Respiratory System Flashcards

Respiratory Systems

• The respiratory system facilitates gas exchange.
• Adult humans typically take 12-20 breaths per minute.
• Diffusion is sufficient for gas exchange in small organisms due to the high surface area to volume ratio. Diffusion is the movement of substances from areas of high concentration to areas of low concentration.
• Rate of oxygen uptake must match the rate of diffusion across the membrane.
• Gills are used by aquatic organisms to take up oxygen from water. They are thin tissue filaments that are highly branched and folded to increase surface area and are close to vasculature, hence dissolved oxygen in water rapidly diffuses across the gills into the bloodstream.
• Insects use a tracheal system, which consists of a network of small tubes made of chitin that carries oxygen to the entire body.
• Spiracles are openings along the thorax and abdomen that connect to the tubular network, allowing O2 to enter and CO2 to exit
• Young amphibians use gills to breathe and don't leave the water; some maintain gills for life.
• Adult amphibians have lungs, but also use diffusion across the skin and their skin needs to be moist.
• Amniotes like mammals, birds, crocodiles, and turtles use the rib cage and corresponding muscles for respiration by expanding and contracting the chest cavity.
• Snapping turtles use muscles and gravity to breathe with a fused rib cage.
• Mammals use pulmonary ventilation (breathing).
• During inhalation, air enters the nasal cavity where it is warmed and humidified.
• The respiratory tract is coated with mucus that traps particulates and seals tissues from direct contact with air.
• Particulate matter is removed in the nasal passages via mucus and cilia.
• Warming, humidifying, and removing particles is important to prevent damage to the trachea and lungs.
• From the nasal cavity, air passes through the pharynx (throat) and the larynx (voice box) before entering the trachea.
• The trachea funnels inhaled air to the lungs and exhaled air back out.
• The trachea is a cartilaginous cylinder that sits in front of the esophagus and extends from the larynx into the chest cavity, where it divides into the two primary bronchi at the midthorax.
• It is made of incomplete rings of hyaline cartilage and smooth muscle.
• Cartilage provides strength and support, keeping the airway open.
• The trachea is lined with mucus-producing goblet cells and ciliated epithelia. Cilia propel foreign particles trapped in the mucus toward the pharynx.
• The right lung is larger and contains three lobes; the left lung is smaller and contains two lobes.
• The muscular diaphragm aids breathing and marks the end of the thoracic cavity.
• The lungs contain air passages called bronchi. The two main bronchi divide into secondary bronchi, tertiary bronchi, and bronchioles.
• Respiratory bronchioles lack cartilage and rely on inhaled air to support their shape.
• Alveolar sacs resemble bunches of grapes tethered to the end of the bronchioles, each containing many alveoli.
• Alveoli are made of thin-walled cells that look like tiny bubbles and are in direct contact with capillaries of the circulatory system.
• Oxygen (O_2) diffuses from alveoli into the blood.
• Carbon dioxide (CO_2) produced by cells diffuses from the blood into alveoli to be exhaled.
• There are approximately 300 million alveoli per lung, giving lungs a spongy consistency and a surface area of approximately 75m2.
• The nasal cavity hairs and mucus trap small particles.
• Lungs use mucus to trap small particles such as pollen and pathogens.
• Bronchi and bronchioles use cilia to move mucus and particles back up the throat.

