Lecture-12-Animal-Fo_38874 - CH 40: Basic Principles of...

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Unformatted text preview: CH 40: Basic Principles of Animal Form & Function • Natural selection favors variations that suit the animal to its environment. – Form fits function: fusiform body plan of aquatic animals aids movement through water variations in bill size & form due to differences in types of prey that are eaten – Physical laws limit animal form & size • Body size of animals affected by constraints on skeletal structure & the amount of musculature to move limbs. • Form & function are examined by studying the anatomy of structures & their physiology (how they function) Exchange with the Environment Limits an Animal’s Body Plan • Exchange = movement of dissolved solutes across plasma membrane of cells; recall: rate of exchange ∝ surface area amount of material exchanged ∝ volume Unicellular forms: direct exchange with outside environment Multicellular forms: all cells must have access to a suitable aqueous environment; those with a simpler body plan enables exchange between its cells & the external environment. single cell Body cavity is open to external environment; fluid bathes inner cells • Large, multicellular animals: surface area to volume ratio becomes an issue solution? – Internal body comprised of highly branched & folded surfaces (tissues) to facilitate exchange. – Outer surface serves to protect these internal structures & provide form to the body. • Body fluids (interstitial fluid) surround Microvilli of intestine cells; exchange between circulatory fluid (blood) & interstitial fluid enables body cells to gain nutrients & rid waste. Network of tubules in the lungs & kidneys Hierarchy of Body Plan Organization • Cells Tissues Organs Organ Systems – Emergent properties via successive levels of organization – Organs comprised of multiple tissues each possessing unique physiological functions. – Organ systems: each “part” has a specific role that together with the other “parts” complete a particular function. • mouth, esophagus, stomach, accessory organs, intestines, & anus of the digestive system • The specialization of complex body plans is based on various combinations of particular cell and tissue types: – – – – Epithelial tissue Connective tissue Muscle tissue Nervous tissue Tissues: all four types present in stomach Sheets of cells: covers outer body; lines inner cavities & organs. Secretion & Absorption Densely packed (tight junctions) Bind, support, protect other tissues. Cells embedded in an extracellular matrix of fibers (collagen, elastin) Types: Loose & Fibrous connective tissue, Cartilage, Bone, Blood, Adipose Responsible for body movements; large energy consumer in the body. Cardiac, skeletal, smooth muscle types Detect stimuli & transmit information via electrochemical signals (nerve impulses) Neurons & Glial cells Coordination of Body Function • Communication with & coordination of tissue, organ & organ system functions occur via the endocrine system and nervous system • Endocrine system: hormone release in response to stimulus; hormones interact with target cells. – Slower acting; control gradual changes that affect the body: growth & development, digestion, metabolism • Nervous system: direct communication with specific tissues, organs via nerve impulses through neurons; much faster than endocrine system. Feedback Loops Maintain the Internal Environment • Animals either conform or regulate their internal environment in response to external conditions. – Regulator: utilizes internal control mechanisms to regulate internal changes to the surrounding environment: example ‐ body temperature control of a mammal maintain constant body temp regardless of external temperature. – Conformer: internal conditions conform to the external conditions Example ‐ temperature response of fish body temp conforms to external temp of water – The same animal may conform to certain conditions, while regulating others. Homeostasis: Regulating Physiological Systems • Homeostasis is the maintenance of constant internal conditions in the body. – Information required to determine what action is required – The basic concept of this control is shown: Homeostatic range Parameter out of range serves as a stimulus corrective action needed “error signal” Upper & Lower Set points Feedback information: in range or out of range? Sensor detects stimulus Response: physiological activity triggered to return system to set point range Homeostasis relies mainly on negative feedback to reduce the stimulus. Temperature Control by Negative Feedback error temperature set point error Deviate from set point: error signal Correct deviation and reverse to return to the set point (negative feedback). Physiological responses to stimuli are not instantaneous; homeostasis reduces (but does not eliminate) changes in the internal environment. Positive feedback mechanisms act by amplifying the stimulus rather than reducing it. Form & Function Combine to Regulate Internal Temperature (thermoregulation) • Thermoregulation is critical to survival as biochemical & physiological processes are sensitive to changes in body temperature – Proteins and membranes have altered function outside their optimal temperature ranges. • The external environment & internal metabolism provide sources of heat for thermoregulation: – Endotherms rely on internal metabolic heat production • Mammals, birds • Maintain constant body temperature over a wide temperature range – Ectotherms depend on external heat sources • Amphibians, lizards, snakes, turtles, many fishes, most invertebrates • Consume less food, and can tolerate wide fluctuations in internal body temperature; rely on behavioral mechanisms (seek shade or sunlight to cool or warm themselves) – Endothermy/Ectothermy are not mutually exclusive Balancing Heat Loss & Gain • Heat source vs. Body