Skin and Body Membranes: Structure, Function, and Clinical Relevance

Skin and Body Membranes

Classification of Body Membranes

Body membranes are essential structures that cover and protect surfaces, line cavities, and anchor organs within the body. They also secrete fluids that reduce friction during movement.

• Protect body surface

• Line body cavities

• Cover inner surfaces of hollow organs

• Act as anchors

• Cover internal organs

• Secrete lubricating fluids to reduce friction

There are two major types of body membranes:

1. Epithelial membranes

2. Connective tissue membranes

Epithelial Membranes

Epithelial membranes are classified based on their location and function:

• Cutaneous Membranes: The skin, covering the body surface.

• Mucous Membranes: Line body cavities that open to the exterior (e.g., digestive, respiratory tracts).

• Serous Membranes: Line body cavities closed to the exterior. These have two layers:

  • Parietal layer: Lines cavity walls

  • Visceral layer: Covers organs (viscera)

Serous Fluid and Membranes

Serous fluid is secreted between parietal and visceral layers to reduce friction.

• Parietal peritoneum

• Visceral peritoneum

• Parietal pleura

• Visceral pleura

• Parietal pericardium

• Visceral pericardium

Connective Tissue Membranes

Connective tissue membranes include synovial membranes, which line fibrous capsules surrounding joints and secrete lubricating fluid.

• Synovial membranes: Found in joints, line bursae, and tendon sheaths

Integumentary System

The integumentary system consists of the skin, hair, nails, sweat glands, and oil glands. It serves as the body's first line of defense and helps regulate water loss.

• Keratin: A protein that hardens skin and prevents water loss

Structure of the Skin

Layers of the Skin

The skin is composed of three main layers, each with distinct functions:

1. Epidermis

   • a. Stratum corneum – tough, horny outer layer

   • b. Stratum lucidum (not present in thin skin) – clear layer

   • c. Stratum granulosum – granular layer

   • d. Stratum spinosum – spiny layer

   • e. Stratum basale (germinativum) – base layer

2. Dermis

   • a. Papillary layer

   • b. Reticular layer

3. Hypodermis (subcutaneous layer)

Skin Color

Skin color is determined by several pigments:

• Melanin – brown pigment

• Carotene – orangish pigment

• Erythema – redness

• Pallor – blanching

• Cyanosis – blue coloration due to poor oxygen levels

• Jaundice – yellowish tint

• Bruises (hematoma) – clotted blood mass

Homeostatic Imbalance: Decubitus Ulcer

Decubitus ulcer (pressure sore) occurs when prolonged pressure reduces blood flow to the skin, causing tissue damage.

Cutaneous Glands

Exocrine Glands

Exocrine glands in the skin include:

• Sebaceous glands (oil glands) – secrete sebum

• Sudoriferous glands (sweat glands) – about 2.5 million in the body

  • Eccrine glands – found everywhere, produce sweat

  • Apocrine glands – secrete fatty acids and proteins (found in armpit and genital areas)

Hair and Nails

• Hair: Contains keratin; arrector pili muscle causes hair to stand up

• Nails: The lunula (Latin for "little moon") is the crescent-shaped area at the base of the nail

Burns and Skin Injury

Degrees of Burns

Burns are classified by depth and severity:

• 1st Degree Burn – superficial; redness

• 2nd Degree Burn – partial thickness; blisters

• 3rd Degree Burn – full thickness; skin does not heal by itself, may require skin graft

• 4th Degree Burn – extends deeper into bone, muscle, or tendons; may require surgery or amputation

Rule of Nines

The Rule of Nines is used to estimate the percentage of body surface area affected by burns.

Infections, Allergies, and Skin Disorders

• Athlete's foot – fungal infection (Tinea pedis)

• Boils, carbuncles – bacterial infection (often Staphylococcus aureus)

• Cold sores – herpes simplex virus

• Contact dermatitis – allergic response

• Impetigo – bacterial infection (Staphylococcus)

• Psoriasis – autoimmune disorder

• Wart – viral infection

• Ringworm – fungal infection

Skin Cancer

Skin cancer is the most common type of human cancer. Types include:

• Basal Cell Carcinoma – most common

• Squamous Cell Carcinoma

• Malignant Melanoma

ABCDE rule for melanoma detection:

• A – Asymmetry

• B – Border irregularity

• C – Color

• D – Diameter

• E – Evolution

Developmental Aspects of Skin Membranes

• Lanugo – downy hair in newborn infant

• Vernix – white covering on newborn infant

• Milila – white spots on infant

• Alopecia – baldness

Homeostatic Imbalance

• 4.1 Melanin, skin cancer

• 4.2 Decubitus Ulcer

• 4.3 Cyanosis

• 4.4 Acne, Blackhead, Whitehead, Seborrhea (Cradle Cap)

• 4.5 Hair loss

Table: Types of Epithelial Membranes

Type	Location	Function
Cutaneous	Skin (external body surface)	Protection, prevents water loss
Mucous	Lines cavities open to exterior (e.g., digestive, respiratory tracts)	Secretion, absorption, protection
Serous	Lines closed body cavities (e.g., thoracic, abdominal)	Reduces friction between organs

Additional info:

• Figures referenced (e.g., skin micrograph, structure of nail, Rule of Nines) are important for visual understanding but not included in these notes.

• Keratin is a fibrous structural protein found in skin, hair, and nails.

• Homeostatic imbalances can manifest as skin color changes, ulcers, or abnormal growths.