Respiratory System: 25 MCQs with answers

To exchange gases between air and blood

Alveoli are tiny air sacs where oxygen diffuses into the blood and carbon dioxide diffuses out.

Diaphragm

The diaphragm contracts and flattens during inhalation, increasing thoracic volume.

It decreases

During exhalation, the diaphragm relaxes and thoracic volume decreases, pushing air out.

Production of red blood cells

Red blood cell production occurs in bone marrow, not the respiratory system.

False

The diaphragm contracts and moves downward during inhalation.

True

About 98% of oxygen is carried bound to hemoglobin in red blood cells.

Oxygen

Oxygen is the primary gas exchanged in the alveoli, where it diffuses into the blood.

Alveoli

The alveoli are the tiny air sacs in the lungs where the exchange of oxygen and carbon dioxide occurs.

Air enters the lungs

Inhalation is the process where air enters the lungs, allowing oxygen to be taken in.

They assist in lung expansion

The intercostal muscles assist in expanding the chest cavity during inhalation, facilitating lung expansion.

To exchange gases

The primary purpose of the respiratory system is to facilitate the exchange of gases, primarily oxygen and carbon dioxide.

Carbon Dioxide

Carbon dioxide is produced as a waste product during cellular respiration and is expelled from the body during exhalation.

To carry oxygen

Hemoglobin is a protein in red blood cells that binds to oxygen, allowing it to be transported throughout the body.

It relaxes and moves upwards

During exhalation, the diaphragm relaxes and moves upwards, decreasing the volume of the thoracic cavity and pushing air out.

Medulla Oblongata

The medulla oblongata is the part of the brain that controls the autonomic functions of breathing.

To filter and humidify air

The nasal cavity filters, humidifies, and warms the air before it enters the lungs.

Nose → trachea → bronchi → bronchioles → alveoli

Air passes through the nose, trachea, bronchi, bronchioles, and finally reaches the alveoli.

It reduces surface tension to prevent alveolar collapse

Surfactant lowers surface tension, preventing alveoli from collapsing during exhalation.

Blood pH

Blood pH affects oxygen transport but not the diffusion process across the alveolar membrane.

Higher in alveoli

Alveolar PO2 is about 104 mmHg, while venous blood PO2 is about 40 mmHg, creating a gradient for diffusion.

Bicarbonate ions

About 70% of CO2 is transported as bicarbonate ions after conversion in red blood cells.

It decreases pH

CO2 reacts with water to form carbonic acid, which lowers blood pH.

Increased tidal volume

Tidal volume increases to bring more air into the lungs during exercise.

Movement of chloride into red blood cells to balance charge during CO2 transport

The chloride shift maintains electrical neutrality when bicarbonate exits red blood cells.

Carbon dioxide levels in the blood

Chemoreceptors primarily respond to changes in CO2 and pH, not oxygen, under normal conditions.