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 -Ventilation (V E ) -Gas transport (GT) -Tissue respiration (TR) -Functional anatomy of the RS -Basic mechanism of V E -Biophysics of V E -Pressure-volume relations of lung and chest -Elastic and non-elastic properties of lungs and thorax

Resp is the use of O 2 by the living cell for oxidation of nutrients. This result in production of CO 2. Resp can be divided into 4 main events; 1) pulmonary vent 2) gas diffusion 3) gas transport 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 (P total = P 1 + P 2 + P 3 ……). V E = fr X V T

Dalton’s Law Dalton’s Law: Each gas in a mixture of gases exerts a pres commensurate with its own conc (partial pressures) –O 2 is 21% of air Therefore, at 760mmHg(atmospheric pres), the PO 2 =0.21 X 760=160mmHg Partial pres of water (P H 2 0): 47 mmHg Partial pres of water (P H 2 0): 47 mmHg At 760mmHg, PO 2 = (760-47) X 0.21 = 150 mmHg

Gas transport The gases are transported in the blood in 2 forms; either 1- Dissolved in the plasma, OR 2- Combine with Hb Under normal circumstances, approx 97-99% of O 2 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 O 2 ) and anaerobic resp (does not require O 2 ). Aerobic resp: It is the normal process by which food substances are broken down and oxidized to provide energy. Glucose + O 2 → CO 2 + H 2 O + energy released Glucose + O 2 → CO 2 + H 2 O + energy released Anaerobic resp: It means that energy can be derived from food substances without the simultaneous utilization of O 2. Glucose → lactic acid + much less energy released Glucose → lactic acid + much less energy released

Functional anatomy of the RS 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 gas exchange between inspired air and blood in the pulmonary circulation, supplying O 2 and removing CO 2, 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 1- The Conducting zone, and 2- The respiratory zone. 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 V E Breathing consists of 2 phases; inspiration (active process) and expiration (passive process). During inspi: The diaphragm and intercostals muscles contract. The diaphragm moves downwards ↑ the vol of the thoracic cavity, and the intercostals muscles pulls the ribs up expanding the rib cage and further ↑ this vol. During expi: The diaphragm and intercostals muscles relax. This returns the thoracic cavity to its original vol, ↑ the air pressure in the lungs, and forcing the air out.

Biophysics of V E : Pres vol relationship of the lungs and chest 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 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.

Elastic properties of the lungs and thorax Compliance is defined as a change in vol resulting from a change in pres. Because compliance is an expression of the distensibility of the elastic resp system, measured values of compliance depend upon the elastic recoil properties of the lungs and chest wall. Elastic recoil pres means that when the airways are open and there is no airflow, elastic recoil pressure is equal to transpulmonary pressure. Pstl = Palv - Ppl Elastic properties of the thorax: If the volume of the thorax-diaphragm is reduced by contraction of the muscles of expiration, the chest wall tends to resist compression and, by tending to recoil outward to its resting vol, creates a –ve pres within the system.

Volume-pressure relationships of isolated lungs

Volume-pressure relationships of isolated chest wall