Flashcards in Systems Physiology Deck (674)
What are the main functions of the skin?
Protection, sensation, thermoregulation, metabolic, physical and sexual identity
What are some of the protective functions of the skin?
Physical barrier to bacteria
Excessive dehydration, UV radiation
Physical, chemical, thermal insults
Penetration of drugs & chemicals
What are the metabolic functions of the skin?
Adipose tissue is a major energy store
Vitamin D synthesised in epidermis
What are the three layers of the skin?
Dermis - dense irregular CT, highly vascular, many sensory receptors
Hypodermis - loose CT contains adipose tissue
What type of epithelial cells make up the epidermis?
What are the four major layers of the epidermis?
(Stratum lucidum in v thick skin between SG & SC)
What is keratinocyte?
Epithelial cell that produces keratin
Is abundant in the epidermis and has abundant intercellular junctions (desmosomes and adherens)
Family of fibrous structural proteins
Intermediate filament made of 4 protofilaments which are pairs of coiled coils of 2 a-helices
Acidic (1) and basic (2) types
Is abundant in stratum corneum in soft form (undergone keratinisation) S-S bonds of cysteine define soft/hardness
Describe the germ layer
Stem cells and transit amplifying cells sitting on basement membrane
SC - unlimited self renewal, TA - limited division before terminal differentiation
What is keratinisation?
Migration of keratinocytes, which become tightly bound by desmosomes, from basal to corneal layer
Describe the stratum spinosum
Very thick layer; at least 3-4 cells thick
Has numerous desmosomes giving cells prickly appearance
Prominent nuclei and cytoplasmic basophilia-active protein synthesis, highly expressed keratin
Describe stratum granulosum
2-3 cells thick
Large, numerous basophilic keratohyalin granules - filaggrin, involucrin
Synthesise glycoprotein granules - intercellular cementing substance
Cell death occurs at the outermost layer
Describe the stratum corneum
Dead, terminally differentiated cells with unique morphology and staining
Fused flattened cells lacking organelles, filled with mature keratin providing protective barrier of skin
Thick, cornified cell envelope beneath PM
Describe the dermis
Complex mix of macromolecules supplied by many blood vessels which provides strength and elasticity to skin
Acts a support for epidermis
Split into Papillary and reticular
Describe papillary dermis
Is loose CT
Loosely packed T3 collagen with elastin fibres on superficial layer
Contains many blood capillaries (vascular papillae)
Describe reticular dermis
Closely packed T1 collagen and elastin
Provides mechanical strength of skin
Hydrophilic gel but flexibility decreases with age
GS - amorphous matrix that embeds collagenous and elastic fibres, skin appendages
GAGs - hyaluronic acid, dermatan sulphates, chondroitin sulphates
What is the role of fibroblasts in the dermis?
Repair of dermis
Synthesis of collagen, elastin, proteoglycans
What is the pilosebaceous unit?
Hair follicle and sebaceous gland
What are the two types of hair follicle?
Vellus - body hair
Terminal - scalp, secondary sexual hair
Describe the structure of hair follicles
Dermal papilla in hair bulb at root, contains fibroblasts which control hair growth by supplying growth factors
Matrix - surrounding papilla, keratinocytes produce hair
Bulge further up contains hair follicle stem cells, also repair skin
Shaft - dead, exposed head of hair
Root - 5 concentric layers of epithelial; inner 3 form hair shaft, outer 2 form epithelial sheath
What are the 3 stages of the hair cycle?
Anagen - active growth phase
Catagen - regressive, shaft cut off from blood supply and cells
Telogen - resting, hair sheds off
Describe the sebaceous gland
Exocrine gland which is androgen (male sex hormone) sensitive
Enlarges during puberty causing acne
Mature sebocytes contain sebum, cell ruptures and sebum released into sebaceous duct and onto skin (lubricates skin and hair)
Describe the eccrine sweat gland
Excretory duct - 2 layers of smaller cuboidal cells
Compact secretory coil - single layer of large cuboidal/columnar cells
What is the composition of sweat and its function?
99% water, aides thermoregulation as evaporating water cools skin
Describe the apocrine gland
Large sweat glands - widely dilated lumen in coiled secretory portion
Present in axilla (underarms) and pubic region
Releases volatile milky, viscous fluid that is odourless BO produced by breaking down of fluid by bacteria
Not functional until puberty
Describe a melanocyte
Dendritic (antigen-presenting immune cell) cell in epidermis on BM
Produce melanin in melanosome - eumelanin (brown/black), pheomelanin (red/brown) - which is injected into keratinocytes
Protects against UV
Describe langerhan cells
Dendritic present in basal and spinous layers
Antigen presenting cell that is 1st line of defence, presents antigen to T lymphocytes
Describe merkel and mast cells
Merkel - in stratum basale, sensory perception (differences in texture)
Mast - in dermis, immune response, produces histamine
What is endochondral ossification?
Formation of bone during fetal development from hyaline cartilage (T2 collagen) model
Model provides rough shape of mature bone
Is typical of long bone formation, allows stresses to be handled during growth