Chapter 20: Respiratory System Top Hat Notes PDF

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Chapter 20: Respiratory System 20.2 Introduction 20.2.2 Overview ● Ventilation: the process of moving air from the atmosphere into the alveoli of the lungs, as well as back out again ● External respiration: the exchange of O2 and CO2 between the air in the alveoli and the blood supplying the alveoli ● Transport of O2 and CO2 in blood ● Internal respiration: the exchange O2 and CO2 between the blood and metabolically active cells of the tissues

20.3 Structures of the Respiratory System Pathway formation and gas exchange are two separate processes so the structures of the respiratory system are divided into: ● The conducting division, which provides the passageway for air to move ● The respiratory division, which is where gas exchange occurs

Another way to separate: ● Upper respiratory tract which includes the mouth, nose, pharynx, and the superior end of the larynx ● Lower respiratory tract which includes the vocal folds (cords) of the larynx, trachea, bronchi, bronchioles, and alveoli

20.3.1 Structures of the Conducting Division They provide passage of air, and also warm, humidify, and cleanse it. 1. Mouth

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○ Role is to act in parallel with the nose as a passageway for air entry and exit from the body Nose ○ Primary pathway for respiration ○ Made of external nose and deeper nasal cavities which increase surface area and are lined by a mucous membrane which warm and humidify Pharynx ○ Air passes through here during inhalation and inspiration ○ It is divided into these regions (top to bottom): i. Nasopharynx: acts as a passageway for air ii. Auditory tubes: connect the nasopharynx to the middle ear, allowing for equilibration of pressure (not actually part of the pharynx) iii. Oropharynx: connected to the oral cavity and is a passageway for the digestive and respiratory systems iv. Laryngopharynx: passageway for air and food Larynx ○ It directs air into the trachea and food into the esophagus ○ Contains vocal folds (cords) ○ In order to prevent easy collapse of the larynx and to provide rigid attachments, the walls of the larynx has 3 large, unpaired cartilages and 3 sets of smaller, paired cartilages i. The larger, unpaired cartilages are: 1. Epiglottis which prevents aspiration of ingested materials into the airways by moving the trachea during swallowing 2. Thyroid, the largest and includes the laryngeal prominence aka the Adam’s Apple 3. Cricoid cartilage is the only cartilage that makes a complete ring around the trachea ii. The smaller, paired cartilages provide attachments for vocal folds and muscles of the larynx and consist of: 1. Arytenoid 2. Corniculate 3. Cuneiform Trachea ○ Extends from the larynx into the left and right primary bronchi ○ The inner wall contains ciliated cells and is continuous throughout the bronchi and into the bronchioles and forms the mucociliary escalator i. This system traps particles and sweeps them to the pharynx to be swallowed Bronchi through Terminal Bronchioles ○ At the inferior end of the trachea, the carina, the trachea branches into right and left primary bronchi which enter their side’s lungs and branches into the secondary or lobar bronchi i. There are 3 lobar bronchi on the right and 2 on the left, 1 for each

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20.3.2 Structures of the Respiratory Division Structures include: ● The respiratory bronchioles are formed by the division of terminal bronchioles ○ The connective tissue here is elastic, allowing them to stretch for inhalation and recoil during exhalation ○ Order air would pass through during inhalation: ■ Respiratory bronchiole ■ Alveolar duct ■ Alveolar sac ■ Alveoli ● Alveoli are the structures where gas exchange occurs ○ 700 million ○ Its pores allow air to flow into nearby alveoli to maintain the same pressures ○ 3 different cell types: ■ Type 1 alveolar cell, the most common, forms the majority of the alveolar wall ● Two cells sandwiching a shared basement membrane makes the respiratory membrane ■ Type 2 alveolar cells which secrete surfactant which reduces the surface tension of water molecules in the alveoli ■ Type 3 alveolar cells or alveolar macrophages are immune cells that are resident in the alveoli ● They scavenge microorganisms and particles that were not captured in the mucus linings of the conducting division structures

20.3.3 Lungs

The right lung is divided into 3 lobes: the superior, middle, and inferior lobes, each separated by fissures. The left lung only has 2 and contains a cardiac notch (depression)

that decreases the volume by 25%. The lobes are then divided into bronchopulmonary segments which receive air from a bronchus and blood from an artery. Next is the pulmonary lobule which is formed as the bronchi changes to bronchioles. Lung Pleura Each lung is surrounded by a serous membrane called the pleura. It has 2 layers, the visceral pleura that covers each lung and the parietal pleura that lines the inner wall of the thoracic cavity, mediastinum, and diaphragm. The pleural cavity/space is the area between the 2 layers that contains a small amount of pleural fluid (10-15 ml) that is secreted by mesothelial cells. It helps lubricate membrane surfaces to avoid frictional damage. Pulmonary Blood Flow 1. Right ventricle 2. Large pulmonary trunk 3. Left and right pulmonary arteries 4. Hilum 5. Lobar arteries (originally pulmonary arteries) 6. End of capillaries 7. Venules 8. Pulmonary veins 9. Left atrium The vessels here contain around 18% of a person’s total blood volume

20.4 Ventilation 20.4.1 Pressures and Flows Involved in Ventilation Ventilation is dependent on the ability to create a pressure gradient between the

atmosphere and the alveoli. Gases will flow higher to lower pressure. A Pressure Differentials and Gradients A pressure differential is the difference in pressure between any 2 spaces that are occupied by a gas (or fluid) and is independent on whether or not the gas can move from one space to another. If it can move then it can be described as exhibiting a pressure gradient.

