Chapter 4 Flashcards
Tissue
A group of cells that usually have a common origin in an embryo and function together to carry out specialized activities.
What are the four basic types of tissues?
Epithelial tissue, connective tissue, muscular tissue, and nervous tissue.
Epithelial tissue
Covers body surfaces and lines hollow organs, body cavities, and ducts; it also forms glands. This tissue allows the body to interact with both its internal and external environments.
Connective tissue
Protects and supports the body and its organs. Various types of connective tissues bind organs together, store energy reserves as fat, and help provide the body with immunity to disease-causing organisms.
Muscular tissue
Is composed of cells specialized for contraction and generation of force. In the process, muscular tissue generates heat that warms the body.
Nervous tissue
Detects changes in a variety of conditions inside and outside the body and responds by generating electrical signals called nerve action potentials (nerve impulses) that activate muscular contractions and glandular secretions.
Cell junctions
Are contact points between the plasma membranes of tissue cells.
What are the five basic types of cell junctions?
Tight junctions, adherens junctions, desmosome, hemidesmosomes, and gap junction.
Tight junctions
Consist of weblike strands of transmembrane proteins that fuse together the outer surfaces of adjacent plasma membranes to seal off passageways between adjacent cells.
Adherens junctions
A dense layer of proteins on the inside of the plasma membrane that attaches both to membrane proteins and to microfilaments of the cytoskeleton. Adherens junctions help epithelial surfaces resist separation during various contractile activities, as when food moves through the intestines.
Cadherins
Transmembrane glycoproteins that join cells. Each cadherin inserts into the plaque from the opposite side of the plasma membrane, partially crosses the intercellular space (the space between the cells) and connects to cadherins of an adjacent cell.
Adhesion belts
Adherens junctions that encircle a cell (similar to the way a belt encircles your waist).
Desmosome
Contain plaque and have transmembrane glycoproteins (cadherins) 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. Instead, a desmosome plaque attaches to elements of the cytoskeleton known as intermediate filaments, which consist of the protein keratin.
Hemidesmosomes
Resemble desmosomes, but they do not link adjacent cells. The transmembrane glycoproteins in hemidesmosomes are integrins rather than cadherins. On the inside of the plasma membrane, integrins attach to intermediate filaments made of the protein keratin. On the outside of the plasma membrane, the integrins attach to the protein laminin, which is present in the basement membrane. Thus, hemidesmosomes anchor cells not to each other but to the basement membrane.
Gap junctions
Contain connexins and connexons. Gap junctions allow the cells in a tissue to communicate with one another.
Connexins
Membrane proteins that form connexons.
Connexons
Tiny fluid-filled tunnels that connect neighbouring cells and allow ions and small molecules to diffuse from the cytosol of one cell to another.
What are the two differences between epithelial and connective tissue?
- The number of cells in relation to the extracellular matrix (the substance between cells). In an epithelial tissue many cells are tightly packed together with little or no extracellular matrix, whereas in a connective tissue a large amount of extracellular material separates cells that are usually widely scattered.
- An epithelial tissue has no blood vessels, whereas most connective tissues have significant networks of blood vessels.
______ almost always forms surface layers and is not covered by another tissue. An exception is ______.
Epithelial tissue, the epithelial lining of blood vessels where blood constantly passes over the epithelium.
Epithelial tissue
Cells arranged in continuous sheets, in either single or multiple layers. The various surfaces of covering and lining epithelial cells often differ in structure and have specialized functions.
What is the functional role of epithelial tissue?
Functionally, epithelial tissue protects, secretes (mucus, hormones, and enzymes), absorbs (nutrients in the gastrointestinal tract), and excretes (various substances in the urinary tract).
Exchange of substances between an epithelial tissue and connective tissue occurs through ______.
Diffusion
A ______ allows epithelial tissue to constantly renew and repair itself.
High rate of cell division.
Basement membrane
is a thin extracellular layer found between an epithelial tissue and a connective tissue; attaches and anchors the epithelium to its underlying connective tissue; consists of two layers, the basal lamina and reticular lamina.
Basal lamina
One of the layers of basement membrane; is closer to, and secreted by, the epithelial cells.
Reticular lamina
One of the layers of basement membrane; is closer to the underlying connective tissue.
What are the two types of epithelial tissue?
Surface epithelium and glandular epithelium
Surface epithelium
Forms the outer covering of the skin and some internal organs. It also forms the inner lining of blood vessels, ducts, body cavities, and the interior of the respiratory, digestive, urinary, and reproductive systems.
Glandular epithelium
Makes up the secreting portion of glands such as the thyroid gland, adrenal glands, sweat glands, and digestive glands.
What are the two characteristics that types of surface epithelium are classified according to?
- Arrangement of layers
- Cell shapes
Simple epithelium
A single layer of cells that functions in diffusion, osmosis, filtration, secretion, or absorption.
Pseudostratified epithelium
Appears to have multiple layers of cells because the cell nuclei lie at different levels and not all cells reach the apical surface; it is actually a simple epithelium because all its cells rest on the basement membrane.
Stratified epithelium
Consists of two or more layers of cells that protect underlying tissues in locations where there is considerable wear and tear.
Squamous cells
Are thin, which allows for the rapid passage of substances through them.
Cuboidal cells
Are as tall as they are wide and are shaped like cubes or hexagons. They may have microvilli at their apical surface and function in either secretion or absorption.
Columnar cells
Are much taller than they are wide, like columns, and protect underlying tissues. Their apical surfaces may have cilia or microvilli, and they often are specialized for secretion and absorption.
Transitional cells
Change shape, from squamous to cuboidal and back, as organs such as the urinary bladder stretch (distend) to a larger size and then collapse to a smaller size.
Glandular epithelium
Main function of glandular epithelium is secretion.
Gland
Consists of epithelium that secretes substances into ducts (tubes), onto a surface, or eventually into the blood in the absence of ducts. All glands of the body are classified as either endocrine or exocrine.
Endocrine glands
AKA hormones; endocrine secretions have far-reaching effects because they are distributed throughout the body by the bloodstream.
Exocrine gland
Exocrine secretions have limited effects as some of them would be harmful if they entered the bloodstream; are classified as either unicellular or multicellular.
Unicellular glands
Are single-celled glands (Eg. Goblet cells are important unicellular exocrine glands that secrete mucus directly onto the apical surface of a lining epithelium).
Multicellular glands
Most endocrine glands are multicellular glands; composed of many cells (Eg. sudoriferous (sweat), sebaceous (oil), and salivary glands).
How are multicellular glands categorized?
They are categorized according to two criteria: 1.) whether their ducts are branched or unbranched and 2.) the shape of the secretory portions of the gland.