Module 17 Respiratory System

Transcription

1 Module 17 Respiratory System Objective 1. List the functions of the respiratory system. Name the four respiratory processes. Assignment: Tortora, p. 874 or Wiley Plus 23 Chapter Opener Functions: 1. Provides for gas exchange 2. Helps regulate blood ph 3. Contains smell receptors 4. Filters incoming air 5. Produces vocal sounds 6. Excretes water and heat The four processes carried out by the respiratory system are: 1. Pulmonary ventilation: moving air into and out of the lungs 2. External respiration: exchange of gases at the alveoli of the lungs 3. Transport of respiratory gases to the tissues 4. Internal respiration: exchange of gases between blood and tissue 818

2 Objective 2. Describe functions for each of the structures of the respiratory system: nose and paranasal sinuses, pharynx, larynx, trachea, bronchi, pleural membranes, ribs and thoracic wall, diaphragm and intracostal muscles, phrenic nerves and pulmonary plexus. Be able to identify each of these on a diagram or photograph. Assignment: Tortora, pp , , 891 or Wiley Plus 15.2 Anatomy of Autonomic Motor Pathways & 23.1 Respiratory System Anatomy Let s turn our attention to the parts of the respiratory system. Anatomically, these structures can be divided into the upper and lower respiratory system. The nose, paranasal sinuses, and pharynx make up the upper respiratory system. The larynx, or voice box separates the upper from lower respiratory system. The larynx, trachea, bronchi, and lungs make up the lower respiratory system. We ll begin with the structures of the upper respiratory system. The nose is made up of hyaline cartilage which gives it flexibility. Air enters through the external nares (nostrils). Nose hairs actually have a function (besides distinguishing older men)! The hairs act as a filter for all of the crap you might breath in. In the internal nose are scroll-like bones that make up the nasal conchae also called turbinates. The conchae provide a turbulent area that air passes through before reaching the rest of the respiratory passages. The conchae are lined with a mucous membrane which helps trap foreign particles and warms and humidifies the air, The olfactory epithelium is near the superior nasal concha which increases the surface area and mixes the air to help with olfaction. 819

3 Objective 2. Describe functions for each of the structures of the respiratory system: nose and paranasal sinuses, pharynx, larynx, trachea, bronchi, pleural membranes, ribs and thoracic wall, diaphragm and intracostal muscles, phrenic nerves and pulmonary plexus. Be able to identify each of these on a diagram or photograph. Sinuses are cavities within cranial and facial bones that are lined with a mucous membrane. These spaces lighten the weight of the head so we have an easier time carrying our head around. They also serve as chambers that resonate sound as we speak or sing. Remember how funny you sound when your sinuses are stuffed up with a cold. If we walked around on all fours our sinuses would easily drain. Because humans have evolved to walk on two feet, our sinuses don t drain as easily. They may trap microorganisms and fluid and we find ourselves with a nasty sinus infection! The pharynx or throat is a hollow tube that starts at the posterior part of the internal nares and descends to the opening of the larynx. The pharynx serves as a passageway for air and food, is a resonating chamber for sound, and houses the tonsils. The pharynx can be divided into three anatomical regions. Nasopharynx: Lies behind the internal nares and has a purely respiratory function. Eustachian tubes (auditory tubes) Houses the pharyngeal tonsils (adenoids) Oropharynx: Lies behind the mouth with both reparatory and digestive functions. Houses the palatine tonsils (removed in a tonsillectomy) and the lingual tonsils Laryngopharynx: Lies inferior to the oropharynx and opens into the larynx and esophagus Respiratory and digestive functions 820

4 Objective 2 (continued). Describe functions for each of the structures of the respiratory system: nose and paranasal sinuses, pharynx, larynx, trachea, bronchi, pleural membranes, ribs and thoracic wall, diaphragm and intracostal muscles, phrenic nerves and pulmonary plexus. Be able to identify each of these on a diagram or photograph. The larynx or voice box connects the laryngopharynx with the trachea. It sits in the midline of the neck anterior to the esophagus and superior to the trachea. The hyoid bone, an unattached, free-floating U- shaped bone, sits superior to the larynx. The opening of the larynx is the glottis. Folds of tissue, the vocal chords, and the opening between them make up the glottis. Vibrations caused by air passing the vocal chords produces sound. The greater the pressure, the louder the sound. Tension on the vocal chords produces pitch. Men s vocal folds become thicker and longer during puberty under the influence of male sex hormones (androgens) producing a lower pitched voice. 821

