Respiratory system

1. The main job of the respiratory system is to get oxygen into the body and waste gases out of the body. It is the function of the respiratory system to transport gases to and from the circulatory system.

2. Respiration is a vital function of all living organisms.

3. Respiration occurs at two different levels:

a. The level of the cell. In the mitochondria of eukaryotic cells, aerobic respiration requires oxygen to break down glucose, releases carbon dioxide, and produces large amounts of atp. This level of respiration is called internal respiration or cellular respiration.

b. The level of the organism. An organism must get oxygen into its cells and carbon dioxide back out. This level of respiration is called external respiration because the exchange of gases takes place with the external environment. The exchange of gases, oxygen (O2) and carbon dioxide (CO2) between air and blood.

4. External respiration involves the respiratory system.

5. A respiratory system is a group of organs working together to bring about the exchange of oxygen and carbon dioxide with the environment.

6. A single-celled organism living in water (diffusion) gets its oxygen directly from its surroundings (the water). The oxygen easily diffuses across the cell membrane. Carbon dioxide also diffuses across the cell membrane; thus single-celled organisms do not need a respiratory system.

7. In multicellular organisms, each cell consumes oxygen and produces carbon dioxide. Large multicellular organism must have a respiratory system to ensure the effective exchange of gasses with the atmosphere quickly and efficiently to survive.

8. This occurs every time an organism takes a breath.

9. The atmosphere of planet earth is approximately 78% nitrogen and 21% oxygen. The remaining 1% is made up of carbon dioxide, water vapor, and other trace gases.

10. Humans are air breathers; our respiratory system has adapted to these concentrations of gases in the atmosphere. If the amount of oxygen falls much below 15 %, our respiratory system will be unable to provide enough oxygen to support cellular respiration.

The passage of air and the respiratory structures

1. The human respiratory system consist of the nose, nasal cavity, pharynx, larynx, trachea, smal ler conducting passageways (bronchi and bronchioles), and lungs.

2. The respiratory system may be divided into the upper respiratory tract and the lower respiratory tract.

3. The upper respiratory tract consists of the parts outside the thoracic (chest) cavity: the air passages of the nose, nasal cavities, pharynx (windpipe), larynx (voice box), and upper trachea.

4. The lower respiratory tract consists of the parts found in the thoracic (chest) cavity: the lower trachea and the lungs themselves.

5. Air enters the respiratory system through the mouth or nose.

6. Air entering the nose passes into the nasal cavity. The nasal cavity is richly supplied with arteries, veins, and capillaries, which bring nutrients and water to its cells.

7. As air pushes back from the nasal cavity, it enters the pharynx. The pharynx is located in the back of the mouth and serves as a passageway for both air and food. When food is swallowed, a flap of cartilage, called the epiglottis, presses down and covers the opening to the air passage (ever have food go "down the wrong way"?).

8. From the pharynx, the air moves through the larynx, the upper end of the trachea, and into the trachea (windpipe), which leads directly to the lungs.

9. These passageways provide a direct connection between the outside air and some of the most delicate tissue in the body.

10. These passageways must filter out dust, dirt, smoke, bacteria, and a variety of other contaminants found in air.

11. The first filtering is done in the nose. The nose will do three things to the air we breathe in:

a. Filter the air b. Warm the air c. Provide moisture (water vapor or humidity) to the air.

12. As air passes through the nasal cavities it is warmed and humidified, so that air that reaches the lungs is warmed and moist.

13. The nasal airways are lined with cilia and kept moist by mucous secretions. The combination of cilia and mucous helps to filter out solid particles from the air an warm and moisten the air, which prevents damage to the delic ate tissues that form the respiratory system.

14. The moisture in the nose helps to heat and humidify the air, increasing the amount of water vapor the air entering the lu ngs contains.

15. This helps to keep the air entering the nose from drying out the lungs and other parts of our respiratory system.

16. When air enters the respiratory system through the mouth, much less filtering is done. It is generally better to take in air through the nose.

17. At the top of the trachea is the larynx (voice box or adam's apple). Inside, and stretched across the larynx are two highly elastic folds of tissue (ligaments) called the vocal cords. Air rushing through the voice box causes the vocal cords to vibrate producing sound waves.

18. From the larynx, the warmed, filtered, and moistened air passes downward into the thoracic cavity through the trachea.

19. The walls of the trachea are made up of c -shaped rings of tough flexible cartilage. These rings of cartilage protect the trachea, make it flexible, and keep it from collapsing or over expanding.

