BIO 114 Exam 3 Study Guide: Gas Exchange, Circulation, Nervous System, Sensory Systems, Animal Movement, and Chemical Signals

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Chapter 42: Gas Exchange and Circulation

Fick’s Law of Diffusion and Gas Exchange

Fick’s Law of Diffusion describes the rate at which gases diffuse across membranes, which is fundamental to understanding respiratory systems in animals.

Fick’s Law Equation: The rate of diffusion (R) is given by: where:
- D = diffusion coefficient (depends on the substance and medium)
- A = surface area for diffusion
- Δp = difference in partial pressure of the gas across the membrane
- d = thickness of the membrane
Application: Gas exchange is maximized by increasing surface area (A), increasing the partial pressure difference (Δp), and decreasing membrane thickness (d).

Evolutionary Adaptations Affecting Fick’s Law Variables

Animals have evolved various adaptations to optimize gas exchange according to Fick’s Law.

Increased Surface Area: Structures like alveoli in lungs and lamellae in gills increase A.
Thin Membranes: Respiratory surfaces are often only a few cells thick to minimize d.
Maintaining Partial Pressure Gradients: Ventilation and perfusion maintain high Δp.

Countercurrent Flow in Gills

Fish gills use a countercurrent exchange system to maximize oxygen uptake.

Countercurrent Flow: Water flows over gill lamellae in the opposite direction to blood flow, maintaining a gradient for O2 diffusion along the entire length.
Efficiency: This system allows fish to extract up to 80-90% of the oxygen from water.

Breathing Mechanisms: Amphibians, Mammals, and Birds

Amphibians: Use positive pressure breathing by forcing air into lungs.
Mammals: Use negative pressure breathing by expanding the thoracic cavity (diaphragm contraction).
Birds: Have unidirectional airflow through lungs and air sacs, providing continuous fresh air and high efficiency.

Efficiency of Mammalian Lungs (Fick’s Law)

Large Surface Area: Millions of alveoli provide extensive area for gas exchange.
Thin Barriers: Alveolar and capillary walls are extremely thin.
Partial Pressure Gradient: Maintained by ventilation and blood flow.

Diaphragm and Inhalation

Diaphragm Contraction: Lowers the floor of the thoracic cavity, increasing volume and decreasing pressure, causing air to flow in.

CNS Regulation of Breathing

Medulla Oblongata: Monitors CO2 levels (via pH) and controls breathing rate.
Feedback Mechanism: Increased CO2 leads to increased breathing rate.

Hemoglobin Structure and Oxygen Binding

Structure: Hemoglobin is a tetrameric protein with four heme groups, each binding one O2 molecule.
Cooperative Binding: Binding of O2 to one subunit increases affinity in others.

Hemoglobin Oxygen Affinity and the Bohr Shift

Bohr Shift: Decreased pH or increased CO2 reduces hemoglobin’s affinity for O2, facilitating oxygen release in tissues.

CO2 Transport in Blood

Dissolved in Plasma: ~7% as CO2
Bound to Hemoglobin: ~23% as carbaminohemoglobin
As Bicarbonate: ~70% converted to HCO3- by carbonic anhydrase

Formed Elements in Blood

Red Blood Cells (Erythrocytes): Transport O2 and CO2
White Blood Cells (Leukocytes): Immune defense
Platelets: Blood clotting

Cardiac Cycle Elements

Systole: Contraction phase (pumping blood)
Diastole: Relaxation phase (chambers fill with blood)
Sequence: Atrial systole → Ventricular systole → Diastole

Arteries, Arterioles, and Pressure

Thick Walls: Arteries and arterioles have thick, elastic walls to withstand high pressure from the heart.

Capillaries and Pressure

Thin Walls: Capillaries are one cell thick for exchange but cannot withstand high pressure, which is reduced before blood enters them.

Veins vs. Arteries

Veins: Thinner walls, larger lumen, contain valves to prevent backflow, operate under low pressure.
Arteries: Thicker, more muscular and elastic walls, no valves, high pressure.

Lymphatic System Operation

Function: Returns excess interstitial fluid to the bloodstream, absorbs fats, and provides immune defense.
Structure: Network of vessels, lymph nodes, and organs.

Chapter 43: Nervous System

Major Divisions of the Vertebrate Nervous System

Central Nervous System (CNS): Brain and spinal cord; processes information.
Peripheral Nervous System (PNS): Nerves and ganglia; transmits signals to and from CNS.

Production of Resting Potential

Resting Potential: The voltage difference across a neuron's membrane at rest, typically -70 mV.
Mechanism: Maintained by Na+/K+ pumps and selective permeability to K+.

Characteristics of an Action Potential

All-or-None: Action potentials occur fully or not at all.
Phases: Depolarization, repolarization, and hyperpolarization.

Parts of a Neuron and Support Cells

Neuron: Dendrites (input), cell body (integration), axon (output), axon terminals (synapse).
Support Cells (Glia): Astrocytes, oligodendrocytes (CNS), Schwann cells (PNS), microglia.

Voltage-Gated Channels and Action Potentials

Voltage-Gated Na+ Channels: Open during depolarization, allowing Na+ influx.
Voltage-Gated K+ Channels: Open during repolarization, allowing K+ efflux.