5 Objective 2 (continued). Describe functions for each of the structures of the respiratory system: nose and paranasal sinuses, pharynx, larynx, trachea, bronchi, pleural membranes, ribs and thoracic wall, diaphragm and intracostal muscles, phrenic nerves and pulmonary plexus. Be able to identify each of these on a diagram or photograph. Nine pieces of cartilage make up the larynx: Single cartilage: Thyroid: (Adam s apple). Forms the anterior surface of the larynx Epiglottis: Leaf shaped piece of hyaline cartilage that closes over the larynx when food or liquids are swallowed. The epiglottis allows gases such as oxygen through the larynx into the trachea. Cricoid: A ring of hyaline cartilage that forms the inferior portion of the larynx. Paired cartilage: Arytenoid: Influence changes in position and tension of the vocal folds. Corniculate and Cuneiform: Support the vocal folds and the epilglottis The thyroid and cricoid cartilages serve as landmarks for making an emergency airway. A tracheostomy tube is inserted between these two pieces of cartilage. A tracheotomy is the procedure of cutting ( tomy) the trachea. A tracheostomy means to form a mouth or an opening ( stomy) in the trachea. This is a semi-permanent or permanent procedure used for patients with long-term needs such as a patient with oral cancer. 822

6 Objective 2 (continued). Describe functions for each of the structures of the respiratory system: nose and paranasal sinuses, pharynx, larynx, trachea, bronchi, pleural membranes, ribs and thoracic wall, diaphragm and intracostal muscles, phrenic nerves and pulmonary plexus. Be able to identify each of these on a diagram or photograph. The trachea or windpipe is a semi-rigid passageway for air that s about 12 cm (5 inches) long. Incomplete cartilage rings resembling the letter C surround the trachea giving it support and preventing collapse of the trachea, especially during inhalation. The trachea is anterior to the esophagus. The posterior surface of the trachea is shared with the esophagus. The trachea divides into the right and left primary bronchi. The bronchi resemble an inverted tree, branching into divisions of secondary bronchi, tertiary bronchi, and eventually into the tiny bronchioles and terminal bronchioles. The right primary bronchus extends more vertically, is wider, and shorter than the left. Because of this, an aspirated object is more likely to lodge in the right bronchus than the left. The carina is an internal ridge where the trachea divides into the right and left bronchus. The carina (Latin for boat prow) is used as a landmark when performing a bronchoscopy or visual examination of the bronchi. The carina is very sensitive area for triggering the cough reflex. 823

7 Objective 2 (continued). Describe functions for each of the structures of the respiratory system: nose and paranasal sinuses, pharynx, larynx, trachea, bronchi, pleural membranes, ribs and thoracic wall, diaphragm and intracostal muscles, phrenic nerves and pulmonary plexus. Be able to identify each of these on a diagram or photograph. The right and left lungs are slightly different. The right lung contains 3 lobes while the left contains 2. This is because the apex of the heart rests at the medial portion of the left lung, the cardiac notch. The apex or superior part of the lung rests slightly above the clavicle. The base of the lungs rests on the diaphragm. The anterior, lateral, and posterior surfaces of the lungs rest against the ribs. The primary bronchi, blood vessels, lymphatic vessels, and nerves enter the lungs at the hilum, an opening on the medial surface of each lung. The primary bronchi branch to form secondary bronchi, one for each lobe of the lung. The secondary bronchi further branch to form bronchioles which divide into several alveolar ducts. These ducts end in grape-like clusters called alveoli. The alveoli provide a large surface area for the exchange of gases. It s estimated that the lungs contain 300 million alveoli, giving a surface area about the size of a racquetball court for gas exchange! 824

8 Objective 2 (continued). Describe functions for each of the structures of the respiratory system: nose and paranasal sinuses, pharynx, larynx, trachea, bronchi, pleural membranes, ribs and thoracic wall, diaphragm and intracostal muscles, phrenic nerves and pulmonary plexus. Be able to identify each of these on a diagram or photograph. The lungs, like other visceral organs, are covered with a double-walled serous membrane. Remember that serous membranes line organs and body cavities that do not open to the external world. A serous membrane consists of areolar connective tissue covered by simple squamous epithelium (mesothelium). The visceral pleura adheres to the lung. The parietal pleura adheres to the chest wall. Between the two pleura is a small space, the pleural cavity which contains pleural fluid. This fluid reduces friction. We would hate to be in pain every time we took a breath! The pleural fluid allows easy movement as the lungs expand and contract. The fluid also allows the two layers of the membrane to adhere to each other because of the surface tension it creates. If the membrane becomes inflamed, a condition called pleurisy occurs which can be extremely painful because of friction between the two layers. Excess fluid may accumulate in the pleural cavity due to inflammation. This serious condition, called pleural effusion, makes it difficult to breathe. The visceral organs of the thoracic cavity are protected by the ribs and sternum. The volume of the thoracic cavity changes due to contractions of muscles expanding this area. We will learn more about this in Objective

