Respiratory system: the organ system - class-VII

• The pharynx, or throat, is the passageway leading from the mouth and nose to the oesophagus and larynx. 
• The pharynx permits the passage of swallowed solids and liquids into the oesophagus, and conducts air to and from the trachea, or windpipe, during respiration. 
• The pharynx also connects on either side with the cavity of the middle ear by way of the Eustachian tube and provides for equalization of air pressure on the eardrum membrane, which separates the cavity of the middle ear from the external ear canal. Hence, The short tube leading from the nose is pharynx.

• The diaphragm is a part of the abdominopelvic cavity.
•  It is located below the thoracic cavity and above the pelvic cavity.
•  Its dome-shaped roof is the thoracic diaphragm, a thin sheet of muscle under the lungs, and its floor is the pelvic inlet, opening into the pelvis. Hence, the diaphragm is a dome-shaped muscle.

• The nasal cavity and the mouth meet at the pharynx, or throat, at the back of the nose and mouth. 
• From there, air quickly enters the second part of your respiratory system, the trachea or windpipe. 
• The trachea is a tube that delivers air to the lungs, the third and most important part of your respiratory system. Hence, Air goes from the pharynx to. trachea.

• The bronchi (or bronchus) are the air passages into the lungs that begin at the end of the trachea. 
• There are two bronchi, one for each lung. 
• The bronchus divides into smaller branches known as segmental bronchi, which divide again into bronchioles, Hence, Bronchi divide into bronchioles.

Most carbon dioxide (about 70%) is transported in the blood as bicarbonate ions (HCO3-) dissolved in the plasma.

The respiratory system, including the lungs and bronchial tree, is derived from the endoderm germ layer.

The pneumotaxic center in the pons regulates respiratory rhythm by sending neural signals that can reduce the duration of inspiration and increase the respiratory rate. This is a key respiratory control mechanism. Option A is incorrect because about 70% of CO₂ is transported as bicarbonate, not by hemoglobin. Option C describes silicosis, not lung fibrosis. Option D - cigarette smoking causes bronchitis, not primarily inflammation of bronchi.

The conducting part of the respiratory system includes the nose, pharynx, larynx, trachea, bronchi, and bronchioles. Its primary functions are to transport, filter, warm, and humidify the air. The alveoli are the specific site for gas exchange, which is part of the respiratory zone, not the conducting zone.

Statement (c) is correct as functional residual capacity is the volume of air remaining in the lungs after a normal expiration. Statement (d) is correct as total lung capacity is the maximum volume of air the lungs can hold after a forced inspiration. Statement (a) is incorrect because inspiration is primarily facilitated by the diaphragm and external intercostal muscles, not internal ones. Statement (b) is incorrect because a healthy human typically breathes about 6000-8000 ml of air per minute.

Respiratory quotient if the protein is 0.8-0.9

Gas exchange occurs across the respiratory membrane, which consists of the alveolar wall and the capillary wall.

Respiratory bronchioles are the final branches of the bronchial tree, which then divide into alveolar ducts that lead to the alveolar sacs.

The alveolus is the functional unit of the lung where the actual exchange of oxygen and carbon dioxide takes place.

Alveolar air contains approximately 13.1% oxygen and 5.3% carbon dioxide, reflecting the exchange that has occurred with the blood.

The total surface area of the alveoli in human lungs is estimated to be between 70 and 100 square meters, facilitating efficient gas exchange.

Alveolar air composition is approximately 14% oxygen, 6% carbon dioxide, and 80% nitrogen. This differs from atmospheric air due to the continuous exchange of gases in the lungs.

Pulmonary ventilation is the total volume of air moved into and out of the lungs per minute. Alveolar ventilation is lower because it excludes the air that remains in the anatomical dead space where no gas exchange occurs.

Oxygen diffuses from the alveoli into the blood because the partial pressure of oxygen in the alveoli (approx. 104 mmHg) is higher than that in the deoxygenated pulmonary capillary blood (approx. 40 mmHg).

