الملخص في فسيولوجيا الجهاز التنفسي لطلاب الطب المستوى الثاني Anatomy Review Summary • The respiratory system consists of the nose, pharynx, larynx, trachea, bronchi, and lungs. • The visceral pleura covers the surface of the lungs. The parietal pleura covers the mediastinum and the diaphragm and lines the thoracic wall. • The lungs contain the bronchial tree, the branching airways from the primary bronchi through the terminal bronchioles. • The respiratory zone of the lungs is the region containing alveoli, tiny thin-walled sacs where gas exchange occurs. • Oxygen and carbon dioxide diffuse between the alveoli and the pulmonary capillaries across the very thin respiratory membrane. ================= Pulmonary Ventilation Summary • Muscle activity causes changes in the volume of the thoracic cavity during breathing. • Changing the thoracic cavity volume causes intrapulmonary and intrapleural pressure changes, which allow air to move from high pressure to low pressure regions. • Airway resistance is normally low, but nervous stimulation and chemical factors can change the diameter of bronchioles, thereby altering resistance and airflow. • Lung compliance is normally high due to the lung's abundant elastic tissue and surfactant's ability to lower the surface tension of the alveolar fluid. ================= Gas Exchange Summary • Gas laws show the relationship between partial pressure, solubility, and concentration of gases. • Gases diffuse along their partial pressure gradients, from regions of high partial pressure to regions of low partial pressure. • External respiration: O2 loads from alveoli into pulmonary capillaries, and CO2 unloads from pulmonary capillaries into alveoli. • Internal respiration: O2 unloads from systemic capillaries into cells and CO2 loads from cells into systemic capillaries. • Efficient gas exchange depends on several factors including surface area, partial pressure gradients, blood flow and airflow. • During external respiration, ventilation-perfusion coupling maintains airflow and blood flow in proper proportions for efficient gas exchange. ================= Gas Transport Summary O2 is transported in two ways: • dissolved in plasma • bound to hemoglobin as oxyhemoglobin The O2 saturation of hemoglobin is affected by: • PO2 • pH • Temperature • PCO2 • BPG CO2 is transported in three ways: • dissolved in plasma • bound to hemoglobin as carbaminohemoglobin • converted to bicarbonate ions O2 loading faciliates CO2 unloading from hemoglobin. This is known as the Haldane effect. CO2 loading, through the formation of hydrogen ions, facilitates O2 unloading from hemoglobin. The effect of decreased pH on O2 unloading is known as the Bohr effect. ================= Control of Respiration Summary • The basic rhythm of breathing is set by the inspiratory center, located in the medulla. Other respiratory centers, located in the medulla and pons, also control breathing. • Chemoreceptors monitor the PCO2, pH, and PO2 of arterial blood and alter the basic rhythm of breathing. - CO2, reflected by changes in pH, is the most important stimulus controlling ventilation. - pH changes due to metabolic acids also alter ventilation. - O2 stimulates ventilation only when the blood PO2 is very low. • Other factors, such as voluntary control, pain and emotions, pulmonary irritants, and lung hyperinflation, also play roles in controlling ventilation. • The control of ventilation during exercise, while complex and not fully understood, involves multiple inputs including chemical and neural factors تعاريف مهمة Glossary Acetylcholine - One of the principal neurotransmitters of the autonomic nervous system. It also functions in the brain and at neuromuscular junctions in skeletal muscles. Affinity - The degree of attraction between a molecule and the substance it binds to. Allergic reactions - An excessive immune response to a harmless antigen. Alveolar duct - An elongated air passageway completely lined by alveoli. Alveolar fluid - The liquid film that coats the alveolar walls, composed primarily of water. Alveolar sac - Clusters of alveoli that open into a common space. Alveoli - Thin-walled, air-filled sacs in which gas exchange occurs. Alveolus - A thin-walled air-filled sac in the lungs where gas exchange occurs. Arteries - Blood vessels that carry blood away from the heart. Arterioles - Very small arteries which carry blood to capillaries. Basement membrane - Extracellular material that supports an epithelial tissue. Bohr effect - The change in hemoglobin's affinity for oxygen in response to changes in pH. By forming hydrogen ions, carbon dioxide loading faciliates oxygen unloading. Boyle's Law - The pressure of a gas is inversely proportional to the volume of its container. Increasing the volume of a container decreases the pressure. Decreasing the volume of a container increases the pressure. BPG - 2,3-biphosphoglycerate, a unique compound that binds reversibly with hemoglobin. It is produced by red blood cells as they break down glucose by the anaerobic process called glycolysis. Brainstem - The part of the brain composed of the medulla oblongata, the pons and the midbrain. Bronchial tree - The branching network of airways, from the primary bronchi through the terminal bronchioles, that conducts air within each lung. Bronchiole - A very small air passage without supporting cartilage. Buffer - A chemical substance or a system that minimizes changes in pH by releasing or binding hydrogen ions. Capillary - The smallest of the blood vessels; the site of exchange between the blood and the tissue cells. Carbaminohemoglobin - The form of hemoglobin which is bound to carbon dioxide. Cartilage - A tough, flexible, supporting connective tissue. Cerebellum - The brain region most involved in producing smooth coordinated skeletal muscle activity. Cerebrospinal fluid - Plasmalike fluid within the brain ventricles, the central canal of the spinal cord, and the subarachnoid space surrounding both the brain and spinal cord. It protects and nourishes the central nervous system. Abbreviated as CSF. Chemoreceptors - Sensory receptors that respond to changes in various dissolved chemicals. Conducting zone - The airways, from the nasal cavity through the terminal bronchioles, that conduct air to the respiratory zones of the lungs. Control centers - One of the components of homeostatic control mechanisms; determines the normal range within which a variable is to be maintained, analyzes the input it receives and then determines the appropriate response. CSF - Cerebrospinal fluid; plasmalike fluid within the brain ventricles, the central canal of the spinal cord, and the subarachnoid space surrounding both the brain and spinal cord. It protects and nourishes the central nervous system. Dalton's Law - Dalton's Law of Partial Pressures states that in a mixture of gases, the total pressure equals the sum of the partial pressures exerted by each gas. The partial pressure of each gas is directly proportional to its percentage in the total gas mixture. Diaphragm - The muscle that separates the thoracic cavity from the abdominopelvic cavity; it contracts during inspiration. Diffusion - The net movement of molecules and ions from regions of higher concentration to regions of lower concentration until equilibrium is reached. Effectors - One of the components of homeostatic control mechanisms; provides the means for the control center's response (output) to the stimulus. Information flows from the control center to the effector along the efferent pathway. Epinephrine - A hormone released from the adrenal medulla during exercise or stress, which augments the effects of the sympathetic nervous system; also called adrenaline. Expiration - Exhalation; act of expelling air from the lungs. Expiratory - Pertaining to exhalation; act of expelling air from the lungs. External nares - The external openings leading into the nasal cavities; also called the nostrils. External respiration - The exchange of gases between the alveoli in the lungs and the pulmonary capillaries. Fibrosis - The abnormal formation of fibrous connective tissue. Globin - The protein portion of the hemoglobin molecule. Glossopharyngeal nerve - Cranial nerve IX; a mixed nerve with many functions including carrying sensory and motor fibers to and from the tongue and pharynx, and carrying sensory fibers from the carotid and aortic bodies and the carotid sinus. Haldane effect - The increase in carbon dioxide unloading from hemoglobin in response to oxygen unloading. Hemoglobin - A molecule found in red blood cells which functions in oxygen and carbon dioxide transport; it is composed of 4 polypeptide chains and 4 red iron-containing heme groups. Henry's Law - The amount of gas which dissolves in a liquid is proportional to both the partial pressure and the solubility of the gas. Histamine - A chemical released by basophils, mast cells and other cells in response to an injury or an allergen. Homeostasis - The maintenance of a relatively stable internal environment of the body. Hyperinflation - Excessive inflation of the lungs during very deep inspiration. Hyperventilation - Ventilation that is higher than necessary to maintain normal blood gas levels. Hypoventilation - Ventilation that is too low to maintain normal blood gas levels. Inspiration - Inhalation; drawing air into the lungs. Inspiratory - Pertaining to inhalation; drawing air into the lungs. Inspiratory center - A group of neurons, located in the medulla oblongata, which sets the basic rhythm of breathing by automatically initiating inspiration; also known as the dorsal respiratory group. Internal respiration - The exchange of gases between the tissue cells and the systemic capillaries. Interstitial fluid - The fluid found in the spaces between tissue cells. Intrapleural pressure - The pressure within the pleural cavity. Intrapulmonary pressure - The pressure within the alveoli of the lungs; also called intra-alveolar pressure. Lactic acid - Product of anaerobic metabolism, especially in skeletal muscle tissue. Larynx - Part of the respiratory passageway located between the trachea and the pharynx. It keeps the airway open, prevents food from entering the airway, and produces sounds. Lung - One of the paired respiratory system organs (right and left lungs) in which gas exchange occurs. Lung compliance - The ease with which the lungs expand. Macrophage - Protective cell that removes debris and microbes by phagocytosis. Mediastinum - The region of the thoracic cavity between the lungs. Medulla - Medulla oblongata; the inferior part of the brainstem which contains critical autonomic reflex centers, and serves as a link between the spinal cord and the superior regions of the brain. Metabolic rate - The body's rate of energy expenditure (usually expressed per hour); the total heat produced by all the chemical reactions and mechanical work of the body. Mount Whitney - The highest peak in the lower 48 states; part of the Sierra Nevada mountain range; it is 14,495 feet (4,418 meters) high. Nasal cavity - A space within and posterior to the external nose. Neurotransmitter - Molecules released from synaptic vesicles in neuron axon terminals; bind to receptor sites on target cells, stimulating or inhibiting them. Norepinephrine - The major neurotransmitter released by the sympathetic nervous