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+ BIOL 370 > Lecture 13.1: Dormancy and Muscle Atrophy > Flashcards

Lecture 13.1: Dormancy and Muscle Atrophy Flashcards

1
Q

What is dormancy?

A

‘physiological time out’ involving adjustments that reduce metabolic demands to enhance survival in response to harsh environmental condition

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2
Q

What is the classic definition of hibernation?

A

state of inactivity and reduced responsiveness to stimuli

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3
Q

What is the advanced (Geiser’s) definition of hibernation?

A

regulated state where metabolic rate is reversibly suppressed to < 10% of resting values for several days, with corresponding decreases in Tb

  • involves a fall in Tb below 10ºC (controlled drop in body temperature), and its metabolic rate falls by over 90% for longer than 1 day
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4
Q

What is torpor?

A

similar to hibernation, but the decrease in metabolic rate and Tb are less severe and lasts < 24 hours before being reversed

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5
Q

Do small animals hibernate?

A

yes – the most profound demonstration of hibernation is observed in small mammals, where Tb can decrease to as low as 2ºC

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6
Q

Do large animals hibernate?

A

yes – no mammal larger than 10 kg will undergo a decrease in Tb to meet Geiser’s definition (advanced definition) of hibernation, but they still hibernate

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7
Q

What are the 3 axes of dormancy that can differentiate dormancy types across animal taxa?

A
  • induction
  • recalcitrance
  • magnitude
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8
Q

Axes of Dormancy

What does induction and recalcitrance describe?

A

describe the degree to which the dormancy is endogenously PROGRAMMED and centrally mediated (ie. driven by central nervous system and endogenous time-keeping mechanisms) vs. RESPONSIVE (a direct response to an adverse environment)

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9
Q

Axes of Dormancy

Induction – Programmed vs. Responsive

A
  • programmed: committed before environment deteriorates
  • responsive: immediate response to limiting factor
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10
Q

Axes of Dormancy

Recalcitrance – Programmed vs. Responsive

A
  • programmed: high recalcitrance, refractory
  • responsive: no recalcitrance, environmentally sensitive
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11
Q

Axes of Dormancy

What does magnitude describe?

A

describes the dormancy-specific degree of plasticity in a range of traits, including metabolic rate

  • deep: inactive, profound metabolic suppression
  • shallow: active, mild metabolic suppression of physiological traits and conditions
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12
Q

What is the dormancy spectrum?

A

differentiates the dormancy types across animal taxa

  • programmed vs. responsive
  • deep vs. shallow

two extremes

  • programmed and deep
  • responsive and shallow
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13
Q

Name some organisms and where they are on the dormancy spectrum.

A
  • long-tongued nectar bat – shallow and responsive
  • edible dormouse – deep and responsive
  • arctic ground squirrel – deep and programmed
  • short-beaked echidna – shallow and programmed
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14
Q

What is estivation?

A

dormancy in response to a hot arid environment to address food scarcity and the dry environment

  • involves controlled loss of water (up to 80% water loss)
  • involves decrease in basal metabolic rate
  • goal is survival
  • ie. desert frogs
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15
Q

What is diapause?

A

developmentally programmed dormancy

  • usually timed to a harsh environmental condition
  • ie. Artemia sp. (brine shrimp)
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16
Q

What are obligate hibernators?

A

hibernators that follow an endogenous circannual rhythm and hibernate each year, regardless of environmental conditions (ie. very cold, food scarcity)

  • PROGRAMMED for hibernation every year
  • ie. ground squirrel
17
Q

What are facultative hibernators?

A

mammals where the expression and characteristics of hibernation is not consistent and depends largely on the environment

  • if one year the environment is not harsh and food is still available, hibernation time may differ or may not occur at all
  • ie. Syrian hamster
18
Q

What are the three broad phases of obligate hibernation?

A
  • preparation
  • hibernation period – smaller phases within include initiation, maintenance, potentiation
  • emergence (activation)
19
Q

Time Course of Obligate Hibernation

What happens to metabolism and cell cycle, locomotor activity, reproductive activity, and energy storage during the preparation phase?

