Understanding Gases Gas will always move from a

Understanding Gases Gas will always move from a region of high pressure to a region of low pressure. Applying Boyle's law: If the volume inside thoracic cavity , the pressure .

Ventilation and Respiration Pulmonary ventilation is the movement of air between the atmosphere and the alveoli, and consists of inhalation and exhalation. – Ventilation, or breathing, is made possible by changes in the intrathoracic volume.

Ventilation and Respiration In contrast to ventilation, respiration is the exchange of gases. – External respiration (pulmonary) is gas exchange between the alveoli and the blood. – Internal respiration (tissue) is gas exchange between the systemic capillaries and the tissues of the body.

Ventilation and Respiration External respiration in the lungs is possible because of the implications of Boyle’s law: The volume of the thoracic cavity can be increased or decreased by the action of the diaphragm, and other muscles of the chest wall. – By changing the volume of the thoracic cavity (and the lungs – remember the mechanical coupling of the chest wall, pleura, and lungs), the pressure in the lungs will also change.

Ventilation and Respiration Changes in air pressure result in movement of the air. – Contraction of the diaphragm and external intercostal (rib) muscles increases the size of the thorax. This decreases the intrapleural pressure so air can flow in from the atmosphere (inspiration). – Relaxation of the diaphragm, with/without contraction of the internal intercostals, decreases the size of the thorax, increases the air pressure, and results in exhalation.

Ventilation and Respiration Certain thoracic muscles participate in inhalation; others aid exhalation. – The diaphragm is the primary muscle of respiration – all the others are accessory.

Ventilation and Respiration The recruitment of accessory muscles greatly depends on whether the respiratory movements are quiet (normal), or forced (labored).

Ventilation and Respiration (Interactions Animation) In the following animation, the mechanical coupling mechanism can be understood by relating the concepts of the gas laws to the unique anatomical features of the airways, pleural cavities, and muscles of respiration. • Pulmonary Ventilation You must be connected to the internet to run this animation

Airflow and Work of Breathing Differences in air pressure drive airflow, but 3 other factors also affect the ease with which we ventilate: 1. The surface tension of alveolar fluid causes the alveoli to assume the smallest possible diameter and accounts for 2/3 of lung elastic recoil. Normally the alveoli would close with each expiration and make our “Work of Breathing” insupportable. • Surfactant prevents the complete collapse of alveoli at exhalation, facilitating reasonable levels of work.

Airflow and Work of Breathing 2. High lung compliance means the lungs and chest wall expand easily. – Compliance is decreased by a broken rib, or by diseases such as pneumonia or emphysema.

Airflow and Work of Breathing

Measuring Ventilation can be measured using spirometry. – Tidal Volume (VT) is the volume of air inspired (or expired) during normal quiet breathing (500 ml). – Inspiratory Reserve Volume (IRV) is the volume inspired during a very deep inhalation (3100 ml – height and gender dependent). – Expiratory Reserve Volume (ERV) is the volume

Measuring Ventilation Spirometry continued – Vital Capacity (VC) is all the air that can be exhaled after maximum inspiration. • It is the sum of the inspiratory reserve + tidal volume + expiratory reserve (4800 ml). – Residual Volume (RV) is the air still present in the lungs after a force exhalation (1200 ml). • The RV is a reserve for mixing of gases but is not available to move in or out of the lungs.

Measuring Ventilation Old and new spirometers used to measure ventilation.

Measuring Ventilation A graph of spirometer volumes and capacities

Measuring Ventilation Only about 70% of the tidal volume reaches the respiratory zone – the other 30% remains in the conducting zone (called the anatomic dead space). – If a single VT breath = 500 ml, only 350 ml will exchange gases at the alveoli. • In this example, with a respiratory rate of 12, the minute ventilation = 12 x 500 = 6000 ml. • The alveolar ventilation (volume of air/min that actually reaches the alveoli) = 12 x 350 = 4200 ml.

Exchange of O 2 and CO 2 Using the gas laws and understanding the principals of ventilation and respiration, we can calculate the amount of oxygen and carbon dioxide exchanged between the lungs and the blood.

