BIOL160 Chapter 34 Respiration PDF

BIOL160 Chapter 34 Respiration 1  34.1 Why Exchange Gases and What Are the Requirements for Gas Exchange?  34.3 How Is Air Conducted Through the Human Respiratory System?  34.4 How Does Gas Exchange Occur in the Human Respiratory System?...

BIOL160 Chapter 34 Respiration 1  34.1 Why Exchange Gases and What Are the Requirements for Gas Exchange?  34.3 How Is Air Conducted Through the Human Respiratory System?  34.4 How Does Gas Exchange Occur in the Human Respiratory System? 2 34.1 Why Exchange Gases and What Are the Requirements for Gas Exchange?  The exchange of gases supports cellular respiration  As cellular respiration converts the energy in nutrients (such as sugar) into the ATP that supplies cellular energy, the process requires a steady supply of O2 and generates CO2 as a waste product  Respiration, is the process by which organisms exchange gases with the environment, taking in oxygen and releasing CO2, in support of cellular respiration 3 34.1 Why Exchange Gases and What Are the Requirements for Gas Exchange?  Gas exchange in all organisms ultimately relies on diffusion  All animals facilitate diffusion through three adaptations 1. Respiratory surfaces remain moist, because cell membranes are always moist, and only gases dissolved in water can diffuse into or out of cells 2. Respiratory surfaces are very thin to minimize diffusion distances 3. Respiratory surfaces have a sufficiently large surface area in contact with the environment to allow adequate gas exchange by diffusion to meet the needs of the organism  During diffusion, individual molecules move from areas of high concentration to areas of lower concentration, so gas exchange by diffusion requires concentration gradients of gases 4 34.3 How Is Air Conducted Through the Human Respiratory System?  The respiratory system in humans and other mammals can be divided into two parts 1. The conducting portion, which consists of a series of passageways that carry air into and out of the gas-exchange portion of the respiratory system 2. The gas-exchange portion within the lungs, where oxygen and carbon dioxide are exchanged through the blood 5 34.3 How Is Air Conducted Through the Human Respiratory System?  The conducting portion of the respiratory system carries air to the lungs  The conducting portion carries air to the lungs and contains the apparatus that makes speaking possible - Air enters through the nose or mouth and passes through the nasal or oral cavity into a chamber called the pharynx - It then travels to the larynx , or “voice box,” where sounds are produced - The opening to the larynx is guarded by the epiglottis, a flap of tissue supported by cartilage 6 7 34.3 How Is Air Conducted Through the Human Respiratory System?  The conducting portion of the respiratory system carries air to the lungs (continued)  During normal breathing, the epiglottis is tilted upward, allowing air to flow into the larynx  During swallowing, the epiglottis folds downward and covers the larynx, directing substances into the esophagus  Within the larynx are the vocal cords, bands of elastic tissue controlled by muscles  Muscular contractions can cause the vocal cords to partially obstruct air passage through the larynx  Exhaled air causes the vocal cords to vibrate, producing the tones of speech or song 8 34.3 How Is Air Conducted Through the Human Respiratory System?  The conducting portion of the respiratory system carries air to the lungs (continued)  Inhaled air travels past the larynx into the trachea, a flexible tube whose walls are reinforced with semicircular bands of stiff cartilage  The trachea splits into two bronchi, one leading to each lung  In the lung, each bronchus branches repeatedly into ever smaller tubes called bronchioles  Bronchioles lead to microscopic alveoli, the tiny air sacs where gas exchange occurs 9 34.3 How Is Air Conducted Through the Human Respiratory System?  Air is inhaled actively and exhaled passively - Breathing occurs as inhalation and exhalation cause bulk flow of air into and out of the lungs - Inhalation occurs when the chest cavity is enlarged - The lower boundary of the chest cavity is formed by a sheet of muscle, the diaphragm, which domes upward when relaxed - During inhalation, the diaphragm is contracted, which pulls it downward - The rib muscles also contract, lifting the ribs up 10 34.3 How Is Air Conducted Through the Human Respiratory System?  Air is inhaled actively and exhaled passively (continued) - Breathing occurs as inhalation and exhalation cause bulk flow of air into and out of the lungs (continued) - Exhalation occurs spontaneously when the muscles that cause inhalation are relaxed - As the diaphragm relaxes, it domes upward; at the same time, ribs move downward and inward - Both of these movements decrease the size of the chest cavity, forcing air out of the lungs 11 34.3 How Is Air Conducted Through the Human Respiratory System? 