Enzyme Activity and Thermoregulation

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Questions and Answers

What happens to enzyme activity at high temperatures when excessive heat is generated?

Oxidative stress is reduced due to increased enzyme efficiency.

Enzymes become more rigid and retain their functionality.

Proteins may denature and lose their functional shape. (correct)

Enzyme activity increases linearly with temperature.

How does the body size of species relate to their thermal resistance?

Smaller species are generally more thermally resistant.

Larger species are typically more hypoxia tolerant due to higher oxygen stores. (correct)

Thermal resistance is independent of body size.

Larger species lose heat more rapidly than smaller species.

What effect does low temperature have on enzymatic reactions?

It increases the rate of reaction by lowering activation energy.

It does not favor the reaction and prevents reaching activation energy. (correct)

It enhances the rigidity of enzymes, increasing their specificity.

It causes enzymes to denature, making them more effective.

What is the primary consequence of the Surface Area to Volume ratio (SA:V) in larger species?

They can store more heat but have reduced nutrient efficiency. Signup and view all the answers

What is the relationship between mass-specific metabolic rate and body size?

Smaller species have a higher mass-specific metabolic rate. Signup and view all the answers

What occurs when there is an increase in sodium (Na+) levels in the blood?

ANP is released to increase kidney filtration. Signup and view all the answers

How does the body respond to dehydration in terms of thirst motivation?

Activation of osmoreceptors in the brain. Signup and view all the answers

What role does cortisol play in the osmoregulation of saltwater fish?

Enhances Na+/K+ ATPase activity. Signup and view all the answers

What is the effect of prolactin on freshwater fish regarding osmoregulation?

Stimulates excretion of ions and increases water intake. Signup and view all the answers

How do diadromous fish such as salmon adapt to their varying salinity environments?

By switching between freshwater and saltwater hormonal adaptations. Signup and view all the answers

What is the primary function of UCP1 in brown adipose tissue?

To facilitate the direct heat generation without ATP Signup and view all the answers

What initiates the activation of UCP1 in response to cold stimuli?

Release of norepinephrine from the CNS Signup and view all the answers

How does torpor differ from hibernation?

Torpor can be reversed, while hibernation cannot Signup and view all the answers

What vascular adaptation helps to maintain core body temperature during cold exposure?

Heat exchange through counter current mechanisms Signup and view all the answers

Which group of mammals is suggested to have ancestral traits related to torpor?

Monotremes, marsupials, and eutherians Signup and view all the answers

Which physiological mechanism is NOT associated with daily heterothermy?

Inhibition of metabolism for long durations Signup and view all the answers

What is the relationship between body size and fasting endurance regarding torpor in small and large species?

Fasting endurance decreases with increased body size Signup and view all the answers

What effect does the cold environment have on the metabolism of hibernators?

It induces a state of significantly lower metabolic rate Signup and view all the answers

What physiological change primarily prepares anadromous fish for migration from freshwater to seawater?

Increase in cortisol levels Signup and view all the answers

How does the prolactin level change when migrating back to freshwater as adults?

Prolactin increases depending on distance from spawning river Signup and view all the answers

What adaptation occurs over time to address the challenges faced during migration?

CORT expression increases Signup and view all the answers

Which design feature is specific to an open circulatory system?

Hemolymph in discrete vessels Signup and view all the answers

What is the primary mechanism for blood perfusion in a closed circulatory system?

Heart's pumping action Signup and view all the answers

Which structure primarily prevents backflow in the heart?

Valves Signup and view all the answers

What type of heart mechanism allows the atrium to empty before the ventricle contracts?

Myogenic signal Signup and view all the answers

What characteristic distinguishes a closed circulatory system from an open one?

Blood remains within the vessels Signup and view all the answers

What is the role of prostaglandins in pain perception?

They are synthesized by COX enzymes. Signup and view all the answers

Which of the following statements about gas messengers is true?

Nitric oxide is a vasodilator produced by NO synthase. Signup and view all the answers

What distinguishes neurosecretory cells from epithelial endocrine cells?

Neurosecretory cells are derived from the CNS. Signup and view all the answers

What is the primary function of the adrenal cortex?

To secrete mineralocorticoids and glucocorticoids. Signup and view all the answers

How do direct acting hormones differ from tropic hormones?

Tropic hormones stimulate other glands to release hormones. Signup and view all the answers

Which statement best characterizes the stress response?

The primary response enhances the release of catecholamines and cortisol. Signup and view all the answers

What is one of the first physiological responses to acute stress?

Increased blood flow to muscles. Signup and view all the answers

Which of the following correctly describes the adrenal medulla's function?