9 Objective 2 (continued). Describe functions for each of the structures of the respiratory system: nose and paranasal sinuses, pharynx, larynx, trachea, bronchi, pleural membranes, ribs and thoracic wall, diaphragm and intracostal muscles, phrenic nerves and pulmonary plexus. Be able to identify each of these on a diagram or photograph. The inferior portion of the lungs rest on a large, domeshaped muscle, the diaphragm. This muscle, which forms the floor of the thoracic cavity, is the most important muscle that powers breathing. Contraction of this muscle enlarges the thoracic cavity enabling inhalation (more about this to come). The diaphragm is responsible for about 75% of the air that enters the lungs during normal quiet breathing. The internal intercostal muscles make up the intermediate layer of the intercostal space. These muscles help decrease the size of the thoracic cavity during forced exhalation. The phrenic nerve arises from the cervical plexus at levels C3, C4, and C5. It stimulates the diaphragm muscle to contract, enabling inspiration. The mnemonic C3, 4, 5, keep the diaphragm alive can help you remember the origin of this important spinal nerve. 826

10 Objective 2 (continued). Describe functions for each of the structures of the respiratory system: nose and paranasal sinuses, pharynx, larynx, trachea, bronchi, pleural membranes, ribs and thoracic wall, diaphragm and intracostal muscles, phrenic nerves and pulmonary plexus. Be able to identify each of these on a diagram or photograph. The lungs receive both sympathetic and parasympathetic innervations. Remember that the sympathetic nervous system enables the fight or flight response. If you were running from a saber-tooth tiger (or on a hot date) you would need more air to your lungs. Under sympathetic stimulation, smooth bronchial muscle dilates. Sympathetic nervous outflow arises from the thoracolumbar region of the spinal cord. Sympathetic nerves that innervate the lungs have cell bodies in the intermediate horn (sides of the gray matter) in the T1- T4 areas of the spinal cord. The nerves synapse at the sympathetic chain ganglia (along the sides of the spinal cord). The nerves enter the lungs at the hilus forming the pulmonary plexus. Remember that the parasympathetic nervous system enables the rest and repose response. Think post- Thanksgiving dinner; breathing is barely necessary when one is semi-comatose digesting on the couch! Parasympathetic stimulation causes mucus secretion and constriction of bronchial smooth muscle. The parasympathetic nerve innervating the lungs is Cranial nerve X, the vagus nerve, using acetylcholine as the neurotransmitter. 827

11 Objective 3. Define conducting zone and respiratory zone. Define upper and lower respiratory tracts. Assignment: Tortora, p. 875 or Wiley Plus 23.1 Respiratory System Anatomy The respiratory tract is divided into the conducting zone and the respiratory zone. The conducting zone consists of all of those structures that bring the air to the alveoli where gas exchange will occur. The nose, pharynx, larynx, trachea., bronchi, bronchioles and terminal bronchioles are all part of the conducting zone. The function of the conducting zone is to filter, warm, moisten and conduct the air to the lungs. The respiratory zone is where gas exchange takes place in the lungs. Respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli make up the respiratory zone. As mentioned previously, the respiratory tract is also divided into the upper and lower portions. The upper respiratory tract includes the nasal cavity, oral cavity, and the pharynx. Although views differ as to the proper classification of the larynx, the text classifies it as part of the upper respiratory tract. The lower respiratory tract includes the trachea and all components of the lungs. The upper respiratory tract is full of endogenous (normal) flora. The lower respiratory tract should be sterile. Sputum, an abnormal, thick, mucus (spit mixed with respiratory secretions) is often cultured if a physician suspects pneumonia. As the patient coughs up the sputum (sorry for the visual!) it mixes with normal microorganisms of the upper respiratory tract. The microbiologist must discern between the normal flora and any harmful pathogens. 828

12 Objective 4. List each of the structures through which air passes during inspiration. Assignment: Tortora, p. 875 or Wiley Plus 23.1 Respiratory System Anatomy Let s summarize by looking at the travel itinerary for an air molecule. Remember that the molecule must first travel through cavities and tubes that make up the conducting zone. Think of it as going down a big water slide before it makes its final splash in the respiratory zone. The molecule travels from the outside world through the mouth or nose (depending on your personal preference). It then must make it down the pharynx, through the larynx, and down the trachea. From here there s a choice involved. The molecule may either make a right or left turn into the right or left primary bronchus. Now the branching begins and each air molecule can take many different paths through the secondary bronchi, tertiary bronchi, and the tiny bronchioles. These bronchioles end in the basic unit of the lung, the lobule. We are now entering the respiratory zone where oxygen and carbon dioxide will be exchanged. Each lobule contains a lymphatic vessel, an arteriole, a venule, and a branch from a terminal bronchiole. The terminal bronchioles subdivide into tiny respiratory bronchioles. At the end of the respiratory bronchioles we find the grape-like clusters of alveoli where gas exchange occurs. The oxygen from our air molecule diffuses into the bloodstream, traveling out to the tissues where it s needed for metabolism. 829

