Chapter 40 Animal Form and Function By: Pham Tran & Princess Montemayor Overview: Diverse Forms, Common Challenges Common set of problems: obtain oxygen, nourish themselves, excrete waste products and move Anatomy is the study of the structure of an organism Physiology is the study of the functions an organism performs Natural selection can fit structure to function 40.1 Physical laws and the environment constrain animal size and shape • Size and shape, “body plans” or “designs,” affect the way an animal interacts with its environment • Physical laws limit the evolution of an organism’s form • Convergence evolution occurs because natural selection shapes similar adaptation when diverse organisms face the same environmental challenge Exchange with the Environment • Size and shape also affect how an animal exchanges energy and materials with its surroundings • Body plan must allow all living cells to be bathed in an aqueous medium, a requirement for maintaining the fluid integrity of the plasma membranes • Exchange with the environment occurs as substances dissolved in the aqueous medium diffuse and are transported across the cells’ plasma membranes Amoeba (unicellular protist), entire surface area is in contact with the environment. Hydra consists of two layers of cells with an aqueous environment circulating in and out of the hydra’s mouth, being directly in contact to every one of its cells – exchanging materials with it. 40.2 Animal form and function are correlated to all levels of organization Tissues are groups of cells with a common structure and function Classified under four main categories: Epithelial tissue Connective tissue Muscle tissue Nervous tissue Epithelial Tissue • Epithelial tissue covers the outside of the body and lines organs and cavities within the body • Some are tightly packed to function as a barrier against mechanical injury, microbes and fluid loss. • Glandular epithelia absorb or secrete chemical solutions. • Form a mucous membrane: secrete mucus that lubricates the surface and keeps it moist. (Epithelial tissue cont.) Simple epithelium has a single layer of cells Stratified epithelium has multiple tiers of cells. “Pseudostratified” epithelium is single-layered but appears stratified because the cells vary in length. Shape of the cells at exposed surface may be cuboidal, columnar, or squamous Connective Tissue • Connective tissue functions mainly to bind and support other tissues. • Sparse population of cells scattered through an extracellular matrix • Tissue fibers made of protein: – Collagenous fibers – Elastic fibers – Reticular fibers Connective tissue (cont.) Collagenous fibers are made of collagen, most abundant protein in animal kingdom Non-elastic, does not tear easily Ex. Skin on the back of hand Elastic fibers are long threads made of a protein called elastin. Rubbery quality that complements the nonelastic strength of collagenous fibers Connective tissue (cont.) • Reticular fibers are very thin and branched. • Composed of collagen and continuous with collagenous fibers to form a tightly woven fabric that joins connective tissue to adjacent tissues – Fibroblasts secrete the protein ingredients of the extracellular fibers. – Macrophages are amoeboid cells that roam the maze of fibers, engulfing foreign particles and the debris of dead cells by phagocytosis. Muscle Tissue • Muscle tissue is composed of long cells called muscle fibers that are capable of contracting, usually when stimulated by nerve signals. • Myofibrils made of the proteins actin and myosin and serve as contracting units. • Vertebrate body has three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle Nervous Tissue • Nervous tissue senses stimuli and transmits signals in the form of nerve impulses from one part of the animal to another. • Functional unit is the neuron or nerve cell, specialized to transmit nerve impulses. • Most animals, nervous tissue is concentrated in the brain, the control center that coordinates the animal’s activity. Organ and Organ Systems • Tissues are combined into functions called organs. • Many of the organs of vertebrates are suspended by sheets of connective tissue called mesenteries in moist or fluid-filled body cavities. • Mammals have a thoracic cavity housing the lungs and heart that is separated from the lower abdominal cavity by a sheet of muscle called the diaphragm. Organ and Organ Systems (cont.) Organ systems are groups of organs that work together to carry out the major body functions of most animals. Efforts of all systems must be coordinated for an animal to survive. 40.3 Animals use the chemical energy in food to sustain form and function • Bioenergetics limits an animal’s behavior, growth, and reproduction and determines how much food it needs. • Food provides energy-containing molecules after digested, serves to generate ATP • Metabolic rate – the amount of energy an animal uses over time; the sum of all the energyrequiring biochemical reactions occurring over a given time interval Bioenergetics of an animal : an overview Bioenergetic Strategies Two basic strategies found in animals: Endothermic: bodies are warmed by heat generated by metabolism Ectothermic: gain heat through external sources Metabolic rate is inversely related to size 40.4: Many animals regulate their internal environment within relatively narrow limits Internal environment of vertebrates is called the interstitial