MD110 Anatomy & Physiology

Chapter 5:  The Integumentary System and Body Membranes

 

I.                    Classification of Body Membranes

A.     Classification of body membranes

1.      Epithelial membranes – composed of epithelial tissue and underlying layers of connective tissue.

2.      Connective tissue membranes – composed largely of various types of connective tissue

B.     Epithelial Membranes

1.      Cutaneous membrane – the skin

2.      Serous membrane – simple squamous epithelium on a connective tissue basement membrane

a.       Types

                                                                                                                                       i.      Perietal – line walls of body cavities

                                                                                                                                     ii.      Visceral – cover organs found in body cavities

b.      Examples

                                                                                                                                       i.      Pleura – parietal and visceral layers line walls of thoracic cavity and cover the lungs.

                                                                                                                                     ii.      Peritoneum – parietal and visceral layers line walls of abdominal cavity and cover organs in that cavity.

c.       Diseases

                                                                                                                                       i.      Pleurisy – inflammation of the serous membranes that line the chest cavity and cover the lungs.

                                                                                                                                     ii.      Peritonitis – inflammation of the serous membranes in the abdominal cavity that line the walls and cover the abdominal organs.

3.      Mucous membranes

a.       Line body surfaces that open directly to the exterior

b.      Produce mucus, a thick secretion that keeps the membranes soft and moist.

C.     Connective tissue membranes

1.      Do not contain epithelial components

2.      Produce a lubricant called synovial fluid

3.      Examples are the synovial membranes in the spaces between joints and in the lining of bursal sacs.

II.                 The Skin

A.     Structure – two primary layers called the epidermis and the dermis

1.      Epidermis

a.       Outermost and thinnest primary layer of skin

b.      Composed of several layers of stratified squamous epithelium.

c.       Stratum germinativum – innermost layer of cells that continually reproduce, and new cells move toward the surface.

d.      As cells approach the surface, they are filled with a tough, waterproof protein called keratin and eventually flake off.

e.       Stratum Corneum – outermost layer of keratin-filled cells.

f.        Pigment-containing layer – epidermal layer that contains brown pigment cells called melanocytes, which produce the brown pigment melanin.

g.       Blisters – caused by breakdown of union between cells or primary layers of skin.

h.       Dermal-epidermal junction – specialized area between two primary skin layers.

2.      Dermis

a.       Deeper and thicker layer of the two primary skin layers and composed largely of connective tissue

b.      Upper area of dermis characterized by parallel rows of peg-like dermal papillae

c.       Ridges and grooves in dermis form pattern unique to each individual (basis of fingerprinting)

d.      Deeper areas of dermis filled with network of tough collagenous and stretchable elastic fibers.

e.       Number of elastic fibers decreases with age and contributes to wrinkle formation

f.        Dermis also contains nerve endings, muscle fibers, hair follicles, sweat and sebaceous glands, and many blood vessels

B.     Appendages of the skin

1.      Hair

a.       Soft hair of fetus and newborn called lanugo

b.      Hair growth requires epidermal tubelike structure called hair follicle

c.       Hair growth begins from hair papilla

d.      Hair root lies hidden in follicle; visible part of hair called shaft.

e.       Alopecia – hair loss

f.        Arrector pili – specialized smooth muscle that produces “goose bumps” and causes hair to stand up straight

2.      Receptors

a.       Specialized nerve endings – make it possible for the skin to act as a sense organ

b.      Meissner’s corpuscle – capable of detecting light touch

c.       Pacinian corpuscle – capable of detecting pressure

3.      Nails

a.       Produced by epidermal cells over terminal ends of fingers and toes

b.      Visible part called nail body

c.       Root lies in a groove and is hidden by cuticle

d.      Crescent-shaped area nearest root called lunula

e.       Nail bed may change color with change in blood flow

4.      Skin glands

a.       Types

                                                                                                                                       i.      Sweat or sudoriferous

                                                                                                                                     ii.      Sebaceous

b.      Sweat of sudoriferous glands

                                                                                                                                       i.      Types

1.      Eccrine sweat glands

a.       Most numerous, important, and wide-spread of the sweat glands.

b.      Produce perspiration or sweat which flows out through pores on skin surface.

c.       Function throughout life and assist in body heat regulation.

