Chapter 33 Respiration BSC 1005 Tidwell Bulk Flow down a pressure gradient Gases are transported between the respiratory system and the tissues by the bulk flow of blood as it is pumped throughout the body Gases are exchanged between the tissues and the circulatory system by diffusion at the tissues O2 moves out of the capillaries into tissues and CO2 moves from the tissues to the capillaries Concurrent Exchange maintain a relatively constant concentration gradient water and blood flow in opposite directions within the gill Terrestrial animals have internal respiratory structures o Internal respiratory structures are used by most terrestrial animals to help keep o Two examples of these types of respiratory structures are the tracheae in insects the respiratory surfaces moist and lungs in vertebrates Tracheae are elaborately branched internal tubes that deliver air to the body cells o Air enters tracheae though abdominal openings spiracles o The spiracles open into tracheae that branch into smaller tubes tracheoles which deliver air close to each body cell for O2 and CO2 exchange o Some insects use abdominal contractions to enhance air movements into and out of spiracles are chambers containing moist respiratory surfaces that are protected within the Lungs body where water loss is minimized and the body wall provides support o Amphibians use gills for respiration as aquatic larvae and a simple sac like lung when they metamorphose into the adult form o The bird lung has adaptations that allow exceptionally efficient gas exchange providing adequate O2 to support the enormous demands of flight Birds use seven to nine inflatable air sacs which do not exchange gases but rather act as reservoirs for air Bird lungs are rigid and filled with thin walled tubes parabronchi which are open at both ends allowing air to flow completely through the lungs The parabronchi are surrounded by tissue riddled with microscopic spaces and a dense capillary network that allows gas exchange The human respiratory system can be divided into two parts o The conducting portion a series of passageways that carry air into and out of the gas exchange portion of the respiratory system Page 1 of 3 Chapter 33 BSC 1005 Tidwell 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 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 Inside the lung each bronchus branches repeatedly into ever small tubes called bronchioles Bronchioles lead to microscopic alveoli the tiny air sacs where gas exchange occurs A network of capillaries covers most of the alveolar surface 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 o The gas exchange portion where gases are exchanged with the blood in tiny sacs within the lungs Oxygen transport o 98 of the Oxygen carried by the blood is bound to hemoglobin 2 of the Oxygen is dissolved in and carried by the plasma o Each hemoglobin molecule can carry up to four Oxygen molecules o As oxygen binds hemoglobin the protein changes shape which alters its color oxygenated blood is bright cherry red and deoxygenated blood is maroon red Carbon dioxide transport o CO2 from cellular respiration in the body cells diffuses into nearby capillaries and then is carried in the blood stream to the respiratory membranes of the alveoli Alveoli capillaries have a higher CO2 concentration than that of the alveolar air thus CO2 diffuses down a concentration gradient into the alveolar air which is then exhaled o CO2 is transported in the blood in three ways As bicarbonate ions 70 Bound to hemoglobin 20 Dissolved in plasma as CO2 10 o Bicarbonate ions are formed in red blood cells when CO2 combines with water using the enzyme carbonic anhydrase Page 2 of 3 Chapter 33 BSC 1005 Tidwell The respiratory center is located in the medulla portion of the brain just above the spinal cord o Nerve cells in the respiratory center generate cyclic action potentials that cause contractions followed by passive relaxation of respiratory muscles o The respiratory center receives input from several sources and adjusts the breathing rate and volume to meet the body s changing needs o Breathing rate can be primarily modified by CO2 receptors located in the medulla that adjust the breathing rate to maintain a constant low level of CO2 in the blood while also ensuring that O2 levels remain adequate o As a backup system there are also O2 receptors in the aorta and carotid arteries that stimulate the respiratory center to increase the rate and depth of breathing if O2 levels in the blood drop Page 3 of 3