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Epithelial Tissues

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Kaity Bastedo

on 31 October 2013

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Transcript of Epithelial Tissues

Epithelial Tissues
Introduction to Tissues
-A layer or group of similar cells with a common function

-can be distinguished by cell size, shape, organization and function

-Four major types: Epithelial, Connective, Muscle, and Nervous

-found throughout the body
-cover body surfaces and organs
-form the inner linings of body cavities
-lines hollow organs
-always has a free (apical) surface exposed to the outside or internally to an open space
Squamous: thin flattened cells
-Intercellular Junctions: structures that connect cell membrane
(ex. Desomosome-->enables skin cells to form a reinforced structural unit)

-Tight junction: membranes of adjacent cells that converge and fuse

-Gap Junctions: tubular channels that connect cell membranes of certain other cells (ex. heart muscle and muscle of the digestive tract)
-Allow nutrients, ions and other small molecules to move between them

Cuboidal: cubelike cells
Columnar: elongated cells
Stratified: two or more layers of cells
Simple: Single layer of cells
Basement membrane: thin nonliving layer that anchors epithelium to underlying connective tissue
*As a rule, epithelial tissues lack blood vessels
-Readily divide so injuries heal rapidly as new cells replace lost or damaged ones

-Tightly packed which enables them to form an effective protective barrier in structures such as the outer layer of the skin & the lining of the mouth
lines the follicles of the thyroid gland
-Fit tightly together and their nuclei are usually broad and thin

-Substances pass through them easily

-Common at sites of diffusion and filtration
-Line the air sacs of the lungs where oxygen and carbon dioxide are exchanged

-Forms the walls of capillaries
-lines the inside of blood and lymph vessels
-covers the membranes that cover the body cavities
-b/c its so thin and delicate, its easily damaged

Simple Cuboidal Epithelium
Stratified Cuboidal Epithelium
- Stratified Cuboidal Epithelium: consists of two or three layers of cuboidal cells that form the lining of a lumen (the inside space of a tubular structure)
-this tissue is composed of two or three layers of cube shaped cells

-lines the larger ducts of mammary glands, sweat glands, salivary glands, and pancreas

-forms the lining of developing ovarian follicles and seminiferous tubules (parts of the male and female reproductive system)

-it functions in protection

- It also forms the lining of developing ovarian follicles and seminiferous tubules, which are part of the male and female reproductive systems
consists of several layers of cells (two or three)

-theses superficial cells are elongated, whereas the basal layers consist of cube shaped cells

- basal layer is the deepest layer of the epidermis, outer covering of skin in mammals

-Stratified Columnar Epithelium
is found in the male urethra and the ductus deferens and in part of the pharynx
- pharynx is an organ in the digestive system and respiratory system

-the function of this tissue is protection

consists of a layer of cube shaped cells
essentially located spherical nuclei
lines the kidney tubules and ducts of certain glands such as salivary, pancreas and liver
functions in tubular secretions in kidneys and tubular reabsorption
in glands, it secrets glandular products
Simple Squamous Epithelium
Simple Columnar Epithelium
simple columnar epithelium
Glandular Epithelium
Glandular Epithelium is composed of cells specialized to produce and secrete substances into ducts or body fluids.
Found within columnar or cuboidal epithelium
, and compose glands.
The skin and lining of the digestive tract, which secrete products onto open surfaces, are called exocrine glands.

Endocrine glands secrete their products into tissue fluid or blood.
An exocrine gland can contain a simple cell or be multicellular. They can be divided into simple and compound glands.

5 Types of Glands (and fluids)
Tubular-epithelial lined tubes
Alveolar-form saclike dilations
Merocrine: release fluids by exocytosis (Pancreatic fluid, saliva)
Apocrine: Lose portions of glandular bodies through secretion (mammary glands, ceruminous in ear canal)
Holocrine: Release entire cells (skin)
-composed of a single layer of elongated cells whose nuclei are usually at the same level near the basement membrane
-cells can be ciliated or nonciliated
(cilia extend from the free surfaces of the cells, and they move constantly
nonciliated simple columnar epithelium lines the uterus and portions of the digestive tract
cells are elongated, so this tissue is thick which enables it to protect underlying tissue
cells-> specialize for absorption
-often have many cylindrial processes extending from their free surfaces, called MICROVILLI
-increase the surface area of the cell membrane
goblet cells-> specialized flask-shaped glandular cells that are scattered among the cells of the simple columnar epithelium
-secrete a protective fluid called mucus on the free surface of the tissue

Types of Merocrine Fluids
Serous fluid is watery, with a high concentration of enzymes
Serous fluid lines the thoracic and abdominopelvic cavities and are associated with visceral and parietal membranes

Mucus is rich in mucin, a glycoprotein.
Mucus is found in the digestive, reproductive, and respiratory systems for protection

Mucus and goblet cells secrete mucus
Types of Glands
Where Serous Fluids and Mucus are located
Stratified Columnar Epithelium
Transitional Epithelium
-specialized to change in response to increased tension
-forms the inner lining of the urinary bladder and lines the ureters and superior urethra
-when the wall of one of these organs contracts, the tissues consist of several layers of cuboidal cells
-when the organ is distended, the tissue stretches and the physical relationships among the cells change
-transitional epithelium also forms a barrier that helps prevent the contents of the urinary tract from going back into the intestines/internal environment
Pseudostratified Columnar Epithelium
-not all of them contact the free surface
Stratified Squamous Epithelium
- consists of many layers of cells, making this tissue thick

-these cells appear layered but they are not
-a layer effect occurs because the nuclei are at two or more levels in the row of aligned cells
-the cells vary in shape
-these cells commonly have cilia, which extend from the free surfaces of the cells.
-Goblet cells scattered throughout this tissue secret the mucus, which the cilia sweep away
lines the passages of the respiratory system.
the mucous covered linings are sticky and they trap dust and microorganisms that enter the air.
then the cilia moves the mucus and its captured particles upward and out of the airways

-cells nearest the free surface are flattened the most
-those in the deep layers, where cell division occurs are cuboidal or columnar.
-as newer cells grow, older ones are pushed farther and farther outward, where they flatten.
-example: epidermis (outermost layer of skin)

-keratinization: when older cells are pushed outward and create a protein called keratin, then these older cells harden and die.
-this produces a covering of dry and tough protective skin preventing substances from escaping and microorganisms from entering.

-lines the oral cavity, esophagus, vagina and anal canal.
-in these parts, the tissue is not keratinized; it stays soft and moist and the cells on it surfaces remain alive.
Types of Tubular/Alveolar Glands
Branched tubular
Coiled tubular
Branched alveolar
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