The pleura are membranes that secrete a lubricating fluid, which allows free movement of the lungs against the chest wall while breathing. The alveolar sacs are sacs of many alveoli (clusters of chambers), that help exchange oxygen and carbon dioxide in the lungs. The bronchioles are the passageways by which air passes through the nose or mouth to the alveoli (air sacs) of the lungs. Each lobe of the lung has the same physiologic function, bringing oxygen into the bloodstream and removing carbon dioxide. So, the correct option is 'alveolar sacs'.

The air present inside the alveoli or the alveolar air usually has a higher amount of oxygen than carbon dioxide. The approximate composition of alveolar air under normal condition is 14% oxygen, 6% carbon dioxide, and 80% nitrogen.

So, the correct answer is '14% oxygen, 6% carbon dioxide, 80% nitrogen'.

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• When the internal intercostal muscles contract and diaphragm relax, the ribs move .downward and inward and the diaphragm becomes convex {dome shaped), 
• thus decreasing the volume of the thoracic cavity and increasing the pressure inside as compared to the atmospheric pressure outside. This will cause the air to move out (expiration).

While respiration atmospheric air is drawn in a carbon dioxide is released out, diffusion of gases takes place in the alveolar tissue which is then carried by blood, then diffusion of gases take place between blood and tissues, oxygen is utilized by cells for catabolic reactions, and the resultant carbon dioxide is released from the body.

  (i) Diaphragm contracts to help in (1) inspiration while the contraction of abdominal muscles helps in (2) forced expiration.

(ii) Vital capacity of trained athletes is (3) higher than that of non-athletes while the vital capacity of non-smokers is (4) higher than that of smokers.

(iii) Alveolar PO2 is (5) higher than the venous PO2 while arterial PO2 is (6) lower than the alveolar PO2.

So, the correct answer is '(1)-inspiration, (2)-forced expiration, (3)-higher, (4)-higher'.

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The diaphragm is the dome-shaped sheet of muscle and tendon that serves as the main muscle of respiration and plays a vital role in the breathing process. The diaphragm separates the thoracic cavity containing the heart and lungs, from the abdominal cavity and performs an important function in respiration: as the diaphragm contracts, the volume of the thoracic cavity increases and air is drawn into the lungs.

The diaphragm functions in breathing. During inhalation, the diaphragm contracts and moves in the inferior direction, thus enlarging the volume of the thoracic cavity (the external intercostal muscles also participate in this enlargement). This reduces intra-thoracic pressure.

Breathing involves two stages, inspiration during which atmospheric air is drawn in and expiration by which the alveolar air is released out. The movement of air into and out of the lungs is carried out by creating a pressure gradient between the lungs and the atmosphere. Inspiration can occur if the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure, i.e., there is a negative pressure in the lungs with respect to atmospheric pressure. Similarly, expiration takes place when the intra-pulmonary pressure is higher than the atmospheric pressure. The diaphragm and a specialised set of muscles external and internal intercostals between the ribs, help in generation of such gradients.

• A hiccup is an involuntary contraction of the diaphragm involving a reflex arc, that may repeat several times per minute. 
• Once triggered, the reflex causes a strong contraction of the diaphragm followed by about 0.25 seconds later by closure of the vocal cords, which results in the classic "hic" sound. 
• Hiccups may occur individually, or they may occur in bouts. 

Breathing or pulmonary ventilation is a process where the nasal and oral cavities inhaled the air and enter into the lungs through the pharynx, larynx and trachea. Air is also exhaled through the same pathway. While larynx, pharynx and trachea are involved the changes to the volume and air pressure in the lungs trigger  breathing. During the process of  inhalation, the diaphragm and external intercostal muscles contract thereby elevating the rib cage. With the increase in the volume of the lungs, air pressure drops letting the air rush in. Similarly, during exhalation, the muscles relax letting the lungs become smaller, which raises the air pressure and helps to expel the air.

