Respiratory Unit

Airway Resistance

Airway resistance to airflow is normally so small that very small pressure differences produce large volumes of airflow. Physical, neural, and chemical factors affect airway radii and therefore resistance.

During Exhelation

Alveolar pressure is greater than atmospheric pressure. Intrapleural pressure becomes less negative. The diaphragm relaxes. Lung volume decreases. The causes inhalation/inspiration is flattening (downward movement) of the diaphragm

Hyperventilation

Alveolar ventilation exceeds the metabolic demands. Leads to respiratory alkalosis from hypocapnia/low CO2 levels. Is caused by anxiety, head injury, or severe hypoxemia. Increased alveolar PO2 Decreased alveolar PCO2

hypoventilation

Alveolar ventilation is inadequate in relationship to the metabolic demands. Leads to respiratory acidosis from hypercapnia/highCO2 levels Is caused by airway obstruction, chest wall restriction, or altered neurologic control of breathing.

Asthma

Asthma is a disease characterized by intermittent episodes in which airway smooth muscle contracts strongly, markedly increasing airway resistance. The basic defect in asthma is chronic inflammation of the airways, the causes of which vary from person to person and include, among others; allergy, viral infections, and sensitivity to environmental factors. The underlying inflammation makes the airway smooth muscle hyperresponsive and causes it to contract strongly in response to such things as exercise (especially in cold, dry air), tobacco smoke, environmental pollutants, viruses, allergens, normally released bronchoconstrictor chemicals, and a variety of other potential triggers.

What does the Oxygen Hemoglobin dissociation curve Show?

At normal resting systemic arterial PO2, hemoglobin is almost 100% saturated with oxygen.

Boyle's Law

Boyle's law is represented by the equation P_1 V_1=P_2 V_2 At constant temperature, the relationship between the pressure (P) exerted by a fixed number of gas molecules and the volume (V) of their container is as follows: An increase in the volume of the container decreases the pressure of the gas, whereas a decrease in the container volume increases the pressure. In other words, in a closed system, the pressure of a gas and the volume of its container are inversely proportional. During ventilation, a volume change leads to a pressure change, which then leads to the flow of air until the pressures are equilibrated.

Lung compliance Increases

Emphysema

Chronic Bronchitis

Hypersecretion of mucus and chronic productive cough that lasts at least 3 months of the year and for at least 2 consecutive years Pathophysiology The production of mucus associated with chronic bronchitis is due to increased in Goblet Cell size. Inspired irritants increase mucous production, size and number of mucous glands, and bronchial edema; mucus is thicker than normal Hypertrophied bronchial smooth muscle Hypoxemia and hypercapnia Airways collapse early in expiration, trapping gas in the lung

Causes of decreased arterial PO2 (Hypoxic Hypoxia ) in Disease

Hypoventilation may be caused by •A defect anywhere along the respiratory control pathway, from the medulla through the respiratory muscles •Severe thoracic cage abnormalities •Major obstruction of the upper airway The hypoxemia of hypoventilation is always accompanied by an increased arterial P_CO2. •Drugs such as opiates that suppress the central respiratory centers. The hypoxemia of hypoventilation is accompanied by an increased arterial P_CO2. Diffusion impairment: results from thickening of the alveolar membranes or a decrease in their surface area. In turn, it causes blood P_O2 and alveolar P_O2 to fail to equilibrate. Often, it is apparent only during exercise. Arterial P_CO2 can be normal because carbon dioxide diffuses more readily than oxygen, decreased if the hypoxemia reflexively stimulates alveolar ventilation, or increased if the impairment is severe enough to limit CO_2 diffusion. Diffuse interstitial fibrosis is an example of a diffusion impairment. A Shunt is: •An anatomical abnormality of the cardiovascular system that causes mixed venous blood to bypass ventilated alveoli in passing from the right side of the heart to the left side. An example is a hole between the right and left atria of the heart (called a patent foramen ovale [PFO]). Look back to Figure 13.21 to see how blood flowing from the right atrium directly into the left atrium would bypass oxygenation in the lung and lower the arterial P_O2. •An intrapulmonary defect in which mixed venous blood perfuses unventilated alveoli. Arterial P_CO2 usually does not increase because the effect of the shunt on arterial P_CO2 is counterbalanced by the increased ventilation reflexively stimulated by the hypoxemia. Ventilation-perfusion inequality: is by far the most common cause of hypoxemia. Arterial P_CO2 may be normal or increased, depending upon how much ventilation is reflexively stimulated. There are many lung diseases including chronic obstructive lung disease that causes hypoxia in this way.