12 34.3 How Is Air Conducted Through the Human Respiratory System?  Breathing rate is controlled by the respiratory center of the brain  Unlike the heart muscle, the diaphragm and rib muscles used in breathing are not self- activating - Each contraction causing inhalation is stimulated by impulses from nerve cells - These impulses originate in the respiratory center, which is located in the medulla, a portion of the brain just above the spinal cord  The respiratory center receives input from several sources and adjusts the breathing rate and volume to meet the body’s changing needs - The respiratory rate is primarily regulated by CO2 receptors, also located in the medulla - These adjust the breathing rate to maintain an extremely constant, low level of CO2 in the blood, while ensuring that O2 levels remain adequate 13 34.4 How Does Gas Exchange Occur in the Human Respiratory System?  Gas exchange occurs in the alveoli  Gases enter and leave the blood by diffusion within the lungs  The human lung provides a moist, well-protected air cavity where exquisitely fragile membranes separate atmospheric air from the bloodstream  Alveoli cluster around the end of each bronchiole like a bunch of grapes, providing a huge surface area for diffusion  In an average adult, the two lungs combined have approximately 300 million alveoli 14 34.4 How Does Gas Exchange Occur in the Human Respiratory System?  Gas exchange occurs in the alveoli (continued)  The insides of the alveoli are coated with a thin layer of watery fluid containing a surfactant (a detergent-like substance composed of proteins and lipids), which prevents the fragile alveolar surfaces from sticking together and collapsing when air is exhaled 15 34.4 How Does Gas Exchange Occur in the Human Respiratory System?  Gas exchange occurs in the alveoli (continued)  A network of capillaries covers most of the alveolar surface  The walls of the alveoli consist of a single thin layer of epithelial cells  The respiratory membrane, through which gases diffuse, consists of epithelial cells of the alveoli and the endothelial cells that form the wall of the capillary across which gas exchange occurs 16 34.4 How Does Gas Exchange Occur in the Human Respiratory System? from the to the pulmonary vein pulmonary artery capillary capillary walls alveolar wall respiratory (air) membrane surfactant fluid protein fibers Oxygen diffuses into Carbon dioxide diffuses the red blood cells into the alveolus 17 34.4 How Does Gas Exchange Occur in the Human Respiratory System?  Oxygen and carbon dioxide are transported in blood using different mechanisms  Blood picks up oxygen from the air in the lungs and supplies it to the body tissues, simultaneously absorbing CO2 from the tissues and releasing it into the lungs  These exchanges occur because diffusion gradients favor them - In the lungs, O2 is high and CO2 is low, whereas in body cells, CO2 is high and O2 is low 18 34.4 How Does Gas Exchange Occur in the Human Respiratory System?  Nearly all (about 98%) of the O2 carried by the blood is bound to hemoglobin, a large protein that gives red blood cells their color  Each hemoglobin molecule can carry up to four O2 molecules, each bound to each of four iron-containing heme groups embedded in the protein  As oxygen binds hemoglobin, the protein changes its shape, which alters its color; oxygenated blood is bright cherry-red, and deoxygenated blood is maroon-red 19 34.4 How Does Gas Exchange Occur in the Human Respiratory System? 20 34.4 How Does Gas Exchange Occur in the Human Respiratory System?  CO2 from cellular respiration in the body cells diffuses into nearby capillaries, then is carried in the bloodstream to the respiratory membranes of the alveoli  Blood transports CO2 in three different ways  Roughly 10% is dissolved in the plasma  About 20% is bound to hemoglobin  And most of it (about 70%) combines with water to form bicarbonate ions (HCO3) in the following reaction: - CO2  H2O H  HCO3 21 34.4 How Does Gas Exchange Occur in the Human Respiratory System?  The HCO3 then diffuses into the plasma  Most of the H remains bound to hemoglobin in the red blood cells  These reactions keep the amount of CO2 dissolved in the plasma low, which increases the gradient for CO2 to diffuse into the plasma from the body cells, where CO2 levels are relatively high  The reaction producing bicarbonate ions is reversed as the blood flows through capillaries surrounding the alveoli, where CO2 is low:  H  HCO3 CO2  H2O  The CO2 then diffuses into the air in the alveoli, and the air is exhaled from the lungs while the H2O remains in the blood 22 (air in alveolus) CO2 transport from the tissues to the lungs 23