Respiratory System Mcat

The respiratory system serves several important functions, including gas exchange, regulation of body temperature, and control of blood pH. Gas exchange occurs in the alveoli of the lungs and the tiny capillaries that surround them. The exchange involves the diffusion of carbon dioxide (CO2) from capillary blood into alveolar air and the simultaneous diffusion of inhaled oxygen from alveolar air into capillary blood. This process is passive and is driven by the differential partial pressures of oxygen and CO₂ between the capillary blood and alveolar air. The concept of partial pressure is explained by Henry’s Law, which states that the amount of dissolved gas in a liquid is proportional to the partial pressure of gas above the surface of the liquid.

Functions of the Respiratory System

The respiratory system serves several important functions, including gas exchange, regulation of body temperature, and control of blood pH. Gas exchange occurs in the alveoli of the lungs and the tiny capillaries that surround them. The exchange involves the diffusion of carbon dioxide (CO2) from capillary blood into alveolar air and the simultaneous diffusion of inhaled oxygen from alveolar air into capillary blood. This process is passive and is driven by the differential partial pressures of oxygen and CO₂ between the capillary blood and alveolar air. The concept of partial pressure is explained by Henry’s Law, which states that the amount of dissolved gas in a liquid is proportional to the partial pressure of gas above the surface of the liquid.

The respiratory system also plays a small role in thermoregulation, or the regulation of the body’s internal temperature. This occurs through the dilation and constriction of capillary beds in the nose and trachea, which help dissipate heat or conserve it, depending on the body’s needs. In some animals, evaporation of water and mucus secretions through the respiratory system facilitates heat loss during panting. Additionally, the respiratory system helps control blood pH by adjusting the respiratory rate in response to changes detected by chemoreceptors in the brainstem. When blood pH is too low, the respiratory rate increases to rid the body of excess CO2, raising blood pH. Conversely, decreased respiration conserves CO2 to lower blood pH when the pH becomes too high.

• Functions of the respiratory system
  • Gas exchange
  • Regulation of body temperature
  • Control of blood pH
  • Occurs between alveoli and capillaries
  • CO₂ diffuses from capillary blood into alveolar air and is exhaled
  • Oxygen diffuses from alveolar air into capillary blood and binds to hemoglobin in red blood cells
  • Passive process (diffusion) due to differential partial pressures of O₂ and CO₂
  • Henry’s Law – amount of dissolved gas in a liquid is proportional to the partial pressure of gas above the surface of that liquid
  • Minor role in respiratory system
  • Capillary beds in nose and trachea adjust blood flow to dissipate or conserve heat
  • Evaporation of water and mucus secretions aids in heat loss (panting)
  • Chemoreceptors in brainstem detect changes in arterial CO₂ concentration
  • Respiratory rate changes based on blood pH
    • Low blood pH (acidic) – increase in respiratory rate to expel more CO₂
    • High blood pH (basic) – decrease in respiratory rate to retain more CO₂

    

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    What role do alveoli and capillaries play in the gas exchange process of the respiratory system?

    Alveoli are small air sacs in the lungs where gas exchange occurs. They are surrounded by a network of tiny blood vessels called capillaries. During gas exchange, oxygen from the air in the alveoli diffuses into the capillaries to be used in the body, while carbon dioxide from the blood in the capillaries diffuses into the alveoli to be expelled through expiration. This process is essential for delivering oxygen to the body’s tissues and removing waste products, ensuring proper cellular functioning.

    How does diffusion facilitate gas exchange in the respiratory system?

    Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration. During the gas exchange process, oxygen and carbon dioxide move by diffusion across the thin walls of the alveoli and capillaries, which are only one cell layer thick. Oxygen in the alveolar air diffuses into the blood in the capillaries, where its concentration is lower, while carbon dioxide in the capillaries diffuses into the alveolar air, where its concentration is lower. This passive process is driven by the concentration gradients of the gases and enables effective gas exchange.

    What is the significance of thermoregulation in the respiratory system?

