integumentary system

what makes up the integumentary system

skin and accessory structures (glands, hair, nails)

functions of the skin

protection, detection of stimuli, thermoregulation, excretion through glands

layers of the skin

epidermis, dermis, hypodermis

epidermis

surface layer; stratified squamous epithelial layer; avascular (lack of blood vessels)

stratified squamous epithelium

protective tissue with multiple layers of cells, arranged with flattened (squamous) cells on the surface over deeper, taller cells

specialised cells within epidermis

keratinocytes, langerhans cells, melanocytes, merkel cells

keratinocytes

skin cells responsible for protecting from microbial invasion, shielding from UV exposure, and maintaining skin hydration by producing fibrous keratin

langerhans cells

immune cells originating in bone marrow, reside in epidermis as a dense network providing protection (immune system)

melanocytes

synthesises melanin in melanosomes through a process called melanogenesis. interact with endocrine, immune, inflammatory and central nervous systems, activity is also regulated by extrinsic factors (e.g. UV radiation, drugs)

merkel cells

touch receptors, made of a sensory nerve ending which ends in a tactile disc

renewal of the epidermis

1) keratinocytes divide rapidly in stratum basal
2) daughter cells push upwards through epidermal layers (stratum spinosum, stratum granulosum)
3) the cells gradually flatten, keratin fibres accumulate within
4) outermost skin cells (stratum corneum) dry out and are shed

2) daughter cells push upwards through epidermal layers (stratum spinosum, stratum granulosum)

3) the cells gradually flatten, keratin fibres accumulate within

4) outermost skin cells (stratum corneum) dry out and are shed

psoriasis

caused by increased keratinocyte proliferation

dermis

middle, thickest layer; connective tissue layer containing collagen and elastic fibres, providing strength & flexability; two layers - dermal papillae and reticular layer

features of the dermis

blood vessels, glands, hair follicles, fibroblasts, smooth muscle, nerves, adipocytes, macrophages, lymphatics

hypodermis

subcutaneous layer, loose connective tissue lair containing fat cells (adipocytes), connective tissue fibres interwoven with dermis, thins with age and varies throughout body

functions of the hypodermis

protects underlying bones/muscles, maintains body temp, stores energy

sebaceous glands

produce sebum, exocrine glands (secretions releases directly into hair shaft, holocrine secretion - cell disintegrates to release contents), not present in palm or soles

functions of sebaceous glands

prevents water loss or gain, inhibits growth of bacteria, lubrication of skin & hair, protects hair shaft & surrounding skin

sweat glands

produce sweat for cooling and waste removal, two types: apocrine and eccrine

apocrine sweat glands

ducts open into hair follicle, leading to skin's surface, associated with odour, found in areas with many hair follicles (axillae, pubic region, areola of breast etc)

eccrine sweat glands

ducts open onto epidermis (directly on skin's surface), found over most of the body, regulates body temp, not found on margin of lips, tympanic membrane and part of external genitalia

sensory receptors

found throughout the skin, each type responds to specific stimuli (pain, temp, touch etc), nerve fibres in skin send signals to brain, control blood flow and adjust gland secretions