Gas exchange in Mammals

Gas Exchange in Mammals Delivery of O 2 to gas exchange surface (alveoli) and removal of CO 2 from capillaries and out of the body (ventilation). Delivery of O 2 to gas exchange surface (alveoli) and removal of CO 2 from capillaries and out of the body (ventilation).

In Larger Organisms Diffusion alone cannot meet the needs of the inner-most cells of larger organisms. They have a higher demand for O 2 and removal of CO 2. Diffusion alone cannot meet the needs of the inner-most cells of larger organisms. They have a higher demand for O 2 and removal of CO 2. Larger organisms must have some form of internal transport system for gases. Larger organisms must have some form of internal transport system for gases.

Pathway Air (outside)  nasal passages (or mouth)  pharynx  larynx  trachea  bronchus  bronchiole  alveoli  bloodstream

Nasal passages - Air is warmed and moistened. Dust and bacteria removed by mucous and nasal hairs (cilia).

Cilia - creates wave-like movement to sweep mucous upwards to be expeled at the mouth/nose (along with trapped debris)

Cilia animation a.htm a.htm a.htm a.htm

Trachea Hollow tube held open by ‘C’ shaped bands of cartilage. It branches into the two bronchi (one: bronchus) which also have cartilaginous rings.

Alveolus Bronchus then branch into smaller tubes called bronchioles which lead into grape-like clusters of thin-walled air sacs called alveoli (one: alveolus) which are surrounded by blood capillaries.

Oxygen diffuses across the moist lining of the alveoli into the capillaries. Oxygen diffuses across the moist lining of the alveoli into the capillaries. CO 2 diffuses out of the capillary and into the air in the alveoli. CO 2 diffuses out of the capillary and into the air in the alveoli.

Surfactant Lipoprotein produced by alveolar cells Lipoprotein produced by alveolar cells Reduced surface tension (if no surfactant – lung cannot inflate normally) Reduced surface tension (if no surfactant – lung cannot inflate normally)

Pigment Oxygen is picked up by a red pigment called haemogoblin (in red blood cells) and is carried around the body in the circulatory system. Oxygen is picked up by a red pigment called haemogoblin (in red blood cells) and is carried around the body in the circulatory system. As the blood carrying the oxygen (oxygenated blood) passes through the body the haemoglobin releases oxygen which diffuses into the cells. As the blood carrying the oxygen (oxygenated blood) passes through the body the haemoglobin releases oxygen which diffuses into the cells.

Other bits  Diaphragm is a sheet of muscle at bottom of these cavities  Pleural membrane lines each cavity and covers each lung, and encloses pleural space (which contains fluid to help membranes slide past each other during breathing)

Breathing/Ventilation

Inhalation – Breathing In Diaphragm contracts (lowered), intercostal muscles contract - lifts ribs up and out. Diaphragm contracts (lowered), intercostal muscles contract - lifts ribs up and out. Increases volume of chest cavity  cause the air from outside to rush in and fill up the increased space. Increases volume of chest cavity  cause the air from outside to rush in and fill up the increased space.

Exhalation – Breathing out Diaphragm and intercostal muscles relaxes Diaphragm and intercostal muscles relaxes Diaphragm moves up and the ribs down Diaphragm moves up and the ribs down Air is forced out as the volume in the chest cavity returns to normal. Air is forced out as the volume in the chest cavity returns to normal.

The breathing action (diaphragm etc.) uses considerable energy but allows the animal to change the rate of gas exchange quickly to suit activity/environment requirements. The breathing action (diaphragm etc.) uses considerable energy but allows the animal to change the rate of gas exchange quickly to suit activity/environment requirements.

Alveoli ↑ ’s surface area exposed for diffusion of O 2 into capillaries and CO 2 out into alveoli. Alveoli ↑ ’s surface area exposed for diffusion of O 2 into capillaries and CO 2 out into alveoli. 300 million alveoli creates 40x the surface area of the body. 300 million alveoli creates 40x the surface area of the body. Increased Surface Area for Gas Exchange

Moist Surfaces Moist surface within nasal passages, alveoli and capillaries help O 2 in air to dissolve into the watery substance for diffusion into capillaries. Moist surface within nasal passages, alveoli and capillaries help O 2 in air to dissolve into the watery substance for diffusion into capillaries.

Thin Exchange Surface Thin surface of alveoli and capillaries ↓ ’s barrier for diffusion of O 2 into capillaries and CO 2 out. Thin surface of alveoli and capillaries ↓ ’s barrier for diffusion of O 2 into capillaries and CO 2 out.

A more specialised system is required for the increased size of the animal to deal with: → the inefficiency of diffusion over longer distances → higher demand for O 2 and removal of CO 2. Internal lungs are well protected from: → physical damage → drying out in a dry environment. Enables mammals to have a wider range of habitats e.g. dry, wet, water on land. Lungs have a higher surface area to maximise rate of diffusion of O 2 into capillaries and removal of CO 2. Then the O 2 and CO 2 is transported around the body in the bloodstream of the circulation system.

Blood vessels in the lung

Some more interesting info/pictures Warning – some pictures are a bit gory – so stop here if you are sensitive to blood and gore.

Figure 23–8 Cross-section of the lung and heart

Normal lung tissue Smoker’s lung tissue Cilia can be immobilized by smoking

Cystic fibrosis Faulty chloride channel leads to thick mucus  difficult to clear  blockage and infection Normal lung tissue Lung tissue from cystic fibrosis patient

Black lung disease An electron micrograph scan of coal dust (marked by dark patches) in lung tissue infected with black lung disease. A disease found primarily in older coal workers, black lung is characterized by thickening and scarring of lung tissue.

Pneumothorax : air trapped in the chest cavity. (Tension pneumothorax: life- threatening) Pneumothorax : air trapped in the chest cavity. (Tension pneumothorax: life- threatening)