Membranes Overview

Membranes

• Membranes are tissues that cover or line other tissues and organs.
• Four types of membranes:
  • Serous membranes
  • Mucous membranes
  • Cutaneous membranes
  • Synovial membranes

Serous Membranes

• Line body cavities that do not have openings to the outer surface.
• Line the thorax, abdomen, and organs in these cavities.
• Made of simple squamous epithelium (mesothelium) over loose connective tissue.
• Secrete serous fluid for lubrication to allow smooth movement of organs.
• Examples: Pleura (lines the thoracic wall and lungs), Pericardium (encloses the heart), and Peritoneum (lines the abdominopelvic cavity and organs).

Mucous Membranes

• Line cavities and tubes that open to the outside.
• Specialized cells (e.g., goblet cells) secrete mucus for lubrication and protection.
• Found in nose, mouth, digestive tract, respiratory tract, urinary, and reproductive systems.
• Consist of various types of epithelium over connective tissue (lamina propria).

Synovial Membranes

• Form the inner lining of synovial joints.
• Composed of fibrous connective tissue over loose connective tissue and adipose tissue.
• Secrete synovial fluid for lubrication and cushioning.

Cutaneous Membrane

• Skin, a dry membrane with multiple functions.

Skin Functions

• Protection from dehydration and foreign substances
• Contains sensory receptors
• Regulates body temperature
• Synthesizes vitamins and excretes substances

Skin Layers

• Epidermis (outer layer, stratified squamous epithelium)
• Dermis (deep layer, many different tissues—connective tissue, epithelial, smooth muscle, nerves)
• Basement membrane (connects epidermis to dermis)
• Subcutaneous layer / Hypodermis (loose connective tissues - not part of skin)

Cells of the Epidermis

• Keratinocytes (most abundant, produce keratin protein)
• Melanocytes (produce melanin, pigment)
• Merkel cells (sensory receptors for touch)
• Langerhans cells (macrophages)

Epidermal Layers (deep to superficial)

• Stratum Corneum (dead, outermost layer)
• Stratum Lucidum (clear layer, only in thick skin)
• Stratum Granulosum (granular layer, keratinocytes toughen)
• Stratum Spinosum (spiny layer, several cell layers)
• Stratum Basale (deepest layer, actively dividing cells)

Callus and Bedsores

• Callus: thickening of epidermis due to persistent friction
• Bedsores (pressure ulcers): pressure reduces blood flow, causing tissues to break down

Melanocytes

• Specialized cells in the epidermis that produce melanin.
• Melanin protects the body cells from UV sunlight.
• Melanin accumulates to shield from harmful UV radiation.
• Determines skin color.

Accessory Organs of Skin

• Hair follicles
• Sebaceous glands (produce sebum)
• Sweat glands (produce sweat)
• Nails

Skin Color

• Melanin (produced by melanocytes)
• Carotene (yellow-orange pigment from certain foods)
• Hemoglobin (pinkish hue from red blood cells)
• Excess exposure to the sun can result in problems (e.g., skin cancer, etc.)

Burns

• First-degree burns: damage to epidermis only, heals in 2-3 days.
• Second-degree burns: damage to epidermis and portions of upper dermis, heals within 2-3 weeks.
• Third-degree burns: damage to all skin layers, including hypodermis, and nerves, usually requires skin grafts.

Explore the four types of membranes that line and cover the tissues and organs in the body. This quiz will examine the characteristics and functions of serous and mucous membranes, detailing their locations and types of cells involved. Test your knowledge on the essential roles these membranes play in bodily functions.