Epithelial and Connective Tissues Notes

Briefly covered, revisited in muscular, cardiovascular, and nervous system studies.

Cells are densely packed and arranged in sheets.
Numerous junctions to prevent tearing and breakage.
Attached to the basement membrane via hemidesmosomes.
Nerve supply present (sensitive to damage).
Avascular (no blood supply).
Example: Paper cut - painful due to nerve supply, but no bleeding because the cut wasn't deep enough to damage the connective tissues.
Blisters: Damage to epithelial tissue without immediate bleeding.
High mitotic rate (cell division) for continuous renewal and protection against wear and tear.

Classified by cell shape and layer arrangement.
- Simple: One layer.
- Stratified: Multiple layers.
- Pseudostratified: Appears stratified but is a single layer (nuclei at different levels).
Cell Shapes:
- Squamous: Flat, thin cells (like scales).
- Cuboidal: Cube-shaped cells.
- Columnar: Column-shaped (long) cells, found in the intestine where control of substance entry and exit is required.
Combinations: Squamous simple, cuboidal simple, columnar simple, squamous stratified, cuboidal stratified, columnar stratified.

Specialized for secretion.
Endocrine Glands: Secrete substances inside the body (e.g., hormones).
- Example: Thyroid hormone secretion.
Exocrine Glands: Secrete substances outside the body.
- Examples: Sweat glands (water-based secretion), oil glands, milk-based secretion.
- Structure consists of multiple layers with a lumen or duct.
- Examples: Wax glands, digestive glands, salivary glands, pancreas.
Goblet cells: Unicellular glands that secrete mucus.
Exocrine Gland Types:
- Sweat glands
- Oily glands
- Salivary glands
Glandular Epithelium Secretion Types:
- Merocrine Secretion:
  - RNA transcribed in the nucleus.
  - Protein creation and modification via endoplasmic reticulum and Golgi apparatus.
  - Vesicles fuse with the plasma membrane to release secretions (e.g., amylase and lysozyme in saliva).
  - Amylase: Breaks down sugars (starch) in the mouth.
  - Lysozyme: Found in saliva.
- Apocrine Secretion:
  - Vesicles pinch off from the cell, including part of the cell membrane.
  - Example: Milk production (high fat content due to phospholipids and cholesterol from the cell membrane).
- Holocrine Secretion:
  - Cell accumulates vesicles, then the entire cell ruptures and releases its contents (oily secretion).
  - Example: Sebaceous glands in the skin.
  - Underlying cells undergo mitosis to replace lost cells.

Cells scattered in the extracellular matrix.
No free surfaces.
Highly vascularized (except tendons and cartilage).
- Tendon damage requires stitching due to poor vascularization.
- Cartilage damage (e.g., cauliflower ear) results in calcification due to poor blood supply.

Various cell types:
- Adipocytes: Fat storage with nucleus squeezed to the periphery; cushion organs.
- Red blood cells
- Neutrophils
Fibers:
- Elastic Fibers: Made of elastin; allow bending without breaking.
- Collagen Fibers: Most abundant protein; provide strength and prevent tearing.
- Reticular Fibers: Interconnect cells, forming a network to keep cells in place.
Fibroblasts: Secrete fibers and ground substance.
Immune Cells:
- Macrophages: Perform phagocytosis (engulf bacteria, debris, viruses).
- Mast Cells: Release histamine (alarm signal) causing vasodilation, itchiness, and inflammation.
- Plasma Cells: Secrete antibodies.
- Neutrophils: Destroy microbes via phagocytosis.
- Eosinophils: Protect against parasitic infections and are involved in allergic responses.
Ground Substance:
- Water-based substance with organic molecules (e.g., hyaluronic acid, glucosamine).
- Allows substance exchange between blood and cells.
- Can be calcified (e.g., calcium phosphate in bones).