6.4 GAS EXCHANGE

Ventilation Gas Exchange Cell Respiration ATP energy + 6CO 2 + 6H 2 0  C 6 H 12 O 6 + 6O 2 Air O 2 diffuses into alveolus CO 2 diffuses out of alveolus O 2 diffuses into lung capillary O 2 diffuses out of body capillary into cell O 2 is a reactant for aerobic cell respiration CO 2 is a product of aerobic cell respiration CO 2 diffuses into body capillary out of cell CO 2 diffuses out of lung capillary

Ventilation The process of inhaling and exhaling – bringing air into and out of lungs.

Gas Exchange The diffusion of gasses (O 2 and CO 2 ) across a cell membrane. This occurs: 1. Between the capillaries and alveoli of the lungs O 2 enters the bloodstream CO 2 leaves 2. In capillary beds around the body O 2 exits the bloodstream CO 2 enters

Cell Respiration Takes place in your cells. 6O 2 + C 6 H 12 O 6  6CO 2 + 6H 2 O + ATP energy Aerobic cell respiration requires mitochondria – happens when oxygen is present. Anaerobic cell respiration occurs in the cytosol – happens when oxygen is NOT present, produces lactic acid (which makes your muscles sore)

WHY? Define ventilation. [1] Deduce why we need a ventilation system. Try to write down 2 – 3 reasons Hint: imagine life as a single celled organism Hint: consider diffusion

Ventilation system diagram

WHY: A ventilation system is needed to maintain high concentration gradients in the alveoli. We want O 2 to diffuse from the alveoli into the capillary We want CO 2 to diffuse out of the capillary into the alveoli.

Alveoli Alveoli are adapted to perform gas exchange: The have a LARGE surface area (to volume ratio) They have a LARGE and dense capillary network surrounding them. Their walls are a single cell- layer thick There is a film of moisture around them.

Video

Type I Pneumocytes Each alveolus has a single layer of cells (epithelium) Most epithelium cells in the alveolus are Type I Are adapted to carry out gas exchange: Thin & flattened cells How to remember: I is a “thin” # and so are the cells

Type II Pneumocytes Each alveolus has a single layer of cells (epithelium) 5% of epithelium cells in the alveolus are Type II Rounded cells Secrete fluid to coat inner surface of alveoli Moisture allows O 2 in alveolus to dissolve, then diffuse to the blood in alveolar capillaries Provides area from which CO 2 can evaporate into air and be exhaled How to remember: II is a “thicker” # and so are the cells

HOW do we breathe? The mechanism of Ventilation

Inhaling 1. We draw air into the lungs by contracting & lowering our diaphragm. Our external intercostal muscles are contracting, drawing the ribs outwards. This causes an overall increase in lung volume and decrease in lung pressure.

Exhaling 1. We push air out of the lungs by relaxing & raising our diaphragm. In “quiet breathing” our external intercostal muscles are relaxing. In “forced breathing” our internal intercostal muscles and abdominal muscles contract to force more air out of the lungs. This causes an overall decrease in lung volume and increase in lung pressure.

Antagonistic Muscle Action InspirationExpiration DiaphragmMoves DOWNWARDS and flattens Moves UPWARDS and becomes more domed RibcageMoves UPWARDS and OUTWARDS Moves DOWNWARDS and INWARDS Ventilation involves two pairs of opposite movements that change the volume and the pressure inside the thorax Antagonistic muscles work opposite of each other. One contracts while the other relaxes EXTERNAL INTERCOSTAL MUSCLES DO THIS INTERNAL INTERCOSTAL MUSCLES DO THIS

Antagonistic pairs of muscles are needed to cause these movements.

Pulmonary Disorders Chronic Bronchitis Emphysema Asthma Lung Cancer

Time since quittingBeneficial health changes that take place 20 minutesBlood pressure and pulse rate return to normal. 8 hours Nicotine and carbon monoxide levels in blood reduce by half, oxygen levels return to normal. 24 hoursCarbon monoxide will be eliminated from the body. Lungs start to clear out mucus and other smoking debris. 48 hoursThere is no nicotine left in the body. Ability to taste and smell is greatly improved. 72 hoursBreathing becomes easier. Bronchial tubes begin to relax and energy levels increase weeksCirculation improves monthsCoughs, wheezing and breathing problems improve as lung function is increased by up to 10%. 1 year Risk of a heart attack falls to about half that of a smoker. 10 yearsRisk of lung cancer falls to half that of a smoker. 15 yearsRisk of heart attack falls to the same as someone who has never smoked.