The Respiratory System - Flashcards (30 QA)

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• Course: Applied Animal Biology ANIM1020 – The Respiratory System.
• Instructor: Dr Suresh Krishnasamy (SFHEA), University of Queensland.
• Role: Lecturer in Interdisciplinary Agricultural Studies; Deputy Chair (Curriculum); Affiliate Academic – Institute for Teaching and Learning Innovation.
• Context: This set of notes is derived from the lecture transcript provided (PAGEBYPAGE).

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• Learning outcomes for the lesson:
  • Relate the function of the respiratory system to its structure.
  • Illustrate how the respiratory systems of different species are adapted for their environment.
• Inspiration for the lecture comes from Chapter 15 of the recommended textbook.

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• Defining respiration: the system that takes up oxygen and discharges carbon dioxide to satisfy energy requirements.
• The term respiration denotes the exchange of respiratory gases between the organism and its environment, and between the cells of the body and the tissue fluid bathing them.
• Foundational idea: with the exception of energy used by animal life in the deep ocean, all energy used by animals is derived from solar energy.
• Key concepts: gas exchange, energy flow, and the relationship between respiratory gases and metabolism.

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• Primary function of the respiratory system:
  • Bring O$2$ into the body and remove CO$2$ from it.
  • Works in concert with the cardiovascular system.
• Secondary functions:
  • Phonation (voice production).
  • Regulation of body temperature.
  • Regulation of acid–base balance.
  • Sense of smell.

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• External respiration: exchange of O$2$ and CO$2$ between inhaled air and pulmonary capillaries.
• Internal respiration: exchange of O$2$ and CO$2$ between blood in systemic capillaries and all cells/tissues of the body.
• Structuring the Respiratory System (conceptual framework separating external and internal processes).

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• Respiration by individual cells: cells exchange gases directly with the environment.
• Evolutionary note: strategies shared by aquatic and terrestrial species; invertebrates often primitive forms of respiration.
• Gills:
  • Finely divided, highly vascularized organs that provide surfaces for gas exchange.
  • Strategy used by aquatic species.
• Overall, this page situates the cellular level of respiration and introduces gills as a major aquatic gas-exchange surface.

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• Alternative gas-exchange networks:
  • Tracheae (a network of tubes) in insects: very effective; circulatory system not required for gas transport in insects.
  • Lungs: vascularized, sac-like internal organs for gas exchange with air; strategy used by terrestrial species.
• Takeaway: different anatomical approaches to achieving gas exchange, tailored to environments (air vs water).

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• Explore visuals: Mammals, Birds, Fish, Amphibians, and other vertebrates highlighted as examples of respiratory adaptations.
• Emphasis on cross-species comparison to illustrate environmental adaptations.

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• Visuals continue (Mammals, Birds, Fish, Amphibians) to emphasize diversity of respiratory forms across vertebrates.

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• Respiratory Tract: division into Upper and Lower respiratory tracts.
• Components listed under the Upper respiratory tract: Nose, Cavity, Tongue, Larynx, Trachea, Bronchi; and Lungs under the Lower tract.
• Context: image-based reference to further reading on feline respiratory topics.

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• Nose anatomy:
  • External nares with nasal cartilages.
  • Nasal cavity including nasal meatus and conchae.
  • Paranasal sinuses.
  • The nasal planum: pigmented, hairless, rostral surface of the external nose.
  • Philtrum: midsagittal external crease in the nasal planum.
• Function: initial contact with inhaled air and set-up for conditioning air before it reaches the lungs.

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• The nasal cavity structure:
  • Essentially a tube with a wall formed by skull bones, occupied by nasal conchae; sinuses are extensions.
• Primary functions of the nasal cavity:
  • Olfaction (sense of smell).
  • Air modification: warming and cleaning incoming air.
  • Trigger sneezing as a reflex to clear irritants.

