Homeostatis

Describe the cost of endothermy, and the effect of body size on metabolic rate and temperature homeostasis.

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Poikilotherm:

: an animal whose body temperatures varies within the environment.

Describe mechanisms for temperature homeostasis in both ectotherms and endotherms, including during different times of day and different seasons.

Acclimatization (to adapt to a new temp/environment) to seasonal changes often includes adjusting insulation. Growing a thicker fur in the winter is an example. The changes help endotherms keep a constant body temp year-round. Acclimatization in ectotherms often includes adjustments at the cellular level. Cells may produce variants of enzymes that have the same function but different optimal temps. Some ectotherms that experience sub-zero body temps protect themselves by producing "antifreeze" proteins that prevent ice formation in their cells.

Give an example of an endothermic animal that is sometimes a poikilotherm...

Bats and hummingbirds may periodically enter an inactive state in which they maintain a lower body temperature.

Define homeostatis and explain how feedback control is used to maintain it.

Homeostatis moderates but doesn't eliminate changes in the internal environment. It's an interplay between external factors that tend to change the internal environment and internal control mechanisms that oppose these changes Feedback control: Homeostasis in animals relies on negative feedback. Negative feedback is a control mechanism that reduces or damps the stimulus. For example: when you exercise, you produce heat which increases body temperature. Your nervous system detects this increase and triggers sweating. The sweat helps your body to return your body temperature to its set point and eliminating the stimulus. .

Describe the mechanisms of heat transfer relevant to animals. (5)

Insulation: reduces the flow of heat between animals body and it's environment. Insulation can include hair or feather or layers of fat or blubber. The essence of thermoregulation is maintaining a rate of heat gains that equals the heat that was loss. Animals use mechanisms that either reduce heat exchange overall or favor heat exchange in a particular direction. Circulatory Adaptations: In response to changes in temperature of their surroundings, many animals alter the amount of blood (and hence heat) flowing between their body core and their skin. Nerve signals that relax the muscles of the vessel walls result in vasodilation, a widening of superficial blood vessels. This increases blood flow. In endotherms, this usually warms the skin and increases the transfer of body heat to the environment by radiation, conduction, and convection. Vasoconstriction is the opposite. It reduces blood flow and heat transfer by decreasing the size of blood vessels. Countercurrent exchange (an example of circulatory adaptations): the transfer heat between fluids that are flowing in opposite directions. Arteries carrying warm blood to the animal's extremities are in close contact with veins conveying cool blood in the opposite direction. The blood in the veins continues to absorb heat as it passes warmer and warmer blood traveling in the opposite direction in the arteries. As the blood in the veins approach the center of the body, it's is as almost at warm as the body core. This minimizes the heat loss. Cooling by Evaporative Heat Loss In situations where the environmental temperatures are higher than the organisms body. Evaporation is the only way to keep body temperature from rising. Water absorbs heat when it evaporate. This heat is carried away from the body surface as water vapor. This can happen through sweat glands. Some animals also use panting to increasing evaporation. Behavioral Responses Many ectotherms maintain a nearly constant body temperature by seeking warm places when cold. When hot, they may bathe or move to cool areas. Adjusting Metabolic Heat Production Since endotherms have a body temp that is higher than their environment, they must counteract continual heat loss. They can vary heat production (thermogenesis) to match changing rates of heat loss. The production of heat is increased by muscle activity such as shivering (contracting) and moving. Certain hormones can cause mitochondria to increase their metabolic activity and produce heat instead of ATP. (nonshivering thermogenesis) Some mammals also have brown fat that is specialized for rapid heat production.

What is positive feed back?

Positive feedback: is a control mechanism that amplifies rather than reduces the stimulus. Positive feedback do not play a role in homeostatis but instead helps drive processes to completion. For example: During childbirth, the pressure of the baby's head against the sensor near the opening of the mother's uterus stimulates the uterus to contract. These contractions result in greater pressure against the opening of the uterus, heighten the contractions and therby causing even greater pressure until the baby is born.

Why is the term "cold blooded" inaccurate for describing ectoderms.. and "warm blooded" for endotherms.

Warm blooded decribes animal that has the higher body temp than their enviroment. This can be misleading because at times ectotherms may have a higher body temp that the temp of their enviroment. So they are not always cold blooded. While back in the sun, lizards may still have a higher blood temp than their environment. Endothems aren't always "Warm blooded" either. Hibernating mammals have to be have a lower body temperture in order for hibernation to work

stimulus:

a fluctuation in the variable above or below the set point.

Response:

a physiological activity that helps return the variable back to the set point.

regulator:

an animal that uses internal mechanism to control internal change in the face of external fluctuation.

Ectodermic:

animals that gain most of their heat from external sources. Example: most invertebrates, many fishes and reptiles and amphibians are ectodermic. many adjust their body temperatures by behavioral means such as sitting in the sun when its cold or sitting in the shade when it's hot. Because their heat source is mostly external, ectotherms don't need as much food as endotherms. This would be an advantage if food is limited. They also tolerate larger fluctuations in their internal temperature.

homeotherm:

animals with a constant body temperature.

conformer:

it allows it's internal condition to change in accordance with external changes in the variable.

Sensor:

it detects the stimulus

set point:

maintain a variable at a particular point.

Conduction:

the direct transfer of thermal motion (heat) between molecules of objects in contact with each other. As when a lizard sits on a hot rock.

Radiation:

the discharge of electromagnetic wave by all objects warmer than absolute zero. A lizard absorbs heat radiating from the sun and radiates a smalled amount of energy to the surrounding air.

Evaporation:

the removal or heat form the surface of a liquid that is losing some of it's molecules as gas. Evaporation of water from a lizard's moist surfaces that are exposed to the environment has a strong cooling effect.

Convection:

the transfer of heat by the movement of air or liquid past a surface. As when a breeze contributes to heat loss from a lizard's dry skin or when blood moves from the body core to the extremities.

Endothermic:

they are warmed mostly by heat generated by metabolism. Humans, animals, birds, some fishes and reptiles are endothermic. Some insect species are also endothermic.