W2 Lecture 2 28/02 Flashcards
Layers of skin
Epidermis, dermis, hypodermis
Epidermis
Epithelium (stratified squamous), upper layers dead, filled with keratin (waxy protein), living cells replaced every 35-45 days
Epidermis keratinocytes
Keratinocytes - squamous epithelial cells, Stem cells – in the basal layer, Contain keratin – protein, tough and non-polar (water insoluble), Also have lipids interspersed (also non-polar)
Other cells in the epidermis
Melanocytes – epithelial cells, make melanin
Tactile (Merkel) cells – epithelial cells, detect touch, connect to a neuron
Dendritic cells – immune cells
Protection versus UV
Less cells in palms/soles, skin colour depends on production rates, eumelanin is brown/black - absorbs UV
Genetics - albinism
Autosomal recessive disorder
Defect in melanin production/distribution
Very pale skin
May affect eyes
Sensitive to UV damage
Dendritic cells
Antigen presenting cells, Forms a near, continuous network, Detect invaders, Actually connective tissue cells
Tactile cells
Formerly called Merkel cells, Epithelia adapted to detect touch, Connect to neurons (nerve cells)
Function of keratinocytes (cell type of the epidermis)
Barrier to polar molecule movement and pathogen
Function of melanocytes (cell type of the epidermis)
Produce melanin, protect from UV
Function of dendritic cells (cell type of the epidermis)
Monitor skin bacteria, detect pathogens
What does dermis contain??
Neurons, blood vessels, receptors, hair follicles, sweat glands
What are the two layers of the dermis?
Papillary and reticular
Papillary
20%, loose (aerolar) connective tissue, superficial
Contains blood vessels, neurons, tactile cells
Fingerprints
Reticular
80%, dense connective tissue, much collagen and elastin, deeper, form stretch marks, continuous with hypodermis
Lines of cleavage
Formed by collagen and elastin, in parallel bundles, important in surgery
Hypodermis
Subcutaneous layer, mainly adipose tissue
insulation, infants and elderly have less
The dermis of the skin is deep relative to..
Epidermis
Which layer of the dermis is strongest and why?
Reticular layer - dense CT has more structural properties
Which layer of the skin is deep relative to the dermis and is made of adipose cells?
Hypodermis/ hypodermic
What do adipose cells contain and what is their function in this layer of skin?
Fat (lipids) for insulation
Skin secretions
- low pH retards bacterial multiplication – sweat
- sebum oils and defensins kill bacteria
Dendritic cells of epidermis and macrophages of dermis
Present foreign antigens to white blood cells
Dilation
Heat loss (conduction) & prevent heat gain
Constriction
Heat retention
Sweat Glands
Epithelial ducts project into dermis/hypodermis. Have nerve and blood supply. Secrete onto epidermal surface. Cuboidal and columnar epithelium.
Eccrine - skins (sweat glands cont.)
All over skin, secrete water
Apocrine
In axillary regions. Secrete water + protein, oil
Sebaceous glands
Secrete sebum (oil). Most on hair follicles
Parts of the hair
Shaft, Follicle/root, Bulb, Papilla, Arrector pili, Sebaceous gland
What type of tissue are hair follicles and sweat glands made from?
Epithelial tissue
5 main modalities of cutaneous sensations
Pressure, touch, temperature, pain, itch
Free nerve endings
Are the branching tips of sensory neurons; are unprotected & nonspecific; can respond to tactile, pain, and temperature stimuli
Root hair plexus
Monitor distortions and movements across the body surface; adapt rapidly
Tactile Discs
Fine touch and pressure receptors; are extremely sensitive tonic receptors with very small receptive fields.
Merkel Cells
Unusually large epithelial cells in the stratum germinativum of the skin.
Tactile discs (Merkel) (touch)
Epidermis
Tactile (Meissner’s) corpuscles
Dermis
- in hairless skin
Hair follicle receptors
Dermis
- detect hair bending
Lamellar (Pacinian) corpuscles (pressure)
Dermis
- especially vibration
Bulbous corpuscles (ruffini endings)
Deep dermis, hypodermis
- deep continuous pressure
Heat (temperature)
Nerve endings, deeper in the dermis
Cold
Nerve endings, more superficial in the dermis
Nociceptors (pain)
Fast pain and slow pain
Different kinds respond to: (4)
Excessive heat, pinch, chemicals (acid), (itch)
What are the four sensation modalities?
Touch, pressure, temperature, pain, + itch
What are pain receptors called?
Nociceptors. They are modified nerve endings.
In which layer of skin are most of these sensations detected?
Dermis
What is a burn?
Temperature damage to skin. Classified by the level of penetration to which damage occurs.
First degree
Top layer of skin or epidermis
Second degree
Middle layer of skin or dermis
Third degree
Deepest layer of skin or hypodermis