Temperature – Poikilotherms: animals whose body temperature varies with the environment. – Homeotherms maintain a relatively constant body temperature – No fixed relationship between heat source (ectotherm, endotherm) & body temperature (poikilotherm, homeotherm) Some ectotherms can be homeothermic & some endotherms can periodically behave as poikilotherms (e.g., hibernating mammals) • Thermoregulation is based on controlling exchange of heat with the environment. Heat exchange occurs via four processes: – – – – Radiation Conduction Convection Evaporation • Heat transfer: heat flows from warmer to cooler object • Animals must balance heat gain & heat loss: Heat gain by a body due to Heat loss by emitted radiation a body due metabolism + convection to these + absorbed = + conduction radiation processes + evaporation heatin = heatout • Animals possess adaptations that reduce overall heat exchange or favor heat exchange in a particular direction. – Mechanisms in mammals (endotherms) often involve the skin, part of the integumentary system – Adaptations: Insulation: fur, feathers, & fat reduces flow of heat out of the body Vasodilation: increases the diameter of blood vessels in the skin, ↑ blood flow, ↑ transfer of body heat to environment Vasoconstriction: ↓ blood flow to skin, ↓ transfer of body heat to environment Adaptations to Control Heat Exchange (continued) • Counter current heat exchanger: – Reduces heat loss to environment – Heat passes from vessels carrying warmed blood to those carrying cooler blood. – Countercurrent arrangement maintains heat transfer along entire length of exchanger. – Occurs in fish, aquatic birds, mammals • Cooling by evaporative heat loss: – Heat gain by endotherms can be offset by evaporative cooling: terrestrial animals lose water by evaporation across the skin or by breathing. Water absorbs considerable heat when it vaporizes. – Adaptations: sweating and panting • Behavioral responses: – Seek sun, shade, or huddle close together; orient body to maximize heat absorption or heat loss. Adaptations to Control Heat Exchange (continued) • Adjustment of Metabolic Heat Production – Endotherms generally maintain body temps > external environment; must offset constant heat loss by varying heat production – As external temperature becomes cooler: body heat loss is greater, thus the body must generate more heat to offset the loss • Thermogenesis (heat production): increase by moving or muscle shivering; brown fat – mitochondria in this tissue generates heat rather than ATP. • Some ectotherms: can induce shivering response & blood vessel dilation/constriction response. • Acclimitization: homeostatic adjustment to changes in exter‐ nal environment – Thermoregulatory adjustments to changes in seasonal temperatures: Thicker coat of fur in winter, shed in summer Cellular level: enzyme variants with same function, but optimized for particular temperatures; production of “antifreeze” molecules; saturation/unsaturation of membrane lipids. Physiological Thermostats of Endotherms • Feedback mechanisms of mammals regulate body temperature. – Hypothalamus: sensor that controls thermoregulation. (the thermostat) – Warm receptors signal hypothalamus when temp ↑ • Initiate cooling mechanisms: vasodilation, sweating – Cold receptors signal hypothalamus when temp ↓ • Initiate cooling mechanisms: vasoconstriction, shivering, ↑metabolic heat production • Fever: elevated body temperature rise due to a temporary increase in the hypothalamic set point. Energy Requirements • Animals utilize food sources to obtain energy to fuel metabolic processes and carry out various activities. – How much energy is need to stay alive? Measurement of metabolic rate (O2 consumed, CO2 released, heat produced) – Basal Metabolic Rate (BMR): minimum metabolic rate to sustain vital processes (for an organism at rest, not growing, & not eating) • Endotherm: 1600‐1800 kcal/day (adult human male) – Standard Metabolic Rate (SMR): minimum metabolicrate for an ectotherm taken at a specific temperature • 60 kcal/day (alligator @ 20⁰C); (compare with endotherm value above) • Metabolic Rate vs. Size – Among various sized animals, metabolic rate increases with body size – In terms of BMR per kg of tissue vs. body size, the relationship is inversed smaller animals have higher BMR per kg tissue than larger ll ones. • The relationship of metabolic rate to size affects the energy consumption by an organism – Higher rate of calorie consumption required for smaller animals to maintain each gram of body weight. = higher breathing rate & heart rate, constantly foraging for food. • Activity increases metabolic rate above the BMR or SMR – Average daily rate of energy usage = 2‐4xBMR/SMR for most animals [humans: 1.5xBMR] • Energy conservation: response to extreme temperatures, or lack of food. – Torpor: short‐term reduction in activity & lowering of metabolic rate – Hibernation: longer‐term torpor Summary • The size & shape (form) of an animal affect how it interacts with the environment. – Physical laws place limits on the extent of animal form and size – Natural selection favors variations that fit organisms to their environment – Studying anatomy & physiology reveals how these adaptations work. • Exchange with the environment – Internal organization changes to facilitate optimal exchange as organism becomes more complex (single cell v multicellular) • Organization: cells tissues organs organ systems – tissue types: nervous, muscle, epithelial, & connective • Homeostasis & control via feedback loops • Thermoregulation (endothermy & ectothermy) – Adaptations for thermoregulation • Energy & Metabolic rate ...
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This note was uploaded on 04/23/2010 for the course BIOL 1361 taught by Professor Knapp during the Spring '05 term at University of Houston.

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