6.4 Gas Exchange

Outline the role of the parts of an alveolus in a human lung

Alveolus as an oval with scalloped edges- maximizes surface area for gas exchange. Alveolus wall is a single layer of Type 1 pneumocytes- minimizes distance gases have to travel between the blood in the capillary and the air in the alveolus. Lumen of alveolus- volume of air for gas exchange. Surfactant produced by Type II pneumocytes- reduces surface tension and prevents collapse of alveolus when air is exhaled. Bronchial tube ending at alveolus- tube for transport of air into and out of the alveolus. Capillary surrounding outside of the alveolus- minimizes distance gases have to travel between the blood in the capillary and the air in the alveolus. Capillary wall is a single cell thick- minimizes distance gases have to travel between the blood in the capillary and the air in the alveolus.

Draw a diagram showing the structure of an alveolus and an adjacent capillary

Alveolus drawn as an oval with scalloped edges. Alveolus wall drawn as a single line (representing 1 cell thick). Alveolus lumen empty. Thin layer of surfactant drawn inside alveolus wall. Alveolar duct ending at alveolus. Capillary drawn as a tube surrounding outside of the alveolus. Capillary wall drawn as a single line (representing 1 cell thick). Capillary lumen narrow. Red blood cell(s) within capillary lumen. Arrow to indicate direction of blood flow through the capillary. Arrow to indicate diffusion of O2 from alveolus lumen into capillary red blood cell. Arrow to indicate diffusion of CO2 from capillary into alveolar lumen.

Outline the effects of mild and vigorous exercise on ventilation rate.

Both ventilation rate and tidal volume increase with increased intensity of exercise. During exercise the rate of cellular respiration increases and as a result more carbon dioxide is produced by the cells. The carbon dioxide production in the tissues exceeds the rate of breathing it out, which will lead to a drop in the pH of the blood. Chemoreceptors detect the change in blood pH and send nerve impulses to the breathing center of the brain. The brain responds by sending nerve impulses to the diaphragm and intercostal muscles which will contract more frequently (increasing ventilation rate) and with more force (increasing tidal volume).

State the relationship between gas pressure and volume.

Boyle's Law describes the relationship between the pressure and the volume of a gas. The law states that as volume increases, pressure decreases and vice versa. The mechanics of ventilation follow Boyle's Law. When the volume of the lungs changes, the pressure of the air in the lungs changes in accordance with Boyle's Law. If the pressure is greater in the lungs than outside the lungs, then air rushes out. If the pressure is lower in the lungs than outside the lungs, then air rushes in.

State the role of cartilage in the trachea and bronchi.

Cartilage is a strong but flexible tissue. The cartilage in the trachea and bronchi form incomplete rings that support the structures while still allowing them to move and flex during breathing. If cartilage was not present then the trachea and bronchi would collapse inward during exhalation.

Distinguish between ventilation, gas exchange and cell respiration

Cell respiration depends on gas exchange and gas exchange depends on ventilation. Ventilation is the movement of air into and out of lungs via inhalation and exhalation. Ventilation involves muscle movement. Gas exchange is the movement of carbon dioxide and oxygen between the alveoli and blood and between blood and tissue cells. Cell respiration is the release of energy through the oxidation of glucose. Aerobic cell respiration occurs in mitochondria.

Outline the direction of movement of the diaphragm and rib-cage during expiration.

During expiration (exhalation) the external intercostal muscles relax and the the internal intercostal muscles contract, moving the rib-cage down and in. The diaphragm relaxes and abdominal oblique muscles contract, pushing the diaphragm up and into a domed position. Together, these motions decrease the volume of the thorax.

Outline the direction of movement of the diaphragm and rib-cage during inspiration.

During inspiration (inhalation) the external intercostal muscles contract and the rib-cage moves up and out. The diaphragm also contracts, moving down and flattening. Together, these motions increase the volume of the thorax.

Outline the structure and function of external intercostal muscles.