Hypoxia

Hypoxia is a deficiency of oxygen at the tissue level. Hypoxia can be classified into four general categories: Anemic hypoxia or carbon monoxide hypoxia: the arterial P_O2 is normal but the total oxygen content of the blood is decreased because of inadequate numbers of erythrocytes, deficient or abnormal hemoglobin or competition for the hemoglobin molecule by carbon monoxide Ischemic hypoxia: blood flow to the tissues is too low Histotoxic hypoxia: the body's cells are unable to use O_2 because a toxic agent has interfered with the cell's metabolic machinery (cyanide causes this). Hypoxemic hypoxia (hypoxemia): reduced arterial P_O2 (can be caused by lack of oxygenated air, pulmonary problems, lack of ventilation-perfusion matching). ) One cause of hypoxic hypoxia in disease is diffusion impairment of O2 resulting from decreased alveolar surface area.

lung compliance

Lung compliance (C_L ) is defined as the magnitude of the change in lung volume (〖∆V〗_L ) produced by a given change in the transpulmonary pressure: C_L=〖∆V_L〗∕〖∆P〗_tp The greater the lung compliance, the easier it is to expand the lungs at any given change in transpulmonary pressure. Compliance can be considered the inverse of stiffness. There are two major determinants of lung compliance: •The stretchability of the lung tissues •The surface tension at the air-water interfaces within the alveoli

Figure 13.32 A Simplified Depiction of the Brainstem Centers That Control Respiratory Rate and Depth

Morphine, barbiturates, fentanyl, and heroin, suppress the medullary inspiratory neurons, and death from overdose of these drugs can be due to the cessation of breathing.

Figure 3.25 Heme in 2 dimensions (look at it in pp)

Most oxygen is transported in the blood bound to hemoglobin.

Respiratory Distress syndrome of the newborn

Neonatal respiratory distress syndrome (NRDS) is more common in premature infants born six weeks or more before their due dates. It usually develops within the first 24 hours after birth. Symptoms include rapid, shallow breathing and a sharp pulling in of the chest below and between the ribs with each breath. Treatment includes medication to keep the lungs open, breathing support, and oxygen therapy.

Major Stimuli for the Central and Peripheral Chemoreceptors

Peripheral chemoreceptors—carotid bodies and aortic bodies— respond to changes in the arterial blood. They are stimulated by •Significantly decreased P_O2 (hypoxia) •Increased H1 concentration (metabolic acidosis) •Increased P_CO2 (respiratory acidosis) Central chemoreceptors—located in the medulla oblongata— respond to changes in the brain extracellular fluid. They are stimulated by increased P_CO2 via associated changes in H^+ concentration. Chemoreceptors- Receptors in the aortic and carotid bodies

Functions of the respiratory system

Provides oxygen to the blood Eliminates carbon dioxide from the blood Regulates the blood's hydrogen ion concentration (pH) in coordination with the kidneys Forms speech sounds (phonation) Defends against inhaled microbes Influences arterial concentrations of chemical messengers by removing some from pulmonary capillary blood and producing and adding others to this blood Traps and dissolves blood clots arising from systemic veins such as those in the legs

facts about pulmonary surfactant

Pulmonary surfactant is a mixture of phospholipids and protein. It is secreted by type II alveolar cells. It lowers the surface tension of the water layer at the alveolar surface, which increases lung compliance, thereby making it easier for the lungs to expand. Its effect is greater in smaller alveoli, thereby reducing the surface tension of small alveoli below that of larger alveoli. This stabilizes the alveoli. A deep breath increases its secretion by stretching the type II cells. Its concentration decreases when breaths are small. Type II alveolar cells are among the last cells to mature during fetal development. In babies born prematurely, type II alveolar cells are often not ready to perform their functions. Production in the fetal lung occurs in late gestation and is stimulated by the increase in cortisol (glucocorticoid) secretion that occurs then.

The Airway (Structures and Zones)

Structures that comprise the airways include: •Nose, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and alveoli Airways beyond the larynx can be divided into two zones: •the respiratory zone extends from the respiratory bronchioles down and is the region where alveoli exchange gases with the blood, and •the conducting zone from the top of the trachea to the end of the terminal bronchioles, which contains no alveoli and does not exchange gases with the blood.

Site of Gas exchange: The Alveoli

The alveoli are tiny, hollow sacs whose open ends are continuous with the lumina of the airways. Most of the air-facing surfaces of the wall are lined by a continuous layer, one cell thick, of flat epithelial cells termed type I alveolar cells. Interspersed between them are type II alveolar cells that produce a detergent-like substance called surfactant. The total alveolar-capillary surface area is very large, and this permits the rapid exchange of large quantities of oxygen and carbon dioxide by diffusion. In some of the alveolar walls, pores permit the flow of air between alveoli.

