10. The Skin,
Regulation of Body Temperature.
& BMR
By the end of this lecture, the student should be able to:
oDescribe the microscopic anatomy of the skin.
oAcquire knowledge of the functions of the skin.
oList the methods of measurement of human body temperature oIdentify the factors affecting human body temperature
oExplain how the normal body temperature is maintained oDescribe body temperature abnormalities
oDefine fever, heat stroke and hypothermia.
oDefine Anabolism and catabolism
oDefine basal metabolic rate and conditions of its measurement.
oOutline factors affecting basal metabolic rate.
Objectives
2 The microscopic anatomy of the integumentary system; the skin.
Functions of the skin.
Regulation of body temperature.
Factors affecting body temperature.
Fever, heat stroke and hypothermia.
Metabolism
Basal metabolic rate
Outlines
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The integumentary system(I.S)
The I.S. consists of skin and its accessory structures (hair ,nail & glands ).
Skin is the largest organ of the body. It consists of :
Epidermis: It is an outer, thinner layer; & composed of epithelium
Dermis: It is an inner, thicker layer & is composed of connective tissue.
Hypodermis (Subcutaneous layer not part of skin). It is for:
♦ Fat store ,
♦ Blood vessels (large)
♦ Pacinian corpuscles (sensitive to pressure).
1. The largest organ of the body is _____
A. Skin B. Liver C. Heart D. Lung
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Skin appendages:
1. External or obvious:
Nails : the colour of which, texture , & shape are useful in the diagnosis of many systemic diseases.
Hairs : the distribution of which is determined by genetic & endocrine processes.
2. Internal or hidden:
Sebaceous glands.
Sweat glands.
Erector pili.
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Features of the skin
The skin is the largest organ in the body. In an adult : its weight is 15% of the TBW i.e. 10Kg., & its surface area is about 1.5-2.0m2 .
It is the natural dressing of the body.
Its thickness varies. It is thickest over the soles & thinnest over the eyelids.
Its colour varies according to race & region. In the same
person , the colour varies from one area to another according to the degree of exposure to the sunlight.
Using a magnifier you can see many lines that are parallel
& circular on the palms & soles in a very specific way that varies from one person to another & known as fingerprints.
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Functions of the skin
Sensory functions.
Absorptive functions.
Protective & preventive functions.
Secretory functions including synthesis of Vitamin D
Regulation of body temperature.
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Sensory functions
Numerous nerve endings(in the skin) serve the function of pain, touch , hot & cold, pressure, vibration, stretch & hair movements.
These sensations give us information about the immediate environment. They also play a
protective role.
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Absorptive functions:
The skin can absorb some drugs easily e.g.
chloroform , ether , & steroids. Absorption is increased by massage.
Some gases like oxygen & carbon dioxide can pass through skin.
Absorption power is enhanced by
inflammation of the skin. This is very
important to remember on prescribing topical therapy containing steroids or toxic substances .
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Protective functions
The skin protects the body from harmful external effects such as mechanical , physical , chemical , or biological.
*The skin resists mechanical effects by: The stratum cornium (fixed &
hard)., The dermis (connective flexible tissue) & Sub-cutaneous tissue(
which acts as a pillow.)
* The skin is a poor conductor of heat .Hence it protects from sever cold & sever hot & helps to keep the core body temperature constant.
*The skin resists harmful radiation found in the UV light (carcinogenic solar radiation of the wave length 320 nm. (UVB is of 280-320nm has a carcinogenic effect).
*The stratum cornium (cornified layer) is water resistant .This resists water loss & gain through the skin if the body is immersed in water.
*The skin protects against micro organisms by its germicidal secretions.
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Secretory functions:
External secretions of the skin:
Sweat: sweat is a watery secretion containing NaCl , protein metabolites e.g. urea , ammonia, uric acid etc. -volume ½ - 5 lit./day .
secreted by sweat glands that are of two types:
-The eccrine sweat glands &the apocrine sweat glands their ducts open into hair sheath. They become active after puberty .
Decomposing of their secretion by bacteria is responsible for the unpleasant odour of the axillae in some people.
Sebum:20gm/day is secreted by the sebaceous glands. It lubricates the skin & makes it more resistant to water, chemicals &
microorganisms as it is acidic & contains some metabolites.