Each rib is connected to the rib below it by both external and internal intercostal muscles. The external intercostal muscles are located on the outer surface of the ribs and are positioned at a diagonal in between each rib. The external intercostal muscles are responsible for forced and quiet inhalation. Contraction of the external intercostal muscles elevates the ribs and spreads them apart, resulting in the inhalation of air from the atmosphere.

Outline the structure and function of internal intercostal muscles.

Each rib is connected to the rib below it by both external and internal intercostal muscles.The internal intercostal muscles are located on the inner surface of the ribs (deeper than the external intercostal muscles) and are positioned at a diagonal in between each rib.The internal intercostal muscles are responsible for forced exhalation. Contraction of the internal intercostal muscles depresses the ribs and pulls them closer together, resulting in the forced exhalation of air from the lungs.

Outline the reason why gas exchange is less effective in people with emphysema.

Emphysema damages alveoli, reducing the surface area available for gas exchange. With less surface area, with each breath less oxygen is able to diffuse into the blood from the air and less carbon dioxide is able to diffuse from the blood into the air.

Outline the causes of emphysema.

Emphysema is a lung disease caused by the weakening and rupturing of alveoli. As a result there are larger air spaces instead of many small ones. Having fewer and larger damaged sacs means there is a reduced surface area for the exchange of oxygen into the blood and carbon dioxide out of it. Smoking is the leading cause of emphysema.

Outline how epidemiological studies contributed to understanding the association between smoking and lung cancer.

Epidemiological studies often track the association between behaviors and disease. In the 1950's, epidemiologists observed links between tobacco use and cancer. Cancer rates increased with increased use of tobacco. The correlation spurred additional research which was able to show a direct, causal, relationship between tobacco use and cancer.

Define "epidemiology."

Epidemiology is the study and analysis of the distribution, patterns and determinants of health and disease conditions in defined populations.

Define "expiration" as related to lung ventilation.

Expiration = exhalation = breathing out. The process that causes air to leave the lungs.

Outline the pressure and volume changes that occur in the lungs during normal expiration.​

Expiration occurs when the external intercostal muscles and the diaphragm relax, causing a decrease in size of the thoracic cavity and recoil of the lungs. The volume of the alveoli sacs decreases, increasing internal air pressure in accordance with Boyle's Law. The air pressure inside the lungs increases above that of air outside the body. Because gases move from regions of high pressure to low pressure, air rushes out of the lungs.

Define gas exchange

Gas exchange is the diffusion of gases from an area of higher concentration to an area of lower concentration across an organism's membranes.

Outline the purpose of gas exchange in humans

Gas exchange must occur so that cells have oxygen for performing aerobic respiration. Oxygen is the final electron acceptor in the oxidation of glucose during cellular respiration. Without oxygen, aerobic respiration will stop. Additionally, the carbon dioxide waste product of the respiration must leave the cells. It is very dangerous if carbon dioxide builds up in the body, so blood carries the carbon dioxide to the lungs where it is released into the air with exhalation.

Describe how the structure of the lung increases surface area for gas exchange

Gas exchange occurs more quickly with larger surface areas. The lungs have a large surface area from having many alveoli. The alveoli themselves have a large surface area because the cells that make up their wall have a flattened, thin shape. A typical pair of human lungs contain about 300 million alveoli, producing 70m2 of surface area.

Outline the mechanism of gas exchange in humans

Gas exchange occurs through diffusion. Diffusion is the net movement of molecules from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in concentration and is a passive process (no energy input). In humans, oxygen diffuses into capillaries at the lungs and into tissue cells throughout the body. Carbon dioxide diffusion out of the tissue cells throughout the body and then out of the blood in the lungs.

State the location of gas exchange in humans

In humans, gas exchange occurs in the lungs with the exchange of oxygen and carbon dioxide between the air of the external environment and the body fluids of the internal environment. Gas exchange also occurs in the body tissues, where oxygen is taken up by the tissues and the CO2 that the tissues have created is diffused back into the blood for transport back to the lungs or gills to be released.

