Anatomy and Physiology

• Anatomy is the biological form of an organism.
• Physiology constitutes the biological functions an organism performs.
• The comparative study of animals reveals that form and function are closely correlated.
• Many structures are specialized for a particular function.

Animal Size and Shape

• Size and shape affect how an animal interacts with its environment.
• An animal's body plan is programmed by the genome, which evolved over millions of years.
• Physical laws govern strength, diffusion, movement, and heat exchange.
• Properties of water limit possible shapes for fast-swimming animals.
• Convergent evolution often results in similar adaptations of diverse organisms facing the same challenge.
• Thicker skeletons are required to support larger animals.

Exchange with the Environment

• Materials, such as nutrients, waste products, and gases, must be exchanged across animal cell membranes.
• The exchange rate is proportional to a cell's surface area, and the amount of exchange material is proportional to the cell's volume.
• Single-celled organisms in water have sufficient surface area for all necessary exchanges.
• Multicellular organisms with a saclike body plan featuring one hole for consuming food and expelling waste have body walls that are only two cells thick to facilitate the diffusion of materials.
• In flat animals like tapeworms, most cells are in direct contact with the environment.
• More complex organisms have compact masses of cells with complex internal organizations.
• Evolutionary adaptations, including specialized and extensively branched or folded structures, enable sufficient exchange with the environment.
• Interstitial fluid fills the space between cells and links exchange surfaces to body cells.
• A complex body plan is useful for animals living in variable environments as it helps to maintain a relatively stable internal environment.

Hierarchical Organization

• Most animals are composed of cells organized into tissues with different functions.
• Tissues make up organs, which together make up organ systems.
• Some organs, like the pancreas, belong to more than one organ system.
• Four main types of animal tissues exist:
  • Epithelial
  • Connective
  • Muscle
  • Nervous

Epithelial Tissue

• Epithelial tissue covers the outside of the body and lines the organs and cavities within the body.
• It features closely joined cells.
• The shape of these cells may be cuboidal (like dice), columnar (like bricks on end), or squamous (like floor tiles).
• The arrangement of epithelial cells may be simple (single cell layer), stratified (multiple tiers of cells), or pseudostratified (a single layer of cells of varying length).

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.
• Three types of connective tissue fibers all are made of protein:
  • Collagenous fibers provide strength and flexibility
  • Reticular fibers join connective tissue to adjacent tissues
  • Elastic fibers stretch and snap back to their original length
• Connective tissue contains cells, including fibroblasts, which secrete the protein of extracellular fibers, and macrophages, which are involved in the immune system.
• In vertebrates, the fibers and foundation combine to form six major types of connective tissue:
  • Loose connective tissue binds epithelia to underlying tissues and holds organs in place
  • Fibrous connective tissue is found in tendons, which attach muscles to bones, and ligaments, which connect bones at joints
  • 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 contract to enable muscles.
• Muscle tissue in the vertebrate body is divided into three types:
  • Skeletal muscle or striated muscle, is responsible for voluntary movement.
  • Smooth muscle is responsible for involuntary body activities.
  • Cardiac muscle is responsible for contraction of the heart.

Nervous Tissue

• Nervous tissue functions in the receipt, processing, and transmission of information.
• Nervous tissue contains neurons, or nerve cells, which transmit nerve impulses, and glial cells, or glia, which support cells.

Coordination and Control

• Control and coordination within a body depend on the endocrine and nervous systems.
• The endocrine system releases signaling molecules called hormones into the bloodstream.
• A hormones may affect one or more regions throughout the body.
• Hormones are relatively slow acting, but can have long-lasting effects.
• Hormones often coordinate gradual changes affecting the entire body.
• The nervous system transmits information between specific locations.
• The information conveyed depends on a signal's pathway, not the type of signal.
• Nerve signal transmission is very fast.
• The process involves nerve impulses and chemical signals.
• The endocrine and nervous systems often work in close coordination.
• They coordinate rapid responses to the environment.

Feedback Control

• Animals manage their internal environments by regulating or conforming when faced with environmental fluctuations.
• 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.

Homeostasis

• Homeostasis is how organisms maintain a "steady state" or internal balance regardless of the external environment.
• In humans, body temperature, blood pH, and glucose concentration are each maintained at a constant level.
• Fluctuations above or below a set point serve as a stimulus and are detected by a sensor.
• A control center generates output that triggers a response.
• The response returns the variable to the set point.
• Homeostasis can adjust to acclimatization of external environment.
• Acclimatization is a temporary change during an animal's lifetime.
• Adjusting to low oxygen pressure at high altitudes is an example.

