RESPIRATORY PHYSIOLOGY Dr. Waheeb Alharbi

References (1) Physiological basis of medical practice. By; John B. West (2) Medical physiology By; Arthur C. Guyton & John E. Hall (3) Concise Human Physiology By; M. Y. Sukkar, H. A. El-Munshid & M. S. m. Ardawi

Lecture 1 Defin of resp Func of resp Vent Gas trans Tissue resp Functional anatomy of the resp system Basic mechanism of vent Biophysics of vent

Resp is the use of O2 by the living cell for oxidation of nutrients Resp is the use of O2 by the living cell for oxidation of nutrients. This result in production of CO2. Resp can be divided into 4 main events; 1) pulmonary vent 2) gas diffu 3) gas trans 4) regulation of resp Vent is the movement of air between the environment and the alveoli. It can be spontaneous or artificial. Air is a mixture of gases. According to Dalton’s Law, the total pres of a mixture of gases is the sum of the pres of the individual gases (Ptotal = P1 + P2 + P3 ……). VE = fr X VT

Dalton’s Law Dalton’s Law: Each gas in a mixture of gases exerts a pres commensurate with its own conc (partial pressures) Oxygen is 21% of air At 760mmHg(atmospheric pres), the PO2=0.21 X 760=160mmHg Partial pres of water (P H20): 47 mmHg At 760mmHg, PO2 = (760-47) X 0.21 = 150 mmHg

Gas transport The gases are transported in the blood in 2 forms; 1- Dissolved in the plasma 2- Combine with Hb Under normal circumstances, more than 98% of the O2 in a given vol of blood is transported in RBCs, bound to Hb.

Tissue respiration It means getting energy out of glucose. The most efficient form of resp is aerobic (require O2) and anaerobic resp (does not require O2). Aerobic resp: It is the normal process by which food substances are broken down and oxidized to provide energy. Glucose + O2 → CO2 + H2O + energy released Anaerobic resp: It means that energy can be derived from food substances without the simultaneous utilization of O2. Glucose → lactic acid + much less energy released

Functional anatomy of the resp system Anatomy of the resp system is composed of; 1) the resp air ways 2) the lungs 3) the resp muscles 4) the neural centers The main function of the lungs is to provide continuous GE between inspired air and blood in the pulmonary circulation, supplying O2 and removing CO2, which is then cleared from the lungs by subsequent expiration. The functional structure of the lung can be divided into; 1- The Conducting zone, and 2- The respiratory zone. The Conducting zone (air flow): Air comes into the nose and the mouth through the pharynx, larynx and then through the trachea. The respiratory zone (gas diffusion): It begins when alveoli start to appear in the walls of the bronchioles.

Basic mechanism of vent Breathing consists of 2 phases; inspiration (active process) and expiration (passive process). During inspi: The diaphragm and intercostals muscles contract. The diaphragm moves downwards increasing the vol of the thoracic cavity, and the intercostals muscles pulls the ribs up expanding the rib cage and further increasing this vol. During expi: The diaphragm and intercostals muscles relax. This returns the thoracic cavity to its original vol, increasing the air pressure in the lungs, and forcing the air out.

Biophysics of vent: Pres vol relationship of the lungs and chest Compliance means the ability to expand or stretch. The compliance of a container is the change in its vol that results from imposing a press differences across its walls. The larger the vol change in response to a given pres change, the greater the compliance. Factors affecting the compliance include; 1) the connective tissue structure of the lung 2) the level of surfactant production 3) the mobility of the thoracic cage The significance of the balance of forces between the lung and chest wall is evident in what happens during thoracic surgery or penetrating injury to the chest. Pleural pressure: It is the pres in the narrow space between the lung pleura and chest wall pleura. Alveolar pressure: It is the pres inside the lung alv.