Respiratory System and Tissues Flashcards

Not only does the MCAT require a basic knowledge of respiratory function, but it also constantly relates it to other systems through concepts like the bicarbonate buffer, hemoglobin’s affinity for oxygen, and the immune role of the respiratory tract. Use these cards to master the respiratory system, as well as skin and other epithelial tissue types.

1
Q

Name three major functions of the respiratory system.

A
  • Gas exchange
  • Filtration of particulate matter
  • Thermoregulation
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2
Q

Explain the relationship between gas exchange and cellular metabolism.

A

Aerobic cellular respiration requires oxygen and releases carbon dioxide as a waste product. Gas exchange removes this unwanted CO2 from the cells and replaces it with O2 from the environment.

Specifically, O2 is required for the electron transport chain, while CO2 is produced mainly during the Krebs cycle.

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3
Q

List the structures of the respiratory tract in order, beginning at the entrance for incoming air and ending at the site of gas exchange.

A
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4
Q

Define:

lung

A

The lung is the major organ in the respiratory system, acting to provide a site for gas exchange. Humans have two lungs that are connected to the outside environment via the respiratory tract.

The prefix “pulmo-“ and the root word “pleura” are often used to refer to the lungs and their associated structures.

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5
Q

Define:

larynx

A

The larynx is a cartilagenous structure that contains the vocal cords. It sits directly below the pharynx and above the trachea.

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6
Q

Define:

pulmonary alveoli

A

In the lungs, alveoli are small sacs at the ends of bronchioles. Each alveolus is enclosed by an epithelial lining and surrounded by pulmonary capillaries.

Alveoli are the site of gas exchange between the environment and the bloodstream. Oxygen moves from the alveoli to the capillaries, while carbon dioxide travels in the opposite direction.

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7
Q

In which pulmonary structure(s) is the activity of surface tension most relevant?

A

Surface tension, or the tendency of liquid molecules to associate with each other, is related to the alveoli.

Surface tension causes liquids to form spherical droplets, maximizing their contact with other liquid particles. Since the alveoli contain fluid, this property would tend to make alveoli collapse and is countered by the action of surfactant.

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8
Q

What substance serves to decrease surface tension in the alveoli?

A

Surfactant decreases surface tension and prevents the alveoli from collapsing.

Pulmonary surfactant is amphipathic, meaning that its molecules possess both hydrophobic and hydrophilic groups.

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9
Q

Premature infants often suffer from respiratory distress syndrome, a condition that involves insufficient surfactant production. What effect will this condition likely have on the alveoli?

A

It will cause the alveoli to collapse.

Surfactant serves to lower surface tension in the fluid associated with the alveolar lining. Without surfactant, this fluid will tend to minimize its own surface area, collapsing into the hollow interior of the alveolus and making inhalation very difficult.

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10
Q

The image below depicts a number of alveoli surrounded by pulmonary capillaries. What type of transport is used by gases to travel between these two structures?

A

The gases travel via diffusion.

Since gases are small and nonpolar, they are easily able to diffuse through cell membranes. Gas exchange is a passive process, meaning that oxygen and carbon dioxide move down their concentration gradients without using ATP.

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11
Q

Compare the partial pressure of carbon dioxide in the pulmonary capillaries to that in the alveoli.

A

The pulmonary capillaries have a higher partial pressure of CO2.

The pulmonary capillaries bring deoxygenated blood, which is CO2-rich, in close contact with the alveoli. If CO2 is to diffuse from the bloodstream to the alveolar interior, it must travel down its concentration gradient. The alveoli, then, must contain comparatively less carbon dioxide than the capillaries.

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12
Q

Place the following terms in order according to their oxygen partial pressures, from the lowest PO2 to the highest.

  • Alveolar air
  • Atmospheric air
  • Blood from the pulmonary artery
A

Blood from the pulmonary artery < alveolar air < atmospheric air

The pulmonary artery carries deoxygenated blood from the heart to the lungs, so it contains a comparatively low amount of O2. It’s easy to assume that the alveoli contain only atmospheric air, but they also hold residual carbon dioxide from the previous respiration, resulting in a slightly lower oxygen partial pressure than that of atmospheric air.

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13
Q

What are the steps involved in inspiration?

A
  1. The diaphragm and external intercostal muscles contract, expanding the thoracic cavity.
  2. The lungs expand along with the surrounding cavity, lowering their internal pressure.
  3. Air flows from the comparatively high-pressure environment to the low-pressure lungs.
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14
Q

What is the significance of the term “negative pressure breathing?”

A

It describes the mechanism of inspiration. The pressure inside the lungs becomes lower than atmospheric pressure, causing air to flow inward.

Negative pressure also relates to MCAT physics. Remember that absolute pressure can never have a negative value. Instead, it is the gauge pressure that is negative, meaning simply that it is lower than ambient pressure.

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15
Q

Name the main muscles involved in inspiration.

A

Inspiration involves both the diaphragm and the external intercostals.

Both muscles contract to enlarge the thoracic cavity. The diaphragm flattens downward, while the external intercostals push outward.

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16
Q

The diaphragm is composed of which of the three types of muscle?

A

The diaphragm consists of skeletal muscle.

For the MCAT, skeletal muscle can usually be considered to be voluntary. The diaphragm is a notable exception, since it can be consciously contracted but is usually under involuntary control.

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17
Q

Name the main muscles involved in expiration.

A

Normal expiration is passive, requiring no muscular involvement. Expiration that is consciously forced involves the internal intercostals.

Other muscles aid in both expiration and inspiration, but they are not necessary to know for the MCAT.

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18
Q

During exhalation, the diaphragm must be in which state?

A

The diaphragm must be relaxed.

When relaxed, the diaphragm becomes rounded, pushing upward and decreasing the volume of the thoracic cavity. Lower volume results in increased pressure, forcing air outward.

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19
Q

What measurement describes the volume of air inhaled per breath during normal breathing?

A

Tidal volume

The tidal volume of an average human is approximately 500 mL.

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20
Q

What is the difference between inspiratory and expiratory reserve volume?

A

Inspiratory reserve volume (IRV) refers to the maximum volume of air that can be inhaled in addition to a normal inhalation, while expiratory reserve volume (ERV) refers to the maximum volume that can be exhaled in addition to a normal exhalation.​

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21
Q

The sum of IRV, ERV, and tidal volume can be described by which lung measurement?

A

IRV, ERV, and tidal volume combine to form the lungs’ vital capacity.

Vital capacity is the largest volume that can possibly be inhaled or exhaled.

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22
Q

What measurement describes the volume of air that always remains in the lungs, regardless of the force of exhalation?

A

Residual volume

Since the residual volume never leaves the lungs, it cannot be directly measured, but must be calculated using the other lung volumes.

23
Q

What is the difference between total lung capacity and vital capacity?

A

Total lung capacity (TLC) includes the entire volume of air that can be held in the lungs, while vital capacity (VC) only includes the volume that can be inhaled or exhaled.

TLC is equal to the sum of vital capacity and residual volume.

24
Q

If inspiratory reserve volume and tidal volume are known, what additional measurements are needed to calculate residual volume?

A

Total lung capacity and expiratory reserve volume

ERV, IRV, and tidal volume can be added to find vital capacity. From there, residual volume can be found by subtracting vital capacity from total lung capacity.

25
Q

Which substance, secreted by membranes in the nasal passages, helps protect the lungs from foreign particles?

A

The protective substance is mucus.

In the respiratory tract, mucus functions as part of the innate immune system. Mucous membranes also exist in the stomach.

26
Q

Which organelle associated with respiratory epithelium would be seriously impaired by the inhibition of microtubule synthesis?

A

Cilia, small hairlike organelles that line much of the respiratory tract, are composed of microtubules. Cilia function to protect the lungs by moving mucus and particles toward the throat.

The MCAT often tests other microtubule-based structures, including the cytoskeleton and spindle apparatus.

27
Q

Which type of immune cell is highly active in the alveoli of the lungs?

A

Macrophages

While macrophages exist throughout the body, specialized cells known as alveolar macrophages are present only in the lungs. If exposed to a pathogen, these cells can perform phagocytosis and release factors that activate other immune cells.

