thyroid glands and the ducts of some glands such as the pancreas
Function: Secretion and absorption
Covering and lining Epithelial: Nonciliated simple columnar epithelium
Description: single layer of nonciliated column like cells with nuclei near the base of cell; contains goblet cells and cells with microvilli in some locations
Location: lines the gastrointestinal tract, ducts of many glands, and gallbladder
Function: Secretion and absorption
Cilliated simple columnar epithelium
Description: Single layer of ciliated column-like cells with nuclei near base; contains goblet celss in some locations
Location: lines some bronchioles of respritory tract, uterine tubes, uterus, ducts of the testes, some paranasal sinuses, central canal of spinal cord and ventricles of the brain
Function: moves mucus and other substance by ciliary action
Pseudostratified columnar epithelium
Description: not a true stratified tissue; nuclei of cells are at different levels; all cells are attached to the basement membrane but not all reach the apical surface.
Location: Pseudostratified cilliated columnar epithelium lines the airways of most of upper respritory tract; pseudostratified noncilliated cilumnar epithelium lines larger ducts of many glands, and part of male uretha
Function: Secretion and movement of mucus by ciliary action(ciliated); absorption and protection (nonciliated)
stratified squamous epithelium
Description: several layers of cells; cuboidal to columnar shape in deep layers; squamous cells form the apical layer and several layers deep to it; cells from the basal layer replace surface cells as they are lost.
Location: keratinized variety form superficial layer of skin; non keratinized variety lines wet surfaces such as lining of the mouth, esophagus, part of the larynx, part of the pharynx, and vagina, and covers the tongue
Stratified cubodial epithelium
Description: two or more layers of cells in which the cells in the apical layer are cube shaped
Location: ducts of adult sweat glands and esophageal glands and part of male uretha
Function: protection and limited secretion and absorbtion
stratified columnar epithelium
- Description: several layers of irregularly shaped cells; only the apical layer has columnar cells
- Location: lines part of the uretha, large excretory ducts of some glands, small areas in anal mucous membrane, and part of conjunctive of the eye
Function: Protection and secretion
- Description: appearance is variable
- Location: lines urinary bladder and portions of ureters and urethra
- Function: Permits distension
- A gland my consist of a single cell or a group that secrete substances into ducts(tubes), onto surfaces, or into blood.
- - all glands are classified as either endocrine or exocrine
the function is secretion, which is accomplished by glandular cells the often lie in clusters deep to the covering and lining epithelium
Description: Secretory products (hormones) diffuse into blood after passing through interstitual fluid
Location: Examples include, pituitary gland at the bas of brain, pineal gland in brain, thyroid and parathyroid glands near larynx (voice box)
Functions: produce hormones that regulate various body activities
Description: Secretory products released into ducts
Location: sweat, oil and aear wax glands of skin, digestive glands such as salvatory glands
Function: Produce substances such as sweat, oil, ear wax, saliva, or digestive enzymes
Exocrine glands: Merocrine glands
- -are synthesized on ribosomes attached to the ER; processed, sorted and packaged by the golgi; and released from the cell in secretory vesicles
- -most exocrine glands of the body are Merocrine glands
Exocrine glands: Apocrine
accumulate their secretory product at the apical surface of the secreting cell. Then, that portion of the cell pinches off from the rest of the cell to release secretion
Exocrine glands: Holocrine glands
accumulate secretory product in thier cytosol. As the secretory cell matures, it ruptures and becomes the secretory product