A&P Ch.5 Integument

Primary Functions of the Skin

1. Protection

2. Temperature regulation

3. Sensation

4. Metabolic Functions

5. Blood Reservoir

6. Waste Elimination

Skin Protection

• chemical- sweat and oily discretions kill bacteria, melanin prevents damage to DNA caused by UV radiation

• physical- barrier, prevents things like bacteria from entering the body

• Biological- dendritic cells in skin stimulate immune responses, macrophages destroy large-sized invaders

Skin Temperature Regulation

changes in blood supply to the skin (closer to skin if too hot, closer to organs if too cold), and in sweat gland activity allows for maintenance of normal internal body temperature

Skin Sensation

Exteroceptors- sensory receptors

• respond to stimuli arising outside the body

• can be nociceptors (pain), thermoreceptors (temp.), mechanoreceptors (mechanical: touch, vibration, pressure)

Skin Metabolic Functions

involved in vitamin D (required for absorption of calcium from digestion) , cells in skin produce (only if in sunlight)

Skin Blood Reservoir

about 5% of blood volume can be found in integumentary (can also store blood)

can be moved by central nervous system (thermoregulation- when organs need to be more active, need more blood)

Skin Waste Elimination

sweat allows for elimination of small amount of certain nitrogenous wastes

Two Layers Present in Skin

1. Epidermis: outermost epithelial portion- stratified squamous epithelium, unvascularized

2. Dermis: innermost connective tissue portion (makes most skin by mass), vascularized (for dilation and constriction of blood vessels)

Hypodermis

lies deep within the dermis but is not a true structure of integument

composed of adipose tissue (lipids, fats)

functions: attachment, protection, insulation, energy source

subcutaneous fat- attaches skin to muscle

Cell Types found in Epidermis

1. Keratinocytes

2. Melanocytes

3. Dendritic Cells

4. Merkel Cells

Keratinocytes

cells in epidermis, produce keratin protein, most frequent + large, make up stratified squamous

gives epidermis protective qualities (tough and dry)

Melanocytes

cells in epidermis, contain organelle melanosome, produces melanin pigment → which is transferred to keratinocytes

melanin migrates to the “sunny side” of the keratinocyte (protects nucleus)

Dendritic Cells

cells in epidermis, “presenting” cells- help activating immune

latches to what does not belong, puts on display for immune system cells

Merkel Cells

Present at epidermal-dermal junction, functions as sensory receptor- important for touch

Layers of Epidermis (deep → superficial)

1. Stratum basale

2. Stratum spinosum

3. Stratum granulosum

4. Stratum lucidum

5. Stratum corneum

Stratum Basale

deepest layer of epidermis, single layer of dividing cells attached to dermis- rapid division seen here

composed mostly of keratinocytes, 10-25% are melanocytes

Stratum Spinosum

after the basale layer, cells contain pre-keratin protein- thick bundles of filaments that resist tension

dendritic cells are most abundant here

Stratum Granulosum

after the spinosum layer, accumulation of two granule (packages inside cell) types

• Keratohyaline- forms true Keratine protein- first layer in epidermis with true Keratin

• Lammelar granules- contains water-resistant glycolipid

Stratum Lucidum

after the granulosum layer, cells at this layer are nonliving, not found in “thin” skin

Statum Corneum

most superficial layer of epidermis, cells are not living, makes up most of epidermal thickness

glycolipids between cells help waterproof this layer

Keratin inside cells protects from friction/abrasion

Dermis

made of strong and flexible connective tissue

fibroblasts and macrophages dominate

semifluid matrix

collagen and elastic fibers abundant

Two layers of Dermis

1. papillary dermis

2. reticular dermis

Papillary Dermis

more super layer of the dermis

has projections called dermal papillae

can have pain receptors (nociceptors) and tactile (touch) corpuscles-receptors

projections indent epidermis- form friction ridges- genetically determines → fingerprints

Reticular Dermis

deep to papillary dermis

forms cleavage lines in the skin- not visibly external

forms flexure lines at/near joints- externally visible- lines on hands

Three Pigments of Skin Color

1. melanin

2. carotene

3. hemoglobin

Melanin

skin pigment- dark colored polymer (black/brown)

skin pigmentation dependent on amount of melanin produced by melanocytes

Carotene

yellow-orange pigment

accumulates in startum correum + adipose tissue

can be used in body to produce vitamin A- used for vision, and important for epidermal health

Hemoglobin

pink/red skin pigment

from blood, not direct skin pigment

oxygenated pigment- very red when bonded to O2- red when you exercise

Skin Appendages

Hair (Pili)

Nails

Hair (pili)

consist of dead, hard keratinized cells

• root

• shaft

functions: sensory (nerves wrapped around root), protection (scalp, eyes, nose)

Hair Follicle

results from fold extending from epidermal surface into dermis

has hair matrix- base of follicle, produces new cells, hair growth

matrix activity is cyclical- in division or resting phases, then falls out

Root hair plexus

found at base of hair follicle

contains nerve endings, sensory function- sends message to brain

Dermal papilla (hair papilla)

provides capillaries to hair matrix- gets blood, so cell division

Arrector pili

smooth muscle cells attached to follicle

contraction pulls hair follicle and hair upright

Hair Follicle Shape and Texture

• round= straight hair

• oval= wavy/slightly curly

• flattened= very curly

Hair Thinning

experienced my most people at older ages- hair loss exceeds growth

Hair Balding

hair follicles respond to androgen hormones differently with time, hairs become vellums, many are shed before emerging from the follicle

on X chromosome- males only have one so do not have multiple sets of hair info

Nails

contain hard keratin (hardest)

nail matrix- responsible for nail growth

protective functions and dexterity of fingers

Skin Glands

sweat glands and sebaceous glands (oil glands)

Sweat Glands

exocrine glands- composed mostly of water, contains salts and metabolic wastes (nitrogenous)

two types- eccrine and apocrine

Eccrine Sweat Glands

found almost everywhere, abundant in palms, soles of feet, and forhead

ion directly to skin surface at a pore

merocrine mode of secretion

body temp. regulation

Apocrine Sweat Glands

located in axillary and anogenital areas

merocrine mode of secretion*

empty into hair follicles- then released to skin

same components as sweat from eccrine glands- but have some lipids and proteins

pheromonal role maybe

Sebaceous Glands

secretes sebum, mostly lipid-based substance

functions: lubricant for skin/hair, slows water loss from epidermis (oily skin), kills bacteria