Mod2-Obj6: The skin Flashcards
skin contains the 4 primary tissues
1.) Stratified squamous Epithelial tissue in the epidermis 2.) Connective tissue In the dermis 3.) Smooth muscle tissue In the arterioles attached to hairs 4.) Nervous tissue In sensory nerves
The skin
Largest and heaviest organ
-Covers the entire body and weighs 4-5kg
-Part of the integumentary system (skin, glands, hair, nails)
Integument=covering
Layers of the skin
Consists of 2 layers 1.) Epidermis Outer epithelial layer 2.) Dermis Supporting layer of dense connective tissue
Hypodermis
Loose connective tissue and fat
- Anchors skin to the body
- Not part of the skin
The epidermis: Avascular
Like other epithelium
-Oxygen and nutrients obtained from dermis
The epidermis: Dynamic steady state
Cells constantly die and renew
-New cells originate from stem cells
The epidermis: Constant renewal
Epidermis replaced every 25-45 days
The epidermis
Cells move from deepest layer to more superficial layer
- Flatten
- Produce large amounts of keratin
- Continually replenished
The 5 epidermal layers (strata)
- ) Stratum basale (basal/deepest layer)
- ) Stratum spinosum
- ) Stratum granulosum (cells begin to die)
- ) Stratum lucidum
- ) Stratum corneum (most superficial layer)-cells are dead, produce large amounts of keratin providing waterproofing for the surface of the body
The epidermis: Stratum corneum (top)
20-30 cell layers
-Dead keratinised flattened cells
The epidermis: Stratum basale (bottom)
Stem cells
-Old cells pushed to surface
5 cells of the epidermis
1.) Karatinocytes Produces keratin 2.) Melanocytes Produces melanin 3.) Merkel cells Touch receptors (tactile) 4.) Langerhanan's cells Immune system (macrophages), bone marrow
The dermis
-Bulk of the skin Connective tissue -Fibroblasts and macrophages -Collagen and elastin fibres -Strength and flexibility
Dermis contains
- Blood vessels
- Nerves and sensory receptors
- Glands
- Hair follicles
Blood supply to the skin
Dense capillary network in hypodermis
-Capillary loops project up through dermis
Blood flow through loops regulates by capillary sphincters
-temperature control (homeostasis)-vasoconstriction/vasodilation
Nerve supply to the skin: Network of nerve fibres
Dense network of fibres
Control:
-Blood flow (via sphincter)
-Glandular secretion i.e.) sweat
Nerve supply to the skin: Sensory information
Collect sensory information
- Pain
- Temperature
- Touch and pressure
6 Functions of the skin
- ) Protection (chemical, physical, biological)
- ) Sensation
- ) Metabolic function
- ) Blood reservoir
- ) Excretion
- ) Temperature regulation
Function of the skin: Protection
Offered by chemical, physical and biological barriers
Protection: Chemical barriers
- Low pH secretions (acid mantle) prevent bacterial growth
- Defensins secreted by skin to kill bacteria/fungi
- Melanin protects DNA in underlying cells from UV damage
Protection: Physical/mechanical barriers
- Keratin and oily secretions block most water and water soluble substances
- Some penetration of skin by lipid-soluble substances, some drugs (topical)
Protection: Biological barriers
Macrophages dispose of viruses and bacteria that penetrate the epidermis
Functions: Sensation
Cutaneous sensation
3 receptor types (providing information about external environment)
Function: Sensation; Pain receptors
Noiceceptors
Function: Sensation; Temperature receptors
Thermoreceptors
Function: Sensation; Touch, pressure and vibration receptors
Mechanoreceptors
Functions: Metabolism
Synthesis of vitamin a precursor
Functions: Blood reservoir
Can hold 5% of blood volume
Functions: Excretion
Nitrogenous wastes and salts excreted in sweat
Function: Temperature regulation
At elevated temperature dermal blood vessels dilate and sweat gland activity increases
-Cools the body
Function: Temperature regulation (heat input and output balanced)
- Monitored by thermoreceptors
- Information sent to thermoregulatory centre (hypothalamus)- set point
- Coordinated response via circulatory system (vasoconstriction/vasodilation) and sweat glands
- Homeostasis
Skin colour: Melanin
Produced by melanocytes
- Melanin migrates to keratinocytes
- Forms ‘pigment shields’ for DNA
Skin colour: Freckles and pigment moles
Local accumulation of melanin
Skin colour: Melanocytes stimulated when exposed to sunlight
Darker skin produces more melanin
Diseases and altered colour: Cyanosis (blue)
Lack of oxyhaemoglobin
Diseases and altered colour: Erythema (redness)
Inflammation, allergy, fever
Diseases and altered colour: Pallor (white)
Anaemia, low BP, stress
Diseases and altered colour: Jaundice (yellow)
Liver disorder
Diseases and altered colour: Bronzing (metallic bronze)
Adrenal cortex problem or pituitary gland tumor
Diseases and altered colour: Bruises (black/blue)
Blood clots
Development and ageing
The effects of abrasion, sun, chemicals
- Skin thins-Cell number
- Wrinkles form-Collagen&elastin
- Dry and itchy-Oil and sweat glands
- Increased chance of skin cancer-Melanocyte number
- Age spots, hair loss, grey hair, colder skin, thicker nails
