KINE 2031 Lecture Notes - Cell Nucleus, Catecholamine, Histology

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May 7th, 2012
EPITHELIA
Tissues: groups of similar cells and extracellular products that carry out a common function, such as providing
protection or facilitating body movement. Tissues are formed from the three primary germ layers (ectoderm,
mesoderm, and endoderm). The 4 tissue types vary in structure, function of their specialized cells and the
presence of the ECM.
Histology: the study of tissues and their relationships within organs.
THE 4 primary TYPES OF TISSUES ARE:
Epithelial
Connective
Muscle
Nervous
EPITHELIAL TISSUE
Structure of Epithelial Tissue
Basement Membrane: A thin extracellular layer that
physically separates the epithelial tissue from the
underlying connective tissue. Made of both the Basal
Lamina and Reticular Lamina.
acts as a regulator for movement of molecules to the
deeper connective tissue
acts to anchor epithelium to the underlying
connective tissue
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Functions: Epithelia may have several functions, although no single epithelium performs all of them. These
functions include:
Physical Protection/Barrier: Epithelial tissues protect both exposed and internal surfaces from dehydration,
physical, mechanical or chemical injury. i.e. skin - in severe burns, dehydration is a primary concern
Selective permeability: All epithelial cells act as “gatekeepers,” in that they regulate the movement of materials
into and out of certain regions of the body. All substances that enter or leave the body must pass through an
epithelium. Sometimes an epithelium exhibits a range of permeability; that is, it may be relatively impermeable to
some substances, while at the same time promoting and assisting the passage of other molecules by absorption or
secretion. The structure and characteristics of an epithelium may change as a result of applied pressure or stress.
i.e. walking around without shoes may increase the thickness of calluses on the bottom of the feet, which could
alter or reduce the movement of materials across the epithelium.
Absorption: Regulates the passage of substances into the body. i.e. absorption occurs in the organs such as the
small intestines, which is lined with epithelial tissue. i.e. lungs allow oxygen to diffuse in and CO2 to diffuse out.
Sensations: contain some nerve endings to detect changes in the external environment at their surface. These
sensory nerve endings and those in the underlying connective tissue continuously supply information to the
nervous system concerning touch, pressure, temperature, and pain. i.e. receptors in the epithelium of the skin
respond to pressure by stimulating adjacent sensory nerves. Additionally, several organs contain a specialized
epithelium, called a neuroepithelium, that houses specific cell receptors responsible for the senses of sight, taste,
smell, hearing, and equilibrium.
Secretions: modified epithelial cells group together to form glands. two different categories of glands.
1. Exocrine glands contain ducts or tubes to
transport or secrete.
i.e. Salivary Glands.
2. Endocrine glands that do NOT have ducts or
tubes. Chemicals produced by these glands
(hormones) are released into the environment
surrounding the gland, and pass into the
capillaries and are transported throughout the
circulatory system.
i.e. Thyroid Gland, Catecholamines
(both formed by epithelial tissue)
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Classification of Epithelial Tissue
Squamous: cells are flat, wide, and somewhat irregular in shape. The nucleus looks like a
flattened disc. The cells are arranged like irregular, flattened floor tiles.
Cuboidal: cells are about as tall as they are wide. The cells do not resemble perfect cubes,
because they do not have squared edges. The cell nucleus is spherical and located within
the center of the cell.
Columnar: cells are slender and taller than they are wide. The cells look like a group of
hexagonal columns aligned next to each other. Each cell nucleus is oval and usually
oriented lengthwise and located in the basal region of the cell.
Cell Layers
Simple: one cell layer thick, and all of these epithelial cells are in direct contact with the basement membrane.
Stratified: contains two or more layers of epithelial cells. Only the cells in the deepest (basal) layer are in contact
with the basement membrane.
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