Basic Principles of Animal Form and Function Chapter 40 Basic Principles of Animal Form and Function

Physical Laws and Animal Form The need to exchange materials with the environment place certain limits on the range of animal forms 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 Fusiform shape in fast swimmers  Tuna Shark Penguin Dolphin 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

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

Multicellular Organism…simple Multicellular organisms with a sac body plan have body walls that are only two cells thick, facilitating diffusion of materials Mouth Gastrovascular cavity Diffusion Diffusion Hydra (b) Two cell layers

Multicellular Organism … complex External environment Mouth Food CO2 O2 Animal body Respiratory system Blood 50 µm 0.5 cm 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). Cells Heart Nutrients Circulatory system 10 µm Interstitial fluid Digestive system The lining of the small intestine, a diges- tive organ, is elaborated with fingerlike projections that expand the surface area for nutrient absorption (cross-section, SEM). Excretory system Inside a kidney is a mass of microscopic tubules that exhange chemicals with blood flowing through a web of tiny vessels called capillaries (SEM). Anus Unabsorbed matter (feces) Metabolic waste products (urine) Organisms with more complex body plans have highly folded internal surfaces specialized for exchanging materials

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

Tissue Structure and Function Different types of tissues have different structures that are suited to their functions Tissues are classified into four main categories Epithelial Connective Muscle nervous

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

Stratified squamous epithelia Simple squamous epithelia 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. Simple Stratified Columnar Cuboidal Squamous Pseudostratified A simple columnar epithelium A stratified columnar epithelium A pseudostratified ciliated columnar epithelium Stratified squamous epithelia Cuboidal epithelia Simple squamous epithelia Basement membrane 40 µm

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

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

Muscle Tissue Muscle tissue Is composed of long cells called muscle fibers capable of contracting in response to nerve signals Three types Skeletal Cardiac Smooth

Nervous Tissue Nervous tissue Senses stimuli and transmits signals throughout the animal Neurons Cell body Axon Dendrite

Muscle and Nervous tissue MUSCLE TISSUE 100 µm Skeletal muscle 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

Organs and Organ Systems In all but the simplest animals different tissues are organized into organs In some organs (like the stomach) tissues are arranged in layers At a higher level of organization, organ systems carry out the major body functions of most animals 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.

Organ Systems Organ systems in mammals

Bioenergetics Animals are Heterotrophs Animals consume food for the chemical energy stored in the molecules Energy is required for all life processes The flow of energy through an animal, its bioenergetics Ultimately limits the animal’s behavior, growth, and reproduction Determines how much food it needs

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

Metabolic rate The amount of energy an animal uses in a unit of time

Measuring Metabolic rate One way is to determine the amount of oxygen consumed or carbon dioxide produced by an organism This photograph shows a ghost crab in a respirometer. Temperature is held constant in the chamber, with air of known O2 concentration flow- ing through. The crab’s metabolic rate is calculated from the difference between the amount of O2 entering and the amount of O2 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.

Bioenergetic Strategies Birds and mammals are mainly endothermic Bodies are warmed mostly by heat generated by metabolism They typically have higher metabolic rates Capable of intense, long-duration activity Amphibians and reptiles other than birds are ectothermic They gain their heat mostly from external sources They have lower metabolic rates Incapable of intense activity over long periods

Influences on Metabolic Rate

Size and Metabolic Rate Metabolic rate per gram Is inversely related to body size among similar animals Each gram of mouse consumes 20 times the calories as each gram of elephant

Activity and Metabolic Rate Basal metabolic rate (BMR) Is the metabolic rate of an endotherm at rest 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

Energy expenditures per unit mass (kcal/kg•day) Energy Budgets Different species of animals use the energy and materials in food in different ways, depending on their environment An animal’s use of energy is partitioned to BMR (or SMR), activity, homeostasis, growth, and reproduction 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)

Regulating the Internal Environment Animals regulate their internal environment within relatively narrow limits The internal environment of vertebrates (where our cells live) is the interstitial fluid. It is very different from the external environment Homeostasis A dynamic balance between external changes and the animal’s internal control mechanisms that oppose the changes

Regulating and Conforming Regulating and conforming are two extremes in how animals cope with environmental fluctuations Regulator Uses internal control mechanisms to moderate internal change in the face of external, environmental fluctuation Conformer Allows its internal condition to vary with certain external changes

Mechanisms of Homeostasis Mechanisms of homeostasis moderate changes in the internal environment A homeostatic control system has three functional components receptor control center effector Response No heat produced Room temperature decreases Heater turned off Set point Too hot Set point Control center: thermostat increases on cold Heat

