What are tissues & what are the 4 basic kinds?
A group of closely associated cells that perform related functions and are similar in structure. There is epithelium, connective, muscle and nervous tissues
Define Epithelium
A sheet of cells that covers a body surface or lines a cavity and acts as an interface and as boundaries
What are the function of epithelium?
- Protection
- Sensory reception
- Secretion
- Formation of slippery surfaces for movement
- Absorption
- Ion transport
- Filtration
What are some special characteristics of epithelium?
- Cellularity
- Specialized contacts - cell junctions
- Polarity (free upper apical surface & lower basal surface)
- Support by connective tissue
- Avascular but innervated
- Regeneration
What are the three classifications for epithelium based on shape?
- squamous
- cuboidal
- columnar
Where would you find simple squamous epithelial cells?
Sites of rapid diffusion such as the lining of the lung alevoli, lining of the blood vessels, and body cavity linings
What is endothelium?
a simple squamous epihelium that lines the interior circulatory vessels and heart
What is mesothelium?
Simple squamous epithielium that lines the perioneal, plural and pericardial cavities and covers the viscera
Where would you mostly find simple cuboidal epithelium?
ducts of glands, more in the small duct.
Also in the pigmented layer of the retina, surface of the ovary and the follicular cells of the thyroid
Where are some common locations of simple columnar epithelium?
gallbladder
epithelium of digestive and uterus
uterine glands
Where would you find pseudostratifed epithelium?
found in the lining of the respiratory system and in the excretory ducts of the male reproductive system.
where would you find stratified squamous cells?
found where protection and transport are required, GI tract, vagina, and skin
where would you find transitional epithelium?
lines the walls of the urinary tract
what is the difference between exocrine and endocrine glands?
Exocrine - external secretion onto body surfaces or into body cavities
Endocrine - secrete hormones to target organs
How are exocrine glands classified?
unicellular or multicellular
unicellular goblet cells are scattered within epithelial lining of intestines and respiratory tubes
what are some examples of exocrine gland products?
sweat glands of skin oil glands of skin salivary glands of mouth liver pancreas mammary glands
What are the three epithelial surface features?
- Lateral - adhesion proteins, tongue
- Basal - basal lamina
- Apical
Describe the structure and functions of the five main types of cell junctions.
- Tight junctions
- inhibit the passage of substances between cells and prevent the contents of these leaking out into blood or tissue - Adherens junctions
- contain plaque which attaches to membrane proteins and to microfilaments. Cadherins join the cells. Adherin junctions help epithelial surfaces resist separation during contractile activities - Desmosomes
- this plaque attaches to intermediate filaments which contributes to the stability of cells and prevent epidermal cells from separating under tension - Gap junctions
- connexins form connexons connect neighbouring cells. Allows communication between cells. - Hemidesmosomes
- do not link adjacent cells and integrins attach to IFs and therefore hemidesmosomes anchor cells to the basement membrane
What are the major differences between epithelial and connective tissue?
- Number of cells - epithelial tissue contains tightly packed cells with little or no extracellular matrix. In connective tissue there is a large amount of ECM.
- Epithelial tissue has no blood vessels, whereas connective has a vast network of blood vessels.
- Epi forms surface layers and arent covered by another layer of tissue.
Because of 2 & 3 epi tissue is always found adjacent to connective tissue which enables exchange with blood.
what are the two forms of epithelium?
- covering and lining
2. glandular epithelium
