Unit 3: Gaseous Exchange

Comprehensive practice flashcards for Unit 3: Gaseous Exchange, covering the mechanisms of breathing, cellular respiration, animal and plant comparative gaseous exchange adaptations, human respiratory anatomy, transport of oxygen and carbon dioxide, lung capacities, homeostatic regulation, altitude effects, diseases, smoking impacts, and artificial respiration.

How is breathing defined in contrast to gaseous exchange and cellular respiration?

Breathing is the mechanical process whereby air moves in and out of the lungs.

What is gaseous exchange?

The exchange of oxygen ($O_2$) and carbon dioxide ($CO_2$) across a gaseous exchange surface.

What is cellular respiration?

The gradual release of energy from organic compounds (glucose) in the presence of oxygen.

Why is the continuous removal of carbon dioxide ($CO_2$) critical for the body?

An increased $CO_2$ concentration in the body can dangerously lower the pH of body fluids.

What are the six structural requirements for an effective gaseous exchange system or surface?

1. Large surface area (to maximise exchange)
2. Thin (for quick and easy diffusion)
3. Moist (gases must be in solution to diffuse through a membrane)
4. Properly ventilated (for good $O_2$ supply and $CO_2$ removal)
5. Transport system (for efficient transport of gases)
6. Well protected (because it is very thin and fragile)

What is diffusion as defined in the gaseous exchange notes?

The movement of molecules from a high concentration to a low concentration until equilibrium is reached.

What structure serves as the main gaseous exchange surface in a dicotyledonous plant?

The outer surface of the spongy mesophyll cells, which are large, round parenchyma cells with large intercellular air spaces and moist cell walls.

How does Planaria accomplish gaseous exchange without specialized respiratory organs?

Its entire outer surface acts as a gaseous exchange surface with a very large outer surface area to volume ratio, allowing $O_2$ and $CO_2$ to diffuse directly through its thin body wall.

How does an earthworm keep its gaseous exchange surface moist?

Its skin is kept moist by mucus secreted from the skin epidermis as well as coelomic fluid secreted onto the skin.

How does air enter and travel through the gaseous exchange system of a locust?

Air enters through spiracles on the thorax and abdomen, passes into tracheas, and then into smaller branching tracheoles where $O_2$ diffuses into cells.

What adaptation prevents water loss in terrestrial insects like locusts?

An outer exoskeleton that is impermeable to water.

How is gaseous exchange carried out across the gills of a bony fish?

Fish have four gills on each side of the head in the gill chamber. Water flows into the mouth and over gill filaments richly supplied with blood capillaries; dissolved $O_2$ diffuses into capillary blood and $CO_2$ diffuses out into the water flowing out through the gill slits.

Which three main components make up the human respiratory system?

Air passages, lungs, and respiratory muscles.

What is the function of the three turbinate bones and superficial capillaries in the nasal cavity?

Turbinate bones divide each nasal cavity into three passages, and superficial blood capillaries warm the incoming air.

What three functions are performed by the mucus secreted by goblet cells in the air passages?

1. Traps dust and germs
2. Acts as an antiseptic to prevent inhaled germs from multiplying
3. Moistens incoming air to prevent gaseous exchange surfaces from drying out

What is the function of the cilia found on the columnar epithelial cells lining the air passages?

They continuously perform sweeping movements away from the lungs to carry dust- and germ-laden mucus toward the outside (to be coughed up or swallowed).

Identify the structure shown at the top of the larynx and state its function.

The epiglottis; it closes the glottis (the opening to the trachea) during swallowing to prevent food from entering the trachea and choking the person.

Why do the C-shaped cartilage rings of the trachea open toward the back against the oesophagus?

The open posterior side, covered by involuntary muscle tissue, allows the oesophagus to expand as food moves down through it during swallowing.

What type of cartilage rings hold the bronchi open, and what happens to cartilage support as bronchi branch into bronchioli?

Bronchi are held open by O-shaped cartilage rings; as they branch into smaller bronchioli, they lose their cartilage support.

How many lobes do the right and left human lungs possess?

The right lung has $3$ lobes, while the left lung has $2$ lobes.

What is the pleura, and what is the role of intrapleural fluid?

The pleura is a double membrane surrounding each lung; intrapleural fluid between the membranes prevents friction when the lungs expand and contract.

Identify the microscopic structures depicted, which form the actual gaseous exchange surface of the human lung.

Alveoli (grouped into infundibula) surrounded by capillary networks, both consisting of a single layer of squamous epithelium (endothelium).

Why is normal inhalation classified as an active process?

It requires active contraction of the diaphragm (which flattens) and the external intercostal muscles (which lift the ribs upwards and outwards).