Propagation of Action Potentials

Continuous Conduction: In unmyelinated axons, action potentials move sequentially along the membrane.
Saltatory Conduction: In myelinated axons, action potentials jump between nodes of Ranvier, increasing speed.

Synaptic Communication

Chemical Synapses: Neurotransmitters released from presynaptic neuron bind to receptors on postsynaptic cell.
Electrical Synapses: Direct cytoplasmic connections via gap junctions (less common).

Excitatory vs. Inhibitory Neurotransmitters

Excitatory: Cause depolarization (e.g., glutamate).
Inhibitory: Cause hyperpolarization (e.g., GABA).

Neuronal Integration

Summation: Neurons integrate multiple inputs (spatial and temporal summation) to determine if threshold is reached for action potential.

Organization of the Vertebrate Brain

Major Regions: Forebrain (cerebrum, thalamus, hypothalamus), midbrain, hindbrain (cerebellum, pons, medulla).

Human Forebrain (Cerebrum) Areas and Functions

Cerebral Cortex: Higher cognitive functions, sensory perception, voluntary movement.
Thalamus: Sensory relay.
Hypothalamus: Homeostasis, hormone regulation.

Somatic, Autonomic, Sympathetic, and Parasympathetic Systems

Somatic: Voluntary control of skeletal muscles.
Autonomic: Involuntary control of smooth muscle, cardiac muscle, glands.
Sympathetic: "Fight or flight" responses.
Parasympathetic: "Rest and digest" responses.

Chapter 44: Sensory System

Conveyance of Sensory Information to CNS

Transduction: Sensory receptors convert stimuli into electrical signals (action potentials).
Transmission: Action potentials travel along sensory neurons to the CNS.

Gated Ion Channels

Function: Open or close in response to stimuli (mechanical, chemical, or voltage), altering membrane potential.

Types of Sensory Receptors

Mechanoreceptors: Detect pressure, stretch, vibration (e.g., touch, hearing).
Chemoreceptors: Detect chemicals (e.g., taste, smell).
Photoreceptors: Detect light (e.g., rods and cones in eyes).
Thermoreceptors: Detect temperature changes.
Nociceptors: Detect pain.

Soundwave Detection and Action Potentials in the Inner Ear

Mechanism: Sound waves vibrate the tympanic membrane, transmitted via ossicles to cochlea, where hair cells transduce mechanical energy into action potentials.

Differentiation of Sound Frequency in Mammals

Basilar Membrane: Different regions vibrate in response to different frequencies, allowing pitch discrimination.

Olfactory Receptor Function

Mechanism: Odorant molecules bind to receptors on olfactory neurons, triggering action potentials to the olfactory bulb.

Invertebrate vs. Vertebrate Eyes

Simple Eyes: (e.g., vertebrates) Single lens focuses light on retina.
Compound Eyes: (e.g., insects) Multiple ommatidia, each with its own lens, provide a mosaic image.

Rods vs. Cones

Rods: Sensitive to low light, no color vision.
Cones: Detect color, function best in bright light.

Photoreceptor Function

Mechanism: Light absorption changes the shape of photopigments, altering membrane potential and generating action potentials.

Chapter 45: Animal Movement

Three Kinds of Muscle and Muscle Cells

Skeletal Muscle: Voluntary, striated, multinucleate.
Cardiac Muscle: Involuntary, striated, branched, intercalated discs.
Smooth Muscle: Involuntary, non-striated, spindle-shaped.

Sliding Filament Mechanism of Muscle Contraction

Mechanism: Myosin heads bind to actin filaments and pull them inward, shortening the sarcomere.
ATP: Required for myosin head detachment and re-cocking.

Link Between Muscle Contraction and Nerve Impulse

Excitation-Contraction Coupling: Action potential in motor neuron releases acetylcholine, triggering Ca2+ release in muscle, leading to contraction.

Types of Skeletons

Hydrostatic Skeleton: Fluid-filled cavity (e.g., earthworms).
Exoskeleton: External skeleton (e.g., arthropods).
Endoskeleton: Internal skeleton (e.g., vertebrates).

Chapter 46: Chemical Signals

Role of Hormones in Regulating Body Processes

Hormones: Chemical messengers secreted by endocrine glands, regulate growth, metabolism, reproduction, and homeostasis.

Lipophilic vs. Hydrophilic Hormones

Lipophilic Hormones: (e.g., steroids) Pass through cell membranes, bind to intracellular receptors.
Hydrophilic Hormones: (e.g., peptides) Bind to cell surface receptors, use second messengers.

Peptide Hormone Signal Transduction

Mechanism: Peptide hormones bind to membrane receptors, activating intracellular signaling cascades (e.g., cAMP pathway).

Hypothalamus and Pituitary Connections

Hypothalamus: Produces releasing/inhibiting hormones.
Posterior Pituitary: Stores and releases hormones made by hypothalamus (e.g., ADH, oxytocin).
Anterior Pituitary: Produces its own hormones in response to hypothalamic signals (e.g., growth hormone, ACTH).

Insulin vs. Glucagon Effects on Blood Glucose

Hormone	Source	Effect on Blood Glucose
Insulin	Beta cells (pancreas)	Lowers blood glucose by promoting uptake and storage
Glucagon	Alpha cells (pancreas)	Raises blood glucose by stimulating glycogen breakdown and gluconeogenesis