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• Sinuses: air-filled cavities within bones, lined with ciliated mucous epithelium, communicating with the nasal cavity via narrow openings.
• Examples by skull bone:
  • Maxillary sinus (within the maxilla), not always present in dogs.
  • Frontal sinus (within the frontal bone).
• Proposed function of sinuses: to lighten skull weight, allowing larger muscle-attachment areas; potential mechanical/structural advantages.

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• From the nasal cavity to the pharynx:
  • Air enters the pharynx, a region at the back of the mouth shared by respiratory and digestive systems.
  • Pharynx divisions: nasopharynx (dorsal) and oropharynx (ventral) separated by the soft palate.
  • Soft palate prevents food from entering nasal chambers during swallowing.
  • Oropharynx conducts food to the oesophagus; nasopharynx conducts inspired air to the larynx. Air can also reach respiratory passages via the mouth (mouth breathing).

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• The larynx (voice box):
  • Located below the division of pharynx into trachea and oesophagus; partly within the mandible rami and extending caudally into the neck.
  • Contains vocal folds and vestibular folds, enabling phonation.
  • Primary roles: protect lower airways, assist respiration, and enable sound production.

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• Swallowing mechanics and airway protection:
  • During swallowing, suprahyoid muscles pull the larynx superiorly/anteriorly; the epiglottis tips inferiorly to cover the laryngeal inlet, preventing food entry into lower respiratory tubes.
  • Cough reflex: entry of non-air substances into the larynx triggers a cough to expel material.
  • Suprahyoid muscles widen the pharynx to receive food by pulling the hyoid bone anteriorly.
• Epiglottis role: part of airway protection during swallowing.

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• Trachea anatomy:
  • Wide, hollow tube connecting the larynx to the bronchi.
  • Lumen maintained open by approximately 20 C-shaped rings of hyaline cartilage.
  • Gaps between rings bridged by the trachealis muscle and fibrous tissue, allowing flexibility during breathing.
  • In the thorax, the trachea divides into left and right bronchi toward the lungs.

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• Tracheal wall structure (four layers):
  • Mucosa: innermost layer; ciliated pseudostratified columnar epithelium with goblet cells.
  • Submucosa: areolar connective tissue with blood vessels and nerves.
  • Hyaline cartilage layer: supportive rings forming the tracheal structure.
  • Adventitia: outermost layer of areolar connective tissue anchoring the trachea to surrounding tissues.

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• Mammalian lungs are variable in size and shape but share fundamental function.
• Adaptations across mammals reflect environmental demands:
  • Seals: lungs adapted for underwater endurance.
  • Predators (wolves, jaguars): lungs supporting sustained sprinting.
  • Bats: lungs adapted for efficient flight.

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• Left lung anatomy in dogs/cats: divided into cranial and caudal lobes; left cranial lobe further subdivided into cranial/caudal portions but shares a common lobar bronchus.
• Right lung anatomy: four lobes – cranial, middle, caudal, and accessory.
• Note on lobes: spatial arrangement overlaps in 3D; exact lobar positions are approximated in two-dimensional depictions.

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• Diaphragm and lung mechanics:
  • Lungs are powered by the diaphragm, a dome-shaped musculotendinous sheet separating thoracic and abdominal cavities.
  • During inspiration, the diaphragm contracts, increasing thoracic volume and decreasing thoracic pressure, drawing air in.
  • During expiration, the diaphragm relaxes, reducing thoracic volume and allowing air to exit.
• “Pressure-driven” ventilation: the movement of gases is governed by pressure differences between the chest cavity and the atmosphere.
• Species note: the diaphragmatic angle and mechanics differ among species (e.g., steeper in ruminants than in horses).

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• Bronchi and bronchioles: conducting airways
• Bronchi:
  • Contain cartilaginous rings (C-shaped) for structural support.
  • Larger diameter than bronchioles; located at the front of the airway.
  • Function: conducting, warming, and cleaning air; large airways.
• Bronchioles:
  • Lack cartilaginous support; walls contain smooth muscle and elastic tissue.
  • Smaller diameter; connected to alveoli via respiratory surfaces.
  • Function: conduction of air and gas exchange surfaces (as bronchioles become alveolarized).
• Key distinction: bronchi = primarily conducting; bronchioles = conduction plus gas exchange as they transition to alveoli.