13 Objective 5. Describe the histology of the respiratory epithelium. State a function for each kind of epithelium. Assignment: Tortora, pp. 177, or Wiley Plus 4.3 Epithelial Tissue & 23.1 Respiratory System Anatomy Remember that function denotes structure. This is true of the tissues of the respiratory tract. Tissues vary throughout the respiratory tract to meet specific functions. Parts of the pharynx and larynx are lined with stratified squamous epithelium for protection (think tortilla chips!). Most of the conducting portion of the respiratory tract is lined with pseudostratified columnar ciliated cells, also called the respiratory epithelium. This epithelium also contains goblet cells which produce mucus. The mucus and the cilia form the mucocillary escalator which transports foreign particles out of the respiratory tract. The trachea lies anterior to the esophagus. The trachea is supported by C shaped rings of hyaline cartilage which prevent the trachea from collapsing, blocking the conduction of air. 830

14 Objective 5 (continued). Describe the histology of the respiratory epithelium. State a function for each kind of epithelium. Smooth muscle lines the bronchi and bronchioles. This is important to control the diameter of the airways. When you re exercising and gasping for air, the sympathetic nervous system stimulates the bronchi and bronchioles to dilate, allowing the passage of more air to the lungs. When you re sleeping on the couch after your strenuous workout, the airways constrict under parasympathetic stimulation and secretions increase. Inflammatory conditions such as asthma also cause constriction of the airways, trapping air within the lungs. As we move deeper into the respiratory zone, the epithelium changes. Alveoli are lined with two types of epithelium. Type I alveolar cells are simple squamous epithelium. These cells are the site of gas exchange. They are by far the most numerous cell lining the alveoli. The capillaries carrying red blood cells are also lined with a single layer of squamous epithelium. These cells, along with the type I alveolar cells, form the alveolar-capillary (A-C) membrane, a thin membrane that gases can easily diffuse across. Type II alveolar cells, are simple cuboidal epithelium, and secrete surfactant. This is a soap-like substance that decreases surface tension allowing easier inflation of the alveoli and preventing the collapse of alveoli after exhalation. Alveolar macrophages are there for clean up of large particles and invaders. 831

15 Objective 6. Define pulmonary ventilation, inspiration, and expiration. Assignment: Tortora, pp or Wiley Plus 23.2 Pulmonary Ventilation Respiration: The process of gas exchange in the body. Pulmonary Ventilation: The inhalation and exhalation of air. This involves the exchange of air between the atmosphere and the alveoli of the lungs. Inhalation: Movement of air into the lungs from the atmosphere. Active process requiring muscle action Exhalation: Movement of air out of the lungs into the atmosphere. Passive process during quiet breathing due to the elastic recoil of the lungs Active (muscle help) during vigorous exercise or certain disease conditions causing difficult expiration (chronic obstructive pulmonary diseases) 832

16 Objective 7. Define: Boyle s Law. Explain the application of Boyle s Law to inspiration and expiration. Assignment: Tortora, p. 890 or Wiley Plus 23.2 Pulmonary Ventilation Let s shift our attention to two important physics laws and principles behind these laws that will help us understand respiration. The idea that a gas is made up of little billiard balls zipping around and colliding with each other is called by the rather fancy name The Kinetic Molecular Theory. There are five principles in the theory: 1. There is a lot more space between gas particles than the gas particles themselves occupy. 5. The average speed of the particles is related to the temperature Particles move in a straight line until they collide. They move in different directions and have different speeds. 3. The particles in a gas don t interact with each other much, if at all. 4. When particles collide, all the energy goes into bouncing, and none is absorbed by the particle. In the 19th century, a number of scientists stated Gas Laws. These laws were absorbed into the Kinetic Molecular Theory but we still learn them by the name of the person who stated them first.

17 Objective 7 (continued). Define: Boyle s Law. Explain the application of Boyle s Law to inspiration and expiration. Boyle s Law says that pressure (which we can think of as the number of collisions with the walls of the container) times volume is a constant at constant temperature. Human bodies are at a constant temperature of 37 C. If pressure goes up, volume goes down. (If you press on a syringe, its volume decreases). If volume goes up, pressure goes down. (That is, there is more room between the molecules and fewer collisions). BoylesLaw/ 834

18 Objective 8. State the pressures in the structures of the respiratory system during inspiration and expiration. Assignment: Tortora, pp or Wiley Plus 23.2 Pulmonary Ventilation Boyle s law has a direct application to the principles governing inspiration and expiration. During inspiration, contraction of the diaphragm and external intercostals muscles increase the volume of the thoracic cavity. As we just learned, as the volume increases, pressure decreases. The pressure in the thoracic cavity is now slightly less than atmospheric pressure. Following the principle of diffusion, air will flow from high to low pressure into the thoracic cavity. During deep, labored breathing, additional muscles are used to further enlarge the thoracic cavity. The accessory muscles include the sternocleidomastoid which elevates the sternum, the scalene muscles and pectoralis minor which elevate ribs. During inhalation the lifting of the sternum acts as the handle of a pump while the ribs elevate up and out like the handles of a bucket. 835

