The Respiratory System Chapter 44

Respiration Cellular respiration – in the mitochondria (see chapter 7) Organismic respiration – O 2 from the environment is taken up and delivered to individual cells; CO 2 generated by the cells is excreted to the environment In organisms more than 1mm thick diffusion occurs too slowly to support life – specialized respiratory structures are needed

Adaptations Structures must be moist for diffusion across the surface A rich supply of blood is important The larger the surface area of the structure, the more efficient the gas exchange Gills – specialized for oxygen removal from water; tend to collapse out of water Lungs – often located deep inside body to minimize desiccation Advantages of air-breathing: Air contains a higher %age of O 2 compared to water O 2 diffuses faster and requires less energy to move through the less dense air than water

Mammalian Respiratory System Nostrils and nasal cavities: Filters, warms, moistens air Pharynx – joins with the throat and connects to larynx or voice box; rings of cartilage hold it open Epiglottis – closes up and over the larynx during swallowing Trachea: Also has rings of cartilage Divides into bronchial tubes Lungs: Left lung has two lobes; the right has three Both are surrounded by the pleural membrane Bronchial tubes divide many times into bronchioles that end in alveoli Alveoli: Each lung has surface area the size of a tennis court They are lined with one layer of epithelial cells

Breathing Inhalation: Volume of thoracic cavity is increased by the contraction of the diaphragm and intercostal rib muscles This decreases the air pressure inside the lungs and outside air rushes in Exhalation: Diaphragm relaxes and thoracic cavity volume decreases, putting pressure on air in lungs Pulmonary surfactant – a phospholipid mixture is released by the alveoli and reduces the surface tension of the water molecules within them This reduces the work of breathing This chemical is missing in preemies which is why they may need to be placed on a respirator

Transportation of oxygen Plasma alone can hold 0.25 mL of O 2 per 100 mL But this O 2 diffuses into the RBCs and combines with hemoglobin – now blood can carry 20 mL/100 mL When combined with O 2, hemoglobin is bright red & called oxyhemoglobin This reaction is easily reversible and oxyhemoglobin releases O 2 into the body tissues

Transportation of CO 2 10% dissolves in blood plasma 30% enters RBCs and binds with hemoglobin (but in a different spot than O 2 ) 60% moves through plasma as bicarbonate ions (HCO 3 - ) In plasma, CO 2 combines with H 2 O to form carbonic acid

Regulation of Breathing CO 2 concentration is the most important chemical stimulus for regulating respiration rate Chemoreceptors in the medulla, aorta, & carotid arteries send impulses when stimulated to increase rate when CO 2 levels are high Breathing is involuntary but can be controlled for short periods of time

Respiratory Health Issues Cardiopulmonary resuscitation May keep a person alive until normal breathing reflexes return Hyperventilation Not enough CO 2 is present in the blood, increasing its acidity and constricting blood vessels Hypoxia Not enough O 2 in the blood Decompression syndrome If outside pressure is less than the total pressure of gases in the blood, they will come out of solution and form bubbles