4 tissue types
- Epithelium
- Muscle
- Nerve
- Connective tissue
epithelium
A sheet of cells that line all body surfaces, cavities and tubular organs
How do epithelial layers get nutrients
Through diffusion, because they are avascular
Where does epithelium come from
Arises from all 3 embryonic germ layers (ectoderm, endoderm, and mesoderm)
5 Characteristics of epithelium
- Arises from embryonic germ layers
- Comprised of tightly packed cells
- Avascular
- All require renewal and are capable of regeneration and repair
- Epithelial sheets are polarized
Epithelial apical surface
exposed to the external environment
Epithelial basal surface
Lies on a supporting connective tissue which is separated from the epithelium by a basement membrane.
Basement membrane
Consists of specialized collagenous fibers (basal lamina) and other adhesive molecules (laminin).
-Visible under light microscopy
Basal lamina
Anchors the epithelial sheet to the underlying tissue. Only visible with electron microscopy
Epithelial cell types
- Simple (single layer of cells)
- Stratified (Comprised of 2 or more layers of cells. Top layer defines epithelium)
Simple cells
- Simple Squamous
- Simple cuboidal
- Simple columnar
- Pseudostratified columnar
Simple squamous
Cells are flat. Gases and liquids can diffuse easily. Line most internal surfaces
3 types of simple squamous
- Endothelium (line blood vessels, lymphatics, and the heart
- Mesothelium (Line serous body cavities and outer tubular organs in the abdomen)
- Epithelium-no special name (Line small tubules in the kidney
Simple cuboidal
Width and height of cells are equal. Line small ducts
Simple columnar
Height of cells is greater than width. Line much of the GI tract and have secretory and absorptive capability
Pseudostratified columnar
Cells are columnar.
- All cells touch the basal lamina, but not all cells reach the lumen
- Found where particulate matter is moved (reproductive and respiratory tracts) usually have cilia
Stratified epithelium
Comprised of 2 or more layers of cells. Top layer defines the epithelium
3 types of stratified epithelium
- Stratified squamous
- Stratified cuboidal and columnar
- Transitional
Stratified squamous
Surface cells are squamous, cells of other layers are polyhedral (usually serves a protective role).
2 Types of stratified squamous
- Keritinized (dry, cornified); Surface cells synthesize keratin; a cytoplasmic protein that is abrasion resistant (skin)
- Non-keratinized (wet); Surface cells are viable (esophagus)
Stratified cuboidal and columnar
Surface layer defined as cuboidal or columnar. Other cells vary in shape. Line large ducts
Transitional
Layered epithelium that changes appearance (between cuboidal and columnar) depending upon its state of distension. Cells appear (poofy when relaxed. Usually just found in the bladder
7 functions of the epitheilium
- Protection (Skin)
- Secretion (exocrine glands)
- Absorption (intestines)
- Excretion (kidney tubules)
- Sensation (taste buds)
- Transportation (trachea)
- Reproduction (testes)
4 types of connective tissues
- Blood
- Supportive Connective Tissue (cartilage and bone)
- Adipose Tissue
- Connective tissue proper
