Chapter 14: Breathing and Exchange of Gases

Answer: The diaphragm is a dome-shaped muscle that plays a crucial role in breathing. During inspiration, the diaphragm contracts and flattens, increasing the volume of the thoracic cavity and decreasing the intra-thoracic pressure, allowing air to be drawn into the lungs. During expiration, the diaphragm relaxes and returns to its dome shape, decreasing the thoracic volume and increasing the pressure to expel air.

Answer: Oxygen and carbon dioxide are exchanged by diffusion in the respiratory system because this process is driven by concentration gradients. Oxygen moves from areas of high partial pressure in the alveoli to lower partial pressure in the blood, while carbon dioxide moves from higher partial pressure in the blood to lower partial pressure in the alveoli. Active transport is unnecessary as diffusion is efficient for gas exchange due to the small size and high permeability of these molecules through the respiratory membranes.

Answer: Hemoglobin is a protein found in red blood cells that binds to oxygen. Each molecule of hemoglobin can bind up to four molecules of oxygen, forming oxyhemoglobin. This enables the efficient transport of oxygen from the lungs to the tissues. Oxygen binding is dependent on the partial pressure of oxygen, which changes between the lungs and tissues, facilitating loading and unloading.

Answer: People living at high altitudes adapt to lower oxygen levels through increased breathing rate and depth (hyperventilation), increased red blood cell production, higher hemoglobin levels, and increased capillarization in tissues to enhance oxygen delivery. Over time, these adaptations improve oxygen uptake and usage in low oxygen environments.

Answer: When carbon dioxide levels in the blood increase, it leads to a decrease in blood pH, activating chemoreceptors in the medulla. This stimulates the respiratory center to increase the rate and depth of breathing to expel more carbon dioxide and restore normal pH levels.

Answer: The oxygen dissociation curve shows the relationship between oxygen saturation of hemoglobin and partial pressure of oxygen. It is sigmoidal due to cooperative binding, where each oxygen molecule binding increases the likelihood of further binding. This curve shifts right with increased temperature, CO2, and H+ concentration, promoting oxygen release to tissues.

Answer: Pulmonary surfactants are lipoproteins secreted by alveolar cells that reduce surface tension in the alveoli, preventing their collapse and making it easier for the lungs to expand during breathing. This ensures stable and effective gas exchange by maintaining alveolar integrity.

Answer: Smoking damages the respiratory tract, leading to chronic inflammation, reduced lung function, and impaired gas exchange. It introduces toxins that can cause COPD, emphysema, and cancer. Smoking decreases ciliary function, affecting mucus clearance and increasing infection risk.

Answer: Breathing rate is directly influenced by CO2 concentration. High CO2 levels increase acidity (lower pH) in the body, stimulating chemoreceptors that trigger the brain to increase breathing rate, enhancing CO2 elimination to stabilize pH.

Answer: The respiratory system has several defense mechanisms, including nasal hairs and mucous lining to trap particles, cilia to move debris out of the airways, immune cells like macrophages in the alveoli to engulf pathogens, and reflexes like coughing to expel foreign substances.