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6.4 & D6 O2 is vital to life! Oxygen is required for cellular respiration Humans can survive for only a few minutes without oxygen (3-4 minutes is enough to cause some brain damage) Air is 78% nitrogen, 21% oxygen, and 1% other gases including carbon dioxide C6H12O6 + glucose 6O2 6CO2 + 6H2O + ATP oxygen carbon dioxide water Waste products From the food we eat! energy The primary responsibility of the respiratory system is to provide O2 from the ambient (outside) air to the blood and to pick up waste gas, CO2 from the blood and transport it out of the body Protects body from microorganisms Respiratory system also provides sound by vocal cords (in larynx) these cords vibrate as air is forced past them, producing sound Nostrils and Nasal Cavity or Mouth Pharynx Glottis Larynx Trachea right bronchus left bronchus (into right lung) (into left lung) bronchioles alveoli bronchioles alveoli Air enters through the mouth and or nose. The air is warmed and moisten in the nasal passages and mouth before entering the lungs. (Prevents damage to the thin tissues surrounding the lungs) Tiny hairs and mucus line the nasal passage to filter dust and airborne particles and prevent them from entering the lungs. Air then moves to the pharynx (throat). During swallowing, the epiglottis closes the passage to the respiratory tract. During breathing, the glottis (the opening to the trachea) stays open. Air passes the larynx (the voice box) and flows to the trachea. The trachea (windpipe) is a semi-rigid tube. ◦ It’s rigidity is because it is made of rings or cartilage (“cartilaginous rings”) which keep the walls strong and open The cells of trachea secrete mucus that can trap foreign objects that were not stopped in nasal cavity microscopic cilia (hair-like structures) then work to “sweep” out trapped substances back to the pharynx once in pharynx these substances can be swallowed or expelled Coughing and sneezing will aid the cilia in removing the foreign substances The trachea then branches into two bronchi (singular= bronchus). Each bronchi is connected to a lung. The bronchi branch into smaller tubes called bronchioles The bronchioles end in a cluster of alveoli (singular = alveolus) An alveolus is a tiny sac in the lung, at the end of a bronchiole, where gas exchange occurs. Each cluster of alveoli is surrounded by a network of capillaries (small blood vessels). O2 from the air that enters the alveolus, dissolves onto the moist surface of the alveoli and diffuses into the capillaries to be transported by red blood cells to the rest of the body Meanwhile, CO2 leaves the capillaries and diffuses into the alveolus so it can be exhaled. NOTE: It is important that alveoli are moist. The moisture allows the oxygen to diffuse through the alveolar membrane into the capillaries. (DIFFUSION: the movement of particles from an area of high concentration to low concentration) See pages 311, 313 Type I pneumocytes ◦ Most of the cells in the epithelium ◦ Flattened cells ◦ cytoplasm ~0.15µm thick Type II pneumocytes ◦ About 5% of the alveolar surface ◦ Rounded cells ◦ Secrete a fluid (pulmonary surfactant) to coat the inner surface of the alveoli keeping it moist so that: a) Gases (O2) can dissolve before diffusing into alveolar capillaries b) Prevent the sides of the alveolus from sticking to each other The fluid secreted by the type II pneumocytes contains a pulmonary surfactant. The molecules are similar to phospholipids They form a monolayer on the surface of the moist alveolar walls with the hydrophobic tails pointing out (to the alveolar lumen) preventing walls from sticking together and collapsing. Hydrophobic Hydrophilic http://www.histology.leeds.ac.uk/respiratory/respiratory.php The alveoli are very thin. They are only one cell thick!! This allows for diffusion to occur easily across the alveoli. (Capillaries are also only one cell thick which also facilitates diffusion) Each lung contains approximately 150 million alveoli. That’s 300 million alveoli in total!!! Having so many alveoli increases the surface area for gas exchange. (If all the alveoli in an adult pair of lungs were flattened out, their combined surface are would be equal to half a tennis court!) 