Respiratory System

Respiratory System

8.1 Respiratory Structures • Air flows through a sequence of structures from the nose to the lungs allowing for the exchange of oxygen-poor air for oxygen-rich air • The nostrils are one of the major entryways into the body lined with a mucosal cell layer, which secretes mucus • They are also equipped with nose hairs

Combined, these specializations filter and trap particulate matter • A rich blood supply in the sinuses allows the presence of large numbers of WBC, which offer another layer of protection

The pharynx is another common passageway • When the epiglottis is open, air is able to pass through the larynxand into the trachea • The larynx contains the vocalcords, two tendons that adjust the pitch of sounds according to how taut they are

The trachea conducts air into the bronchi and the bronchi pass the air along into the increasingly smaller branches of the air passageways called bronchioles • The continual branching of the bronchioles forms the bronchioletree • Each of these passageways contain C-shaped rings of cartilage to prevent collapse

The bronchioles eventually end at the alveoli • The alveoli are the blind sac-like endings of the bronchioles • The millions of alveoli provides a great deal of surface area for the diffusion of gases • They are specialized in a number of ways:

Alveolar walls are only one cell thick which aids the diffusion of gases • They have a coating of lipoproteins over their inner surface, which helps maintain surfacetension,preventing them from collapsing and sticking together during exhalation

They are equipped with stretch receptors which send a signal to the medulla oblongata when the alveoli are full triggering exhalation • The alveolar surfaces are highly vascularized by the pulmonary capillaries which ensures maximum diffusion of gases and helps ensure that the alveoli do not dry out (prevent the efficient diffusion of gases)

8.2 Mechanics of Breathing • The respiratory center is located in the medulla oblongata • It is sensitive to concentrations of CO2 and H+ ions in blood plasma • Both are toxins resulting from cell metabolism and need to be excreted

When their concentrations get to a critical level, the medulla oblongata sends nerve impulses to the diaphragm and the intercostalmuscles (between ribs) to initiate contraction • When the diaphragm contracts, it moves down; when the intercostal muscles contract, they move the rib cage up and out

The combined effect of these motions is to increase the volume of the thoraciccavity • This creates a negative pressure (vacuum effect) in the cavity and air is drawn in through the trachea • Inhalation is an active process requiring ATP for muscle contractions

The surfaces of the lungs are covered with a pleural membrane; a second outer pleural membrane coats the inside of the thoracic cavity • This double membrane not only allows the surface of the lungs to slide over the body wall easily (without abrasion) but also seals off the thoracic cavity

A puncture to the chest wall will result in air being drawn in through the puncture wound, putting pressure on the surface of the lung causing it to collapse • This is called pneumothorax

When the stretch receptors on the surface of the alveoli detect that the alveoli are stretched open, they respond by signaling the medulla oblongata to stop contracting the diaphragm and intercostal muscles • When the diaphragm relaxes, it bows upwards; when the rib muscles relax, gravity pulls the rib cage down and in • These actions put pressure on the expanded thoracic cavity, which causes exhalation

The aortic arch and the carotid arteries contain chemorecepters that are sensitive to the oxygen content in blood • If it is critically low, they will help initiate the inhalation response (this is a secondary condition)

VIDEO

Review • The medulla oblongata controls the breathing rate by monitoring the concentration of • Oxygen • Carbon dioxide • Oxyhemoglobin • carbaminohemoglobin

The medulla oblongata controls the breathing rate by monitoring the concentration of • Oxygen • Carbon dioxide • Oxyhemoglobin • carbaminohemoglobin

The breathing center is located in the • thalamus • Cerebrum • Hypothalamus • Medulla oblongata

Which of the following correctly describes the muscle activity during exhalation? • Diaphragm relaxes; intercostal muscles relax • Diaphragm relaxes; intercostal muscles contracts • Diaphragm contracts; intercostal muscles relax • Diaphragm contracts; intercostal muscles contracts

