Epithelial Tissue
Epithelial Tissue – all over the body, covers the body’s organs and all surfaces.Key component of Epithelial Tissue – Basement Membrane – anchors epithelial tissue. It shows up as a dark line or boundary. Epithelial tissue general characteristics:
- Tightly packed cells
- Little intra cellular material or matrix
- Lack blood vessels
- Usually in areas of high cellular turnover and replaced frequently
- Functions can include protection, secretion, absorption, excretion and sensory reception
Principles of identifying Epithelium:
1. Find the Basement Membrane
2. What is the shape of the cell directly above the basement membrane (flattened or round sac, cube, column, or something else?
3. How many layers?
Simple Squamous Epithelium
Identification: 1. Thin flattened sacs, 2. Single Layer
Role: Diffusion – thin structure allows for easy transport across cell. Gas exchange in lungs and blood vessels. Lines many cavities that are associated with exchange.
Simple Cuboidal Epithelium
Identification: 1. Cubes with centrally located nuclei, 2. Single Layer
Role: Secretion glands and kidneys. Also absorption in kidneys.
Simple Columnar Epithelium
Identification: 1. Columns with nuclei lined up near the basement membrane, 2. Single layer.
Role: Protection of underlying tissues in the uterus, stomach, and intestines. Secretes digestive fluids and can absorb nutrients.
Bigger cells allow for more protection of a single layer cell. Balance of absorption and protection. Cells can be ciliated. In the intestines cells have microvilli. Microvilli increases surface area for absorption. Some columnar cells contain goblet cells, which secrete mucus.
Pseudostratified Columnar Epithelium
Identification: 1. Something else shaped cells, 2. One layer. This epithelium can look like other layers, but key identification reveals nuclei at various positions but no true layers.
Role: Protect respiratory tubes. Line the respiratory tubes and sweeps away debris with help of cilia and goblet cells.
Stratified Squamous Epithelium
Identification: 1. Round sacs. 2. Many, many layers. The cells become flattened and dead like further away from basement membrane.
Role: Protection! Especially areas with abrasion, such as skin, mouth, throat, vagina, and anal canal. May undergo keratinization – process of cells hardening which increases protective value. Only occurs where tissue can dry out, such as the skin. Not moist areas.
Stratified Cuboidal Epithelium
Identification: 1. Cube shaped, 2. Two to three layers.
Role: Secretion. Mammary glands, sweat, glands, and pancreas. More cells for secreting products and level of protection.
Stratified Columnar Epithelium
Identification: 1. Columns, 2. Several layers.
Role: In vas deferens, male urethra, and part of the pharynx.
Transitional Epithelium
Identification: 1. Something else shaped. Can be tear shaped or stretched like, 2. Several layers.
Role: Urinary bladder – changes shape when stretch to accommodate – distensibility. Keeps urine from going into internal cavity. Looks different when stretched compared to empty.
Glandular Epithelium
Role: Produce and secrete substances.
Types
1.Exocrine – Secrete into ducts –
2. Endocrine – Secrete into body fluids –
Classified based on the way they release products.
Merocrine Glands – Exocytosis -Fluid products. (Ex pancreas)
Two types: Serous – watery, Mucus – Thicker and more protective.
Apocrine Glands – Release small chunks or portions of cell with secretion (Ex. Mammary gland)
Holocrine Glands – Release entire cell (whole thing breaks apart and is released with products Ex. sebaceous (oil) glands).