    Thermoregulation is the process by which the body maintains its internal temperature within a narrow range, regardless of external conditions. The respiratory system plays a small role in thermoregulation by releasing heat through evaporation from the moist surfaces of the lungs during exhalation. When we breathe in, air is warmed and humidified within the nasal passages and upper airways. When we breathe out, this warm, moist air releases heat from the body, helping to maintain the optimal internal temperature. Additionally, increasing the respiratory rate during physical activity can help dissipate extra heat generated by muscles.

    How does the respiratory system help maintain blood pH levels?

    The respiratory system helps maintain blood pH by regulating the partial pressure of carbon dioxide (PCO2) in the blood. Carbon dioxide can be dissolved in the blood as bicarbonate ions (HCO₃ – ), which act as a buffer to maintain pH levels. The chemoreceptors in the medulla oblongata and carotid and aortic bodies monitor changes in blood pH and, in response, signal the respiratory muscles to alter the respiratory rate. If blood pH drops (indicating acidosis), the respiratory rate increases to expel more carbon dioxide, raising pH. Conversely, if blood pH rises (indicating alkalosis), the respiratory rate decreases, retaining carbon dioxide, lowering pH.

    How does Henry’s law apply to the efficiency of the respiratory system?

    Henry’s law states that, at a constant temperature, the amount of a gas that dissolves in a liquid is directly proportional to the partial pressure of that gas above the surface of the liquid. In the context of the respiratory system, this law helps explain the efficiency of gas exchange in the alveoli and capillaries. As the partial pressure of oxygen is higher in the alveolar air than in the blood, oxygen diffuses from the alveoli into the capillaries. Similarly, as the partial pressure of carbon dioxide is higher in the blood than in the alveoli, it diffuses from the capillaries into the alveoli. This ensures a continuous supply of oxygen to the body’s tissues and the removal of waste products such as carbon dioxide.

    Respiratory and Cardiovascular Systems for the MCAT: Everything You Need to Know

    Learn key MCAT concepts about respiratory and cardiovascular systems, plus practice questions and answers

    

    (Note: This guide is part of our MCAT Biology series.)

    Part 1: Introduction to respiratory and cardiovascular systems

    Part 2: Structure and function of the respiratory system

    a) Structure of the respiratory system

    b) Gas exchange

    c) Thermoregulation

    d) Protection against disease

    Part 3: Breathing mechanisms

    a) Diaphragm, rib cage, and differential pressure

    b) Resiliency and surface tension effects

    c) Volumes and capacities

    Part 4: Gas exchange and regulation

    a) Diffusion and differential partial pressure

    b) Henry’s law

    c) pH control and nervous system control

    Part 5: Overview of the circulatory system

    a) Components of the circulatory system

    b) The heart

    Part 6: Overview of blood

    a) Blood composition

    b) Blood flow

    c) Gas exchange by blood

    Part 7: Regulation from other systems

    a) Nervous system control

    b) Endocrine system control

    Part 8: High-yield terms

    Part 9: Practice passage and answers

    Part 10: Practice standalone questions and answers

    Part 1: Introduction to respiratory and cardiovascular systems

    The respiratory and circulatory systems are two of the most important body systems to know for the MCAT, and they often go hand in hand. This section will first talk about the respiratory system and then move to the circulatory system, detailing the structure and functions of both. Finally, we’ll provide an MCAT-style practice passage along with a set of standalone questions.

    This topic is medium to high yield, so it is important to understand it for the MCAT. Let’s get started!

    Part 2: Structure and function of the respiratory system

    The respiratory system is traditionally associated with breathing, but for the MCAT we need to go into a little more detail. This section will first cover the components and structure of the respiratory system, and then we’ll talk about the general functions of the respiratory system, which include gas exchange, thermoregulation, and protection against disease and particulate matter.

    a) Structure of the respiratory system

    Air enters the body first through the nose and mouth and then travels through the pharynx, which is located at the back of the mouth and also carries food. Following the pharynx is the epiglottis, which is the cap that covers the larynx when swallowing so that food goes down the esophagus instead of the larynx. Air continues on into the larynx, which contains the vocal cords that vibrate during speaking, and it then moves to the trachea, which is commonly referred to as the windpipe.

