Exchange with the Environment An animal’s size and shape directly affect how it exchanges energy and materials with its surroundings Exchange 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

Mouth Gastrovascular cavity Diffusion Diffusion Diffusion Single cell Two cell layers

Multicellular organisms with a sac body plan have body walls that are only two cells thick, facilitating diffusion of materials More complex organisms have highly folded internal surfaces for exchanging materials

External environment CO2 Food O2 Mouth 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 Digestive system Interstitial fluid Excretory system 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). Anus Inside a kidney is a mass of microscopic tubules that exchange chemicals with blood flowing through a web of tiny vessels called capillaries (SEM). Unabsorbed matter (feces) Metabolic waste products (urine)

Tissue Structure and Function Tissues make up organs, which together make up organ systems Different tissues have different structures that are suited to their functions Tissues are classified into four main categories: epithelial, connective, muscle, and nervous

Simple Stratified columnar columnar epithelium epithelium 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 columnar epithelium Stratified columnar epithelium Pseudostratified ciliated columnar epithelium Cuboidal epithelia Stratified squamous epithelia Simple squamous epithelia Basement membrane 40 µm

Chondrocytes Collagenous fiber Loose connective tissue Chondroitin 120 µm Chondrocytes Collagenous fiber Loose connective tissue Chondroitin sulfate Elastic fiber 100 µm Cartilage Fibrous connective tissue Adipose tissue Fat droplets Nuclei 150 µm 30 µm Blood Central canal Red blood cells Bone White blood cell Osteon Plasma 700 µm 55 µm

Multiple nuclei Skeletal muscle Muscle fiber Sarcomere Cardiac muscle MUSCLE TISSUE 100 µm Multiple nuclei Skeletal muscle Muscle fiber Sarcomere Cardiac muscle Nucleus Intercalated disk 50 µm Nucleus Smooth muscle Muscle fibers 25 µm NERVOUS TISSUE Neuron Process Cell body Nucleus 50 µm

Epithelial tissue covers the outside of the body and lines the organs and cavities within the body Connective tissue mainly binds and supports other tissues Muscle tissue consists of long cells called muscle fibers, which contract in response to nerve signals It is divided in the vertebrate body into three types: skeletal, cardiac, and smooth Nervous tissue senses stimuli and transmits signals throughout the animal

Lumen of stomach Mucosa: an epithelial layer that lines the lumen Submucosa: a matrix of connective tissue that contains blood vessels and nerves Muscularis: consists mainly of smooth muscle tissue Serosa: a thin layer of connective and epithelial tissue external to the muscularis 0.2 mm

Influences on Metabolic Rate Metabolic rates are affected by many factors besides whether an animal is an endotherm or ectotherm Two of these factors are size and activity Amphibians and reptiles other than birds are ectothermic: They gain their heat mostly from external sources Ectotherms generally have lower metabolic rates

Activity and Metabolic Rate The basal metabolic rate (BMR) is the metabolic rate of an endotherm at rest Activity greatly affects metabolic rate Different species use energy and materials in food in different ways, depending on their environment Use of energy is partitioned to BMR, activity, homeostasis, growth, and reproduction

Maximum metabolic rate 500 A = 60-kg alligator A H 100 H A A = 60-kg human 50 H Maximum metabolic rate (kcal/min; log scale) 10 H 5 H A 1 A 0.5 A 0.1 1 second 1 minute 1 hour 1 day 1 week Time interval Key Existing intracellular ATP ATP from glycolysis ATP from aerobic respiration

Endotherms Ectotherm 800,000 340,000 8,000 4,000 438 Human 233 Python Reproduction Basal (standard) metabolism Temperature regulation Growth Activity Annual energy expenditure (kcal/yr) 340,000 8,000 4,000 60-kg female human from temperate climate 4-kg male Adélie penguin from Antarctica (brooding) 0.025-kg female deer mouse from temperate North America 4-kg female python from Australia Total annual energy expenditures. The slices of the pie charts indicate energy expenditures for various functions. 438 Human Energy expenditure per unit mass (kcal/kg•day) 233 Python Deer mouse Adélie penguin 36.5 5.5 Energy expenditures per unit mass (kcal/kg•day). Comparing the daily energy expenditures per kg of body weight for the four animals reinforces two important concepts of bioenergetics. First, a small animal, such as a mouse, has a much greater energy demand per kg than does a large animal of the same taxonomic class, such as a human (both mammals). Second, note again that an ectotherm, such as a python, requires much less energy per kg than does an endotherm of equivalent size, such as a penguin.