Asthma Continued

The first aim of therapy for asthma is to reduce the chronic inflammation and airway hyperresponsiveness with anti-inflammatory drugs, particularly leukotriene inhibitors and inhaled glucocorticoids. The second aim is to overcome acute excessive airway smooth muscle contraction with bronchodilator drugs, which relax the airways. For example, one class of bronchodilator drugs mimics the normal action of epinephrine on beta-2 (b-2) adrenergic receptors. Another class of inhaled drugs block muscarinic cholinergic receptors, which have been implicated in bronchoconstriction.

The Control of Respiration

The neurons responsible for the cyclic nature of respiratory muscle function are located in the brainstem. The medullary inspiratory neurons receive inhibitory neural input from the pons and also from pulmonary stretch receptors.

Facts about Brainstem Centers That Control Respiratory Rate and Depth Long Description:

The respiratory rhythmicity center consists of a dorsal respiratory group, which controls the diaphragm and external intercostal muscles, and a ventral group, which controls the muscles of forced expiration. The control of respiration by centers in the brainstem can be over-ridden by higher brain centers when speaking, breath-holding, undergoing emotional reactions, and experiencing pain.

The Respiratory System

The respiratory system is intimately associated with the circulatory system and is responsible for taking up oxygen from the environment and delivering it to the blood, as well as eliminating carbon dioxide from the blood. Respiration involves the following 4 steps: •Pulmonary ventilation •Exchange of O_2 and CO_2 between alveolar air and blood in lung capillaries •Transport of O_2 and CO_2 through pulmonary and systemic circulation •Exchange of O_2 and CO_2 between blood in tissue capillaries and cells in tissues

chronic obstructive pulmonary disease (COPD)

The term chronic obstructive pulmonary disease (COPD) refers to emphysema, chronic bronchitis, or a combination of the two. These diseases cause severe difficulties not only in ventilation, but in oxygenation of the blood. Emphysema is caused by destruction and collapse of the smaller airways. Lung compliance increased. Chronic bronchitis is characterized by excessive mucus production in the bronchi and chronic inflammatory changes in the small airways. The cause of obstruction is an accumulation of mucus in the airways and thickening of the inflamed airways.

Lung Compliance and Surfactant

The type II alveolar cells secrete the detergent-like substance known as surfactant. Surfactant markedly reduces the cohesive forces between water molecules on the alveolar surface. Therefore, surfactant lowers the surface tension, which increases lung compliance and makes it easier to expand the lungs. Type II alveolar cells are among the last cells to mature during fetal development. In babies born prematurely, type II alveolar cells are often not ready to perform their function. They would be at risk of alveolar collapse due to too much surface tension in the alveoli.

Inhalation/Inspiration

The volume of air flowing into the alveoli during inhalation/inspiration is increased when there is an increase in the pressure gradient from the atmosphere to the alveoli.

pneumothorax

This condition occurs when air leaks into the space between the lungs and chest wall. A blunt or penetrating chest injury, certain medical procedures, or lung disease can cause a pneumothorax. Symptoms include shortness of breath. When a pneumothorax is large, a needle or tube is used to remove excess air.

Co2 can be transferred in the blood in which of the following forms?

1. Dissolved in plasma 2.Dissolved in the cytosol of erythrocytes 3. Bound to hemoglobin After CO2 is produced by tissues, in what form is most of that carbon transported to the lungs for removal from the body? As dissolved HCO3-

An individual with emphysema might Experience:

1. Increased arterial PCO2 2. Decreased arterial PO2 3. Increased respiratory rate

Clinical Applications

A striking example of what occurs when surfactant is deficient is the disease known as respiratory distress syndrome of the newborn. This is a leading cause of death in premature infants, in whom the surfactant-synthesizing cells may be too immature to function adequately. Because of low lung compliance, the affected newborn infant can inspire only by the most strenuous efforts, which may ultimately cause complete exhaustion, inability to breathe, lung collapse, and death. Current therapy includes assisted breathing with a mechanical ventilator and the administration of natural or synthetic surfactant given through the infant's trachea.

brainstem centers

What brain center has neurons that fire mainly during inspiration and have input to the spinal motor neurons that activate the diaphragm and inspiratory intercostal muscles? The dorsal respiratory group of the medulla oblongata.

Respiratory Alkolysis

When a person hyperventilates, there are lower than normal levels of PCO2 and hydrogen ion in arterial blood, a condition called respiratory alkalosis.

anatomical dead space

When each successive tidal volume arrives in the lungs, the anatomical dead space from the previous breath enters the alveoli, along with 350 milliliters of the current breath.

acid base problems

You walk into your dorm room and find your roommate in the midst of anxiety-induced hyperventilation. You're unable to calm her down, so you call an ambulance. When she arrives at the ER, which of the following is her likely diagnosis? Respiratory alkalosis. Maria is a patient in the ward who was recently in a motor vehicle accident. Her injuries are causing her a lot of pain, and as a consequence to the morphine she's been given, her respiratory rate is quite low. Which of the following is likely the case? The level of H+ ions in her blood has increased.