Aerobic Cellular Respiration and Gas Exchange

Aerobic Cellular Respiration

• Cells require oxygen for survival and energy production through aerobic cellular respiration.
• Glucose reacts with oxygen to create carbon dioxide and water, releasing energy.
• 64% of the released energy is thermal energy.
• The remaining 36% is stored in adenosine triphosphate (ATP) molecules.
• ATP powers cellular functions like growth, movement, and molecule synthesis.
• The formula for ATP production is ADP + Phosphate + Energy → ATP

Gas Exchange and Ventilation

• Gas exchange involves oxygen diffusion into cells and carbon dioxide diffusion out.
• Simple organisms directly exchange gases through their cell membranes.
• Multicellular organisms have specialized systems (e.g., lungs) for gas exchange to reach internal cells.
• Two primary locations for gas exchange are cells and lungs.
• Lungs facilitate oxygen diffusion into the bloodstream, and the subsequent delivery to body cells.
• Oxygen diffuses from the bloodstream into tissue fluid, and then into cells.
• Carbon dioxide travels in the reverse direction—from cells to lungs.
• Ventilation (breathing) moves air rich in oxygen into the lungs and air rich in carbon dioxide out.

Respiratory Structures

• The human respiratory system has crucial components:
  • A thin, permeable respiratory membrane for efficient diffusion.
  • A large surface area for gas exchange.
  • An ample blood supply to facilitate transport.
• The air pathway includes the nose/mouth, pharynx, trachea, bronchi, and bronchioles terminating in alveoli.
• Nasal passages warm and humidify the air and filter particles.
• The trachea (windpipe) is reinforced by cartilage rings to maintain its shape.
• Cilia in the trachea move trapped particles upwards for expulsion.
• Alveoli—tiny sacs—are the site of gas exchange, with a massive surface area (enough to cover a tennis court).

Gas Exchange in the Alveoli

• Alveoli air is humidified and at body temperature (37°C) — these conditions are necessary for oxygen's ability to diffuse across the membrane.
• The respiratory membrane (one cell thick) efficiently facilitates gas diffusion.

Partial Pressures

• Air pressure is measured in kilopascals (kPa).
• At sea level, air pressure is 101.3 kPa, decreasing with altitude.
• Partial pressure measures the pressure of each gas in a mixture (e.g., oxygen's part of air pressure).
• Oxygen makes up approximately 20.9% of ambient air; carbon dioxide comprises 0.0391%.
• Oxygen partial pressure (PO2) at sea level and 101.3kPa is 21.17 kPa.
• Carbon dioxide partial pressure (PCO2) at sea level and 101.3kPa is 0.0397 kPa.

Oxygen Transport and Diffusion

• Alveolar PO2 is higher than capillary PO2; this drives oxygen diffusion into the blood.
• Hemoglobin carries most of the oxygen (98.5%) in the blood, as oxyhemoglobin, increasing blood's oxygen-carrying capacity significantly (70x).
• At the tissues, oxygen diffuses from the blood into cells.

Carbon Dioxide Transport and Diffusion

• Carbon dioxide, a cellular respiration byproduct, diffuses from tissues into the bloodstream.
• Transport routes for CO2 include:
  • Dissolved in plasma (7%).
  • Bound to hemoglobin (20%) as carbaminohemoglobin.
  • Reacting with water to form carbonic acid, dissociating into bicarbonate and hydrogen ions (73%).
• Maintaining blood pH is critical; CO2 removal is essential for this.
• The reactions in the lungs reverse the bicarbonate/CO2 conversion to allow CO2 release.

Altitude Effects

• Reduced atmospheric pressure at higher altitudes decreases the partial pressure of oxygen, affecting diffusion rates.
• Altitude sickness occurs with decreased oxygen supply, marked by symptoms like shortness of breath.
• The body adapts to lower oxygen levels through erythropoietin (EPO) production, which increases red blood cell count.

Mechanism of Ventilation

• Inspiration: Intercostal muscles and diaphragm contract, increasing lung volume and reducing pressure, drawing air into the lungs.
• Expiration: Intercostal muscles and diaphragm relax, decreasing lung volume and increasing pressure, forcing air out of the lungs.

Lung Capacity

• Lung capacity measures the maximum air volume in the lungs, involving tidal volume, inspiratory reserve volume, expiratory reserve volume, and residual volume.
• Vital capacity is the maximum amount of air exhaled after a maximal inspiration.

The Need for Circulation

• Unicellular and some simple multicellular organisms don't need a circulatory system because cells are in direct contact with the environment.
• Multicellular organisms need a circulatory system to transport oxygen, nutrients, and remove waste products, as most cells are not in direct contact with the environment.

Key Functions of the Circulatory System

• Delivering oxygen from lungs.
• Delivering nutrients from digestive system.
• Delivering hormones from endocrine system.
• Delivering immune factors.
• Removing metabolic wastes.
• Maintaining body temperature.

Fundamental Features of Circulation

• A circulating fluid (blood).
• A network of tubes (vessels).
• A pump (heart).

Open vs. Closed Circulatory Systems

• Open circulatory systems are found in invertebrates; blood (hemolymph) isn't always contained in vessels.
• Closed circulatory systems, found in vertebrates, have blood confined within vessels, leading to faster flow and greater pressure.

Components of Blood

• Blood is a connective tissue comprising cells (cellular components) suspended in plasma (intercellular matrix).
• Cellular components include red blood cells (erythrocytes), white blood cells (leukocytes), and platelets.
• Plasma is a protein-rich fluid with oxygen, carbon dioxide, nutrients, waste products, and various proteins and ions.

Blood Vessels

• Arteries carry blood away from the heart.
• Arterioles are the smallest arteries, regulating blood flow.
• Capillaries are tiny vessels where exchange occurs between blood and tissues.
• Venules and veins return blood to the heart.

Blood Pressure

• Blood pressure is the force of blood against artery walls.
• Systolic pressure is the maximum during heart contraction; diastolic pressure is the minimum during heart relaxation.
• Normal blood pressure is typically around 120/80 mm Hg.

High and Low Blood Pressure

• High blood pressure (hypertension) damages artery walls, increasing stroke and heart attack risk; a healthy lifestyle can help prevent or manage hypertension.
• Low blood pressure (hypotension), if not symptomatic, is not a concern.

Structure of the Heart

• The heart is a muscular pump with atria (receiving chambers) and ventricles (pumping chambers).
• Valves ensure one-way blood flow.
• The left ventricle has a thicker wall to pump blood throughout the body.
• The heart's own blood supply, powered by coronary arteries and veins, is essential.

Cardiac Cycle

• The cardiac cycle consists of diastole (relaxation and filling) and systole (contraction and emptying).
• Heart sounds (lub-dub) result from valve closure.

Regulation of Heart Rhythm

• Heart rhythm is initiated by the sinoatrial (SA) node (pacemaker).
• The sympathetic and parasympathetic nervous systems modulate heart rate.

Electrocardiogram (ECG)

• ECG measures electrical activity of the heart.
• Waves on the ECG correspond to different stages of the cardiac cycle.

This quiz covers key concepts of aerobic cellular respiration and gas exchange processes in organisms. You'll learn how cells utilize oxygen and glucose to produce energy in the form of ATP, as well as how gases are exchanged throughout the body. Test your understanding of these essential biological functions and their importance for life.