Question

The structural and functional unit of lung is
a. Alveoli
b. Trachea
c. Bronchiole
d. Bronchus

Answer 1

Hint: Lungs are the primary organs of the respiratory system in humans and many other animals including a few fish and some snails. In mammals and most other vertebrates, two lungs are located near the backbone on either side of the heart. Their function in the respiratory system is to extract oxygen from the atmosphere and transfer it into the bloodstream, and to release carbon dioxide from the bloodstream into the atmosphere, in a process of gas exchange.

Complete answer: In order to answer this question we need to go through the structure of lungs in detail.
Lungs are the most important organs of the tract. They’re suspended within the cavity of the thorax. The lungs are surrounded by two thin membranes called pleura, which secrete a fluid that enables the lungs to maneuver freely within the cavum. This can be necessary therefore the lungs can expand and contract during breathing. Lungs are split into sections. These are called lobes, and that they are separated from one another by connective tissues. The left lung is smaller and contains only two lobes. The smaller left lung allows room for the center, which is simply left of the middle of the chest.

Lung tissue consists mainly of alveoli. These tiny air sacs are the functional units of the lungs where gas exchange takes place. Oxygen within the air inside the alveoli is absorbed by the blood within the mesh-like network of little capillaries that surrounds each alveolus. The blood in these capillaries also releases greenhouse emission into the air inside the alveoli. The lungs receive blood from two major sources. They receive deoxygenated blood from the center. This blood absorbs oxygen within the lungs and carries it back to the guts to be pumped to cells throughout the body. The lungs also receive oxygenated blood from the guts that gives oxygen to the cells of the lungs for metabolic processes.

Function of lungs
The method by which the respiratory system protects itself is named mucociliary escalator. From the nose through the bronchi, the tract is roofed within the epithelium that contains mucus-secreting goblet cells. The mucus traps particles and pathogens within the incoming air. The epithelium of the tract is additionally covered with tiny cell projections called cilia. Cilia constantly move in a very sweeping motion upward toward the throat, moving the mucus and trapped particles and pathogens faraway from the lungs and toward the surface of the body. The material that moves up the mucociliary escalator to the throat is far from the tract by clearing the throat or coughing. The amount of oxygen and dioxide within the blood must be maintained within a limited range for the survival of the organism. Cells cannot survive for long without oxygen, and if there's an excessive amount of CO$_2$ within the blood, the blood becomes dangerously acidic. If there's insufficient CO$_2$ within the blood, the blood becomes too basic.

The system works hand-in-hand with the nervous and cardiovascular systems to keep up homeostasis in blood gases and pH. It is the amount of carbonic acid gas instead of the extent of oxygen that's most closely monitored to take care of blood gas and pH homeostasis. The extent of dioxide within the blood is detected by cells within the brain, which speed up or block the speed of breathing to bring the greenhouse gas level within the traditional range. Faster breathing lowers the greenhouse emission level; slower breathing has the alternative effects. During this way, the amount of CO$_2$ and oxygen, yet as pH, are maintained within normal limits.

The respiratory system also works closely with the vascular system to take care of homeostasis. The respiratory system exchanges gases between the blood and also the outside air, but it needs the circulatory system to hold them to and from body cells. Oxygen is absorbed by the blood within the lungs then transported through an unlimited network of blood vessels to cells throughout the body where it's needed for aerobic respiration. The identical system absorbs dioxide from cells and carries it to the system for removal from the body.

The lungs serve a protective role. Several blood-borne substances, like some forms of prostaglandins, leukotrienes, serotonin and bradykinin, are excreted through the lungs. Drugs and other substances may be absorbed, modified or excreted within the lungs. The lungs filtrate small blood clots from veins and stop them from entering arteries and causing strokes.

The lungs also play a pivotal role in speech by providing air and airflow for the creation of vocal sounds, and other paralanguage communications like sighs and gasps.

Therefore, the correct answer is a, alveoli.


Additional information: In addition to their function in respiration, the lungs have a variety of other functions. They’re involved in maintaining homeostasis, helping within the regulation of vital sign as a part of the renin–angiotensin system. The inner lining of the blood vessels secretes angiotensin-converting enzyme (ACE) an enzyme that catalyses the conversion of angiotensin I to Hypertension. The lungs are involved within the blood's acid-base homeostasis by expelling carbon nic acid gas when breathing.


Note: In embryonic development, lungs begin to develop as an outpouching of the foregut, a tube which works on to make the upper part of the system. When the lungs are formed the fetus is held within the fluid-filled amnion and then they are not functioning to breathe. Blood is additionally diverted from the lungs through the blood vessel. At birth however, air begins to meet up with lungs, and therefore the diversionary duct closes, so the lungs can begin to breathe. Lungs only fully develop in infancy.