Lecture 19 - Skin Structure And Function Flashcards
Other term for the Skin
The integumentary system
General Structure of the skin (Macroscopic)
3 layers
Epidermis
Dermis
Hypodermis
Primary functions of the skin
-Protection and repair
-Thermoregulation and excretion of waste (ions)
-Lubrication (sebaceous glands release oil onto surface
-Energy storage (Hypodermis)
-Vitamin D synthesis
-Absorption (water, O2)
-Aesthetics (communication, attraction)
-Sensation (has receptors)
What are the 4 layers in the Epidermis?
Stratum Corneum
Granular Layer
Stratum spinosum
Basal cell layer
What is the extra layer of cells in thick skin?
Stratum lucidum
A transparent layer ONLY on Palms and Soles of feet
How are cells held together laterally in the epidermis?
Adherens junctions
How are cells/layers held together Basically/Apically?
By desmosomes
Function of epidermis
Prevent water loss (keratinised layer of squames)
Prevents pathogenic entry
Synthesis keratin
What is the Stratum Corneum?
Outermost layer (made of dead keratinocytes/squames)
Continuously sheds
Granular layer structure (What type of cell? What does it contain?)
Stratfied squamous epithelial cells
Lamellar bodies (contain lipids needed to form water barrier)
Tonofibrils and Keratohyalin granules (Make keratin matrix)
Stratum spinosum (what does it do and what does it contain? What type of cell?
Cuboidal epithelium
Produces lamellar bodies
Langerhans cells/Epidermal dendritic cells = Macrophage of the skin most prominent here
Basal cell layer structure and function, what type of clell?
Tall columnar epithelial cells
Where keratinocytes are produced
As keratinocytes differentiate they migrate away from basal layer towards Stratum Corneum
Make intermediate keratin filaments called TONOFILAMENTS
Where Melanocytes are found
3 Layers of the dermis
Papillary layer = Upper layer (Nipples of skin here)
Reticular layer - Lower layer (has appendages of skin, hair, sebaceous glands , sweat glands, blood vessels)
Dermal papillae - Region between ridges of epidermis and dermis
Dermis functions:
Is IRREGULAR DENSE CONNECTIVE TISSUE
Hairs and Sweat glands = Thermoregulation
Contains sensory structures (mechanoreceptors)’
Gives structure to the skin and so body shape
Where is the Hypodermis?
Lowest layer of skin (not considered part of the skin though)
Structure of the Hypodermis
Mainly adipose tissue
Loose connective tissue so contains fibroblasts/macrophages and protein fibres
Functions of the Hypodermis
Energy storage
Insulator for heat generated from muscles
Shock absorption
Connects skin to muscles and bone underneath
Makes hormones like leptin (appetite)
What do Keratinocytes do?
Make Keratin
What are Rete ridges?
The ridges/protrusions of the epidermis into the dermis
Mucous Membranes structure (3 layers)
Epithelial layer (cells attached to basal Lamina)
Lamina Propria (connective tissue, blood capillaries, lymph vessels)
Muscularis Mucosae (Smooth muscle fibres)
What is a skin appendage?
Skin associated structures that serve a particular function
List 4 skin appendages
Hair follicles
Sebaceous glands
Sweat glands
Nails
2 Main types of hair
-Vellus (Replaces Languo hairs that are only present on the developing fetus)
-Terminal
Vellus hair structure/features
Short
Thin
Light coloured
Soft
Terminal Hair structure/features
Long
Wide
Dark
Coarse
Where are Vellus hairs found around the body?
Over most surfaces
NOT on palms, soles of feet, glans penis and glans clitoris etc…
Where are Terminal hairs found?
Head (scalp, eyebrows, nasal passage)
Axillae = armpit
External genital region
Hair functions
Thermoregulation
Sexual Attraction
Sensation
Protection
Hair in Thermoregulation
Arrector pilli muscles contract when cold to make hair stand up
Act as partial barrier to UV
Hair in sexual attraction
Hairs trap oils secreted by Apocrine Sweat Glands
Oils attract opposite sex
Hairs in Sensation
Have sensory nerve endings in bulb
Detects air movement/vibrations
Provides sensory awareness
Hair in Protection
Prevent entry of dust and pathogens in body
Eyebrows reduce amounts of light and sweat entering eyes
Axilla hair (armpit) removes sweat from the body
What type of muscle fibres do arrector pili muscles consist of?
