Epithelial Tissue

Histology - Study of tissues defined as group of cells of similar structure that perform a common function. Tissue is a french word meaning "to weave"different tissue are woven together. Some tissue have nonliving material called extracellular matrix.-

Four Major tissue types

2 .Muscle Tissue**: Movement, cells are named muscle fibers and are close together. They are excitable as they move or make movements

3 .Nervous Tissue:Brain and spinal cord, regulate and control body functions. Contains two cells neurons and supporting cells

1.Epithelial Tissues- type of tissue that covers or lines parts of our body , blood vessels , epidermis, cells close together outer layer of skin, inner layer surfaces of most body organ,stomach, respiratory tubes, lining of peritoneal cavity.


Glandular epithelium forms most of the body gland.

**4. Connective Tissue**: Contain large amount of extracellular matrix. Its functions are to support, holds tissue fluids and protection from disease

Characteristics Common to all types of Epithelia

Classification of Epithelia- epithelial cells are classified by the number of layers and the shape of the cells

The number of layers

Shape

Squamous Cells-are flat cells with flat disc shaped nuclei

Cuboidal Cells-Cube shaped cells with spherical centrally located nuclei

3.Cellularity -Epithelia composed of almost entirally cells, cells are seperated by extracelular materi**al

4.Specialized contacts- adjacent epithelial cells are directly joined at many points by special cell junctions

  1. Polarity- All epithelia have free apical surface and attached basal surface

Apical Surface-the open space of a cavity, tuble,gland or hallow organ

Basal Surface- lies on a thin supporting sheet called basal lumina which is part of the basement membrane**

2.Avascular but innervated-lacks blood vessels , epithelial cells get their nutrients from capillaries in the underlying connective tissue. Epithelial cells have nerve endings .
Example: When there is cut and there is no blood but it hurts. There is no blood due epithelia cells not having blood vesssels but it hurts due the nerve endings

1.Support by connective tissue- All epithelial tissue in the body are supported by underlying layer of connective tissue **

5.Regeneration-epithelial cells can regenerate make new cells as long as they get adequate nutrition

B.More Than One Layer: Stratified Epithelial Tissues

A.One Layer: Simple Epithelial Tissues

Simple Cuboidal Epithelium- Single layer of cubelike cells with large spherical central nuclei,square circular shaped cells

Simple Columnar Epithelium: Single layer of tall cells with round to oval nuclei ,some cells bear cillia layer , contains goblet cells(mucus),rectangular shaped cells

Simple squamous epithelium-single layer of flattened cells with disc shaped central nuclei and cytoplasm.Thin, flat cells

Location: Kidney glomeruli, air sacs of lungs, lining heart, blood vessels, lymphatic vessels, lining of ventral body cavity

Function: Rapid transport of molecules/Allows passage of materials by diffusion and filtration in sites where protection is not important produces lubricating fluid

Location: Kidney tubules ducts,, and secretory portions of small glands , ovary surface

Function: Secretion and absorption(allow rapid passage through epithelial layer)

Location: Nonciliated, digestive tract, stomach to rectum gallbladder , excretory ducts of some glands, ciliated lines of small bronchi, uterine tubes, some parts of uterus

Function: Absorption,secretion of mucus, enzymes

Pseudostratified Columnar Epithelium : Single layer of cells of differing heights some not reaching the free surface nuclei seen at different layers. May contain goblet cells(produce secretion)mucus and cilia(move fluid). Falsely stratified, one layer.Columnar cell shaped.

Location: Nonciliated in male's sperm-carrying ducts and ducts of large glands, ciliated variety lines the trachea , upper respiratory tract

Function: Secretion of mucus, ciliary action

Stratified cuboidal epithelium-cuboidal cell in apical region, two layer cells , protects underlying tissue from glandular secretion. Forms ducts of large glands, two layer of cubelike cells

Stratified columnar epithelium-Columnar cell in apical region, two layer cells, protects underlying tissue, several cell layers

Transitional epitheliium: Looks some what like stratified squamous and stratified cuboidal , cells dome shaped or squamous like, depends on how much organs stretches

Stratified squamous epithelium-Squamous cells in apical region, multiple layer of cells

Location: Lining of esophagus, mouth, vagina, epidermis of skin

Function: Protects underlying tissues in areas that abrasion can occur

Funtion: protection

Location: Sweat glands(large ducts), mammary glands, and salivary glands

Function:: protection , secretion

Loation: Rare,male urethra, large ducts of some glands

Function: Stretches,changes shape for example when a bladder is full , protection

Location: Lines ureters, bladder and some parts of urethra

Different kinds of Exocrine glands: glands secrete their products onto surfaces for example, skin or body cavities(digestive tube)- Secretion is local, include: sweat glands, oil glands of skin, salivary glands in mouth,liver(secretes bile),pancreas(secrete digestive enzymes),Mammary galnd(screte milk). Excroine glands have ducts that carry products to epithelial surfaces.=

Unicellular (One Celled) Ex. goblet cells-secreted within epithelial lining of intestine and respiratory tubes in between columnar cells

Multicellular exocrine glands"has two specific epithelium wall duct and sensory unit of secretory epiithelium, simplest glands, supports connective tissue surrounding unit that contain blood vessels and nerve fibers.

Multicellular glands are classified by their structures

Compound glands-have a brached duct

Simple glandss- unbranched duct

Categorized by secretory units

Tubular-senscretory cells form tubes

Alveolar or acinar(grape/berry ) -secretory cells form spherical sacs /small hollow cavity

Tubuloalveolar- contain both tubular secretory units and alveolar units

Produce mucin- which is glycprotein/sugar protein which disolves in H2O during secretion. Mucin pluls water produces viscous , slimy mucus.

Mucus- covers, protects and lubricates many internal body surfaces

Function

Absorption- brings small molecules into cells**

Diffusion- Movement of molecules down their concentration gradient

Secretion - Releases molecules from cells

Filtration- Passage of small molecules

Protection - Underlying tissues

sensory reception*