Thermoregulation

• Thermoregulation is the process by which animals maintain an internal temperature within a normal range.
• Endothermic animals generate heat by metabolism and include birds and mammals.
• Ectothermic animals gain heat from external sources and include invertebrates, fishes, amphibians, and nonavian reptiles.
• Endotherms can maintain a stable body temperature, even with large fluctuations in environmental temperature.
• Endothermy is more energetically expensive than ectothermy.
• Ectotherms generally tolerate greater variation in internal temperature.
• The body temperature of a poikilotherm varies with its environment.
• The body temperature of a homeotherm is relatively constant.
• The relationship between heat source and body temperature is not fixed, i.e., not all poikilotherms are ectotherms.
• Hibernating mammals have fluctuating body temperatures, whereas some marine fish have very stable temperatures.
• Organisms exchange heat by 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.
• Insulation is especially important for marine mammals such as whales and walruses.
• Regulation of blood flow near the body surface significantly affects thermoregulation.
• Many endotherms and some ectotherms can alter the amount of blood flowing between the body core and the skin.
• Vasodilation increases blood flow in the skin and facilitates heat loss.
• Vasoconstriction decreases blood flow in the skin and lowers heat loss.
• The arrangement of blood vessels in many marine mammals and birds allows for countercurrent exchange. Countercurrent heat exchangers transfer heat between fluids flowing in opposite directions and thereby reduce heat loss.
• Arteries and veins are located adjacent to each other, and the direction of flow is opposite.
• Many animals lose heat through evaporation of water from their skin.
• Sweating or bathing moistens the skin to help cool an animal down.
• Panting, or breathing with short, quick breaths, increases the cooling effect in birds and many mammals.
• Ectotherms, and sometimes endotherms, use behavioral responses to control body temperature.
• They may seek warm places when cold and orient themselves toward heat sources.
• When hot, they bathe, move to cooler areas, huddle (crowd together), or change orientation to minimize heat absorption.
• Thermogenesis is the adjustment of metabolic heat production to maintain body temperature.
• Thermogenesis is increased by muscle activity such as moving or shivering.
• Birds and some nonavian reptiles can also raise body temperature through shivering.
• Nonshivering thermogenesis occurs when hormones cause mitochondria to increase their metabolic activity.
• Some mammals have a tissue called brown fat that is specialized for rapid heat production.
• It is found in the infants of many mammals and in adult mammals that hibernate.
• The amount of brown fat in human adults varies depending on the temperature of the surrounding environment.
• Birds and mammals can vary their insulation to acclimatize to seasonal temperature changes.
• Lipid composition of cell membranes may change with temperature, and unsaturated lipids keep membranes fluid at low temperatures.
• Some ectotherms produce "antifreeze" compounds at subzero temperatures to prevent ice formation in their cells, and antifreeze proteins can be found in fish.
• Thermoregulation in mammals is controlled by the hypothalamus.
• The hypothalamus triggers heat loss or heat-generating mechanisms.
• Fever, a response to some infections, reflects an increase in the normal range for the biological thermostat.
• Some ectothermic organisms seek warmer environments to increase their body temperature in response to certain infections.

Energy Requirements

• Bioenergetics constitutes the overall flow and transformation of energy in an animal.
• Bioenergetics determines an animal's nutritional needs and relates to its size, activity, and environment.
• Organisms can be classified by how they obtain chemical energy.
• Autotrophs, such as plants, harness light energy to build energy-rich molecules.
• Heterotrophs, such as animals, harvest chemical energy from food.
• 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 constitutes the sum of all the energy an animal uses in a unit of time.
• Metabolic rate can be determined by measuring an animal's heat loss (calorimetry), the amount of oxygen consumed or carbon dioxide produced (indirect calorimetry), or the 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.
• Both rates assume a nongrowing, fasting, and nonstressed animal.
• Ectotherms have much lower metabolic rates than endotherms of a comparable size.
• The BMR of an adult male ranges from 1600-1800 kcal/day, while the female BMR ranges from 1300-1500 kcal/day.
• The SMR of an alligator is 60 kcal/day at 20°C.
• Metabolic rates are affected by many factors besides whether an animal is an endotherm or ectotherm.
• Key factors include age, sex, size, activity, temperature, and nutrition.
• Metabolic rate is proportional to body mass to the power of three-quarters (m3/4.).
• 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.
• Activity greatly affects metabolic rate for both endotherms and ectotherms.
• The maximum metabolic rate an animal can sustain is inversely related to the duration of the activity.
• The average daily rate of energy consumption is two to four times BMR (endotherms) or SMR (ectotherms) for most terrestrial animals.
• The fraction of an animal's energy budget devoted to activity depends on factors such as environment, behavior, size, and thermoregulation.
• Torpor is a physiological state of decreased activity and metabolism.
• Torpor enables animals to save energy while avoiding difficult and dangerous conditions.
• Hibernation is long-term torpor that is an adaptation to winter cold and food scarcity.