Scenario 1

Students should be able to:-

  1. Describe the structure and functions of skin.
  2. Describe the general structure and behaviours of human cells.
  3. Describe wound healing in the skin (at molecular, cell, and tissue levels).
  4. Distinguish between the terms: scratch, cut, abrasion and bruise.

Describe the structure and function of the skin.

Good source of information and more detail can be found here.


Stratum Corneum (Horny Layer) – 25-30 layers of flat dead cells, filled with Keratin, constantly shed and replaced by upward movement of cells. Stratum lucidum – only appears in thick skin 3-5 layers of clear, flat, dead cells containing droplet of eleidin, an intermediate before keratin. Stratum Granulosum - Granular layer – 3-5 layers of flattened cells, in this levels the nuclei break down and die, the cells contain granules of keratohyalin which becomes keratin. Stratum Spinosum – 8-10 layers of polyhedral cells that fit closely together, cells shrink when prepared for miscroscopy and so appear to have spines. Contains melanocytes and keratinocytes. Stratum Basale - Basal Layer – single layer of cuboidal to columnar shaped cells contains stem cells, which divide generating new cells, and melanocytes. The stem cells produce keratinocytes which push up to become the other layers.

Epidermal Layer Mnemonic:

Stratum Basalus
Stratum Spinosum
Stratum Granulosum
Stratum Lucidum
Stratum Corneum



Subcutaneous Connects skin to underlying structures and insultes body, contains areolar connective tissue and adipose tissue (fat cells) and nerve endings called lamellated or pacinian corpuscles.
Endothelial cells; line the blood vessels and the heart to provide as frictionless surface as possible for the blood to travel along and form new blood vessels at the site of wounds and within the granular tissue of scars.
Epithelial cells; cells of the epidermis of the skin.
N.B. Although most skin appendages are situated in the dermis they belong to the epidermis.

Skin Function

Regulates water loss in the body through sweat glands and temperature through blood flow. Also innervation of Hair/Good Pimples.
Waterproof barrier/ First body defence system to pathogens.
UV rays absorbed by melanin. Protection from friction and shearing forces.
Nerves allow us to interact with surroundings/ relay danger to reflex centre.

Skin Healing

Epidermal wound healing

  • In response to injury basal epidermal cells in the area of the wound break their contacts with the basement membrane.
  • These cells then enlarge and migrate as a sheet until the cells from opposing sides of the wound meet in the middle.
  • The continued migration is stopped by contact inhibition.
  • While some epidermal cells are migrating, epidermal growth factor is stimulating the others to divide and replace the ones that have left.
  • Migration continues until the wound is resurfaced then the migrated cells divide to form new strata. This happens with in 24 to 48 hours of the wound.

Dermal Wound

"His Injury Didn't Prevent Masturbation."

Chronology of Tissue Repair (See Below)

After tissue injury the body moves to maintain HAEMOSTASIS. Damage to endothelial lining releases activation factors which activate platelets to proliferate and to release certain chemicals involved in the response. The platelets initially adhere to each other and then to the sticky collagen and fibrinogen fibres exposed at the wound. Fibrin and Fibronectin then cross-link to form an initial platelet plug. Prostoglandins and thromboxanes released from activated platelets serve to constrict vessels to prevent blood loss until the other mediators are summoned. This constriction peaks between 5-10 minutes. This leads to the INFLAMMATION stage...Platelets also release pro-inflammatory chemicals such as cytokines, serotonin and histamine, which serve to increase cell proliferation and migration to the area, and to cause vasodilation which peaks at about 20 minutes after wounding, to increase blood flow to the area and to allow for diapedesis of leucocytes. Within an hour of wounding, thehe acute immune response increases the proportion of neutrophils in the blood in the first instance, from approximately 60% to about 95% of all leucocytes. Macrophages replace neutrophils within 2 days of wounding to become the predominant leucocyte involved in phagocytosis. T cells are also present which increase the activity of Macrophages. The inflammation last until all of the debris has been removed in the DEMOLITION phase. The Macrophages remove damaged tissue as well as debris. 2-3 days after injury the PROLIFERATION phase begins which serves to lyse the temporary clot and to lay down granulation tissue in the form of collagen and there is continued growth of blood vessels (angoigenesis.) Epithelial cells are stimulated by growth factors to increase in size and multiply to bridge the wound. MATURATION phase; The collagen fibres allign to give optimal tensile strength.The scab sloughs off once the epidermis is restored to normal thickness. Collagen fibres become more organised, fibroplasts decrease in number, and blood vessels are restored to normal.

Cut, Scratch, Abrasion, Bruise

Straight wound from a sharp edge, knife. Blood vessels cut straight bleed. Laceration - cut with rough edges.Inceration are clean cut wounds.
a small mark or cut.
A graze; a minor wound in which the surface of the skin or a mucus membrane is worn away by rubbing or scraping
An area of skin discolouration caused by the escape of blood from ruptured underlying vessels following injury. Changes colour through red, blue, purple, green and yellow as the hB in the tissue is chemically broken down and reabsorbed


Cleaning; with antiseptic or running water, gloves for our protection
Stop bleeding; applying pressure and elevating above the heart.
Closing the wound; if needed with suturing or joining of some kind (discussed next week) superficial wounds are best left to heal naturally.
Covering; with a dressing may promote healing and prevent infection.


Definition; Mark on the skin from wound healing. Growth of non-specialized tissue to replace dead cells.
First Intention: Only achievable in clean surgical wounds or in contaminated wounds that have been debrided (removal of dead tissue and foreign matter to clean an open wound) to provide clean wound edges though all layers and which can be approximated readily with the use of sutures. This type of healing is characterised by minimal development of granulating fibrous tissue in the scar and suture tracks there by achieving regeneration.
Second intention healing: This type of healing occurs in wounds that were too contaminated to close even after debridement, that is the wound could not be converted to a clean wound suitable for primary closure, or wounds that developed serious infections after closure. In second intention healing granulation tissue grows from the base of the wound and epithelial cells migrate inwards from the edges of skin to fill in the defect. This type of healing takes longer than regeneration due to a greater loss of original tissue, and a great production of granulation tissue which forms the resultant scar, large tissue surfaces may require skin grafting.
Keloid; Scars that extend beyond the boundaries of the original wound
Excessive collagen production
Smooth hard nodules
Persistent and may continue to enlarge
Hypertrophic;Raised scar site but stays within the boundary of the original wound
Due to increase cell size not division
Fades within 12 months

A and E

See Vocational studies notes for full explanation.
Immediate assessment of patient
Documents important information
First aid, other needed procedures
Monitors patient
Informs family

Co-ordinates treatment
Evaluates patient
Evaluates effectiveness
Arranges admission/discharge