Animal Form and Function

Evolution of Animal Size and Shape

Animal body plans and sizes have evolved in response to physical laws and environmental pressures. These adaptations influence how animals move, exchange materials, and maintain homeostasis.

• Diffusion: Movement of molecules from high to low concentration.

• Movement: Locomotion strategies are shaped by body form.

• Heat Exchange: Body shape affects heat retention and loss.

• Strength: Structural adaptations support body mass and function.

• Streamlined Bodies: Fast swimmers (e.g., fish) have bodies that are rounded at the front and tapered at the rear to reduce drag.

• Example: Locomotion in water demonstrates adaptation to minimize resistance.

Exchange with the Environment

Material Exchange in Animals

Animals must exchange nutrients, waste, and gases with their environment to survive. This exchange occurs across the plasma membrane and is influenced by surface area and volume.

• Exchange rate is proportional to surface area; amount exchanged is proportional to volume.

• The plasma membrane acts as a selective barrier; sufficient surface area is needed to accommodate volume.

• Larger organisms have more cells, not necessarily larger cells.

• Complex bodies offer advantages: protection, energy release control, stable environment maintenance, and dispersion.

Animal Tissue and Signaling Cells

Tissue Types

Animal bodies are composed of four main tissue types, each with specialized functions.

• Epithelial: Covers body surfaces and lines cavities.

• Connective: Supports, binds, and protects organs.

• Muscle: Enables movement.

• Nervous: Transmits signals for communication.

Signaling Cells

• Endocrine: Secretes hormones for regulation.

• Nervous: Transmits electrical impulses.

Regulation: Homeostasis and Thermoregulation

Homeostasis

Homeostasis is the maintenance of a steady internal physiological condition. It requires a control system with sensors, a control center, and a triggered response.

• Can change due to conditions or cyclic alterations.

• Acclimatization: Physiological adjustment to environmental changes.

Thermoregulation

Animals regulate body temperature through various strategies.

• Warm-blooded (Homeothermic): Maintain relatively constant body temperature.

• Cold-blooded (Poikilothermic): Variable body temperature.

• Endothermic: Body temperature mainly dependent on internal heat generation.

• Ectothermic: Body temperature mainly dependent on external heat sources.

Heterothermy

• Partial Endothermy: Animals reduce metabolic rate seasonally (e.g., at night).

• Facultative Endothermy: Normally ectothermic animals can generate heat when needed.

• Regional Endothermy: Localized areas of higher temperature in the body.

• Gigantothermy/Inertial Endothermy: Large-bodied animals maintain constant temperature due to size.

Balancing Heat Loss and Gain

Heat Transfer Processes

Animals balance heat loss and gain through four main processes:

• Radiation

• Evaporation

• Convection

• Conduction

Heat always transfers from objects of higher temperature to lower temperature.

Preventing Heat Loss

• Insulation: Hair, feathers, and adipose tissue reduce heat loss.

• Circulation: Vasodilation/vasoconstriction and countercurrent exchange regulate heat distribution.

Behavioral Responses

• Seeking warm or cool places.

• Thermogenesis (heat production).

• Shivering and muscle contraction.

Fever

• Fever increases body temperature, often in response to infection.

• It is a regulated resetting of the body thermostat, increasing chemical reactions and interfering with bacterial replication.

Torpor and Hibernation

Energy Conservation Strategies

Animals use torpor and hibernation to cope with challenging energy budgets.

• Torpor: Short-term physiological state of decreased activity and metabolism.

• Hibernation: Long-term torpor as adaptation to cold and food scarcity.

Energy Requirements in Relation to Size, Activity, and Environment

Bioenergetics

Bioenergetics is the study of energy flow and transformation in animals.

• Heterotrophs: Obtain chemical energy from food.

• Metabolic Rate: Sum of all energy used by an animal over time.

• Measured by heat loss or oxygen consumption.

• Basal Metabolic Rate (BMR): Minimum metabolic rate for non-growing, non-eating endotherms.

• Standard Metabolic Rate (SMR): Minimum metabolic rate for non-growing, non-eating ectotherms.

Animal Nutrition

Dietary Requirements

Animals require chemical energy, organic building blocks, and essential nutrients from their diet.

• ATP is produced from carbohydrates, fats, and proteins.

• Building blocks: sugars and protein amino acids.

• Essential nutrients: vitamins, minerals, and trace elements.

Ingestion and Digestion

Feeding Methods

• Filter Feed

• Bulk Feed

• Fluid Feed

• Substrate Feed

Digestion Types

• Mechanical Digestion: Chewing, grinding, churning.

• Chemical Digestion: Breaking bonds via hydrolysis.

Oral Cavity, Pharynx, and Esophagus

• Teeth cut, mash, grind, and chew food to increase surface area.

• Saliva lubricates food and buffers acid; amylase begins starch breakdown.

• Esophagus moves food to stomach via peristalsis.

Digestion in the Stomach

• Stomach stretches to accommodate meals.

• Chemical Digestion: Hydrochloric acid (HCl) unfolds proteins, allowing pepsin to attack bonds. pH is 1.5–2.5.

• Mechanical Digestion: Churning mixes food.

Digestion in the Small Intestine

• Most enzymatic hydrolysis of macromolecules occurs here.

• Duodenum: First section where stomach contents mix with enzymes from pancreas, liver, and gallbladder.

Absorption and Processing

• Small Intestine: Jejunum and ileum; nutrient absorption across villi.

• Large Intestine: Includes colon, cecum, and rectum; cecum ferments plant material, colon recovers water.

Digestive Systems: Invertebrates

• Gastrovascular cavity: Only one opening for digestion (e.g., cnidarians).

