Human Biology

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Respiratory System/Cell Respiration

Reading Material

The respiratory system generally includes tubes, such as the bronchi, used to carry air to the lungs, where gas exchange takes place. The diaphragm muscle at the base of the tho-racic cavity pulls air in and pushes air out. Respiratory systems of various types are found in a wide variety of organisms.

In humans and other mammals, the respiratory system consists of the airways, the lungs, and the respiratory muscles that mediate the movement of air into and out of the body. Within the alveolar system of the lungs, molecules of oxygen and carbon dioxide are pas-sively exchanged, by diffusion (movement of simple molecules from high to low concen-tration), between the gaseous environment and the blood. Thus, the respiratory system facilitates oxygenation of the blood while simultaneously removing carbon dioxide and other gaseous metabolic wastes from the circulation.

Upper respiratory tract (URT) The conducting zone begins with the nose, which open into the nasal cavity. The primary functions of the nasal passages are to: 1) filter, 2) warm, 3) moisten, and 4) provide reso-nance in speech. The pharynx, or throat behind the oral cavity leads to the larynx (voice-box), which contains the vocal cords, and connects to the trachea (wind pipe).

Lower respiratory tract (LRT) The trachea leads down to the chest where it divides into the right and left "main stem" bronchi, which then stem into smaller branches called bronchioles.

The bronchioles lead to the respiratory zone of the lungs which consists of alveoli, the multi-lobulated sacs in which most of the gas exchange occurs.

Ventilation Ventilation is air going into and out of the lungs and is carried out by the muscles of the chest.

Control Ventilation occurs under the control of the nervous system which is controlled by the brain. This area of the brain forms the respiration regulatory center, a series of intercon-nected nerve cells within the lower and middle brain stem which coordinate respiratory movements.

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Inhalation (breathing in) Inhalation is initiated by the diaphragm and supported by the external intercostal muscles (muscles of the ribs). Normal resting respirations are 10 to 18 breaths per minute.

Inhalation is driven primarily by the diaphragm. When the diaphragm contracts down-ward, the ribcage expands and the contents of the abdomen are moved downward. This results in a larger thoracic(chest) volume(size).

During forced inhalation, as when taking a deep breath, the external intercostal(chest) muscles and accessory muscles further expand the chest cavity.

Exhalation (breathing out) Exhalation is generally a passive process, however active or forced exhalation is achieved by the abdominal and the internal intercostal muscles.

The lungs have a natural elasticity; as they recoil from the stretch of inhalation, air flows back out until the pressures in the chest and the atmosphere reach equilibrium.

During forced exhalation, as when blowing out a candle, expiratory muscles including the abdominal muscles and internal intercostal muscles, generate abdominal and thoracic pressure, which forces air out of the lungs.

Circulation The right side of the heart pumps blood from the heart to the lungs. Once the gas ex-change process is complete, the blood is returned to the left side of the heart. The pul-monary circulation has a very low resistance, due to the short distance within the lungs, compared to the systemic circulation, and for this reason, all the pressures within the pulmonary blood vessels are normally low as compared to the pressure of the systemic circulation loop.

Virtually all the body's blood travels through the lungs every minute. The lungs add and remove many chemical messengers from the blood as it flows through the pulmonary capillary bed . The fine capillaries also trap blood clots that have formed in systemic veins.

Gas exchange The major function of the respiratory system is gas exchange. As gas exchange occurs, the acid-base balance of the body is maintained as part of homeostasis.

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This chart on page 1, shows the parts associated with the RESPIRATORY SYSTEM. Breathing is the process by which oxygen in the air is brought into the lungs and into close contact with the blood. which absorbs it and carries it to all parts of the body. At the same time the blood gives up waste matter (carbon dioxide), which is carried out of the lungs with the air breathed out.

Important Structures and Terminology The SINUSES are hollow spaces in the bones of the head. Small openings connect them to the nasal cavity. The functions that they serve are not clearly understood, but include helping to regulate the temperature and humidity of air breathed in, as well as to lighten the bone structure of the head and to give resonance to the voice.

The NASAL CAVITY (nose) is the preferred entrance for outside air into the respiratory system. The hairs that line the inside wall are part of the air-cleansing system.

Air also enters through the ORAL CAVITY (mouth), especially in people who have a mouth-breathing habit or whose nasal passages may be temporarily obstructed, as by a cold virus.

The ADENOIDS are overgrown lymph tissue at the top of the throat. When they inter-fere with breathing, they are generally removed. The lymph system, consisting of nodes (knots of cells) and connecting vessels, which carry fluid throughout the body. This sys-tem helps resist body infection by filtering out foreign matter, including germs, and pro-ducing cells (lymphocytes) to fight them.