Shedded stratum cornium : are dead cells that are shed spontaneously or by wash mechanically or by soaps.
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Secretory functions:
Internal secretions of the skin:
Melanin: the colour of the skin & hair. This is controlled by MSH.
In Man ACTH has an MSH activity
Keratin: It is a fiberous protein. It is formed by the keratinocytes. It gives the skin strength & elasticity .It exists in 2 forms: I- Soft keratin
found in the skin. II- Hard keratin
found in the hair & nails.
Histamine & Heparin-like substance: by the mast cells.
Vitamin D3 (cholicalciferol) : it can be synthesized in the skin from 7-dehydrocholesterol under the effect of ultra violet light. It is the precursor for the active form of vitD3 after its activation in the liver &
then in the kidney to becom1,25DHC a hormone now known as calcitriol & involved in calcium homeostasis.
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2. ____ is secreted by the skin and give skin and hair their colour
A. Keratin B. Melanin C. Vitamin D D. Sebum
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3. Secretory function of the skin include secretion of _______
A. Vitamin C B. Vitamin B12 C. Vitamin D D. Vitamin A
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HUMAN BODY TEMPERATURE
16In young adult:
Normal Temp: 37 ºC± 0.5 (core or internal body temp).
Skin temp: (shell or outer body temp) < core temp.
Body Temperature
In young adult:
Normal 37 ºC ± 0.5 (
core or internal body temp).
Skin temp (
shell or outer body temp) < core temp.
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4. Normal core body temperature is ____
A. 35 ºC ± 0.5 B. 36 ºC ± 0.5 C. 37 ºC ± 0.5 D. 38 ºC ± 0.5
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Methods of Measuring Body Temperature
Variable according to site (oral , rectal , skin).
◙ Oral temp →37 ºC.
◙ Rectal temp →↑ 0.5 ºC.
◙ Axillary temp → ↓ 0.5ºC.
(Axillary meansunder the arm)
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1-Age:
↓ temp in old age.
2-Sex:
↑ temp 0.5 ºC in ♀ in second half of menstrual cycle & during pregnancy by progesterone.
3-Physical activity :
• Exercise , anxious → ↑ temp.
• Relaxed , sleep → ↓ temp.
FACTORS AFFECTING BODY TEMP
FACTORS AFFECTING BODY TEMP..cont
214-Emotional state:
↑ Tensing of muscles →↑ temp .
5-Circadian rhythm or diurnal variation:
•↓0.5 ºC →during sleep & early morning.
•↑ 0.5 ºC → during afternoon.
REGULATION OF BODY TEMPERATURE
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HEAT LOSS BY:
1. NON-EVAPORATIVE HEAT LOSS
a)Radiation (60%):In form of infrared from hot to cold objects.
b)Conduction (3%):From hot objects to surrounding objects in-direct contact
c)convection (15%):Heat →air and water→carried away by convection current as wind.
2. EVAPORATIVE HEAT LOSS (22%)
a)Insensible perspiration: During rest ( 24 ºC) b)Sweating: At temp of 32 ºC -43 ºC.
Evaporation of 1ml water → loss of about 0.58 C.
c)Heat loss via urine & stool (1%)
____________________________________________________________
Convection: the transfer of heat by the circulation or movement of the heated parts of a liquid or gas.
REGULATION OF BODY TEMP…cont
5. NON-EVAPORATIVE HEAT LOSS include all of the following except ____?
A. Radiation B. Conduction C. convection
D. Insensible perspiration
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REGULATION OF BODY TEMP…cont
A) INCREASING (HIGH) BODY TEMPERATURE
High body temperature increases heat loss in the body through:
1. Increased blood flow to the skin 2. Decreased metabolic rate
3. Behavioral responses 4. Sweating
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6. High body temperature increases heat loss in the body through _____
A. Decreased Blood Flow to Skin B. Increased metabolic rate
C. Sweating D. Shivering
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REGULATION OF BODY TEMP…cont
1. Increased Blood Flow to Skin
In response to high temperature, through autonomic nervous system, blood vessels are dilated, thus blood flow to the skin increases.
Heat is lost by radiation, conduction, convection and evaporation.
helps cooling of the blood that is flowing through the skin.