    From the trachea, bronchi branch out and carry the air in and out of the lungs, and these further branch out into secondary bronchi, tertiary bronchi, and bronchioles. These bronchioles finally end with alveoli, which are microscopic sacs that are covered with blood capillaries to facilitate gas exchange. This entire succession of branching out into smaller tubes serves the purpose of increasing surface area for gas exchange. Alveoli contain a coating layer called surfactant, which is a soapy substance that prevents the alveoli from collapsing in on themselves.

    

    The lungs are the main organ of the respiratory system, and they are the site of gas exchange between bronchi/alveoli and the blood. The lungs are covered by a membrane known as pulmonary pleura as well as an outer membrane known as the parietal pleura that keeps the lungs in place. These pleural membranes prevent the lungs from collapsing in on themselves, and they have a space in between them known as the pleural cavity, which is a thin layer of lubrication that allows for sliding movement between the two pleurae. Because of this cavity, there is a pressure between the two pleura that keeps them together and anchors the lungs to the chest.

    b) Gas exchange

    The most basic function of the lungs and the respiratory system as a whole is gas exchange. Cells need oxygen to engage in aerobic respiration, and the waste product is carbon dioxide. As a result, there must be a constant exchange of oxygen into the body and carbon dioxide out of the body.

    The detailed description of gas exchange appears in Part 4 of this chapter, but the general mechanism is very simple. Once blood returns from the body to the heart, it is then sent to the lungs to interact with the alveoli. Each of the tiny alveoli has many capillaries running across it, and thus there is ample surface area for gas to be exchanged. Due to the microscopic nature of the alveoli and capillaries, there is only about one cell distance that carbon dioxide and oxygen have to diffuse to provide oxygen to the body.

    c) Thermoregulation

    The respiratory system plays a large role in the maintenance of homeostasis. Both the air passing through the lungs and blood in the body can maintain thermoregulation by dissipating heat to the external environment through evaporative cooling. In some animals, such as dogs, the process is made more efficient by panting. Panting brings warm air from the lungs and warm blood in the tongue in contact with the cooler external environment.

    For the respiratory system, the nasal and tracheal capillary beds are close to the outside of the body, which causes heat to be released. These capillaries can also be expanded or contracted as a response to being too cold or too hot. When the body is too hot, the capillaries expand, causing more blood to flow through these external capillaries and lose heat. When this occurs, it is known as vasodilation, and the opposite, capillaries getting smaller, is known as vasoconstriction. The role of blood vessels in thermoregulation is not limited to the respiratory system, but it is one of the ways the respiratory system is able to help control body temperature.

    d) Protection against disease

    The respiratory system can also prevent diseases and small particles from entering the body. In the path of airflow in and out of the body, there are two zones: the conduction zone and the respiratory zone.

    The conduction zone consists of the anatomy spanning from the nose/mouth to the primary bronchi. This is known as the conduction zone because the cells are too thick to facilitate meaningful gas exchange, and the function is to simply bring the air to the alveoli.

    In the conduction zone, particles are filtered using two primary methods: mucus membranes and cilia. Small nose hairs known as cilia waft mucus and any trapped particles upwards and outwards using the ciliary escalator. Specialized cells known as goblet cells secrete a sticky mucus, and other cells known as epithelial cells have cilia which sweep the mucus towards the pharynx. Together, the mucus traps the particles and pathogens and moves to the pharynx, where it can be either swallowed or coughed out.

    In the respiratory zone, which spans from the bronchi to the alveoli, a mucus membrane or cilia would interfere with gas exchange, so another mechanism of disease protection must be present. Here, alveolar macrophages, which roam around in the alveoli, engulf any foreign particles that they encounter.