Cellular Respiration and Gas Exchange

• Respiration involves gas exchange, specifically oxygen intake and carbon dioxide removal.
• Cellular respiration is a metabolic process where cells convert biochemical energy from nutrients into adenosine triphosphate (ATP), releasing waste products.
• Gas exchange is the process by which oxygen and carbon dioxide move between the bloodstream and the lungs.
• The respiratory system facilitates gas exchange, supplying oxygen to the body for cellular respiration and eliminating carbon dioxide.

Cellular Respiration

• Aerobic respiration requires oxygen and produces ATP, carbon dioxide, and water.
• Anaerobic respiration occurs without oxygen, producing less ATP and byproducts like lactic acid.
• Glycolysis is the initial stage, breaking down glucose into pyruvate in the cytoplasm.
• The Krebs cycle (Citric Acid Cycle) oxidizes pyruvate in the mitochondrial matrix, generating ATP, NADH, and FADH2.
• The electron transport chain uses NADH and FADH2 to produce a large amount of ATP via oxidative phosphorylation in the inner mitochondrial membrane.
• One glucose molecule yields approximately 32 ATP molecules in aerobic respiration.

Respiratory System Anatomy

• The nasal cavity filters, warms, and humidifies incoming air.
• The pharynx serves as a passageway for both air and food.
• The larynx contains the vocal cords and is essential for sound production.
• The trachea is a cartilaginous tube that conducts air to the lungs.
• The bronchi branch from the trachea into each lung.
• Bronchioles are smaller air passages branching from the bronchi within the lungs.
• Alveoli are tiny air sacs where gas exchange occurs with the capillaries.

Oxygen Transport Mechanisms

• Oxygen is transported in the blood primarily bound to hemoglobin in red blood cells.
• Hemoglobin can bind up to four oxygen molecules.
• The binding of oxygen to hemoglobin is influenced by partial pressure of oxygen (PO2), pH, temperature, and concentration of 2,3-diphosphoglycerate (2,3-DPG).
• The oxygen-hemoglobin dissociation curve illustrates the relationship between PO2 and hemoglobin saturation.
• A rightward shift indicates decreased affinity of hemoglobin for oxygen (occurs with increased temperature, decreased pH, or increased 2,3-DPG).
• A leftward shift indicates increased affinity of hemoglobin for oxygen (occurs with decreased temperature, increased pH, or decreased 2,3-DPG).
• Myoglobin in muscle tissue has a higher affinity for oxygen than hemoglobin, facilitating oxygen storage in muscles.

Carbon Dioxide Removal

• Carbon dioxide is transported in the blood in three forms: dissolved in plasma, bound to hemoglobin (carbaminohemoglobin), and as bicarbonate ions.
• Most carbon dioxide is converted into bicarbonate ions within red blood cells via carbonic anhydrase.
• Carbon dioxide reacts with water to form carbonic acid, which dissociates into hydrogen ions and bicarbonate ions.
• The chloride shift maintains electrical neutrality by exchanging bicarbonate ions for chloride ions across the red blood cell membrane.
• In the lungs, the process reverses, converting bicarbonate back into carbon dioxide, which is then exhaled.
• The Haldane effect describes how oxygen concentrations determine carbon dioxide affinity to hemoglobin. Lower oxygen levels increase carbon dioxide loading onto hemoglobin.

Respiration and Gas Exchange

• Ventilation is the process of moving air in and out of the lungs.
• Inspiration involves contraction of the diaphragm and intercostal muscles, increasing thoracic volume and decreasing pressure.
• Expiration is typically passive, resulting from the relaxation of respiratory muscles, decreasing thoracic volume and increasing pressure.
• Tidal volume is the amount of air inhaled or exhaled during normal breathing.
• Vital capacity is the maximum amount of air that can be exhaled after a maximum inhalation.
• Residual volume is the air remaining in the lungs after maximal exhalation.
• Total lung capacity is the sum of vital capacity and residual volume.
• Partial pressure gradients drive the movement of oxygen from the alveoli into the blood and carbon dioxide from the blood into the alveoli.
• Alveolar ventilation is the amount of air reaching the alveoli per minute.
• The ventilation-perfusion ratio (V/Q) describes the balance between alveolar ventilation and pulmonary blood flow.
• Imbalances in V/Q can lead to hypoxemia (low blood oxygen) and hypercapnia (high blood carbon dioxide).
• The respiratory center in the brainstem controls the rate and depth of breathing.
• Chemoreceptors in the brain and blood vessels monitor carbon dioxide, oxygen, and pH levels, influencing respiratory rate.
• Hering-Breuer reflex prevents over-inflation of the lungs via stretch receptors.