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REGULATION OF BODY TEMP…cont
2. Decreased Metabolic Rate
The metabolic rate changes through a decrease in the secretion of thyroxine
This results in a decrease in metabolic rate
The decrease in metabolic rate causes less heat production in the body.
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REGULATION OF BODY TEMP…cont
3. Behavioral Responses
We change our behavioral responses by:
▪ staying still (decreasing activity)
▪ staying in the shade
▪ air conditioning
▪ wearing less clothing
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REGULATION OF BODY TEMP…cont 4.Sweat
Secretion of sweat from sweat glands is controlled by the sympathetic nervous system.
Sweat cools by evaporating from the body.
Sweat doesn’t work in a humid environment.
Rising Body Temperature
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REGULATION OF BODY TEMP…cont
B) FALLING BODY TEMPERATURE Falling body temperature causes:
1. Decrease blood flow to the skin 2. Increase in metabolic rate
3. shivering
4. behavioral responses
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REGULATION OF BODY TEMP…cont
1.Decreased Blood Flow to Skin
In response to falling temperatures
▪ the sympathetic nervous system causes the blood
vessels to constrict, thus blood flow to the skin decrease
▪ decreases the transfer of heat from the internal body organs to the skin
▪ allows less heat to be lost from the body surface
▪ cools the skin
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REGULATION OF BODY TEMP…cont
2. Increase the Metabolic Rates
▪ The hypothalamus stimulates the adrenal medulla by sympathetic nerves to secrete adrenaline and noradrenaline into the blood.
▪ This increases cellular metabolism, increasing heat production &
maintain internal body temperature.
▪ The hypothalamus also stimulates the anterior pituitary to secrete thyroid stimulating hormone (TSH).
▪ The thyroid gland releases thyroxine into the blood
▪ This increases metabolic rate, increasing body temperature.
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7. The ____ hormone increases metabolic rate leading to increasing body
temperature
A. Cortisone
B. Testosterone C. Thyroxine
D. Growth hormone
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REGULATION OF BODY TEMP…cont
3. Shivering
Shivering is rhythmic muscle contractions occurring at a rate of around 10 to 20 per second.
The hypothalamus stimulates parts of the brain that increase skeletal muscle tone.
This increases body heat production.
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REGULATION OF BODY TEMP…cont
4.Behavioral Responses
We change our behavioral responses by:
• huddling (to get together, or draw oneself together).
• curling into a ball (form spiral or curved shape).
• putting on more clothes.
• using a heating device (Heaters).
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REGULATION OF BODY TEMP…cont Falling Body Temperature – Skin
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THERMOREGULATORY system is composed of:
• Receptors: Thermoreceptors in skin & hypothalamus.
• Control center: hypothalamus
It compares the received impulses with its set-point( 37 ºC)
If body temp > set point →anterior hypothalamus → ↑ heat loss & ↓ heat production .
If body temp < set point → posterior hypothalamus → ↑heat production &↓ heat loss.
• Effectors:
Skin( sweat glands & blood vessels).
skeletal muscles.
Endocrine glands.
TEMP REGULATING MECHANISMS
The control center for
thermoregulation is ________
A. Frontal lobe B. Hypothalamus C. Cerebellum
D. Medulla E. Spinal cord
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Control centre (set point)
Effectors
(muscles or glands) Receptors
Response
(change is corrected) Stimulus
(change occurs in internal environment)
Change is compared to the set point
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FEVER:
•It is defined as a body temperature above the normal range due to an increase in the temperature regulatory set-point.
HEAT STROKE:
Cause: exposure to humid weather or to severe fever → depression of heat regulating center & death.
Treated by:
Immersion in ice bath & drinking saline Sponge with alcohol.
Antipyretic drugs.
HYPOTHERMIA:
A drop of body temp to low level with slow metabolic&
physiologic processes.
BODY TEMP ABNORMALITIES
(Fever, Heat Stroke & Hypothermia)
Role of the skin in Regulation of body temperature:
The skin responds to heat by:
Cutaneous vasodilatation. This increases blood flow to the skin.
Sweating which cools the body by evaporative heat loss .
The skin responds to cold by:
cutaneous vasoconstriction. This decreases blood flow to the skin.
Hair erection (horripilation) in hairy animals.
