Exam 2 Worksheets Flashcards

Question

What anatomical feature of the trachea ensures that it stays patent (open)?

Answer 1

C-shaped hyaline cartilages

Answer 2

Cross-sectional area

Answer 3

To hold the lungs to the thoracic wall

Answer 4

Endothelial cells of pulmonary capillaries

Answer 5

The amount of smooth muscle increases in the smaller passageways of the bronchial tree

Answer 6

The pleurae create one continuous pleural cavity for both lungs

Answer 7

Atmospheric pressure is the pressure of the air on the body. Intrapulmonary pressure is the air pressure within the lung air spaces, or alveoli, so its sometimes called the intra-alveolar pressure. Intrapleural pressure is the pressure within the pleural cavity. Relationships: Atmospheric pressure is the same as intrapulmonary pressure in between breaths, because the air in the lungs equilibrates with the outside air. When the intrapulmonary pressure is less than atmospheric pressure, air flows into the lungs. When intrapulmonary pressure is greater than atmospheric pressure, air moves out of the lungs. Intrapleural pressure is ALWAYS less than the intrapulmonary pressure (i.e. is a negative pressure) and this relationship helps keep the lungs (or alveolar spaces) inflated and keeps the lungs from collapsing. The intrapleural pressure is negative due to a combination of factors, including the tendency of the alveoli to recoil and get smaller, the tendency of the thoracic cage to expand, and the suction (or clinginess) created by the pleural fluid which makes the visceral pleura tend to cling to the parietal pleura, and causes the lungs to adhere to the thoracic wall.

Answer 8

The transpulmonary pressure is the difference between the intrapulmonary pressure and the intrapleural pressure. (Ppul – Pip) It is usually expressed as an absolute value. If the intrapulmonary pressure is 760 mm Hg, and the intrapleural pressure is 756 mm Hg, or -4 mm Hg relative to the intrapulmonary pressure, then the tranpulmonary pressure is 4 mm Hg. The transpulmonary pressure is the pressure that keeps the lungs from collapsing. The size of the transpulmonary pressure will dictate the size of the lungs. The greater the transpulmonary pressure, the more inflated the lungs become. If the transpulmonary pressure falls to zero the lungs will collapse. Sometimes the descriptions of intrapleural pressure and transpulmonary pressure sound similar. They are both critical to preventing lung collapse, but are different ways of expressing the same concept. Because of this, I would never ask you to distinguish between these two on an exam.

Answer 9

The puncturing of the parietal pleura allows for the intrapleural pressure to equilibrate to the atmosphere. In this situation the intrapleural pressure would be equal to the intrapulmonary pressure and the transpulmonary pressure would drop to zero resulting in a collapsed lung. However, this only effects the lung with the punctured pleura, as each lung is encased in its own pleural cavity allowing each lung to operate somewhat independently

Answer 10

The pressure of a gas within a container is inversely related to the volume of the container. In a container that contains a gas, if the volume of that container is reduced, the pressure of the gas increases. If the volume of the container increases, the pressure decreases. This law can be described mathematically as P1V1 = P2V2, where P is pressure and V is volume. In pulmonary ventilation, the thoracic cavity and lungs act like a container. The pressure within the lungs and alveolar air spaces is the intrapulmonary pressure (or intra-alveolar pressure). When the inspiratory skeletal muscles contract, the thoracic cavities and lungs enlarge, so the intrapulmonary pressure decreases. Since intrapulmonary pressure is now less than atmospheric pressure, air flows down its pressure gradient and enters the lungs. When the inspiratory skeletal muscles relax, the thoracic wall and lungs recoil back to their original size (get smaller), and the intrapulmonary pressure increases. Since intrapulmonary pressure is greater than atmospheric pressure, air moves out of the lungs, down its concentration gradient.

Answer 11

The repeating pattern of quiet inspiration and quiet expiration is commonly referred to as ventilation or breathing. The amount of air moved during this process is the tidal volume (usually around 500 mL). Quiet inspiration is an active process and requires the contraction of the diaphragm and external intercostal muscles, which cause an increase in the thoracic cavity volume, a decrease in intrapulmonary pressure and air flow into the lungs. Quiet expiration is a passive process and therefore only requires the relaxation of the diaphragm and external intercostal muscles. The natural recoil of the lungs and the thoracic wall cause an increase in intrapulmonary pressure and air flows out of the lungs. Forced inspiration is an active process that requires the recruitment of additional muscles including the sternocleidomastoid, scalenes, serratus anterior. These muscles help increase the volume of the thoracic cavity beyond what is seen in quiet inspiration, thus allowing for the movement of more air. Forced expiration is also an active process that requires the recruitment of the internal intercoastal muscles and the abdominal wall muscles. Contraction of these muscles help decrease the volume of the thoracic cavity beyond what is achieved with quiet expiration, again allowing for a greater movement of air.

Answer 12

The three factors that can impact the efficient of pulmonary ventilation include airway resistance, alveolar surface tension, and lung compliance. • Airway resistance is controlled by smooth muscles that line the bronchioles. Contraction of the smooth muscles causes bronchoconstriction which decreases the diameter of the airway, increases resistance and therefore decreases airflow. Relaxation of the smooth muscles produces bronchodilation, or increased diameter of the airway. Bronchodilation decreases resistance and therefore increases airflow. • Alveolar surface tension is created by the thin layer of fluid on the inner surface of the alveoli. The molecular attraction between the water molecules creates high surface tension which make the alveoli tend to collapse, just like a plastic bag with a few drops of water in it. Collapsed alveoli are extremely difficult to inflate, limiting gas exchange. However, surfactant secreted by the type II alveolar cells decreases surface tension, keeping the alveoli open. • Lung compliance refers to how easy it is for the lungs to stretch or expand at a given transpulmonary pressure. Things that can decrease lung compliance are increasing alveolar surface tension (which makes the alveoli hard to inflate), limiting chest wall movement (broken ribs or weak muscles), or inhibiting lung movement within the thoracic cavity. Decreased lung compliance leads to decreased pulmonary ventilation.

Answer 13

While respiratory volumes and capacities won’t diagnose a specific disease, they can be useful for evaluating loss of respiratory function and following the progression or recovery from a respiratory disease. Knowing which volumes or capacities are impaired or deviate from expected normal can help distinguish between obstructive pulmonary diseases or restrictive pulmonary diseases. Obstructive pulmonary diseases are often diseases in which patients experience increased airway resistance. In obstructive disease, it’s harder to push air out of the lungs. Obstructive diseases include chronic bronchitis, emphysema, asthma and cystic fibrosis. Patients with obstructive disease might exhibit increased total lung capacity (TLC), increased functional residual capacity (FRC) and increased residual volume (RV). In other words, more air stays in the lungs because it’s hard to push out. The lungs might hyperinflate, but its harder to push air out. Restrictive pulmonary diseases usually involve a decrease in total lung capacity. Examples of restrictive disease include tuberculosis, pneumonia or fibrosis where there is an increase in non-elastic tissue in the lungs, so its harder to inflate the lungs. In these diseases, the vital capacity (VC), total lung capacity (TLC), functional residual capacity (FRC) and residual volume may decline (RV). In these diseases, its harder to to expand the lungs – in other words, there is a decrease in overall compliance.