fluid. Fluid fills spaces between vertebrate cells, exchanges nutrients and wastes with blood contained in microscopic vessels called capillaries Animals tend to maintain relatively constant conditions in their internal environment, even when the external changes There are times during development of an animal when major changes in internal environment are programmed to occur. Ex: The balance of hormones in human blood is altered radically during puberty and pregnancy Homeostasis: steady state or internal balance A dynamic state, an interplay between outside factors that tend to change the internal environment and internal control mechanisms that oppose such changes Regulating and Conforming Regulating and conforming are two extremes in how animals cope with environmental fluctuations An animal is a regulator for a particular environmental variable if it uses internal control mechanisms to moderate internal change in the face of external fluctuation An animal is a conformer for a particular environment variable if it allows its internal condition to vary with certain external changes. Regulating and conforming represent extremes on a continuum and no organism is a perfect regulator or conformer. An animal may maintain homeostasis while regulating some internal conditions and allowing others to conform to the environment Nonliving example of negative feedback : control of room temperature Mechanisms of Homeostasis Mechanism of homeostasis moderate changes in the internal environment. Any homeostatic control system has three functional components: (1) Receptor: detects change in some variable of the animals internal environment, such as a change in body temperature (2) Control Center: processes information it receives from the receptor and directs an appropriate response by the (3) effector. Example: Regulation of Room Temperature In this case, the control center, a thermostat, contained the receptor, which is a thermometer. When the room temperature falls below a set point, the thermostat switches on the heater, the effector. When the thermometer detects a temperature above the set point, the thermostat switches the heater off. This type of control is called negative feedback, because a change in the variable being monitored triggers the control mechanism to counteract further change in the same direction Owing to a time lag between reception and response, the variable drifts slightly above and below the set point, but the fluctuations are moderate Negative-feedback mechanisms prevent small changes from becoming too large; most homeostatic mechanisms in animals operate on this principle of negative feedback. Positive feedback involves a change in some variable that triggers mechanism that amplify rather than reverse the change. Regulated change is essential to normal body functions Over the short term, homeostatic mechanisms keep body temperature close to a set point, whatever it is at that particular time, but long term, it allows regulated change in the body’s internal environment Animals use a considerable amount of energy from eaten food to maintain favorable internal conditions 40.5: Thermoregulation contributes to homeostasis and involves anatomy, physiology, and behavior Thermoregulation: the process by which animals maintain an internal temperature within a tolerable range Critical to survival because most biochemical and physiological processes are sensitive to changes in body temperature. Although different animals adapt to different environment temperatures, each has an optimal temperature range Thermoregulation helps keep the body temperature within that optimal range, enabling cells to function most effectively, even as the external temperature fluctuates Ectotherms and Endotherms One way to classify thermal characteristics of animals is to emphasize the role of metabolic heat in determining body temperature Ectotherms (invertebrates, fishes, amphibians, lizards, snakes, turtles) gain most of their heat from the environment. They have such a low metabolic rate that the amount of heat generated is too small to affect their body temperature Tolerate greater variation in internal temperature than endotherms Endotherms ( Mammals, birds, some reptiles and fish, and insects) can use metabolic heat to regulate their body temperature; in cold temperatures, they generate enough heat to keep their bodies warmer than their surroundings. Many maintain high and stable internal temperatures even as the temperature of their surroundings fluctuates. Animals not classified as ectotherms or endotherms based on whether they have variable or constant body temperatures, a common misconception. It’s the source of heat used to maintain body temperature that distinguishes ectotherms from endotherms. Another misconception is that ectotherms are “cold-blooded” and endotherms are “warm-blooded” Ectotherms don’t necessarily have low body temperatures Ectothermy and endothermy aren’t mutually exclusive thermoregulatory strategies. Endothermy has several important advantages Being able to generate a large amount of heat metabolically, along with other biochemical and physiological adaptations associated with endothermy enables endotherms to perform vigorous activity for much longer than is possible for most ectotherms. Enables terrestrial animals to maintain stable body temperatures in the face of environmental temperature fluctuations that are generally more