Gas Exchange

• Atmospheric gas is a mixture of nitrogen (N2; 78.6%), oxygen (O2; 20.9%), water vapor (H2O; 0.5%), and carbon dioxide (CO2; 0.04%).
• Each gas exerts a pressure, and the pressure for an individual gas in the mixture is the partial pressure of that gas.
• Partial pressures contribute to diffusion.
• Different animals have different lung capacities. Larger animals usually have larger lung capacities.
• Blue whales have a lung capacity of 5000L, while humans have approximately 6L.
• Tidal volume (TV) is the air that is inspired and expired during a normal breath.
• Expiratory reserve volume (ERV) is the additional amount of air that can be exhaled after a normal exhalation.
• Inspiratory reserve volume (IRV) is the additional amount of air that can be inhaled after a normal inhalation.
• Residual volume (RV) is the amount of air left after the expiratory reserve volume is exhaled.
• Boyle’s law states that pressure and volume are inversely related.
• As volume decreases, pressure increases, and vice versa.
• There is always a slightly negative pressure within the thoracic cavity, which aids in keeping the airways of the lungs open.
• If pressure in the lungs is less than atmospheric pressure, air will enter the lungs.
• During inhalation, intercostal muscles and the diaphragm contract, expanding the thoracic cavity and lowering lung pressure relative to the atmosphere, causing air to rush into lungs.
• Diffusion is the movement of a substance down a concentration gradient.
• Blood that is low in oxygen and high in carbon dioxide undergoes gas exchange with air in the lungs.
• During exhalation, intercostal muscles and the diaphragm relax, shrinking the thoracic cavity and increasing lung pressure, causing air to rush out of lungs.
• Each lung is surrounded by a membranous sac called the pleural sac.
• The visceral pleura contacts the lung, and the parietal pleura contacts the thoracic cavity.
• The intrapleural space contains a small amount of fluid that protects the tissue and reduces the friction generated as the lungs contract and relax.
• Alveolar ventilation is the amount of air exchanged in alveoli. The respiratory rate in humans is typically 12-15 breaths per minute.
• There are two ways to keep the alveolar ventilation constant: increase the respiratory rate while decreasing the tidal volume of air per breath, or decrease the respiratory rate while increasing the tidal volume per breath.

Respiratory diseases and transport

• The air-tissue/water interface of the alveoli has a high surface tension. This surface tension pulls the surfaces of the alveoli in toward one another after exhalation.
• To avoid cells collapsing on each other, cells of the lungs produce surfactant, a mixture of phospholipids and lipoproteins that lower surface tension.
• Babies born prematurely sometimes do not produce enough surfactant and have a harder time inflating lungs (respiratory distress syndrome).
• They typically produce enough surfactant on their own by week ~34.
• Two main causes of decreased gas exchange are compliance (how well the lungs expand) and resistance (how much obstruction exists in the airways).
• In restrictive diseases, the lungs cannot fully expand, meaning breaths are less full. Examples include respiratory distress syndrome, pulmonary fibrosis (stiff airways), and pulmonary edema.
• In obstructive diseases, the air from inhalation cannot be fully exhaled, making respiration less efficient. Examples include bronchitis, asthma, and emphysema.
• Most oxygen—98.5%—is bound to a protein called hemoglobin.
• Hemoglobin is a protein found in red blood cells made of four subunits that surround a central iron-containing heme group.
• Each subunit binds one oxygen molecule, for a total of four per hemoglobin.
• The binding of oxygen to hemoglobin can be plotted as a function of the partial pressure of oxygen in the blood versus the relative Hb-oxygen saturation.
• The resulting graph—an oxygen dissociation curve—is sigmoidal, or S-shaped. As the partial pressure of oxygen increases, the hemoglobin becomes increasingly saturated with oxygen.
• Environmental factors like blood pH, CO_2 levels, and body temperature can affect oxygen-carrying capacity and delivery.
• More oxygen is needed to reach the same hemoglobin saturation level when the pH is lower.
• In sickle cell anemia, the shape of the red blood cell is crescent-shaped, elongated, and stiffened, reducing its ability to deliver oxygen.
• Thalassemia is a defect in either the alpha or the beta subunit of Hb. Patients with thalassemia produce a high number of red blood cells that have less hemoglobin.
• CO_2 is transported by dissolving directly into the blood plasma (5%), binding to hemoglobin (10%), or being carried as a bicarbonate ion (85%).
• Carbon monoxide (CO) has a greater affinity for hemoglobin (Hb) than oxygen (O_2).
• When carbon monoxide is present, it binds to hemoglobin preferentially over oxygen. This is dangerous.