Traces the skin from early chordates through fishes, amphibians, reptiles, birds and mammals, noting how the epidermis, glands and keratinised layers change at each stage. It then covers embryological origins of the epidermis, dermis and hypodermis, key signalling pathways, skin stem cells, and developmental abnormalities such as Blaschko's lines and ichthyosis. Several mnemonics and a recap question set are included.
Inside: 9 sections · 16 flashcards · 9 min
Topic 65 of 105 in the MU Sofia syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 9 sections, about 1,230 words (9 min of reading), with 16 flashcards.
In this note
Phylogeny and development of the skin
Structure and Function of the Skin
Skin Derivatives
Phylogenetic Evolution of Skin
Embryological Development of the Skin
Skin Stem Cells and Renewal
Developmental Abnormalities of the Skin
RECAP QUESTIONS
MNEMONICS
Structure and Function of the Skin
The skin is the outermost covering of the body in all vertebrates.
It has three main layers:
Epidermis – the outer layer, derived from ectoderm
Dermis – the middle layer, derived from mesoderm
Hypodermis (subcutaneous tissue) – located beneath the dermis, composed of loose connective tissue and fat cells
Functions of the skin:
Acts as a protective barrier against mechanical damage, pathogens, and UV radiation
Minimizes water loss in terrestrial animals
Participates in thermoregulation, vitamin D synthesis, and storage of water and fat
Contains sensory receptors, blood vessels, hair follicles, and skin glands
Dermal papillae project into the basal layers of the epidermis and contain capillaries and sensory nerve endings
Skin Derivatives
The skin can give rise to several specialized structures:
Scales – bony (in fishes) or horny (in reptiles)
Feathers – found in birds
Hair – characteristic of mammals, derived from the epidermis
Claws, nails, and hooves – all derived from epidermis in mammals
Glands – such as sebaceous and sweat glands, found in mammals
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