20. The cells that line the trachea produce mucus; the mucus helps to capture things still in the air (dust and microorganism s), and is swept out of the air passageway by tiny cilia into the digestion system.

21. Within the thoracic cavity, the trachea divides into two branches, the right and left bronchi. Each bronchus enters the lung on its respective side. The lungs are the site of gas exchange between the atmosphere and the blood. The right lung has three divisions or lobes, and is slightly larger than the two lobed left lung. The lungs are inside the thoracic cavity, bounded by the rib c age and diaphragm. Lining the entire cavity and encasing the lungs are pleura membranes that secrete a mucus that decreases friction from the movement of the lungs during breathing.

22. The further branching of the bronchial tubes is often called the bronchial tree.

23. Imagine the trachea as the trunk of an upside down tree with extensive branches that become smaller and small er; these smaller branches are the bronchioles.

24. Both bronchi and bronchioles contain smooth muscle tissue in their walls. This muscle tissue controls the size of the air passage.

25. The bronchioles continue to subdivide until they finally end in clusters of tiny hallow air sacs called alveoli. Groups of alveoli look like bunches of grapes. All exchange of gases in the lungs occurs in the alveoli.

26. The alveoli consist of thin, flexible membranes that contain an extensive network of capillaries. The membranes separate a gas from liquid. The gas is the air we take in through our respiratory system, and the liquid is blood.

27. The functional unit of the lungs is the alveoli ; it is here that the circulatory and respiratory systems come together, for the purpose of gas exchange. All exchange of gases in the lungs occurs in the alveoli. Each lung contains nearly 300 million alveoli and has a total surface area about 40 times the surface area of your skin.

Mechanism of breathing

1. Breathing is the entrance and exit of air into and from the lungs.

2. Ventilation is the term for the movement of air to and from the alveoli.

3. Every single time you take a breath, or move air in and out of your lungs, two major actions take place.

a. Inhalation - also called inspiration, air is pulled into the lungs.

b. Exhalation - also called expiration, air is pushed out of the lungs.

4. These two actions deliver oxygen to the alveoli, and remove carbon dioxide.

5. The continuous cycles of inhalation and exhalation are known as breathing. Most of us breathe 10 to 15 times per minute.

6. The lungs are not directly attached to any muscle, so they cannot be expanded or contracted.

7. Inhalation and exhalation are actually produced by movements of the large flat muscle called the diaphragm and the intercostal (between the ribs) muscles.

8. The diaphragm is located along the bottom of the rib cage and separates the thoracic cavity from the abdominal cavity.

9. Before inhalation the diaphragm is curved upward into the chest. During inhalation, the diaphragm contracts and moves down, causing the volume of the thoracic cavity to increase.

10. When the diaphragm moves down, the volume of the thoracic cavity increases and the air pressure inside it decrease s.

11. The air outside is still at atmospheric pressure, to equalize the pressure inside and out, the air rushes through the trachea into the lungs - inhaled.

12. When the diaphragm relaxes, it returns to its curved position. This action causes the volume of air in the thoracic cavity to decrease.

13. As the volume decreases, the pressure in the thoracic cavity outside the lungs increases. This increase the air pressure and causes the lungs to decrease in size.

14. The air inside the lungs is pushed out or exhaled.

15. We generally breathe with the diaphragm and intercostal muscles (rest), under extreme conditions we can use other muscles in our thoracic cavity to breathe (activity).

16. Since our breathing is based on atmospheric pressure, the lungs can only work properly if the space around them is sealed.

17. When the diaphragm contracts, the expanded volume in the thoracic cavity quickly fills as air rushes into the lungs. If there is a small hole in the thoracic cavity, the respiratory system will not work.

18. Air will rush into the cavity through the hole, upset the pressure relationship, and possibly cause the collapse of a lun g.

Gas exchange and transport (figure 46-17)

1. Chemical analysis of the gases that are inhaled and exhaled:

gas inhaled -vs- exhaled o2 20.71% 14.6% co2 0.04% 4.0% h2o 1.25% 5.9%

2. Three important things happen to the air we inhale:

a. Oxygen is removed

b. Carbon dioxide is added

c. Water vapor is added.

3. This occurs in the alveoli in the lungs; our lungs consist of nearly 300 million alveoli where gas exchange occurs (the exchange of carbon dioxide and oxygen).

4. Blood flowing from the heart enters capillaries surrounding each alveolus and spreads around the alveolus. This blood contains a large amount of co2 and very little o2.

