Basic Principles of Animal Form and Function (Animal form and function are…
Basic Principles of Animal Form and Function
Animal form and function are correlated at all levels of organization
An animal’s size and shape are fundamental aspects of form that significantly affect the way the animal interacts with its environment.
As a requirement for maintaining the fluid integrity of the plasma membrane of its cells, an animal’s body must be arranged so that all of its living cells are bathed in an aqueous medium.
In most animals, combinations of various tissues make up functional units called organs, and groups of organs work together as organ systems.
Occurring in sheets of tightly packed cells, epithelial tissue covers the outside of the body and lines organs and cavities within the body.
Connective tissue functions mainly to bind and support other tissues.
Macrophages are amoeboid cells that roam the maze of fibers, engulfing bacteria and the debris of dead cells by phagocytosis.
Nervous tissue senses stimuli and transmits signals in the form of nerve impulses from one part of the animal to another. Muscle tissue is responsible for body movement.
The functional unit of nervous tissue is the neuron, or nerve cell, which includes extensions called axons that are uniquely specialized to transmit nerve impulses.
Nervous tissues also include glial cells, or glia, which nourish, insulate, and replenish neurons.
Feedback control maintains the internal environment in many animals
An animal is a regulator for a particular environmental variable if it uses internal control mechanisms to moderate internal change while external conditions fluctuate.
An animal is a conformer for a particular environmental variable if it allows its internal condition to vary as external conditions fluctuate.
Homeostasis is a general process by which organisms maintain a “steady state” or internal balance.
Animal bodies achieve homeostasis by maintaining a variable, such as body temperature or solute concentration, at or near a particular value or set point.
Homeostasis in animals relies largely on negative feedback, a control mechanism that reduces or “damps” the stimulus.Unlike negative feedback, positive feedback is a control mechanism that amplifies rather than reduces the stimulus.
The normal range of homeostasis may change by acclimatization, a process by which an animal adjusts to changes in its external environment.
Homeostatic processes for thermoregulation involve form, function, and behavior
Thermoregulation is the process by which animals maintain their internal temperature within a tolerable range.
Endothermic animals, such as birds and mammals, use metabolic heat to regulate their body temperature. Ectothermic animals, such as snakes and most fishes, gain most of their heat from the external environment.
In mammals, several of these mechanisms involve the integumentary system, including the skin, hair, and nails.
A major thermoregulatory adaptation in mammals and birds is insulation: hair, feathers, or fat layers.
Another circulatory adaptation is countercurrent exchange, the transfer of heat or solutes in between fluids that flow in opposite directions.
Nerve cells that control thermoregulation (and other aspects of homeostasis) are concentrated in a brain region called the hypothalamus.
Energy requirements are related to animal size, activity, and environment
The flow of energy through an animal—its bioenergetics—determines how much food it needs and is related to the animal’s size, activity, and environment.
The amount of energy an animal uses in a unit of time is called its metabolic rate—the sum of all the energy-requiring biochemical reactions that occur during a given time interval.
The metabolic rate of a nongrowing endotherm at rest, with an empty stomach and experiencing no stress, is called the basal metabolic rate (BMR).
The metabolic rate of a resting, fasting, nonstressed ectotherm is called its standard metabolic rate (SMR).
Some animals deal with severe conditions by an adaptation called torpor, a physiological state in which activity is low and metabolism decreases.
Hibernation is long-term torpor that is an adaptation to winter cold and food scarcity.