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SECTION 35.2, PAGES 656-659 Breathing and Transport of Gases.

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1 SECTION 35.2, PAGES 656-659 Breathing and Transport of Gases

2 Breathing Inspiration/Inhalation- the act of moving air into the lungs. Diaphragm contracts and moves down Expiration/Exhalation- the act of moving air out of the lungs. Diaphragm relaxes and moves up Diaphragm- a horizontal muscle that divides the thoracic cavity from the abdominal cavity Terrestrial vertebrates use these methods to ventilate their lungs, moving air into and out of the respiratory tract.

3 All terrestrial vertebrates except birds use a tidal ventilation mechanism (the air moves in and out by the same route; the air coming into the lungs mixes with the air exiting, which decreases gas-exchange efficiency). Mammals need to burn calories in order to maintain their internal temperature, and burning calories requires oxygen. Humans have relatively large bodies, thus they have a greater need for oxygen, which is why they have lungs and a circulatory and respiratory system instead of relying on simple diffusion.

4 Birds use a one-way ventilation mechanism (the trachea carries incoming air to a set of posterior air sacs, past the lungs. The air then goes through the lungs and into a set of anterior air sacs. From here, the air is expelled. This method has improved gas- exchange efficiency). This ventilation system is thought to be a result of bird ancestors, the dinosaurs.

5 Humans The act of breathing is involuntarily controlled by the respiratory center, a group of nerve cells in the medulla oblongata of the brain that rhythmically sends out nerve impulses. The respiratory center sends signals through the spinal cord to the diaphragm and intercostal nerves to the intercostal muscles (which expand and shrink the chest cavity) located on the rib cage, creating inspiration. Expiration occurs when the respiratory center stops sending the neuronal signals to the diaphragm and intercostal nerves. When volume increases, pressure decreases and vice versa. Therefore, when the lungs inhale due to the flexing of the diaphragm, they have less volume and therefore more pressure, and vice versa. This pressure helps push out the air when exhaling.

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7 The pons is another area of the brain that has a role in controlling autonomic functions. It connects the cerebral cortex to the medulla oblongata and helps transfer messages between the brain and spinal cord. The medulla oblongata is an area in the brain, and therefore a part of nervous system. It controls autonomic functions such as breathing, digestion, sneezing, and swallowing.

8 The activity of the respiratory center can be influenced by both nervous and chemical input. Nervous Input: Forced inhalation causes stretch receptors in the alveolar walls to send out inhibitory nerve impulses from the inflated lungs to the respiratory center, which stops the respiratory center from sending out nerve impulses.

9 Chemical Input: When CO2 enters the blood, it reacts with water and releases H+ ions. When the concentration of H+ ions in the blood rises, and thus the blood pH decreases, the respiratory center increases the breathing rate. Chemoreceptors (sensory receptors that are sensitive to chemical stimulation) in the carotid bodies (structure located at the branching of the carotid arteries) and in the aortic bodies (sensory receptors in the aortic arch) stimulate the respiratory center, and thus increase the rate of breathing. This occurs when the body is trying to maintain homeostasis during intense exercise.

10 Gas Exchange External respiration- the exchange of gases in the lungs Internal respiration- the exchange of gases in the tissues Diffusion moves gases in and out of the blood vessels locates in lungs and tissues. Partial pressure is the amount of pressure each gas exerts. If the partial pressure of oxygen or CO2 is different on opposite sides of a membrane, they flow down the concentration gradient, from higher pressure to lower pressure.

11 External Respiration Ventilation causes the alveoli (air sacs) of the lungs to have a higher partial pressure of oxygen (notated as P O2 ) and a lower partial pressure of CO2 (notated as P CO2 ) than the blood in the pulmonary capillaries. This facilitates gas exchange in the lungs. Pulmonary- “of the lungs” When blood enters the lungs by means of the pulmonary capillaries, some of the hemoglobin in the blood carry either CO2 or H+ ions.

12 While CO2 can be carried into the lungs by hemoglobin molecules, most of the CO2 is carried as bicarbonate ions, HCO 3 -, in the plasma. These ions can act as buffers to keep blood pH from getting too acidic. In red blood cells, the enzyme carbonic anhydrase quickens the breakdown of carbonic acid, releasing CO2. H+ + HCO 3 - -> H 2 CO 3 -> H 2 O + CO 2 | Carbonic acid

13 Oxygen that enters the lungs is usually in the form of oxyhemoglobin, a combination of hemoglobin (Hb) and oxygen. Oxyhemoglobin is a result of a chemical reaction inside the red blood cells. Hb + O 2 -> HbO 2 | | (deoxyhemoglobin) (oxyhemoglobin)


15 Internal Respiration The tissue cells in the human body undergo cellular respiration, which means they’re constantly giving up oxygen. This creates a lower partial pressure of O2 and a higher partial pressure of CO2 in the tissues than in red blood cells found in the systemic capillaries. Thus, the exchange of gases in the tissues.

16 Blood coming into the systemic capillaries is red because it contains red blood cells that have oxyhemoglobin. Tissues have higher temperatues and lower pHs than that of the lungs, making it easier for oxyhemoglobin to give up its O2 molecule here. HbO 2 -> Hb + O 2 This reaction provides O2 to move down its concentration gradient from the blood cells to the tissue cells.

17 CO2 enters the blood from the tissues because there is a higher partial pressure inside of the tissues than in blood. Cells continuously produce CO2, which collects in tissue fluid. Once CO2 diffuses into the blood, it enters red blood cells. Some of it then binds with the protein portion of hemoglobin to form carbaminohemoglobin, however most of the CO2 combines with water to form bicarbonate ions. CO 2 + H 2 O -> H 2 CO 3 -> H+ + HCO 3 - | | (Carbonic acid) (Bicarbonate ion) The enzyme carbonic anhydrase speeds up this reaction. The HCO 3 - then diffuses out of the red blood cells and into the plamsa


19 The release of H+ ions would disrupt the homeostasis of the body, seeing as the blood pH would be disrupted. However, the “globin” portion of “hemoglobin” binds with the H+ ions to form reduced hemoglobin, or HbH+. Blood that leaves the systemic capillaries are a deep maroon color because of the red blood cells containing reduced hemoglobin.

20 The blood becomes more acidic with more CO2. The decreased pH causes hemoglobin to more easily release its oxygen in order to properly supply the body. Bohr Effect- “decreased affinity of hemoglobin for oxygen caused by an increase of carbon dioxide; the oxyhemoglobin dissociation curve is displaced to the right because of higher partial pressure of carbon dioxide and lower pH.” – http://medical- http://medical-


22 Sources: Mader, Sylvia S. Biology. 10th ed. New York: McGraw-Hill, 2010. Print.

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