Membranes in Human Anatomy

Membranes are thin sheets or layers of tissue that cover structures or line cavities.
Two major categories of membranes:
- Mucous membranes: Comprised of epithelium and connective tissue (CT), lining cavities open to the body's exterior (e.g., digestive, respiratory).
- Serous membranes: Also consist of epithelium and CT, but line cavities not open to the exterior (e.g., pleural, peritoneal membranes).
Other types of membranes include cutaneous (skin), synovial (joint cavities), and periosteum (surrounding bones).

Five major symptoms include:
- Redness
- Heat
- Swelling
- Pain
- Disturbance of function
Inflammatory mediators:
- Histamine
- Kinins
- Prostaglandins
- Leukotrienes
Inflammation process:
- Damage from a splinter introduces bacteria and triggers mediator release.
- Capillaries dilate, causing redness, and increase permeability, leading to edema (swelling).
- White blood cells (WBCs) migrate to the infection site to phagocytize bacteria and debris.

Initial stage: Fresh wounds disrupt the epidermis and dermis, leading to clot formation.
Approximately one week post-injury: A scab forms, and new epidermis begins to regenerate.
By two weeks: The epithelium fully covers the wound; fibroblasts generate granulation tissue.
One month later: The wound closes completely; scab sloughs off, and granulation tissue is replaced by new CT.

Attaches skin to underlying structures (bone/muscle).
Supplies skin with blood vessels and nerves.
Composed mainly of loose connective and adipose tissue, containing half of the body’s fat reserves.

Dermis: Strong and flexible connective tissue, containing collagen, elastic fibers, and various structures like sweat glands and hair follicles.
- Thicker than the epidermis (10-20 times).
- Papillary layer: Contains Meissner’s corpuscles, dermal papillae supplying the epidermis.
- Reticular layer: Dense connective tissue with collagen bundles, forming lines of cleavage.

Made of stratified squamous epithelium.
Upper layers are dead and keratinized; lower layers contain living cells.
Replaced every 35-45 days, serving as a barrier against water loss and abrasion.

Stratum basale: Deepest layer; actively dividing and nourished by diffusion.
Stratum spinosum: Several layers thick; contains spinelike projections.
Stratum granulosum: Thin layer; keratinization begins as cells die and flatten.
Stratum lucidum: Translucent, only in thick skin (palms and soles).
Stratum corneum: Thickest layer, composed of dead keratin-filled cells, providing water resistance.

Melanin: Group of pigments responsible for skin color; protects against UV radiation.
Carotene: Yellow pigment accumulating in skin, giving a slight yellowish tint.
Hemoglobin: Contributes to skin color through blood circulation.

Hair: Covers most of the body; composed of shaft, follicle, root, and papillae.
Hair color: Determined by melanin content; texture influenced by cross-sectional shape.
Nails: Made of tightly packed keratinized cells; important for grasping and protection.
Sebaceous glands: Produce sebum to prevent drying; usually linked to hair follicles.
Sweat glands: Include:
- Eccrine glands: Common, found throughout the body, especially palms and soles.
- Apocrine glands: Found in specific areas (axillae, genitalia) and linked to hair follicles.
Modified glands:
- Mammary glands (produce milk).
- Ceruminous glands (produce earwax).

Allergies: Contact dermatitis as an allergic response.
Infections: Can be viral (herpes, measles), fungal (ringworm), or bacterial (impetigo).
Genetic diseases: Psoriasis leads to dry, scaly skin; increased skin cell production.
Burns:
- 1st degree: Affects only the epidermis, causing redness.
- 2nd degree: Affects epidermis and part of dermis, causing blisters.
- 3rd degree: Destroys all skin layers, possible skin grafting required.
Skin Cancer:
- Basal cell carcinoma: Common and least malignant.
- Squamous cell carcinoma: Cancer from the cells in the stratum spinosum; induced by sun exposure.
- Malignant melanoma: Dangerous cancer originating from melanocytes.