skin structure and function

how many sections does the skin consist of?

3. it is the largest organ of the body.

name the skin layers.

1. epidermis

2. dermis

3. subcutaneous layer

name the 5 layers of the epidermis (and nicknames).

1. stratum corneum (horny layer)

2. stratum lucidum (transparent/clear layer)

3. stratum granulosum (granular layer)

4. stratum spinosum (prickle cell layer)

5. stratum germinatium (basale/base layer)

what is the stratum corneum (horny layer)?

• several layers of keratinised cells, consists of 25-30 layers of keratinised (dead) skin cells.

• keratin makes the skin waterproof.

• the superficial layers are constantly shed (completely replaces every 28 days), until the age 25-30, when regeneration slows down.

what is the stratum lucidum (transparent layer)?

• this layer is more evident in the palms of hands + soles of feet.

• consists of small, tightly packed cells.

• acts as a barrier controlling transmission of water through the skin.

what is the stratum granulosum (granular layer)?

• keratinisation (the process of living → dead cells) takes place in this layer.

• the cells contain granules of kerato-hyalin (precursor to keratin)

what is the stratum germinativum (basal layer)?

• deepest layer of the epidermis.

• its lower surface is attached to the dermis, from which it receives nutrients from blood.

• the development of a new cell (mitosis) occurs here. this leads to general displacement of the older cells towards the surface.

• melanin is formed by melanocytes in this layer.

• mitosis in stratum germinativum → desquamation (natural shedding of skin) from stratum corneum.

name the 2 layers in the dermis.

1. upper layer - papillary layer.

2. lower layer - reticular layer.

what is the dermis composed of?

• composed of layers of connective tissue.

• tough + elastic, consisting of white fibrous tissue (collagen) , keeps skin supple + tight.

• yellow elastic fibres (elastin), keeps everything where it should be. when fibres break, things sag.

what is the papillary layer in the dermis?

• its rigged surface pushes up into the epidermis as papillae.

• papillary layer continues round the hair follicles as a connective tissue sheath.

what is the reticular layer in the dermis?

• contains collagen + elastin + reticular fibres, making tissues strong + flexible, and all the structures of the dermis.

what are sensory nerve endings?

• sensitive to any stimulus on the outside of the body.

• provides an early warning system, sending messages via sensory nerves to the brain + spinal cord.

what are the 4 types of sensory nerve endings?

• pain

• pressure

• temperature

• touch

what are sebaceous glands?

• situated on the outside of the hair follicle.

• secrete an oily substance called sebum, which lubricates skin + hair.

• secretion of sebum is increased at puberty + decreases with age.

• found all over the body except palms of hands + soles of feet.

• largest + most evident on the back, forehead, scalp, cheeks + chin.

what are blood vessels?

• the dermis is a highly vascular structure, full of blood capillaries.

• brings many valuable nutrients to the top of the skin + aids the removal of waste product + carbon dioxide.

what are lymphatic vessels?

• form a network through the dermis, removing waste products + excess water.

what type of sweat glands does the dermis contain?

• apocrine

• eccrine (make you clammy/hot)

what are apocrine sweat glands?

• situated in the dermis.

• secrete substances such as fats, sugars, proteins + pheromones (sexual attractants).

• found in armpits + pubic region.

• start to function at puberty.

what are eccrine sweat glands?

• the type of sweat that makes you feel clammy + warm.

• found everywhere, mainly palm of hands, forehead, soles of feet + armpits.

• occur in large numbers.

• secretion of these glands are called sweat, contains water + sodium chloride, together with small amounts of urea, uric acid ammonia + lactic acid.

• they control body temperature + eliminate waste products.

what is the subcutaneous layer?

• found under the dermis.

• contains adipose tissue (fat cells).

• reduces heat loss through skin + protects from harsh blows.

• consists of bundles of loosely connected tissue, fats cells, blood + lymph vessels.