Animal Form and Function

Introduction

• Anatomy is the biological form of an organism.
• Physiology refers to the biological functions an organism performs.
• The comparative study of animals reveals a close correlation between form and function.

Exchange with the Environment

• Nutrients, waste products, and gases must be exchanged across the cell membranes of animal cells.
• The rate of exchange is proportional to a cell's surface area, whereas the amount of exchange is proportional to a cell's volume.
• A single-celled organism living in water has sufficient surface area to carry out all necessary exchange.
• Multicellular organisms with a saclike body plan have body walls that are only two cells thick, facilitating the diffusion of materials.
• Evolutionary adaptations, such as specialized, extensively branched, or folded structures, enable sufficient exchange with the environment.

Hierarchical Organization of Body Plans

• Most animals are composed of specialized cells organized into tissues that have different functions.
• Tissues make up organs, which together make up organ systems.
• Some organs, such as the pancreas, belong to more than one organ system.

Exploring Structure and Function in Animal Tissues

• Different tissues have different structures suited to their functions.
• Tissues are classified into four main categories: epithelial, connective, muscle, and nervous.

Epithelial Tissue

• Epithelial tissue covers the outside of the body and lines the organs and cavities within the body.
• It contains cells that are closely joined.
• The shape of epithelial cells may be cuboidal, columnar, or squamous.
• The arrangement of epithelial cells may be simple, stratified, or pseudo-stratified.

Connective Tissue

• Connective tissue mainly binds and supports other tissues.
• It contains sparsely packed cells scattered throughout an extracellular matrix.
• The matrix consists of fibers in a liquid, jellylike, or solid foundation.
• Connective tissue contains cells, including fibroblasts that secrete the protein of extracellular fibers and macrophages involved in the immune system.
• There are three types of connective tissue fiber, all made of protein: collagenous, reticular, and elastic fibers. -Collagenous fibers provide strength and flexibility. -Reticular fibers join connective tissue to adjacent tissues. -Elastic fibers stretch and snap back to their original length.
• In vertebrates, the fibers and foundation combine to form six major types of connective tissue: loose connective tissue, fibrous connective tissue, bone, adipose tissue, blood, and cartilage. -Loose connective tissue binds epithelia to underlying tissues and holds organs in place. -Fibrous connective tissue is found in tendons and ligaments. -Bone is mineralized and forms the skeleton. -Adipose tissue stores fat for insulation and fuel. -Blood is composed of blood cells and cell fragments in blood plasma. -Cartilage is a strong and flexible support material.

Muscle Tissue

• Muscle tissue is responsible for nearly all types of body movement.
• Muscle cells consist of filaments of the proteins actin and myosin, which together enable muscles to contract.
• It is divided in the vertebrate body into three types: -Skeletal muscle (voluntary movement) -Smooth muscle (involuntary body activities) -Cardiac muscle (contraction of the heart).

Nervous Tissue

• Nervous tissue functions in the receipt, processing, and transmission of information.
• Nervous tissue contains: Neurons (nerve cells) that transmit nerve impulses.
• Glial cells (glia, support cells).

Coordination and Control

• Control and coordination within a body depend on the endocrine system and the nervous system.
• The endocrine system transmits chemical signals called hormones to receptive cells throughout the body via blood.
• Hormones are relatively slow acting but can have long-lasting effects.
• The nervous system transmits information between specific locations.
• The information conveyed depends on a signal's pathway, not the type of signal, and nerve signal transmission is very fast.
• Faced with environmental fluctuations, animals manage their internal environment by either regulating or conforming.
• A regulator uses internal control mechanisms to control internal change in the face of external fluctuation.
• A conformer allows its internal condition to vary with certain external changes.
• Animals may regulate some environmental variables while conforming to others.
• Feedback control maintains the internal environment in many animals.

