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Respiratory physiology

الكلية كلية طب حمورابي     القسم الكلية ذات القسم الواحد     المرحلة 2
أستاذ المادة امجد حسن عباس المنصوري       14/11/2016 06:53:14
The study of respiratory physiology is important to medicine, because many of the respiratory diseases (e.g., cystic fibrosis, asthma, emphysema, pulmonary hypertension, and pneumonia) impact many of the subspecialties, from pediatrics, to internal medicine, to surgery, and to geriatrics. The human lungs are so efficiently designed that gas exchange can increase >20-fold to remove carbon dioxide and to supply oxygen to tissues in order to meet the body’s energy demands.

Lecture Outline
• Functional anatomy
• Ventilation
• Gas exchange
• Gas transport in blood
• Regulation of ventilation
Functional anatomy
The respiratory system is composed of the conducting airways and the respiratory airways.

Figure: respiratory system

Conducting and Respiratory Airways
The conducting airways include the nose, mouth, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles. As their name suggests, these airways conduct air to the respiratory airways; they do not participate in gas exchange.
The bronchi are > 1 mm in diameter and have cartilaginous rings that protect them from collapsing during expiration. They are not embedded in the lung parenchyma, so their diameter is not dependent on lung volume.
The bronchi branch to form bronchioles that are smaller in diameter and have no supporting cartilage. They are embedded within lung parenchyma, and their diameter expands and contracts with lung volume.


Figure: conductive zone

Innervation:
Smooth muscles innervated by autonomic nervous system:
- parasympathetic - muscarinic - bronchoconstriction
- sympathetic - beta2 - receptors – bronchodilation -mainly to adrenalin

The respiratory airways include the respiratory bronchioles (i.e., bronchioles with alveoli in their walls; and alveolar ducts.
Alveoli: There are ~300 million alveoli in adult lungs, each being ~250?m in diameter. Their walls are composed of a simple squamous epithelium, primarily type I pneumocytes. Each alveolus is encased by pulmonary capillaries, which are sandwiched between the lumens of adjacent alveoli.
The total surface area available for gas exchange is ~150 m2.
Alveoli first begin to appear on the respiratory bronchioles, marking the start of the respiratory portion of the lung. These alveoli are isolated initially, then become more numerous and are collected into sacs. Each sac has a central open space, or alveolar duct, that is continuous with the lumen of its respiratory bronchiole. The alveolar walls are composed of squamous epithelium and are in direct contact with the pulmonary capillaries for gas exchange to occur. Connective tissue with abundant elastic fibers is found throughout the branches of the bronchial tree and the alveoli. These contribute substantially to the elastic recoil of the lungs during expiration.

Figure: respiratory zone

Removal of Inhaled Particles
With its surface area of 50 to 100 square meters, the lung presents the largest
surface of the body to an increasingly hostile environment. Various mechanisms for dealing with inhaled particles have been developed.
Large particles are filtered out in the nose. Smaller particles that deposit in the conducting airways are removed by a moving staircase of mucus that continually sweeps debris up to the epiglottis, where it is swallowed. The mucus, secreted by mucous glands and also by goblet cells in the bronchial walls, is propelled by millions of tiny cilia, which move rhythmically under normal conditions but are paralyzed by some inhaled toxins.
The alveoli have no cilia, and particles that deposit there are engulfed by large wandering cells called macrophages. The foreign material is then removed from the lung via the lymphatics or the blood flow. Blood cells such as leukocytes also participate in the defense reaction to foreign material.


المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .