Epithelial Tissue and Cell Biology Lecture

Cellularity: This is the primary characteristic of epithelial tissue, referring to the density of the cells. The tissue is comprised almost entirely of cells with very little extracellular material between them. In a light microscope, epithelial tissue resembles a wall of cells.
Avascularity: Epithelial tissue is characterized by the absence of blood vessels within the tissue itself. The prefix "a-" denotes absence, and "vascular" refers to blood or bleeding. Because it lacks blood vessels, it has no direct blood supply of its own.
High Regenerative Capacity: Epithelial cells are capable of regenerating rapidly to replace lost or damaged tissue.

Cilia: These are hair-like structures used to move substances across the surface of the tissue.
- Cilia are capable of autonomous movement.
- In the respiratory system, cilia filter out dust and help move mucus.
- In the fallopian tubes, cilia facilitate the movement of the egg cell.
- Nasal hairs are explicitly not considered to be cilia.
Stereocilia: Unlike regular cilia, stereocilia do not move by themselves. They require the assistance of surrounding liquids, such as mucus, to move.
Microvillus (Microvilli): These are thin, finger-like projections on the cell surface. Their primary function is to catch and absorb nutrients for the cell.

Tight Junctions, Desmosomes, and Hemidesmosomes: These three structures serve to glue and hold the tissue together.
- Tight Junctions: These are long junctions that are not as tight as desmosomes.
- Desmosomes: These appear very dark under microscopy and are extremely tight, providing strong adhesion between cells.
- Hemidesmosomes: These are also tight but specifically serve to connect the epithelial tissue to the matrix cells, particularly the basal lamina.
Basal and Reticular Lamina: Both layers provide structural support to the tissue.
- Basal Lamina: Located on the top layer of the basement membrane, it specifically supports the epithelial tissue.
- Reticular Lamina: This layer supports and connects the epithelial tissue to the underlying connective tissue.

Sidedness: Polarity refers to the fact that epithelial tissue has specific sides, meaning each side is functionally and structurally different from the others.
Apical Surface: The superficial or top surface that is exposed to the exterior or a body cavity.
Basal Surface: The bottom surface that is attached to the basement membrane.

Nucleus: Known as the brain or control center of the cell.
Mitochondria: The powerhouse of the cell. It converts food into chemical energy known as $ATP$ ( $\text{adenosine triphosphate}$ ), which is required for the cell to perform its functions.
Golgi Apparatus: Operates as the "post office" of the cell. It receives, modifies, and packages lipids and proteins.
Endoplasmic Reticulum (ER): Functions as the "factory" of the cell, producing materials that are then sent to the Golgi apparatus.

Simple Epithelia: Consists of a single layer of cells. Found in organs such as the kidneys and the alveoli (alveolus) of the lungs.
Stratified Epithelia: Consists of more than one layer of cells.
Connective Tissue and Minerals: Tissues such as adipose tissue are included in broader classifications. Calcified matrices within the body contain minerals such as calcium and phosphate.

Pheromones: These are substances produced inside the body that work outside the body to attract other human beings or animals.
Modes of Secretion: Secretion involves the production and release of substances from glands.
- Eccrine/Serous Type: Produces a clear or watery secretion. These glands are located all over the body, notably on the forehead and palms. They are active from birth.
- Apocrine Type: Produces a thick, odorless secretion. However, it develops a bad odor when combined with bacteria. These are located in the axilla (armpit), inward or groin area, and the breasts (specifically in females). Secretion increases during stress or tension, indicating a lack of homeostasis.
- Sebaceous/Oily Type: Produces an oily scent.

Commuting and Traffic: A student traveling from Kolomolok to General Santos (Jenson) arrived late due to traffic. The student has been commuting for this year and has made the trip at least $30$ times. There is a warning to be aware of traffic when traveling desde $6:00\,AM$ .
Visitor and Promotion: A visitor from a dental clinic mentioned a promotion for dental cleaning (pasta) and unlimited family checkups for a unit price of $499\,Pesos$ .
Hygiene Advice: For those dealing with body odor issues related to bacterial interaction with sweat, using products like Betadine (methadine) from a pharmacy is suggested as an alternative to standard deodorant.
Muscle Types: Smooth muscle is identified as the third type of muscle mentioned in the sequence following the discussion on glands.