Chapter 40 Basic Principles of Animal Form and Function

Constraints on Size An animal’s size and shape are referred to as a body plan or design. It is limited mainly due to its surface area to volume ratio. Organisms must be able to exchange gases, nutrients, and water with the external environment. Additionally, they must also be able to get rid of wastes.

Tissues Tissues are groups of cells with a common structure and function. There are 4 main classes of tissue: 1. Epithelial 2. Connective 3. Muscle 4. Nervous

1. Epithelial Tissue Occurs in sheets Lines the inside and outside of the body and its cavities. Often are tightly packed, joined with tight junctions and protects against mechanical injury and fluid loss.

1. Epithelial Tissue The criteria for classifying epithelia are the number of layers and the shapes of the cells. 1. Simple epithelium--single layer 2. Stratified epithelium-- multiple layers 3. Cuboidal cells--dice like 4. Columnar--like columns 5. Squamous--like floor tiles

2. Connective Tissue Functions to bind and protect other tissues. They are sparse and are linked together by a web of fibers secreted by the cells of the tissue itself. There are 3 kinds: 1. Collagenous fibers--make of collagen, non- elastic. 2. Elastic fibers--are long threads made of elastin. Provides elasticity and complements collagen. 3. Reticular fibers--are thin and branched. Forms fabric that joins connective tissue to adjacent tissues.

3. Muscle Tissue Composed of long muscle fibers. Large numbers of contractile units called myofibrils are arranged in parallel within the cytoplasm of these cells. Myofibrils are made of actin and mysosin. Vertebrates have 3 types of muscle: skeletal, cardiac, and smooth.

4. Nervous Tissue Senses stimuli and transmits nerve impulses from one part of the body to the next. The neuron is the functional unit. Axon Dendrite

Tissues Most animals consist of different tissues organized into organs. These organs are organized into organ systems that carry out the major body functions of most animals.

Bioenergetic Strategies There are two main bioenergetic strategies: Endothermy Ectothermy Homeostasis is the steady state, and it is the physiological process by which animals maintain their internal environment.

Regulating and Conforming Regulating and conforming are two extremes by which animals cope with their environmental fluctuations.

Regulation An animal is a regulator for an environmental variable if it uses internal control mechanisms to moderate internal change in the face of external fluctuations. Example: Freshwater fish. They can maintain a stable internal concentration of solutes in the blood and interstitial fluid.

Conforming An animal is a conformer for an environmental variable if it allows an internal condition to conform to the external environment. Example: Some spider crabs live in salt water and don’t regulate their internal environment. They conform to their surroundings.

Regulating and Conforming No animal is a perfect regulator or conformer. They regulate their internal process while conforming to others with regard to the external environment.

Homeostasis Homeostatic mechanisms moderate changes in internal environments and have 3 functional components: 1. A receptor 2. A control center 3. An effector

The Receptor Detects a change in the internal environment of an animal. Example: Body temperature.

The Control Center Processes the information it receives and directs an appropriate response. Example: Brain.

The Effector The effector displays the appropriate response. Example: Shivering, dilation or constriction of blood vessels.

For Example: The regulation of room temperature. The control center is the thermostat and it contains a receptor called the thermometer. When the temp falls below a set point, it switches the heater (the effector) on. When the thermometer senses the temp is above the set point, it switches the heat off--negative feedback.

Negative Feedback Occurs when the variable being monitored counteracts any further change in the same direction. There are only slight variations above and below the set point in a negative feedback system. Most homeostatic mechanisms in an animal operate under this principle.

Positive Feedback On the other hand occurs where a change in an environmental variable triggers mechanisms that amplify the change. Example: During childbirth, the head against the uterine wall stimulates more contractions in the uterus. Positive feedback completes childbirth.

Thermoregulation This is the process by which animals maintain an internal temperature within a tolerable range. This ability is critical to survival because enzyme function and membrane permeability is dramatically affected by large changes in temperature.

Thermoregulation In general, ectotherms tolerate a greater variation in internal temperature than do endotherms. Endotherms regulate their high internal temperature as their surroundings fluctuate. Ectotherms regulate their temperature more so by behavioral means.

Heat Exchange Endotherms and ectotherms use 4 modes of heat exchange: 1. Conduction 2. Convection 3. Radiation 4. Evaporation

Thermoregulatory Functions Thermoregulators function by balancing heat loss with heat gain. There are 5 general categories to assist with this: 1. Insulation 2. Circulatory Adaptation 3. Evaporative Cooling 4. Behavioral Responses 5. Adjusting Metabolism

1. Insulation Fat, hair, and/or feathers help to reduce heat flow between the organism and the surroundings. The integumentary system in mammals acts as this insulating layer.

2. Circulatory Adaptations Vasodilation, vasoconstriction work together to transfer body heat form the core to the surroundings. Vasodilation--vessels get larger. Vasoconstriciton--vessels get smaller.

3. Evaporative Cooling Many animals have structural adaptations that enable them to take advantage of evaporation as a way of controlling body temperature. For Example: Sweat glands, panting, and mucous secretions.

4. Behavioral Adaptations Behavioral responses are used by endotherms and ectotherms as a means to control body temperature. Basking in the sun Migration Hibernation

5. Adjusting Metabolism There are a variety of ways by which animals can control their body temperature by changing their metabolic activity. In some mammals, hormones can stimulate mitochondria to generate heat instead of ATP--non-shivering thermogenesis.

5. Adjusting Metabolism In other mammals, a layer of brown fat is found in the neck region and is specialized in rapid heat production. Some female pythons can increase their body temperature when incubating eggs.

5. Adjusting Metabolism Humans have nerve cells concentrated in the hypothalamus to control thermoregulation. These nerve cells are grouped together and function as a thermostat regulating mechanisms that increase or decrease heat loss.