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

Mechanisms of Homeostasis A homeostatic control system has three functional components: a receptor, a control center, and an effector Most homeostatic control systems function by negative feedback, where buildup of the end product shuts the system off In positive feedback, a change in a variable triggers mechanisms that amplify rather than reverse the change

Response No heat produced Heater turned off Room temperature decreases Set point Too hot Set point Set point Too cold Control center: thermostat Room temperature increases Heater turned on Response Heat produced

Ectotherms and Endotherms Thermoregulation is the process by which animals maintain an internal temperature within a tolerable range Ectotherms include invertebrates, fishes, amphibians, and reptiles Endotherms include birds and mammals In general, ectotherms tolerate greater variation in internal temperature than endotherms

40 River otter (endotherm) 30 Body temperature (°C) 20 Largemouth bass (ectotherm) 10 10 20 30 40 Ambient (environmental) temperature (°C)

Endothermy is more energetically expensive than ectothermy It buffers the animal’s internal temperatures against external fluctuations It also enables the animal to maintain a high level of aerobic metabolism Organisms exchange heat by four physical processes: conduction, convection, radiation, and evaporation

Radiation Evaporation Convection Conduction

Balancing Heat Loss and Gain In thermoregulation, physiological and behavioral adjustments balance heat loss and gain Five general adaptations help animals thermoregulate: Insulation Circulatory adaptations Cooling by evaporative heat loss Behavioral responses Adjusting metabolic heat production

Insulation Insulation is a major thermoregulatory adaptation in mammals and birds It reduces heat flow between an animal and its environment Examples are skin, feathers, fur, and blubber In mammals, the integumentary system acts as insulating material

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 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 an arrangement of blood vessels called a countercurrent heat exchanger Countercurrent heat exchangers are important for reducing heat loss Some bony fishes and sharks also have countercurrent heat exchangers

Canada goose Pacific bottlenose dolphin Blood flow Artery Vein Vein 33° 30° 27° 20° 18° 10° 9°

Skin Artery Vein Blood vessels in gills Capillary network within muscle Heart Artery and vein under the skin Dorsal aorta Great white shark

Cooling by Evaporative Heat Loss Many types of animals lose heat through evaporation of water in sweat Panting augments the cooling effect in birds and many mammals Bathing moistens the skin, helping to cool an animal down

Both endotherms and ectotherms use behavioral responses to control body temperature Some terrestrial invertebrates have postures that minimize or maximize absorption of solar heat

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

Feedback Mechanisms in Thermoregulation Mammals regulate body temperature by negative feedback involving several organ systems In humans, the hypothalamus (a part of the brain) contains nerve cells that function as a thermostat

Internal body temperature 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. Increased body temperature (such as when exercising or in hot surroundings) Body temperature decreases; thermostat shuts off cooling mechanisms. 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. Thermostat in hypothalamus activates warming mechanisms. Skeletal muscles rapidly contract, causing shivering, which generates heat.

Adjustment to Changing Temperatures In acclimatization, many animals adjust to a new range of environmental temperatures over a period of days or weeks Acclimatization may involve cellular adjustments or (as in birds and mammals) adjustments of insulation and metabolic heat production

Torpor and Energy Conservation Torpor is a physiological state in which activity is low and metabolism decreases 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

Additional metabolism that would be necessary to stay active in winter 200 Actual metabolism Metabolic rate (kcal per day) 100 Arousals 35 Body temperature 30 25 20 Temperature (°C) 15 10 5 –5 Outside temperature Burrow temperature –10 –15 June August October December February April

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 adapted to feeding patterns

Animations and Videos Bozeman – Thermoregulation Bozeman - Anatomy and Physiology Bozeman - Organ Systems Chapter Quiz Questions – 1 Chapter Quiz Questions – 2