Smooth
What type of Gland in terms of secretion is the Sebaceous gland?
Holocrine gland
What does the Sebaceous gland produce?
Sebum (oily waxy substance)
Functions of sebaceous gland
Lubricate skin and hair
Reduce water loss from skin and hair
Reduce damage of epidermis from friction
Protect from moisture and UV damage
Where are sebaceous glands found?
Face and Scalp
Eyelids
Penis
Labia
Nipples
Lip
Are sweat glands Endocrine or exocrine glands?
Exocrine
Secrete substances (Sweat) via a duct onto epithelial cells
2 Types of sweat gland
Eccrine Sweat glands
Apocrine sweat glands
Where are Eccrine sweat glands found and their purpose?
All over the body
Cooling
Where are apocrine sweat glands found and their purpose?
Mainly axilla (Armpit)
Perianal areas
Produces sweat that has odor once activated (pheromones)
Location of Nails
Distal surface of phalanges (fingers and toes)
Nail structure
Made of Alpha keratin
Nail plate
Nail matrix
Nail bed
Functions of nails
Protection of distal phalanx
Enhances precise delicate movements
A tool (extended precision grip) e.gg pull splinter out
Types of Mechanoreceptors found in the skin
End bulbs
Free nerve endings
Tacitle discs (Merkel discs/corpuscle and Meissner discs)
Pacinian corpuscle
Ruffini’s corpuscle
Root hair plexus
What do End Bulbs detect?
A Thermoreceptor
TEMPERATURE
What do free nerve endings detect?
Pain (Have nociceptors)
What do Meissner corpuscles detect?
Light touch, vibration
What frequency of vibration do Meissners’ corpuscles detect?
Between 10 to 50Hz
What do Pacinian Corpuscles detect?
Pressure/vibration
What frequency of vibration do Pacinian corpuscles detect?
Between 100-1000Hz
What do Krause end bulbs detect?
Cold temperature
What do Ruffini’s corpuscles detect?
Joint movements and tissue stretch
What do merkel cells/discs detect?
Light touch
What are the 2 types of skin?
Hairy Skin (Thin)
Non-Hairy Skin (Thick)
What are the exceptions to the rule of Hairy skin being thin and non hairy skin being thick?
Lips
Back of pinna
Some areas of external genitalia
Where is Non-Hairy (Thick) skin located?
Palmar surface of hands
Plantar surface of feet
Area between fingers and toes
Structure of Non-Hairy (Thick) skin
No hair follicles
No sebaceous glands
NO arrector pili muscles
THICK Stratum Corneum
Stratum lucidum present (transparent layer only in thick skin)
Pronounced/large rete ridges
Regular shaped Dermal papillae
Thin (Hairy) skin structure
Hair follicles present (Vellus and/or terminal)
Sebaceous glands
Arrector pili muscles
Smaller rete ridges
Irregular shaped dermal papillae
NO STRATUM LUCIDUM
How to differentiate between Hairy (Thin) and Non-Hairy (Thick) skin
Non hairy/ thin = deep rete ridges and extended dermal papillae
Thick skin = thinner dermis but thicker Stratum Corneum in epidermis
How is the structure of Non-hairy (thick) skin relevant to its function
Prevent tissue loss due to abrasion (thick stratum Corneum)
Increased friction between skin and surfaces (No sebaceous glands so no lubricating sebum)
Increased sensation (MANY mechanoreceptors)
Where are Melanocytes located?
Basal cell layer
What are melanosomes?
Organelles produced by melanocytes
What do melanosomes do?
Synthesis melanin
What is the function of melanin?
Covers the nuclei of cells in the Epidermis to protect DNA from UV damage
(Stops formation of Thymine dimers)
What are Langerhans cells?
Macrophages residing in the epidermis
They are dendritic cells (present pathogenic antigens to Reticuloendothelial system)
Where are Langerhans cells found?
Most prevalent in Stratum spinosum