2.      Apocrine sweat glands

a.       Found primarily in axilla and around genitalia

b.      Secrete a thicker, milky secretion quite different from eccrine perspiration

c.       Breakdown of secretion by skin bacteria produces odor

3.      Sebaceous glands

a.       Secrete oil or sebum for hair and skin lubrication

b.      Level of secretion increases during adolescence

c.       Amount of secretion regulated by sex hormones

d.      Sebum in sebaceous gland ducts may darken to form a blackhead

e.       Acne Vulgaris – inflammation of sebaceous gland ducts.

C.     Functions of the skin

1.      Protection – first line of defense

a.       Against infection by microbes

b.      Against ultraviolet rays from sun

c.       Against harmful chemicals

d.      Against cuts and tears

2.      Temperature regulation

a.       Skin can release almost 3000 calories of body heat per day.

                                                                                                                                       i.      Mechanisms of temperature regulation

1.      Regulation of sweat secretion

2.      Regulation of flow of blood close to the body surface

3.      Sense organ activity

a.       Skin functions as an enormous sense organ

b.      Receptors serve as receivers for the body, keeping it informed of changes in its environment

III.               Disorders of the skin

A.     Skin Lesions

1.      Elevated lesions – cast a shadow outside their edges

a.       Papule – small, firm, raised lesion

b.      Plaque – large raised lesion

c.       Vesicle – blister

d.      Pustule – pus filled lesion

e.       Crust – scab

f.        Wheal (hive) – raised, firm lesion with a light center

2.      Flat lesions – do not cast a shadow

a.       Macule – flat, discolored region

3.      Depressed lesions – cast a shadow within their edges

a.       Excoriation – missing epidermis as in a scratch wound

b.      Ulcer – crater-like lesion

c.       Fissure – deep crack or break

B.     Burns

1.      Treatment and recovery or survival depend on total burn area involved and severity or depth of the burn.

2.      Estimating body surface area using the “Rule of Nines” in adults

a.       Body divided into 11 areas of 9% each

b.      Additional 1% of body surface area around genitals

3.      Classification of burns

a.       First Degree (partial thickness) Burns – only surface layers of epidermis involved

b.      Second Degree (partial thickness) Burns – involve the deep epidermal layers and always cause injury to the upper layers of the dermis.

c.       Third Degree (Full thickness) Burns – characterized by complete destruction of the epidermis and dermis.

                                                                                                                                       i.      May involve underlying muscle and bone

                                                                                                                                     ii.      Lesion is insensitive to pain because of destruction of nerve endings immediately after injury – intense pain is soon experienced.

C.     Skin infections

1.      infection

2.      Tinea – fungal infection (mycosis) of the skin; several forms occur.

3.      Warts Impetigo – highly contagious staphylococcal – benign neoplasms caused by papillomavirus

4.      Boils – furuncles; staphylococcal infection in hair follicles

D.     Vascular and inflammatory skin disorders

1.      Decubitus ulcers (bedsores) develop when pressure slows down blood flow to areas of the skin.

2.      Urticaria or Hives – red lesions caused by blood loss from blood vessels

3.      Scleroderma – disorder of vessels and connective tissue characterized by hardening of the skin; two types: localized and systemic.

4.      Psoriasis – chronic inflammatory condition accompanied by scaly placques

5.      Eczema – common inflammatory condition characterized by papules, vesicles, and crusts; not a disease itself but a symptom of an underlying condition

E.      Skin Cancer

1.      Three common types

a.       Squamous cell carcinoma – the most common type, characterized by hard raised tumors

b.      Basal cell carcinoma – characterized by papules with a central crater; rarely spreads

c.       Melanoma – malignancy in a nevus (mole); the most serious type

2.      The most important causative factor in common skin cancers is exposure to sunlight

3.      Kaposi sarcoma, characterized by purple lesions, is associated with AIDS and other immune deficiencies.