system; also a hormone released from the adrenal medulla which augments the effects of the sympathetic nervous system. Oxygen-hemoglobin dissociation curve - The graph of the relationship between the partial pressure of oxygen and the degree of hemoglobin saturation with oxygen. Oxyhemoglobin - The form of hemoglobin which is bound to oxygen. Parasympathetic- The subdivision of the autonomic nervous system concerned with conserving and restoring body energy. Parietal pleura - The part of the pleurae that lines the thoracic wall and the mediastinum, and covers the superior surface of the diaphragm on each side of the thoracic cavity. Partial pressure - The pressure exerted by an individual gas in a mixture of gases; it is directly proportional to the percentage of the gas in the total gas mixture. pH - The measure of the relative acidity or alkalinity of a solution: hydrogen ion concentration in moles per liter. Pharynx - The muscular tube extending from the nasal cavity to the esophagus and larynx; also called the throat. Plasma - The fluid portion of the blood. Pleurae - The two-layered serous membrane that surrounds each lung. Pleural cavity - The slit-like space between the visceral and parietal pleurae. Pleural fluid - Serous lubricating fluid within the pleural cavity, secreted by the pleurae. Pneumothorax - The presence of air in the intrapleural space; reversed by closing the "hole" and drawing air out of the intrapleural space with chest tubes. This allows the lung to reinflate and resume its normal function. Polypeptide - A molecule composed of a chain of amino acids. Pons - The part of the brainstem which connects the medulla oblongata to the midbrain and provides linkages between different levels of the central nervous system. Works with medullary respiratory centers to affect respiratory rate and depth. Primary bronchus - One of the two large respiratory tubes (right and left primary bronchi) that branches from the trachea and enters a lung Proprioceptors - Sensory receptors located in muscles and joints that respond to changes in body position and movement Pulmonary capillary - The smallest type of blood vessel which serves as the site of gas exchange between the blood and the alveoli. Pulmonary circuit - The system of blood vessels that serves gas exchange in the lungs, i.e., pulmonary arteries, capillaries, and veins. Receptors - A specialized cell or part of a neuron which responds to a specific type of stimulus, and converts it into an electrical signal. Resistance - Hindrance of air flow. Respiratory bronchiole - Bronchioles that contain scattered alveoli in their walls. Respiratory distress syndrome - A condition peculiar to premature babies, in which too little surfactant is produced to keep the alveoli inflated between breaths. May be treated by spraying natural or synthetic surfactant into the respiratory passageways. Respiratory membrane - The very thin membrane through which gas exchange occurs in the lungs; composed of the simple squamous epithelium lining the alveoli, the endothelium of the pulmonary capillary walls, and their fused basement membranes. Respiratory zone - The lung region containing alveoli, where gas exchange occurs. Saturation - The degree to which the binding sites on a molecule are occupied. Secondary bronchus - A respiratory tube that branches from a primary bronchus and leads into one lung lobe. Serous membrane - Moist membranes found in closed ventral (anterior) body cavities. Simple squamous epithelium - A very thin epithelium made up of one layer of flattened cells called Type I cells. Smooth muscle - Muscle consisting of spindle-shaped, nonstriated muscle cells; under involuntary control. Solubility - The quantity of a molecule which dissolves in a liquid, the quality of being soluble. Surface tension - The force of attraction between water molecules at an air-water surface, which draws water molecules closer together. Surfactant - A detergent-like mixture of phospholipids and lipoproteins that lowers the surface tension of water; produced by surfactant-secreting (Type II) cells. Surfactant-secreting cell - Cuboidal cell found within an alveolus which secretes surfactant, a mixture of molecules which lowers the surface tension of water molecules lining the alveolus; also called Type II cell. Systemic capillary - The smallest type of blood vessel which serves as the site of substance exchange between the blood and the tissue cells. Systemic circuit - The system of blood vessels that serves gas exchange in the body tissues. Terminal bronchiole - The smallest, final type of bronchiole in the conducting zone. Tertiary bronchus - A respiratory tube that branches from a secondary bronchus and leads into one bronchopulmonary segment of the lung. Trachea - The respiratory tube that extends from the larynx to the primary bronchi. Vagus nerve - Cranial nerve X; a mixed nerve with many functions including carrying parasympathetic fibers to the viscera and sensory fibers from the carotid and aortic bodies, the carotid sinus and most viscera. Vasoconstrict - Contraction of smooth muscle in the wall of a blood vessel, narrowing its diameter. Vasodilate - Relaxation of smooth muscles in the wall of a blood vessel, enlarging its diameter. Veins - Blood vessels that carry blood toward the heart. Ventilation-perfusion coupling - Mechanisms which maintain the correct proportion between alveolar airflow and pulmonary capillary blood flow, including constriction and dilation of arterioles and bronchioles. Ventricle - Cavity within the brain, filled with cerebrospinal fluid. Visceral pleura - The part of the pleurae that covers the external surface of each lung..