Answer 14

The anatomical dead space is the volume of the conducting zone structures. It is important to consider when discussing respiratory efficacy because it means that not all of the air moved in the tidal volume participates in gas exchange. Approximately 150 mL of air moved during the tidal volume is within the anatomical dead space, which means that only 350 mL of air is actually participating in gas exchange. By taking the dead space into account when you consider pulmonary ventilation, you will have a better understanding of how much air is reaching the alveoli for gas exchange.

Answer 15

Minute ventilation is the ventilation rate (number of breaths per minute) times the tidal volume. Alveolar ventilation takes into account the anatomical dead space and is the ventilation rate times the tidal volume minus the anatomical dead space. The alveolar ventilation gives a better indication of the amount of fresh air that is flowing into the alveoli to participate in gas exchange. To get the most effective ventilation, you want to know how much fresh air is reaching the alveoli, and is not stuck in the dead space. Since the anatomical dead space is the same in a given individual, increasing the volume of breathing (i.e. deep breaths) enhances the flow of fresh air to the alveoli more than shallow, fast breathing. In shallow, fast breathing most of the inspired air never reaches the air spaces and is stuck in the dead space. In deep, slow breathing, a greater percentage of each inspired breath reaches the alveoli.

Answer 16

P1V1 =P2V2

Answer 17

An increase in thoracic volume

Answer 18

The air remaining in the lungs and alveoli

Answer 19

When the lungs are expanded the most

Answer 20

The volume of the conducting zone

Answer 21

Dalton’s law states that the total pressure of a mixture of gases is the sum of the pressures of the individual gases that make up that mixture, and the partial pressure of each gas within a mixture is proportional to the percentage of the gas in the mixture. The air that we breathe is made of a mixture of gases including the respiratory gases, oxygen and carbon dioxide. We can determine the partial pressure of oxygen and carbon dioxide in air based on the percentage they contribute to air. Henry’s law states that when a gas is in contact with a liquid, the gas will dissolve in the liquid in proportion to its partial pressure and its solubility. How these laws help us understand gas exchange: Dalton’s law helps us understand how oxygen and carbon dioxide will behave in a mixture of gases, and how their partial pressures are determined. Henry’s law helps us understand how oxygen and carbon dioxide will move from the air of the alveolus to the blood (dissolve) based on their pressure gradients and their relative solubility. Both oxygen and carbon dioxide will move by simple diffusion and move from an area of high partial pressure to an area of lower partial pressure until they reach equilibrium. This explains how oxygen will diffuse from the alveolus (air) to the blood and carbon dioxide will diffuse from the blood to the alveolus (air) in the lungs and oxygen will diffuse from the blood to the tissue cells and carbon dioxide will diffuse from the tissue cells to the blood in the systemic capillary beds.

Answer 22

Atmospheric air is composed mostly of (in order of greatest percent contribution) nitrogen, oxygen, water, and carbon dioxide. About 99% of atmospheric air is composed of the combination of nitrogen and oxygen, and carbon dioxide contribute less than 1% together. In alveolar air, the same gases contribute, but the partial pressures of water and carbon dioxide are much higher – because of the moisture added to air in the respiratory passageways, and because of the carbon dioxide produced by the cells during cellular respiration and eliminated in the alveoli (for exhalation).

Answer 23

There are three primary explanations for this mismatch. First, gas exchange is constantly occurring in the alveoli, such that oxygen is always diffusing out and carbon dioxide is always diffusing in. This is not an activity normally observed in the atmosphere at large. Second, humidification occurs along respiratory passageways. The humidification allows for the development of water vapor pressure, which becomes part of the total gas mixture modulating the ratio of each gas partial pressure to the total pressure. Finally, gases mix in the respiratory passageways such that not all of the oxygen inspired enters the alveoli and not all of the carbon dioxide expired escapes the conducting system.

Answer 24

The variables that can affect the efficiency of external respiration or pulmonary gas exchange, include partial pressure gradients and gas solubility, thinness and surface area of the respiratory membrane, and ventilation- perfusion coupling. The partial pressure gradients of oxygen and carbon dioxide dictate the direction of gas flow. In external respiration the partial pressure of oxygen is around 104 mm Hg in the alveoli and 40 mm Hg in the pulmonary capillary. Because of this pressure gradient, oxygen will diffuse from the alveolus (air) into the capillary (blood). The partial pressure of carbon dioxide in the alveolus is around 40 mm Hg and 45 mm Hg in the pulmonary capillary. This pressure gradient facilitates the diffusion of carbon dioxide from the capillary into the alveoli. The respiratory membrane adds to the efficiency of pulmonary gas exchange due to its thinness and the large number of alveoli in the lungs (millions). Simple diffusion is most efficient over short distances and over a large surface area. Any disease that decreases the number of healthy alveoli (surface area available) such as emphysema, or increases the thickness of the respiratory membrane (fibrosis, pneumonia, scarring) will decrease the efficiency of gas exchange. Ventilation-perfusion coupling is the process by which the ventilation of air into the alveoli is matched to the perfusion of blood through the surrounding pulmonary capillary. For optimal gas exchange, there must be a close match between the amount of gas reaching the alveoli (which we call ventilation), and the amount of blood flow through the pulmonary capillaries (we call perfusion). In other words, you want the blood supply to go to the areas of the lungs that are getting the best air flow to the healthiest alveoli, and you also want the best airflow to go to the areas of the lung that have the healthiest blood supply. This is regulated by PO2 and PCO2 levels.

Answer 25

Both the bronchiole diameter (which determines air flow or ventilation) and arteriole diameter (which determines blood flow to the capillary beds) are controlled by local autoregulatory mechanisms that continuously respond to local conditions. The partial pressure of oxygen controls blood perfusion, where an increase in pressure increases perfusion and a decrease in pressure decreases perfusion. The partial pressure of carbon dioxide controls ventilation, where an increase in pressure increases ventilation and a decrease in pressure decreases ventilation. If the ventilation (air flow) isn’t very good (could be due to blocked bronchioles, buildup of mucus), local O2 is low because the blood carries oxygen away faster than ventilation can replenish it. As a result local arterioles constrict, which redirects blood to capillary beds in other areas of the lung that are getting better airflow. If the air flow is good, the local levels of PO2 increases (fresh air). The high PO2 levels stimulate arteriole dilation, which increases blood flow to the capillary beds in this area with healthy alveoli. Bronchioles change their behavior based on local CO2 levels. Bronchioles servicing areas where alveolar PCO2 levels are high will dilate, allowing CO2 to be eliminated from the body more quickly (this corresponds to areas that have good blood supply, so are bringing lots of CO2 for elimination). Bronchioles serving areas where CO2 is low will constrict (corresponds to low blood flow).