19 Objective 8 (continued). State the pressures in the structures of the respiratory system during inspiration and expiration. Exhalation is a passive process during quiet breathing. Elastic recoil of the chest wall and lungs causes the volume in the thoracic cavity to decrease. As the volume decreases, the pressure increases. Pressure is now higher in the thoracic cavity than atmospheric air and air flows out from high to low pressure. During forced exhalation, abdominal muscles and the internal intercostals contract further decreasing the volume of the thoracic cavity and increasing the pressure. 836

20 Objective 9. Describe the forces which promote collapse of lung and those which oppose lung collapse. State why pneumothorax leads to atelectasis. Assignment: Tortora, p. 885 or Wiley Plus 23.1 Respiratory System Anatomy Air may leak into the pleural cavity from trauma to the lung or a spontaneous rupture of a bleb, a weak spot on the lung. The pressure of the air does not allow the lung to fully inflate and a pneumothorax or collapsed lung may occur. Physicians treat a pneumothorax by placing a chest tube between the ribs in the wall of the thoracic cavity. This allows the air to flow out. The tube is then removed or sealed off and the hole in the chest wall repaired so the lungs can spontaneously re-inflate. 837

21 Objective 10. State the four respiratory volumes and four respiratory capacities. Identify each of these on a spirogram. Assignment: Tortora, pp or Wiley Plus 23.3 Lung Volumes and Capacities Pulmonary function can be tested using a spirometer, which measures the volume of air exchanged during breathing and the respiratory rate. The record of this measurement is called a spirogram. Four respiratory volumes and four respiratory capacities are measured: Respiratory volumes: Tidal Volume (VT): Volume of air inspired or expired during normal quiet breathing Inspiratory Reserve Volume: All of the air that you can breathe in from the top of tidal volume (during a very deep inhalation). Expiratory Reserve Volume: All of the air that you can breathe out from the bottom of tidal volume during a forced exhalation. Residual Volume: Air still present in lung tissue after the thoracic cavity has been opened. 838

22 Objective 10. State the four respiratory volumes and four respiratory capacities. Identify each of these on a spirogram. Respiratory capacities are combinations of specific lung volumes: Inspiratory capacity: The sum of tidal volume and inspiratory reserve volume. Functional residual capacity: The sum of residual volume and expiratory reserve volume. Vital capacity: The sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume. Total lung capacity: Sum of vital capacity and residual volume 839

23 Objective 11. State Dalton s Law. State Henry s Law. Explain how each is relevant to external and internal respiration. Using these laws, compare and contrast human physiology at normal atmospheric pressure and at high pressure. Assignment: Tortora, pp , 899 or Wiley Plus 23.4 Exchange of Oxygen and Carbon Dioxide The exchange of gases at the alveoli and the tissues is explained by 2 physical laws: Dalton s Law and Henry s Law. Dalton s Law says that the particles in a gas don t care about each other. In a mixture of different gases (gas A and gas B and gas C), the pressure due to gas A is exactly equal to its proportion in the mixture. For Earth s atmosphere, 21% of the atmosphere is oxygen, so 21% of the atmospheric pressure is due to oxygen. We call this the partial pressure of oxygen. We represent the partial pressure of oxygen as PO2 or po2; the partial pressure of CO2 as PCO2; and so forth. The element argon is 1% of the Earth s atmosphere. What percentage of atmospheric pressure is contributed by argon? Henry s Law says the amount of a gas that is dissolved in a liquid is directly proportional to the partial pressure of the gas. In the body much more CO2 is dissolved in blood plasma than O2 because it is 24x more soluble than oxygen. A hyperbaric chamber increase the atmospheric pressure of oxygen, and more dissolves in solution (the blood). 840

24 Objective 11 (continued). State Dalton s Law. State Henry s Law. Explain how each is relevant to external and internal respiration. Using these laws, compare and contrast human physiology at normal atmospheric pressure and at high pressure. When Olympians came to Salt Lake City to compete, they had to contend with the high altitude. Atmospheric pressure decreases as we ascend in altitude. Henry s Law states that if the atmospheric pressure of oxygen is lower, less will dissolve in solution. Altitude sickness may occur because of the lack of oxygen dissolved in the blood. Ultimately pulmonary vessels may vasoconstrict increasing pulmonary pressure. Fluid may be pushed out of the vessels leading to the serious condition of pulmonary edema. Lack of oxygen to the brain may lead to cerebral edema and subsequent death. The opposite condition may occur with scuba divers. For every 30 feet that a diver descends, atmospheric pressure increases by 1 atm (760 mmhg). A much larger amount of nitrogen than normal is now dissolved in the blood because of the high pressure. If a diver ascends too rapidly, nitrogen may come out of solution leading to joint and lung damage, a painful condition called the bends. 841

