Gas Exchange, Immune Systems, and Thermoregulation

Vocabulary flashcards covering core biological concepts across gas exchange mechanisms, immune system components, and thermoregulatory strategies.

Cellular respiration

The biochemical process occurring within mitochondria that utilizes $O_2$ to generate cellular energy, producing $CO_2$ as a byproduct.

Physical respiration

The physical movement of air or gas from the external environment to the internal tissues and mitochondria, which includes ventilation.

Diffusion limit

The effective threshold distance of approximately $1\,mm$, beyond which passive oxygen diffusion is insufficient to meet cellular metabolic needs.

Cutaneous gas exchange

Gas exchange taking place directly across the outer skin or body surface, as seen in lungless salamanders and newborn dunnarts.

Fick's Law factors

Physical principles governing gas diffusion rates, where exchange is optimized by increasing surface area, increasing the partial pressure gradient, and decreasing diffusion distance.

Spiracles

External pores on an insect's body that open into the tracheal network and can close to reduce water loss.

Tracheal system

An internal network of spiracles, tracheae, and tracheoles in insects that delivers atmospheric gases directly to metabolic tissues.

Ram ventilation

A respiratory method in swimming aquatic organisms, such as certain sharks, where forward movement with an open mouth continuously forces water over the gills.

Buccal ventilation

A mechanism in fish where muscular pumping of the floor of the throat draws water into the mouth and drives it across the gills.

Opercular pumping

The active movement of the operculum (gill cover) in fish to pump water through the gill cavity.

Countercurrent exchange (fish gills)

An arrangement where water and blood flow in opposite directions across lamellae, preserving a partial pressure gradient along the entire exchange interface.

Tidal ventilation

A bidirectional breathing mechanism in terrestrial mammals where air enters and exits through the same passageway, resulting in dead time during exhalation.

Surfactant

A fluid containing amphipathic molecules secreted by pneumocytes that lines alveoli to reduce surface tension and prevent alveolar collapse.

Unidirectional ventilation

An avian gas exchange system utilizing anterior and posterior air sacs and parabronchi to maintain a continuous, one-way flow of fresh air across respiratory surfaces.

Haemoglobin

An iron-containing respiratory pigment in vertebrate red blood cells that reversibly binds up to 4 $O_2$ molecules per protein.

Haemocyanin

A copper-containing respiratory pigment found in arthropods and molluscs (such as octopuses and crabs) that turns blue when oxygenated.

Stomata

Microscopic openings on leaf surfaces that open and close to facilitate $CO_2$ uptake for photosynthesis while regulating water vapor loss.

Spongy mesophyll

A loosely packed leaf tissue layer containing extensive air spaces to facilitate gas diffusion to photosynthetic cells.

Aerenchyma

Specialized internal plant tissue featuring longitudinal air channels that transport gases between shoot and root systems.

Mycelium

The mass of microscopic hyphae forming the vegetative body of a fungus, providing a large surface area for gas exchange via simple diffusion.

Pathogen

A disease-causing microorganism or agent, such as specific pathogenic bacteria, viruses, fungi, or parasites.

Innate immunity — external physical barriers

The immediate, non-specific first line of defense consisting of protective physical and chemical structures (e.g., skin, waxy cuticles, mucus, stomach acid).

Nictitating membrane

A translucent third eyelid found in certain amphibians, reptiles, birds, and camels that sweeps across the eye to protect it from debris.

Mucociliary escalator

A defensive mechanism in the respiratory tract where ciliated epithelial cells push mucus-trapped particles upward toward the throat.

Pattern recognition receptors (PRRs)

Receptors on innate immune cells that detect conserved molecular structures common to broad classes of pathogens.

PAMPs / MAMPs

Pathogen- or microbe-associated molecular patterns (e.g., flagellin, peptidoglycans, viral RNA) that are essential to pathogen survival and recognized by PRRs.

Phagocytes

Innate white blood cells that engulf, internalize, and digest pathogenic invaders.

Natural killer cells

Innate immune lymphocytes that recognize and destroy compromised, virus-infected, or cancerous host cells.

