SKIN STRUCTURE & FUNCTION [CSEC HSB]

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SYLLABUS REFERENCE 

CSEC HSB 

[B5.4] relate the structures of the skin to their functions. 

CSEC Biology 

[B7.11] relate the structure of the human skin to its function in temperature regulation. 

FUNCTIONS OF THE SKIN 


Protection 

  • Protects tissues beneath from mechanical injury and abrasion 
  • Protects from toxic chemicals and bacterial invasion 
  • Protects from desiccation as a result of evaporation 
  • Protects from the destructive effects of ultraviolet (UV) radiation in sunlight. 

Nutrition & Food Storage 

  • Vitamin D can be synthesised in the skin, with exposure to sunlight 
  • Long-term energy storage in the form of lipids, in the adipocytes. These fat cells are held in the adipose layer in the dermis of the skin 

Sensitivity 

  • Contains numerous sense organs which are sensitive to:
    • Temperature 
    • Touch 
    • Pain 
  • This contributes towards making humans aware of changes in their surroundings. 
  • This sensitivity also protects by initiating voluntary and involuntary withdrawal actions, such as:
    • Voluntarily moving away from heat 
    • Reflex withdrawal of fingers from a hot object, preventing further damage. 

Temperature Regulation 

It helps to keep the body temperature constant via:
  • sweat production 
  • changes in blood flow 

Teeth, hair, nails and mammary glands, all of which have their own functions, are essentially modifications of the skin. 

STRUCTURE OF THE SKIN 




  • Skin is the largest organ in the body. 
  • When looking at a cross-section, one can divide the skin into two main layers:
    • Epidermis 
    • Dermis 
  • Each of these layers contain sub-layers and several other structures. 



The Epidermis 

  • This layer consists of several sub-layers. The three most important layers are:
    • Germinative layer (Stratum germinativum) 
    • Granular layer (Stratum granulosum) 
    • Cornified layer (Stratum corneum) 
  • Blood vessels are absent in this layer, so nutrients and oxygen are obtained via diffusion and active transport from capillaries in the dermis. 

Germinative Layer 

  • Includes actively dividing cells. New epidermis comes from here. 
  • Melanin is produced here. This chemical absorbs UV and determines skin colour. 
  • Contains cells that produces the protein keratin. Keratin is used in the production of hair, nails, and the skin's outer layer. 
  • Infoldings produces sweat glands, hair follicles, and fingernails. 

Granular Layer 

  • Living cells recently pushed from the germinative layer. 
  • These cells are gradually pushed to the outside by the accumulation of new cells beneath them. 
  • Deposits of keratin are formed in them as these cells are pushed outward. 
  • As they move to the surface, they lose their nuclei, and become flattened. 

Cornified Layer 

  • Flat dead cells full of keratin. 
  • This makes a tough, bacteria-resistant, waterproof coat, which makes it a barrier between the human and their environment. 
  • The cells of this region are continually worn away and replaced from beneath. 
  • Palms and soles of feet have a very thick cornified layer. 

The Dermis 

  • A layer of connective tissue which has relatively few cells. 
  • It has many collagen fibres and a small number of elastic fibres. 
  • In the dermis, you would find:
    • blood capillaries 
    • nerve endings 
    • lymphatic vessels 
    • sweat glands 
    • hair and hair follicles 
    • sebaceous glands 




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