Test: Human Physiology: Respiratory System - 3 - Grade 11 MCQ

Blood is the medium of transport for oxygen and carbon dioxide. About 97 per cent of oxygen is transported by RBCs in the blood. The remaining 3 per cent of oxygen is carried in a dissolved state through the plasma. Nearly 20-25 per cent of carbon dioxide is transported by RBCs, whereas 70 per cent of it is carried as bicarbonate ions. About 7 per cent of carbon dioxide is carried in a dissolved state through plasma.

Human beings have a significant ability to maintain and moderate the respiratory rhythm to suit the demands of the body tissues. This is done by the neural system. A specialised centre present in the medulla region of the brain called as respiratory rhythm centre, is primarily responsible for this regulation.
So, the correct answer is option B.

The respiratory system includes the nose, mouth, throat, voice box, windpipe, and lungs. Air enters the respiratory system through the nose or the mouth. If it goes in the nostrils (also called nares), the air is warmed and humidified.

RBCs contain a very high concentration of the enzyme, carbonic anhydrase and minute quantities of the same is present in the plasma too. This enzyme facilitates the production of carbonic acid from carbon dioxide and water. It also catalyzes the dissociation of carbonic acid into bicarbonate ions and protons.
Thus, the correct answer is option A.

• The motivation for voluntary forced breathing comes from the brain.
• It is the brain that sends signals to the muscles in the chest and abdomen to contract and expand, resulting in breathing.
• This is also known as diaphragmatic breathing.

Alveoli is a characteristic feature of mammalian lungs. The pulmonary alveoli from the terminal ends of the respiratory tree and from these the branches out the alveolar sacs and ducts which act as efficient sites for gaseous exchange.  Besides the epithelial layer and extracellular matrix, these contain collagen and elastic fibres. which stretch as the alveoli are filled with air and spring back to expel carbon dioxide during exhalation. Though, a small amount of air is always present which prevents the lungs from collapsing. 
So, the correct option is 'An efficient system of ventilation with little residual air'.

Human blood contains a buffer of carbonic acid (H₂CO₃) and bicarbonate anion 
(HCO₃^-) in order to maintain blood pH between 7.35 and 7.45, as a value higher than 7.8 or lower than 6.8 can lead to death. In this buffer, hydronium and bicarbonate anion are in equilibrium with carbonic acid.

Carbon monoxide has 210 times greater affinity for haemoglobin than oxygen. A small environmental concentration will thus cause toxic levels of carboxyhemoglobin. The affinity of carbon monoxide for myoglobin is even greater than for haemoglobin 1. Binding to cardiac myoglobin causes myocardial depression, hypotension and arrhythmias. Cardiac decompensation results in further tissue hypoxia and is ultimately the cause of death. Thus, option B.

At high altitudes, there is a decrease in oxygen hemoglobin saturation. This hypoxic condition causes hypoxia-inducible factor 1 (HIF- 1) to become stable and stimulates the production of erythropoietin (EPO), a hormone secreted by the kidneys. EPO stimulates red blood cell production from bone marrow in order to increase hemoglobin saturation and oxygen delivery. Thus, the total number of RBC increases.

During normal breathing , the volume of air inspired or expired is known as tidal volume. It's value is approximately 500ml which is very low as compared to vital capacity (3400ml- 4800ml), inspiratory reserve volume (2500ml-3000ml) and expiratory reserve volume (1000ml-1100ml).
So, the tidal volume has the lowest value.

• The oxygen-carrying capacity of hemoglobin is decreased.
• When the pH of human blood decreases, it becomes more acidic and the oxygen-carrying capacity of hemoglobin is reduced due to changes in its structure.
• This can lead to a decrease in red blood cell count as well.

Alveoli are the primary sites of exchange of gases. Exchange of gases also occurs between blood and tissues. Oxygen and carbon dioxide are exchanged at these sites by simple diffusion mainly based on pressure/ concentration gradient. Solubility of the gases as well as the thickness of the membranes involved in diffusion are some important factors that can affect the rate of diffusion. The diffusion membrane is made up of three major layers namely, the thin squamous epithelium of alveoli, the endothelium of the alveolar capillaries. However, its total thickness is much less than a millimetre.
Therefore, the correct answer is option B.

In carbon monoxide poisoning there is decrease in free haemoglobin. 

External respiration is the exchange of gases with the external environment, and occurs in the alveoli of the lungs. ... The actual exchange of gases occurs due to simple diffusion. Energy is not required to move oxygen or carbon dioxide across membranes.

Haemoglobin, is the iron-containing oxygen-transport metalloprotein in the red blood cells of almost all vertebrates as well as the tissues of some invertebrates. Hemoglobin in blood carries oxygen from the lungs or gills to the rest of the body. it's a respiratory pigment.

Concentration of carbonic acid does not increase in blood due to presence of Na⁺. The bicarbonate buffering system of blood is an important buffer system in the acid-base homeostasis of living things, including humans. In plasma, by phosphate buffers, the alkaline phosphates combines with carbonic acid (H₂CO₃) and forms sodium bi carbonate.

Na₂HPO₄ + H₂CO₃ ⇄ NaH₂PO₄ + NaHCO₃
 

Larynx is the other name of voice box.
Epiglottis is the lid of larynx
Trachea is known as wind pipe.
Alveoli are air sacs where gas exchange takes place.

• When a patient inhales polluted air containing an unusually high concentration of carbon monoxide (CO), it can have detrimental effects on their health.
• Carbon monoxide is a toxic gas that is produced by the incomplete combustion of fossil fuels, such as in car exhaust or faulty heating systems.

• In the blood, carbon dioxide (CO₂) dissolves and combines with water (H₂O) to form carbonic acid (H₂CO₃).
• A reaction facilitated by an enzyme called carbonic anhydrase increases the rate of the reaction by releasing hydrogen ions (H⁺) and bicarbonate ions (HCO₃^-).
• Carbonic acid is then dissociated into hydrogen ions (H⁺) and bicarbonate ions (HCO₃^-).
• The increased concentration of hydrogen ions from the dissociation of carbonic acid lowers the pH of the blood, making it more acidic.
• This pH change is important for maintaining the acid-base balance in the body.

Hiccup is also called as a hiccough. It is an involuntary activity of the diaphragm. During hiccups, the diaphragm muscle shows several involuntary contractions.When the diaphragm muscle contracts, the opening between the vocal cords snaps shut to check the inflow of air.This results in the hic or hiccup sound. This results due to irritation of the nerves.

Respiratory centre of brain is stimulated by increased conc. of CO² in blood , and to lesser extent by decreased conc. of O². This stimulation causes an increase in the rate & depth of breathing , thus blowing off excess CO² and reducing blood acidity.

RBCs contain a very high concentration of the enzyme, carbonic anhydrase and minute quantities of the same is present in the plasma too. This enzyme facilitates the reaction between carbon dioxide and water to form carbonic acid and its dissociation into bicarbonate ions and protons.

Haemoglobin is a red coloured iron containing pigment present in the RBCs. Oxygen can bind with haemoglobin in a reversible manner to form oxyhaemoglobin. Each haemoglobin molecule can carry a maximum of four molecules of oxygen. Binding of oxygen with haemoglobin is primarily related to partial pressure of oxygen. Partial pressure of carbon dioxide, hydrogen ion concentration (pH) and temperature are the other factors, which can affect this binding.

Therefore, the correct answer is B.