Gas Exchange

IB Learning Objectives Distinguish between ventilation, gas exchange and cell respiration

All Living things Respire. Why living things must respire (breathe): Cellular Respiration – controlled release of energy in the form of ATP from organic processes in the cell C6H12O6 + O2 ---> 6CO2 + 6H20 + ATP Gas Exchange -- Exchange of gases (Oxygen, Carbon Dioxide) between an organism and it environments Ventilation - process of "changing" or replacing gas (Oxygen, Carbon Dioxide) in a space (ex: lungs)

IB Assessment Statement Explain the need for a ventilation system

6.4.2 Explain the need for a ventilation system.(3) A ventilation system is needed to maintain concentration gradients in the alveoli 
 The steep concentration gradient across the respiratory surface is maintained in two ways: by blood flow on one side and by air flow on the other side. The ventilation system replaces diffuses oxygen (keeping the concentration high) and removes carbon dioxide (keeping the concentration low). This means oxygen can always diffuse down its concentration gradient from the air to the blood, while at the same time carbon dioxide can diffuse down its concentration gradient from the blood to the air.

IB Learning Objective Draw and label a diagram of the ventilation system, including trachea, lungs, bronchi, bronchioles and alveoli

Gas exchange in multicellular animals (i.e. Mammals) A ventilation system is a pumping mechanism that moves air into and out of the lungs efficiently, thereby maintaining the concentration gradient for diffusion.

Ventilation System of Mammals Lungs are housed in the thorax Thorax – an airtight chamber formed by the rib cage. The thorax is housed by ribs and its muscles called intercostal muscles.

Ventilation System of Mammals Diaphragm – A sheet of muscle that separated the thorax from the abdomen Pleural Membrane- internal surface of thorax, which secretes pleural fluid Pleural Fluid - is a lubricating fluid from blood plasma that protects the lungs from friction during breathing movements

LE 42-24 Rib cage gets Rib cage Air smaller as Air expands as inhaled rib muscles relax Rib cage expands as rib muscles contract Air inhaled Air exhaled Lung Diaphragm INHALATION Diaphragm contracts (moves down) EXHALATION Diaphragm relaxes (moves up)

Ventilation System of Mammals LE 42-23 Branch from pulmonary vein (oxygen-rich blood) Terminal bronchiole artery (oxygen-poor Alveoli 50 µm Colorized SEM SEM Nasal cavity Left lung Heart Larynx Pharynx Esophagus Trachea Right Bronchus Bronchiole Diaphragm Lungs connect to the mouth via the trachea The trachea divides into 2 bronchi, on to each lung Within the lungs the bronchi divide into even smaller bronchioles

Ventilation System of Mammals The smallest bronchioles end in air sacs called alveoli. LE 42-23 Branch from pulmonary vein (oxygen-rich blood) Terminal bronchiole artery (oxygen-poor Alveoli 50 µm Colorized SEM SEM Nasal cavity Left lung Heart Larynx Pharynx Esophagus Trachea Right Bronchus Bronchiole Diaphragm

The Human Respiratory System Bronchioles subdivide into millions of tiny air sacs called alveoli. Alveoli Bronchiole The respiratory system is responsible for the exchange of oxygen and carbon dioxide. After reaching the lungs, the trachea branches into smaller and smaller tubes called bronchioles, which end in alveoli, or air sacs.

The Human Respiratory System Alveoli are grouped in clusters. Alveoli have thin, moist walls A network of capillaries surrounds each alveolus. Pulmonary artery Pulmonary vein The respiratory system is responsible for the exchange of oxygen and carbon dioxide. Capillaries

Gas exchange takes place in the alveoli. LE 42-23 Branch from pulmonary vein (oxygen-rich blood) Terminal bronchiole artery (oxygen-poor Alveoli 50 µm Colorized SEM SEM Nasal cavity Left lung Heart Larynx Pharynx Esophagus Trachea Right Bronchus Bronchiole Diaphragm Gas exchange occurs by diffusion across the membrane of an alveolus and a capillary. Capillary

IB Learning Objective Draw and label a diagram of the ventilation system, including trachea, lungs, bronchi, bronchioles and alveoli

IB Learning Objective Describe the features of alveoli that adapt them to gas exchange.

Gas exchange takes place in the alveoli. LE 42-23 Branch from pulmonary vein (oxygen-rich blood) Terminal bronchiole artery (oxygen-poor Alveoli 50 µm Colorized SEM SEM Nasal cavity Left lung Heart Larynx Pharynx Esophagus Trachea Right Bronchus Bronchiole Diaphragm Gas exchange occurs by diffusion across the membrane of an alveolus and a capillary. Capillary

Cellular Respiration and Gas exchange Diffusion: Gas exchange between an individual cell and its environment takes place by diffusion Gases will diffuse (move) across the cell membrane from an area of high concentration to an area of low concentration.