Answer 26

External Respiration: In the lungs, during external respiration or pulmonary gas exchange, the PO2 of alveolar air is ~104 mm Hg, while the PO2 in the deoxygenated blood arriving at the pulmonary capillary beds is ~40 mm Hg. At the same time, the PCO2 in the blood arriving at the pulmonary capillary beds is ~45 mm Hg (high from the tissues), and is only 40 mm Hg in the alveolar air. These pressure gradients favor the diffusion of oxygen from the alveolus to the blood, and carbon dioxide from the blood to the alveolus. Oxygen will diffuse into the pulmonary capillary until the PO2 in the blood reaches equilibrium with the PO2 in the alveolar air (104 mm Hg), carbon dioxide will diffuse until the PCO2 in the blood reaches equilibrium with the PCO2 in the alveolar air (40 mm Hg)

Answer 27

Internal Respiration: In the tissues, during internal respiration or tissue gas exchange, the PO2 of the blood arriving at the systemic capillary beds is ~100 mm Hg (usually slightly less than at the lungs because of a slight mixing of deoxygenated venous blood added to the oxygenated blood traveling in the pulmonary veins back to the heart). The PO2 in the tissue cells is ~40 mm Hg (and can be even lower in active tissues) because the tissue cells are using oxygen in the process of cellular respiration to make ATP as fast as it arrives. There is a strong gradient for oxygen to move from the blood to the tissue cells. Oxygen will diffuse into the tissue cells until the PO2 of the blood leaving the capillary bed is the same as the PO2 of the tissue cells (at equilibrium = 40 mm Hg). At the same time, the tissue cells are producing CO2 as a waste product of cellular respiration. The PCO2 in the tissue cells is ~45 mm Hg, and is only 40 mm Hg in the blood arriving at the capillary bed. Carbon dioxide will diffuse from the tissues to the blood, until it reaches equilibrium (~45 mm Hg in the blood leaving the capillary bed).

Answer 28

About 98.5% of oxygen is transported bound to hemoglobin molecules. Each hemoglobin molecule is made up of 4 subunits, each of which has an iron-containing heme group that binds an oxygen molecule. Since there are 4 heme groups, each hemoglobin molecule can carry 4 oxygen molecules if it is fully saturated (100% saturated). Only 1.5% of oxygen is transported dissolved directly in the blood plasma because oxygen is poorly soluble in water (it has low solubility).

Answer 29

``` Each hemoglobin molecule is made up of 4 polypeptide chain subunits, each of which has an iron-containing heme group that binds an oxygen molecule. Since there are 4 heme groups, each hemoglobin molecule can carry 4 oxygen molecules if it is fully saturated (100% saturated). If hemoglobin is partially saturated, 1, 2, or 3 O2 molecules are bound. If 1 oxygen is bound, hemoglobin is 25% saturated, if 2 are bound, hemoglobin is 50% saturated. If 3 oxgyen molecules are bound, hemoglobin is 75% saturated. The binding of oxygen to hemoglobin exhibits cooperativity. This means that after the first oxygen molecule binds to hemoglobin, the hemoglobin changes shape and increases its affinity for oxygen – so the 2nd, 3rd and 4th oxygen molecules bind more easily. The opposite happens when hemoglobin is unloading (releasing) oxygen. After the first oxygen molecule is released, the next oxygen is more easily released, and so on. The affinity (binding strength) of hemoglobin for oxygen changes with the extent of oxygen saturation, and both loading and unloading of oxygen are very efficient. ```

Answer 30

The oxygen-hemoglobin dissociation curve is a plot that describes the relationship between the partial pressure of oxygen and the percent saturation of the hemoglobin. In other words, the curve describes the binding affinity of hemoglobin for oxygen at different partial pressures of oxygen. In general, the curve demonstrates that as the partial pressure of oxygen decreases the percent hemoglobin saturation also decreases. The relationship however, is not linear. At partial pressures above 80 mm Hg hemoglobin is near 100% saturation. When the pressure drops below 80 mm Hg the curve becomes more exponential, decreasing rapidly. This exponential property suggests the oxygen release is cooperative in nature and explains the rapid loading and unloading of hemoglobin in the lungs and at the tissues respectively. At high partial pressures of oxygen, such as in the lungs, hemoglobin has a high affinity for oxygen and is nearly 100% saturated. At lower PO2, such as 40 mm Hg, the binding affinity is lower, which allows hemoglobin to release some of its oxygen molecules, as would be necessary at the tissues. Because hemoglobin has such a high affinity for oxygen at PO2 = 100 mm Hg, it is very easy for hemoglobin to pick up oxygen in the lungs, and it will hold on to its oxygen as it is traveling through the systemic arteries (you don’t want oxygen released until it reaches the tissues). At the tissues, when PO2 is 40 mm Hg or less, hemoglobin has a lower affinity for oxygen, so is able to release oxygen where it is needed.

Answer 31

The Bohr effect is a weakening of the hemoglobin-oxygen bond caused by declining blood pH (increased H+ levels) and increased PCO2, which are all typical of actively metabolizing tissues. This causes the oxygen- hemoglobin dissociation curve to shift to the right, which allows hemoglobin to release more of its oxygen where its needed (in active tissues). Increasing temperature, PCO2 and hydrogen ion levels all shift the dissociation curve to the right. (Decreased temperature, increased pH and decreased PCO2 all shift the dissociation curve to the left and cause hemoglobin to hold on to more of its oxygen – because its not needed at less active tissues).

Answer 32

Approximately 7% of carbon dioxide is transported to the lungs dissolved in plasma. Another 20% is transported bound to hemoglobin forming carbaminohemoglobin. The binding site for carbon dioxide is not the same as the binding site for oxygen – while oxygen binds to a heme group, carbon dioxide binds to the globin part of hemoglobin. The remaining 70% of carbon dioxide is transported as a bicarbonate ion in the plasma. This +- transfer follows the following reaction, CO2 + H2O ⇌ H2CO3 ⇌ H + HCO3 , which can be reversed in the lungs.

Answer 33

The amount of carbon dioxide transported in blood is affected by the degree to which blood is oxygenated. The lower the PO2 and the lower the saturation of hemoglobin with oxygen, the more CO2 that blood can carry. This is the Haldane effect and reflects the greater ability of reduced hemoglobin to form carbaminohemoglobin and to buffer H+ by combining with it. The Haldane effect encourages CO2 exchange in both the tissues and the lungs. In the tissues, as hemoglobin releases its oxygen, carbon dioxide binds to hemoglobin, forming carbaminohemoglobin. In the pulmonary capillaries, hemoglobin uptake of oxygen facilitates the release of CO2. As hemoglobin becomes saturated with O2, the H+ released combines with HCO3-, helping to unload the CO2.

Answer 34

These two effects are synergistic. As CO2 enters the blood at the tissues, it causes more oxygen to dissociate from hemoglobin (the Bohr effect). The dissociation of oxygen allows more CO2 to bind (the Haldane effect).

Answer 35

``` Carbon monoxide (CO) is a colorless, odorless gas formed from the burning of fossil fuels or the incomplete combustion of any carbon source – like wood. Hemoglobin has a much greater affinity for CO than oxygen (~200X) – so CO binds very tightly to Hb and even very low levels of CO can outcompete oxygen for that binding site. When carbon monoxide is bound to Hb instead of oxygen, there is inadequate delivery of oxygen to the tissues, leading to hypoxia, which can be fatal. CO poisoning is very dangerous because it doesn’t produce the normal signs of hypoxia such as cyanosis or respiratory distress. Instead, the victim is confused, nauseous and has headache – common symptoms of many illnesses and may go back to bed, instead of moving to fresh air. Victims of CO poisoning are treated by hyperbaric (high pressure) therapy if available or 100% oxgyen to try and increase the amount of oxygen in the blood. A simple solution for all households is to have carbon monoxide detectors in the home. ```

Answer 36

decrease in pH (acidosis) weakens the hemoglobin-oxygen bond

Answer 37

Ventilation-perfusion coupling

Answer 38

Chloride shifting

Answer 39

Partial pressure gradient

Answer 40

Number of red blood cells

Answer 41

CO2 +H2O ⇌ H2CO3 ⇌H +HCO3 Carbon dioxide combines with water to produce carbonic acid. The carbonic acid rapidly dissociates to hydrogen When carbon dioxide enters the blood, hydrogen ions are produced, as described in the equation: +- ion plus bicarbonate ion. Changes in respiratory rate or depth can alter blood pH dramatically by altering the amount of carbon dioxide and therefore, carbonic acid in the blood. Slow, shallow breathing (hypoventilation) allows CO2 to accumulate in the blood. As a result, carbonic acid levels increase, and blood pH drops. Conversely, rapid, deep breathing (hyperventilation) quickly flushes CO2 out of blood, reducing carbonic acid levels and increasing blood pH.