It secretes hormones that act shortly after they are released. Signup and view all the answers

Study Notes

Enzyme Activity and Temperature

Too high temperature (Tb) can denature proteins
Too low temperature (Tb) slows down enzyme activity

Body Size and Homeothermy

Larger species are more thermally resistant, fasting resistant, have more energy stores, and are more hypoxia tolerant
Surface Law: smaller species have higher surface area to volume ratio, which leads to faster heat loss
Mass-specific metabolic rate (MSMR) is higher in smaller species
Smaller species have shorter fasting endurance

Thermogenesis

Uncoupling protein 1 (UCP1) in brown adipose tissue (BAT) allows protons to enter the mitochondrial matrix without generating ATP, producing heat
GDP blocks UCP1 activity, resuming ATP synthesis
Cold stimulus triggers the release of norepinephrine, which activates UCP1
Acclimation can increase BAT and UCP1 levels

Thermoregulatory Mechanisms

Altering Tb-Ta gradient:
- Vasoconstriction reduces blood flow to extremities
- Countercurrent heat exchange: warm blood from the core transfers heat to veins, warming cold blood returning from extremities
Torpor/Fasting:
- Reversible state of reduced metabolic rate and body temperature
- Occurs when Ta is below lower critical temperature (LCT)
- Fasting endurance decreases with body size due to energy stores
- Small species have higher MSMR, allowing for torpor
Daily Heterothermy:
- Variation in MR over 24 hours
- Seen in small mammals and birds
Seasonal Endothermy:
- True hibernation:
  - Dramatic reduction in MR and Tb
  - Rely on body stores and cached food
- Seasonal lethargy:
  - Inhibition of metabolism, allowing body temperature to drop to 30°C
- Estivation:
  - Small reduction in Tb and MR to conserve resources
Regional endothermy:
- Active heating of specific organs
- Prostaglandins, generated by COX pathway, contribute to localized heat production

Gas Messengers

Lipid-soluble molecules that act through paracrine signaling
Short half-life
Nitric oxide (NO) is a vasodilator produced by nitric oxide synthase

Control of Endocrine Secretions

Neurohemal organs contain neurosecretory cells, which release neurohormones
Pituitary gland:
- Posterior pituitary (neurohypophysis): releases hormones synthesized in the hypothalamus (AVP, CRH, oxytocin)
- Anterior pituitary (adenohypophysis): releases hormones synthesized by epithelial endocrine cells
Adrenal gland:
- Adrenal cortex: produces steroid hormones (aldosterone, CORT)
- Adrenal medulla: produces catecholamines (epinephrine, norepinephrine)

Stress Response

Stress disrupts homeostasis and elicits physiological and behavioral responses
Primary response:
- Increase in catecholamines and CORT
Secondary response:
- Effects on target tissues, including gene expression and pathway activation
Tertiary response:
- Changes in metabolism and anti-predator behavior

Osmoregulation

Dehydration:
- Angiotensin II triggers thirst by activating osmoreceptors in the brain
Increased sodium (Na+) levels:
- ANP is released to increase kidney filtration and decrease aldosterone production to reduce Na+ reabsorption
Diadromous fishes:
- Catadromous: spawn in saltwater (SW)
- Anadromous: spawn in freshwater (FW)
Hormonal regulation in fish:
- Cortisol (CORT): "Saltwater adapting hormone"
  - Increases Na+/K+ ATPase activity to retain ions in SW
- Prolactin: "Freshwater adapting hormone"
  - Decreases Na+/K+ ATPase activity to conserve ions in FW
Smoltification:
- Physiological and morphological changes for anadromous fish transitioning from FW to SW
- CORT levels increase before migration to SW, as it is a slow-acting hormone

Circulatory System

Open circulatory system:
- Single-chambered heart, hemolymph flows through vessels, sinuses, and lacunae
- Lower resistance, but slower flow
Closed circulatory system:
- Blood remains within vessels, multi-chambered heart
- Higher resistance, but faster flow
Heart:
- Primary mechanism for blood circulation
- Other mechanisms: elastic recoil of arteries, smooth muscle contraction, skeletal muscle movement
- Valves: prevent backflow
- Pacemaker: sets heart rhythm
- Myocardium: heart muscle, regulates force of heartbeat
- Axillary hearts: provide localized blood flow

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Description

Explore the relationship between enzyme activity and temperature, along with mechanisms of thermoregulation. Understand how body size impacts thermal resistance and metabolic rates in various species. Delve into thermogenesis and the role of brown adipose tissue in heat production.