04 tissue level/historgy

Superior vs Inferior
- Superior: Toward the head (e.g., head superior to feet).
- Inferior: Toward the feet (e.g., feet inferior to head).
Proximal vs Distal
- Proximal: Closer to the center of the body (e.g., hips are proximal).
- Distal: Further from the center of the body (e.g., fingers distal to the wrist).
Basal vs Superficial
- Basal: Refers to the bottom or lower part.
- Superficial: Refers to structures closer to the surface (e.g., skin is superficial to underlying tissues).

Hierarchical Organization of Biological Systems
- Chemical: Atoms and molecules.
- Cellular: Cells, the basic unit of life.
- Tissue: Groups of similar cells working together.
- Organ: Different tissues forming a functional unit.
- Organ System: Groups of organs working together.
- Organism: A living individual.

Four Primary Types of Tissues
1. Epithelial Tissue
  - Covers body surfaces and lines cavities.
  - Functions include protection, absorption, secretion, and sensation.
  - Varieties include simple and stratified (e.g., simple squamous, stratified cuboidal).
2. Connective Tissue
  - Supports and binds other tissues.
  - Types include loose connective, dense connective (regular and irregular), cartilage, bone, and blood.
  - Functions include support, insulation, transportation, and storage.
3. Muscle Tissue
  - Responsible for movement.
  - Types include skeletal (voluntary), smooth (involuntary), and cardiac (involuntary, striated).
4. Nervous Tissue
  - Composed of neurons and glial cells.
  - Functions in signaling and controlling bodily functions.

Common Features
- Composed of closely packed cells with minimal extracellular matrix.
- Exhibits polarity (apical and basal surfaces).
- Avascular (lacks blood vessels); nutrients via diffusion from underlying tissues.
- High regenerative capacity (rapidly replace lost cells).
Types of Epithelial Tissue
1. Simple Epithelium
  - Simple Squamous: Thin, allows diffusion (e.g., alveoli, blood vessels).
  - Simple Cuboidal: Secretion and absorption (e.g., kidney tubules).
  - Simple Columnar: Absorption and secretion (e.g., digestive tract).
2. Stratified Epithelium
  - Stratified Squamous: Protects against abrasion (e.g., skin, esophagus).
3. Pseudostratified Columnar: Appears stratified but is a single layer (e.g., trachea).
4. Transitional: Allows stretching (e.g., bladder).

Connective Tissue Functions
- Provides support and structure for body organs.
- Stores energy (e.g., adipose tissue).
- Connects different tissues and organs.
- Transports substances (e.g., blood).
Types of Connective Tissue
1. Loose Connective Tissue
  - Areolar: Flexible, found under epithelial tissues.
  - Adipose: Stores energy, provides insulation.
  - Reticular: Forms supporting framework for organs.
2. Dense Connective Tissue
  - Dense Regular: Parallel collagen fibers (e.g., tendons).
  - Dense Irregular: Random arrangement (e.g., dermis, joint capsules).
3. Cartilage
  - Hyaline: Smooth, covers joints (e.g., articular surfaces).
  - Fibrocartilage: Tough, provides support (e.g., intervertebral discs).
  - Elastic: Flexible (e.g., ear, epiglottis).
4. Bone
  - Compact and Spongy Bone: Provides structure, stores minerals.
5. Blood
  - Transports gases, nutrients, and waste products.

Types of Muscle Tissue
1. Skeletal Muscle
  - Voluntary, striated, multinucleated.
  - Facilitates movement; attached to bones.
2. Smooth Muscle
  - Involuntary, non-striated, single nucleus.
  - Found in walls of hollow organs (e.g., blood vessels, intestines).
3. Cardiac Muscle
  - Involuntary, striated, branched, single nucleus.
  - Found only in the heart; responsible for pumping blood.

Components of Nervous Tissue
- Neurons: Transmit signals through electrical impulses.
- Glial Cells: Supportive cells that protect and nourish neurons.

Types of Cell Junctions
1. Tight Junctions: Prevent leakage between cells (e.g., intestinal epithelium).
2. Gap Junctions: Allow communication between cells (e.g., cardiac muscle).
3. Desmosomes: Provide structural support and strength to tissues (e.g., skin).