Structure and Function of the Pulmonary System
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Transcript of Structure and Function of the Pulmonary System
Structure and Function of the Pulmonary System
Pulmonary System
• Made up of two lungs– Where gas exchange takes place
• Airways– To get air to lungs
• Blood vessels– To circulate oxygen and carbon dioxide
• Chest wall – To move air in and out of lungs through
pressure changes and protect lungs
Airways• Can divide respiratory system into two
parts:– Upper respiratory tract : nasal cavity, pharynx– Lower respiratory tract: larynx, trachea,
bronchi, bronchioles, alveoli
• Upper respiratory tract serves to conduct air into the body, and filter, warm and humidify the air.
Lungs
• Two lungs
• Right lung has 3 lobes and two fissures
• Left lung has 2 lobes and one fissure
• Blood vessels and bronchi enter at hilus
Alveoli
• Small, thin air sacs surrounded by a “hair net” of capillaries
• Most of the walls of the alveoli are made up of simple squamous epithelium, called Type 1 alveolar cells. Gas exchange takes place through these cells
Other cells of the alveoli
• Type II alveolar cells produce surfactant (lipoprotein) to decrease the surface tension of water in the lungs– Premature infants – respiratory-distress
syndrome of the newborn
• Alveolar macrophages, or “dust cells” phagocytize foreign particles and microbes
Respiratory membrane• Made of alveolar type I cell, endothelium
of capillary and their basement membranes.
• As thin as possible for gas exchange which takes place by diffusion from areas of high partial pressure to low partial pressure
• Any disorder that thickens the membrane decreases gas exchange.
• Usually, about one third of the pulmonary vessels are perfused at one time, so if right heart output increases does not increase arterial pressure in lungs, simply perfuse more vessels.
• Lungs are surrounded by pleural membranes : parietal pleura and visceral pleura
• Separate by the mediastinum
• Enclosed in the thoracic cavity.
Pulmonary ventilation (breathing)
• Takes place by decreasing the pressure inside the thoracic cavity, and allowing atmospheric pressure to force air into lungs.
• Thoracic cavity is expanded primarily by the contraction and lowering of the diaphragm, but is aided by expansion of chest by contraction of the external intercostal muscles.
Expiration
• Is normally a passive process due to the relaxing of the inspiratory muscles and the elastic recoil of the lungs.
Respiratory volumes
• Amount of air moved in and out of lungs
• Tidal volume is the amount of air moved with a normal breath
• Minute volume of respiration = tidal volume X breaths per minute
Peripheral Chemoreceptors
• Carotid bodies and aortic bodies
• Stimulated by oxygen concentration decrease
• Send impulses to respiratory centers, and breathing increases
• Not triggered until O2 is very low (50 mm Hg)
Oxygen transport• Gases move down partial pressure gradient.
• 98 % of oxygen is bound to the iron in hemoglobin as oxyhemoglobin (HbO2)
• Rest is dissolved in plasma
• 4 Iron atoms per hemoglobin molecule
• 1 hemoglobin molecule can hold up to 4 molecules of oxygen
• Amount of oxygen on hemoglobin is determined by partial pressure of oxygen.
Carbon Dioxide Transport• 7 % is dissolved in plasma
• 23 % combines with the amino groups of the hemoglobin forming carbaminohemoglobin
• 70 % is converted to bicarbonate ions
Control of pulmonary circulation• In most areas of the body, hypoxia causes
vasodilation.
• Low oxygen concentrations in the alveoli of the lungs cause vasoconstriction.
• This sends blood to areas of the lung that have higher oxygen concentrations
• Chronic alveolar hypoxia can lead to permanent pulmonary artery hypertension, which can lead to right heart failure.
• Acidemia also causes pulmonary artery constriction