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Chapter 40 Basic Principles of Animal Form and Function

Overview: Diverse Forms, Common Challenges Animals inhabit almost every part of the biosphere Despite their amazing diversity All animals face a similar set of problems, including how to nourish themselves

The comparative study of animals Reveals that form and function are closely correlated Figure 40.1

Natural selection can fit structure, anatomy, to function, physiology By selecting, over many generations, what works best among the available variations in a population

Concept 40.1: Physical laws and the environment constrain animal size and shape Physical laws and the need to exchange materials with the environment Place certain limits on the range of animal forms

Physical Laws and Animal Form The ability to perform certain actions Depends on an animal’s shape and size

Evolutionary convergence Reflects different species’ independent adaptation to a similar environmental challenge Figure 40.2a–e (a) Tuna (b) Shark (c) Penguin (d) Dolphin (e) Seal

Exchange with the Environment An animal’s size and shape Have a direct effect on how the animal exchanges energy and materials with its surroundings Exchange with the environment occurs as substances dissolved in the aqueous medium Diffuse and are transported across the cells’ plasma membranes

A single-celled protist living in water Has a sufficient surface area of plasma membrane to service its entire volume of cytoplasm Figure 40.3a Diffusion (a) Single cell

Multicellular organisms with a sac body plan Have body walls that are only two cells thick, facilitating diffusion of materials Figure 40.3b Mouth Gastrovascular cavity Diffusion Diffusion (b) Two cell layers

Organisms with more complex body plans Have highly folded internal surfaces specialized for exchanging materials

External environment Food CO 2 O 2 Mouth Animal body Respiratory system Circulatory system Nutrients Excretory system Digestive system Heart Blood Cells Interstitial fluid Anus Unabsorbed matter (feces) Metabolic waste products (urine) The lining of the small intestine, a digestive organ, is elaborated with fingerlike projections that expand the surface area for nutrient absorption (cross-section, SEM). A microscopic view of the lung reveals that it is much more spongelike than balloonlike. This construction provides an expansive wet surface for gas exchange with the environment (SEM). Inside a kidney is a mass of microscopic tubules that exhange chemicals with blood flowing through a web of tiny vessels called capillaries (SEM). 0.5 cm 10 µm 50 µm Figure 40.4

Concept 40.2: Animal form and function are correlated at all levels of organization Animals are composed of cells Groups of cells with a common structure and function Make up tissues Different tissues make up organs Which together make up organ systems

Different types of tissues Have different structures that are suited to their functions Tissues are classified into four main categories Epithelial, connective, muscle, and nervous Tissue Structure and Function

Epithelial Tissue Epithelial tissue Covers the outside of the body and lines organs and cavities within the body Contains cells that are closely joined

Epithelial tissue EPITHELIAL TISSUE Columnar epithelia, which have cells with relatively large cytoplasmic volumes, are often located where secretion or active absorption of substances is an important function. A stratified columnar epithelium A simple columnar epithelium A pseudostratified ciliated columnar epithelium Stratified squamous epithelia Simple squamous epithelia Cuboidal epithelia Basement membrane 40 µm Figure 40.5

Connective Tissue Connective tissue Functions mainly to bind and support other tissues Contains sparsely packed cells scattered throughout an extracellular matrix

Connective tissue Collagenous fiber Elastic fiber Chondrocytes Chondroitin sulfate Loose connective tissue Fibrous connective tissue 100 µm 100 µm Nuclei 30 µm Bone Blood Central canal Osteon 700 µm 55 µm Red blood cells White blood cell Plasma Cartilage Adipose tissue Fat droplets 150 µm CONNECTIVE TISSUE Figure 40.5

Muscle Tissue Muscle tissue Is composed of long cells called muscle fibers capable of contracting in response to nerve signals Is divided in the vertebrate body into three types: skeletal, cardiac, and smooth

Nervous Tissue Nervous tissue Senses stimuli and transmits signals throughout the animal

Muscle and nervous tissue MUSCLE TISSUE Skeletal muscle 100 µm Multiple nuclei Muscle fiber Sarcomere Cardiac muscle Nucleus Intercalated disk 50 µm Smooth muscle Nucleus Muscle fibers 25 µm NERVOUS TISSUE Neurons Process Cell body Nucleus 50 µm Figure 40.5

Organs and Organ Systems In all but the simplest animals Different tissues are organized into organs

In some organs The tissues are arranged in layers Figure 40.6 Lumen of stomach Mucosa. The mucosa is an epithelial layer that lines the lumen. Submucosa. The submucosa is a matrix of connective tissue that contains blood vessels and nerves. Muscularis. The muscularis consists mainly of smooth muscle tissue. 0.2 mm Serosa. External to the muscularis is the serosa, a thin layer of connective and epithelial tissue.