Exchange of O 2 and CO 2 • Dalton’s Law states that each gas in a mixture of gases exerts its own pressure as if no other gases were present. – The pressure of a specific gas is the partial pressure Pp. – Total pressure is the sum of all the partial pressures. – Atmospheric pressure (760 mm. Hg) = PN 2 + PO 2 + PH 2 O + PCO 2 + Pother gases • Since O 2 is 21% of the atmosphere, the PO 2 is 760 x 0. 21 = 159. 6 mm. Hg.

Exchange of O 2 and CO 2 Each gas diffuses across a permeable membrane (like the AC membrane) from the side where its partial pressure is greater to the side where its partial pressure is less. – The greater the difference, the faster the rate of diffusion. – Since there is a higher PO 2 on the lung side of the AC membrane, O 2 moves from the alveoli into the blood. – Since there is a higher PCO 2 on the blood side of the AC membrane, CO 2 moves into the lungs.

Exchange of O 2 and CO 2 P N 2 = 0. 786 x 760 mm. Hg = 597. 4 mm. Hg P O 2 = 0. 209 x 760 mm. Hg = 158. 8 mm. Hg P H 2 O = 0. 004 x 760 mm. Hg = 3. 0 mm. Hg PCO 2 = 0. 0004 x 760 mm. Hg = 0. 3 mm. Hg Pother gases = 0. 0006 x 760 mm. Hg = 0. 5 mm. Hg Total = 760. 0 mm. Hg Partial pressures of gases in inhaled air for sea level

Exchange of O 2 and CO 2 • Henry’s law states that the quantity of a gas that will dissolve in a liquid is proportional to the partial pressures of the gas and its solubility. – A higher partial pressure of a gas (like O 2) over a liquid (like blood) means more of the gas will stay in solution. – Because CO 2 is 24 times more soluble in blood (and soda pop!) than in O 2, it more readily dissolves.

Exchange of O 2 and CO 2 Even though the air we breathe is mostly N 2, very little dissolves in blood due to its low solubility. – Decompression sickness (“the bends”) is a result of the comparatively insoluble N 2 being forced to dissolve into the blood and tissues because of the very high pressures associated with diving. • By ascending too rapidly, the N 2 rushes out of the tissues and the blood so forcefully as to cause vessels to “pop” and cells to die.

Transport of O 2 and CO 2 In the blood, some O 2 is dissolved in the plasma as a gas (about 1. 5%, not enough to stay alive – not by a long shot!). Most O 2 (about 98. 5%) is carried attached to Hb. – Oxygenated Hb is called oxyhemoglobin.

Transport of O 2 and CO 2 is transported in the blood in three different forms: 1. 7% is dissolved in the plasma, as a gas. 2. 70% is converted into carbonic acid through the action of an enzyme called carbonic anhydrase. + • CO 2 + H 2 O H 2 CO 3 H + HCO 3 - 3. 23% is attached to Hb (but not at the same binding sites as oxygen).

Transport of O 2 and CO 2 The O 2 transported in the blood (PO 2 = 100 mm. Hg) is needed in the tissues to continually make ATP (PO 2 = 40 mm. Hg at the capillaries). CO 2 constantly diffuses from the tissues (PCO 2 = 45 mm. Hg) to be transported in the blood (PCO 2 = 40 mm. Hg) Internal Respiration occurs at systemic capillaries

Transport of O 2 and CO 2 • The amount of Hb saturated with O 2 is called the Sa. O 2. – Each Hb molecule can carry 1, 2, 3, or 4 molecules of O 2. Blood leaving the lungs has Hb that is fully saturated (carrying 4 molecules of O 2 – oxyhemoglobin). • The Sa. O 2 is close to 95 -98%. – When it returns, it still has 3 of the 4 O 2 binding sites occupied. • Sa. O 2 = 75%

Transport of O 2 and CO 2 The relationship between the amount of O 2 dissolved in the plasma and the saturation of Hb is called the oxygen-hemoglobin saturation curve. – The higher the PO 2 dissolved in the plasma, the higher the Sa. O 2.