Answer 42

There are two groups of neurons in the medulla that help regulate respiratory rate and rhythm – the ventral respiratory group (VRG) and the dorsal respiratory group (DRG). The VRG generates inspiration and expiration, so is called the rhythm generating center. It contains groups of neurons that fire during inspiration and others that fire during expiration. When inspiratory neurons fire, they activate phrenic nerve and intercostal nerves to stimulate the diaphragm and external intercostal muscles. When expiratory neurons fire, output from phrenic and intercostals stops, inspiratory muscles relax and the lungs recoil, causing expiration. Cyclic on/off activity of inspiratory and expiratory neurons repeats continuously and produces a respiratory rate of 12-16 breaths per minute. This normal rate and rhythm is called eupnia. Breathing stops when VRG neurons are suppressed, as can occur during an overdose of opiates or alcohol. The DRG acts as in integrating center – it collects sensory information from chemoreceptors and peripheral stretch receptors and communicates this information to the VRG. The pons contains the pontine respiratory group which helps to smooth the transitions between inspiration and expiration. This helps us breath appropriately during exercise and vocalization (speech production).

Answer 43

The most important factors that regulate breathing rate and depth are changing levels of CO2, O2 and H+ in arterial blood. Chemoreceptors for these are found in the brainstem (central chemoreceptors) and peripheral chemoreceptors are located in the carotid arteries and aortic arch. Levels of carbon dioxide are the most potent in regulating breathing and therefore are the most closely controlled. As CO2 levels rise (hypercapnia) in the brain, H+ is formed which stimulates central chemoreceptors and stimulate the respiratory centers to increase the depth and rate of breathing, in order to blow off excess CO2. When CO2 levels are low, respiration is inhibited, and breathing becomes shallow. Peripheral chemoreceptors are sensitive to low O2 levels, but normally blood PO2 affects breathing only indirectly by influencing peripheral chemoreceptor sensitivity to PCO2 levels. Low PO2 augments PCO2 effects, but high PO2 levels diminish the effectiveness of CO2 stimulation. When PO2 levels fall below 60 mm Hg, it becomes the major stimulus for respiration, and stimulates the respiratory centers to increase ventilation. Decreases in arterial pH can stimulate respiratory centers to increase ventilation in order to blow off CO2 to restore blood pH. Other factors: Hypothalamus and limbic system can alter breathing based on emotions, we can voluntarily control our breathing through conscious control by way of the cerebral cortex. Irritants in the airways can activate cough or sneeze reflexes, and stretch receptors in the lungs send a message to the respiratory centers when the lungs are inflated. When the stretch receptors are activated due to lung inflation, sensory signals trigger inhibitory impulses that end the inspiratory phase and allow expiration to occur. Receptors in joints and muscles influence breathing patterns during exercise

Answer 44

The partial pressure of oxygen and carbon dioxide in the blood influence the activity of central and peripheral chemoreceptors and therefore regulate respiratory rate. The partial pressure of carbon dioxide has a more dominant role. Carbon dioxide can easily cross the blood brain barrier. Once in the brain extracellular fluid, carbon dioxide and water form carbonic acid, which dissociates into a hydrogen ion and a bicarbonate ion. The hydrogen ion can bind to central chemoreceptors that directly affect the medullary respiratory centers. An increase in partial pressure of CO2 will trigger hyperventilation, while a decrease will trigger hypoventilation. Peripheral chemoreceptors are sensitive to low O2 levels, but normally blood PO2 affects breathing only indirectly by influencing peripheral chemoreceptor sensitivity to PCO2 levels. Low PO2 augments PCO2 effects, but high PO2 levels diminish the effectiveness of CO2 stimulation. When PO2 levels fall below 60 mm Hg, it becomes the major stimulus for respiration, and stimulates the respiratory centers to increase ventilation.

Answer 45

Hyperventilation is an increase in the rate and depth of breathing that exceeds the body’s need to remove CO2. Usually hyperventilation results in PCO2 levels becoming lower than usual (hypocapnia), which can lead to other results, such as decreased stimulation to breathe.

Answer 46

COPD and asthma are both obstructive diseases. In obstructive pulmonary disease, it is very difficult to force air out of the lungs and air becomes trapped in the alveoli. Either because the airways are inflamed and tend to collapse during exhalation, or because of a loss of elastic recoil in the alveoli (emphysema). However, COPD is a chronic condition which is irreversible, while asthma occurs in acute attacks which are reversible (there are periods which are symptom free). COPD is associated with chronic bronchitis and emphysema leading to dyspnea (difficulty breathing), coughing, pulmonary infections, and eventually respiratory failure. Asthma results from an abnormal response to an allergen that enters into the conducting system. Clinical symptoms can be similar and include dyspnea, coughing, wheezing and chest tightness.

Answer 47

Cystic fibrosis is caused by a gene mutation that affects a particular type of chloride channel that allows chloride to leave cells. If chloride can’t leave cells, water can’t follow – this makes the mucus that normally coats the respiratory mucosa stickier than usual – as a result the cilia of the muco-ciliary escalator get gummed up and can’t move the mucus up and out of the air passageways. The mucus accumulates, which makes bacterial infections more common, and the increased infections and inflammation of the lungs cause permanent damage.

Answer 48

There are two types of sleep apnea, obstructive or central. In obstructive sleep apnea, the soft tissues of the pharynx sag and obstruct the airways. Obstructive sleep apnea can be worse in obesity. In central apnea, there is a reduced stimulation to breathe from the respiratory centers in the brainstem. This can be made worse when patients are taking opiate pain relievers, or when a person is in medication-assisted treatment for substance abuse disorder. Both types of sleep apnea are characterized by periods in which the patients stops breathing while they are sleeping. These periods of apnea, or breathing cessation, can occur up to 30-50 times per minute and result in decreased blood oxygen levels and excessive daytime sleepiness. In most cases, a person with is not aware of these repeated awakenings because they occur below the level of consciousness. As a result, people with sleep apnea frequently complain of daytime sleepiness, fatigue, and/or insomnia. This poor sleep may also cause problems with memory, concentration, and mood changes. Also, in people with sleep apnea, repeated episodes of falling oxygen levels lead to a variety of physiological changes that can lead to cardiovascular disease and high blood pressure.

