mnsr 24 Flashcards
the main functions of the skin
skin provides integument covering and has four main functions
1- protection : tough hide to protect against physical trauma , uv light by the melanin pigment, countinous unbroken line for microorganisms
2- thermoregulation: sweat and hair to provide insulation
3- metabolism: produces vitamin d used for the of calcium and phosphate metabolism
4- sensation: for pain, pressure, and temperature
the skin has been an area of
organ of sensory and nervous structure in asctreal metazoan.Embryologically the nervous system arise contiounsly from skin’s ectoderm.
Skin is the
largest organ ( 12.5 - 16.7 ) and is continuous w/ urigental tract ( penis/ vagina and urethera ) and digestive tract ( mouth and anus )
the two type of the skin
1- glabrous: thick and hairless e.g: soles of the feet and palms
2- hairy: thinner and most skin areas
The protective layer of the skin against phsycial chemical and microbial layer is
epidermis ( 0.06-0.1 mm thick )
The epidermis arises from
embryonic ectoderm
epidermis gives rise to
sweat glands
mammary glands
sebcoutnous glands
It predominantly consist of:
keranocytes arranged in stratified squamous epithelium starting at the basal membrane and moves outwards and becomes coreococytes in a process called: desquamation
The process of keranocytes maturing to corenocytes in the basal membrane is called
desquamation
The entire epidermal cycle takes
27 days
The layers of the epidermis from top to bottom
1- stratum corenuem: thick outer layer composed of flattened fused cells and composed mainly of keratin. Corneum is covered with oily secretion from the sebaceous gland called: sebum
2- straum lucidum: only thick skin, clear homogenous, layer without nuclei or organelle.
3- stratum granulosm: showing granules within the cells
4- stratum spinosum: aka prickle layer- growing skin showing early keratin synthesis
5- stratum basale ( basal layer): a proliferative layer of basophilic columnar or cuboidal cells
The color of the human skin is due to 3 factors
( skin pigmentation )
1- inherited yellow color from carotene at the subcutaneous fat
2- concentration of oxygenation of the heamoglobin in the dermal capalliries
3- Special branched cells scattered through the stratum basal the pigment in these cells is called: melanin and produces melanocytes. protects us against uv radiation.
A patch of dark pigment on the skin aka mole is called melanocytic nevus and small percentage of it will become cancerous aka melanoma
Keratinised structures
- most mammals have: foot pads
- higher primates have: friction ridges on palms and soles of the feet
- the tip of the fingers have fingerprint: dermatoglyph
- nails, claws , hooves are other kerantised structures
is an elongated rod of kernatised cells
hair shaft and grows from the root ( the hair bulb ) lying in the dermis layer
the hair bulb is the
base of a pit sunk in the dermis called : hair follicle
follicle cells is continuous with
epidermis
during early —- the —- grows down into the —- to form —-
- early fatal life
- the epidermis
- dermis
- cellular shaft
cells of the hair shaft are
dead kernatised epidermal cells expect the base where the growing germinal matrix exists
the germinal matrix forms a
cap over a vascularised plug of dermal tissue called the dermal papilla
the germinal matrix is connected to the
overlying epidermis by the cellular external root sheath and the entire structure is called: pilosebaceous unit
the proliferation in the cells in the germinal matrix produces
hair growth
- initially these cells r pushed up the centre of the epidermal down growth
- as the move further from the papilla blood supply they become kerantized and die
- initial cells transform into: hair cortex w a single outer layer of hair cuticle
the hair follicle consist of ( check the structure in the slides )
- medulla ( seldom seen)
- cortex( kernatised cells )
- cuticle( single layer of overlapping kernatised cells )
- internal root sheath: produces further division of germinal matrix cells which pushes up between external root sheath and the hair follicle
the hair shaft is help in position from
external and internal root sheath ( ERS AND ERS )
Hair grows in a
cyclical basis
growth phase in young adult is
~3 years and 85% of scalp hair is in growth phase followed by the degeneration of the follicle.
the sebaceous gland is derived from
ERS and produces sebum into the follicle that has mild fungistatic and bacteriostatic action
hair position can be elevated bt
arrestor pillus muscle attached to the hair bulb and the epidermis
Other glands in the skin
1- sebaceous gland ( oil)
2- sudoriferous gland ( sweat )
3- ceruminous ( ear wax )
40 mammary gland
is connected to the hair follicle and forms the pilosebaceous unit
-sebaceous gland that produces sebum to protect the skin and the hair.
- releases secretions via holocrine mechanisms into the hair follicle shaft
- located over most of he body/skin expect palms and soles of the feet
The 2 types of sudoriferous ( sweat) gland
1- apocrine - ducts open in the hair follicles asL armpits, pubic region, areola of the breast
2- eccrine: ducts terminate as sweat pores at the epidermis. Throughout the skin except lips,nailbeds, and eardrums
- This gland is coiled tubular gland , secretory portion lines fascia within a duct up to the skin surface , secretes sweat for thermoregulation
ceruminous glands are
ducts open either directly onto the surface of the external auditory ear canal or into the duct of sebaceous glands.
secretion combines w sebum associated w sebcaous gland to from cerumen aka ear wax
- to protect the ear from foreign materials as dust
are highly modified derivatives of sweat glands
mamamry glands and the milk production is under hormonal control.
Mammary glands develop by the thickening of the epidermis - the milk lines - in the abdominal walls
dermis is prodmintly composed of
fibroblast which secretes and organises large amount of ECM.
ECM is mainly fibrillar collagen as type 1,111, v, elastin
papillary dermis is
wish in vasculature and have nerve ending, thermo/cryoreceptors
reticular dermis is
- thicker of the 2 substrata
- dense connective tissue contains elastin network and proteoglycan
- provides structural support for the skin
dermis is derived from —- and is — in thickness
mesoderm and is 2 mm thick
dermis is composed of
- collegen , elastin fibers ( strength and elasticity)
- blood vessels ( thermoregulation , immune function
- nerves
- fibroblast - forms collegen and elastin
- mast cells - inflammatory responses to pathogens and injuries
- lymphatics
- epedrimal appendages
- glycosaminoglycan; hyaluronic acid, chondotrion surfaces and glycoprotein ( retains h20 and provides moisture to the epidermis )