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• Bronchi classification by branching:
  • Primary bronchi: branch from the trachea at the tracheal bifurcation.
  • Secondary (lobar) bronchi: branch within the lungs.
  • Tertiary (segmental) bronchi: located near the bottom of the lungs, just above the bronchioles.
• Trend: diameter decreases from primary to tertiary bronchi.

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• Bronchioles classification within a pulmonary lobule:
  • Lobular/preterminal bronchioles: branch to form terminal bronchioles.
  • Terminal bronchioles: lined with simple cuboidal epithelium and lack goblet cells.
  • Respiratory bronchioles: minimal gas exchange; composed of non-ciliated cells; lead to alveoli.
• Structural progression: from conducting airways to gas-exchange-capable regions.

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• Alveolar air sacs arrangement:
  • Alveoli first located in bronchioles extending from their lumens.
  • Respiratory bronchioles become increasingly alveolated with branches of alveolar ducts; deeply lined with alveoli.
  • Each duct opens into five or six alveolar sacs; alveoli cluster on these sacs.
  • Each alveolus is wrapped by capillaries covering about $70\%$ of its area.
• Functional significance: high surface area for diffusion of gases from air to blood.

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• Alveolus structure:
  • Epithelial lining: simple squamous epithelium.
  • The alveolar membrane (respiratory membrane) spans multiple layers:
  • A layer of alveolar lining fluid containing surfactant.
  • The epithelial layer and its basement membrane.
  • A thin interstitial space between the epithelial and capillary membranes.
  • A capillary basement membrane that often fuses with the alveolar basement membrane.
  • The capillary endothelial membrane.
  • Overall membrane thickness ranges from $0.2\ \mu m$ to $0.6\ \mu m$ at its thinnest/thickest parts (facilitating diffusion).
• Function: optimized diffusion pathway for gas exchange.

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• Major alveolar cell types:
  • Alveolar macrophage (phagocytic cell) – moves within alveolar lumens and connective tissue.
  • Type I pneumocytes: squamous, extremely thin cells forming the structure of the alveoli; non-replicating and susceptible to toxins; larger cell type.
  • Type II pneumocytes: produce pulmonary surfactant to lower surface tension; can differentiate to replace damaged Type I cells.
• Importance: macrophages defend alveolar spaces; Type I provide gas exchange surface; Type II maintain surface chemistry and repair capacity.

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• Diaphragm details (special mention):
  • Dome-shaped musculotendinous sheet separating thoracic and abdominal cavities.
  • In neutral position, its cranial portion aligns with the 6th rib.
  • In inspiration, the diaphragm contracts, expanding the thoracic cavity and drawing air in.
  • In expiration, the diaphragm relaxes.
• Comparative note: the diaphragm is steeper in the ruminant thorax than in the horse, affecting ventilation mechanics.

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• Birds (avian respiratory system): overview
• Key features:
  • Relatively small lungs plus nine air sacs.
  • Air sacs fill large portions of the chest and abdominal cavities and connect to air spaces within bones.
  • Air flows directly through the lungs and into the adjacent air sacs, maintaining a constant lung volume.
  • Because of the air sacs, the lungs inflate but do not deflate to take in more oxygen; this unidirectional flow increases oxygen availability for diffusion.

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• Diaphragm absence in birds:
  • Birds lack a diaphragm; respiration is regulated by movements of the sternum and ribs.
• Flow of air through the avian system (two-breath cycle):
  • First inhalation: air enters through the nostrils into the trachea and bronchi, filling the posterior air sacs.
  • First exhalation: air moves from the posterior air sacs into the lungs.
  • Second inhalation: air moves from the lungs into the anterior air sacs.
  • Second exhalation: air moves from the anterior air sacs back into the trachea and out-of-body via the nostrils.
• Result: unidirectional air flow through the lungs yields a continuous supply of relatively fresh air for gas exchange during both inhalation and exhalation, supporting high metabolic demands of flight.