Answer 49

Lung cancer is the leading cause of cancer death for both men and women in North America. Nearly 90% of lung cancer cases result from smoking, so it is considered a preventable cancer. Because lung cancer is very aggressive and metastasizes rapidly and widely, most cases are not diagnosed until they are well advanced. Lung cancer seems to result when the normal respiratory system defenses are overwhelmed and can’t protect the lungs from inhaled chemical and biological irritants. Smoking paralyzes the cilia that clear mucus from the airways, allowing irritants and pathogens to accumulate. The cocktail of free radicals and other carcinogens in tobacco smoke eventually can cause mutations in epithelial cell DNA can lead to uncontrolled division and growth that translates into lung cancer.

Answer 50

Medulla and pons

Answer 51

Rising blood pressure

Answer 52

Voluntary cortical control

Answer 53

Helps retain carbon dioxide in the blood

Answer 54

The five major functions of the integumentary system are: protection, sensation, thermoregulation, excretion, and vitamin D synthesis. Thermoregulation in the skin is regulated through negative feedback loops. If body temperature drops below the normal range, thermoreceptors in the skin will detect this change and signal to neurons in the hypothalamus that body temperature is dropping. The hypothalamus will release hormones that will constrict peripheral blood vessels in the hands and feet to reduce heat loss. Remember a great deal of heat in our bodies is carried by the blood. This peripheral vessel constriction will keep a larger percentage of the blood closer to the body core, and reduce heat loss. If body temperature rises above the normal range thermoreceptors in the skin will again detect this change and signal the hypothalamus. Signals from the hypothalamus will increase sweating and vasodilation of the arteries in the skin. The net effect of this response in a reduction in body temperature and a return to a normal physiological range.

Answer 55

The most common cell of the integument is the keratinocyte. These cells are found in all layers of the epidermis. There functions change as they move through the layers of the epidermis, but in general they act to produce keratin, a fibrous structural protein and lamellar granules that will establish a water barrier. Melanocytes are epithelial cells located in the stratum basale of the epidermis that function to produce melanin for keratinocytes. Dendritic cells originate in the bone marrow and migrate to the epidermis, in particular the stratum spinosum, where they extend process between keratinocytes. Dendritic cells can phagocytose foreign particles and act to recruit immune system cells following injury or pathogen exposure. Merkel cells are sensory receptors that lie at the epidermis/dermis junction. These cells are sensory receptors for touch and transmit signals to nerve endings in the dermis. The dermis does not have a specific population of individual cells that perform specific functions, but it does contain many of the accessory structures of the integument including hair follicles and sweat glands.

Answer 56

Thick skin is going to be present on the palms of the hand, fingertips, and soles of the feet; thin skin will cover the rest of the body. Thick skin has 5 total layers in the epidermis, including the stratum lucidum, which is not seen in thin skin, which has only 4 layers. Finally, hair is only observed in thin skin.

