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