1. Large surface area ◦ This means there are more sites for diffusion 2. Thin ◦ Short Distance for gases to move These eight small spheres with radius 1unit have the same total volume as the one larger sphere with radius 2, but they have four times the total surface area 3. Moist ◦ Gases need to dissolve before passing through membranes 4. Good Blood supply ◦ Maintains concentration gradient Lungs are situated in the thoracic (chest) cavity and are surrounded by a double-walled sac, called the pleural membrane The inner layer of this sac is attached to the outside of the lungs The outer layer of this sac is attached to the inside of the rib cage A thin space exists between the double wall which is filled with a fluid. This is known as the pleural space Because of surface tension, the double wall behaves like two plates of glass stuck together by a film of water. They can slide over one another, but are difficult to separate This allows movement of lungs to be coupled with the movement of rib cage When you breathe in, your rib cage moves up and out the outer layer of the pleural membrane moves up too pulls the inner layer of the pleural membrane which pulls the lungs up and out too! the act of ambient air exchange via the process of inhalation and exhalation (movement of gases between lungs and environment) humans ventilate or fill the lungs by the process of breathing (alternating inhalation and exhalation) the process is best described as negative pressure breathing which works by pulling air down into the lungs air moves from an area of high pressure to an area of low pressure so how do the lungs create a low pressure so that air can move inwards? In between the ribs are muscles called intercostal muscles When muscles contract, they become shorter When muscle relax, they are elongated. Oftentimes, a muscle relaxes because it is pulled into a elongated state by another muscle contracting. These are known as antagonistic pair of muscles Inspiration and expiration involve opposite movements working together as antagonistic pairs. 1) External intercostal muscles contract and lift the rib cage which pulls the lungs up and out - this increases the volume (space) in the lungs At the same time the internal intercostal muscles are relaxed. lung volume = lung pressure (because there is more space) 2) a dome shaped muscle called the diaphragm is located under the lungs (forms bottom wall of thoracic cavity) During inhalation the diaphragm contracts and moves downward (flattens) pushing the relaxed abdomen wall out. this further increases lung volume increased lung volume caused by these 2 events reduces the air pressure in the lungs to a point where the air pressure in lungs is less than air pressure outside body (negative pressure) the result is that air moves inward, from higher pressure to lower pressure 1) The internal intercostal muscles contract and pulling the ribcage and the lungs back down and in. Meanwhile the external intercostal muscles relax 2) The diaphragm relaxes and is pushed upward into a domed shaped by abdominal muscles contracting. External Intercostal muscles contract (lungs move up and out) Diaphragm contracts and moves down Lung volume increases and pressure decreases (because more space) External intercostal muscles relax (lungs move down and in) Diaphragm relaxes and moves up Lung volume decreases and pressure increases (because less space) http://www.pennmedicine.org/encyclopedia/ em_DisplayAnimation.aspx?gcid=000018&pti d=17 When you eat ribs what you are really eating is intercostal muscle! If the diaphragm was ripped or torn it would not be able to regulate pressure in thoracic cavity. Normally an individual takes approximately 12 breaths per minute However, this can vary depending on circumstances (physical activity will increase rate and depth of breathing) The maximum volume of air that can be taken into the lungs During normal breathing, only a small fraction of the total capacity enters our lungs. Lung capacity depends on sex, body type, and life style. Males, non-smokers, and athletes tend to have larger lung volumes the volume of air an individual inhales or exhales with each breath averages about 250mL to 500mL in humans only a fraction of total lung capacity because after you exhale some air still remains in the lungs even if you exhale forcefully air remains the maximum volume of air that can be exhaled after (beyond) a tidal volume exhalation the maximum volume of air that can be inhaled after (beyond) a tidal volume inhalation the maximum volume of air that can be inhaled or exhaled during forced breathing MALES: 4.4 L - 4.8 L FEMALES: 3.4 L – 3.8 L always 1 - 1.5 L less than total lung capacity because if lungs become completely deflated they would collapse the amount of air remaining in the lungs after a maximum exhalation because it is impossible to completely collapse the alveoli We’ve been using respiration as a general term for the entire process of gas exchange in our bodies. Some other respiration definitions: ◦ External respiration ◦ Internal respiration ◦ Cellular Respiration involves the exchange of gases (O2 & CO2) between the alveoli and the blood (capillaries) The blood then carries O2 to all cells of the body Body cells involves the exchange of gases between the capillaries and the cells (Interstitial Fluid is the fluid between cellsthe gases dissolve into it before moving into body cells or capillaries) Blood Vessel/ capillary Interstitial fluid occurs at cellular level When O2 gas diffuses across into the mitochondria it is used in the biochemical reaction of cellular respiration to make ATP. CO2 is produced as a waste product C6H12O6 + glucose 6O2 6CO2 + 6H2O + ATP oxygen carbon dioxide water energy Gas exchange takes place at the approximately 300 million alveoli found in the human lungs Gasses diffuse on the moist surface of the alveoli where the capillary beds are located in close proximity to the alveoli Gas exchange occurs because there is a pressure difference When you inhale, oxygen is taken into the lungs Therefore, there is a higher oxygen pressure in alveoli (alveoli = high O2 and low CO2) Heart sends deoxygenated blood to the lungs to pick up this oxygen Therefore, there is a lower oxygen pressure in capillaries (capillaries = low O2 and high CO2) Hence O2 flows from the moist alveoli surface (high O2) to the blood capillaries (low O2) Oxygen is not very water soluble and so O2 gas binds with the iron atom found in each hemoglobin molecule and is transported in this manner to the body cells HEMOGLOBIN – blood protein that transports oxygen (When oxygen is attached it is called oxyhemoglobin) (HbO) Oxygen is then transported to body cells to be used for cellular respiration where CO2 is produced as a by-product CO2 must be transported back to the lungs to be exhaled (CO2 moves from capillaries (high) to alveoli (low) High Pressure O2; Low pressure CO2 Low Pressure O2; High pressure CO2 The differences in pressure also allows for internal respiration (gas exchange at the cells) When the oxygenated blood reaches the body cells, there is a high pressure of O2 and a low pressure of CO2 in the capillaries and a low pressure of O2 and high pressure of CO2 in the cells http://highered.mcgrawhill.com/sites/0072507470/student_view0/c hapter23/animation__gas_exchange_during_r espiration.html http://highered.mcgrawhill.com/sites/0072507470/student_view0/c hapter23/animation__movement_of_oxygen_ and_carbon_dioxide.html 1. 2. The transport of CO2 back to the lungs occurs by three different methods: 7% of CO2 dissolves in blood plasma (liquid part of blood) and is carried by plasma 23% binds to amino groups of hemoglobin (forms carboaminohemoglobin) and is transported 3. 70% is transported as bicarbonate ions CO2 is converted to bicarbonate because it reacts with water (assisted by the enzyme carbonic anhydrase) in plasma reaction produces carbonic acid acid immediately breaks down into a hydrogen ion and a bicarbonate ion (HCO3-) CO2 + H2O ⇄ H2CO3 ⇄ H+ + HCO3- breathing is an involuntary activity – one can alter their breathing pattern for only a short time before the body regains control it is the concentration of CO2 in the blood that controls the rate of breathing our breathing control centers are located in two areas of the brain the medulla oblongata and the pons The control centers monitor the carbon dioxide levels in blood and regulate breathing appropriately how does brain know that carbon dioxide is high? Remember, carbon dioxide changes into H2CO3 and then into H+ and HCO3- An increase in H+ causes a drop in pH (more H+ in blood therefore, more acidic) (Blood pH needs to remain within a pH of 7.35 – 7.45) the blood flows to the brain Sensors (chemoreceptors) in the medulla detect these changes When medulla gets this signal it increases the individual’s breathing rate to help eliminate the extra carbon dioxide (increases the rate of contraction of the intercostal muscles) Other sensors in the walls of the aorta and carotid arteries in neck (major branches of aorta) can also detect changes in pH of blood The sensors send nerve impulses to medulla Medulla adjusts breathing rate (Sensors in aorta and carotid arteries can also detect changes in O2 levels in blood, however it is mostly the CO2 that will control breathing) Nerve impulses are sent to medulla which adjusts breathing rate (by increasing intercostal muscle action) Two sets of nerves travel from medulla to the lungs The intercostal nerves stimulate the intercostal muscles The phrenic nerves stimulate the diaphragm https://www.ted.com/talks/david_blaine_how _i_held_my_breath_for_17_min?language=en
