Introduction Physiology Flashcards
What are the main integumentary components of the integument?
Cutaneous membrane structures
- Epidermis and dermis layers
Accessory organs/structures
- Hair and nails
- Exocrine/sebaceous and sweat glands
- Sensory receptors and nerve fibers
- Cutaneous plexus
**hypodermis is not part of the integument and separates the integument from the deep fascia
The three skin layers of the integument
1) epidermis
- derived from ectoderm
- composed of stratified squamous epithelium with outer keratinization layer
- purpose is to create a multi-purpose barrier between internal and external environments
2) dermis
- derived from mesoderm
- composed of connective tissues and gives skin its strength and elasticity
- also contains sensory nerves and blood vessels and its job is to provide sensation and blood supply to the dermis
3) hypodermis (subcutaneous layer)
- NOT part of the integument technically
- contains nerves/blood and lymph vessels as well as 50% of total body fat
- function is to facilitate mobility of the skin and contribute to thermal insulation
What are the two types of skin?
Thick and thin skin
- thick = >5mm thick palms/and soles of feet and has thicker epidermis
- thin = 2-3mm thick with narrow epidermal ridges (finger tips)
What are common age related changes seen in the integument?
Fewer melanocytes
Drier/thinning epidermis
Reduced blood supply and slower skin repair
Altered hair and fat distribution as well as fewer active follicles
Decreased perspiration
elderly people are also more prone to heat stress due to impaired blood flow and atrophy of the subcutaneous fat
Two types of hair
Terminal hairs
- large, coarse, dark pigmented
- includes scalp and armpit hair
Vellus hairs
- smaller, shorter and delicate
- found on the general body surface
What is the hair called on neonates?
Lanugo
- is super thin and unpigmented
- replaced with vellus hairs shortly after birth
Hair regions and associated structures
Hair shaft:
- begins deep within hair follicle
Hair root:
- anchors the hair into the skin
- includes the hair bulb which is the bottom-most portion of the root and is where new hair is generated
Root hair plexus
- collection of sensory nerves that surround the base of the follicle
Arrector pili
- smooth muscle attached to hair folllicles
- contract hair when activated
Structures associated with nails
1) nail body
- visible portion of nail and is bordered by lateral nail grooves and nail folds
- covers the nail bed which is the underlying epidermis
2) lunula
- pale crescent part of the proximal nail body
3) nail root
- epidermal fold where nail production occurs
4) eponychium
- portion of the stratum corners of the nail root that extends over exposed nail
5) hyponychium
- area of thickened stratum corneum under the free edge of the nail
What are the three types of exocrine secretions used by the integumentary exocrine glands?
1) merocrine secretion
- releases membrane-bound secretory vesicles
2) apocrine secretion
- “pinches” off portions of the rim of cells in order to secrete secretory products
3) holocrine secretion
- mature cell dies and becomes the secretory product itself
Sebaceous glands
Holocrine glands that discharge sebum onto the hair follicules and skin surface
- contractions of arrector pili muscle causes the release of sebum
Sebum = mixture of triglycerides, cholesterol, proteins and electrolytes and consists of some antimicrbial properties
Apocrine vs merocrine sweat glands
Apocrine
- compound coiled tubular glands w/ large secretory acini
- limited to axilla, groin and nipples
- secretes contents into hair follicles
- produces viscous/sticky cloudy and odorous secretions
- possible function in olfactory communications
- strongly influenced by hormones
- **does NOT contribute to temperature regulation
Merocrine
- simple coiled tubular glands
- found pretty much everywhere (highest number is on palms and soles)
- small secretory acini
- produce water secretions with electrolytes
- controlled by the nervous system
- secrete contents onto skin surface directly
- important in thermoregulation and antibiotic properties
Receptors in the dermis
Meissner corpuscles
- mechanoreceptor
- found in the papillary layer
- detect light touch pressure and vibrations
Lamellated (Pacinian) corpuscles
- mechanoreceptor
- found in dermal and hypodermis layers
- detect deep pressure and vibration
Ruffini corpuscles
- mechanoreceptor
- found in the reticular layer
- sensitive to pressure and stretching of skin
Receptors in the epidermis
Free nerve endings
- found between epidermal cells
- sensitive to touch and pressure
Tactile (merkel) discs
- found in the deepest layer of the epidermis (basale)
- detects texture and steady pressure
Barrier function of the skin
Shields against UV radiation and mechanical damage
(physical shield)
- also fungi/bacteria and viruses (microbial shield)
- also against allergens and irritants. (chemical shield)
Immunity functions of the skin
Activates mast cells, macrophages and APCs (dermal dendrocytes) as well as fibroblasts
Releases histamine, PGE, leukotrienes, cytokines
- this dilates the blood vessels and increases capillary permeability
Convection
Heat transfer through a fluid or gas that carries heat between the body and environment
- caused by molecular motion
- usually water or air
- *convective heat loss is proportional to the difference between skin and ambient temperature
Radiation
Energy that is radiated or transmitted in the form of rays or waves/particles
- occurs between skin and solid bodies in theenvironment
- *rate is proportional to the temperature difference between the skin and the object
8 primary functions of the skin
Protection from injury
Barrier to prevent dehydration
Regulation of body temperature
Non-specific defensive barrier to microorganisms and immunocompetent dendritic cells
Excretion of salts
Synthesis of vitamin D
Sensory organ to the external environment
Sexual signaling
What are the three phases of hair and nail growth
1) growth (anagen) phase
2) regression (catagen) phase
3) resting (telogen) phase
What are the 2 layers of hair growth?
