3.15 – The Respiratory System The Importance of Gas Exchange Organisms require oxygen to oxidize glucose in the mitochondria of cells, in order to produce energy in the form of ATP A gas exchange system functions to bring oxygen to cells via a transport system (blood and vessels) Waste products of cellular respiration (CO2) are transported from cells to the gas exchange surface to be excreted Respiration and Breathing breathing (ventilation) – process by which air enters and leaves the lungs external respiration – exchange of gases between air and blood internal respiration – exchange of gases between blood and ECF cellular respiration – process by which glucose is broken down to release energy stored in chemical bonds all gas exchange surfaces must be moist, provide adequate surface area, and be able to transport gases to cells and back again earthworms use their entire skin as a gas exchange surface amphibians and aquatic organisms use folded and branched gills to increase surface area for the diffusion of gases

The Human Respiratory System (Fig. 3, P. 219) humans are endothermic (“warm-blooded) with a high oxygen demand air enters through nostrils nasal navity separated from mouth cavity by bony platform (hard palate) sagging shelves (turbinate bones) increase surface area incoming air is warmed by blood vessels in skin, moistened by secretions of epithelial tissue, filtered by mucus and hairs pharynx is a muscular tube common to digestive and gas exchange systems epiglottis is a leaf-shaped flap which seals the opening of the trachea during swallowing larynx (voice box) is a cartilagenous structure that surrounds the anterior end of the trachea vocal cords are two flaps of cartilage across trachea that vibrate as air passes through; pitch changed by contraction of muscle holding cords in place (see Fig. 4, P. 219)

trachea consists of incomplete cartilage rings imbedded in smooth muscle, prevent windpipe from collapsing (esophagus runs down dorsal surface) branch into 2 cartilagenous bronchi, surrounded by smooth muscle to decrease diameter of air passage bronchi continuously branch into non-cartiliagenous bronchioles, each terminating in many alveoli (150 million in each lung) surrounded by a network of capillaries where gas exchange occurs inner lining of trachea, bronchi, and bronchioles covered by cilia and mucus-producing goblet cells (Fig. 5, P. 220) cilia constantly sweep bacteria, dust, and pollen that gets trapped in mucus, up and out out of lungs (“bronchiole escalator”) gas exchange surface must be moist and of sufficient surface area for diffusion to occur

How We Breathe (Fig. 7&8, P. 221) pleural (lung) cavity is closed, glottis is only opening air will always move from high to low pressure during inspiration, diaphragm muscles contract and move down (flatten), external intercostal muscles (between ribs) contract, moving ribcage up and out internal pressure less than external  air moves into lungs to equalize pressure during expiration, diaphragm and intercostal muscles relax, pulling ribs in and down  increased pressure in pleural cavity  air moves out of lungs to equalize pressure fluid-filled double pleural membrane reduces friction during breathing a hole in the pleural cavity makes it impossible to establish pressure differences (collapsed lung)(remember Mark Wahlberg in “Three Kings”?)

Control of Breathing alternating pattern of inspiration and expiration controlled by the autonomic nervous system, by nerve impulses from a breathing centre in brain CO2 levels are monitored and breathing rate increases with CO2 concentration  Control of Breathing Activity

Breathing in Extremes  at high altitudes, O2 concentration is low  breathing rate and red blood cell production increases to compensate  under water, regulators of air supply compensate for pressure changes with depth  pure O2 is deadly when breathed below 7 m Sections 3.15 Questions – P. 223-224, #1-9 Activity 3.16 – Determining Lung Volumes