Thermo-Regulatory Mechanism

THERMO-REGULATORY MECHANISM

Q. 1

Which is the primary gland responsible for thermoregulatory sweating in humans?

 A

Apocrine gland

 B

Eccrine gland

 C

Sebaceous gland

 D

Holocrine gland

Q. 1

Which is the primary gland responsible for thermoregulatory sweating in humans?

 A

Apocrine gland

 B

Eccrine gland

 C

Sebaceous gland

 D

Holocrine gland

Ans. B

Explanation:

Human sweat glands are generally divided into two types:

apocrine and eccrine.

The eccrine gland is the primary gland responsible for thermoregulatory sweating in humans.

Eccrine sweat glands are distributed over nearly the entire body surface.

Apocrine glands are located only in genital, axillary and mammary areas.

Ref: Rook’s textbook of dermatology, 8th edition, Pg 3.12

Q. 2

All the following mechanisms occur in a neonate for heat production, EXCEPT:

 A

Shivering

 B

Breakdown of brown fat with adrenaline secretion

 C

Universal flexion like a fetus

 D

Cutaneous vasoconstriction

Q. 2

All the following mechanisms occur in a neonate for heat production, EXCEPT:

 A

Shivering

 B

Breakdown of brown fat with adrenaline secretion

 C

Universal flexion like a fetus

 D

Cutaneous vasoconstriction

Ans. A

Explanation:

Non shivering thermogenesis or breaking of brown fat is the main method of heat production in the newborn.
Shivering which is a major mechanism of heat production in adults is rarely seen in newborn
. In newborns, brown fat is located in the upper back and neck, mediastinum and around the kidneys. They contain high store of triglycerides which are broken down during metabolic process to produce glycerol and fatty acids which in turn releases heat. 

 

 

 

Mechanisms of heat production in newborn are:

 

  • Newborn’s mechanism of heat production is primarily through increased metabolic process. Cold stress increases the metabolism and thus requiring an increase in oxygen and calorie consumption.
  • Vasoconstriction of blood vessels.
  • Increase in metabolic rate and muscular activity.
  • Non shivering thermogenesis

 

Ref: Universal Newborn Hearing Screening  edited by Lynn G. Spivak page 121, Examination of the Newborn: An Evidence Based Guide  By Anne Lomax page 56.

 


Q. 3

The first physiological response to high environmental temperature is:

 A

Sweating

 B

Vasodilatation

 C

Decreased heat production

 D

Non-shivering thermogenesis

Q. 3

The first physiological response to high environmental temperature is:

 A

Sweating

 B

Vasodilatation

 C

Decreased heat production

 D

Non-shivering thermogenesis

Ans. B

Explanation:

First response to high environmental temperature is cutaneous vasodilation.

 
Ref: Ganong’s Review of Medical Physiology, 21st Edition, Page 257

Q. 4

In human being, the least useful physiological response to low environmental temperature is:

 A

Shivering

 B

Vasoconstriction

 C

Release of thyroxine

 D

Piloerection

Q. 4

In human being, the least useful physiological response to low environmental temperature is:

 A

Shivering

 B

Vasoconstriction

 C

Release of thyroxine

 D

Piloerection

Ans. D

Explanation:

Piloerection is not important in the human being. 

Ref: Textbook of Medical Physiology By Guyton, 11th Edition, Page 895.

Q. 5

Which of the following is responsible for non-shivering thermogenesis in adults?

 A

Thyroid hormone

 B

Brown fat between the shoulders

 C

Noradrenaline

 D

Muscle metabolism

Q. 5

Which of the following is responsible for non-shivering thermogenesis in adults?

 A

Thyroid hormone

 B

Brown fat between the shoulders

 C

Noradrenaline

 D

Muscle metabolism

Ans. B

Explanation:

Brown adipose tissue is involved in metabolism, particularly at times when heat generation is necessary. Thus, the tissue is extremely active in some species, in animals exposed to cold (nonshivering thermogenesis), and in heat production in the newborn. Though not a prominent tissue in humans, it is present in normal individuals, where it could be responsible for “diet-induced thermogenesis.” It is reduced or absent in obese persons.

The tissue is characterized by a well-developed blood supply and a high content of mitochondria and cytochromes, but low activity of ATP synthase. Metabolic emphasis is placed on oxidation of both glucose and fatty acids.
 