Gas exchange takes place in the alveoli. LE 42-23 Branch from pulmonary vein (oxygen-rich blood) Terminal bronchiole artery (oxygen-poor Alveoli 50 µm Colorized SEM SEM Nasal cavity Left lung Heart Larynx Pharynx Esophagus Trachea Right Bronchus Bronchiole Diaphragm Gas exchange occurs by diffusion across the membrane of an alveolus and a capillary. Capillary

Gas Exchange inside a cell example Gas exchange takes place in the alveoli. Oxygen diffuses into the blood. O2 Gas exchange occurs by diffusion across the membrane of an alveolus and a capillary. Capillary

Gas Exchange inside a cell example Carbon dioxide in the blood diffuses into the alveolus. O2 CO2 Gas exchange occurs by diffusion across the membrane of an alveolus and a capillary.  Capillary

Features of the Alveolus that make it great for gas exchange Large total surface area – 700 million in our lungs, providing 70m2 in total surface area. 30-40 times greater than the surface area of our skin Surface Area – greater the surface area faster the rate of diffusion.

Features of the Alveolus that make it great for gas exchange Walls of alveoli very thin, consisting of a single layer of flattened cells, Thin walls decrease the length of the diffusion path. The shorter the diffusion path the greater the rate of diffusion Thus the respiratory path must be as thin as possible. Walls of the alveoli have elastic properties meaning they can stretch during inhalation and then shrink back to their original size during exhalation.

Features of the Alveolus that make it great for gas exchange Surface of alveoli walls are covered with a film/ layer of moisture Oxygen gas dissolves in water lining of alveoli. Oxygen diffuses into the blood when it is dissolved in solution. Prevents the walls of the alveoli from sticking together Surrounded by a dense network of capillaries.

Features of the Alveolus that make it great for gas exchange Alveoli is surrounded by a dense network of capillaries. Network of capillaries around each alveolus supplied deoxygenated blood from pulmonary artery and draining into pulmonary veins. This maintains the concentration gradient of O2 and CO2.

Gas exchange occurs across capillaries, whose walls are one cell thick We have 50,000 miles of them Few human cells are > 100 μm from a capillary Red blood cells Capillary wall

6.4.3 Describe the features of alveoli that adapt them to gas exchange.(2) Large surface area due to the combined spherical shape (600 million alveoli = 80 m2) Flattened epithelial cells of alveoli and close association with capillaries Short diffusion distance from alveoli to blood (0.5-1.0 um) Dense capillary network Moist surface for the solution of gases

Gas exchange Animations Ventilation http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP15104 Gas exchange: http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter25/animation__gas_exchange_during_respiration.html Repiratory system tutorials http://www.getbodysmart.com/ap/respiratorysystem/menu/menu.html Lung Transplant Ted Talk https://www.youtube.com/watch?v=T2EmuyHoMAI Opera Sing with a lung transplant https://www.youtube.com/watch?v=cvO9i0QkQbE

IB Learning Objective Explain the mechanism of ventilation of the lungs in terms of volume and pressure changes caused by the internal and external intercostal, muscles, the diaphragm and abdominal muscles

Breathing ventilates the lungs The process that ventilates the lungs is breathing, the alternate inhalation and exhalation of air LE 42-24 Rib cage expands as rib muscles contract Air inhaled Lung Diaphragm INHALATION Diaphragm contracts (moves down) Rib cage gets smaller as relax exhaled EXHALATION Diaphragm relaxes (moves up)

How a Mammal Breathes Mammals ventilate their lungs by negative pressure breathing, which pulls air into the lungs The thorax is an air tight chamber, thus as volume changes in the lungs, so does pressure. Boyles Gas Law = P1V1=P2V2

How a Mammal Breathes Inhalation (inspiration) – Volume increases Lung volume increases as the: External rib muscles (external intercostal muscles) contract and cause the rib cage to move up. and diaphragm contract (moves downs) Internal rib muscles (internal intercostal muscles) relax.

How a Mammal Breathes Inhalation (inspiration) – Volume increases Ribs will move upwards & outwards increasing volume Diaphragm moves down increasing volume Increasing Volume, Lowers Pressure (Boyles Law) Air moves from high pressure to low pressure. Thus air will move from the atmosphere into the lungs.

How a Mammal Breathes Exhalation – Expiration – Decreasing Volume Lung volume decrease as the Internal rib muscles ( internal intercostal muscles) contract moving the rib cage up and out and diaphragm relaxes (moves up) Internal rib muscles (external intercostal muscles) relax. Decrease volume/ increases the pressure in the lungs and air is forced out

How a Mammal Breathes Exhalation – Expiration – Decreasing Volume The ribs move downwards and inwards, and the diaphragm moves up. Volume is decrease Decreasing Volume, increasing Pressure (Boyles Law) Air moves from high pressure to low pressure. Thus, air from the lungs will be pushed towards the atmosphere.

LE 42-24 Rib cage gets Rib cage Air smaller as Air expands as inhaled rib muscles relax Rib cage expands as rib muscles contract Air inhaled Air exhaled Lung Diaphragm INHALATION Diaphragm contracts (moves down) EXHALATION Diaphragm relaxes (moves up)

The respiratory system When the diaphragm contracts, the chest cavity expands, and the lungs fill with air Fig. 42.24