The TONSILS are lymph nodes in the wall of the pharynx that often become infected. They are an unimportant part of the germ-fighting system of the body. When infected, they are generally removed.

The PHARYNX (throat) collects incoming air from the nose and passes it downward to the trachea (windpipe).

The EPIGLOTTIS is a flap of tissue that guards the entrance to the trachea, closing when anything is swallowed that should go into the esophagus and stomach. The epiglot-tis is only activated when we swallow.

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The nasal cavity, oral cavity, and pharynx make up the upper respiratory tract:

The LARYNX (voice box) contains the vocal cords. It is the place where moving air be-ing breathed in and out creates voice sounds.

The ESOPHAGUS is the passage leading from the mouth and throat to the stomach. It plays no bearing on the respiratory system.

The TRACHEA (windpipe) is the passage leading from the pharynx to the lungs.

The RIBS are bones supporting and protecting the chest cavity. They move to a limited degree, helping the lungs to expand and contract.

The trachea divides into the two main BRONCHI (tubes), one for each lung. Each is individually called a bronchus. These, in turn, subdivide further into bronchioles.

The RIGHT LUNG is divided into three LOBES, or sections. The left lung is divided into two LOBES.

The PLEURA are the two membranes, that surround each lobe of the lungs and separate the lungs from the chest wall.

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The bronchial tubes are lined with CILIA (like very small hairs) that have a wave-like motion. This motion carries MUCUS (sticky phlegm or liquid) upward and out into the throat, where it is either coughed up or swallowed. The mucus catches and holds much of the dust, germs, and other unwanted matter that has invaded the lungs and thus gets rid of it.

The DIAPHRAGM is the strong wall of muscle that separates the chest cavity from the abdominal cavity. By moving downward, it creates suction to draw in air and expand the lungs.

The smallest subdivisions of the bronchi are called BRONCHIOLES, at the end of which are the alveoli (plural of alveolus).

The ALVEOLI are the very small air sacs that are the destination of air breathed in. The CAPILLARIES are blood vessels that are imbedded in the walls of the alveoli. Blood passes through the capillaries, brought to them by the PULMONARY ARTERY and taken away by the PULMONARY VEIN. While in the capillaries the blood discharges carbon dioxide into the alveoli and takes up oxygen from the air in the alveoli.

The larynx, trachea, bronchi, bronchioles, and alveoli make up what is called the lower respiratory tract:

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OUTLINE NOTES

- we ventilate or breathe an average of 10-18 times per minute.

- the purpose is to perform gas exchange

- when we inhale the diaphragm contracts downward so air can move into the body

- air passes in through either the nasal or oral cavity

- the nasal cavity is the preferred pathway because it can filter, moisten, and warm incoming air which prepares it for the lungs.

- oxygen then moves over the pharynx and downward past the larynx into the trachea.

- if we swallow the epiglottis (which covers the opening to the larynx) closes off the trachea to direct the contents of what we swallow down the esophagus instead so we do not block the airway and choke.

- the trachea is lined with rings of cartilage so that is has a constant diameter.

- the trachea is medial, while the lungs are lateral.

- the trachea divides into two branches called bronchi which lead into the lungs.

- the bronchi further divide into smaller and smaller pathways called bronchioles.

- the bronchioles lead to microscopic air sacs called alveoli.

- we have millions of alveoli in our lungs, each of which are designed to perform gas exchange.

- surrounding every single alveoli are microscopic blood vessels called capillaries.

- these pulmonary capillaries allow for an exchange of material.

- oxygen and carbon dioxide always move from areas of high concentration to areas of low concentration which is called diffusion.

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- oxygen passes into the blood, while carbon dioxide passes out of the blood.

- the respiratory center of the brain monitors the amounts of oxygen and carbon dioxide in the blood.

- high amounts of carbon dioxide makes the blood acidic thusly lowering the pH, which can result in acidosis.

- the brain in this case will speed up ventilation to bring more oxygen into the body thusly rating the pH back to normal levels. (negative feedback)

- when levels are normal ventilation slows.

- our ventilation rate also changes with activities we perform, the more demand on our cells the more oxygen is required the faster we ventilate and at rest in bed the slower we ventilate.

- emotions can also effect our ventilation rate; when excited we breathe faster or hyperventilate in extreme cases.

- environmental conditions can also impact our ventilation, for example; high altitudes have a lesser oxygen supply and can effect how we get oxygen into our body. When there is a below normal amount of oxygen in the atmosphere this is termed hypoxia.

- asthma is a condition where an irritant in the environment can cause the muscular linings of the airways, specifically the bronchioles to constrict, thusly restricting breathing. This is alleviated with steroid inhalers.

