Biology 12 Respiration Divisions of Respiration Breathing: entrance and exit of air into and out of the lungs External Respiration: exchange of gases(o2 and CO2) between air (in alveoli) and blood Internal Respiration: exchange of gases between blood and tissue fluid Cellular Respiration: production of ATP in cells. Breathing: The normal rate is about 14 to 20 times a minute. Taking in of air is called Inspiration and the forcing out of air is called Expiration. 1. Nasal cavity - warms and moistens air, cilia filter out debris. 2. Pharynx - common passageway for air to trachea and food to esophagus. 3. Larynx - at top of trachea, voice box - contains vocal cords. 4. Trachea - wind pipe, held open by rings of cartilage, contains mucus to trap debris and cilia to sweep it out. 5. Bronchus - divides off trachea, one to each lung (pl = bronchi) 6. Lung - exchange of gases between air and blood 7. Bronchioles - smaller airways, end in alveoli. 8. Alveoli - not shown, site of gas exchange within lungs.
Alveoli: sack-like structures at the end of each branch of the bronchioles. Supplied with a net-work of capillaries which pick up oxygen which we breathe in. Carbon dioxide diffuses into them from the blood and we breathe it out. The walls are very thin. Pleural Membranes: The membranes which enclose the lungs themselves. The outer pleural membrane adheres closely to the walls of the chest and diaphragm and the inner is fused to the lungs. The two membranes lie very close to one another, being separated by a thin film of fluid. Pleural membranes help keep the lungs inflated and allow the lungs to move freely and without friction in the thoracic cavity. Cilia: Lining the upper air-way (trachea and bronchi) there are ciliated cells which help to keep the wind-pipe free of debris. Smoking is known to destroy the cilia.
Nervous System Control of Breathing: During inspiration the Respiratory Center (in the medulla oblongata) stimulates the rib (intercostal) muscles and the diaphragm to contract. Nerve impulses from the expanded lungs then inhibit the respiratory center. Lack of stimulation causes the rib muscles and diaphragm to relax and expiration follows. When the concentration of CO 2 and H + ions (also HCO 3 - ions) reach a certain level in the blood, the breathing center in the medulla oblongata is stimulated. So inspiration will occur. Oxygen levels in the blood do not affect the breathing centre directly. Low oxygen levels do stimulate special receptors in the aorta and carotid arteries (called aortic and carotid bodies) which send a message to the brain to tell the person to breathe in. Mechanics of Breathing Diaphragm - contracts, pulls down and flat Rib muscles - contract (shorten) Ribs - move up and out Thoracic cavity size - increases Thoracic cavity pressure - decreases Diaphragm - relaxes, up and domed Rib muscles - relax Ribs - move down Thoracic cavity size - decreases Thoracic cavity pressure - increases
Exchange of Gases
Oxyhemoglobin - HbO 2 The red protein based chemical Hemoglobin has the ability to combine with oxygen to form oxyhemoglobin. It is in this form that oxygen is transported in the blood. Carbaminohemoglobin - HbCO 2 Most of the carbon dioxide transported in the blood stream is carried in the form of Bicarbonate ions (see below) but a very small amount can be carried combined with hemoglobin to form Carbaminohemoglobin Hb can transport more O 2 than CO 2, therefore, excess CO 2 combines with water in the plasma forming carbonic acid (H 2 CO 3 ). This acid dissociates into bicarbonate ions (HCO - 3 ) and H + ions. An increase in H + causes the ph of the blood to drop (become acidic). Oxyhemoglobin releases its O 2 and combines with the H + ions to form reduced hemoglobin (HHb) Therefore, Hb acts to buffer the blood. Connections: Actively metabolizing cells need O 2 and they produce CO 2. The following balance shows what happens in the blood capillaries surrounding actively metabolizing cells.