Homeostasis

• Organisms use homeostasis to maintain a "steady state" or internal balance regardless of the external environment.
• Homeostasis can adjust to changes in the external environment, a process called acclimatization.
• In humans, body temperature, blood pH, and glucose concentration are each maintained at a constant level.
• For a given variable, fluctuations above or below a set point serve as a stimulus; these are detected by a sensor and trigger a response.
• The response returns the variable to the set point
• Set points and normal ranges can change with age or show cyclic variation.
• Homeostasis in animals relies largely on negative feedback, which helps to return a variable to a normal range.
• Positive feedback amplifies a stimulus and does not usually contribute to homeostasis in animals.

Thermoregulation

• Thermoregulation is the process by which animals maintain an internal temperature within a tolerable range.
• Endothermic animals generate heat by metabolism; birds and mammals are endotherms.
• Ectothermic animals gain heat from external sources; ectotherms include most invertebrates, fishes, amphibians, and nonavian reptiles.
• Homeostatic processes for thermoregulation involve form, function, and behavior.
• The body temperature of a poikilotherm varies with its environment. -Poikilotherm: an organism that cannot regulate its body temperature except by behavioral means like basking or burrowing.
• The body temperature of a homeotherm is relatively constant. -Homeotherm: an organism that maintains its body temperature at a constant level by its metabolic activity.
• Organisms exchange heat by four physical processes: radiation, evaporation, convection, and conduction.
• Heat regulation in mammals often involves the integumentary system: skin, hair, and nails.
• Five adaptations help animals thermoregulate: -Insulation -Circulatory adaptations -Cooling by evaporative heat loss -Behavioral responses -Adjusting metabolic heat production
• Insulation is a major thermoregulatory adaptation in mammals and birds.
• Skin, feathers, fur, and blubber reduce heat flow between an animal and its environment.
• The arrangement of blood vessels in many marine mammals and birds allows for countercurrent exchange, the transfer of heat between fluids flowing in opposite directions, thereby reducing heat loss.
• Many types of animals lose heat through evaporation of water from their skin. -Sweating or bathing moistens the skin, helping to cool an animal down. -Panting increases the cooling effect in birds and many mammals.
• Both endotherms and ectotherms use behavioral responses to control body temperature.
• Thermogenesis is the adjustment of metabolic heat production to maintain body temperature
• Thermogenesis is increased by muscle activity such as moving or shivering.
• Nonshivering thermogenesis takes place when hormones cause mitochondria to increase their metabolic activity.
• Birds and mammals can vary their insulation to acclimatize to seasonal temperature changes.
• Some ectotherms produce "antifreeze” compounds to prevent ice formation in their cells when temperatures are subzero.
• Thermoregulation in mammals is controlled by a region of the brain called the hypothalamus.
• Some ectothermic organisms seek warmer environments to increase their body temperature in response to certain infections.

Energy Requirements in Animals

• Bioenergetics is the overall flow and transformation of energy in an animal.
• It determines how much food an animal needs and it relates to an animal's size, activity, and environment.
• Energy-containing molecules from food are usually used to make ATP, which powers cellular work.
• After the needs of staying alive are met, remaining food molecules can be used in biosynthesis.
• Biosynthesis includes body growth and repair, synthesis of storage material such as fat, and production of gametes.
• Metabolic rate is the amount of energy an animal uses in a unit of time.
• Metabolic rate can be determined by: -An animal's heat loss -The amount of oxygen consumed or carbon dioxide produced -Measuring energy content of food consumed and energy lost in waste products
• Basal metabolic rate (BMR) is the metabolic rate of an endotherm at rest at a "comfortable" temperature.
• Standard metabolic rate (SMR) is the metabolic rate of an ectotherm at rest at a specific temperature.
• Ectotherms have much lower metabolic rates than endotherms of a comparable size.
• Smaller animals have higher metabolic rates per gram than larger animals.
• The higher metabolic rate of smaller animals leads to a higher oxygen delivery rate, breathing rate, heart rate, and greater (relative) blood volume compared with a larger animal.
• Torpor is 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.
• Estivation, summer torpor, enables animals to survive long periods of high temperatures and scarce water.
• Daily torpor is exhibited by many small mammals and birds and seems adapted to feeding patterns.