Effects of Aging on the Respiratory System The primary function of the respiratory system is to exchange oxygen and carbon dioxide. Inhaled oxygen enters the lungs and reaches the alveoli. The layers of cells lining the alveoli and the surrounding capillaries are each only one cell thick and are in very close contact with each other.
In the lung, the pulmonary alveoli are spherical outcroppings of the respiratory bronchioles and are the primary sites of gas exchange with the blood.
Alveoli are peculiar to mammalian lungs; different structures are involved in gas exchange in other vertebrates. The alveoli consist of an epithelial layer and extracellular matrix surrounded by capillaries.
In some alveolar walls there are pores between alveoli. There are two major alveolar cell types in the alveolar wall: Type I cells that form the structure of an alveolar wall Type II cells that secrete surfactant to lower the surface tension The alveoli have an innate tendency to collapse because of their spherical shape, small size, and surface tension.
Phospholipids, which are called surfactants, and pores help to equalize pressures and prevent collapse.
The alveoli have radii of about 0. Pulmonary gas exchange is driven by passive diffusion, which does not require energy for transport.
Substances move down a concentration gradient. Oxygen moves from the alveoli high oxygen concentration to the blood lower oxygen concentration. Conversely, carbon dioxide has a higher concentration in the blood than in the air.
The oxygen first dissolves in the fluid in the interstitial tissues and diffuses into the blood. Oxygen binds to hemoglobin in the red blood cells, which allows a greater amount of oxygen to be transported by the blood.
Although carbon dioxide and oxygen are the most important molecules exchanged, other gases will also be transported between the alveoli and blood in relation to the water solubility of the gas the ability of the gas to bind to hemoglobin.
Water vapor is also excreted through the lungs, due to humidification of inspired air by the lung tissues. Molecules with a high affinity for hemoglobin, such as carbon monoxide, can be added to the blood in high concentrations.
Most gases reach equilibrium with the blood before the red blood cells leave the alveolar capillaries. However, carbon monoxide is stored in such high concentrations in the blood, due to its strong binding to hemoglobin, that equilibrium is not reached before the blood leaves the alveolar capillary.
Thus, the concentration of carbon monoxide in the arterial system can be used to assess the resistance of the alveolar walls to gas diffusion.
Thus, transport of carbon monoxide is 'diffusion limited'. Gases that reach equilibrium before the blood leaves the alveolar capillaries are 'perfusion limited'.
The lungs contain about million alveoli, each wrapped in a fine mesh of capillaries. The lungs are constantly exposed to airborne pathogens and dust particles. The body employs many defenses to protect the lungs, including small hairs cilia lining the trachea and bronchi supporting a constant stream of mucus out of the lungs, and reflex coughing and sneezing to dislodge mucus contaminated with dust particles or micro-organisms.
For efficient gas exchange, the ratio of alveolar ventilation and capillary perfusion should be matched for each lung subunit. Ventilation of a subunit can be lowered by obstruction with fluid, particulates, mucous or tumors. Perfusion can be lowered by pulmonary embolism.
Homeostatic responses in the lungs minimize the mismatching of ventilation and blood flow. For example, alveolar epithelia secrete vasodilating substances in response to normal levels of oxygen.
The blood that enters the pulmonary capillaries is the systemic venous blood which enter the lungs via the pulmonary arteries. Due to differences in partial pressures across the alveolar-capillary membrane, O2 diffuses into the blood and CO2 diffuses out.
The more pulmonary capillaries participating in this process, the more total O2 and CO2 that can be exchanged. The magnitude of the difference between the alveolar PO2 and arterial PO2 can be used to detect the presence of some lung diseases.•Diffusion is passive, driven only by the difference in O Gas Exchange •Gas exchange is driven by differences in partial pressures •Blood returning from the systemic circulation, Pulmonary vein CO 2 O 2 Pulmonary artery O 2 CO 2 Alveolar gas CO O 2 P = mm Hg P = 40 mm Hg O 2 CO 2.
Chapter Respiratory System • Pulmonary gas exchange (external respiration) is c. driven by the gradient between inspired air and alveolar blood d.
less efficient than diffusion of carbon dioxide REVIEW The efficiency of pulmonary gas exchange is. The clinical condition continuously improved with sufficient pulmonary gas exchange. The pECLA was removed after 8 days, and the patient was successfully weaned from mechanical ventilation.
The respiratory system is an integrated network of organs and tubes that coordinates the exchange of oxygen and carbon dioxide between an organism and its environment.
Apr 24, · Human alveolusPulmonary gas exchange is driven by passive diffusion and thus does not require energy for exchange. Substances move down a concentration gradient. Oxygen moves from the alveoli (high oxygen concentration) to the blood (lower oxygen concentration, due to the continuous consumption of oxygen in the body).Status: Resolved.
Transport across a cell membrane is a tightly regulated process, because cell function is highly dependent on maintain strict concentrations of various molecules. When a molecule moves down its concentration gradient is it participating in passive transport; moving up the concentration gradient requires energy making it active transport.