28
Q

Define:

hypoxia

A

Hypoxia refers to the condition of oxygen deprivation, usually due to low oxygen levels in the blood.

On the MCAT, prefixes and suffixes can often help in discerning a word’s significance. If this term were unfamiliar, the prefix “hypo-,” meaning “low” or “under,” could give away its meaning: low oxygen.

29
Q

What homeostatic system relates to the equation below?

H2O + CO2 ⇔ H2CO3 ⇔ H+ + HCO3-

A

The bicarbonate buffer functions according to this equation and is the main homeostatic method of maintaining constant pH in the blood.

The equation for the bicarbonate buffer is reversible, meaning that it can progress in either direction to reach an equilibrium. Most MCAT questions on this topic involve the use of Le Châtelier’s principle.

30
Q

In the first step of the bicarbonate buffer, dissolved carbon dioxide reacts with water in the plasma. Which acid is produced by this reaction?

A

Water and carbon dioxide combine to form carbonic acid (H2CO3).

Carbonic acid is often confused with bicarbonate (HCO3-), since the “bi” prefix can be misunderstood to mean “two” protons. It’s important to remember that bicarbonate is actually the conjugate base of carbonic acid. The MCAT often tests this distinction.

31
Q

How does the respiratory system respond to low blood pH levels?

A

Low pH, or acidity, in the blood results in an increased respiratory rate.

Consider the equilibria involved in the blood buffer:

H2O + CO2 ⇔ H2CO3 ⇔ H+ + HCO3-

Acidic blood has a high proton concentration, which will shift the reaction to the left to regain equilibrium. This will result in the production of water and carbon dioxide. To excrete this additional CO2, breathing rate must increase.

32
Q

Rapid or excessive breathing, commonly known as hyperventilation, results in an abnormally high rate of CO2 exhalation. What condition can be caused by prolonged hyperventilation?

A

High blood pH, or alkalosis, can result.

More than any other factor, blood pH level depends on CO2 concentration. If respiratory rate is increased above normal levels, more CO2 will be exhaled than usual, and the bicarbonate buffer equilibrium will shift away from the production of hydrogen ions. With fewer protons, blood will become basic or alkaline.

33
Q

If a normal individual suddenly began inhaling air with a significantly higher partial pressure of O2, what immediate effect would this have on her plasma pH?

Assume that her rates of respiration, carbon dioxide exhalation, and carbon dioxide production remain unchanged.

A

Plasma pH would be unaffected.

While blood pH depends directly on CO2 concentration, its relationship to O2 levels is much more indirect. Oxygen is not part of the bicarbonate buffer system, so if all else remained the same, it would have no immediate effect on pH.

34
Q

Oxygen concentration in blood vessels is monitored by two clusters of peripheral receptors, shown below. What are the names of these two structures?

A

The aortic and carotid bodies are part of the peripheral nervous system. They function as chemoreceptors and signal the brain when O2 levels are low.

35
Q

How will the aortic body respond if it senses low plasma O2 levels?

A

As part of the peripheral nervous system, the aortic body must first send an impulse to the brain, which can then increase respiratory rate.

Specifically, both the aortic and carotid bodies signal the medulla oblongata, which controls involuntary actions such as breathing.

36
Q

What physiological value has the strongest effect on the brain’s control of respiratory rate?

A

Plasma CO2 levels (which determine plasma pH)

The brain contains its own chemoreceptors, but they monitor only blood pH and CO2 levels. These central receptors stimulate a stronger response than the peripheral bodies. For the MCAT, then, consider respiration to be more directly affected by CO2 than O2.

37
Q

Human tissue is broadly categorized into which four basic types?

A

Epithelial, connective, nervous, and muscle tissue

38
Q

What are the major functions of epithelial tissue?

A

Epithelial tissue forms the external and internal linings of the body. Its main functions include protection and the facilitation of movement of materials between organs.

Specifically, epithelium can be specialized for absorption (as in the small intestine), secretion (as in the kidney) or diffusion (as in the alveoli), or it can serve multiple roles.

39
Q

Epithelial cells can be classified according to their shape or their arrangement in layers. With regard to shape, what are the three categories of epithelial cells?

