chapter 5 easy notes

Chapter 5

The integumentary system is crucial for maintaining various life-sustaining functions and consists of two main layers of skin, the epidermis and dermis, along with the hypodermis beneath them.

Layers of the Skin

  • Epidermis: The superficial, thinner layer composed primarily of keratinocytes; provides a barrier to the external environment.

  • Dermis: Located beneath the epidermis, made of connective tissue that contains blood vessels, nerves, and other structures.

  • Hypodermis (subcutaneous layer): Not part of the skin itself; consists of areolar and adipose tissue, serving as insulation and cushioning.

Cells of the Epidermis

  1. Keratinocytes: Produce keratin, the primary protein in the skin.

  2. Melanocytes: Produce melanin, the pigment responsible for skin color.

  3. Langerhans cells: Involved in the immune response.

  4. Merkel cells: Function in the sensation of touch.

Layers of the Epidermis

  • Stratum Basale: Deepest layer, where cell division occurs.

  • Stratum Spinosum: Contains several layers of keratinocytes.

  • Stratum Granulosum: Site of keratinization, where cells begin to die.

  • Stratum Lucidum: Present only in thick skin (palms and soles).

  • Stratum Corneum: Outermost layer comprised of dead keratinized cells.

Thick vs. Thin Skin

  • Thick Skin: Has all five layers of epidermis, found on palms and soles, thicker dermis.

  • Thin Skin: Contains only four layers, covering most other body surfaces, with a thinner dermis.

Layers of the Dermis

  • Papillary Region: Upper layer, areolar connective tissue; contains dermal papillae and capillaries.

  • Reticular Region: Deeper layer, dense irregular connective tissue; contains hair follicles, sebaceous glands, and sweat glands.

Diseases of the Skin

Common conditions include:

  • Albinism: Lack of melanin production.

  • Vitiligo: Loss of melanocytes leading to skin patches.

  • Skin cancers: such as basal cell carcinoma, squamous cell carcinoma, and malignant melanoma.

Hair Structure

  • Shaft: The visible part of hair.

  • Root: Below the surface, embedded in the follicle.

  • Follicle: The sheath that surrounds the root, includes dermal and epithelial root sheaths.

Hair Growth Stages

  1. Growth stage – cells of matrix divide

  2. Regression stage – hair moves away from blood supply in papillary and follicle atrophies

  3. Resting stage – old hair root falls out; new growth begins

Types of Hair

  • Lanugo: Fine, soft hair on fetuses.

  • Vellus: Short, fine hair (peach fuzz).

  • Terminal Hair: Thick, dark hair in certain areas after puberty.

Hair and Skin Color

Hair and skin color are determined by the amount and type of melanin produced:

  • Eumelanin: Brown/black pigment.

  • Pheomelanin: Yellow/red pigment.

  • Carotene and hemoglobin also affect pigmentation.

Skin Glands

  • Sebaceous (oil) glands: Produce sebum to lubricate skin.

  • Eccrine sweat glands: Assist in thermoregulation.

  • Apocrine sweat glands: Produce sweat in response to stress and hormonal changes.

  • Ceruminous glands: Produce earwax.

Nails

Structure includes:

  • Nail body: Visible part of the nail.

  • Nail root: Buried in the skin, site of growth.

  • Eponychium: Overlaps the nail root, protecting it.

Functions of the Skin

  • •  Thermoregulation: Regulates body temperature through sweat and blood flow.

    •  Blood Reservoir: Stores a significant amount of blood, which can be diverted when necessary.

    •  Protection: Acts as a barrier to pathogens and physical injury.

    •  Cutaneous Sensations: Contains nerve endings that provide sensations of touch, temperature, and pain.

    •  Excretion and Absorption: Helps in the excretion of waste products and the absorption of certain substances.

    •  Synthesis of Vitamin D: Crucial for calcium absorption, initiated by sunlight exposure on the skin.

Wound Healing

Involves:

  • Inflammatory Phase – clot forms

  • Migratory Phase – clot becomes a scab

  • Proliferative Phase – growth of epithelial cells beneath scab

  • Maturation Phase – scab sloughs off once epidermis restored

    Development of the Epidermis and Dermis

  • Epidermis: Develops from the ectoderm during embryonic development.

  • Dermis: Develops from mesoderm, primarily composed of mesenchyme.

Aging in Skin

Aging leads to:

  • Wrinkles

  • Dehydration and cracking

  • Sweat production decreases

  • The numbers of functional melanocytes decrease which results in gray hair and atypical skin pigmentation

  • Subcutaneous fat is lost and skin thickness decreases

  • Nails may become more brittle