Dermatology and Musculoskeletal

SystemPhysiology of the Skin

Lorentz E. Wittmers Jr.June 6, 2008

Contact Information

• 7934 (UMD SOM, room 351)

• 525-6273 (home)

• lwittmer@.umn.edu

• Updated 9:30 -- 6/3/08

Gunther von Hagens’Body Worlds

The whole-body plastinate demonstrateson the one hand how vulnerable man lookswithout the skin to protect him, and on the other hand the nature of the skin as an independent organ when there is no longera body inside of it.

Sixteen-century copper engraving Of flayed manholding aloft his own Skin.

The artist was probably Gaspar Becerra, himself an anatomist, who assisted Michelangeloin painting The SystineChapel.

Michelangelo’s Last Judgment portraying the martyred St.Bartholomew fully restoredin his resurrected body whileholding his own flayed skin.

Study Objectives

• Describe the normal anatomy of the skin.• What is the difference between “apical” and “non

apical” skin?• Describe the function of the epidermis.• How is skin blood flow regulated?• How does skin blood flow change with respect to

skin and core temperature?• Describe the pathophysiology of Raynauds

phenomenon. • Describe the pathophysiology of type 2 DM skin

problems.

Anatomy of the skin

Importance of skin in medical diagnosis!

You can….SeeFeel Sample ManipulateDamageTreat

IT !!!

Terminology

• Apical (glabrous) skin • is present in the palmar surface of the hand, plantar surface of the

foot, and the face. Apical skin is mainly involved in thermoregulation. It contains a large number of arteriovenous (A-V)shunts maintained in the constricted state by sympathetic tone.

• Nonapical (nonglabrous --hairy) skin• is present over most of the body surface. The blood flow is primarily

nutritive in function with intrinsic myogenic, sympathetic and endothelial regulation comparably involved.

Skin function - an overview• Control of water loss

• Temperature regulation

• Response to physical abuse

• Site of local immune response

• Protection against damaging agents

• Site of sensory input (pain, pressure and temperature receptors)

• Response to ultraviolet radiation (Melanin and vitamin D production)

Skin blood flow

• Anatomy of blood vessel arrangement

Two circulation levels connected by AVA

General features of skin blood flow

• Range- 0 to 7 L/min (total body)

• A-V anastamosis

• Skin color –blood volume and oxygen saturation

• Countercurrent flow patterns, somewhat important in heat conservation

Countercurrent flow patterns,

H H H H

hhhh

H-h

H is not much different than h

Skin blood flow and thermoregulation

Overview of thermoregulation:

Physics of heat exchange mechanisms

radiationconduction

convection

evaporation

Mechanisms of heat exchange with the environment

• Radiation

• Conduction

• Convection

• Evaporation

Heat transfer by radiation

T(1) =37 C T(2) = 10 C

Heat flow

H = AaKa[T(1)-T(2)](1/distance)

Heat transfer by conduction

T = 37 C T =10 C

Heat flow

H = Ab Kb[(T1)-T(2)]

Heat transfer convection

T = 37 C

Wind

T = 10 C

Heat flow

H= Kc(wind velocity)AKc2[T(1)- T(2)]

Evaporation

• Insensible water loss

skin

respiratory tract

• Sweating

Evaporation continued

skin

water PH2Oskin

PH2Oair = humidity

heat

water

H= AK(sw rate) [PH2Oskin – PH2Oair]

CORE TEMPERATURE

Defined as: the temperature of the brain, heart, lungs and gastrointestinal tract.

Measurement:Sublingual (oral)Rectal TympanicAxillaryEsophagealGastrointestinal (pill-transmitter)Aortic (arterial blood)

Core temperature with changing ambient temperature

• Thermal neutral zone

• Lower critical temperature

• Upper critical temperature

BMR = basal metabolic rate

Core temperature

central control of thermoregulation

Preoptic &Anteriorhypothalmus

Internal temperature

Skin temperature

Internal temperature

Skin temperature

Heat dissipation

Cutaneous vasodilation

Sweating

(-)

Heat dissipationCutaneous vasoconstriction

Heat generationshivering

(-)

Response to Heat and Cold• Resting skin blood flow –

250 ml/min• Measurement of skin

blood flow – laser Doppler flow meter and venous occlusion plethysmography

• Response to heating – threshold and sensitivity

Reflex neural control of skin blood flow.

A. Innervation.

• sympathetic adrenergic vasoconstrictor nerves• sympathetic vasodilator nerves

B. Vasoconstrictor control of body temperature.

• tonic activity of constriction controls temperature between LCT and UCT – the thermal neutral zone.

• Withdrawal of VC yields 10-20% increase in blood flow.

Skin circulation with hot and cold exposure

• C. The vasodilator system is only activated during environmental stress such as exercise or high ambient temperature.

• Neural component early response

• nitric oxide – 30% of total vasodilation on total body heating.

• D. Blood pressure control and skin blood flow.

• decreased blood pressure in normothermia results in vasoconstriction.

• decreased blood pressure in hyperthermia results in substantial withdrawal of vasodilation activity in addition to vasoconstriction.

• E. Skin blood flow and exercise.

• Competing demands on skin blood flow:

• initial constriction of skin, kidneys and splanchnic beds muscle

• as internal temperature rises, dilation to facilitate heat loss (under exercising conditions, the rise is less for any given internal temperature)

In a hot environment – large demands for blood supply to both skin and muscle.

Possible adjustments:

• increase in cardiac output• increase in vasoconstriction in splanchnic and renal

circulation• shift in blood flow from muscle to skin (muscle will shift to

anaerobic metabolism)• However, increased skin blood flow has its limits

Bad end is circulatory collapse.

Local control of skin blood flowWarming

• Phase 1 – C-fiber afferents – axon reflex resulting in vasodilation (transmitters - substance P, Nerokinin A, and calcitonin gene-related peptide)

• Phase 2 – nitric oxide dependent vasodilation

Rsponse to local heating- Control

Local skin Temp

Axon reflexSensory nerve cellreceptor

To CNS

Blood vessel

skin

f

Axon reflexSensory nerve cellreceptor

To CNS

Blood vessel

skin

F

heat

Tx with L-NAME

Blocked Cutaneous Nerve

Blocked Axon Reflex

Skin flow response to cold“cold induced vasodilation”

Fin

ger

tem

per

atu

re

One Minute

Hand in ice water

Cooling profound vasoconstrictioncold-induced vasodilation

Pathophysiology of Skin

• Type 2 diabetes mellitusobservation– increased risk of heat illness during heat spells!!!

Possible mechanisms:

Impaired response to local heating—vasodilator system

Impaired reflex control of skin blood flow (sweating and blood pressure control problems)

Pathophysiology of Skin

• Raynaud phenomenon (incidence 3-5%)hyperactive vasoconstriction initiated by

cold or emotional stressMechanism: local adrenergic processes including up-regulation

or sensitization of post synaptic 2- receptor in the digits,

Endothelin 1 CGRP*

cgrp=calcitonin gene-related peptide

Treatment with Pavlovian Conditioning

Treatment with Pavlovian Conditioning

• Air temp 0 degres C

• Water temp 43 degrees C

• Time 10 min

• 27 (MWF)

3/day-3wksR

R

TxC

13

10

Finger tempOn cold exposure

summary

Cutaneousarteriol

Local temp NO

Sensory afferents

Sympathetic vasoconstrictor nerves

Sympathetic vasodilator nerves

(-)

(+)

(+)

NE, NPY

?CGRP,NKA,SP

SKIN AND INTERNALTEMPERATURE

(+)

(+)

•stop