External Respiration Practice Flashcards

A set of 40 vocabulary flashcards covering the concepts of external respiration, ventilation types, gas-exchange systems, and species-specific respiratory anatomy based on Chapter 23.

External Respiration

The process of transporting $O_2$ from the environment to the gas-exchange membrane and removing $CO_2$ in the opposite direction.

Gas-exchange membrane

Thin tissue, typically consisting of $1-2$ layers of epithelial cells, that separates an animal's internal body fluids from the external medium.

Ventilation

The bulk flow (convection) of air or water to and from the gas-exchange membrane.

Gills

Evaginated breathing organs that project outward into the medium and are used for respiration.

Lungs

Invaginated breathing organs that form internal pockets into which the animal breathes the medium.

External gills

Exposed breathing organs ventilated by ambient water currents or waving movements, such as those seen in salamander larvae.

Internal gills

Breathing organs enclosed under a protective cover that must be actively ventilated, commonly found in fish.

Dual (bimodal) breathers

Animals that possess the ability to use both water-breathing and air-breathing organs, such as amphibians using lungs and skin.

Active ventilation

A process where the animal uses metabolic energy, such as muscles or cilia, to move the medium across respiratory surfaces.

Passive ventilation

A process where environmental currents move the medium across respiratory surfaces at no metabolic cost to the animal.

Unidirectional flow

A pattern where the medium flows over the gas-exchange surface in only one direction, allowing for countercurrent exchange.

Tidal (bidirectional) flow

A pattern where the medium flows in and out via the same passages, as seen in mammalian lungs.

Partial pressure

The pressure that a specific gas, such as $O_2$, contributes to a mixture, reflecting how much is available to diffuse into tissues.

Tidal exchange

A gas-exchange system where fresh air mixes with stale air, resulting in an $O_2$ partial pressure at the exchange surface that is below atmospheric levels.

Cocurrent (concurrent) exchange

An exchange system where medium and blood flow in the same direction, allowing them to approach equilibrium with each other.

Countercurrent exchange

An efficient exchange system where medium and blood flow in opposite directions, maintaining a favorable partial-pressure gradient along the entire surface.

Cross-current exchange

A gas-exchange system where blood flow breaks into multiple streams that each cross part of the medium's path, found in bird lungs.

Capacitance coefficients

A property describing how much gas dissolves per unit of partial pressure; notably, water has a much higher coefficient for $CO_2$ than air.

Hypoxia

A condition that occurs when the circulatory and respiratory systems cannot provide enough $O_2$ to meet cellular demands.

HIF-1 (hypoxia-inducible factor 1)

An ancient transcription factor made of $\alpha$ and $\beta$ subunits that activates gene transcription in response to low $O_2$ levels.

Erythropoietin

A hormone stimulated by HIF-1 and HIF-2 that increases red blood cell production to enhance $O_2$-carrying capacity.

Angiogenesis

The growth of new blood capillaries, promoted by HIF-1 during hypoxia to shorten the diffusion distance from capillaries to cells.

Cutaneous respiration

Breathing through the skin, which varies from $100\%$ in lungless salamanders to almost nothing in mammals and birds.

Central pattern generators (CPGs)

Groups of neurons in the brainstem medulla that generate the rhythmic bursts of action potentials required for breathing commands.

Apnea

A period during intermittent breathing where no breathing occurs, characterized by inflated lungs and a closed glottis.

Secondary lamellae

Thin, plate-like folds on fish gill filaments that serve as the actual sites of gas exchange.

Buccal pressure pump

A mechanism in fish that creates positive pressure to force water through the gill array into the opercular cavity.

Opercular suction pump

A mechanism in fish that creates negative pressure by lateral expansion to suck water from the buccal cavity through the gills.

Unicameral lung

A single-chambered, open central cavity lung found in most lizards and snakes.

Multicameral lung

A lung subdivided by major septa into multiple smaller chambers, associated with more active lifestyles in animals like monitor lizards and crocodilians.

Anatomical dead space

The conducting airways, including the trachea and most bronchioles, where no significant gas exchange occurs.

Respiratory airways

The parts of the mammalian lung where gas exchange takes place, including respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.

Alveoli

Tiny sacs in the lungs, numbering approximately $500\,million$ in humans, that provide a total gas-exchange surface area of about $130\,m^2$.

Pulmonary surfactant

A mix of phospholipids and proteins that reduces surface tension in the alveoli to prevent collapse during exhalation.

Diaphragm

A dome-shaped sheet of muscle and connective tissue unique to mammals that flattens during contraction to increase thoracic volume.

Parabronchi

Parallel tubes that serve as the structural and functional units of the avian lung for unidirectional airflow.

Air sacs

Thin-walled, poorly vascularized structures in birds that act as bellows to push air through the rigid lungs during both inhalation and exhalation.

Tracheae

Gas-filled tubes in the insect tracheal system that open to the atmosphere via spiracles.

Spiracles

The external openings of the insect tracheal system that can be controlled to reduce evaporative water loss.

Plastron

A permanent, incompressible film of gas trapped by water-repelling hairs on some aquatic insects that functions as a permanent gill.

Carried bubble:

water beetles carry a conspicuous gas bubble under their wings or at the abdomen tip —→ spiracles open into bubble, allowing O2 in bubble to be consumed; bubble acts as a gill; needs to be renewed at surface