• Alimentary canal: More advanced, unidirectional digestion.

Digestive Systems: Fermentation

• Ruminants: Specialized digestive tracts for cellulose digestion (e.g., cattle, sheep, camels, goats).

Four Compartments

• Rumination: Regurgitation and re-chewing of undigested material.

Digestive Systems: Avian

• No teeth; crop stores food.

• Two-chambered stomach: proventriculus (enzymes) and gizzard (grinding).

• Most chemical digestion occurs in small intestine; some fermentation in cecum.

Regulation of Digestion and Energy Storage

• Food intake is regulated to match energy expenditure.

• Hypothalamus: Controls hunger and satiety.

• Blood sugar level: Regulates hunger and energy storage.

Circulation

Circulatory Systems

Circulatory systems link cells throughout the body, moving fluid via a series of pipes and pumps.

• Single Circulation: One pump (atrium and ventricle), slower pace, found in fishes.

• Double Circulation: Two circuits (systemic and pulmonary/pulmocutaneous), found in amphibians, mammals, and birds.

Arteries, Veins, and Capillaries

• Arteries: Thick, strong, elastic; accommodate high pressure and regulate blood flow.

• Veins: Thinner walls; return blood at lower pressure.

• Capillaries: Smallest, site for diffusion; every cell is in close proximity.

Blood Components and Function

• Plasma: Contains ions, proteins, regulates osmotic pressure, transports substances, defends, and buffers pH changes.

• Cellular Elements: Red blood cells (erythrocytes) and white blood cells (leukocytes).

Blood Clotting

• Prevents loss of blood from ruptured vessels via constriction and coagulation.

• Enzyme Cascade: Allows clotting to occur quickly with safety margin to prevent spontaneous coagulation.

Insect and Crustacean Circulation

• Circulatory system carries nutrients, metabolites, and hormones; not involved in respiration (low pressure).

Gas Exchange (Respiration)

Importance of Oxygen

Oxygen is essential for energy production via oxidation of food, producing CO2 and H2O.

• Aquatic animals: Take up oxygen from water.

• Terrestrial animals: Take up oxygen from air.

• Small or low-metabolic-rate animals can use body surface for gas exchange.

Respiratory Structures

• Specialized organs for oxygen uptake and CO2 release.

• Most important process: Movement of oxygen from external medium to cells.

Tracheae – Insect Respiration

• Insects have a hard cuticle covered with wax, impermeable to gases and water.

• Gas exchange occurs via tracheal system: air-filled tubes (tracheae) connect to outside via spiracles.

• Tracheal system delivers oxygen directly to tissues.

• Basic system: 12 pairs of spiracles (3 thoracic, 9 abdominal).

Gills

• Thin areas of skin or specialized structures for gas exchange in aquatic animals.

• Ventilation: Movement of water over gills.

Mammalian Respiratory System

• Lungs divided into small sacs (alveoli) to increase surface area for gas exchange.

• Air pathway: Nasal cavity → pharynx → trachea → bronchioles → alveoli.

• Surfactants prevent alveoli from collapsing due to surface tension.

Bird Respiration

• Lungs are small and compact; air passes through parabronchi for efficient gas exchange.

Regulation of Respiration

• Ventilation is regulated by CO2 concentration in the lungs.

• Small increases in CO2 have significant physiological effects.

Osmoregulation and Excretion

Regulating Chemical Composition

Animals balance water and solute intake and loss to maintain homeostasis.

• Osmotic Pressure: Created by osmosis between solutions separated by a semipermeable membrane.

• Osmolarity: Solute concentration (measured in moles per liter).

• Hyperosmotic: Body fluids more concentrated than surroundings.

• Hypoosmotic: Body fluids less concentrated than surroundings.

Terminology

• Osmoconformer: Body fluids conform to external osmolarity.

• Osmoregulator: Actively regulate osmolarity independent of environment.

• Euryhaline: Tolerate wide range of salinities.

• Stenohaline: Tolerate narrow range of salinities.

Marine and Freshwater Adaptations

• Marine invertebrates: Usually osmoconformers.

• Marine teleost fish: Hypoosmotic; compensate for water loss by drinking and excreting salts via gills.

• Elasmobranchs (sharks, rays): Osmoconformers and ion regulators; sodium excreted by kidney, rectal gland, and gills.

• Freshwater animals: Hyperosmotic; uptake ions via gills, excrete dilute urine.

• Marine birds: Salt glands excrete excess salt.

Excretion of Nitrogenous Wastes

• Most metabolic wastes are dissolved in water for excretion.

• Nitrogenous wastes are breakdown products of proteins and nucleic acids.

Excretory Processes

• Body fluid contacts selectively permeable membrane; blood pressure drives filtration.

• Reabsorption recovers useful molecules and water.

• Nonessential solutes and wastes are excreted.

Excretory Systems: Invertebrates

• Malpighian tubules: Remove nitrogenous wastes and regulate osmolarity.

Excretory Systems: Vertebrates

• Kidneys: Regulate osmolarity and excretion.

• Nephron: Functional unit; single long tubule and ball of capillaries (glomerulus) surrounded by Bowman's capsule.

Nephron Function

• Filtrate passes from blood into Bowman's capsule.

• Filtrate contains salts, glucose, amino acids, and other small molecules.

• Descending loop of Henle: Water reabsorption.

• Ascending loop of Henle: NaCl removal.

• Distal tubule: Regulation of K+ and NaCl.

• Collecting duct: Processes urine; water and solutes reabsorbed as needed.

Additional info: The nephron's structure and function are essential for maintaining water and electrolyte balance in vertebrates.