1) matrix zone = mitotic activity occurs
2) keratogenous zone = keratinization of hair cells occurs
What layer of the skin forms the hyponychium and eponychium of the nail?
Stratum corneum layer
What are two common nail shape variants that are highly linked to specific diseases?
Pitted or distorted nails = check for psoriasis
Nail clubbing = check for blood or pulmonary disorders (some type of anemia or chronic hypoxia)
What are the three cell types in merocrine (eccrine) sweat glands?
Basal clear cells:
- secrete water and electrolytes
Apical dark cells:
- secrete glycoproteins and defensins.
- secretes cathelidicin and dermicidin
Myoepithelilal cells
- only function to increase contractile activity of the other two cells
How does the perception of pain work?
Acute inflammation causes injuried cells to release chemical mediators which includes substance P.
- substance P both activates nerve ending nociceptors and also triggers degranulation of mast cells of histamine to induce vasodilation
Conduction
Heat transfer between a body and a solid material of different temperature (ice, hot sand, etc.)
- minimal heat gain or loss under most normal condtions
Evaporation
Heat transfer via a liquid (sweat) being directly converted into a gas and releasing energy
- *rate is independent of the temperature gradient between skin and environment
What are glomus bodies?
Arterial-venous anastomoses that are found in the skin
- apical skin = very high density
- nonapical skin = very low density and gains most blood flow via capillaries
Difference between preganglionic and postganglionic sympathetic fiber actions on skin
Preganglionic
- releases ACh
- causes vasodilation and formation of bradykinin
Postganglionic
- releases NE
- causes vasoconstriction
- strong sympathetic activity causes mass vasoconstriction and diaphroetic skin (cold clammy and sweaty)
Where are the primary temperature-sensitive neurons located?
In the preoptic area/ganglion
- are warm sensative neurons which promote sweating and vasomotor dilation
- receives inputs from skin temperature thermoreceptors
Dorsomedial hypothalamus
- are cold sensative neurons and receive inputs form skin temperature thermoreceptors
- generates thermogenesis command neurons
- shiver of the skeletal muscle fibers
- increased thermogenesis of the Brown adipose tissues
**both of these antagonize each other based on thermoreceptor inputs from skin
What nucleus of the hypothalamus controls body temperature?
Anterior hypothalamus
- regulates body temperature and controls sympathetic nervous system that innervates cutaneous AVMs and vasodilator or constricts based on what is needed.
skin temperature is directly proportional to blood flow of the skin
What receptor in cellular membranes allows H+ ions to bypass ATP synthase and generate heat rather than ATP?
UCP1
- upregulated in cold temperatures
CF and sweating
Defective CFTR receptors prevent the ability to reabsorb chloride ions before seat comes out of the merocrine sweat glands
- the inability to reabsorb chloride causes a major increase in negative charge which prevents sodium from being reabsorb as well leading to salt loss and salty sweat.
How does skin regulate vitamin D
Sunlight upregulates natural 7-dehydrocholesterol production in the skin
- this leads to secosterol -> cholecalciferol production (Vitamin D3)
- vitamin D3 enters the liver and then the kidneys to eventually become activated into 1,25 dihydro (activated D-3)
Melanocytes
Are neural crest derived cells that primary function is to produce melanin that is contained in melanosomes to be secreted to neighboring keratinocytes as needed
- Are located in the stratum basale of the epidermis
Function of melanin = provide color to skin/hair/eyes and photoprotection against ionizing radiation
- contains eumelains and pheomelanins
How is melanin produced
Oxidation of tyrosine AAs into 3,4 dihydroxyphenylalanine (DOPA)
DOPA is then transformed into eumelanin
albunism occurs when melanocytes either cant produce melanin or are too low in numbers to keep up
Griscelli syndrome
Mutation in the myosin Va gene
- produces silvery hair and partial albinism and immunodeficiencies
Glucocorticoid function on skin
Loosens intercellular connections of epidermis and results in decreased effectiveness of the barrier
Thyroid hormone function on skin
maintains normal blood flow to the sub papillary plexus of the skin
Sex hormones function on skin
Stimulates epidermal cell division and increases thickness of the epidermal layer
Also accelerates wound repair
Increases number of dendritic cells protection against cancer cells and pathogens
Growth factors effects on the epidermis
Stimulate cell growth and cell division in both the dermis and epidermis
Epidermal growth factor (EGF)
Promotes cell division in the deeper epidermal layers, keratin production, epidermal repair and secretion by epithelial glands and salivary glands
Growth hormone effects on the skin
Stimulates fibroblast activity and collagen synthesis
Stimulates basal cell division
Thickens epidermis
Promotes wound repair
4 phases of skin regeneration
1) inflammatory phase
- bleeding and injury occurs at the site of injury which triggers substance P to be released from damaged cells
- substance P casues degranulation of mast cells and inflammation response
2) migratory phase
- begins scab formation and galati on tissue formation
- patrolling macrophages remove debris and pathogens
- rapid cell division and migration along wound edges to replace missing cells occurs
3) proliferation phase
- deeper portions of the scab dissolve and fibroblasts produce new collagen fibers and ground substance
4) scarring phase
- formation of healed scar tissue
4 stages of damage recognition and repair mechanism
1) coagulation
- formation of the fibrin-platlet clot
2) inflammation
- leukocyte recruitment
3) proliferation
- neovascularization and formation of granulomation tissue
4) remodeling and resolution
