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SkinSkin SkinSkin It completely covers the body & It completely covers the body &
is continuous with the is continuous with the membranes lining body orificesmembranes lining body orifices
It is the largest organ of the It is the largest organ of the body, of 1.5 to 2 m body, of 1.5 to 2 m ²²surface areasurface area
Epidermis Composition: st. keratinised sq. ep.Thickness : varies, thickest on the palms &
solesColor: varies from white to black, No blood vessels , but deeper layers are
bathed in interstitial fluid of dermisIt is regenerated continuously every 2-4
weeksLayers ( strata)
Differentiation
- Cells move from basal layer to stratum corneum
1) Synthesis & modification of proteins, especially keratins
2) Appearance of new organelles, reorganization of organelles, loss of organelles
3) Change in cell size & shape
4) Changes in properties of membranes
5) Dehydration
6) Desquamation
• Maintenance of healthy epidermis:1. Desquametion of keratinized cells2. Effective keratinizatrion of cells
approaching surface3. Continual cell division of germinal
layer
Fingerprints • Projection of cells in the dermis
called papillae. They cause ridges of different pattern in every individual, their impression makes Fingerprints
Dermis• Composition: mainly of collagen, but
also contains elastic,reticular fibers&muscular tissue
• NB:(facial expressions are due to the skeletal muscle connection to the dermal collagen fibers to produce: smile, frown, eyebrow movement…)
• Striae?
Structures in it:1. Blood & lymph vessels2. Sensory nerve endings3. Sweat gland & their
ducts4. Hairs, arrector pili m &
sebaceous glands
Sweat glandsMerocrineApocrine
•Found in thick skin•Simple coiled tubular•Ducts are long & run zigzag to open on the surface of epidermis•cool the body
•Found in thin skin of axilla, pubic region, found only near hair folliclesand respond to stress andsexual arousal•Large sweet glands•Start function at puberty•Produce milky secretion fatty acids→ support bacteria →body odor
Sebaceous Glands
• Oily secretion called sebum that contains broken-down cells
• anti-bacterial properties• flexibility of cutaneous
membrane
Ceruminous Glands
• secretion combines with sebum to produce earwax
• waterproof• keeps eardrum flexible• bitterness repel mites &• other pests
Mammary Glands
• modified apocrine sweat gland• thicker secretions containing
proteins and fats• released by ducts that open at
the nipple
Hypodermis• A sub dermal layer of adipose tissue or otherwise calledsubcutaneous fat; which is made up of loose, fibroustissue, rich in blood vessels, lymphatic vessels andnerves;• The base of hair follicles and the coiled tubes of sweatglands may also project down into the hypodermis;• This is the layer that pads the body, serves as an energyreservoir and provides thermal insulation, (it isdifferently distributed in females vs males)
Functions of Hairs • Sensation• Communication• Facial, pubic and axillary hair• Eyebrows• Protection• Barrier• Guard hairs in nose• Eyebrows• Thermoregulation
Different body hair types
• lanugo -- fine, unpigmented fetal hair
• vellus -- fine, unpigmented hair of children and women
• terminal hair -- coarse, long, pigmented hair of scalp,
• pubic and axillary regions
Structure of Hair and Follicle
• Hair is filament of keratinized cells• shaft is visible above skin; root is below
within follicle• Follicle is oblique tube within the skin• bulb is swelling in base where hair
originates• vascular tissue (papilla) in bulb
provides nutrients
• Epithelial root sheath is an extension of the epidermis (lies next to hair root)
• Connective tissue root sheath is derived from the dermis (surrounds it)
• Hair receptors entwine each follicle
• Piloerector muscles : smooth muscles that cause goose bumps
Nails
• Clear, hard derivative of stratum corneum
densely packed cells filled with hard keratin
• Flat nails allow for fleshy, sensitive fingertips
Functions of skin1. Protection 2. Regulation of body temp3. Formation of vit. D4. Cutaneous sensation5. Absorption6. Excretion 7. Psychological and social functions• appearance and social acceptance• facial expression and nonverbal communication
Sensory functions•. It is equipped with a variety of nerve endings that react to heat, cold, touch, texture, pressure, vibration, and tissueinjury (pain);
• The sensory receptors are specially abundant on theface, palms, fingers, soles, nipples and genitals. thereare relatively few on the back, and joint areas;
• Some receptors are naked dendrites that penetrate intothe epidermis, and most others are limited to the dermisand hypodermis, where specialized connective tissuesgive the nerve cells more selective sensitivity toparticular stimuli.
hair folliclereceptors
Meissner’s(tactile)corpuscles
Ruffiniendings
Pacinian(Lamellated)corpuscles
Dermis,around hairfollicle
Dermis(papillae offingertips,palms, lips,eyelids)
Dermis,hypodermis
Dermis,hypodermis
Light touch,texture,vibration (20-40 Hz range
Deep touch,Pressure,vibration (150-300 Hz )
Thermoregulation
• thermoreceptors and sweat glands
• hypothalamus controls cutaneous arteries and sweat glands to
• retain or dissipate heat
Control of body temp• Nervous control1. Temperature regulation center
(hypothalamus)2. Vasomotor center