What are alveoli?

Answer 1

They are tiny air sacs in the lungs that are used for gaseous exchange between the lungs and and the bloodstream.

Answer 2

The alveoli are the final branchings of the respiratory tree and act as the primary gas exchange units of the lung. The gas-blood barrier between the alveolar space and the pulmonary capillaries is extremely thin, allowing for rapid gas exchange. To reach the blood, oxygen must diffuse through the alveolar epithelium, a thin interstitial space, and the capillary endothelium; CO2 follows the reverse course to reach the alveoli.

Answer 3

The alveoli are the final branchings of the respiratory track and act as the primary gas exchange units of the lung.

Answer 4

The alveoli are the final branchings of the respiratory tree and act as the primary gas exchange units of the lung.

Answer 5

The alveoli are the sacs at the end of bronchioles inside the lungs. The walls of the alveolai are very thin (one cell) and this feature means that gaseous exchange can take place - oxygen and carbon dioxide can pass into and out of the lungs.

Answer 6

They are the small sacs in your lungs where gas transfer takes place, the easiest way to inagine them is to think of a bunch of grapes, with the stems being the bronchioles, and the grapes the alveoli.

Answer 7

The alveoli are the final branchings of the respiratory tree and act as the primary gas exchange units of the lung.
i hope this link helps

http://oac.med.jhmi.edu/res_phys/Encyclopedia/Alveoli/Alveoli.HTML

Answer 8

An alveolus (plural: alveoli), is an anatomical structure that has the form of a hollow cavity. 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.[1]

Location
The alveoli are found in the respiratory zone of the lungs.

Structure
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 (pneumocytes):

* Type I cells that form the structure of an alveolar wall
* Type II cells that secrete surfactant to lower the surface tension of water

The alveoli have an innate tendency to collapse because of their spherical shape, small size, and surface tension due to water vapor. Phospholipids, which are called surfactants, and pores help to equalize pressures and prevent collapse.

[edit] Details

The alveoli have radii of about 0.1 mm and wall thicknesses of about 0.2 µm.

Pulmonary 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). Conversely, carbon dioxide is produced by metabolism and has a higher concentration in the blood than in the air.

Oxygen in the lungs first diffuses through the alveolar wall and dissolves in the fluid phase of blood. The amount of oxygen dissolved in the fluid phase is governed by Henry's Law. Oxygen dissolved in the blood may diffuse into red blood cells and bind to hemoglobin. Binding of oxygen to hemoglobin allows a greater amount of oxygen to be transported in the blood. Although carbon dioxide and oxygen are the most important molecules exchanged, other gases are also transported between the alveoli and blood. The amount of a gas that is exchanged depends on the water solubility of the gas the affinity of the gas for hemoglobin. Water vapor is also excreted through the lungs, due to humidification of inspired air by the lung tissues.

Red blood cells transit the alveolar capillaries in about 3/4 of a second. 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. Transport of carbon monoxide is thus termed 'diffusion limited'. Gases that reach equilibrium before the blood leaves the alveolar capillaries are 'perfusion limited', since the amount of the gas exchanged depends solely on the volumetric flow rate of blood past the alveoli.

The lungs contain about 300 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 tonsils in the nasopharynx which traps germs, 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.

You could get more information from the link below...

Answer 9

Alveoli are "lung sacs". They are the little sacs in your lungs where the actual interchange of Oxygen and Carbon Dioxide occur. There are millions of them in each human.

Answer 10

The primary gas exchange units in the lungs.