Lecture 11: Skin Physiology

major functions of skin

• largest organ in the body based on bulk

• protects from desiccation and the environment

• communicates with environment

The major components of the skin are the _______ and ______, and they are _________ dependent.

epidermis

dermis

mutually

Why does skin thickness cary among species, ages, breeds, or sexes?

mechanical stress

body location

species adaptations

layers of the epidermis (top → bottom)

stratum corneum

stratum lucidum

stratum granulosum

stratum spinosum

stratum basale

Which layer of the epidermis acts as a barrier to water loss and pathogens?

most superficial layer of epidermis

stratum corneum

Which layer of the epidermis provides extra protection in specialized regions?

stratum lucidum

Which layer of the epidermis is the keratinization transition, and is prominent in certain areas

Which layer of the epidermis functions in mechanical strength?

stratum spinosum

Which layer of the epidermis is the stem cell layer?

stratum basale

True/False: Differentiation progresses from the basement membrane towards the skin surface.

True

Which epidermal cell type functions mostly in barrier formation?

keratinocyte

Which epidermal cell type functions mostly in UV protection by preventing sunburn and DNA damage, as well as the synthesis of melanin?

melanocyte

Which epidermal cell type functions in antigen prevention, immune tolerance, and prevents autoimmune reactions? This cell is also responsible for the immune-mediated tick resistance of Holstein and Brahman cows.

langerhans

Which epidermal cell type functions in inflammation, immune surveillance, wound healing, and allergic reaction

Which epidermal cell type functions in touch sensations, including fine details and pressure mechanoreceptors?

merkel

basement membrane functions

barrier against pathogens

regulates passage of nutrients and waste

interface between dermis and epidermis

dermis

fibrous connective tissue of skin

functions of the dermis

support and protect epidermis (strength and flexibility)

regulate body temperature (blood vessels and sweat glands)

facilitate sensation (nerve endings and touch, temp, pressure, pain, etc.)

__________ maintain skin health and structure by controlling electrolytes and water (skin hydration).

Mucopolysaccharides

Which layer of the skin is made of a loose fibrous connective tissue and adipose tissue?

hypodermis

Hypodermis functions

• insulation and fat storage

• connect skin to muscle and bone

• protection (fat gives cushion)

functions of hair

mechanical protection for animals (hair, hooves, feathers, etc.)

thermoregulation (retain heat, protect against excessive heat, sweat glands)

protection (physical barrier (sunburn, injury, ect.)

sensory perception

communication

Tactile hairs

sensory perception

thick hair above lips, close to nse, are very sensitive

whiskers on face detect surroundings

carpal whiskers on cats are used for hunting, climbing, senses, environment

stratum corneum epidermal layer

thin in animals with thick, dense fur or hair

thick in humans

Permeability of a substance is determined by the properties and state of the stratum _________.

corneum

two routes for a substance to penetrate skin

transepidermal

transappendageal

transepidermal route of permeation

route used for drug patches

• transcellular → substance must be able to pass through cells (lipid and aqueous components)

• intercellular → substance passes through lipid matrix around cells (route favored by drugs)t

transappendageal route of permeation

pilosebaceous apparatus (sebaceous gland, sebaceous gland duct, follicular epithelium)

hydrated skin is [more/less] permeable

more

A high skin temp [increases/decreases] blood flow and [increases/decreases] permeability

Skin injury or disease [increases/decreases] permeability

increases

Younger skin is [more/less] permeable

more

Thicker skin is [more/less] permeable

less

Small molecules penetrate [easily/difficultly]

easily

lipid soluble substances penetrate [easily/difficultly]

easily

[Ionized/Nonionized] substances penetrate easily.

non-ionized

Longer contact time may [increase/decrease] penetration.

increase

UV radiation penetration level and main effect

epidermis

DNA damage

visible radiation penetration level and main effect

dermis

heating, increase in blood flow, sweat

infrared radiation penetration level and main effect

deep tissues

heating

UVA

aging

UVB

sunburn and vitamin D

UVC

filtered by atmosphere

Photosensitization can be caused by…

drugs or toxins in plants

formation of Vitamin D

7-dehydrocholesterol in skin + UVB irradiation = vitamin D3

herbivores, pigs, and chickens can synthesize vitamin D3 in skin

dietary vitamin D (D2) is required for dogs and cats, as they cannot synthesize it in the skin

Apocrine glands (opens into, secretion, function, distribution)

opens into: hair follicle (ducts to pilosebaceous canal)

secretion: protein/lipid-rich (mix w/ sebum to create pheromones)

function: pheromones and/or cooling

distribution: most domestic animals

Eccrine glands (opens into, secretion, function, distribution)

opens into: skin surface

secretion: watery

function: cooling

distribution: limited in many domestic species

thermoregulatory sweating

warmed blood from the core goes to the periphery and then arrives at the brain → stimulates the hypothalamic thermoregulatory center → sweating if needed

afferent nerve impulses from periphery stimulate the thermoregulatory center in the brain via a reflex mechanism

sweat contains…

Water, Na, K, Cl, urea, ammonia, lactic acid

bacteria action on sweat creates odor

sebaceous glands

associated with hair follicle and open into pilosebaceous canal

secrete sebum → fatty lubricant

Ex. perianal/circumanal glands of dog (modified sebaceous glands with no defined ducts, substance serves as territorial scent marker)

• resemble endocrine glands

• usually released during defaccation

• also in cats and pigs

perianal/circumanal glands of dog

• modified sebaceous glands with no defined ducts

• substance serves as territorial scent marker

• resemble endocrine glands

• usually released during defaccation

• also in cats and pigs

sheep sebaceous glands

associated with wool and hair follicles

cattle sebaceous glands

highly developed

perianal region, horn, hoof, and muzzle regions

secretion of sebum

• secretion is fairly continuous

• skin temp can affect viscosity

• testosterone/androgens stimulatory to sebum production

pheromone/olfactory signal

• species specific

• sebum secreted by different glands have characteristic odors

waterproofing

• acts as emollient to keratinized superficial skin layer

• provides luster to hair coat

• reduces friction

sebum functions

secretion

pheromone/olfactory signal

waterproofing

antimicrobial activity