Representing a level of organization higher than organs Organ systems carry out the major body functions of most animals

Organ systems in mammals Table 40.1

Concept 40.3: Animals use the chemical energy in food to sustain form and function All organisms require chemical energy for Growth, repair, physiological processes, regulation, and reproduction

The flow of energy through an animal, its bioenergetics Ultimately limits the animal’s behavior, growth, and reproduction Determines how much food it needs Studying an animal’s bioenergetics Tells us a great deal about the animal’s adaptations Bioenergetics

Energy Sources and Allocation Animals harvest chemical energy From the food they eat Once food has been digested, the energy-containing molecules Are usually used to make ATP, which powers cellular work

After the energetic needs of staying alive are met Any remaining molecules from food can be used in biosynthesis Figure 40.7 Organic molecules in food Digestion and absorption Nutrient molecules in body cells Cellular respiration Biosynthesis: growth, storage, and reproduction Cellular work Heat Energy lost in feces Energy lost in urine Heat Heat External environment Animal body Heat Carbon skeletons ATP

An animal’s metabolic rate Is the amount of energy an animal uses in a unit of time Can be measured in a variety of ways Quantifying Energy Use

One way to measure metabolic rate Is to determine the amount of oxygen consumed or carbon dioxide produced by an organism Figure 40.8a, b This photograph shows a ghost crab in a respirometer. Temperature is held constant in the chamber, with air of known O 2 concentration flowing through. The crab’s metabolic rate is calculated from the difference between the amount of O 2 entering and the amount of O 2 leaving the respirometer. This crab is on a treadmill, running at a constant speed as measurements are made. (a) (b) Similarly, the metabolic rate of a man fitted with a breathing apparatus is being monitored while he works out on a stationary bike.

An animal’s metabolic rate Is closely related to its bioenergetic strategy Bioenergetic Strategies

Birds and mammals are mainly endothermic, meaning that Their bodies are warmed mostly by heat generated by metabolism They typically have higher metabolic rates

Stem Elongation Amphibians and reptiles other than birds are ectothermic, meaning that They gain their heat mostly from external sources They have lower metabolic rates

The metabolic rates of animals Are affected by many factors Influences on Metabolic Rate

Size and Metabolic Rate Metabolic rate per gram Is inversely related to body size among similar animals

The basal metabolic rate (BMR) Is the metabolic rate of an endotherm at rest The standard metabolic rate (SMR) Is the metabolic rate of an ectotherm at rest For both endotherms and ectotherms Activity has a large effect on metabolic rate Activity and Metabolic Rate

In general, an animal’s maximum possible metabolic rate Is inversely related to the duration of the activity Figure 40.9 Maximum metabolic rate (kcal/min; log scale) 500 100 50 10 5 1 0.5 0.1 A H A H A A A H H H A = 60-kg alligator H = 60-kg human 1 second 1 minute 1 hour Time interval 1 day 1 week Key Existing intracellular ATP ATP from glycolysis ATP from aerobic respiration

Different species of animals Use the energy and materials in food in different ways, depending on their environment Energy Budgets

An animal’s use of energy Is partitioned to BMR (or SMR), activity, homeostasis, growth, and reproduction Figure 40.10a, b Endotherms Ectotherm Annual energy expenditure (kcal/yr) 800,000 Basal metabolic rate Reproduction Temperature regulation costs Growth Activity costs 60-kg female human from temperate climate Total annual energy expenditures (a) 340,000 4-kg male Adélie penguin from Antarctica (brooding) 4,000 0.025-kg female deer mouse from temperate North America 8,000 4-kg female python from Australia Energy expenditure per unit mass (kcal/kg•day) 438 Deer mouse 233 Adélie penguin 36.5 Human 5.5 Python Energy expenditures per unit mass (kcal/kg•day) (b)