Answer 57

``` The layers from the epidermis are as follows from deep to superficial: Stratum basale (basal layer) – single layer of cells where stem cells are constantly diving generating new keratinocytes. Melanocytes are also present in this layer. Stratum Spinosum (prickly layer) – several layers thick, cells contain a system of intermediate filaments (pre-keratin) that act as tension- resisting bundles. Stratum granulosum (granular layer) – several cells thick which begin to undergo keratinization (cells flatten, organelles and nuclei begin to disintegrate). Accumulation of two types of granules. Keratohyaline granules which facilitate keratin formation. Lamellar granules which contain a water-resistant glycolipid that is released in the extracellular space. This glycolipid helps generate an epidermal water barrier. Stratum Corneum (horny layer) – 20-30 cells thick. All cells in this layer are anucleate (without a nucleus) and therefore dead. Cells in this layer are mostly composed of keratin and therefore create a durable “overcoat” for the body protecting against abrasion and penetration ```

Answer 58

The dermis is composed of two layers. The first layer under the epidermis is the papillary layer, which is composed of loose areolar connective tissue. The papillary is relatively thin, making up only 20% of the total dermal thickness. The major structural feature of this layer are the dermal papillae that indent the overlying epidermis and serve as a structure to house capillary loops and sensory nerve endings. In thick skin the dermal papillae are arranged into dermal ridges, which act to indent the overlying epidermis and generate epidermal ridges or fingerprints. Deep to the papillary layer is the reticular layer of the dermis, which accounts for 80% of the dermal thickness and is composed of dense irregular connective tissue. The connective tissue of the reticular layer is composed of collagen and elastic fibers that provide both strength and flexibility. The collagen fibers in this layer run in specific planes throughout the body. These planes of collagen fibers result in stereotypical cleavage lines that are similar in most adults. Surgeons must be mindful of cleavage lines as incisions that run perpendicular to these lines will not heal well and tend to scar. The reticular layer is also important for generating flexure lines, which are dermal folds that occur at joints throughout the body allowing the skin to move and allow joint motions.

Answer 59

Humans have varying skin pigment because melanin ranges in color from orange-red to black. Further, the kind and amount of melanin that is produced by melanocytes will vary between people. This feature of physiology accounts for the vast array of skin pigments we see around the world. The physiological role of melanin is primarily to protect keratinocyte DNA from UV radiation. Melanin is synthesized from tyrosine in melanocytes and packaged into melanosomes. Melanosomes are trafficked to keratinocytes where they release their contents. Melanin will then aggregate above the nucleus for the keratinocytes acting like a UV umbrella protecting all the DNA of the cell.

Answer 60

The integumentary system can sometimes offer important information into the underlying physiology and emotional health of a patient. The skin and nails in particular can give a glimpse into a patient’s health. The color of the skin can indicate that a patient may be anemic (pallor), hypertensive (redness), or have a specific disorder like Addison’s disease (bronzing). The nails can also indicate underlying pathologies including iron deficiency (concave nails) or malnutrition (Beau’s lines). Although other tests would be needed to confirm disease states the skin and nails offer an important, non-invasive and quick mechanism for assessing a patient’s overall health.

Answer 61

The major skin accessory structures include hair, nails, and glands (sweat & sebaceous). Hair is formed by mostly hard keratinized cells that do not flake off during physical trauma. Each individual hair consists of a shaft and a root both containing 3 distinct layers; the outer layers are composed entirely of hard keratinized cells. Within the dermis, the hair is surround by a hair follicle, which at its base forms a hair bulb. The hair bulb is innervated by a number of nerve endings that act as sensory receptors. Thus the hair bulb acts as an additional touch receptor that allows us to detect fine defections of individual hairs (like a mosquito landing on your arm). Each hair is attached to an arrector pili muscle that when contracted causes the hair to stand erect on the skin surface and facilitates the release of sebum by contracting the sebaceous glands that are attached to the hair follicle. Nails, like hair, are also composed of hard keratin containing cells and are analogues to claws and hooves seen in other animal species. New nail cell growth occurs in the nail matrix and will push pervious generations of cells along the nail bed until they reach the free nail edge and are broken off by physical trauma. Nails as discussed above are important clinical indicators of patient well being. There are three types of glands commonly found in the dermal layers of the integument including eccrine sweat glands, apocrine sweat glands, and sebaceous glands. Eccrine sweat glands are the most abundant type of sweat gland seen throughout the body. These glands use merocrine mechanisms to secrete sweat through ducts that empty onto the skin surface. The sweat released from these eccrine glands contains up to 99% water, but can also include salts, waste products (like urea), antibodies, and dermicidin (an antimicrobial peptide). Eccrine glands are controlled by both the sympathetic nervous system and emotional responses. Apocrine sweat glands are similar to eccrine glands in their structure and release mechanisms, but differ in location and composition of sweat. Apocrine sweat glands are concentrated in axillary (armpit) and anogenital regions and release fatty substances and proteins as components of sweat. These additional components of the sweat from apocrine glands interact with bacteria on the skin surface to generate musky or unpleasant odor we associate with secretions in these anatomical locations (i.e. body odor). Sebaceous glands are ducted glands that directly connect with hair follicles. Unlike sweat glands, sebaceous glands secret sebum through holocrine mechanisms. Sebum is an oily substance that acts functionally to lubricate hair, slow water loss, and provide protection against pathogens (like bacteria). Secretion of sebum is potentiated when arrector pili muscles contract forcing sebum out through ducts.

Answer 62

The integument is also the first line of defense used by the immune system to protect the body from pathogens creating a series of barriers for the body. The most obvious barrier is a physical barrier. The many layers of keratinocytes to make up the epidermis along with the glycolipids released in the stratum granulosum create a thick, strong, and waterproof shield that is extremely efficient at keeping the body free from invasion. The integument also generates a chemical barrier via the secretions released through its glands. Together these secretions make up the acid mantle, which generates a low pH environment on the skin surface making it difficult for bacteria to survive. Integumentary secretions like sweat and sebum also contain antimicrobial and antibacterial proteins, such as dermicidin, that can actively attack bacteria and microbes. The final barrier is a biological barrier and includes the activities of immune cells like dendritic cells and dermal macrophages that patrol the layers of the integument and phagocytose any pathogen that they can recognize.

Answer 63

corneum, granulosum, spinosum, basale

Answer 64

dendritic cells — activate the immune system

Answer 65

accumulate the melanin granules on their superficial portion, forming a UV-blocking pigment layer

Answer 66

99% water, sodium chloride, trace amounts of wastes, and vitamin C

Answer 67

It converts modified epidermal cholesterol to a vitamin D precursor important to calcium metabolism.

Answer 68

The first line of defense the body has against pathogens is the surface barriers – skin and mucus membranes. Cells of the first line of defense include keratinocytes and dendritic cells in the epidermis. Although not single cells themselves glands and secretions released by the skin and mucus membranes are critical features of this line of defense. The second line of defense is the innate defenses or the innate immune system. The cells of this defense system are leukocytes, specifically neutrophils, eosinophils, basophils, monocytes/macrophages, and lymphocytes (natural killer cells). The third line of defense is the adaptive immune system, which involves a specific and coordinated response by both B (humoral immunity) and T (cellular immunity) lymphocytes

Answer 69

The skin and mucus membranes act to protect the body by establishing a series of barriers. The most obvious barrier is the physical barrier established by the thick layer of keratinocytes that make up the epithelium of the skin. In addition, to this physical barrier a chemical barrier commonly referred to as the acid mantle of skin is established by the many secretions of integumentary glands that together generate a hostile environment limiting pathogen survival and growth. The mucus membranes include a number of membranes and glandular secretions in areas of the body commonly exposed to the outside world. For example, nasal hairs help protect the respiratory cavities by filtering and/or trapping pathogens present in the air. One of the most important molecules on the mucus membrane is mucin which forms the mucus of the respiratory and digestive pathways. Mucus in addition to lubricating these pathways traps pathogens we are exposed to through the air and the foods we eat. Once trapped the movement of mucus toward the stomach removes these pathogens from compartments of the body where they would otherwise be able to grow and proliferate. Once in the stomach pathogens are exposed to a highly acidic environment where very few can survive.

Answer 70