Transport of O 2 and CO 2 • Measuring Sa. O 2 has become as commonplace in clinical practice as taking a blood pressure. – Pulse oximeters which used to cost $5, 000 can now be purchased at your local pharmacy. 3660 Group, Inc/News. Com

Transport of O 2 and CO 2 • Although PO 2 is the most important determinant of Sa. O 2, several other factors influence the affinity with which Hb binds O 2. – Acidity (p. H), PCO 2 and blood temperature shift the entire O 2 –Hb saturation curve either to the left (higher affinity for O 2), or to the right (lower affinity for O 2).

Transport of O 2 and CO 2 •

Transport of O 2 and CO 2 As blood flows from the lungs toward the tissues, the increasing acidity (p. H decreases) shifts the O 2–Hb saturation curve “to the right”, enhancing unloading of O 2 (which is just what we want to happen). – This is called the Bohr effect. At the lungs, oxygenated blood has a reduced capacity to carry CO 2 , and it is unloaded as we exhale (also just what we want to happen). – This is called the Haldane effect.

Fetal and Maternal Hemoglobin Fetal hemoglobin (Hb-F) has a higher affinity for oxygen (it is shifted to the left) than adult hemoglobin A, so it binds O 2 more strongly. – The fetus is thus able to attract oxygen across the placenta and support life, without lungs.

Control of Respiration The medulla rhythmicity area, located in the brainstem, has centers that control basic respiratory patterns for both inspiration and expiration. – The inspiratory center stimulates the diaphragm via the phrenic nerve, and the external intercostal muscle via intercostal nerves. • Inspiration normally lasts about 2 sec.

Control of Respiration Exhalation is mostly a passive process, caused by the elastic recoil of the lungs. Usually, the expiratory center is inactive during quiet breathing (nerve impulses cease for about 3 sec). – During forced exhalation, however, impulses from this center stimulate the internal intercostal and abdominal muscles to contract.

Control of Respiration Other sites in the pons help the medullary centers manage the transition between inhalation and exhalation. – The pneumotaxic center limits inspiration to prevent hyperexpansion. – The apneustic center coordinates the transition between inhalation and exhalation.

Control of Respiration Other brain areas also play a role in respiration: – Our cortex has voluntary control of breathing. – Stretch receptors sensing over-inflation arrests breathing temporarily (Herring Breuer reflex). – Emotions (limbic system) affect respiration. – The hypothalamus, sensing a fever, increases breathing, as does moderate pain (severe pain causes apnea. )

Control of Respiration (Interactions Animation) • Regulation of Ventilation You must be connected to the internet to run this animation

Response to Pollutants Initial Response – Mucous layer thickens. – Goblet cells over-secrete mucous. – Basal cells proliferate. Normal columnar epithelium in the respiratory tract Advanced Response to Irritation – Mucous layer and goblet cells disappear. – Basal cells become malignant & invade deeper tissue.

Diseases and Disorders Asthma is a disease of hyper-reactive airways (the major abnormality is constriction of smooth muscle in the bronchioles, and inflammation. ) It presents as attacks of wheezing, coughing, and excess mucus production. – It typically occurs in response to allergens; less often to emotion. – Bronchodilators and antiinflammatory corticosteroids are mainstays of treatment. Pulse Picture Library/CMP mages /Phototake

Diseases and Disorders Chronic bronchitis and emphysema are caused by chronic irritation and inflammation leading to lung destruction. Patients may cough up green-yellow sputum due to infection and increased mucous secretion (productive cough). –They are almost exclusively diseases of cigarette smoking.

Diseases and Disorders Pneumonia is an acute infection of the lowest parts of the respiratory tract. – The small bronchioles and alveoli become filled with an inflammatory fluid exudate. • It is typically caused by infectious agents such as bacteria, viruses, or fungi.

Diseases and Disorders Normal Lungs Patient Du Cane Medical Imaging, Ltd. /Photo Researchers, Inc Pneumonia

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