A

Squamous, cuboidal, and columnar

Squamous epithelial cells are flat and thin, while cuboidal cells, as their name implies, appear cubelike. Columnar cells are significantly taller and rectangular.

40
Q

Epithelial cells can be classified according to their shape or their arrangement in layers. With regard to layered arrangement, what are the two categories of epithelial tissue?

A

Simple and stratified

Simple epithelium consists of a layer that is a single cell thick, which is ideal for diffusion and absorption. Stratified epithelium consists of multiple tightly-packed layers and often serves protective purposes.

41
Q

The cells that form capillary walls are part of which major tissue type?

A

Capillary walls are composed of epithelial tissue, specifically simple squamous epithelium. This tissue is only one cell thick, which helps facilitate diffusion.

On the MCAT, you’ll often see the term endothelium used to describe the epithelium that lines blood vessels. This term refers more narrowly to cells that are part of internal linings.

42
Q

The lining of an alveolus is mainly composed of simple squamous epithelium. If alveoli were instead formed from stratified epithelium, what would result?

A

Gas exchange would not occur or would be severely limited.

Stratified epithelium is composed of many layers of cells, and is more impenetrable than simple epithelium. O2 and CO2 would need to diffuse through several cell layers to move in and out, and would be unable to do so efficiently.

43
Q

Blood, cartilage, and bone are part of which basic tissue type?

A

These cell types are examples of connective tissue.

Connective tissue usually fulfills a structural role and is surrounded by an extracellular matrix. Other examples include cartilage, ligaments, fibroblasts, and lymph.

44
Q

Name the largest organ in the integumentary system.

A

The skin is the largest organ not only in the integumentary system, but in the entire human body.

Overall, the integumentary system is tested less than other organ systems on the MCAT, but its functions are still important to know.

45
Q

What are three main functions of the skin?

A
  • Physical protection of internal organs
  • Regulation of body temperature
  • Prevention of water loss
46
Q

What is the difference between sebaceous glands and sweat glands?

A

Sebaceous glands secrete oil, or sebum, to prevent the skin from drying out. These glands are often found near the base of hair follicles.

Sweat glands secrete sweat, a fluid that contains water and electrolytes. The evaporation of sweat serves to decrease body temperature.

47
Q

Which layer of the skin lies between the epidermis and the subcutaneous layer?

A

The dermis is found in the middle of the three layers.

The dermis is also the thickest layer, and contains connective tissue, hair follicles, and glands.

48
Q

A tissue sample taken from the skin contains adipose tissue and collagen, but lacks sebaceous glands. From which layer did this sample most likely originate?

A

It most likely originated from the subcutaneous layer, sometimes called the hypodermis.

The hypodermis is the deepest layer of the skin and is formed mainly from adipose (fat) cells.

49
Q

In the skin, what is the role of keratin?

A

Keratin is a protective protein that forms a watertight layer in the epidermis.

Most epidermal cells are keratinocytes, meaning that they do or did produce keratin. Only the innermost cells of the epidermis are alive.

50
Q

In the skin, what is the role of melanin?

A

Melanin protects the skin from the harmful effects of UV radiation. As a pigment, it also provides skin color.

51
Q

Name two ways in which the skin is involved in thermoregulation.

A
  • In cold conditions, insulation is provided by a layer of fat cells in the subcutaneous layer, or hypodermis.
  • In hot conditions, secretions from sweat glands can lower body temperature.
52
Q

Define:

piloerection

A

Piloerection involves the raising of hairs on the skin in response to cold or fear. The hair forms an insulating layer, assisting in thermoregulation.

The common name for piloerection is simply “goosebumps.”

53
Q

When temperatures are cold, blood vessels near the skin change in diameter. What is the term for this change, and what does it accomplish?

A

In the cold, vessels close to the skin undergo vasoconstriction, or a decrease in diameter. This reduces flow and keeps blood away from the cold exterior environment, where heat can easily be lost.

The opposite process, vasodilation, occurs in hot temperatures. Vessels near the skin widen, allowing more blood near the surface of the body so heat can more readily dissipate.