25 Objective 12. Describe, in detail, the process of external respiration and movement of gases across the alveolar-capillary (A-C) membrane. Assignment: Tortora, pp or Wiley Plus Exchange of Oxygen and Carbon Dioxide External respiration occurs at the alveolarcapillary membrane. External respiration is the diffusion of atmospheric oxygen from the alveoli of the lungs to blood in the pulmonary capillaries. In exchange, CO2 in blood coming from the tissues diffuses into alveolar capillaries and is exhaled. While the alveolar-capillary membrane is very thin (about 0.5 µm) an oxygen molecule must still pass through the alveolar cell membrane, alveolar basement membrane, capillary basement membrane and capillary endothelial cell membrane. (The two basement membranes are fused, which makes the journey that much shorter.) 842

26 Objective 12 (continued). Describe, in detail, the process of external respiration and movement of gases across the alveolar-capillary (A-C) membrane. The diagram below gives a step-by-step breakdown of external respiration. Waste-laden blood from the tissues returns to the heart and then enters the lungs via the pulmonary arteries and arterioles. CO2 diffuse across the alveolar-capillary membrane and is exhaled. O2 from the atmosphere diffuses from the alveoli to the blood. This now oxygen-rich blood returns to the left atrium of the heart via the pulmonary venules and veins. It is then pumped out to the tissues of the body. Remember that gases diffuse independently of one another from an area of high pressure to low pressure. CO2 and O2 are simply diffusing down their concentration gradients. 843

27 Objective 13. Explain ventilation-perfusion coupling. Assignment: Tortora, p. 889 or Wiley Plus 23.4 Exchange of Oxygen and Carbon Dioxide Pulmonary ventilation ( ) is the amount of air entering the lungs each minute. (The V is for ventilation; the dot indicates per minute.) Alveolar ventilation ( ) is the amount of air entering the alveoli each minute. If air enters your lungs, but does not enter the alveoli, then its gases cannot be absorbed into the blood. Perfusion ( ) is the amount of blood that flows through the capillaries each minute. Under hypoxic conditions (low amounts of oxygen) pulmonary blood vessels constrict. This constriction causes blood to move (or shunt) from areas of low oxygen in the lungs to areas of high oxygen. Blood flow is greatest, therefore, in alveoli that have the greatest amount of oxygen flow. This matching of blood flow to oxygen is ventilation-perfusion coupling. A ratio of ventilation to perfusion ( / ) can be calculated and is normally about 1. This means that ventilation (air flow) and perfusion (blood flow) are equally matched. This ratio is changed in disease states that affect oxygen flow or blood flow. For example, if a patient has difficulty breathing, oxygen flow decreases and the ratio is disrupted. If a patient has a blood clot in the lung, blood does not flow and the ratio is again disrupted. If the ventilation/perfusion ratio is disrupted, inadequate exchange of oxygen and carbon dioxide occurs. 844

28 Objective 14. Describe the process of internal respiration. Assignment: Tortora, pp or Wiley Plus 23.5 Transport of Oxygen and Carbon Dioxide Internal respiration is the exchange of O2 and CO2 between systemic capillaries and tissue cells. This exchange occurs in tissues throughout the body. Gases again diffuse from high to low pressure. The tissues are actively using oxygen for metabolism. The partial pressure of oxygen is lower in the tissues and higher in the blood and therefore diffuses into the tissues. CO2 is a waste product of metabolism. Its partial pressure is higher in the tissues than the blood so it diffuses from high to low, leaving the tissues and entering the bloodstream. 845

29 Objective 14 (continued). Describe the process of internal respiration. Carbon dioxide and oxygen are carried through the bloodstream in different forms: Oxygen: 98.5% is carried bound to hemoglobin in RBCs 1.5% is dissolved in the plasma Carbon dioxide: 70% travels through the bloodstream as bicarbonate (HCO3 - ) 23% is bound to hemoglobin 7% is dissolved in the plasma 846

30 Objective 15. Compare and contrast the processes of external and internal respiration. Compare and contrast the partial pressures of oxygen and carbon dioxide during the process of external and internal respiration. Assignment: Tortora, pp , 905 or Wiley Plus 23.4 Exchange of Oxygen and Carbon Dioxide & 23.5 Transport of Oxygen and Carbon Dioxide In summary, external respiration is the exchange of gases between the pulmonary capillaries and the alveoli which contain atmospheric air. CO2 diffuses from the capillaries into the alveoli; O2 diffuses from the alveoli to the pulmonary capillaries. Internal respiration is the exchange of gases between the tissues and the systemic capillaries. Oxygen diffuses into the tissues, carbon dioxide diffuses from the tissues into the bloodstream. 847