Determinants of Gas Pressure Gas pressure is determined by: ● Amount of gas particles ● Temperature ● Volume of space Relationships between pressure and its variables: ● Volume and pressure are inversely related (Boyle’s Law, P1V 1 = P 2V2 ) ● Numbers of particles and pressure are inversely related ● Temperature and pressure are proportionately related Determinants of Flow Flow is measure in units of volume/time

Respiratory Pressures ● Atmospheric pressure: the pressure in the atmosphere that surrounds the body ○ 760 mmHg or 1 atmosphere at sea level ● Intrapulmonary pressure: the pressure in the alveoli ○ The pressure gradient created between atmospheric and intrapulmonary pressures that causes air to move into or out of the lungs ● Intrapleural pressure: measured in the thin space between the visceral and parietal pleura ○ Around 756 mmHg ● Transpulmonary pressure: the pressure differential between the intrapulmonary and intrapleural pressure and represents the forces that tend to collapse the lungs

20.4.2 Process of Ventilation Breathing is a repetitive pattern of respiratory cycles

● A respiratory cycle is a single inspiration and its expiration Breathing During Exertion In order to get more air, an expansion of the thoracic cavity is required. This results from stronger contraction of the diaphragm and external intercostals Non-Respiratory Air Movements The respiratory system also produces air movements as a result of reflexes or conscious action ● Coughing and sneezing result when the respiratory system tried to clear irritants from the airways ● A yawn results from our deepest breath is not associated with exertion ● A hiccup is a spasm of the diaphragm that causes rapid bursts of air through the vocal cords ● Laughing and crying are associated with short bursts of air during expiration ● The Valsalva maneuver is when you try to exhale against a closed airway like a pinched nose and closed mouth

20.4.3 Ventilatory Volumes, Capacities, and Flow Rates When respiratory disease is suspected, spirometry tests are used to assess respiratory function. It can assess breathing patterns, rate, etc. A typical spirometry tracing can be divided into the following respiratory volumes: ● Tidal volume (TV): the volume inhaled and exhaled ○ Average is 500 ml ● Inspiratory reserve volume (IRV): the amount of additional air that can be inhaled in addition to the TV ○ Average is 2,100 to 3,200 ml ● Expiratory reserve volume (ERV): the volume of air that can be forcefully expelled ○ Average is 1,000 to 1,200 ml ● Residual volume (RV): amount of air left in the lungs after a completed ERV ○ Average is 1200 ml Lung capacities represent common combinations of lung volumes. The capacities include: ● Inspiratory capacity (IC): combination of TV and IRV ● Functional residual capacity (FRC): combination of RV and ERV ○ the amount of air left in the lungs after we exhale our tidal volume ● Vital capacity (VC): the combination of ERV, TV, and IRV ○ the total amount of air that a person can move in or out of his or her lungs. ● Total lung capacity (TLC) is IRV, TV, ERV, and RV Dead space air is the air that does not participate in gas exchange

20.5 Gas Exchange

The main purpose of the respiratory system is to provide the conditions that facilitate gas exchange in the lung tissue.

20.5.1 Principles of Gas Exchange A Diffusion and Partial Pressures of Gases The exchange of gases is due to diffusion, where a gas moves from higher to lower concentration. It results from difference in concentration. Partial pressure (written as Px, where x is the gas) represents the contribution of any gas in a mixture to the total pressure. The partial pressure is equal to the total pressure times the fraction of gas. Ex: total atmospheric pressure is 760 mmHg. Because 20.9% (we will consider it as 21%) of air is O2, the partial pressure of O2 (PO2) in atmospheric air at sea level is 760 mmHg x 21% = 159 mmHg

Gas Diffusion Between Air and Blood Calculating the amount of a gas dissolved in a liquid is done by multiplying the partial pressure of the gas in the liquid by the solubility coefficient of that gas

20.5.2 Gas Exchange in the Lungs (External Respiration) In the lungs O2 diffuses from the alveoli into the blood. CO2, which is produced as a result of metabolism, moves from blood to air. Ventilation maintains an adequate supply of O2 in the alveoli and removes the CO2 that transfers out of blood.

20.5.3 Gas Exchange in the Tissues (Internal Respiration) Internal respiration occurs between the systemic capillaries and tissues of the body. It is opposite of that in the alveoli.

20.6 O2 and CO2 Transport in Blood 20.6.1 O2 Transport in Blood

Oxygen is nonpolar and poorly soluble in blood, so hemoglobin provides an alternate method for delivering O2 throughout the body. It transports more than 98% of the O2 in blood while the dissolved fraction represents less than 2%. Each red blood cell has 250-300 million hemoglobin molecules. This means each cell can carry up to 1.2 billion oxygen molecules or 1.24 ml per gram. PO2 of blood determines the degree of Hb saturation. The relationship between the two is provided by the oxyhemoglobin dissociation curve. As PO2 increases, saturation also increases until it reaches 100%....