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Friday, October 19, 2007

Physiology -Chap 4- Outline.2

Chapter 4 (Pgs. 111-118)


Covering and Lining Epithelium

  • The types and covering and lining epithelial tissue are classified according to two characteristics: the arrangement of cells into layers and the shapes of the cells


Arrangement of Cells in Layers

  • Cells are arranged in one or more layers depending on the functions the epithelium performs

~Simple Epithelium: a single layer of cells that functions in diffusion, osmosis, filtration, secretion, and absorption

  • 4 Types:

A.) Simple squamous epithelium

-Consists of a single layer of flat cells (resembles a tile floor)

-Nucleus: a flattened oval sphere

-Not found in body areas that are subject to mechanical stress (wear and tear)

-Lines the heart, blood vessels, and lymphatic vessels (a.k.a. endothelium)

-Forms the epithelial layer of serous membranes (a.k.a. mesothelium)

--Both endothelium and mesothelium are derived from mesoderm

B.) Simple cuboidal epithelium

-Cell nuclei are usually round and centrally located

-Found in the thyroid gland and kidneys

-Performs secretion and absorption

C.) Simple columnar epithelium (non-ciliated and ciliated)

*Oval nuclei near the base

~Non-ciliated Simple Columnar Epithelium~

-Microvilli: fingerlike cytoplasm projections

--increase the surface area of the plasma membrane

--increase the cells rate of absorption

-Goblet Cells: modified columnar epithelial cells

--secrete mucus at their apical surfaces (gives it that goblet look)

--mucus- lubricant for the linings of the digestive, respiratory, & reproductive tracts, and most of the urinary tracts

--mucus- forms a film over the airway surface that traps inhaled foreign particles

~Ciliated Simple Columnar Epithelium~

-Contains cilia at the apical surface

--Cilia beat in unison; move the mucus and any foreign particles toward the throat, to be coughed up and swallowed or spit out

--Coughing/ sneezing speeds up the movement of cilia/mucus

--Help move oocytes expelled from the ovaries through the fallopian tubes into the uterus

-Goblet cells are interspersed among ciliated columnar epithelia in certain parts of the airways of the upper respiratory tract

D.) Pseudostratified columnar epithelium (non-ciliated and ciliated)

*Appears to have several layers because the nuclei of the cells are at various depths

*All cells are attached to the basement membrane; not all reach the apical surface

~Pseudostratified Ciliated Columnar Epithelium~

-Cells that extend to the surface either secrete mucus or bear cilia

--Secreted mucus traps foreign particles

--Cilia sweep away mucus for eventual elimination

~Pseudostratified Non-Ciliated Columnar Epithelium~

-Contains cells without cilia and lacks goblet cells

*Secretion: the production and release of substances such as mucus, sweat, or enzymes

*Absorption: the intake of fluids or other substances such as digested food from the intestinal tract

~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’s cells rest on the basement membrane (therefore it’s a simple epithelium)

-Cells that extend to the apical surface may contain cilia

-Goblet cells secrete mucus

~Stratified Epithelium: consists of two or more layers of cells that protect underlying tissues in locations where there is considerable wear and tear

*Has 2 or more layers of cells

*More durable; can better protect underlying tissues

*Some cells produce secretions

4 Types

A.) Stratified squamos epithelium (keratinized and non-keratinized)

*Apical layer cells are flat

*Deep layer cells vary from cuboidal to columnar

*The basal (deepest) cells continually undergo cell division

*As new cells grow, the cells of the basal layer are pushed upward toward the apical layer

*As they move farther from the deeper layers (and from their blood supply) in the underlying connective tissue, they become dehydrated, shrunken, harder, and then die

*Dead cells lose their cell junctions, are sloughed off, then replaced

~Keratinized Stratified Squamous Epithelium~

-Apical layer and several layers deep to it are partially dehydrated and contain a layer of keratin

--Fibrous protein that helps protect the skin and underlying tissues from heat, microbes, and chemicals

-Forms the superficial layer of the skin

~Non-Keratinized Stratified Squamous Epithelium~

-Found in the lining of the mouth and esophagus

-Does not contain keratin in the apical layer

-Remains moist

*Both types form a first line of defense against microbes

B.) Stratified cubical epithelium

-Cells in the apical layer are cuboidal-- fairly rare

-Mainly serves a protective function; also has a limited role in secretion and absorption

C.) Stratified columnar epithelium

-Usually the basal layers consist of shortened, irregularly shaped cells; only the apical layer has cells that are columnar in shape--uncommon

-Functions in protection and secretion

D.) Transitional epithelium

-Present only in the urinary system; has a variable appearance

-In its relaxed or unstretched state, transitional epithelium looks like stratified cubical epithelium, except that the cells in the apical layer tend to be large and rounded

-As the tissue is stretched, its cells become flatter, giving the appearance of stratified squamous epithelium

-Elastic

-Lines the urinary bladder; it allows it to stretch and hold a variable amount of fluid without rupturing


Cell Shapes

  • Squamous cells: are arranged like floor tiles and are thin, which allows for the rapid passage of substances

  • Cuboidal cells: are as tall as they are wide and are shape d like cubes or hexagons

~May have microvillus 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

~Apical surfaces may have cilia or microvilli

~Often specialized for secretion and absorption

  • Transitional Cells: change shape, from flat to cubical, as organs such as the urinary bladder stretch (distend) to a larger size and then collapse to a smaller size


Papanicolaou Test

  • Papanicolaou Test (a.k.a. Pap test, or Pap smear): involves collection and microscopic examination of epithelial cells that have been scraped off the apical layer of a tissue

  • A very common type of Pap test involves examining the cells from the non-keratinized stratified squamous epithelium of the vagina and cervix of the uterus

~Performed to detect early changes in the cells of the female reproductive system that may indicate cancer or a precancerous condition




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