Ref: Botham K.M., Mayes P.A. (2011). Chapter 25. Lipid Transport & Storage. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper’s Illustrated Biochemistry, 29e.

Q. 6

Which of the following physiological changes occur during fever?

 A

Thermoregulatory centre to shift to new level

 B

Resetting of skin temperature

 C

Both of the above

 D

None of the above

Q. 6

Which of the following physiological changes occur during fever?

 A

Thermoregulatory centre to shift to new level

 B

Resetting of skin temperature

 C

Both of the above

 D

None of the above

Ans. A

Explanation:

Fever is an elevation of body temperature that exceeds the normal daily variation and occurs in conjunction with an increase in the hypothalamic set point [e.g., from 37°C to 39°C (98.6°F to 102.2°F)]. 
 
The processes of heat conservation (vasoconstriction) and heat production (shivering and increased nonshivering thermogenesis) develops until the temperature of the blood bathing the hypothalamic neurons matches the new thermostat setting. Once that point is reached, the hypothalamus maintains the temperature at the febrile level.
 
Ref: Dinarello C.A., Porat R. (2012). Chapter 16. Fever and Hyperthermia. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison’s Principles of Internal Medicine, 18e.

 


Q. 7

Which of the following is the cause of nonshivering thermogenesis in adults?

 A

Noradrenaline

 B

Thyroid hormone

 C

Muscle metabolism

 D

Brown fat between the shoulders

Q. 7

Which of the following is the cause of nonshivering thermogenesis in adults?

 A

Noradrenaline

 B

Thyroid hormone

 C

Muscle metabolism

 D

Brown fat between the shoulders

Ans. A

Explanation:

Nonshivering thermogenesis refers to increase in metabolic rate that is not a result of muscle activity. It appears to be elicited through sympathetic stimulation and circulating catecholamines. Epinephrine and norepinephrine which are released increases metabolic activity and heat generation.

Ref: Guyton and Hall – Textbook of Medical Physiology, 10th Edition, Pages 821, 828-829; Medical Physiology: Principles for Clinical Medicine By Rodney A. Rhoades, 4th Edition, Page 568; Fundamentals of Human Physiology By Lauralee Sherwood, Page 489


Q. 8

Sweating a result of exertion is mediated through:

 A

Adrenal hormones

 B

Sympathetic cholinergic

 C

Sympathetic adrenergic

 D

Parasympathetic cholinergic

Q. 8

Sweating a result of exertion is mediated through:

 A

Adrenal hormones

 B

Sympathetic cholinergic

 C

Sympathetic adrenergic

 D

Parasympathetic cholinergic

Ans. B

Explanation:

B i.e. Sympathetic cholinergic


Q. 9

Heat loss from the body depends mostly on:

 A

Thermoregulatory center

 B

Warming of air during inspiration

 C

On the environmental temperature

 D

Radiation and evaporation

Q. 9

Heat loss from the body depends mostly on:

 A

Thermoregulatory center

 B

Warming of air during inspiration

 C

On the environmental temperature

 D

Radiation and evaporation

Ans. C

Explanation:

C i.e. On the environmental temperature


Q. 10

Under physiological conditions heat acclimatization is accomplished WE.

 A

Decreased Renal Blood Flow

 B

Increased urine sodium

 C

Increased aldosterone secreti on

 D

Excessive sweating

Q. 10

Under physiological conditions heat acclimatization is accomplished WE.

 A

Decreased Renal Blood Flow

 B

Increased urine sodium

 C

Increased aldosterone secreti on

 D

Excessive sweating

Ans. B

Explanation:

B i.e. Increased urine sodium


Q. 11

Endogenous non-shivering thermogens are secreted by all except :

 A

Liver

 B

Spleen

 C

Heart

 D

Small intestine

Q. 11

Endogenous non-shivering thermogens are secreted by all except :

 A

Liver

 B

Spleen

 C

Heart

 D

Small intestine

Ans. B

Explanation:

B i.e. Spleen


Q. 12

During G.A. shivering is abolished by suppression of

 A

Hypothalmus

 B

Thalmus

 C

Cerebral Cortex

 D

Medulla

Q. 12

During G.A. shivering is abolished by suppression of

 A

Hypothalmus

 B

Thalmus

 C

Cerebral Cortex

 D

Medulla

Ans. A

Explanation:

A i.e. Hypothalmus

Temperature regulation during G.A. OWI

  • Normally hypothalmus maintain core body temperatureQ (central blood temperature) within very narrow range (interthreshold range).
  • Temperature of patient undergoing G.A. should be monitored (except for < 15 minutes procedure) by thermistor or thermocouple with a probe placed over tympanic membrane, rectum, nasopharynx, esophagus, bladder & skin.
  • Hypothermia (ie body temperature <36° C) reduces metabolic oxygen requirements, is proved to be protective during times of cerebral or cardiac ischemiaQ
  • Raising body temperature induces vasodialation & sweating while hypothermia triggers vasoconstriction & shivering as compensatory mechanism.
  • During G.A. body cannot compensate for hypothermia because anesthetics inhibit central thermoregulation by interfering with hypothalamic function.Q
  • Spinal & epidural anesthesia also lead to hypothermia by vasodialation & internal redistribution of heat. The accompanying thermoregulatory impairment from regional anesthesia is due to an altered perception of temperature in bloacked dermatomes by hypothalmus as opposed to central effect of G.A.
  • Postanesthetic shivering or shaking that is not related to hyperthermia can be abolished by certain opioids e.g. meperidine, butrophanol & tramadol (but not morphine).

Q. 13

Shivering is controlled by:

September 2012, March 2013

 A

Dorsomedial nucleus

 B

Posterior hypothalamus

 C

Perifornical nucleus

 D

Lateral hypothalamic area

Q. 13

Shivering is controlled by:

September 2012, March 2013

 A

Dorsomedial nucleus

 B

Posterior hypothalamus

 C

Perifornical nucleus

 D

Lateral hypothalamic area

Ans. B

Explanation:

Ans. B i.e. Posterior hypothalamus

Shivering/Shuddering

  • It is a bodily function in response to early hypothermia in warm-blooded animals.
  • When the core body temperature drops, the shivering reflex is triggered to maintain homeostasis.
  • Muscle groups around the vital organs begin to shake in small movements in an attempt to create warmth by expending energy.
  • Shivering can also be a response to a fever, as a person may feel cold, though their core temperature is already elevated.
  • Located in the posterior hypothalamus near the wall of the third ventricle is an area called the primary motor center for shivering.
  • This area is normally inhibited by signals from the heat center in the anterior hypothalamic-preoptic area but is excited by cold signals from the skin and spinal cord.



Q. 14

On exposure to cold, a neonate shows all of the following mechanisms except

 A

Shivering

 B

Crying and flexion of body like fetus position

 C

Cutaneous vasoconstriction

 D

Increased production of noradrenaline for breakdown of brown fat in adipose tissue

Q. 14

On exposure to cold, a neonate shows all of the following mechanisms except

 A

Shivering

 B

Crying and flexion of body like fetus position

 C

Cutaneous vasoconstriction

 D

Increased production of noradrenaline for breakdown of brown fat in adipose tissue

Ans. A

Explanation:

Ans. a. Shivering

On exposure to cold and wet environment, the neonate tries to generate heat by increased activity (crying with agitated movement) and a sympathetic surge that causes vasoconstriction and non-shivering thermogenesis in the brown fat. Babies attempt to conserve heat by peripheral vasoconstriction.”

“Brown fat is a well-vascularized, sympathetically innervated lipid collection located in the axillae, groin, nape of the neck, interscapular area and perinea! area. Cold stress causes the release of norepinephrine that uncouples beta-oxidation in fat with resultant heat generation. Preterm and small-for-gestational age infants have immature thermogenic response because of scanty brown fat stores.”

Role of Brown Fat in Thermogenesis

  • A newborn baby is more prone to develop hypothermia because of large surface area per unit of body weight.
  • In infants, brown fat is an important site of thermogenesis. It results in the so-called non-shivering thermogenesis.
  • Brown fat is located around the adrenal glands, kidney, nape of neck, interscapular and axillary region.
  • Metabolism of brown fat leads to heat production.
  • Blood flowing through the brown fat becomes warm and through circulation, transfers heat to other parts of the body. This mechanism oh heat production is known as non-shivering thermogenesise.Q


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