Mast cells

Innate immune cells that release histamines during tissue damage or infection, initiating the inflammatory response.

Cytokines

Chemical signaling molecules released by immune cells that recruit additional phagocytes, trigger complement release, and activate adaptive immunity.

Complement proteins

A group of plasma proteins that promote phagocyte recruitment, enhance inflammation, and directly lyse pathogen cell membranes.

Inflammation

A localized innate response driven by histamine release that increases vascular permeability, allowing immune cells and proteins to enter infected tissues.

Programmed cell death (plant immunity)

A defensive plant response where infected host cells self-destruct along with surrounding tissue to isolate and contain pathogen spread.

Major Histocompatibility Complex (MHC)

Cell-surface proteins unique to an individual that present self-antigens to prevent autoimmunity and display foreign antigens to T cells.

B cells

Lymphocytes of the humoral adaptive immune system that differentiate into antibody-secreting plasma cells and long-lived memory B cells upon antigen matching.

Antibodies

Proteins produced by plasma cells that specifically bind matching pathogen antigens to neutralize them or mark them for destruction.

Helper T cells

Adaptive lymphocytes that bind presented foreign antigens on phagocytes and release signals to activate B cells and cytotoxic T cells.

Cytotoxic T cells

Adaptive lymphocytes that recognize specific foreign antigens presented on infected cells and destroy those host cells.

Primary immune response

The initial adaptive immune response following first exposure to a pathogen, requiring time to select matching B/T cells and expand effector populations.

Secondary immune response

The rapid, heightened adaptive immune response occurring upon subsequent exposure to a pathogen, driven by pre-existing memory cells.

Vaccination

The deliberate administration of non-pathogenic antigens to elicit a primary immune response and form memory B and T cells without causing disease.

Devil Facial Tumour Disease (DFTD)

A contagious, transmissible cancer in Tasmanian devils that evades host immune clearance by suppressing cell-surface MHC protein expression.

Thermal performance curve

A graphic model showing an organism's performance or fitness relative to body temperature, bounded by upper and lower lethal limits.

Endotherm

An organism that generates the majority of its body heat internally through metabolic processes.

Ectotherm

An organism that relies primarily on external environmental sources to gain body heat rather than metabolic generation.

Homeotherm

An organism that maintains a constant core body temperature over time despite environmental temperature changes.

Heterotherm

An organism whose core body temperature undergoes significant temporal or regional fluctuations.

Thermoneutral zone (TNZ)

The ambient temperature range within which an endotherm maintains core temperature using basal metabolic rate without active thermoregulation.

Thermal conductance

The rate at which heat transfers between an organism's body and its external environment.

Conduction

The direct transfer of thermal energy between two physical bodies in contact.

Convection

The transfer of thermal energy between an organism and a moving fluid or air current.

Thermal radiation

Heat transfer via electromagnetic waves between objects that are not in physical contact.

Piloerection

The erection of hair, fur, or feathers to trap a stationary layer of air next to the skin for thermal insulation.

Regional heterothermy

The strategy of allowing peripheral tissues to drop in temperature while strictly maintaining core body temperature.

Vasoconstriction

The constriction of peripheral blood vessels to reduce cutaneous blood flow and preserve internal body heat.

Countercurrent heat exchange

A vascular arrangement where warm arterial blood flowing to extremities transfers heat to adjacent cool venous blood returning to the core.

Shivering thermogenesis

Rapid, uncoordinated skeletal muscle contractions used to produce metabolic heat during cold exposure.

Non-shivering thermogenesis

Metabolic heat production carried out by brown adipose tissue breaking down lipids directly into heat without muscle contraction.

Vasodilation

The widening of peripheral blood vessels to increase cutaneous blood flow and promote radiative and convective heat loss.

Daily torpor

A brief, daily reduction in core body temperature and metabolic rate used by small endotherms to minimize energy expenditure.

Hibernation

A prolonged seasonal state of metabolic suppression and lowered core body temperature used for long-term energy savings during winter.