Chapter 1: Introduction to Connective Tissue and Membranes

Connective tissue is foundational and consists of layers lining body cavities and covering viscera (organs) and external surfaces.

Four main types of membranes:
- Mucous membranes (often associated with the nose and mouth).
- Coverage: Lines body cavities that open to the exterior.
- Contains: Lamina propria, mucus from goblet cells.
- Serous membranes
- Lines cavities not open to the outside.
- Contains: Simple squamous epithelium producing serous fluid for lubrication.
- Example: Visceral layers in contact with organs (e.g., surrounding heart and lungs).
- Visceral vs. Parietal layers: Visceral is in contact with the organ, while parietal is on the outer connection.
- Cutaneous membrane (skin) - Keratinized stratified squamous epithelium.
- Synovial membranes - Associated with joints producing synovial fluid for lubrication.

Fertilization starts with sperm fertilizing the ovum, forming a diploid cell (zygote).
Mitosis: General cell division involved in growth and repair.
Three embryonic layers formed:
- Ectoderm: Develops into skin, hair, nails, and nervous tissue.
- Mesoderm: Forms muscle, bone, and connective tissues.
- Endoderm: Forms internal organs.

Hypertrophy: Increase in size of existing cells or tissues (cells become larger, not more numerous).
Hyperplasia: Increase in the number of cells in a tissue.
Atrophy: Decrease in cell size and number, often due to aging or inactivity.
Metaplasia: Change of tissue type, e.g. smokers experience changes in airway epithelium.
Dysplasia: Abnormal tissue development; may be precancerous (e.g. cervical dysplasia).
Neoplasia: Out-of-control growth of tissue; can be benign or malignant (cancer).
Necrosis: Irreversible tissue death, often associated with inflammation (e.g. gangrene).

Tissue changes with age; includes decreased collagen and elastin, thickening of membranes, and hair loss.
Importance of good nutrition and maintaining activity to promote healthy tissue and prevent atrophy.

Largest organ of the body, composed of all tissue types:
- Epidermis: Stratified squamous epithelium.
- Dermis: Connective tissues, containing structures like glands, blood vessels, and nerves.
- Subcutaneous layer (hypodermis): Composed of areolar and adipose tissue, not part of the skin but supports it.

Stratum Basale: Deepest layer, site of mitosis producing keratinocytes, contains melanocytes (pigment cells) and tactile cells (Merkel cells).
Stratum Spinosum: Living keratinocytes, contains Langerhans cells (immune response).
Stratum Granulosum: Begins keratinization; cells start to die as they fill with keratin.
Stratum Lucidum: Only in thick skin (e.g. palms, soles); protects against friction.
Stratum Corneum: Outermost layer; dead keratinized cells; protective barrier to infection.

Superior to subcutaneous; contains:
- Papillary Layer: Thin, upper part with dermal papillae increasing surface area contact with epidermis.
- Reticular Layer: Dense connective tissue, deeper layer housing sweat and sebaceous glands, hair follicles, and blood vessels.

Skin color is determined by:
- Melanin level: Produced by melanocytes, absorbing UV light.
- Carotene: Yellow-orange pigment from vegetables (e.g., carrots).
- Hemoglobin: Confers red color upon binding with oxygen.

Sebaceous glands: Produce oil; connected to hair follicles.
Sweat glands:
- Merocrine glands: Most common; produce regular sweat for thermoregulation.
- Apocrine glands: Associated with hair follicles, activated during stress; secretes pheromones.

Grows from follicles; includes:
- Root: Underneath skin.
- Bulb: Contains living cells.
- Follicle: Surrounds the hair root.
Types of hair: Lanugo (fetal), Vellous (fine, soft hair), Terminal (thicker, pigmented).