Respiration and Gas Exchange - BL1004

Respiration - BL1004

• Cellular respiration is a set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into ATP (chemical energy)
• The process supplies oxygen for cellular respiration and disposes of carbon dioxide.
• Organisms have various methods for gas exchange depending on their environment, including specialized respiratory surfaces.

Gas Exchange

• Gas exchange involves getting oxygen (O2) to cells and removing carbon dioxide (CO2).
• Respiratory surfaces can be found in flatworms, fish, terrestrial arthropods, mammals and Protozoa.
• Different organisms use different strategies for gas exchange depending on the environment
• Single-celled organisms (e.g., Amoeba, Paramecium) exchange gases across the plasma membrane by simple diffusion.
• Small invertebrates, like flatworms, exchange gases efficiently across their thin body walls due to their size.
• In flatworms, diffusion is adequate for the animal's needs.

Respiratory Systems

• Specialized respiratory organs increase the surface area for gas exchange in organisms with complex structures.
• Specialized respiratory organs like gills are evaginated structures, while lungs are invaginated structures.
• Types of respiratory organs include: lungs, external gills, and internal gills.
• Descriptive terms for these include: branchial for gills, and pulmonary for lungs -Examples of organs/ organisms with relevant respiratory systems include external gills, internal gills, and lungs
• Starfish breathe using tube feet and gills known as branchial papulae.
• Counter-current exchange is an efficient mechanism for gas exchange in fish gills. During this process, blood flows in the opposite direction to the water current over the gills.
• Blood and water flow in opposite directions.
• This allows for gas exchange in low oxygen.
• The efficiency of countercurrent exchange can also occur in mammals using lungs.
• Different respiratory organ types are seen in various species to aid their specific needs

Tracheal Systems in Insects

• The tracheal system in insects consists of tiny branching tubes that penetrate the body.
• Air sacs serve as reservoirs for organs
• Air enters the tracheae through spiracles.
• Tracheoles are closed tubes and contain fluid.
• When insects are active, fluid is withdrawn to increase the surface area for gas exchange.
• Bellow-like movements are used by larger insects to pump air into the tracheal system.
• Gas-exchange surface (tracheoles) in insects is close to all body cells.
• Circulatory systems play a smaller role in insect respiration.

Amphibians

• Larval amphibians often have gills and use their skin for gas exchange.
• Most adult amphibians use lungs and skin for respiration.
• Some adult amphibians, like mudpuppies (Necturus) and axolotl, retain gills.
• Some salamanders breathe only through highly vascularized skin that needs lots of blood vessels.
• Some frogs hibernate in water and use their skin for breathing.

Birds

• Bird lungs are rigid and do not change volume much during breathing.
• Air sacs expand and contract for breathing.
• Air flows unidirectionally through the bird's gas exchange system.
• This is a crucial component of the bird´s cross-current system
• Air sacs are crucial for efficient oxygen uptake

Mammals - Lungs

• Mammalian lungs have many branching airways (bronchi) and millions of alveoli.
• Alveoli provide a large surface area for gas exchange, proportionate to size.
• The gas exchange surface area of human lungs is equivalent to the surface area of a tennis court
• The barrier between blood and air in mammalian lungs is only two cell layers thick.
• Blood vessels and alveoli are closely interconnected in mammalian lungs

Movement of Air

• Buccal pressure is used for air-breathing in fish and amphibians.
• Suction/ aspiration is used in reptiles, mammals, and birds for breathing.
• Mammals and birds use thoracic and abdominal muscles during breathing.
• Tidal volume in humans is approximately 500 mL.
• Vital capacity in humans is 3.4 to 4.8 liters.
• Residual volume in humans is approximately 1.5 liters

Respiratory Pigments

• Respiratory pigments are required to bind and transport gases.
• O2 has low solubility in water; pigments help overcome this.
• Hemoglobin (Fe) is the respiratory pigment in almost all vertebrates.
• It's in red blood cells.
• Hemocyanin (Cu) is a respiratory pigment found in arthropods and most mollusks.

Oxygen Transport

• Hemoglobin reversibly binds and releases oxygen (O2) according to the partial pressure of oxygen (PO2)
• Loading/ unloading of oxygen happens in the lungs and tissues respectively.