Module 6: Multicellular Animal Body PDF

MODULE 6: THE MULTICELLULAR ANIMAL BODY Interstitial Fluid: In flat animals (e.g. tapeworms), Animal form and function are correlated at all most cells are in direct contact with its environment levels of organization....

MODULE 6: THE MULTICELLULAR ANIMAL BODY Interstitial Fluid: In flat animals (e.g. tapeworms), Animal form and function are correlated at all most cells are in direct contact with its environment levels of organization. = the interstitial fluid of other animals. Anatomy: It is the biological form of an organism. Evolutionary adaptations of more complex organisms enable sufficient exchange with the Physiology: It is the biological functions an organism environment. performs. In vertebrates, the space between cells is filled with Size and shape affect the way an animal interacts interstitial fluid, which allows for the movement of with its environment. The body plan of an animal is material into and out of cells. programmed by the genome, itself the product of millions of years of evolution. HIERARCHICAL ORGANIZATION OF BODY PLANS Most animals are composed of specialized cells organized into tissues that have different functions. EVOLUTION OF ANIMAL SIZE AND SHAPE Physical laws govern strength, diffusion, movement, Tissues make up organs, which together make up and heat exchange. organ systems. Properties of water limit possible shapes for fast Some organs, such as the pancreas, belong to swimming animals. more than one system. As animals increase in size, thicker skeletons are required for support. Convergent Evolution: results in similar adaptations of diverse organisms facing the same challenge. In the ocean, fast swimmers have a streamlined fusiform shape. EXCHANGE WITH THE ENVIRONMENT Nutrients, Waste Products, and Gases: It must be exchanged across the cell membranes of animal cells. Rate of exchange: Should be proportional to a cell's EXPLORING STRUCTURE AND FUNCTION IN ANIMAL surface area while amount of exchange material is TISSUES proportional to a cell's volume. Different tissues have different structures that are suited to their functions. Single-celled organism living in water has sufficient surface area to carry out all necessary exchange. Tissues are classified into four main categories: Epithelial, Connective, Muscle, and Nervous. Multicellular organisms with a saclike body plan have body walls that are only two cells thick, Epithelial Tissue: It covers the outside of the body facilitating diffusion of materials. and lines the organs and cavities within the body. It 10 is a barrier against mechanical injury, pathogen Fibrous Connective Tissue: It is found in tendons and fluid loss [tight junction]. (attach muscles to bones) and ligaments (connects bones at joints). Shape: Be cuboidal (like dice), columnar (like bricks on end), or squamous (like floor tiles). Bone: It is mineralized and forms the skeleton. Bone cells are called Osteocytes. Arrangement: May be simple (single cell layer), stratified (multiple tiers of cells), or Adipose Tissue: It stores fat for insulation and pseudostratified (a single layer of cells of fuel. Its cells are called adipocytes. varying length). Blood: Blood cells and cell fragments in blood The Polarity of Epithelia plasma. Polarity: It means two different faces. The Cartilage: It is a strong and flexible support Epithelial has two surfaces: Apical surface material. Its cells are called chondrocytes. (outer) and Basal surface. Muscle Tissue: It is responsible for nearly all types of Connective Tissue: It mainly binds and supports body movement. Muscle cells consist of filaments of other tissues. It contains sparsely packed cells the proteins actin and myosin, which together scattered throughout an extracellular matrix. The enable muscles to contract. matrix consists of fibers in a liquid, jellylike, or solid foundation. Divided in the vertebrate body into three types: Three Types of Connective Tissue Fiber All of these are made of protein. Skeletal Muscle (Striated Muscle): It is responsible for voluntary movement. Collagenous Fibers: It provides strength and flexibility. Smooth Muscle: It is responsible for involuntary body activities. Reticular Fibers: It joins connective tissue to adjacent tissues. Cardiac Muscle: It is responsible for contraction of the heart. Elastic Fibers: It stretches and snaps back to their original length, The connective tissue also contains cells, including: Fibroblasts: These secrete the protein of extracellular fibers. Macrophages: These are involved in the immune system. Six Major Types of Connective Tissue Nervous Tissue: It functions in the receipt, processing, and transmission of information. It Loose Connective Tissue: It binds epithelia to contains: underlying tissues and holds organs in place. Neurons, or nerve cells, that transmit nerve impulses Glial cells, or glia (support cells) 11  Regulator: It uses internal control mechanisms to control internal change in the face of external fluctuation. Conformer: It allows internal conditions to vary with certain external changes. COORDINATION AND CONTROL It is in response to stimuli. It depends on the endocrine system and the nervous system. Endocrine System: It transmits chemical signals called hormones to receptive cells throughout the body via blood. A hormone may affect one or more regions throughout the body [depending on cells that have receptors for it]. Hormones are relatively slow acting, but can have HOMEOSTASIS long-lasting effects. Used to maintain a “steady state” or internal balance regardless of external environment. Nervous System: It transmits information between specific locations via the axons. In humans, body temperature, blood pH, and glucose concentration are each maintained at a The information conveyed depends on a signal’s constant level. pathway, not the type of signal. Nerve signal transmission is very fast. Mechanisms of Homeostasis It controls changes in the internal environment. Fluctuations above or below a set point serve as a stimulus; these are detected by a sensor and trigger a response. The response returns the variable to the set point. Feedback Control in Homeostasis Negative Feedback: Homeostasis in animals relies largely on negative feedback, which helps to return a variable to a normal range. Positive Feedback: It amplifies a stimulus and does not usually contribute to homeostasis in The Chemical Factor animals. Animals may regulate some environmental variables while conforming to others. 