Chapter 15 Respiratory System

What are the main muscles of inspiration? How do they cause air to be drawn into the lungs?

Diaphragm and external intercostal muscles. The normally dome shaped diaphragm flattens caudally, making the thorax area bigger. The intercostal muscles are oriented in an oblique direction, and when they contract, they also increase the space inside the thorax by lifting the rib cage.

Why do animals cough, sneeze, yawn, sigh, and hiccup?

These are reflexes and are temporary interruptions in the breathing patterns. Coughs and sneezes are due to irritation in the bronchi or trachea and nasal passages, respectively. Sighs expand the lungs slightly and may increase the amount of oxygen intake. Hiccups are spasmodic contractions of the diaphragm followed by sudden closure of the glottis.

What is the primary function of the respiratory system?

To bring oxygen into the body and take carbon dioxide (a waste product of energy production) out of the body.

How do the physical characteristics of the alveoli and the capillaries that surround them facilitate the exchange of gases between the air in the alveoli and the blood in the capillaries?

The wall of each alveolus is extremely thin, and the capillaries which surround the alveoli also have very thin walls, so that exchange (or diffusion) of gases is made easier.

What is the difference between breathing and respiration?

Breathing is the mechanical action of bringing air in to and out of lungs. Respiration is the exchange of oxygen and carbon dioxide by diffusion across the lung cells and then the rest of the body's cells.

How do the pharynx and larynx work together to keep swallowed material from entering the trachea? What role does the epiglottis play in that process?

Breathing stops for a moment, the muscles of the larynx pull it cranially, and the epiglottis covers the opening into the respiratory passage (the larynx).

Why are the hyaline cartilage rings important to the function of the trachea?

Inhalation creates a partial vacuum in the trachea, and the trachea would partially collapse (and not allow enough air in) if the cartilage weren't there to keep the structure open.

What are the main muscles of expiration? How do they push air out of the lungs?

Internal intercostal muscles and abdominal muscles. Internal intercostal muscle contraction makes the ribcage move caudally, making the space in the thorax smaller. Contraction of the abdominal muscles pushes abdominal organs against the caudal surface of the diaphragm, helping the diaphragm to regain its dome-like shape.

Why is negative intrathoracic pressure important to breathing? What happens if it is lost?

It causes a partial vacuum in the thorax compared to the outside atmosphere, and therefore the partial vacuum makes it easier for air to be pulled into the lungs. If it is lost, and free air is in the thorax, the pressures inside and outside the thorax equalize, making the lung collapse (like having pressure on the lung instead of vacuum), so it is difficult for breathing. Free air present in the thorax is call "pneumothorax."

Describe the basic structure of the bronchial tree in the lung

It is basically an upside down tree that starts with one trunk (trachea) and 2 very large branches (bifurcation of the trachea to the right and left sides).

By what mechanisms is inhaled air warmed, humidified, and filtered as it passes through the nasal passages? How do the turbinates aid these processes?

Nasal turbinates increase surface area within the nasal passageway, so all of the functions in the passageway are performed better and more efficiently. Large blood vessels just under the mucosa of the nasal passages help to warm incoming air. Mucus and other fluids on the surface of the nasal passage humidify incoming air. The mucus layer, the cilia just below the mucus, and the twisting and turning of the turbinates combine to capture dust and other foreign particles. The cilia also help make particle head toward the throat where they are swallowed rather than inhaled into the lungs.

What are the secondary functions of the respiratory system?

Production of vocal sounds, regulating body temperature, regulating pH of the body, and aiding in the olfactory sense.

Which main pulmonary blood vessel contains bright red, high-oxygen blood: the pulmonary artery or the pulmonary vein?

Pulmonary artery (remember is "away from the heart") - dark red low oxygen blood; while pulmonary vein (toward the left atrium of the heart after oxygenation in the lungs) is bright red and highly oxygenated.

When a piece of lung from a dead newborn animal is dropped into water, it sinks. What conclusion can be drawn about whether the newborn animal was born dead and never breathed or took some breaths before dying?

Since the lung sank, it means that it was full of water and therefore the animal never took a breath. If it had breathed even for a short time, the lungs would have contained some air and would have floated in water.

Why are the smooth pleural surfaces important to the process of breathing?

Since they are smooth and slightly lubricated, the lungs slide easily along the lining of the pleura when they are expanded during breathing. Makes it easier for the animal to breathe!

Describe how the mechanical respiratory control system maintains a normal, rhythmic, resting breathing pattern.

Stretch receptors in the lungs detect when lungs are inflated and deflated to the right amount. They send nerve impulses to the respiratory center of the brain (the medulla oblongata in the brain stem), which then sends out nerve impulses to either stop inhalation or start inhalation.

When does the chemical respiratory control system kick in and override the mechanical control system?

The chemical system makes adjustments to the mechanical system based on the parameters detected in arterial blood as described in #2 above. This happens to maintain homeostasis, or balance of pH and gases in the blood so that cells in the body stay healthy.

How is the larynx involved in the straining process that aids functions such as defecation?

The closure of the glottis allows the pressure exerted by abdominal muscles to work; otherwise contracting the abdominal muscles would lead to exhalation of air out of the lungs and no pressure on the abdomen as needed.

Describe the basic processes by which oxygen moves from the air in the alveoli into the blood in the alveolar capillaries and how carbon dioxide moves in the other direction.

The gases move across the alveoli by diffusion, the movement of particles from a high concentration to low concentration. Atmospheric oxygen is about 21%, while oxygen-poor blood is about 3%, so oxygen easily diffuses from air into the blood near the alveoli. The carbon-dioxide-rich blood coming from tissues diffuses from its high concentration to low concentration in the air.

What is the hilus of the lung and why is it important?

The hilus of a lung is an area on the medial aspect in which air, blood, lymph, and nerves enter and leave the lung - it is also the only area which keeps lungs fastened to the thorax.

What is the basic difference between the functions of the mechanical and chemical respiratory control systems?

The mechanical system sets a "baseline" respiratory rate and depth. However, the chemical system makes adjustments to the mechanical system based on several parameters detected in arterial blood. These parameters include the carbon dioxide concentration, the pH, and the oxygen content of arterial blood.

What is the mediastinum and what organs and structures are located there?

The mediastinum is the area of the thorax between the lungs - the heart and other structures such as trachea, esophagus, blood vessels, nerves and lymphatic tissue and vessels are located there.

Describe how the respiratory and digestive passageways "switch places" in the pharynx.

The throat or pharynx is a common passageway for both air and food. At the rostral end, the palate divides the pharynx into a dorsal nasal passageway (respiratory passageway) and a ventral digestive passageway (the mouth or oropharynx). However, at the caudal end of the pharynx, the digestive pathway(esophagus) becomes dorsal to the respiratory pathway (larynx and trachea).