Respiration

Oxygen and carbon dioxide exchange: Animals need to obtain sufficient O2 and eliminate CO2.
Cellular respiration: O2 is used in mitochondria, producing CO2 as waste.

Invertebrate structures:
- Epithelium, tracheae, gills.
Vertebrate structures:
- Fish and larval amphibians use gills.
- Adult amphibians use skin/epithelium.
- Reptiles, birds, mammals have lungs.
Gas diffusion: O2 diffuses into the blood, CO2 diffuses out.

External respiration (ventilation): Gas exchange between organism and environment.
Internal respiration: Transport of gases between respiratory organs and tissues, involves blood flow.
Cellular respiration: O2 utilized for ATP production.

Membrane requirements: Plasma membranes need to be in aqueous environment for gas exchange.
Diffusion law: Fick's Law of Diffusion governs the rate (R) of diffusion.
- R = (DAΔP)/d
- A = surface area, ΔP = pressure difference, d = distance, D = diffusion constant.
Evolutionary adaptations: To optimize R, systems increased surface area or decreased distance for gas exchange.

Diffusion limits: Oxygen cannot diffuse efficiently over distances greater than 0.5 mm, necessitating adaptations in multicellular organisms.
Water current creation: In organisms without specialized organs; continuously replaces oxygenated water.
Gills and lungs: Provide extensive surface area and bring external environment close to internal fluid.

Gills: Special extensions enabling higher oxygen extraction from water.
External gills: Found in some fish larvae and salamanders; require continuous movement to access oxygenated water.
Branchial chambers: Mollusks use these to pump water over stationary gills.
- Crustaceans utilize limb movement for water circulation around gills.

Gill structure: Comprised of gill arches and filaments, with lamellae providing increased surface area.
Countercurrent flow system: Blood flows in the opposite direction to water, maximizing oxygenation by maintaining a constant concentration gradient.
Oxygen as limiting gas: Fish possess chemoreceptors to monitor oxygen levels, adjusting respiration accordingly.

Cutaneous respiration: Involves gas exchange through skin, common in amphibians and some turtles.
Tracheal systems: Found in terrestrial arthropods, consisting of small tubes that deliver gases directly to cells via spiracles.

Terrestrial adaptations: Lungs evolved due to the unsupported nature of gills in air and the risk of dehydration.
Breathing mechanisms:
- Amphibians: Positive pressure breathing.
Reptiles: Negative pressure by rib cage expansion.

Alveolar structure: Mammalian lungs have millions of alveoli that enhance surface area for gas exchange.
Respiratory tasks: Air flows via trachea to bronchioles, maximizing efficiency.
Breathing regulation: Under nervous system control. Neuronal signals initiate contractions of the diaphragm and intercostal muscles.

COPD and other diseases: Chronic conditions like asthma and emphysema obstruct flow and impact efficiency.
- Emphysema: Alveolar breakdown, requiring increased energy for breathing.

Hemoglobin's role: Binds oxygen in red blood cells; facilitates transport.
Myoglobin in muscles: Serves as an oxygen reserve during intense activity.
Effect of pH and temperature: Affect hemoglobin’s affinity for oxygen through the Bohr effect.

Primary transport methods: 8% dissolved in plasma, 20% bound to hemoglobin, 72% as bicarbonate ions.
Conversion reactions: Involves water, leading to pH balance and gas exchange dynamics in lungs.

Frog Lungs:
- Structure: Simple, sac-like with few internal divisions.
- Function: Use positive pressure breathing; air is forced into lungs by swallowing air.
Bird Lungs:
- Structure: Highly efficient with a system of air sacs; parabronchi allow for unidirectional airflow.
- Function: Utilize a constant supply of fresh air for gas exchange even during exhalation.
Mammal Lungs:
- Structure: Consist of alveoli clustered at the ends of bronchioles; extensive surface area.
- Function: Perform negative pressure breathing; diaphragm and intercostal muscles expand the thoracic cavity.

Structure: Composed of a network of small tubes (tracheae) that open to the outside through spiracles.
Function: Air enters the tracheae, transporting oxygen directly to tissues. No circulatory system involvement; diffusion is sufficient.

The respiratory centers in the brainstem (medulla oblongata and pons) control the rhythm and rate of breathing.
Chemical sensors detect CO2 and O2 levels in blood, adjusting breathing rates accordingly.
Inhalation and exhalation are regulated by neuronal signals controlling diaphragm and intercostal muscle contractions.

Structure: Comprised of four protein subunits (globins) with iron-containing heme groups that bind oxygen.
Function: Each hemoglobin can carry up to four O2 molecules. Its affinity for O2 decreases in lower pH and higher CO2 (Bohr effect), promoting O2 release in tissues requiring it.

Myoglobin:
- Structure: Contains one heme group, typically found in muscle tissue.
- Function: Stores O2; higher affinity for O2 than hemoglobin for release during intense activity.
Hemoglobin:
- Structure: Composed of four heme groups, found in red blood cells.
- Function: Transports O2 from lungs to tissues and CO2 from tissues back to lungs.

CO2 transport methods include:
- 8% is dissolved in plasma.
- 20% is bound to hemoglobin as carbamino compounds.
- 72% is converted into bicarbonate ions in plasma, which helps maintain blood pH.
Diagrammatically, CO2 is transported from body tissues to the lungs primarily in bicarbonate form, with the help of enzymes like carbonic anhydrase facilitating the conversion.