Respiration

Page 1: Overview of Respiration

• Key topics in respiration:

  • Importance of oxygen

  • Gas Laws: Dalton's and Henry's laws of partial pressure

  • Diverse respiratory apparatus among species (frogs, birds, fish, insects, humans)

  • Role of respiratory pigments, such as Hemoglobin in oxygen transport

  • Gas exchange mechanisms in humans

  • Respiratory adaptations in diving mammals

  • Reference: Campbell Biology (Chapter 42)

Page 2: Historical Context of Oxygen

• Great Oxygenation Event: Introduction of oxygen into Earth's atmosphere.

  • Cyanobacteria produced oxygen via photosynthesis.

  • Caused extinction of anaerobic bacteria, leading to the Earth's first mass extinction.

Page 3: Why Oxygen?

• Oxygen's suitability as an electron acceptor:

  1. Stability of O2 allowed its accumulation in Earth's atmosphere.

  2. Reduction of O2 yields significant free energy release during oxidation.

  3. Aerobic metabolism produces at least four times more energy per glucose molecule than anaerobic pathways.

  4. O2 diffusion across membranes and binding with heme groups in proteins helps in O2 delivery and electron transfer.

Page 4: Gas Exchange Mechanisms

• Requirement for large respiratory surfaces in animals for gas exchange.

  • Gas exchange occurs via diffusion down partial pressure gradients, not concentration gradients.

  • Dalton’s Law: Behavior of gases in mixtures based on partial pressure.

  • Henry’s Law: Behavior of gases dissolved in liquids.

Page 5: Diffusion Without Apparatus

• Illustration of gas exchange via diffusion without a specialized respiratory apparatus.

• Closed circulatory system overview:

  • Heart, interstitial fluid, and blood circulation through capillaries close to the surface of the body.

• Important structures include:

  • Dorsal and ventral auxiliary vessels.

Page 6: Air vs. Water for Respiration

• Animals can extract oxygen from both air and water, but:

  • Water contains much less O2 compared to air.

  • Water is denser (800X) and more viscous (50X), making ventilation more challenging.

  • O2 solubility decreases with increased temperature and solute concentration.

Page 7: Gills in Aquatic Animals

• Gills are specialized outfoldings to maximize gas exchange surface area.

  • Types of gills: external and internal.

Page 8: Fish Gills Functionality

• Fish gills utilize a countercurrent exchange system:

  • Blood flows opposite to water to maintain O2 saturation gradient.

  • Over 80-90% of O2 in water is extracted as it passes over gills.

Page 9: Tracheal Systems in Insects

• Insects possess a tracheal system for direct O2 supply to all body cells.

  • Features include spiracles to minimize water loss and air storage sacs.

  • Allows larger insects to ventilate actively.

Page 10: Breathing in Amphibians

• Frogs use positive pressure breathing to ventilate lungs, forcing air into the trachea.

Page 11: Avian Respiratory System

• Birds possess 8-9 air sacs functionally acting as bellows for continuous airflow.

  • Air flows in one direction through lungs, providing efficient gas exchange.

  • Requires two cycles of inhalation and exhalation.

Page 12: Steps in Avian Respiration

• Diagram of avian respiration:

  • Inhalation: Air sacs fill.

  • Exhalation: Air sacs empty; lungs fill with air.

Page 13: Mammalian Respiratory System

• Air travels through a branching duct system to reach the lungs:

  • Nostrils filter and humidify air; the pharynx directs air and food appropriately.

  • Epiglottis prevents food from entering the trachea during swallowing.

  • Trachea bifurcates into bronchi and further divides into bronchioles.

Page 14: Cleaning the Respiratory System

• Exhaled air moves across vocal cords for sound production.

  • Cilia and mucus clean the respiratory tracts, moving particles up to the pharynx (mucus escalator).

Page 15: Cystic Fibrosis Impact

• Dysfunction in CFTR gene affects chloride and bicarbonate ion balance, leading to thick mucus production, impacting breathing.

Page 16: Role of Alveoli

• Alveoli are air sacs where O2/CO2 exchange occurs:

  • High surface area (~100 m² in humans) but lack cilia, making them prone to infection.

  • Surfactants reduce surface tension to aid in lung function.

  • Preterm infants often lack surfactants requiring artificial administration.

Page 17: Negative Pressure Breathing in Mammals

• Mammals utilize negative pressure breathing, pulling air into the lungs:

  • Volume increase as diaphragm and intercostals contract.

  • Tidal volume: Amount of air inhaled per breath.

  • Vital capacity: Maximum tidal volume.

  • Residual volume: Air remaining post-exhalation.

Page 18: Circulation and Gas Exchange

• Blood arriving in lungs has low O2 and high CO2 partial pressures:

  • O2 diffuses from alveoli into blood; CO2 diffuses into alveoli.

  • In tissue capillaries, O2 diffuses into interstitial fluids, and CO2 into blood.

Page 19: O2/CO2 Loading and Unloading

• O2 loading and unloading dynamics:

  • O2 diffusing from alveoli to lung capillaries and systemically to tissues.

  • CO2 moving from tissues to systemic capillaries and from lung capillaries back to alveolar spaces.

Page 20: Respiratory Pigments

• Respiratory pigments, such as hemoglobin, significantly enhance oxygen transport capacity:

  • Arthropods and some molluscs use hemocyanin;

  • Vertebrates use hemoglobin, consisting of dimers that can bind up to four O2 molecules.