Summarize the muscle contractions required to ventilate the lungs.

Inspiration (inhalation): -External intercostal muscles contract moving rib cage up and out. -Diaphragm contracts becoming lower and flatter. -Additional muscles can be used if a bigger breath is required. Expiration (exhalation): -External intercostal muscles relax and move the rib cage down and in. -Diaphragm relaxes, moving higher and becoming more dome shaped. -Internal intercostal muscles and abdominals contract with forced exhalation.

Define "inspiration" as related to lung ventilation.

Inspiration = inhalation = breathing in. The process that causes air to enter the lungs.

Outline the pressure and volume changes that occur in the lungs during normal inspiration.​

Inspiration occurs when the external intercostal muscles and the diaphragm contract, causing an increase in size of the thoracic cavity and expansion of the lungs. With expansion of the lungs, the volume of the alveoli sacs increases, reducing internal air pressure in accordance with Boyle's Law. The air pressure inside the lungs decreases below that of air outside the body. Because gases move from regions of high pressure to low pressure, air rushes into the lungs.

Outline the causes of lung cancer.

Lung cancer occurs when cells in the lung mutate and divide uncontrollably to form tumors. Smoking is the number one cause of lung cancer. Tobacco smoke contains many chemicals that are known to mutate DNA. The risk of lung cancer increases with the length of time and number of cigarettes smoked. Other causes of lung cancer include: -Particle pollution (very tiny solid and liquid particles that are in the air) -Genetic predisposition -Radon exposure -Other hazardous chemicals (such as asbestos)

List symptoms of lung cancer.​

Lung cancer typically doesn't cause signs and symptoms in its early stages. Signs and symptoms of lung cancer typically occur only when the disease has advanced.Signs and symptoms of lung cancer may include: -A persistent cough -Coughing up blood -Shortness of breath -Chest pain -Voice hoarseness -Unintentional weight loss

Draw a labelled diagram to show the human ventilation system.

Nasal cavity Trachea Bronchi Bronchioles Lungs Alveoli (enlarged as inset) Diaphragm Intercostal muscles

State the symptoms of emphysema.

Shortness of breath and cough are the main symptoms of emphysema. As the disease progresses, other symptoms include: -Fatigue -Weezing -Chest tightness -Anxiety

Outline how the diaphragm and abdominal muscles work as an antagonistic pair during ventilation.

Skeletal muscles work in antagonistic pairs, meaning as one muscle contracts, the other relaxes. Ventilation includes the movement of the following antagonistic muscle pair: Diaphragm (moves down with contraction to increase thorax volume during inspiration) ...is antagonistic with... Abdominal oblique (contracts to push the diaphragm back up towards the thorax during expiration).

Outline how the external and internal intercostal muscles work as an antagonistic pair during ventilation.

Skeletal muscles work in antagonistic pairs, meaning as one muscle contracts, the other relaxes. Ventilation includes the movement of the following antagonistic muscle pair: External intercostal muscles (contract moving rib cage up and out during inspiration) ...is antagonistic with... Internal intercostal muscles (contract moving rib cage down and in during forceful exhalation such as coughing or during exercise).

List treatment options for people with emphysema.

The damage from emphysema is permanent. The ability to breathe properly cannot be fully recovered. Treatment of emphysema aims to ease symptoms and stabilize the condition. Treatments include: -supplemental oxygen -inhaled bronchodilators -inhaled steroids -smoking cessation -lung surgery to remove damaged tissue -lung transplant

Outline the structure and function of the diaphragm.

The diaphragm is a dome-shaped sheet of muscle located just below the lungs. During inspiration (inhalation), the diaphragm contracts and is drawn inferiorly into the abdominal cavity until it is flat. The thoracic cavity becomes larger, drawing in air from the atmosphere. During expiration (exhalation), the diaphragm relaxes and elevates to its dome-shaped position in the thorax. Air within the lungs is forced out of the body when the size of the thoracic cavity decreases.

