MEDI 101 integumentary system (week 4)

integumentary system

• consists of skin and accessory structures

• functions: protection, sensation, temperature regulation, vitamin D production, excretion of wastes

skin

• largest organ

• Accounts for 7% of bodyweight

• Divided into two distinct layers (epidermis and dermis)

• Hypodermis– lies deep to the dermis

stratum basale

• or stratum germinativum

• mitotic layer

• The deepest layer of the epidermis

• Attached to the underlying dermis

• Cells actively divide

• Stem cells that undergo mitosis to form keratinocytes which form the more superficial layers of epidermis

• Contain also Merkel cells (tactile cells) and Melanocytes

stratum spinosum

• spiny layer

• "Spiny" appearance caused by artefacts of histological preparation

• Some mitosis is also seen in its deeper layer

• Contains star-shaped Langerhans cells (dendritic cells)

stratum granulosum

• Consists of keratinocytes with deep staining granules

• two types of granules: keratohyaline granules and lamellated granules

keratohyaline granules

• granules that help form keratin

lamellated granules

• granules that contain a waterproofing glycolipid

stratum lucidum

• clear layer

• Seen only in thick skin (hands & soles)

• Composed of a few rows of flat, dead keratinocytes

stratum corneum

• Thick layer of dead keratinocytes and thickened plasma membranes

• Protects skin against dehydration, abrasion and penetration by microbes.

keratinocytes

• Most abundant cell type in the epidermis

• Arise from the deepest layer

• Produce keratin (a tough fibrous protein)

merkel cells

• also called tactile cells

• Associated with sensory nerve endings

• Detect light touch and pressure

• Seen at dermo epidermal junction

dendritic cells

• also called langerhans cell

• phagocytic cells in stratum spinosum

• Part of the immune system

melanocytes

• produce pigment melanin

• Contribute to skin color

• Protects against UV radiation

• Seen in stratum basale

melanin

• Yellow, reddish brown, or black pigments

• The same number of melanocyte

• Transparency of the skin of Caucasian – Redness due to BV filled with RBC (Hb

carotene

• Orange-yellow pigment from some vegetables

• palms and soles

• Precourseour of Vit-A

haemoglobin

• Red colouring from blood cells in dermal capillaries

• Oxygen content determines the extent of red colouring

redness

• or erythema

• due to embarrassment, inflammation, hypertension, fever, or allergy

pallor

• or blanching

• due to emotional stress (such as fear), anaemia, low blood pressure, impaired blood flow to an area

jaundice

• yellow cast on the skin

• indicates a liver disorder

bruises

• black and blue marks on the skin

• hematomas

albinism

• A genetic disorder with the inability of melanocytes to produce melanin

• Affects the colouring of skin, hair and nails

vitiligo

• The melanocytes in certain areas lose their ability to produce melanin, possibly due to an autoimmune reaction.

• This leads to a loss of colour in patches.

dermis

• The second major layer of the skin

• Richly supplied with blood vessels and nerves

• Has two layers (papillary and reticular)

papillary layer

• superficial

• made of areolar CT

• has dermal papillae or epidermal ridges

• sweat from this later leaves fingerprints on hand and feet

reticular layer

• deep

• 80% of the thickness of the dermis, dense irregular CT

• Has blood vessels, sweat, Arrector pili muscle and sebaceous gland

lamellar corpuscles

• found in reticular layer of dermis

• deep pressure receptors (feeling vibration and deep pressure and proprioception)

hypodermis

• Deep to the skin– also called superficial fascia or subcutaneous layer

• Contains areolar and adipose connective tissues (storage of most body fat)

• Anchors skin to underlying structures

• Helps insulate the body– thermal insulator

• Acts as a shock absorber

hair

• Flexible type of dead, keratinized epithelial structure

• chief parts of hair (root and hair)

• has 3 concetric layers of keratinized cells (medulla, cortex, cuticle)

• Found everywhere on the human body except palms, soles, lips, nipples, parts of the external genitalia, and distal segments of fingers and toes

medulla

• a layer of keratinized cells in the hair

• its the central core

cortex

• a layer on the keratinized cells in the hair

• surrounds the medulla

cuticle

• a layer on the keratinized cells in the hair

• the outermost layer

root

• chief parts of hair

• embedded in the skin and enclosed in a sheath (hair follicle)

shaft

• chief part of the hair

• projects above the skin surface

hair follicles

• extend from the epidermis into the dermis

• the walls have connective tissue root sheath and epithelial root sheath

hair bulb

• deep, expanded end of the hair follicle

root plexus

• a knot of sensory nerves around the hair bulb

arrector pili

• bundle of smooth muscle

• Connect hair follicles to dermal tissue

• Hair stands erect when this contracts (goose bumps)

alopecia areata

• This is a disease that develops when the body attacks its own hair follicles (where hair grows from), which can cause hair loss anywhere on the body.

• not contagious

sebaceous glands

• found over the entire body skin except palms and soles

• exocrine glands

• secrete sebum (An oily substance)

• most are associated with a hair follicle

• sebum soften and lubricates hair and skin which prevents bacterial infection

sweat glands

• also called sudoriferous glands

• sweat is used as a blood filtrate

• has two types of glands (eccrine and apocrine)

eccrine glands

• Most numerous –produce true sweat– everywhere in the body including palms, soles and forehead

• Open via a duct to sweat pores on the skin’s surface

• Produce acidic sweat – 99% water, salts, vitamin C, traces of metabolic waste

• Main Function - in body temperature regulation

apocrine glands

• Larger than eccrine glands and their ducts empty into the hair follicle

• Produce a special kind of sweat and smell

• Ducts empty into hair follicles in the armpit and genitals

• Begin to function at puberty

• Release sweat that also contains fatty acids and proteins (milky or yellowish color)

• Play a minimal role in body temperature regulation

nails

• scale-like modification of epidermis

• made of hard keratin

• parts of the nail: free edge, body and root

first degree burn

• only the epidermis is damaged (superficial), eg: sunburn

second degree burn

• upper part of the dermis is also damaged (partial thickness)

• Blisters appear

• Skin heals with little scarring

third degree burn

• burn that consume all thickness of skin (dermis+epidermis)

• Burned area appears white, red, or blackened

• full thickness burns

• heals with scars

• needs skin grafting.

fourth degree burn

• full thickness burns but extend to deeper tissues

basal cell carcinoma

• Least malignant but most common skin cancer

• Arise from cells of stratum basale

squamous cell carcinoma

• Arise from cells of stratum spinosum

• UV exposure is an important risk factor

malignant melanoma

• Arise from melanocytes

• Highly malignant

• Arises from accumulated DNA damage in a skin cell