Both neutrophils and macrophages are classified as phagocytes. There are two major mechanisms for phagocyte activation, both involve a receptor interaction. In the first mechanism the phagocyte itself expresses a receptor that is capable of binding to a specific pathogen. In this case whenever that pathogen encounters a phagocyte with the appropriate receptor the phagocytic process will be initiated. The second mechanism involves the process of opsonization. In this case the pathogen is coated by antibodies, a phagocytic cell with the corresponding Fc receptor will be able to recognize the bound antibodies and bind the pathogen initiating phagocytosis. Once pathogens are bound the process of phagocytosis will be the same. The pathogen is internalized into the phagocytic cell in a phagosome. The phagosome is fused with a lysosome exposing the pathogen to a series of enzymes that will digest it down into a series of antigens. The antigens are then bound to major histocompatibility complex (MHC) proteins that are inserted into the plasma membrane. Once in the plasma membrane these antigens can be seen by other immune cells.

Answer 71

Natural killer (NK) cells are a type of lymphocyte that is specific to the innate immune system. Like other cells in the innate immune system NK cells are less specific about the type of cells that they will target, but unlike other innate immune system cells NK cells can perform targeted killing of pathogenic cells. NK cells are most likely to target virus-infected or cancerous cells that are expressing membrane proteins demonstrating cellular stress or incorrect MHC proteins. When NK cells are activated they will induce cells to undergo apoptosis (self-destruction).

Answer 72

The inflammatory process begins with tissue damage causing damaged cells and mast cells to release pro- inflammatory molecules including histamines, prostaglandins, and bradykinins. These inflammatory molecules will direct underlying arterioles to vasodilate, increasing blood supply to the area, causing the area to become red and warm to the touch. Sensory nerve ending will become sensitized causing a localized occurrence of pain. Underlying capillaries will increase their permeability allowing cells and fluid to more easily leave the vessels, resulting in a localized edema (swelling). Theses processes generate the four cardinal signs of inflammation – redness, heat, swelling, and pain. The inflammatory molecules will also initiate leukocytosis increasing production of neutrophils in the red marrow. The neutrophils and blood vessels at the site of injury will express cell adhesion molecules (CAMs). This localized expression of CAMs will allow the neutrophils to bind specifically to the walls of the vessels near the site of injury in a process called margination. Neutrophils will then begin the process of diapedesis and squeeze through holes in the vessel walls. Once in the extravascular space the neutrophils will begin the process of positive chemotaxis and move toward the higher concentration of inflammatory molecules that are still being secreted at the site of damage

Answer 73

An antigen presenting cell is any cell that ingests a pathogen and breaks it down into small fragments or antigens; antigen fragments are then bound to proteins (class II MHC proteins) and the antigen MHC complex is inserted into the plasma membrane so that the antigen is displayed on the surface of the cell. The antigen presenting cell then looks for other immune cells to activate with the acquired antigen. There are a number of cells in all three lines of immune system that can act as antigen presenting cells including dendritic cells in the skin, macrophages, and B cells.

Answer 74

The two types of antimicrobial proteins we discussed are the interferons and the complement proteins. Interferons help fight pathogens, specifically viruses, by blocking viral replication in surrounding cells. After a virus invades one cell, that cell begins to produce and release interferon proteins. The interferons can bind to interferon receptors on adjacent cells inducing those cells to upregulate the production of anti-viral proteins. Due to the interferons the surrounding cells become resistant to viral infection and thus limit the number of cells that are lost to the virus. The complement proteins are activated by a number of mechanisms, but once activated they have three mechanisms to fight pathogens. The first is to increase opsonization of the pathogen, making is easier for other immune cells to see. The second mechanism is the enhancement of the inflammatory response. Finally complement proteins can generate a MAC (major attack complex), which produces a pore in the membrane of the pathogen inducing a lysis event.

Answer 75

A fever is any instance when internal body temperature rises above the normal homeostatic range. This process is mediated by pyrogens. The pyrogens act on cells in the hypothalamus to force these cells to increase the normal set point for body temperature. As long as the pyrogens are present the hypothalamus believes that body temperature should be higher than normal

Answer 76

brings more leukocytes to the sight of infection

Answer 77

vasodilation

Answer 78

NK cells are a type of neutrophil.

Answer 79

prevention of immediate hypersensitivity reactions

Answer 80

opsonization

Answer 81

Both the innate and adaptive immune system recognize foreign material and mount a coordinated response utilizing a series of leukocytes to kill many different kinds of pathogens. The innate immune system is a nonspecific system that is always ready and acts quickly with a blanket like approach. The main tools of the innate immune system include the inflammatory response, phagocytosis, and fever. Although effective these tools do not target specific antigens and can, if overactive damage normal health cells. The adaptive immune system is a very specific system that targets specific antigens on a pathogen, but is slow to respond. To have a functional immune system both the innate and adaptive immune system are required and they act to complement each other.

Answer 82

An antigen is anything that displays both immunogenicity and reactivity. Immunogenicity is the ability to stimulate specific lymphocytes to proliferate (clonal selection). Reactivity is the ability to react with activated lymphocytes and released antibodies. An antigen will have at least one antigenic determinate which can bind to one specific antibody in the body. Remember we already have antibodies against almost all pathogens based on genetically acquired knowledge of the world around us. To phrase this another way an antigen has the capacity to bind to a receptor on a naïve lymphocyte (immunogenicity) and then also respond to the clones of that lymphocyte and antibodies that are generated by plasma cells targeting a specific antigenic determinant (reactivity). All antigens will be ‘seen’ by the immune system via antibodies on B cells or T cell receptors on T cells.

Answer 83

All lymphocytes are born in the red bone marrow. B cells will stay in the red bone marrow and mature there. T cells will travel to the thymus to mature. A lymphocyte is said to be immunocompetent when it can recognize one specific antigen; this is accomplished by the expression of antibodies on B cells and T cell receptors on T cells. A lymphocyte is said to be self-tolerant when it will not respond to self-antigens.

Answer 84

Lymphocyte education involves a two test selection process. Both tests require the interaction of a normal cell and a naïve lymphocyte. Each normal cell must display a self-MHC protein and a self-antigen. The first test is a positive selection test. In this test naïve lymphocyte must recognize the self MHC protein with their antigen receptors (i.e. T cell receptor for T cells). Failure to recognize the self MHC will result in cell death. The second test is a negative selection test. In this test naïve lymphocytes must NOT recognize self-antigens. Cells that do bind to self-antigens will be killed. Only 2% of all T cells will pass both tests and will be allowed to leave the thymus. A similar process occurs for B cells but the specific details are less well understood.

Answer 85

The primary humoral immune response begins when a naïve B cell encounters an antigen that binds to its antibody receptor. The binding begins the process of clonal selection and the B cell clones itself. The clones divide and generate both plasma cells and memory cells. Plasma cells make millions of antibodies that are released into the blood supply and are circulated around the body. Memory cells remain in the lymphatic organs where they are primed to respond to the next exposure from the same antigen. The secondary humoral immune response begins when the memory B cell is exposed to the antigen that binds its antibodies. The memory B cell is able to mount an immune response that is both faster and larger in magnitude resulting in a significantly larger number of antibodies produced in a shorter period of time. Thus the secondary response is so enhanced over the primary response because the memory B cell is able to respond faster and with more vigor compared to the naïve B cell.

Answer 86

An antibody is made up of 2 heavy chains and 2 light chains that create a symmetrical Y-shaped structure. The two arms of the Y are called the Fab region or variable region where the antibodies can bind to an antigenic determinant. The stem of antibody is called the Fc region or constant region and is where the antibody can interact with other immune system cells via an Fc receptor. Antibodies can assist the immune system in 5 different ways. The first mechanism is to induce antigen clumping and can take on 3 forms – neutralization (binding to active sites on pathogens), agglutination (binding to cells) and precipitation (binding to soluble antigens). The second antibody function is to act as opsonins and facilitate phagocytosis. The third mechanism is triggering degranulation of leukocytes like mast cells, actively facilitating the inflammatory response. The fourth mechanism is to activate complement proteins and enhance phagocytosis, enhance inflammation, and initiate cell lysis through insertion of MAC. The final mechanism is to activate B lymphocytes to undergo clonal selection and thus recruit the adaptive immune response.

Answer 87

Class I and Class II proteins are antigen receptors that are used to present self and non-self antigens to cells of the immune system. Both types of MHC are synthesized in the rough endoplasmic reticulum and packaged into vesicles that are trafficked to the cell surface. Class I MHC proteins are expressed on all nucleated cells in the body (so almost all cells in the body), while class II MHC proteins are only expressed on antigen presenting cells. For class I MHC, self antigens are transported into the rough endoplasmic reticulum where they bind to MHC proteins and then the whole complex is trafficked to the cellular membrane. If a non-self antigen were present in the cell it would also be transported into the rough endoplasmic reticulum and bind class I MHC. The presence of a class I self MHC protein bound to a non-self antigen would signal a cytotoxic T (CD8+) cell to kill that cell. Class II MHC proteins are synthesized in the rough endoplasmic reticulum of antigen presenting cells. In the antigen presenting cells pathogens are phagocytosed and broken down in phagolysosomes. The phagolysosome can the fuse with the vesicle containing the class II MHC so the non-self antigens can bind the MHC protein. The antigen-MHC complex is then inserted in to the cell membrane for presentation to either a B or T lymphocyte. The most important cell type that interacts with class II MHC is the T helper cell as it will facilitate the activation of both B cells and cytotoxic T cells.