Exhalation is a process to breath out.carbon dioxide is a waste product in the body that release out during exhalation, it is also saturated with water vapor.

Carbon dioxide is released in the process of exhalation in large amount.$CO _2$ dissolves in water and can easily and reversibly form compounds such as carbonic acid and bicarbonates. when it is released out, it is saturated with water vapour and this is the reason for water droplets in the mirror.

The diaphragm is a dome-shaped muscular partition that separates the thoracic cavity, containing the heart and lungs, from the abdominal cavity, containing the digestive organs.

Forced deep breathing (hyperventilation) lowers the partial pressure of CO2 in the blood. Since CO2 is the primary chemical stimulus for breathing, low levels lead to a temporary cessation of breathing (apnea) until CO2 levels rise again.

Breathing involves the contraction and relaxation of the diaphragm and the external intercostal muscles, which change the volume of the thoracic cavity and create the pressure gradients necessary for air movement.

Increased CO2 concentration in the blood (hypercapnia) is detected by chemoreceptors, which signal the respiratory center in the brain to increase the rate and depth of breathing to expel excess CO2.

During breathing, 20% oxygen is taken in and 15% oxygen is exhaled out. Movement of diaphragm is very important during breathing process. Ribs will also move in and out with the diaphragm. It is not possible to breathe by moving the diaphragm along without moving ribs. Even after forceful exhalation, lungs are never fully emptied. Residual volume, that is minimum amount of air in lungs always remain at all times. Eustachian tube connects middle ear cavity with nasopharynx and hence, one can breathe out air through it by closing both nose and mouth.

A)Nasal chamber opens into nasopharynx which is a portion of pharynx – True because It also connects the nasal system of air chambers and the upper end of the trachea. The opening of the mouth into the pharynx is the oropharynx, and the nasal opening is the nasopharynx. The eustachian tube from the middle ear opens into the pharynx on each side.

B)Larynx produces sound during inspiration as well as expiration – True, because, the larynx commonly called the voice box, is an organ in the top of the neck of tetrapods involved in breathing, producing sound. They have skeletal muscle, cartilage of the upper larynx collapses inward during inhalation, causing airway obstruction, results in the creation of sounds.

C)During swallowing, gullet can be covered by a thin elastic cartilaginous flap called Epiglottis – false, because, the epiglottis is a flap in the throat that keeps food from entering the windpipe and the lungs. The flap is made of elastic cartilage covered with a mucous membrane, attached to the entrance of the larynx. It projects obliquely upwards behind the tongue and the hyoid bone, pointing dorsally.

D) The trachea is get divided at the level of 6th thoracic vertebra into right and left primary bronchi – False, because The trachea, commonly called the windpipe, is the main airway to the lungs It divides into the right and left bronchi at the level of the fifth thoracic vertebra, channeling air to the right or left lung.

E)The branching network of bronchi, bronchioles, and alveoli comprise the lungs – True.

So, the correct option is ‘2’.

During inhalation, the diaphragm contracts, thus enlarging the thoracic cavity. This reduces intra-thoracic pressure: enlarging the cavity creates suction that draws air into the lungs. When the diaphragm relaxes, air is exhaled by elastic recoil of the lung and the tissues lining the thoracic cavity in conjunction with the abdominal muscles, which act as an antagonist, paired with the diaphragm's contraction.

An average adult breathes approximately 12 to 16 times per minute at rest. Over 24 hours, this equates to roughly 17,000 to 23,000 breaths, with 22,000 being a commonly cited average estimate.

The medulla oblongata is the primary respiratory control centre. Its main function is to send signals to the muscles that control respiration to cause breathing to occur. The respiratory control centre increase respiratory rate on the account of decrease in blood pH, as the oxygenated blood through veins enter the system, decrease in $CO _2$ levels, increased respiratory rate.