The Integumentary System

INTEGUMENTARY SYATEM

[skin + derivatives = integument ]

$SKIN IS THE LARGEST ORGAN OF THE BODY/LIVER IS THE LARGEST GLAND.[JACK OF ALL TRADES== SKIN]


SKIN= EPIDERMIS [outer] + DERMIS [inner]


EPIDERMIS is ectodermal in origin.[$$ BLOOD VESSELS ABSENT IN THE EPIDERMIS]
DERMIS is mesodermal in origin.


EPIDERMIS is composed of stratified squamous epithelium, and consists of 5 layers.

1.STRATUM CORNEUM =[[$$ str. Corneum of frog contains living non-nucleated flattened cells][=è metachoresis change in skin colour in frog]] outermost layer of dead keratinized cells [keratin is a scleroprotein]. It is **thick at sole and palm. Ecdysis is shedding of stratum corneum.

2.STRATUM LUCIDUM =A thin translucent layer of dying keratinized cells which contain eleidin .*Conspicuous in soles and palms.

3.STRATUM GRANULOSUM = 2 – 4 cells deep layer, containing$ keratohyalin, conspicuous in palm and soles.

4.STRATUM SPINOSUM = CELLS ARE POLYHEDRAL

5.STRATUM BASALE = lowermost layer of columnar epithelium cells which rest on a basement membrane.divide by mitosis to form outer cells.all the keratinized structures and glands are derived from this layer.

[$$stratum spinosum + stratum basale = STRATUM GERMINATIVUM/ malpighii]

DERMIS[CORIUM]

It is a thick sheet of connective tissue present below the epidermis.About 2- 3 times thicker than epidermis.CONNECTIVE TISSUE is areolar which is dense due to abundant fibers.Blood vessels, nerve fibres, glands , muscle fibres, sanse receptors and hair follicles are present in the dermis.
$$[SENSE RECEPTORS ARE DERMAL IN ORIGIN AND HAIR AND GLANDS ARE EPIDERMAL IN ORIGIN]

$ CHROMOPHIL CELLS / MELANOCYTES produce melanin.melanocyte are present/produced in dermis but get incorporated into epidermal cells.$ albino colour /albinism:due to non-synthesis of melanin from melanocytes.[$$$ melanin synthesis: tyrosinàdopaàdopaquinoneàmelanin]

DERMIS = PARS PAPILLARIS + PARS RETICULARIS
PARS PAPILLARIS [outer]= Includes papilla and connective tissue with blood capillaries.
PARS RETICULARIS[inner] = INCLUDES lower thick connective tissue fibres with bigger blood vessels and nerves.

SENSE RECEPTORS^

1.FREE NERVE ENDINGS = SENSITIVE TO pain , touch, pressure.
2.BASKET NERVE ENDINGS / HAIR END ORGANS = TOUCH AND MOVEMENT OF OBJECTS.
3.RUFFINI’S CORPUSCLES = warmth receptors
4.KRAUSE’S END BULBS = cold sensation
5.MEISSNER’S CORPUSCLES = touch
6.PACINIAN CORPUSCLES = tissue vibrations and strong pressure
7.GOLGI-MAZZONI CORPUSCLES = heavy touch a\, pressure joint rotation
8.MERKEL’S CORPUSCLES = constant touch

[$$ VITAMIN D = Skin manufactures vit D from *cholesterol *]


GLANDS FOUND IN THE SKIN[$$ simple coiled tubular glands occur in the dermis of the skin]

1.SWEAT GLANDS = [sudoriferous glands] coiled tubular opening on the skin surface through a pore.secrets sweat [composition:H20, urea, NaCl,etc]

$SWEAT GLANDS ABSENT AT LIP TIPS IN MAN.$$ BUT IN RABBIT PRESENT ONLY ON LIPS, AND RARE ELSE WHERE.SWEAT HELPS IN LOWERING BODY TEMPERATURE]

2.OIL GLANDS/ SEBACEOUS GLANDS = flask shaped, alveolarglands opening into shaft of hair follicles and secrete oil for lubricating hair and skin.

3.lachrymal/lacrimal glands = OCCURS IN THE EYES, secrete tears

4.meibomian glands: SEBACEOUS GLANDS OPENING IN THE EYE LASHES.[ TARSAL
GLANDS/ PALPEBRAL GLANDS]

5.WAX / CERUMINOUS GLANDS = MODIFIED SWEAT GLANDS

6.MAMMARY GLANDS/MILK GLANDS = MODIFIED LOBULATED SWEAT GLANDS

7.SCENT GLANDS = MODIFIED SEBACEOUS GLANDS WHICH SECRETE $$PHEROMONES $$.========è


APPENDAGES OF SKIN-àHAIR AND CLAWS, NAILS, HOOFS FOUND IN THE SKIN.


1.HAIR: A fine kertinised filaments that develop from tubular pits known as hair follicles.Hair papilla present at the lower end of hair follicle is composed of connective tissues and nerve fibres.
Arrector pilli muscles[smooth / involuntary] are for movement of hair, $ GOOSE FLESH=èDUE TO CONTRACTION OF THESE MUSCLES IN COLD]
Bulb/root of the hair introduces new cells.
Besides bulb hair has root[inside skin] and shaf [outside skin]


2.CLAWS, NAILS, HOOFS = These are the keratinized epidermal structures developing from tips of digit.



FUNCTIONS OF THE SKIN

1.streatchable protective shield.
2.regulation of body temperature
3.sense reception
4.screen UV rays
5.synthesis of vit D
6.excretion of waste materials.


$ Body temperature is regulated by : [IOM 1995]=èskin, mouth, lungs
$The loss of heat in a spector inside cinema hall is mainly through [IOM 1995]èCONVECTION
$All of the following structures are found in the dermis except [IOM 1993]è
a.blood vessles c.sweat glands
b.sebaceous glands d.melanocytes
[ans:c]