Concept 40.4: Animals regulate their internal environment within relatively narrow limits The internal environment of vertebrates Is called the interstitial fluid, and is very different from the external environment Homeostasis is a balance between external changes And the animal’s internal control mechanisms that oppose the changes

Regulating and conforming Are two extremes in how animals cope with environmental fluctuations Regulating and Conforming

An animal is said to be a regulator If it uses internal control mechanisms to moderate internal change in the face of external, environmental fluctuation An animal is said to be a conformer If it allows its internal condition to vary with certain external changes

Mechanisms of homeostasis Moderate changes in the internal environment Mechanisms of Homeostasis

A homeostatic control system has three functional components A receptor, a control center, and an effector Figure 40.11 Response No heat produced Room temperature decreases Heater turned off Set point Too hot Set point Control center: thermostat Room temperature increases Heater turned on Too cold Response Heat produced Set point

Most homeostatic control systems function by negative feedback Where buildup of the end product of the system shuts the system off

A second type of homeostatic control system is positive feedback Which involves a change in some variable that triggers mechanisms that amplify the change

Concept 40.5: Thermoregulation contributes to homeostasis and involves anatomy, physiology, and behavior Thermoregulation Is the process by which animals maintain an internal temperature within a tolerable range

Ectotherms Include most invertebrates, fishes, amphibians, and non-bird reptiles Endotherms Include birds and mammals Ectotherms and Endotherms

In general, ectotherms Tolerate greater variation in internal temperature than endotherms Figure 40.12 River otter (endotherm) Largemouth bass (ectotherm) Ambient (environmental) temperature (°C) Body temperature (°C) 40 30 20 10 10 20 30 40 0

Endothermy is more energetically expensive than ectothermy But buffers animals’ internal temperatures against external fluctuations And enables the animals to maintain a high level of aerobic metabolism

Modes of Heat Exchange Organisms exchange heat by four physical processes Figure 40.13 Radiation is the emission of electromagnetic waves by all objects warmer than absolute zero. Radiation can transfer heat between objects that are not in direct contact, as when a lizard absorbs heat radiating from the sun. Evaporation is the removal of heat from the surface of a liquid that is losing some of its molecules as gas. Evaporation of water from a lizard’s moist surfaces that are exposed to the environment has a strong cooling effect. Convection is 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 blood moves heat from the body core to the extremities . Conduction is the direct transfer of thermal motion (heat) between molecules of objects in direct contact with each other, as when a lizard sits on a hot rock.

Balancing Heat Loss and Gain Thermoregulation involves physiological and behavioral adjustments That balance heat gain and loss

Insulation Insulation, which is a major thermoregulatory adaptation in mammals and birds Reduces the flow of heat between an animal and its environment May include feathers, fur, or blubber

In mammals, the integumentary system Acts as insulating material Hair Sweat pore Muscle Nerve Sweat gland Oil gland Hair follicle Blood vessels Adipose tissue Hypodermis Dermis Epidermis Figure 40.14

Many endotherms and some ectotherms Can alter the amount of blood flowing between the body core and the skin Circulatory Adaptations

In vasodilation Blood flow in the skin increases, facilitating heat loss In vasoconstriction Blood flow in the skin decreases, lowering heat loss

Many marine mammals and birds Have arrangements of blood vessels called countercurrent heat exchangers that are important for reducing heat loss Figure 40.15 1 3 In the flippers of a dolphin, each artery is surrounded by several veins in a countercurrent arrangement, allowing efficient heat exchange between arterial and venous blood. Canada goose Artery Vein 35°C Blood flow Vein Artery 30º 20º 10º 33° 27º 18º 9º Pacific bottlenose dolphin 2 1 3 2 3 Arteries carrying warm blood down the legs of a goose or the flippers of a dolphin are in close contact with veins conveying cool blood in the opposite direction, back toward the trunk of the body. This arrangement facilitates heat transfer from arteries to veins (black arrows) along the entire length of the blood vessels. 1 Near the end of the leg or flipper, where arterial blood has been cooled to far below the animal’s core temperature, the artery can still transfer heat to the even colder blood of an adjacent vein. The venous blood continues to absorb heat as it passes warmer and warmer arterial blood traveling in the opposite direction. 2 As the venous blood approaches the center of the body, it is almost as warm as the body core, minimizing the heat lost as a result of supplying blood to body parts immersed in cold water. 3

