0826- Anatomy and function of skin- CG Flashcards
Layers and components of the epidermis
4 Layers (from outside to inside): corneal, lucidum, granular, spinous, basal Components - keratinocytes (major). Starts at the basal layer, then mature and differentiate and migrate to the surface. It produces keratin (cytoskeleton of cell) (see table)
What is the structure and function of keratin?
-Keratins are protein products of keratinocytes and make up its cytoskeleton
Formed from paired acidic and basic keratin monomer –> dimers –> tetramers –> Tetramers assembled with actin and tubulin into tonofilaments forming keratinocyte cytoskeleton.
Different types of keratins formed in different layers
How are the cells of the epidermis kept together?
Upper layers- Desmosomes = macula adherens, responsible for cell-cell adhesion.
Anchored to lower layer
Basement layers/dermis is thrown into folds (rete ridges) to overcome shear stress
Basal cells are anchored to basement membrane via hemi-desmosomes
Basement membrane locked to dermis via collagen type 7)
Components and layers of the dermis
Relatively acellular
Layers: papillary layer (more randomly associated fibres), reticular layer (eosinophilic protein bundles), vascular plexus on the bottom
Mostly connective tissue:
Collagen (major structural component of dermis): stops skin from stretching beyond a certain point; 13 Types- mainly type 1 collagen- stains pink
Elastin- returns skin back to original configuration (loss of elastin= stretch marks)
Ground substance- mucopolysaccharides, (ie hyaluronic acid) . Gives skin turgidity and allows it move around
Rich vascular plexus for blood supply: dermis provide nutrition and support to epidermis (papillary capillary make small loops near junction)
Describe the neural (afferent) components in the dermis
Neural- sensation
Receptors
Pacinian corpuscle- deep dermis, vibration, proprioception
Meissner’s corpuscles- superficial dermis- fine touch, mechanoreceptors
Free nerve endings- mostly nociception
Hair and nails help provide directionality of the sensation (provide counter pressure)
What causes Skin pigmentation?
Melanocytes (formed near the neural crest) produce melanin ( hence brain also contain melanocytes)
Factors affecting pigmentation-
Melanin- synthesised from dopamine polymer (contained in melanosomes, which are exported through the epidermis and given to keratinocytes. Red haired people-defective melanin structure, not enough produced)
Hemoglobin state
Diet: beta carotenes turns skin orange
Describe features of skin (epidermal) Pathology
Keratin mutations
- Pull apart/disintegrate when tension/stress is applied
- Cells move off from matrix
Filaggrin mutations
- orderly desquamation of cells in the stratum corneum layer (due to defect in protein cross-linking)
Describe the anatomy and development of hair
Anchored in dermal papilla, melanocyte layer cover it
Lower- bulb
Middle segment- isthmus
Upper segment- infundibulum
Vellus hair (short, fine, pre-pubertal hair. Not connected to sebaceous gland) – PUBERTY –> terminal hair (darker, longer, adult )
Cuticle: scaly outer layer- gives its integrity. When it wears off = split ends
Inner root sheath and outer root sheath grows out with hair until its self sustaining
Describe the Process of Hair cycling
dermal papilla regulate hair cycling process
Anagen- growth phase (3-4 years)- can be variable in different people
Catagen- follicular regression (couple weeks)
Telogen- shrink into dermis, leaving terminal papillae behind- resting period (couple months)
Mesanagen- renewal phase-
Anagen again
Function of sebaceous gland?
stimulated by presence of androgen hormones- synthesise lipids, ooze out cells into ducts into follicle (sebum) at infundibulum
Helps to maintain healthy skin microflora
Function of the nail, and outline the function of the nail matrix, nail bed, cuticle
Cuticle- sit atop matrix and protect it
Nail matrix (root of nail, similar to …distal end of matrix is half moon, contain a lot of nuclei, responsible for synthesis
Nail bed- skin beneath nail plate. ridges of epidermis and underside of nail have ridges to maximise adhesion
How is sweat produced? What innervates it?
Mechanism: Cl pumped into lumen, Na diffuses across to follow it. Water follows
Na+ is reabsorbed by ductal epithelium resulting in a hypotonic end product (this ability is reduced when not acclimated to heat: lose more Na)
Liquid –evaporate–> gas, absorbing latent heat (cooling)
postganglionic neuron is CHOLINERGIC even though its innervated by SNS
What are the 2 Types of sweat glands:
Eccrine (major glands found all over the body)- heat acclimatisation
Apocrine (in armpits and groin) - odorous due to bacterially-decomposed fatty acids
Name at least 4 functions of the skin
Hydrophobic barrier- lamina lucida (5 keratocytes thick)- transdermal delivery need to go through- lipophilic, ionised particles doesn’t go through
Tight junctions underneath (?desmosomes?)
Dynamic barrier- upward flow of keratinocytes- sheds
Functional inhibition- block microbes using chemicals, ie sebum contain chemicals to inhibit some pathogenic biota, and stimulate normal microflora
Immunologic surveillance- Epidermal: langherhan’s (very common- dendric cells- APC, tolerance induction), keratinocytes (crude APC role, can activate innate immune system- amplify and induce inflammation, T-cells (both innate and adaptive), macrophages,
Dermal dendritic cells (new- APCs)
Thermoregulation- sweat becomes vapor due to perfusion (warms skin)- latent heat disspates when liquid becomes gas. Hence vasodilation also needed
Heat is more of a threat to humans (hence usual state is vasoconstriction so it has capacity to vasodilate more)
Erythroderma (sudden vasodilation)- may go hypotensive
Finger tips- ret ridges for fine manipulation, thick corneum, more sweat glands to moisturise
Psychosocial