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Metabolism
It includes:
1- Anabolism 2- Catabolism
1. Anabolism
is the formation of large organic molecules with uptake of energy.• Anabolic reaction are endergonic (they consume more energy than they produce)
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The formation of large organic
molecules with uptake of energy is called ________
A. metabolism B. catabolism C. anabolism
D. Photosynthesis
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Metabolism
2- Catabolism
is the breakdown of large organic molecules with release of energy for maintainingbody functions.
• Catabolic reaction are exergonic (they produce more energy than they consume).
• 75% of this energy appears as heat.
• 25% of this energy is stored as ATP that can be transformed into work.
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The breakdown of large organic molecules with release of energy for maintaining
body functions is called ________
A. Metabolism B. Catabolism C. Anabolism
D. Photosynthesis
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Anabolic and catabolic reactions
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Metabolism during the absorptive state
Soon after a meal, nutrients as glucose, amino acids, and fatty acids enter the blood.
Two metabolic reaction occur:
1- The oxidation of glucose (50%) &
ATP production occurs in most body cells.
2- the storage of excess energy in hepatocytes ,
adipocytes, and skeletal muscle fibers →for future use (between meal).
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Metabolism during post-absorptive state
• Four hours after the last meal, blood glucose starts to fall.
• Thus, the metabolic challenge is to maintain the
normal blood glucose of 80-110 mg/100 ml of blood.
• This is important for normal functions of:
1. Nervous system (because fatty acids are unable to pass the blood- brain barrier).
2. Red blood cells (because they have no mitochondria).
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Basal Metabolic Rate (BMR)
BMR is the minimum amount of energy required by the body to maintain life at complete physical and mental rest in post
absorptive state.
It is the energy output / square meter of body surface area/hour.
It is measured under the following 3 basal conditions:
• Complete physical & mental rest:
for at least 1/2 an hour but without sleep.
• Post-absorptive state:
12-14hrs after the last meal to avoid specific action of food.
• Comfortable temperature (21-22°C ) :
neither cold nor hot (neither shivering nor sweating).
BMR in young adult male= 40 C / m² / hour.
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11. The minimum amount of energy required by the body to maintain life at complete physical and mental rest in post absorptive state is called ________
A. Basal metabolic rate
B. Specific dynamic action C. Basic metabolic rate
D. Resting metabolic rate E. Minimum metabolic rate
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Factors affecting BMR
A. PHYSIOLOGICAL FACTORS:
1. Age: Old age < youth (↓ 1C every 10 years).
2. Sex: female < male (by 7% due to more fats%)
3. Race: Orientals (Easterns) &Africans < Europeans.
4. Physical habits: Sedentary individuals < athletes.
5. Climate: individuals in hot countries < in cold countries.
6. Dietetic habits: mixed food < protein.
7. Pregnancy: ↑ BMR.
8. Anxiety & tension: ↑ BMR.
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Factors affecting BMR
B. PATHOLOGICAL FACTORS:
INCREASE IN BMR OCCURS WHEN:
Fever or increased body temperature.
Hyperthyroidism (increased thyroid hormones).
Increased epinephrine & nor epinephrine.
Leukemia & diabetes insipidus (DI).
DECREASE IN BMR OCCURS IN:
Hypothyroidism, Hypofunction of adrenal cortex, Hypothermia, &
Nephrotic syndrome.
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Summary
Skin is the largest organ in the body and is composed of dermis and epidermis layers
It has many functions including the regulation of body temperature.
Abnormalities of thermal regulation is seen in fever, heatstroke and hypothermia.
Basal metabolic rate is affected different physiological and pathological factors.
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References
61Principle of Human Physiology 6th Edition, 2006
Gerald J. Torture, Ronald l. Evans, Nicholas p.
Anagnostakos
Harper & Row, Publishers, New York Text Book of Medical Physiology 13th Edition, 2015
Arthur C. Guyton, John E. Hall
W.B. Saunders Company, New York, 2000 Essentials of Medical Physiology
7th Edition, 2018
K. Sembulingam, Prema Sembulingam
Jaypee Brothers Medical Publishers (P) LTD
Ross and Wilson Anatomy and Physiology in Health and Illness Anne Waugh, Allison Grant
13th Edition, 2018
Churchill Livingstone, London, New York
