Skin: The Integumentary System Flashcards
- Describe the organisation and composition of the tissue layers that compose the skin - Relate the formation of skin structures to the organisation of epithelial cells - Explain how the organisaiton of skin structures contribute to the physiology of the integumentary system - Explain how disruption of skin structures may contribute to disease in skin and other organ systems of the body - Relate skin disorders to diseases which affect other organ systems (e.g. Eczema-Asthma, CF in lung v skin)
Functions of the skin
- protection from external environment
- sensory
- absorption (UV = vit D synthesis)
- secretion (sweat, electrolytes, sebaceous oils, phermones)
- body temperature regulation (high surface area to body volume)
- blood reservoir
- aesthetics
Epidermis
- outer layer
- thick keratinised stratified squamous epithelium
- non vascular
- protective
- consists of 4 epithelial cell types
- made up of 5 epithelial cell layers
Dermis
- fibrous connective tissue
- epithelial gland structures (sweat glands, sebaceous glands)
- smooth muscle
- vascular
- sensory
Hypodermis
- not skin
- protective
- adipose and losse
- connective tissue
5 epithelial cell layers of epidermis (outer -> inner)
5) Stratum Corneum: dead cells, hard protein envelope, contain keratin, surrounded by lipids
4) Stratum Lucidium: dead cells, contain disperses kertaohyalins (cells become translucent)
3) Stratum granulosum: Keratohyalin, hard protein envelope, lamellar bodies release lipids, cells die
2) Stratum Spinosum: keratin fibres and lamellar bodies accumulate
1) Stratum Basale: cells divide by mitosis and some new cells become the cells of the more superficial strata (weak junctional strucutres; hemidesmosome)
Kertainocytes
- produce keratin
- primary cell of epidermis
- arise in stratum basale, pushed to surface as continuously mitotic cells reproduce
- cells connected by desmosomes
- kertain is produces as cells migrate, filaggrin causes keratin fibres to dimerise (keratinisation)
- cells flatten and die
Formation of cornified layer of stratum corneum
- formed by dead cells
- fillagrin is hydrolysed to amino acids, which form protective water-proof barrier
- kertains form hard, protective protein matrix
Proteins of the cornified layer of stratum corneum
- loricrin
- involucrin
- trichohyalin
- S100 proteins
- small proline-rich proteins
Formation of granular layer
- profillagrin is expressed
- cleaved to fillagrin, which causes keratin filaments to dimerise and form a matrix
- transglutaminases cross-link
Proteins of the granular layer
- keratins 1 and 10
- keratin 2
- profilaggrin
- transglutaminase 3
Formation of spinous layer
as cells grow upwards, cells express trans glutaminases which cross-link junction complexes
Proteins in spinous layer
- transglutaminases 1 and 5
Formation of basal cell layer and basement membrane
- keratinocytes with stem cell properties
- express keratin isoforms
- key role in wound repair
Proteins in basal cell layer
- keratins 5 and 14
- keratin 15
Role of Filagrin mutations in Eczema
- cracks in skin barrier enable allergens and pathogens to penetrate dermis
- keratin fibres do not form dense, flattened barrier
- inflammation occurs, causing irritation in skin and other organs (e.g. asthma)
- filaggrin mutations reduce amount of filagrin in skin