A

all high

20
Q

Time Course of Obligate Hibernation

What happens to metabolism and cell cycle, locomotor activity, reproductive activity, and energy storage during the hibernation period phase?

A
  • metabolism and cell cycle, locomotor activity, and reproductive activity decrease
  • energy storage stays high, then gradually decreases towards the end of hibernation
21
Q

Time Course of Obligate Hibernation

What happens to metabolism and cell cycle, locomotor activity, reproductive activity, and energy storage during the emergence (activation) phase?

A

traits return to high level of activity

22
Q

What are interbout arousals (IBA)?

A

transient state of activity in which the animal will recover active-like physiological parameters such as body temperature, heart rate, and blood pressure

23
Q

What are the 6 characteristics of hibernation?

A
  • reduced Tb
  • metabolic suppression
  • insulin resistance
  • water loss
  • decreased physiological functions – ie. heart rate, ventilation
  • inactivity
24
Q

Metabolic Suppression Before Cooling

What happens in ground squirrels?

A
  • metabolic rate declines before body temperature decreases
  • lower Tb facilitates further reductions in metabolic rate through thermodynamic effects
25
Q

Mitochondrial Metabolism

Describe the maximal metabolic rate of mitochondria in muscles of hibernating vs. non-hibernating squirrels.

A
  • maximal metabolic rate of mitochondria is lower in muscle from hibernating than non-hibernating squirrels
  • hibernation-induced decrease in mitochondrial metabolism is due to differential phosphorylation of complex I and II of ETS
26
Q

Describe the mechanisms of metabolic rate suppression.

A

Na+/K+ ATPase and protein synthesis are down regulated during hibernation

  • Na+/K+ ATPase activity is lower in almost all tissues of hibernating animals – due to phosphorylation
  • during hibernation in squirrels, [14 C] leucine is not incorporated into the brain, liver, and heart – shows that no protein synthesis was occurring
  • protein synthesis downreguated by phosphorylation of critical enzymes
27
Q

Regulation of Fuel Selection During Hibernation

What is pancreatic triglyceride lipase (PTL)?

A

enzyme that breaks down triglyceride

28
Q

Regulation of Fuel Selection During Hibernation

What is pyruvate dehydrogenase kinase 4 (PDK4)?

A

enzyme that inhibits carbohydrate oxidation

29
Q

Regulation of Fuel Selection During Hibernation

What fuel is used pre-hibernation?

A

mainly carbohydrates are used in the pancreas to secrete insulin

  • high level of insulin in the serum facilitates use of carbohydrates or carbohydrate oxidation
  • high level of insulin inhibits function of PTL – prevents breakdown of triglyceride
  • high level of insulin inhibits function of PDK4 – allows carbohydrate oxidation to occur (inhibitor is inhibited)
30
Q

Regulation of Fuel Selection During Hibernation

What fuel is used during hibernation?

A

switch to using more fatty acids

  • pancreas makes insulin and it accumulates in the pancreas, therefore the serum level of insulin is low
  • no inhibition of PTL – triglycerides and white adipose tissue can be broken down to fatty acids, and go to lipid oxidation
  • no inhibition of PDK4 – carbohydrate oxidation is inhibited
31
Q

Heat Production During Emergence

Describe the changes in temperature once hibernation starts, and once hibernation ends.

A
  • once hibernation starts and temperature decreases to torpor state, there is IBA arising in temperature along with other physiological aspects (regulated pattern of IBA)
  • upon the initiation of arousal, core body temperature increases over a very short time course
  • mechanisms of heat production allow rapid increase in high temperature occurring once hibernation period is over
32
Q

Do animals function normally after a long period of activity?

A

yes – animals go through long period of inactivity, but still come back active and function normally

  • can maintain tissue or re-use/bring them back to an active and functional level after a period of inactivity
  • these studies are important because they are applicable to other things
  • ie. astronauts’ muscle mass also decreases, and they go through some changes
  • ie. people who were in a coma

+ BIOL 370 (15 decks)

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