KIN 3304: Chapter 24 Respiration

-The trachea branches within the mediastinum, giving rise to the right and left primary, or main, bronchi -Each primary bronchus travels to a groove along the medial surface of its lung before branching further. This groove, the hilium, also provides access for entry to pulmonary vessels and nerves. The entire array is firmly an- chored in a meshwork of dense connective tissue. This complex, known as the root of the lung, attaches it to the mediastinum and fixes the positions of the ma- jor nerves, vessels, and lymphatics.

- Right lung has three lobes: superior, middle, inferior - R.L. is shorter than the left, the diaphragm rises on the right side to accommodate the mass of the liver -L.L. has two lobes: superior, inferior - L.L. is smaller than right lung, it accommodates the heart

The primary bronchi and their branches form the bronchial tree. Because the left and right bronchi are outside the lungs, they are called extrapulmonary bronchi. As the primary bronchi enter the lungs, they divide to form smaller passageways. Those branches are collectively called the intrapulmonary bronchi.

-Each terminal bronchiole delivers air to a single pulmonary lobule. Within the lobule, the terminal bronchiole branches to form several respiratory bronchioles; they deliver air to the exchange surfaces of the lungs -The epithelial cells of the respiratory bronchioles and the smaller terminal bronchioles are cuboidal. Cilia are rare, and there are no mucous cells or underlying mucous glands.

-Respiratory bronchioles are connected to individual alveoli and to multiple alve- oli along regions called alveolar ducts. -These passageways end at alveolar sacs, common chambers connected to several individual alveoli -An extensive network of capillaries is associated with each alveolus; the capillaries are surrounded by a network of elastic fibers. This elastic tissue helps maintain the relative positions of the alveoli and respiratory bronchioles

-The alveolar epithelium consists primarily of simple squamous epithelium. The squamous epithelial cells, called type I alveolar cells, are unusually thin and delicate. Type II alveolar cells, are scattered among the squamous cells.

type II alveolar cells, are scattered among the squamous cells. These large cells produce an oily secretion containing a mixture of phospholipids. This secretion, termed surfactant, coats the inner surface of each alveolus and reduces surface tension in the fluid coating the alveolar surface. Without surfactant the alveoli would collapse.

Gas exchange occurs in areas where the basal laminae of the alveolar epithelium and adjacent capillaries have fused. In these areas the total distance separating the respiratory and circulatory systems is very small. Diffusion across this respiratory membrane proceeds very rapidly because (1) the distance is small and (2) the gases are lipid soluble. The membranes of the epithelial and endothelial cells thus do not pose a barrier to the movement of oxygen and carbon dioxide between the blood and alveolar airspaces.

-The respiratory-exchange surfaces receive blood from arteries of the pulmonary circuit -Each lobule receives an arteriole and a venule, and a network of capillaries surrounds each alveolus directly beneath the respiratory membrane. In addition to providing a mechanism for gas exchange, the alveolar capillaries are the primary source of angiotensin-converting enzyme

- peptide hormone, cause blood vessels to constrict - affects BP - also stimulates release of aldosterone ( promotes Na+ in the kidneys, thus B.P. goes up)

- converts circulating angiotensin I to angiotensin II - ACE found in high density in the lungs -ACE inhibitors decrease angiotensin II production - ACE inhibitors found in major drugs against hypertension

The space between the pari- etal and visceral pleurae is called the pleural cavity. Each pleural cavity actually represents a potential space rather than an open chamber, for the parietal and visceral layers are usually in close contact. A small amount of pleural fluid is secreted by both pleural membranes. Pleural fluid covers the opposing surfaces, and this moist, slippery coating reduces friction between the parietal and visceral surfaces during breathing.

Inflammation of the pleurae, a condition called pleurisy, may cause the membranes to produce and secrete excess amounts of pleural fluid, or the in- flamed pleurae may adhere to one another, limiting relative movement. In either form of this disorder, breathing becomes difficult, and prompt medical attention is required.

Pulmonary ventilation, or breathing, refers to the physical movement of air into and out of the bronchial tree. The function of pulmonary ventilation is to maintain adequate alveolar ventilation, the movement of air into and out of the alveoli. Alve- olar ventilation prevents the buildup of carbon dioxide in the alveoli and ensures a continual supply of oxygen that keeps pace with absorption by the bloodstream.

- Air flows from areas of high pressure to lower pressure - The lungs move due to pressure - When there is negative pressure (<760 in the lungs), air moves in - When there is positive pressure, air moves out ( exhalation)

-The diaphragm tenses and flattens as it contracts, and this increases the volume of the thoracic cavity. When the diaphragm relaxes, it arches upward and reduces the volume of the thoracic cavity. -Air is drawn into the lungs when the volume of the thoracic cavity increases, and it is expelled when the volume decreases.

-The external intercostal muscles may assist in inspiration by elevating the ribs. -The internal intercostal muscles depress the ribs and reduce the width of the thoracic cavity, thereby contributing to expiration.

Mechanorecptor reflexes (respond to lung vol and changes in arterial blood pressure) Chemoreceptor reflexes (respond to the changes in pH) Protective reflexes (respond to physical injury or irritation of the respiratory tract)

1) With increasing age, elastic tissue deteriorates throughout the body. The primary impact on the respiratory system is a reduction in the lungs’ ability to inflate and deflate. 2) Movements of the rib cage are restricted by arthritic changes in the rib articulations and by decreased flexibility at the costal cartilages. In combination with the changes noted in (1), the stiffening and reduction in chest movement effectively limit the respiratory volume. This restriction con- tributes to the reduction in exercise performance and capabilities with increasing age. 3 )Some degree of emphysema is normally found in individuals age 50–70. On average, roughly 1 square foot of respiratory membrane is lost each year after age 30. However, the extent varies widely, depending on lifetime exposure to cigarette smoke and other respiratory irritants.