Define "thorax."

The thorax is a part of the anatomy of humans and other animals located between the neck and the abdomen (the chest). The thorax includes the thoracic cavity (contains organs including the heart and lungs) and the thoracic wall (ribs and intercostal muscles).

State the role of smooth muscle fibres in the bronchioles.

The trachea divides into two bronchi (one for each lung) which continue to subdivide before becoming bronchioles. Whereas the bronchi have rings of cartilage that serve to keep them open, the bronchioles are lined with smooth muscle tissue and do not have cartilage. The muscle contracts and expands, effectively controlling the flow of air as it moves to the alveoli.

Outline techniques for measuring ventilation rate.

There are multiple techniques for measuring ventilation rate: 1. A spirometer is a device that measuring the rate of air inspired and expired by the lungs. It operates by measuring the velocity and/or pressure of the airflow as it moves past a sensor. 2. Simple observation and counting number of breaths per minute. 3. Chest belt and pressure sensor that records the rise and fall of the thorax.

Outline techniques for measuring lung tidal volume.

Tidal volume can be determined by measuring the volume of air inhaled and/or exhaled. There are multiple techniques for measuring tidal volume: 1. A spirometer is a device that measuring the volume of air inspired and expired by the lungs. It operates by measuring the velocity and/or pressure of the airflow as it moves past a sensor. 2. Air can be exhaled into a lung volume bag. The bag will trap the exhaled air inside and the volume on the bag's scale can be measured. 3. Air can be exhaled through a tube that ends in a inverted flask of water. The exhaled air will displace a measurable volume of water.

Define "tidal volume."

Tidal volume is the normal volume of air displaced between normal inhalation and exhalation when extra effort is not applied. Tidal volume includes the volume of air that fills the alveoli in the lungs and the volume of air that fills the airways. In a healthy, young human adult, tidal volume is 7 mL/kg of body mass.

Outline the structure and function of Type 1 pneumocytes.

Type I pneumocytes are thin, flat cells that form the structure of the alveoli. Their shape increases the surface area of each cell individually and the surface area of the alveoli collectively. Type I pneumocytes line more than 95% of the alveolar surface. Type I pneumocytes are the location of gas exchange between the alveoli and blood. Their thin shape enables a fast diffusion of gases between the air in the alveoli lumen and the blood in the surrounding capillaries.

Outline the structure and function of Type II pneumocytes.

Type II pneumocytes are larger, cuboidal cells in the alveolar wall that occur less frequently than Type I cells. Type II pneumocytes produce a pulmonary surfactant that is continuously released by exocytosis.

Describe two functions of the fluid secreted by Type II pneumocytes

Type II pneumocytes produce a pulmonary surfactant that is continuously released by exocytosis. Reinflation of the alveoli following exhalation is made easier by the surfactant, which reduces surface tension in the thin fluid coating of the alveoli. Additionally, fluid secreted by Type II pneumocytes facilitates the transfer of gases between blood and alveolar air. The gases dissolve in the moist fluid, helping them to pass across the alveoli surface.

Outline the purpose of ventilation in humans

Ventilation (moving air into and out of lungs) maintains a steep concentration gradient of gases in alveoli of the lungs. New air is continually cycled into and out of the lungs from the atmosphere, ensuring O2 levels stay high in alveoli (and diffuse into the blood) and CO2 levels stay low (and diffuse from the blood). Ventilation maintains the concentration gradient required for gas exchange

Define Ventilation

Ventilation is the moving air into and out of lungs via inhalation and exhalation (breathing).

Define "ventilation rate."

Ventilation rate is the number of breaths per minute . Under non-exertion conditions, the human respiratory rate averages around 12-15 breaths/minute.

Outline the flow of air into the lungs.

When air enters the lungs during inhalation it passes through: Nostrils → Nasal cavity → Pharynx → Larynx → Trachea → Bronchi (with cartilaginous rings) → Bronchioles (without cartilage) → Alveoli.