Biological sciences5

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Information about Biological sciences5

Published on February 28, 2014

Author: vannessangel24




TISSUE LEVEL OF ORGANIZATION TISSUE -A group of similar cells that usually have a common embryonic origin -Group of cells that function together to carry out specialized activities HISTOLOGY - Study of tissues

TISSUE LEVEL OF ORGANIZATION CELL JUNCTIONS -Contact points between the plasma membranes of tissue cells 5 types: Tight junctions Adherens junctions Desmosomes Hemidesmosomes Gap junctions

TISSUE LEVEL OF ORGANIZATION TIGHT JUNCTIONS -Consist of weblike strands of transmembrane proteins that fuse the outer surfaces of adjacent plasma membranes together -Control the passage of substances between cells and prevent the content of organs from leaking into surrounding tissues and blood

TISSUE LEVEL OF ORGANIZATION -Ex. Epithelial tissues that line the stomach, intestines, and urinary bladder ADHERENS JUNCTIONS - Contain plaque, a dense layer of proteins on the inside of the plasma membrane that attaches to both membrane proteins and to microfilaments of the cytoskeleton

TISSUE LEVEL OF ORGANIZATION -It is actually the transmembrane glycoproteins called cadherins that join the cells -Each cadherin inserts into the plaque from the opposite side of the plasma membrane, partially crossing the intercellular space and connects to cadherins of the adjacent cell

TISSUE LEVEL OF ORGANIZATION -In epithelial cells, adherens junctions often form extensive zones called adhesion belts which encircle the cell -Adherens junctions help epithelial surfaces resist separation during various contractile activities, as when food moves through the intestines

TISSUE LEVEL OF ORGANIZATION DESMOSOMES -Also contain plaque and have transmembrane glycoproteins that extend into the intercellular space between adjacent cell membranes and attach cells to one another -However, unlike adherens junctions, the plaque of desmosomes does not attach to microfilaments

TISSUE LEVEL OF ORGANIZATION -Instead, a desmosome plaque attaches to other elements of the cytoskeleton known as intermediate filaments that consist of the protein keratin -The intermediate filaments extend from desmosomes on one side of the cell to the desmosomes on the opposite side of the cell

TISSUE LEVEL OF ORGANIZATION -This arrangement contributes to the stability of the cells and tissue -Ex. Epidermis of the skin, cardiac muscle cells HEMIDESMOSOMES -Resemble desmosomes but they do not link adjacent cells -They look like “half of a desmosome”

TISSUE LEVEL OF ORGANIZATION -The transmembrane glycoproteins are integrins rather than cadherins -On the inside of the plasma membrane, integrins attach to intermediate filaments made of keratin -On the outside of the plasma membrane, the integrins attach to the protein laminin, present in the basement membrane

TISSUE LEVEL OF ORGANIZATION -they do not anchor cells to each other but to the basement membrane GAP JUNCTIONS -Membrane proteins called connexins form tiny fluid-filled tunnels called connexons that connect neighboring cells

TISSUE LEVEL OF ORGANIZATION -The plasma membranes are not fused together as in tight junctions but are separated by a very narrow intercellular gap -Through the connexons, ions and small molecules can diffuse from one cell to another -The transfer of nutrients takes place through the gap junctions in avascular tissues such as the lens and cornea of the eye

TISSUE LEVEL OF ORGANIZATION -They also allow the cells in a tissue to communicate with one another -Ex. Embryo – chemical and electrical signals that regulate growth and cell differentiation -Also enable enable nerve and muscle impulses to spread rapidly among cells (important in nervous system and muscle contraction)

REVIEW!!! Which type of cell junctions allow cellular communication? - GAP JUNCTIONS

REVIEW!!! Which type of cell junctions are found in epithelial tissues? -TIGHT JUNCTIONS -ADHERENS JUNCTIONS -DESMOSOMES -GAP JUNCTIONS

TISSUE LEVEL OF ORGANIZATION TYPES OF TISSUES -Body tissues can be classified into four basic types according to function and structure 4 types: Epithelial tissue Connective tissue Muscular tissue Nervous tissue

TISSUE LEVEL OF ORGANIZATION EPITHELIAL TISSUE -Or epithelium (plural epithelia) -Consists of cells arranged in continuous sheets, in either single or multiple layers -The cells are closely packed and held tightly together by many cell junctions, and there is little intercellular space between adjacent plasma membranes

TISSUE LEVEL OF ORGANIZATION -has a high rate of cell division to constantly renew and repair itself by sloughing off dead or injured cells and replacing them with new ones -Functions: protection, filtration, secretion, absorption, and excretion

TISSUE LEVEL OF ORGANIZATION -Has its own nerve supply -Avascular; it lacks its own blood supply (blood vessels that transport nutrients are in the adjacent connective tissue and delivers by DIFFUSION) -Forms boundaries between body organs; repeatedly subjected to physical stress and injury

TISSUE LEVEL OF ORGANIZATION -The apical or free surface faces the body surface, body cavity, inner lining of an organ or a duct. They may contain cilia or microvilli. -The lateral surface face the adjacent cells. They may contain tight junctions, adherens junctions, desmosomes, and/or gap junctions

TISSUE LEVEL OF ORGANIZATION -The basal surface is opposite the apical surface. It’s the deepest layer of the epithelial tissue that adhere to extracellular materials such as the basement membrane

TISSUE LEVEL OF ORGANIZATION + BASEMENT MEMBRANE -A thin extracellular layer that commonly consists of two layers: Basal lamina – “thin layer” - closer to and secreted by the epithelial cells - contains proteins such as collagen and laminin, also glycoproteins and proteoglycans - laminin adhere to the integrins in hemidesmosomes

TISSUE LEVEL OF ORGANIZATION Reticular lamina - closer to the underlying connective tissue and contains fibrous proteins produced by connective tissue cells called fibroblasts + the basement membrane function as a point of attachment and support for the overlying epithelial tissue

TISSUE LEVEL OF ORGANIZATION -2 types of epithelium: Covering and lining epithelium - Forms the outer covering of the skin and some internal organs -Forms the inner lining of blood vessels, ducts, and body cavities Glandular epithelium - Makes up the secreting portion of glands such as the thyroid, adrenal, and sweat glands

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