severe than in aquatic habitats. Better buffered against external temperature fluctuations compared to ectotherms, but ectotherms can tolerate larger fluctuations in their internal temperatures. Endotherms need to consume more food than ectotherms because being endothermic is energetically expensive Modes of Heat Exchange Regardless if it’s an ectotherm or endotherm, an organism exchanges eat by four physical processes: Conduction: 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 Convection: transfer of heat by the movement of air or liquid past a surface, as when a breeze contributes to heat loss from a lizards dry skin, or blood moves heat from the body core to the extremities Radiation: emission of electromagnetic waves by all objects warmer than absolute zero. Radiation can transfer heat between objects that aren’t in direct contact, as when a lizard absorbs heat radiating from the sun Evaporation: removal of heat from the surface of a liquid that is losing some of its molecules as fast. Evaporation of water from a lizard’s moist surfaces that are exposed to the environment has a strong cooling effect. Balancing Heat Loss and Gain For endotherms, and ectotherms that thermoregulate, the essence of thermoregulation is managing the heat budget so that rates of heat gain are equal to rates of heat loss If heat budget is unbalanced, the animal becomes either warmer or colder Five general categories of adaptations help animals thermoregulate Insulation Circulatory Adaptations Cooling by Evaporative Heat Loss Behavioral Responses Adjusting Metabolic Heat Production Insulation A major thermoregulatory adaptation in mammals and birds that reduces the flow of heat between an animal and its environment and lowers energy cost of keeping warm In mammals, insulating material is associated with integumentary system, the outer covering of the body, consisting of the skin, hair, and nails Skin functions as a thermoregulatory organ by housing nerves, sweat glands, blood vessels, and hair follicles and protects internal body parts from mechanical injury, infection, and drying out. Consists of two layers, the epidermis and the dermis, underlain by a tissue layer called the hypodermis Epidermis is the outermost layer of skin and is composed mostly of dead epithelial cells that continually flake and fall off. New cells pushing up from lower layers replace the cells that are lost. Dermis supports epidermis and contains hair follicles, oil and sweat glands, muscles, nerves, and blood vessels. Hypodermis contains adipose tissue, which includes fat-storing cells and blood vessels. Adipose tissue provides varying degrees of insulation, depending on the species. Insulating power of fur or feathers mainly depends on how much still air the layer traps Mammalian integumentary system Circulatory Adaptations Many endotherms and ectotherms can alter amount of blood (and hence heat) flowing between the body core and the skin Elevated blood flow in the skin results from vasodilation, an increase in the diameter of superficial blood vessels triggered by nerve signals that relax the muscle of the vessel walls. in endotherms, vasolidation usually warms the skin, increasing the transfer of body heat to a cool environment by radiation, conduction, and convection. Vasoconstriction: reduces blood flow and heat transfer by decreasing the diameter of superficial vessels Countercurrent heat exchanger: important for reducing heat loss in may endotherms, including marine animals and birds. In some species, blood can go either through the heat exchanger or bypass it by way of blood vessels. In this way, relative amount of blood that flows through the two paths may vary, adjusting the rate of heat loss as an animal’s physiological state or environment changes. Countercurrent heat exchanger Cooling by Evaporative Heat Loss Many Mammals and birds live in places where thermoregulation requires cooling as well as warming If environmental temperature is above body temperature, animals gain heat from the environment and metabolism, and evaporation is the only way to keep body temperature from rising rapidly. Terrestrial animals lose water by evaporation across the skin and when they breathe. Water absorbs considerable heat when it evaporates; this heat is carried away from the body surface with the water vapor Some animals have adaptations that can greatly augment this cooling effect like panting Many terrestrial mammals have sweat glands controlled by the nervous system Other mechanisms that promote evaporative cooling include spreading saliva on body surfaces, or secreting mucus Behavioral Responses Both endotherms and ectotherms use behavioral responses to control body temperature. Many ectotherms maintain a nearly constant body temperature through simple behaviors. More complex behavioral adaptations in some animals include hibernation or migration All amphibians and most reptiles other than birds are endothermic which means these organisms control body temperature mainly by behavior Optimal temperature range for amphibians varies substantially with the species By moving to a location where solar heat is available, an amphibian can maintain a satisfactory body temperature and when it’s hot, they move to a cooler area Adjusting Metabolic Heat Production Because endotherms generally maintain body temperatures considerably warmer than the environment, they must counteract constant