- restricted abilities to breathe can cause high carbon dioxide levels in the blood and this is referred to as hypercapnia.

- smoking and environmental pollution can damage the cells lining the respiratory tract which can lead to serious conditions like emphysema (alveolar destruction), or lung cancer.

- lung cancer is a deadly form of cancer because lung cells become mutated and no longer serve in the function of gas exchange. These cells proliferate and metastasize often before detection.

- what makes lung cancer so deadly is the fact that many people are not diagnosed at an early stage because most patients are asymptomatic at early onset.

- common symptoms of lung cancer include; chest pain, difficulty breathing, wheezing, nagging cough (for a pro-longed period of time), coughing up blood, weight loss for no reason, excessive fatigue among others.

- tumors in the lung can be seen with x-rays, ct scans, and pet-scans.

- early detection is key.

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The Role of Tissues

- glandular epithelium produces mucus throughout the tract to clean and moisten the air.

- cover and lining epithelium provides protection of all the associated structures.

- muscle tissue controls the movement of air into and out of the lungs via the diaphragm and intercostal muscles.

- nerve tissue monitors oxygen levels and stimulates muscles to control ventilation patterns.

- connective tissues like cartilage serve to protect and maintain the trachea, while blood flows through the lungs so gas exchange can occur.

Assessment

1. The purpose of the respiratory system is to

a. pump blood.

b. perform gas exchange.

c. kill antigens which enter the body through openings.

d. filter the blood.

2. The upper respiratory tract consists of

a. trachea, bronchi, bronchioles, and alveoli.

b. nasal and oral cavities only.

c. nasal cavity, oral cavity, and pharynx.

d. just the nasal cavity.

3. What is the preferred entrance for air into the body?

a. oral cavity

b. pharynx

c. epiglottis

d. nasal cavity

4. The flap of tissue that directs food, water, and incoming air into the appropriate pas

sage way is the

a. esophagus.

b. epiglottis.

c. uvula.

d. tongue.

5. The throat is also known as the

a. pharynx.

b. larynx.

c. trachea.

d. bronchi.

6. The voice-box is also known as the

a. pharynx.

b. larynx.

c. trachea.

d. esophagus.

7. The windpipe is also known as the

a. pharynx.

b. larynx.

c. trachea.

d. esophagus.

8. Which of the following structures play no role on the respiratory process?

a. pharynx

b. bronchioles

c. alveoli

d. esophagus

9. Gas exchange occurs between the alveoli and pulmonary capillaries as oxygen and

carbon dioxide move from high to low concentrations inside the body. This is called

a. osmosis.

b. diffusion.

c. facilitated diffusion.

d. active transport.

10. If you have an infection in your upper respiratory tract, which of the following

structures may be involved?

a. nasal cavity

b. lungs

c. bronchioles

d. alveoli

11. The respiratory rate in humans is influenced by

a. emotions.

b. the brain.

c. blood pH.

d. All the above.

12. The structure of the respiratory tract which covers the opening to the larynx is the

a. epiglottis.

b. trachea.

c. bronchi.

d. bronchiole.

13. The place in the lungs where gas exchange actually occurs is at the

a. bronchi.

b. bronchioles.

c. respiratory bronchioles.

d. alveolar ducts and alveoli.

14. Internal respiration is gas exchange between

a. lungs and the atmosphere.

b. lungs and the tissue cells.

c. lungs and pulmonary capillaries.

d. systemic capillaries and tissues.

15. Hypercapnea refers to

a. elevated oxygen in the blood.

b. elevated carbon dioxide in the blood.

c. elevated calcium levels in the blood.

d. decreased sulfur in the blood.

16. When carbon dioxide levels in the blood increase,

a. pH of the blood increases.

b. the blood becomes more acidic.

c. the blood becomes more basic.

d. the blood is in a positive feedback loop.

17. Sudden constriction of the airways due to an environmental influence is called

a. asthma.

b hyperventilation.

c. apnea.

d. hypocapnea.

18. A below normal amount of oxygen available in the atmosphere can cause a condition

in the body known as

a. apnea.

b. hyperventilation.

c. lung cancer.

d. hypoxea.

19. The right lung possesses

a. 1 lobe.

b. 2 lobes.

c. 3 lobes.

d. 4 lobes.

20. List the 7 structures that air can or may pass over on its way into the lungs.

21. The lungs are positioned _____________________, while the trachea is medial.

22. Explain why exercise would cause us to ventilate at a much faster rate.

23. Use the article on the coronavirus and explain how it affects the respiratory system in

25 to 50 words.

24. How can you protect your respiratory system from the virus?

25. What are the severe complications from the virus?