Feedback Circuits Negative feedback Positive feedback Where buildup of the end product of the system shuts the system off Positive feedback Involves a change in some variable that triggers mechanisms that amplify the change

Thermoregulation The process by which animals maintain an internal temperature within a tolerable range

Ectotherms and Endotherms River otter (endotherm) Largemouth bass (ectotherm) Ambient (environmental) temperature (°C) Body temperature (°C) 40 30 20 10 Ectotherms Include most (but not all) invertebrates, fishes, amphibians, and non-bird reptiles Tolerate greater variation in internal temperature than endotherms Endotherms Include birds and mammals More energetically expensive than ectothermy A few reptiles, fish, and insects are endotherms!

Modes of Heat Exchange Radiation Evaporation Convection Conduction 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. Radiation Evaporation Convection Conduction

Balancing Heat Loss and Gain

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 Cedar Waxwing

Mammalian integument as insulation Skin provides protection from mechanical injury, infection and dessication Skin is important in thermoregulation Adipose tissue of the hypodermis supplies insulation of varying amount depending upon the species Hair Epidermis Sweat pore Muscle Dermis Nerve Sweat gland Hypodermis Adipose tissue Blood vessels Oil gland Hair follicle

Circulatory Adaptations Many endotherms and some ectotherms Can alter the amount of blood flowing between the body core and the skin Vasodilation Blood flow in the skin increases, facilitating heat loss Vasoconstriction Blood flow in the skin decreases, lowering heat loss

Countercurrent Heat Exchangers Many marine mammals and birds have arrangements of blood vessels that are important for reducing heat loss 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 30º 20º 10º 33° 27º 18º 9º Pacific bottlenose dolphin 2 1 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. 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. 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. 1 3

Countercurrent Heat Exchangers Some specialized ENDOTHERMIC bony fishes and sharks also possess countercurrent heat exchangers 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 (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.

Endothermic Insects Many endothermic insects have countercurrent heat exchangers that help maintain a high temperature in the thorax Strong flight muscles generate large amounts of heat when operating Red areas indicate areas of high temp in this winter-active moth

Cooling by Evaporative Heat Loss Heat is lost through the evaporation of water in sweat Some animals pant to cool their bodies Bathing moistens the skin which helps to cool an animal down

Behavioral Responses Posture: Some terrestrial invertebrates have certain postures that enable them to minimize or maximize their absorption of heat from the sun Adjustment of metabolic heat production Many species of flying insects use shivering to warm up before taking flight

Feedback Mechanisms in Thermoregulation 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 Increased body temperature (such as when exercising or in hot surroundings) Homeostasis: Internal body temperature of approximately 36–38C increases; shuts off warming Decreased body temperature (such as when in cold 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. activates warming Mammals regulate their body temperature by a complex negative feedback system that involves several organ systems In humans the hypothalamus contains a group of nerve cells that function as a thermostat

Adjustment to Changing Temperatures Acclimatization Many animals can adjust to a new range of environmental temperatures over a period of days or weeks May involve cellular adjustments (esp. in ectotherms) Change in membrane lipid composition Production of cryoprotectant (antifreezing) molecules Birds and mammals can make adjustments of insulation and metabolic heat production

Torpor and Energy Conservation An adaptation that enables animals to save energy while avoiding difficult and dangerous conditions A physiological state in which activity is low and metabolism decreases 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 Nocturnally feeding bats enter torpor while roosting during the daylight hours A hummingbird may enter turpor on a cold night and have its body temp lower by 25-30 degrees centigrade

Hibernation is long-term torpor An adaptation to winter cold and food scarcity during which the animal’s body temperature declines Periodic arousals may be needed to carry out some body functions that require a high temperature Additional metabolism that would be necessary to stay active in winter 200 Actual metabolism 100 Metabolic rate (kcal per day) Arousals 35 Body temperature 30 25 20 Temperature (°C) 15 10 5 Outside temperature -5 Burrow temperature -10 -15 June August October December February April Belding’s ground squirrel

Bears Grizzly Kodiak Brown Polar Hibernating black bears can go months without eating, drinking, urinating, defecating or exercising The body temperature of a hibernating black bear dips only to about 88 degrees. Much less of a drop than that seen in many hibernating rodents Kodiak Brown Polar Hibernation in black bears does not involve the periodic arousals seen in many hibernating rodents. Bears also slumber less deeply than the rodents.