heat loss Endotherms can vary heat production to match changing rates of heat loss; heat production is increased by such muscle activity as moving or shivering In some mammals, certain hormones can cause mitochondria to increase their metabolic activity and produce heat instead of ATP. This nonshivering thermogenesis (NST) takes place throughout the body, but some mammals also have a tissue called brown fat in the neck and between the shoulders that is specialized for rapid heat production. Through shivering and NST, mammals and birds in cold environments can increase their metabolic heat production by as much as five to ten times the minimal levels that occur in warm conditions. Feedback Mechanisms in Thermoregulation Regulation of body temperature in humans and other mammals is a complex system facilitated by feedback mechanisms Nerve cells that control thermoregulation, as well as those that control many other aspects of homeostasis, are concentrated in a region of the brain called the hypothalamus Hypothalamus contains group of nerve cells that functions as a thermostat, responding to changes in body temperature above or below a set point by activating mechanisms that promote heat loss or gain Nerve cells that sense temperature are in the skin, hypothalamus, and several other body regions Warm receptors signal the hypothalamic thermostat when temperatures when temperatures increase; cold receptors signal temperature decrease. At body temperatures below the normal range, the thermostat inhibits heat loss mechanisms and activates heat-saving ones such as vasoconstriction of superficial vessels and erection of fur, while stimulating heat-generating mechanisms In response to elevated body temperature, the thermostat shuts down heat retention mechanisms and promotes body cooling by vasolidation, sweating, or panting. The thermostat can also respond to external temperature even without changes in body core temperature Adjustment to Changing Temperatures Many animals can adjust to a new range of environmental temperatures over a period of days or weeks, a physiological response called acclimatization Both ectotherms and endotherms acclimatize, but in different ways. In birds and mammals, acclimatization includes adjusting amount of insulation by growing or shedding fur Helps endotherms keep constant body temperature in warm and cold seasons Acclimatization responses in ectotherms often include adjustments at the cellular level. Cells may increase certain enzymes or produce variants of enzymes that have the same function but different optimal temperatures. Membranes may also change proportions of saturated and unsaturated lipids they contain, which helps keep membranes fluid at different temperatures Some ectotherms protect themselves by producing “antifreeze” compounds that prevent ice formation in the cells Cells can often make rapid adjustments to temperature changes. Mammalian cells respond to a marked increase in temperature and to other forms of severe stress by accumulating molecules called stress-induced proteins, including heat shock proteins Within minutes of being shocked, the cells begin synthesizing heat-shock proteins to help maintain the integrity of other proteins that would be denatured by severe heat Stress induced proteins help prevent cell death when an organism is challenged by severe changes in the cellular environment Torpor and Energy Conservation Despite their many adaptations for homeostasis, animals may occasionally encounter conditions that severely challenge their abilities to balance heat, energy, and materials budgets. An adaptation that enables animals to save energy while avoiding difficult and dangerous conditions is torpor, a physiological state in which activity is low and metabolism decreases Hibernation: long-term torpor that is an adaptation to winter cold and food scarcity. When vertebrate endotherms enter torpor or hibernation, their body temperatures decline-in effect, their body’s thermostat is turned down Resulting energy savings due to lower metabolic rate and less heat production are huge; metabolic rates during hibernation can be several hundred times lower than if the animal attempted to maintain normal body temperatures This allows hibernators to survive very long periods on limited supplies of energy stored in the body tissues or as food cached in a burrow Estivation, or summer torpor, also characterized by slow metabolism and inactivity enables animals to survive long periods of high temperatures and scarce water supplies. Many small mammals and birds exhibit a daily torpor that seems to be adapted to their feeding patterns An animals daily cycle of activity and torpor appears to be a built-in rhythm controlled by its biological clock Bibliography Campbell, Neil A., and Jane B. Reece. Biology. AP ed. Vol. 7th. San Francisco: Pearson Education, 2005. Print. E., Marino F. Thermoregulation and Human Performance. NSW: Bathurst, 2008. Print. "Homeostasis." - Definition from Biology-Online.org. Web. 07 Mar. 2012. <http://www.biology-online.org/dictionary/Homeostasis>. Pack, Philips. Biology 2nd Edition. New York: Wiley, 2001. Print. "Tissue (biology)." Wikipedia. Wikimedia Foundation, 03 July 2012. Web. 07 Mar. 2012. <http://en.wikipedia.org/wiki/Tissue_(biology)>. "Thermoregulation." Wikipedia. Wikimedia Foundation, 03 June 2012. Web. 07 Mar. 2012. <http://en.wikipedia.org/wiki/Thermoregulation>.