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• Further detail on avian flow:
  • The air sacs enable unidirectional flow of air through lungs, ensuring fresh air with higher O$_2$ content continually participates in gas exchange.
  • In mammals, air flow is bidirectional, mixing fresh with residual old air, reducing effective O$_2$ diffusion.
• Implication: birds achieve higher diffusion efficiency and metabolic endurance due to unidirectional flow.

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• Summary graphic concept: unidirectional flow in birds vs bidirectional in mammals.
• Takeaway: The avian respiratory system is optimized for high oxygen extraction efficiency during energetically costly activities like sustained flight.

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• Avian respiratory system (summary/visual): reiteration of structural and functional features discussed.

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• Amphibians (intro): overview of amphibian respiration.

Page 35

• Glass frogs and the three respiratory surfaces:
  • Skin: oxygen diffusion through moist skin when submerged.
  • In-mouth (oral mucosa) membrane: breathing surface on the lining of the mouth to extract oxygen.
  • Traditional lungs: conventional air-breathing lungs as another respiratory route.
• Special note: some species exhibit extra or alternative respiratory surfaces beyond lungs.

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• Cutaneous respiration (skin-based):
  • Occurs continuously whether frog is in water or on land.
  • Rich cutaneous blood supply and permeable skin enable gas diffusion.
  • Moist surface is essential for gas diffusion; mucus glands keep skin moist to prevent desiccation.
  • Movement is not required for cutaneous respiration; skin remains exposed to air or water.

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• Buccal respiration (mouth-breathing):
  • Frogs may lack ribs and diaphragm; air intake via mouth is driven by floor-of-mouth movements to expand and draw air in, then force air into lungs by floor-movement and nostril action.
  • Gas exchange occurs when air is directed into lungs; swallowing or mouth movements adjust airflow between buccal cavity and lungs.

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• Buccal respiration continued:
  • In buccal respiration, the mouth remains closed while the nostrils are open.
  • The buccal cavity lining is highly vascularized.
  • Floor-of-mouth movements draw air in and expel air through the open nostrils.
  • The glottis remains closed, preventing air from entering or leaving the lungs through the buccal cavity.
  • At rest, buccal respiration may be the predominant mode; lungs are not always actively ventilated.

Page 39

• Fish (intro): overview of fish respiration.

Page 40

• Fish respiration basics:
  • Gills are the primary gas-exchange organs.
  • Gills consist of feathery gill filaments that provide a large surface area for gas exchange in aquatic environments.
• Rationale for large surface area: water contains relatively low dissolved oxygen; diffusion efficiency increases with surface area.

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• Gill architecture:
  • Four gill arches lined with thin filaments to maximize surface area.
  • Lamellae on filaments contain blood vessels; this arrangement yields a high surface area-to-volume ratio for diffusion.
  • Blood circulates through vessels in the gills in a flow pattern that supports efficient gas exchange.
• Spatial scale: gills occupy a small portion of the body but provide a large effective respiratory surface due to the filaments/lamellae structure.

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• Mechanism of water flow through the fish gills:
  • Water enters the mouth, exits through the operculum after passing over the gills.
  • Water flow is unidirectional, enabling more efficient exchange than bidirectional flow.
• Gill filtration: gill rakers filter out food particles before water passes through the gills.

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• Countercurrent exchange in fish gills:
  • Blood flow in capillaries runs opposite to water flow over lamellae.
  • This arrangement maintains a concentration gradient across the entire gas-exchange surface, maximizing O$_2$ diffusion into the blood.
• Practical consequence: high efficiency of oxygen transfer from water to blood.

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• Schematic illustrating details of gill function, water flow, and countercurrent exchange.
• Emphasizes the continuous maintenance of the diffusion gradient for maximal O$_2$ uptake.