Some specialized bony fishes and sharks Also possess countercurrent heat exchangers Figure 40.16a, b (a) Bluefin tuna. Unlike most fishes, the bluefin tuna maintains temperatures in its main swimming muscles that are much higher than the surrounding water (colors indicate swimming muscles cut in transverse section). These temperatures were recorded for a tuna in 19°C water. (b) Great white shark. Like the bluefin tuna, the great white shark has a countercurrent heat exchanger in its swimming muscles that reduces the loss of metabolic heat. All bony fishes and sharks lose heat to the surrounding water when their blood passes through the gills. However, endothermic sharks have a small dorsal aorta, and as a result, relatively little cold blood from the gills goes directly to the core of the body. Instead, most of the blood leaving the gills is conveyed via large arteries just under the skin, keeping cool blood away from the body core. As shown in the enlargement, small arteries carrying cool blood inward from the large arteries under the skin are paralleled by small veins carrying warm blood outward from the inner body. This countercurrent flow retains heat in the muscles. 21º 25º 23º 27º 29º 31º Body cavity Skin Artery Vein Capillary network within muscle Dorsal aorta Artery and vein under the skin Heart Blood vessels in gills

Many endothermic insects Have countercurrent heat exchangers that help maintain a high temperature in the thorax Figure 40.17

Cooling by Evaporative Heat Loss Many types of animals Lose heat through the evaporation of water in sweat Use panting to cool their bodies

Bathing moistens the skin Which helps to cool an animal down Figure 40.18

Both endotherms and ectotherms Use a variety of behavioral responses to control body temperature Behavioral Responses

Some terrestrial invertebrates Have certain postures that enable them to minimize or maximize their absorption of heat from the sun Figure 40.19

Adjusting Metabolic Heat Production Some animals can regulate body temperature By adjusting their rate of metabolic heat production

Many species of flying insects Use shivering to warm up before taking flight Figure 40.20 PREFLIGHT PREFLIGHT WARMUP FLIGHT Thorax Abdomen Temperature (°C) Time from onset of warmup (min) 40 35 30 25 0 2 4

Mammals regulate their body temperature By a complex negative feedback system that involves several organ systems Feedback Mechanisms in Thermoregulation

In humans, a specific part of the brain, the hypothalamus Contains a group of nerve cells that function as a thermostat Figure 40.21 Thermostat in hypothalamus activates cooling mechanisms. Sweat glands secrete sweat that evaporates, cooling the body. Blood vessels in skin dilate: capillaries fill with warm blood; heat radiates from skin surface. Body temperature decreases; thermostat shuts off cooling mechanisms. Increased body temperature (such as when exercising or in hot surroundings) Homeostasis: Internal body temperature of approximately 36–38  C Body temperature increases; thermostat shuts off warming mechanisms. Decreased body temperature (such as when in cold surroundings) Blood vessels in skin constrict, diverting blood from skin to deeper tissues and reducing heat loss from skin surface. Skeletal muscles rapidly contract, causing shivering, which generates heat. Thermostat in hypothalamus activates warming mechanisms.

Adjustment to Changing Temperatures In a process known as acclimatization Many animals can adjust to a new range of environmental temperatures over a period of days or weeks

Acclimatization may involve cellular adjustments Or in the case of birds and mammals, adjustments of insulation and metabolic heat production

Torpor and Energy Conservation Torpor Is an adaptation that enables animals to save energy while avoiding difficult and dangerous conditions 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 during which the animal’s body temperature declines Additional metabolism that would be necessary to stay active in winter Actual metabolism Body temperature Arousals Outside temperature Burrow temperature June August October December February April Temperature (°C) Metabolic rate (kcal per day) 200 100 0 35 30 25 20 15 10 5 0 -5 -10 -15 Figure 40.22

Estivation, or summer torpor Enables animals to survive long periods of high temperatures and scarce water supplies Daily torpor Is exhibited by many small mammals and birds and seems to be adapted to their feeding patterns

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