What pressure and volume changes occur in the thoracic cavity during normal inhalation?

Thoracic cavity volume increases (enlarges top to bottom, side to side, and front to back), decreasing thoracic and lung pressure below atmospheric pressure, causing $O_2$-rich air to flow in.

Why is normal exhalation classified as a passive process?

It is associated with the relaxation of the diaphragm (returns to dome shape) and external intercostal muscles (ribs move down and inward), reducing thoracic volume without active muscular work.

What muscular actions make exhalation an active, forced process during coughing, sneezing, whistling, or shouting?

The internal intercostal muscles contract (pulling ribs further inward) and abdominal muscles contract (pushing abdominal contents up against the diaphragm).

In the bell jar demonstration model of breathing, what anatomical structures are represented by the glass bell jar, the Y-tube, the balloons, and the rubber sheet?

• Glass bell jar: chest wall
• Glass Y-tube: trachea and bronchi
• Balloons: lungs
• Rubber sheet/plate: diaphragm

What is the primary limitation of the bell jar lung demonstration model?

The glass bell jar cannot move like the chest wall to expand or reduce the thoracic volume further.

According to the representation of gaseous exchange, what occurs at the alveolar level (1 and 6) versus the tissue level (3 and 4)?

At the alveoli: $O_2$ diffuses from alveolar air into blood capillaries (1) and $CO_2$ diffuses from blood into alveoli (6). At the tissues: $O_2$ diffuses from blood into cells (3) and $CO_2$ diffuses from cells into blood (4).

In what two ways is oxygen ($O_2$) transported in the blood?

1. Most $O_2$ combines with haemoglobin in red blood cells to form oxyhaemoglobin.
2. A very small portion dissolves directly in the blood plasma.

In what three ways is carbon dioxide ($CO_2$) transported in the blood?

1. Most combines with water to form carbonic acid, which dissociates into bicarbonate ions.
2. A portion combines with haemoglobin to form carbaminohaemoglobin.
3. The smallest portion dissolves directly in the blood plasma.

Compare the percentage composition of oxygen, carbon dioxide, and nitrogen in inhaled air versus exhaled air.

• Nitrogen: $78\%$ inhaled, $78\%$ exhaled
• Oxygen: $21\%$ inhaled, $15\%$ exhaled
• Carbon dioxide: $0,04\%$ inhaled, $4,0\%$ exhaled

What chemical result confirms that exhaled air contains carbon dioxide in a laboratory test?

Clear lime water turns milky when exhaled air is bubbled through it.

Where are the respiratory and cardiovascular control centres located in the human brain?

In the medulla oblongata.

Where are the chemoreceptors sensitive to blood $CO_2$ concentration located, and how do they respond to an increase?

In the wall of the aorta and at the base of the jugular arteries; they send nerve impulses to the respiratory and cardiovascular centres in the medulla oblongata.

What is total human lung capacity, and what is tidal volume?

Total lung capacity is about $5\,l$ ($5\,000\,cm^3$); tidal volume is the amount of air breathed in and out during normal breathing.

Identify the lung volume marked on the graph as the air remaining in the lungs even after maximum exhalation, which is never exhaled.

Residual volume.

What components constitute the vital capacity of the lungs?

Tidal volume + inspiratory reserve volume + expiratory reserve volume.

How does the body physiologically adapt to prolonged exposure to high altitudes?

Due to reduced atmospheric pressure and lower oxygen availability, the body produces more red blood cells over days or weeks, increasing the $O_2$-carrying capacity of the blood.

What organism causes tuberculosis (TB), and how long does standard antibiotic treatment last?

The bacterium Mycobacterium tuberculosis; treatment lasts about $6\text{ months}$ with an aggressive antibiotic course.

What pathological changes define emphysema?

The walls of the alveoli tear and form holes, blood capillaries disintegrate, and gaseous exchange surface area decreases, leading to a feeling of suffocation.

Name three harmful toxins found in cigarette smoke and state how tar specifically harms air passages.

Nicotine, tar, and carbon monoxide. Tar paralyses the cilia in air passages so mucus and unwanted substances cannot be expelled, causing tar to accumulate.

According to the 30 March 2012 South African smoking legislation amendments, what are the distance limits for smoking near public entrances and swimming areas?

• No closer than $10\,m$ from a door or window leading to a public place.
• No closer than $50\,m$ from the nearest person in a permitted swimming area on beaches.

What rate of ventilation is maintained during mouth-to-mouth resuscitation on an adult patient?

Give $12$ initial breaths, check pulse, and repeat at a rate of $12\text{ breaths per minute}$.