12  Poikilotherm: The body temperature of a poikilotherm varies with its environment. Homeotherm: The body temperature of a homeotherm is relatively constant. Alterations in Homeostasis The relationship between heat source and body Set points and normal ranges can change with age temperature is not fixed (that is, not all poikilotherms or show cyclic variation. are ectotherms). Ectothermic marine fishes and invertebrates Circadian Rhythm: In animals and plants, it governs inhabit waters with such stable physiological changes that occur roughly every 24 temperatures. hours. Metabolic activities undergo daily cycles in Bats drop from 40°C to a few degrees response to the circadian clock. above zero when they enter hibernation. Balancing Heat Loss and Gain Organisms exchange heat by four physical processes: radiation, evaporation, convection, and conduction. HEAT REGULATION IN MAMMALS Acclimatization: A process by which homeostasis It often involves the integumentary system (skin, can adjust to changes in the external environment. hair, and nails). Birds and mammals can vary their insulation to Five adaptations help animals thermoregulate: acclimatize to seasonal temperature changes. insulation, circulatory adaptations, cooling by evaporative heat loss, behavioral responses, and When temperatures are subzero, some ectotherms adjusting metabolic heat production. produce “antifreeze” compounds to prevent ice formation in their cells. Insulation: A major thermoregulatory adaptation in mammals and birds. Skin, feathers, fur, and blubber Homeostatic processes for thermoregulation involve heat flow between an animal and its environment. form, function, and behavior Circulatory Adaptations: Many endotherms and Thermoregulation: It is the process by which animals some ectotherms can alter the amount of blood maintain an internal temperature within a tolerable flowing between the body core and the skin range. (vasodilation and vasoconstriction). Endothermic: Animals can generate heat by The arrangement of blood vessels in many marine metabolism; birds and mammals are endotherms. mammals and birds allows for countercurrent exchange. Ectothermic: Animals gain heat from external They transfer heat between fluids flowing in sources; ectotherms include most invertebrates, opposite directions and thereby reduce fishes, amphibians, and nonavian reptiles. heat loss. Variation in Body Temperature 13 Cooling by Evaporative Heat Loss: Many types of Energy Allocation and Use animals lose heat through evaporation of water Organisms can be classified by how they obtain from their skin. chemical energy. Sweating or Bathing: It moistens the skin, helping Autotrophs: Harness light energy to build energy-rich to cool an animal down. molecules (ex: plants). Panting: It increases the cooling effect in birds Heterotrophs: Harvest chemical energy from food and many mammals. (ex: animals). Behavioral Responses: Both endotherms and QUANTIFYING ENERGY USE ectotherms use behavioral responses to control body temperature. Metabolic Rate: It is the amount of energy an animal uses in a unit of time. Some terrestrial invertebrates have postures that minimize or maximize absorption of solar heat. It can be determined by: An animal’s heat loss Honeybees huddle together during cold weather to The amount of oxygen consumed or carbon retain heat. dioxide produced Measuring energy content of food Adjusting Metabolic Heat Production: consumed and energy lost in waste Thermogenesis is the adjustment of metabolic heat products. production to maintain body temperature. Metabolic Rate and Thermoregulation Thermogenesis is increased by muscle activity such as moving or shivering. Basal Metabolic Rate (BMR): Metabolic rate of an endotherm at rest at a “comfortable” Physiological Thermostats temperature. Thermoregulation in mammals is controlled by a region of the brain called the hypothalamus. Standard Metabolic Rate (SMR): Metabolic rate of an ectotherm at rest at a specific The hypothalamus triggers heat loss or heat temperature. generating mechanisms. Some ectothermic organisms seek warmer environments to increase INFLUENCES ON METABOLIC RATE their body temperature in response to certain Ectotherms have much lower metabolic rates than infections. endotherms of a comparable size. Other key factors: age, sex, size, activity, temperature, and nutrition. Size and Metabolic Rate Metabolic rate is proportional to body mass to the power of three quarters (m3/4). Smaller animals have higher metabolic rates per gram than larger animals. 14 Higher metabolic rate ⇒ leads to a higher oxygen delivery rate, breathing rate, heart rate, and greater (relative) blood volume. Activity and Metabolic Rate Activity greatly affects metabolic rate for endotherms and ectotherms. In general, the maximum metabolic rate an animal can sustain is inversely related to the duration of the activity. For most terrestrial animals, the average daily rate of energy consumption is 2-4 times BMR (endotherms) or SMR (ectotherms). The fraction of an animal’s energy budget devoted to activity depends on several factors: environment, behavior, size, and thermoregulation. 15