Which of the following sequences correctly describes the passage of air into the body? • Pharynx, larynx, trachea, bronchioles, alveoli, bronchi • Pharynx, larynx, trachea , bronchi, bronchioles, alveoli • Pharynx, trachea, bronchi, larynx, bronchioles, alveoli • Alveoli , bronchioles, bronchi, trachea, larynx, Pharynx

8.3 Conditions of Inhaled Air • The air is cleaned by the nose hairs and mucus • The cilia and mucosal lining along the trachea and bronchi catches any other material other than gases • The cilia are in constant motion beating the debris-laden mucus up to the pharynx where it is swallowed or spit out • Temperature of air becomes 37o by the time it reaches alveoli

Inhaled air becomes saturated with water (vapor) as it passes over the mucous-lined passageways

8.4 Gas Exchange • During respiration, gases are exchanged between tissues in two places • Between the air and blood plasma at the alveoli (external respiration) • Between the blood plasma and the fluid in the tissue spaces (internal respiration)

External Respiration • Diffusion of oxygen into the pulmonary capillaries and the diffusion of carbon dioxide into the alveoli • The approximate conditions in the blood at the alveoli are 37o C with a pH of about 7.4 • Under these conditions hemoglobin is free to combine with oxygen

A single hemoglobin molecule in a red blood cell has four bonding sites for oxygen • When the blood is leaving the alveoli, 99% of these bonding sites are occupied • The combination of hemoglobin and oxygen is called oxyhemoglobin (HbO2) • Hemoglobin transports the oxygen to the tissues where internal respiration occurs

Internal Respiration • The blood is slightly warmer (about 38o C) and has a pH of about 7.35 due to the effects of cell metabolism • Hemoglobin is very sensitive to this change and readily releases the oxygen as the blood enters capillary beds • Oxygen diffuses into the tissue spaces along with water that is forced from the plasma

At the venule side of the capillary bed, when water is drawn back into the blood by osmotic pressure, CO2 and other metabolic wastes from cellular respiration also enter the blood • At these temperature and pH conditions most of the CO2 reacts with water in the plasma under the influence of the RBC enzyme carbonic anhydrase

The products (bicarbonate ions and hydrogen ions) have different fates • Bicarbonate ions are one of the most widely known buffers in the human body, they are transported freely in blood plasma • In contrast H+ would cause a decrease in pH if transported freely in blood plasma, so it bonds onto Hb and is transported as reduced hemoglobin (HHb)

The rest of the CO2 is transported in either of two ways: • Bond to Hb and transported as carbaminohemoglobin (HbCO2) • Very little is transported as a dissolved gas in the plasma

At the alveoli the temperature is slightly lowered and the pH is slightly higher than in the tissue spaces • These conditions result in the release of the CO2 and hydrogen from Hb • The enzyme carbonic anhydrase catalyses the reverse of the reaction that it did before

The CO2 released from this reaction as well as that from HbCO2 and the small amount that was transported dissolved in plasma is available to diffuse into the alveoli and be exhaled (part of external respiration) • Some of the water remains as a component of plasma and some is exhaled as vapor • Hb is once again free to bond to oxygen and the cycle repeats itself

Review • Where does HHb get converted to HbO2? • Liver cells • Tissue capillaries • Heart ventricles • Lung capillaries

Where does HHb get converted to HBO2? • Liver cells • Tissue capillaries • Heart ventricles • Lung capillaries

HbO2 releases O2 in the same region as • HCO3- is produced • NH3 is converted to urea • CO2 is removed from plasma • Blood pressure drops below 10mmHg

As the plasma temperature decreases, the amount of CO2 carried by hemoglobin will • Decrease • Remain the same • Increase slightly • Become 99 to 100%

The alveolar walls are moist so that • Bacteria can be trapped • Water vapor can be inhaled • Water vapor can be exhaled • Gases can move freely through the membranes

http://www.youtube.com/watch?v=HiT621PrrO0

Respiratory System