31 Objective 15 (continued). Compare and contrast the processes of external and internal respiration. Compare and contrast the partial pressures of oxygen and carbon dioxide during the process of external and internal respiration. The PO2 is highest in the alveoli where it s about 105 mm Hg. The pressure drops slightly as blood enters the left atrium (100 mm Hg). The PO2 in the tissues is only about 40 mmhg. Thus O2 flows from the higher pressure in the systemic capillaries into the tissues. As blood leaves the tissues, the PO2 drops to approximate that of the tissues, about 40 mm Hg CO2 diffuses in the opposite direction. CO2 is highest in the tissues and in the blood returning to the left atrium and the lungs via the pulmonary arteries (PCO2 45 mm Hg), hence CO2 diffuses into the alveoli. CO2 leaving the lungs and in the systemic circulation traveling to the tissues has a partial pressure of 40 mmhg. This is lower than the tissues (PCO2 45 mm Hg), thus, CO2 diffuses from the tissues to the systemic capillaries The slide at the right depicts the different ways CO2 and O2 are carried in the blood. The mechanisms by which CO2 is carried are discussed further in Objective

32 Objective 16. Be able to label and explain important features of the oxygen-hemoglobin saturation curve. Describe how different conditions (oxygen partial pressure, temperature, carbon dioxide partial pressure) might alter the saturation curve. Compare and contrast the oxygen saturation curve for fetal and adult hemoglobin. Assignment: Tortora, pp or Wiley Plus 23.5 Transport of Oxygen and Carbon Dioxide The O2-Hemoglobin saturation curve shows the proportion of Hb bound to O2. The higher the PO2 (X axis) the more oxygen is bound to Hb (Y axis). Certain conditions influence the O2-Hb saturation curve. During conditions such as exercise, tissues need more oxygen. Actively working tissues generate acids as waste, lowering the ph. A drop in ph shifts the curve to the right, causing more O2 to be released at the tissues (see the red line). 849

33 Objective 16 (continued). Be able to label and explain important features of the oxygenhemoglobin saturation curve. Describe how different conditions (oxygen partial pressure, temperature, carbon dioxide partial pressure) might alter the saturation curve. Compare and contrast the oxygen saturation curve for fetal and adult hemoglobin. Actively working tissues also generate more CO2 as waste. Higher PCO2 levels shift the curve to the right and more O2 is delivered to the tissues. A tissue that is resting generates less CO2. This shifts the curve to the left and less O2 is delivered to the tissues. Actively working tissues also generate heat. Higher temperatures shift the curve to the right, and more O2 is delivered. Resting tissue generates less heat, and less O2 is delivered. When we re sick and have a fever, more O2 is delivered to the tissues helping them fight infection. Ingenious! Fetal Hb has a higher affinity for O2 than adult Hb. When PO2 is low, Fetal Hb can carry up to 30% more O2 than maternal Hb. Because of this, oxygen diffuses easily from maternal to fetal blood. 850

34 Objective 17. State the ways carbon dioxide is carried in the blood, and rank their relative importance. Assignment: Tortora, pp or Wiley Plus 23.5 Transport of Oxygen and Carbon Dioxide The conversion of CO2 to bicarbonate to be carried in the plasma is a somewhat complicated process. First, CO2 combines with H20 in the red blood cell to form carbonic acid (H2CO3 - ). Carbonic acid dissociates to HCO3 and H +. The bicarbonate ions leave the RBC, exchanging for Cl ions. At the alveoli the reaction reverses and CO2 is exhaled. This reaction can be visualized on the graphic below and on the following page. 851

35 Objective 18. State the chemical equation which describes the relationship between carbon dioxide, bicarbonate ion, and carbonic acid in blood. Predict how raising and lowering ph or carbon dioxide concentration will affect this system. Assignment: Tortora, pp , 1072 or Wiley Plus 23.5 Transport of Oxygen and Carbon Dioxide & 27.3 Acid-Base Balance Buffers prevent rapid, drastic changes in ph of body fluids by converting strong acids and bases into weak acids and bases. This is a rapid conversion which takes place in fractions of a second. Most buffer systems in the body consist of a weak acid and a weak base. Buffer reactions can proceed from left to right or right to left. In the carbonic acidbicarbonate buffer system, excess hydrogen ions can be instantly converted to water and carbon dioxide. Under alkaline conditions, water and carbon dioxide are converted to hydrogen and bicarbonate ions. 852

36 Objective 18 (continued). State the chemical equation which describes the relationship between carbon dioxide, bicarbonate ion, and carbonic acid in blood. Predict how raising and lowering ph or carbon dioxide concentration will affect this system. 853

37 Objective 19. Define: hyperventilation, hypoventilation, panting, eupnea, hyperpnea and apnea. Assignment: This page. Because CO2 easily converts to an acid, the respiratory system can help control blood ph by either speeding up breathing to get rid of CO2 or slowing down breathing to retain CO2. Hyperventilation, or excessive ventilation is a mechanism used by the body to lower the blood ph. Hyperventilation during your favorite exam may also lead to alkalosis. (You knew exams were bad for your health!). Hypoventilation retains more CO2. The body may use this mechanism in conditions of alkalosis to increase the ph. Patients with chronic obstructive pulmonary diseases such as emphysema have difficulty exhaling and often build up CO2 leading to acidosis. 854

