Chapter 5 - The Integumentary System

Describe the functions of skin

Skin is first and foremost a barrier

1. Protection

2. Body temperature regulation

3. Cutaneous sensation

4. Metabolic functions

5. Blood reservoir

6. Excretion

List the two layers of skin

1. Epidermis

   • Epithelial cells, outermost layer

2. Dermis

   • Bulk of skin; tough and leathery layer, mostly dense connective tissue

Resting on Subcutaneous tissue

Define the Epidermis

• Superficial layer of the skin

• Keratinized sheet of stratified squamous epithelium

• Avascular but innervated

Epidermis - Layers

1. Stratum corneum (Horny Layer)

   • Most superficial

   • 20-30 layers of dead cells

2. Stratum lucidum (Clear Layer)

   • Only in thick skin

   • Few rows of flat, dead keratinocytes identical to stratum corneum

3. Stratum granulosum (Granular Layer)

   • 1-5 layers of flattened cells, organelles deteriorating; keratinocytes that are undergoing keratinization

     1. Keratohylaine granules → help to form keratin in the upper layers by providing the “glue” that binds pre-keratin intermediate filaments together to form keratin

     2. Lamellar granules → contain a water-resistant glycolipid that is secreted into the extracellular space

4. Stratum spinosum (Prickly Layer)

   • Several layers of keratinocytes unified by desmosomes

5. Stratum basale (Basal Layer)

   • Deepest layer

   • Single row of actively mitotic stem cells

Epidermis - Cell Types & Functions

1. Keratinocytes

   • LOCATION: Predominat cells of the epidermis → Stratum basale (deepest part of the epidermis)

   • DESCRIPTION: Tightly connected by demosomes

     • Millions slough off every day

   • FUNCTION:Produce keratin (protein that gives skin its protective properties)

2. Melanocytes

   • LOCATION: Stratum basale (deepest part of the epidermis

   • DESCRIPTION:Spider-shaped cells located in deepest epidermis

     • Melanosomes are transferred to keratinocytes, where they protect the nucleus from UV damage

   • FUNCTION: Produce pigment melanin, which is packaged into melanosomes

3. Dendritic (Langerhans) cells

   • LOCATION: Arise from bone marrow and migrate to the epidermis

   • DESCRIPTION: Star-shaped macrophages that patrol deep epidermis

   • FUNCTION: key activators of immune system

4. Tactile (Merkel) cells

   • DESCRIPTION: Spiky, hemi-spheral epidermal cells

   • LOCATION: Epidermal-dermal junction

   • FUNCTION: Sensory receptors that sense touch; associated with free nerve endings

Define Dermis

• Layer of skin deep to the epidermis

• Composed mostly of dense irregular connective tissue

• Strong, flexible connective tissue

• Cells include fibroblasts, macrophages, and occasionally mast cells and white blood cells

• Fibers in matrix bind body together

  • Makes up the “hide” that is used to make leather

Dermis - Layers

1. Papillary dermis

   • Thin, superficial layer

   • Areolar connective tissue with interlacing collagen and elastic fibers

   • Many small blood vessels

2. Reticular Layer

   • Deeper layer; Makes up ~80% of dermal thickness

   • Dense irregular connective tissue

     • Many elastic fibers provide stretch-recoil properties

     • Collagen fibers provide strength and resiliency

   • Bind water, keep skin hydrated

Dermis - Function

1. Dense irregular connective tissue

2. Supplied with:

   • Blood vessels

   • Lymphatic vessels

3. Reside within the derms:

   • Epidermal hair follicles

   • Oil glands

   • Sweat glands

Define Sweat Glands

• Also called sudoriferous glands

• FUNCTION: Epidermal gland that produces sweat

• LOCATION: All skin surfaces except nipples and parts of external genitalia contain sweat glands

  • About 3 million per person

Compare and contrast eccrine and apocrine glands

Define Sebaceous (oil) Glands

• LOCATION: Widely distributed, EXCEPT for thick skin of palms and soles

  • Most develop from hair follicles and secrete into hair follicles

  • Relatively inactive until puberty

    • Stimulated by hormones, especially androgens

• FUNCTION: Epidermal glands that produce an oily secretion called sebum

Define Sebum

• STRUCTURE: Oily holocrine secretion

  • Bactericidal (bacteria-killing) properites

• FUNCTION: Softens hair and skin

  • Increase their activity during puberty and are controlled by androgens.

What can influence skin color?

Skin color reflects the amount of pigments (melanin and carotene) in the skin and the oxygenation level of hemoglobin in blood

1. Melanin

   • Dark pigment formed by cells called melanocytes

   • Responsible for color to skin and hair

   • Produced in the stratum basale of the epidermis

2. Carotene

   • Yellow to orange pigment that accumulates in the stratum corneum epidermal layer and in fatty tissue of the subcutaneous tissue

3. Hemoglobin

   • Reddish color of red blood cells in blood vessels that can be seen in Caucasian skin due to translucent skin

   • Circulating through the dermal capillaries

Examples how alterations in skin color can indicate disease

1. Cyanosis

   • Blue skin color → low oxygenation of hemoglobin

2. Pollar (blanching or pale color)

   • Anemia, low blood pressure, fear, anger

3. Erythema

   • Fever, hypertension, inflammation, allergy

4. Jaundice (yellow cast)

   • Liver disorders

   • Newborns

5. Bruises (black and blue marks)

   • Also referred to as ecchymoses or hematomas, are a result of clotted blood beneath skin

   • As clot is broken down, color of bruise changes

Disease and ailments that can affect skin color

1. Basal cell carcinoma

   • DESCRIPTION

     • Least malignant and most common

     • Stratum basale cells (epidermis) proliferate and slowly invade dermis and hypodermis

   • TREATMENT

     • Cured by surgical excision in 99% of cases

2. Squamous cell carcinoma

   • DESCRIPTION

     • Second most common type; can metastasize

     • Involves keratinocytes of stratum spinosum (epidermis)

     • Usually is a scaly-reddened papule on scalp, ears, lower lip, or hands

   • TREATMENT

     • Good prognosis if treated by radiation therapy or removed surgically

3. Melanoma

   • DESCRIPTION

     • Cancer of melanocytes

     • Is most dangerous type because it is HIGHLY metastatic and resistant to chemotherapy

   • TREATMENT

     • Treated by wide surgical excision accompanied by immunotherapy

     • Key to survival is early detection