Chapter 33: Animal Body - Basic Form and Function Notes

Animal Function: Maintaining Homeostasis

• Organisms maintain a stable internal environment (steady state) regardless of external conditions.
• In humans, this includes maintaining constant body temperature, blood pH, and glucose concentration.
• Homeostasis involves:
  • Constant exchange of materials with the environment (open systems).
  • Managing energy requirements.
  • Physical adaptations, behavior, and physiological processes.

Energy Requirements

• Energy needs are related to animal size, activity level, and environment.
• Bioenergetics: The study of overall energy flow and transformation in an animal.
  • Determines food requirements.
  • Related to size, activity, and environment.
• Basal Metabolic Rate (BMR):
  • The average amount of energy used by an organism in a non-active state.

Torpor and Energy Conservation

• Torpor: A physiological state of low activity and decreased metabolism to conserve energy.
• Hibernation: Long-term torpor as an adaptation to winter cold and food scarcity.
• Estivation: Summer torpor that enables animals to survive high temperatures and scarce water.
• Daily torpor: Exhibited by small mammals and birds during the coldest part of the day.

Mechanisms and Control of Homeostasis

• Homeostatic mechanisms moderate changes in the internal environment using feedback loops.
• Negative Feedback Loop:
  • Fluctuations above or below a set point trigger a response.
  • Sensors detect the stimulus and trigger a response.
  • The response returns the variable to the set point, maintaining a normal range.
  • Example: Blood sugar level regulation.
• Positive Feedback Loop:
  • Amplifies a stimulus.
  • Does not usually contribute to homeostasis.
  • Example: The birth of a human infant.
• Acclimatization: Homeostasis can adjust to changes in the external environment.
  • Example: An animal migrating to a higher altitude where the body increases red blood cells to ensure adequate oxygen delivery to tissues due to lower oxygen levels.

Thermoregulation

• Maintaining a relatively constant internal temperature.
  • Essential for enzyme efficiency and preventing protein denaturation.
• Thermoregulatory control is managed by the hypothalamus.
• Heat exchange occurs through:
  • Radiation
  • Convection
  • Conduction
  • Evaporation
• Integumentary system (skin, hair, sweat glands) in mammals aids in heat regulation.
• Five adaptations for thermoregulation:
  1. Insulation: Fur or feathers create an insulating air layer.
  2. Behavioral responses: Animals huddle together during cold weather.
  3. Circulatory adaptations
  4. Cooling by evaporative heat loss
  5. Adjusting metabolic heat production

Endothermy and Ectothermy

• Endothermic animals generate heat through metabolism (birds and mammals).
  • Can maintain a stable body temperature despite environmental fluctuations.
  • More energetically expensive than ectothermy.
• Ectothermic animals gain heat from external sources (most invertebrates, fishes, amphibians).

Animal Tissues

• Four main types of animal tissues:
  • Epithelial Tissues: Line cavities, open spaces, and surfaces.
  • Connective Tissues: Connect tissues, provide support.
  • Muscle Tissues: Generate movement.
  • Nervous Tissues: Generate and send electrical signals.

Epithelial Tissue

• Classified by the number of layers and cell shape.
  • Simple: Single layer.
  • Stratified: Multiple layers.
  • Pseudostratified: A single layer of cells of varying length.

Connective Tissue

• Cells (fibroblasts) embedded in a non-cellular matrix.
• Ground substance contains collagen, elastic, or reticular fibers.
• Connects different tissues, provides body structure; blood has unique functions.

Muscle Tissue

• Three kinds:
  • Skeletal: Voluntary, striated.
  • Smooth: Involuntary, no striations.
  • Cardiac: Involuntary, striated, intercalated discs.

Nervous Tissue

• Functions in the receipt, processing, and transmission of information.
• Contains:
  • Neurons (nerve cells): Transmit nerve impulses.
  • Glial cells (glia): Support cells.

The Neuron

• Main cell of the nervous system, specialized to receive and transmit electrical impulses.
• Structure:
  • Cell body: Contains the nucleus.
  • Dendrites: Receive input.
  • Axon: Transmits impulses.
  • Astrocyte: Regulates the chemical environment of the nerve cell
  • Oligodendrocyte: Insulates the axon for efficient nerve impulse transfer.
  • Axon terminals: Synaptic contacts with other nerve cells.
• Four main types based on axon and dendrite placement.

Glial Cells

• Support, protect, and nourish neurons.
• Outnumber neurons (10:1) in the brain.
• Fulfill many vital functions.
• Most brain tumors are caused by mutations in glia.

Neuron Communication

• Signals occur due to charged cellular membrane (voltage difference).
• Membrane charge changes in response to neurotransmitters and environmental stimuli.

Action Potentials

• Neurons conduct electrical signals called action potentials, generated by ion flow across the cell membrane.
• During an action potential:
  1. Sodium (Na^+) channels open in response to a stimulus, generating an action potential. Na^+ rushes in, making the cell more positive inside.
  2. Sodium channels close as potassium (K^+) channels open, releasing positive charge and returning the inside of the cell to its resting charge.
  3. Positive sodium ions trigger sodium channels to open farther down the axon, generating another action potential.
  4. The action potential continues to travel down the axon.

Chemical Synapse

• Depolarization causes voltage-gated Calcium (Ca^{2+}) channels to open.
• Calcium ions initiate a signaling cascade causing synaptic vesicles (containing neurotransmitter molecules) to fuse with the presynaptic membrane.
• Neurotransmitter is released into the synaptic cleft.
• After neurotransmission, the neurotransmitter must be removed from the synaptic cleft so the postsynaptic membrane can "reset".