Answer 88

T helper cells are really the linchpin in the adaptive immune response (part of the reason AIDS is so devastating!) Following antibody binding to antigens on B cells, most cells will become sensitized but not fully active to the point of initiating clonal selection. A T helper cell is required to bind to the MHC II protein and give the B cell a final push resulting in the formation of memory and plasma cells. Thus without T helper cells the humoral immune response would be muted. Helper T cells also help activated cytotoxic T cells. When a helper T cell binds to an antigen presenting cell it stimulates the antigen presenting cell to express a co-stimulatory molecule and releases cytokines to recruit cytotoxic T cells. In this way cytotoxic T cells can be efficiently recruited and activated by antigen presenting cells, so that they can actively carry out the killing functions necessary for cellular immunity.

Answer 89

Cytotoxic T cells can only see cells that are expressing MHC I (remember CD8 cells bind MHC I). In this way cytotoxic T cells can see most cells in the body, but they will only activate and kill if the MHC I protein is holding a non-self antigen (remember the positive & negative selection). When a cytotoxic T cell interacts with a MHC I non- self antigen complex it can use two mechanisms to kill that cell. The first is the release of perforins and granzymes that will generate a pore in the target cells membrane and then activate apoptosis pathways. The second mechanism is receptor stimulated apoptosis where it is simply the activation of a cellular receptor that begins the apoptosis pathway. The net effect is the same in that the infected cell will undergo apoptosis (programed cell death) and die.

Answer 90

priming the adaptive immunity with a relatively harmless primary exposure

Answer 91

a particle that triggers the adaptive immunity

Answer 92

T-cells would not be able to properly bind to APC's and therefore not be activated by them

Answer 93

results in the formation of plasma cells

Answer 94

The lymphatic system refers to a series of vessels that move fluid from the extracellular space surrounding capillaries toward the heart. Once fluid enters the lymphatic vessels it is referred to as lymph. As lymph travels from the site of collection to the heart it passes through a series of lymph nodes. Lymph nodes are lymphatic organs that act to filter the lymph, removing any pathogens and/or cellular debris that is contained within the lymph. The lymphatic organs are a group of organs located around the body that provide the structural basis for the immune system. These organs include: lymph nodes, tonsils, spleen, Peyer’s patches, the appendix, thymus, and red bone marrow. All lymphoid organs are composed of lymphoid tissue, a type of connective tissue. Note that lymph nodes are considered part of both the lymphatic system and the lymphoid organs and as such act as a cornerstone linking the two together.

Answer 95

Lymphatic capillaries are blind-ended vessels that interdigitate between capillaries placing them in a prime position to collect the excess fluid lost during capillary blood flow. The lymphatic capillaries are composed of a series of overlying epithelial cells in an orientation similar to shingles on a roof. At the end of each of these epithelial cells are a series of filaments that are anchored into the surrounding connective tissue. As fluid builds up in the extracellular space the interstitial pressure begins to exceed the pressure inside the lymphatic vessel. When the interstitial pressure exceeds the lymphatic pressure a space between the overlapping epithelial cells called a minivalve opens allowing fluid to enter the lymphatic capillary. As the pressure in the interstitial space increases the filaments on the ends of the epithelial cells are pulled further allowing the minivales to open even larger. In addition, in times of inflammatory response the lymphatic vessels can becomes even more permeable and allow large proteins like viruses and bacteria to enter the lymphatic vessel. Once inside the lymphatic vessels both the lymph and any protein or cellular debris that is contained within the lymph will pass through a series of lymph nodes on a one way trip back to the heart.

Answer 96

Lymph is any fluid that is contained within a lymphoid vessel. Once that fluid is returned to the vascular system it will no longer be referred to as lymph.

Answer 97

Fluid will first enter the lymphatic system at lymphatic capillaries where the fluid will first be referred to as lymph. The lymphatic capillaries will quickly become collecting vessels. All lymphatic vessels have the 3 tunics seen in the vasculature – tunica interna, tunica intermedia, and tunica externa. Collecting vessels will empty into larger vessels called lymphatic trunks, which will empty into lymphatic ducts. There are only two lymphatic ducts in the body, the right lymphatic duct and the thoracic duct. Each of these ducts has a well defined area of the body that drains into it. Each duct will drain into the venous system at the juncture of the internal jugular and subclavian veins

Answer 98

There are 4 types of lymphatic cells – lymphocytes (B & T cells), macrophages, dendritic cells, and reticular cells. These cells help make up two types of lymphatic tissue, diffuse lymphatic tissue and lymphoid follicles. Both types of lymphatic tissue are loose connective tissue. Diffuse lymphatic tissue is seen throughout the body in areas like the lamina propria of mucus membranes. This tissue is not highly organized but will often consist of reticular fibers generated by reticular cells and a few cells like macrophages or dendritic cells. Lymphoid follicles in contrast are solid, spherical structures packed with lymphoid cells and reticular fibers. Within lymphoid follicles reticular cells generate a meshwork of reticular fibers collectively called a stroma. The other lymphatic cells (lymphocytes, macrophages and dendritic cells) use this meshwork of fibers to anchor themselves in place and survey the lymph as it passes through the lymphoid organ.

Answer 99

Primary and secondary lymphoid organs are all composed of lymphoid tissue and contain the same contingent of lymphoid cells although the amount and location of these cells will vary. Primary lymphoid organs include the thymus and red bone marrow. The major function of primary lymphoid organs is to generate and mature lymphocytes. Both B and T lymphocytes are born in the red bone marrow, however, B cells will stay in the marrow for maturation while T cells will travel to the thymus for maturation. The thymus is the only lymphoid organ that is complexly devoid of B cells. Secondary lymphoid organs include lymph nodes, spleen, tonsils, Peyer’s patches and the appendix. All secondary lymphoid organs are composed of lymphoid follicles and will be seeded with naïve lymphocytes after they have matured in the primary lymphoid organs.

Answer 100

The major function of the lymph node is to filter lymph. It accomplishes this function by creating a slow unidirectional flow of lymph through the node and directing the lymph through its stroma where macrophages are waiting to phagocytose debris and pathogens. Lymph nodes contain a greater number of afferent vessels relative to their efferent vessels – this organization effectively slows the movement of lymph through the node. Once lymph enters the node it is funneled into a subcapsular sinus that surrounds a lymphoid follicle. Within the sinus there are reticular fibers suspending macrophages that will attack foreign bodies. Within the follicle B and T lymphocytes will look for any non-self antigens that might be present in the lymph. The subcapsular sinus will lead into the medullary sinus where additional macrophages wait suspended on reticular fibers to further filter the lymph. Finally, the lymph will exit the node via an efferent vessel.

Answer 101

The spleen is the largest lymphoid organ in the body and its major junction is to filter the blood. In order to perform this function, it receives blood through the large splenic artery. As blood travels through smaller vessels inside the spleen it first passes through regions of white pulp. These regions form cuffs around the arteries and are full of lymphocytes suspended on reticular fibers. Similar to what is observed in lymphoid follicles in the lymph nodes, the white pulp acts as a place where lymphocytes can interact with antigens present in the blood supply and become activated if any antigens bind to their receptors. Once through the white pulp the blood will enter regions of red pulp. The red pulp is the region where aged and defective red blood cells are removed from circulation and phagocytosed by macrophages. Within the red pulp are venous sinuses where sinusoidal capillaries are present. These very permeable capillaries allow red blood cells to leave the blood vessels and be inspected by the surrounding macrophages. Fully functional red blood cells will continue on into the venous system and head back to the heart. Old and damaged red blood cells will be destroyed and their contents recycled for future use.

Answer 102

MALT tissues are found lining the gastrointestinal tract, respiratory passages, and genitourinary organs. These areas are all locations in the body that are exposed to the outside word. Because of their exposure these regions are highly vulnerable to attach from pathogens. Due to this vulnerability the body has equipped these regions with MALT. The MALT structures contain clusters of lymphoid follicles that allow for the destruction of pathogens as well as a convenient site for lymphocyte exposure to pathogen antigens. By locating MALT structures in areas of high pathogen exposure the body actively enhances its adaptive immune system making it easier for lymphocytes to interact with environmental antigens and develop the cells necessary to fight against commonly encountered pathogens.

Answer 103

lymph nodes

Answer 104

more permeable than blood capillaries

Answer 105

Lymph transport depends on the movement of adjacent tissues, such as skeletal muscles.

Answer 106

lower extremities