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• Advantages and limitations of the fish countercurrent system:
  • Advantage: high oxygen uptake without requiring excessive water flow.
  • Advantage: unidirectional water flow ensures continuous exposure of the gas-exchange surface to oxygenated water.
  • Limitation: fish must live in water; gill filaments and lamellae require water to stay separated and hydrated; in air, surface area would dry and diffusion would be compromised.

Page 46

• Specialised breathers (intro): a slide listing species as examples of unique respiratory adaptations.

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• Species examples:
  • Horses
  • Blue snake
  • Sloth
  • Australian lungfish
• These examples illustrate diverse respiratory strategies in response to ecological niches.

Page 48

• Snakes’ respiratory anatomy and breathing:
  • Tract includes external nares, nasal cavity, internal nares, glottis, trachea, bronchi, lungs, and possibly air sacs.
  • External nares communicate with internal nares via the nasal cavity.
  • Internal nares lie in the roof of the oral cavity and communicate directly with the glottis when the mouth is closed.
  • During feeding, the glottis can move laterally to facilitate respiration while large prey is swallowed.
  • Snakes rely largely on intercostal muscles (between ribs) for respiration because they lack a diaphragmatic mechanism.

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• Snake lung organization and specialization:
  • Right lung is fully formed; left lung is vestigial as a small sac.
  • Evolutionarily, snakes exhibit elongated, narrow organs; kidneys are stacked vertically rather than side-by-side.
  • Functional division within the lung: proximal portion near the head participates in gas exchange; distal portion toward the tail acts mainly as an air sac.
• Special note on aquatic snakes: the vestigial left lung can serve as a buoyancy aid.

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• Head-breathing sea snakes:
  • Some species (e.g., Hydrophis cyanocinctus) utilize a network of blood vessels under the skin of the snout/forehead to absorb O$_2$ from seawater and redistribute it to the brain while underwater.
  • This vascular arrangement reduces the risk of brain hypoxia during submerged swimming.

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• Sloths’ respiratory mechanics:
  • Sloths can breathe upside-down for extended periods because the lungs are connected to the rib cage with a tissue that acts like a tape/adherence.
  • This adaptation reduces the energetic cost of breathing when inverted; without adhesions, breathing could be more energetically expensive.

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• Vultures and high-altitude flight:
  • Vultures are large birds with exceptional respiratory efficiency allowing high altitude flight.
  • Their strategy supports long-distance migration using natural jet streams with minimal energetic cost.
• Conceptual link: high lung efficiency supports low-oxygen environments encountered at altitude.

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• Australian lungfish (Neoceratodus forsteri):
  • A lungfish species capable of breathing air; weight up to $10\ \text{kg}$ and length up to $1.25\ \text{m}$.
  • Morphology: compact body with large overlapping scales; broader pectoral and pelvic fins.
• Lungfish description: lung-like lungs derived from swim bladders; air-breathing is intermittent, with gill breathing dominating when water quality is adequate.

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• Australian lungfish respiration details:
  • Lungs are primitive, similar to amphibian lungs.
  • Inner surfaces feature honeycomb-like cavities with rich vascularization.
  • In normal water levels with adequate oxygen, gill breathing predominates; the fish surfaces less often to breathe air.
• Transition between gill and air breathing is environmentally driven (water oxygen content changes with drought).

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• Dry-season behavior of Australian lungfish:
  • When water levels drop (roughly August/September in some regions), isolated waterholes with low oxygen concentration become common.
  • Lungfish survive by switching to atmospheric air breathing, surfacing every 40–50 minutes during dry periods.

Page 56

• Equine (horse) respiratory physiology:
  • Horses are obligate nasal breathers; during exercise, nasal passage resistance accounts for about half of the total respiratory resistance.
  • The rule: "One Breath = One Stride" in cantering/galloping; there is respiratory-locomotor coupling.
  • Breathing is mechanically linked to locomotion; any factor affecting breathing also impacts stride.

