Superficial layers of the upper limb Flashcards
What are the 2 layers of skin?
Dermis and epidermis
What is the function of the epidermis?
Physical and chemical barrier between the body and its exterior environment
What is the function of the dermis?
Provides structural and nutritional support
What percentage of the total body mass comes from the skin?
16%
What is the average total surface area of the skin?
1.8m2
Why is the epidermis known as a stratified squamous epithelium?
It consists of many layers of closely packed cells, the most superficial of which are flattened and filled with keratin.
What are the 4 layers of epidermis from superficial to deep?
Stratum corneum
Stratum granulosum
Stratum spinosum
Stratum basale
What is the additional layer of epidermis only found in some areas?
Where is it located?
Stratum lucindum
Hands and feet, between corneum and granulosum
Describe the stratum basale
Single layer of cells which continually divide to replace those shed from skin
Where re melanocytes located?
What is their function?
Stratum basale
Produce the pigment melanin to protect from UV rays
Describe the stratum spinosum
Thickest layer with ‘prickle cells’ which are linked by numerous processes
Describe the stratum granulosum
Cells gradually accumulate keratohyalin granules which eventually overfill cells, destroying the nuclei and organelles
Describe the stratum corneum
Thickest in palms and soles and contains dead keratinocytes or squames which are continually shed from the surface
Describe the stratum lucindum
Only present in hands and feet. Contains tonofibrils (densely packed keratin filaments)
Which layer of the epidermis contains the most flattened cells?
Stratum corneum
How is the epidermis attached to the dermis?
Interlocking of its downward projections (epidermal ridges or pegs) with upward projections from the dermis (dermal papillae) at a site referred to as the dermoepidermal junction
Why are epidermal pegs structurally important?
They allow the skin to withstand abrasive forces and prevent the formation of blisters
What gives the dermis its strength?
The arrangement of its elastic and collagen fibres
Where is the dermis thin?
Eyelids
Where is the dermis thick?
The back
What causes the appearance of the skin in old age?
Thinning of the dermis and loss of elasticity
What are the 2 layers of the dermis from superficial to deep?
Papillary and reticular layers
What is the thickest layer of the dermis?
The reticular layer
What is the purpose of nails?
They provide a firm base for the pulp of the digit
Why does the nail bed appear pink?
The underlying capillaries supplying from the dermis
What are the 2 types of sweat glands?
Eccrine and apocrine
What is the function of eccrine sweat glands?
What are they controlled by?
Control body temperature and are controlled by the sympathetic nervous system
Where are apocrine sweat glands located?
Axilla, mammary areola and the anogenital region
What is the function of sebaceous glands and where are they found?
Produce sebum which provides a protective covering for the skin
Present throughout the skin except in the palms and soles
How is the blood supply to the skin mediated?
Arteriovenous anastomoses
What do Meissner’s corpuscles detect?
Where are they located?
Light touch
Fingers and lips
What to pacinian corpuscles detect?
Where are they located?
Pressure and vibration
Deep in palms, soles and genitalia
What is a dermatome?
An area of skin supplied by a single spinal nerve
What is the clinical importance of dermatomes?
Diagnosis of problems associated with nerve related disorders, peripheral nerves of spinal injuries
Administration of local anaesthetic
What is the superficial fascia composed of?
Loose connective tissue and subcutaneous fat
Is the superficial fascia thicker in men or women?
Women
Where is fat built up when weight is gained?
Subcutaneous fat in the superficial fascia
Where is superficial fascia absent?
The eyelids, scrotum and penis
Is the superficial fascia homogenous?
No, it can be differentiated into layers by fibrous tissue
Give an example of where superficial fascia is differentiated into layers
The anterior abdominal wall
Consists of:
- fatty layer (Camper’s fascia)
- membranous layer (Scarpa’s layer)
What is another term for deep fascia?
Investing fascia
What is the deep fascia composed of?
Collagen fibres arranged into lines of stress
Describe the appearance of deep fascia in the limbs
Tough white sheet of fibrous tissue which forms a non-elastic tight fitting sleeve
What is the function of the deep fascia?
Keeps underlying structures in position
Assists in venous return
Separates muscles and neurovascular bundles into compartments which limits the spread of infection
What are the 2 main superficial veins of the upper limb?
Cephalic and basilic
How is blood received from the fingers and hand?
Dorsal venous arch on the dorsum of the hand formed from the cephalic and basilic veins
What is the path taken by the cephalic vein?
Begins on the lateral aspect of the hand
Crosses the anatomical snuffbox
Runs up the lateral aspect of the forearm and arm to lie in the deltopectoral groove
Pierces clavipectoral fascia to join the axillary vein
What is the path taken by the basilic vein?
Begins on medial aspect of wrist
Runs up forearm on medial aspect of cubital fossa
Pierces deep fascia in mid-arm to join venae comitantaes of the brachial artery to form the axillary vein
What is the connection between the cephalic and basilic veins?
Median cubital vein in the cubital fossa