Page 21: Binding Affinity and Kd

• The graphical representation of oxygen binding affinity (often depicted using a binding curve) clearly illustrates how hemoglobin's ability to bind oxygen varies with its concentration. The Kd (dissociation constant) values indicate the concentration of oxygen at which hemoglobin is half-saturated. A lower Kd suggests a higher affinity for oxygen, while a higher Kd indicates a lower affinity.

Page 22: Measuring Hemoglobin-O2 Binding

• Various spectrophotometric methods, such as UV-Vis spectroscopy, are utilized to analyze hemoglobin's interactions with oxygen. These methods can distinguish between different states of hemoglobin—specifically, bound (oxyhemoglobin) versus unbound (deoxyhemoglobin). By measuring light absorption at specific wavelengths, researchers can infer the saturation statuses and dynamics.

Page 23: Hemoglobin States

• Hemoglobin exists predominantly in two states:

  1. Tense (T) State:

     • Exhibits a low affinity for O2.

     • Compact structural conformation contributes to low cooperativity, meaning that the binding of one oxygen molecule does not significantly influence the binding of others.

  2. Relaxed (R) State:

     • Has a high affinity for O2 due to its open conformation.

     • Features high cooperativity, allowing the binding of one oxygen molecule to facilitate further binding, enhancing overall oxygen transport efficiency.

Page 24: Hemoglobin Structure

• The heme group within hemoglobin plays a crucial role in oxygen transport. Each heme group contains an iron atom that can reversibly bind to O2. The variations arising from oxy-heme (oxygen-bound) and deoxy-heme (no oxygen) forms result in distinct functional characteristics, influencing hemoglobin's overall oxygen-carrying capacity.

Page 25: Hemoglobin States Summary

• Tense (T) State:

  • Characterized by low affinity and challenging binding, making O2 release easier in low partial pressure environments.

• Relaxed (R) State:

  • Characterized by higher affinity, facilitating easier binding of O2, especially in environments of high oxygen concentration, thus promoting efficient oxygen delivery to tissues.

Page 26: Hemoglobin-O2 Dissociation Curve

• This curve is crucial for understanding hemoglobin's behavior in relation to O2 concentrations. The sensitivity of hemoglobin saturation to changes in oxygen partial pressure is depicted, where the P50 value represents the oxygen partial pressure at which hemoglobin is 50% saturated. It serves as a clinical indicator of hemoglobin function.

Page 27: The Bohr Shift

• The Bohr shift describes the mechanism by which increasing levels of carbon dioxide (CO2) in tissues lead to a reduction in pH (increase in acidity). This shift decreases hemoglobin's affinity for O2, thus facilitating easier oxygen release to respiring tissues—vital for meeting metabolic demands, particularly during exercise.

Page 28: BPG Regulation

• 2,3-BPG (2,3-bisphosphoglycerate) is a compound that can bind to deoxyhemoglobin, influencing hemoglobin's affinity for oxygen. Higher levels of BPG are produced under conditions such as chronic hypoxia or high altitudes, thus facilitating oxygen release to tissues, enabling better adaptations to varying oxygen availability.

Page 29: Myoglobin

• Myoglobin is primarily found in muscle tissue and differs from hemoglobin in several key ways:

  • It is a monomeric protein with no cooperativity, thus binding oxygen independently.

  • Has a much higher affinity for oxygen than hemoglobin, making it ideal for storing oxygen in muscle, especially during intense exercise when rapid oxygen supply is needed.

Page 30: Maternal-Fetal Hemoglobin Interaction

• The interactions between maternal and fetal hemoglobin are pivotal for oxygen transfer during pregnancy. The fetal hemoglobin (HbF) has a higher affinity for oxygen than adult hemoglobin (HbA), facilitating oxygen uptake from the mother. Differences in their respective dissociation curves also contribute to potential blood type incompatibilities during pregnancy.

Page 31: CO2 Transport Mechanisms

• Hemoglobin is critical for CO2 transport in the blood:

  • 7% of CO2 is dissolved directly in plasma,

  • 23% binds to hemoglobin, and

  • 70% is converted into bicarbonate ions (HCO3-) through a reaction catalyzed by carbonic anhydrase. This transport is essential for maintaining acid-base balance.

Page 32: Effects of CO Poisoning

• Carbon monoxide (CO) strongly competes with O2 for binding sites on hemoglobin, forming carboxyhemoglobin (HbCO). This binding effectively reduces the blood’s oxygen-carrying capacity, leading to tissue hypoxia, which can be fatal without prompt intervention.

Page 33: Neural Control of Breathing

• The medulla oblongata acts as the primary control center for breathing, responding to changes in blood oxygen (O2) and carbon dioxide (CO2) levels. Specialized chemoreceptors monitor these levels, providing feedback to maintain homeostasis. The pons also plays a role in fine-tuning respiratory patterns during increased physical activity or stress.

Page 34: Diving Mammals Adaptations

• Diving mammals exhibit remarkable evolutionary adaptations for prolonged underwater survival in environments with limited oxygen availability.

  • For example, Weddell seals can dive for 20 minutes to an hour, while elephant seals can remain submerged for up to two hours.

Page 35: Diving Mammals Physiology

• Notable physiological adaptations in these mammals include:

  • A high blood-to-body volume ratio allows for more efficient oxygen storage,

  • Reduced muscle blood supply during dives helps conserve oxygen for vital organs, and

  • Ability to perform anaerobic respiration post-oxygen depletion, allowing continued activity even in hypoxic conditions.

Page 36: Unique Physiology of Ice Fish

• Ice fish are unique among vertebrates due to their lack of hemoglobin. Instead, they possess high concentrations of antifreeze glycoproteins in their body fluids, which prevent ice crystal formation, allowing them to thrive in extreme cold environments where most other fish cannot survive.