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• Respiratory mechanics in horses during activity:
  • Chest expansion and diaphragm movement drive air movement at rest, during walking/trotting, and during strong exhalation after exertion.
  • In fast canter/gallop, leg movement and diaphragmatic motion primarily drive airflow.
  • Horses tend to hold their breath over jumps; they resume breathing on landing, exhaling first.
• Practical takeaway: training the respiratory system is not straightforward; the horse’s performance is constrained by intrinsic respiratory mechanics.

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• Acknowledgments and contact information for Dr Suresh Krishnasamy (University of Queensland).

• CRICOS code: 00025B.

• Key cross-cutting themes across the pages:

  • Gas exchange is the core function, implemented through different anatomical strategies across taxa (gills in fish, lungs in mammals, air sacs in birds, cutaneous and buccal respiration in amphibians, snake-specific lungs).
  • Structure–function relationships drive environmental adaptation (e.g., unidirectional air flow in birds; countercurrent exchange in fish; diaphragm-driven ventilation in mammals).
  • The respiratory system interfaces with the circulatory system (gas transport in blood), thermoregulation, acid–base balance, phonation, olfaction, and sensory integration.
  • Environmental context shapes respiratory innovations (aquatic vs terrestrial habitats, flight demands, extreme oxygen availability at altitude).

• Notes on mathematical details and quantities encountered in the lecture:

  • Alveolar diffusion area coverage: approximately $70\%$ of alveolar surface area is involved in gas exchange per alveolus.
  • Alveolar membrane thickness: ranges from $0.2\ \mu m$ to $0.6\ \mu m$ at its thinnest to thickest parts.
  • Lung lobe anatomy (approximate): left lung typically has cranial/caudal lobes; right lung contains cranial, middle, caudal, and an accessory lobe.
  • Gases: O$2$ (oxygen) and CO$2$ (carbon dioxide) are the primary gases exchanged; denoted as $ext{O}<em>2$ and $ext{CO}</em>2$ in chemical notation.
  • Airflow concepts: unidirectional (birds) vs bidirectional (mammals) gas flow through lungs; countercurrent exchange in fish gills enhances diffusion efficiency.

• Ethical/philosophical/practical implications:

  • Understanding species-specific respiratory adaptations informs veterinary care, animal welfare, and conservation strategies (e.g., how water quality affects lungfish, how altitude affects avian flight, how exercise impacts equine respiration).
  • Recognizing the limits of respiratory efficiency highlights the need to maintain appropriate environmental conditions (e.g., water oxygenation for fish, air quality for birds and mammals).
  • The diversity of respiratory strategies underscores the value of comparative physiology in explaining how life colonizes a wide range of habitats.

• Connections to foundational principles:

  • Diffusion, surface area-to-volume considerations, and thin respiratory membranes govern gas exchange efficiency.
  • The respiratory system co-evolves with the circulatory system to optimize oxygen delivery and carbon dioxide removal to meet tissue energy demands.
  • The role of surfactant in reducing surface tension (Type II pneumocytes) is essential for maintaining alveolar stability and preventing collapse.

• Formulas and equations (examples in context):

  • Alveolar surface area availability: surface area is effectively utilized to maximize diffusion; numerical reference: approximately $70\%$ of alveolar area participates in gas exchange per alveolus.
  • Diffusion across membranes is influenced by membrane thickness; a thinner membrane enhances diffusion rate; thickness values given: $0.2\ \mu m \leq t \leq 0.6\ \mu m$.
  • Gas exchange directionality and gradient maintenance are illustrated by the countercurrent exchange in fish gills (no simple equation provided in the slides, but conceptually: diffusion rate increases with sustained gradient along the exchange surface).

• Summary takeaway:

  • The respiratory system is a highly adapted, multi-taceted apparatus whose structure directly enables its function across diverse environments. From the unidirectional flow in birds to the countercurrent exchange in fish, and from cutaneous and buccal respiration in amphibians to diaphragm-driven ventilation in mammals, the overarching principle is efficient gas exchange supported by specialized anatomy and physiology. This cross-species perspective helps explain how energy demands shape respiratory design and how environmental pressures drive evolutionary innovations.