5. The concentration of the gases in the blood and the alveolus are not equal (concentration gradient) . This causes the diffusion of co2 from the blood to the alveolus and the diffusion of o2 from the alveolus into the blood. (figure 46-17)

6. The blood leaving the alveolus has nearly tripled the total amount of oxygen it originally carried.

7. Two special molecules help this process of gas exchange work effectively:

a. Macromolecules - soaplike, consisting of phospholipid and protein, they coat the inner surface of the alveolus.

b. Hemoglobin - an oxygen carrying molecule that is a component of blood. Hemoglobin is a red colored protein found in red blood cells. Each hemoglobin molecule has four sites to which o2 atoms can bind. Thus, one hemoglobin molecule can carry up to four molecules of oxygen. Most of the oxygen - 97 percent - moves into the red blood cells, where it combines with hemoglobin.

Regulation of breathing

1. Breathing is such an important function that your nervous system will not let you have complete control of it.

2. Breathing is an involuntary action under control of the medulla oblongata in the lower part of the brain. Sensory neurons in this region control motor neurons in the spinal cord.

3. Although you can consciously controlled breathing to a limited extent-such as holding your breath-it cannot be consciously suppressed. The need to supply oxygen to our cells and remove carbon dioxide is a powerful one.

4. You can only hold your breath until you lose consciousness - then the brain takes control and normal breathing resumes.

5. Carbon dioxide and hydrogen ions (blood acidity) are the primary stimuli that causes us to breathe.

6. The nervous system must have a way to determine whether enough o2 is getting into the blood.

7. Two special sets of sensory neurons constantly check the levels of gases in the blood. These special sensory receptors are sensitive to the levels of gases in the blood, especially the level of carbon dioxide.

8. One set is located in the carotid arteries in the neck, which carry blood to the brain.

9. The other set is located near the aorta, the large artery that carries blood from the heart to the rest of the body.

10. When carbon dioxide dissolves in the blood, it forms an acid known as carbonic acid. Carbonic acid is so unstable that it immediately breaks down into hydrogen ion (h+) and a bicarbonate ions (hco3-).

co2 + h20 h2co3 h2co3 h+ + hco3- 12. Most carbon dioxide travels in the blood as bicarbonate ions. When the blood reaches the lungs, the series of reactions is reversed. The bicarbonate ions combine with a proton to form carbonic acid, which in turn forms carbon dioxide and water. The carbon dioxide diffuses out of the capillaries into the alveoli and is exhaled into the atmosphere.

13. The hydrogen ions change the acidity (ph) of the blood, and it is this change in acidity the special sensory cells respon d to.

14. The lungs of an average person have a total air capacity of about 6.0 liters. Only about 0.6 liter is exchange during normal breathing. This is all the air we need at rest.

15. During exercise, deep breathing forces out much more of the total lung capacity. As much as 4.5 liters of air can be inhaled or exhaled with effort.

16. The maximum amount of air that can be moved into and out of the respiratory system is known as the vital capacity of the lungs.

17. The vital capacity is always 1 to 1.5 liters less than the total capacity because the lungs cannot be completely deflated without serious damage.

18. The extra capacity allows us to exercise for long periods of time. Rather than breathing 12 times a minute, as most of us do at rest, a runner may breath as often as 50 times a minute.

19. For rapid and deep breathing during vigorous exercise you use the muscles of the rib cage.

Addl Summary

The entire process of respiration includes ventilation, external respiration, transport of gases,

internal respiration, and cellular respiration.

The three pressures responsible for pulmonary ventilation are atmospheric pressure,

intraalveolar pressure, and intrapleural pressure.

A spirometer is used to measure respiratory volumes and capacities. These measurement s

provide useful information about the condition of the lungs.

The frontal, maxillary, ethmoidal, and sphenoidal sinuses are air filled cavities that open into the

nasal cavity.

The pharynx, commonly called the throat, is a passageway that extends from t he base of the

skull to the level of the sixth cervical vertebra.

The larynx, commonly called the voice box, is the passageway for air between the pharynx

above and the trachea below.

The trachea, commonly called the windpipe, is the main airway to the lungs.

The trachea divides into the right and left primary bronchi, which branch into smaller and

smaller passageways until they terminate in tiny air sacs called alveoli.

The two lungs contain all the components of the bronchial tree beyond the primary bronchi.

The right lung is shorter, broader, and it is divided into three lobes. The left lung is longer, narrower, and it is divided into two lobes.