38 Objective 20. State the location and function of the respiratory control centers in the brainstem. Assignment: Tortora, pp or Wiley Plus 23.6 Control of Respiration CONTROL OF RESPIRATION NEURAL REGULATION Medulla The function of the medulla rhythmicity area, which has both an inspiratory and an expiratory center, is to control the basic rhythm of respiration. The inspiratory center stimulates the diaphragm via the phrenic nerve, and the external intercostal muscles via intercostal nerves. [Inspiration normally lasts about 2 seconds.] Most of exhalation is a passive process caused by the elastic recoil of the lungs. Usually the expiratory center is inactive during quiet breathing (nerve impulses cease for about 3 seconds). During forced exhalation, however, impulses from this center stimulate the internal intercostals and the abdominal muscles to contract. NEURAL REGUALTION Pons Other sites in the pons help the medullary centers manage the transition between inhalation and exhalation. The pneumotaxic center limits the duration of inspiration, so the lungs don t get too full. The apneustic center coordinates the transition between inhalation and exhalation. 855

39 Objective 20 (continued). State the location and function of the respiratory control centers in the brainstem. OTHER SOURCES OF REGULATION The medulla and pons control the basic rhythm of respiration, but inputs from other areas also have a role. Our cerebral cortex has voluntary control when we want it. Emotions (limbic system) affect breathing. Hypercapnia (hypocarbia) (elevated PCO2), low O2, or acidosis (low ph) stimulate more rapid breathing. Bronchial stretch receptors, sensing overinflation, arrest breathing temporarily (Hering-Breuer reflex). The hypothalamus, sensing a fever, increases breathing. Moderate pain increases breathing. Severe pain causes apnea a temporary cessation of breathing. 856

40 Objective 21. Explain homeostatic mechanisms involved in control of blood gases and ph. Assignment: Tortora, pp or Wiley Plus 23.6 Control of Respiration The body has a built in mechanism to regulate CO2, O2, and H + levels in the blood. Chemoreceptors send input to the inspiratory center to increase respirations if CO2 and/or H + are high or PO2 is low. CO2, H +, O2 = Increase in rate and depth of breathing Can you die by holding your breath? If the PO2 drops below from a normal level of 100 mm Hg to above 50 mm Hg, chemoreceptors are stimulated. You are consciously holding your breath through the influence of the motor cortex. If your PO2 drops below a certain level, fainting (syncope) follows, and the brainstem will take over the work of breathing while you are unconscious. Why can you hold your breath longer if you hyperventilate first? A low PCO2 (below 40 mmhg) does not signal chemoreceptors and will not stimulate the inspiratory center. (The inspiratory center responds to high CO2, not low CO2). So if you hyperventilate, blowing off CO2, the inspiratory center slows and you can hold your breath longer. Why is it dangerous to hyperventilate and then swim underwater? Swimmers were once encouraged to hyperventilate before swimming to be able to hold their breath longer. This is dangerous because O2 levels may fall to a dangerously low condition before the chemoreceptor reflex is activated, causing fainting (syncope). Passing out in the water is usually not a good idea as drowning may occur! 857

41 Objective 22. Summarize the embryonic development of the respiratory system. Explain the role of surfactant in care of premature infants. Assignment: Tortora, pp or Wiley Plus 23.8 Development of the Respiratory System The lungs begin to develop during just the fourth week of pregnancy. The slide on the left shows further development of the fetal lungs. At weeks of pregnancy the lungs become highly vascular and respiratory bronchioles, alveolar ducts, and some primitive alveoli begin to develop. An infant born at 26 weeks may survive, however death frequently occurs because the respiratory system is so immature. From 26 weeks to birth, the alveoli develop. At birth, only about a sixth of the alveoli are present. These continue to develop during the first eight years of life. Remember from Module 2 that water has surface tension. Hydrogen bonding tightly holds water molecules together. This is why your little brother can pour water over the brim of your glass without it spilling over. Alveoli must overcome this surface tension to inflate. 858

42 Objective 22 (continued). Summarize the embryonic development of the respiratory system. Explain the role of surfactant in care of premature infants. Remember also from Module 2 that surfactants act like soap, breaking up hydrogen bonds and reducing surface tension. In the lungs, surfactant is manufactured by type 2 alveolar cells. Surfactant acts to break up surface tension caused by water molecules in the air-liquid interface within the alveoli of the lungs. Surfactant is necessary to prevent the collapse of alveoli on exhalation. Amounts of surfactant sufficient to permit survival of a premature infant are not produced until weeks of gestation. The important role of surfactant in infant respiratory distress syndrome was discovered in the 1950s. After several decades of research, an artificial surfactant was developed. This is given into the airway of the infant at, or shortly after, birth. Immediate improvements in lung function are usually observed. Infant mortality has greatly decreased since the advent of exogenous surfactant therapy. 1 1 Rocca et al. In The Pulmonary Epithelium in Health and Disease. Proud, D (ed). Wiley:Hoboken,