Kaplan MCAT Biology Chapter 6: The Respiratory System

Thoracic cavity

Location of the lungs and heart

Nares

Entry point for air in the respiratory tract located in the nose

AKA nostrils

Vibrissae

AKA nasal hairs

Filters air within nasal cavity

Nasal cavity

Area just behind the nostrils

Removes dirt and particulate matter from the air by filtering with mucous membranes and vibrissae

Warms and humidifies air

Pharynx

Resides behind the nasal cavity and the back of the mouth

Common pathway for air and food

Larynx

Below the pharynx

Pathway for air only

Contains vocal cords

Glottis

Opening of the larynx

Epiglottis

A flap of cartilage that covers the glottis during swallowing so that food doesn't go into the trachea

Trachea

• what is it

• what does it contain

Below the larynx

the windpipe

Composed of about 20 rings of cartilage

Lined with ciliated epithelial cells

Bronchi

Trachea divides into these cartaliginous tubes

Lined with ciliated epithelial cells

Bronchioles

• what is it

• what does it contain

In the lungs

Bronchi divide into these

Not cartaliginous

Alveoli

Tiny balloon-like structures in the lungs

Site of gas exchange

Surfactant

Coats each alveolus to relieve surface tension and prevent alveolus from collapsing on itself

Bronchioles and alveoli (purpose)

Allow for exceptionally large surface area for gas exchange (100 meters squared)

Chest wall

Forms the outside of the thoracic cavity

Pleurae

Membranous sacs that surround each lung

Form closed sacs against which the lungs expand

Visceral pleura

Surface of pleura adjacent to the lung

Parietal pleura

Surface of pleura that is far away from the lung

Diaphragm

• what is it

• what controls it

Thin, muscular structure that divides the thoracic cavity from the abdominal cavity

Under somatic control

Chest wall, back and neck muscles

May contribute to breathing, especially when breathing is labored

Intrapleural space

Space within the pleura

External intercostal muscles

• where are they

• what are they used for

• how are they used

One of the layers of muscles between the ribs that plays a role in INHALATION

Contract to expand the thoracic cavity alongside the diaphragm which also contracts

Relax to contract the thoracic cavity

Intrathoracic volume

Volume of the chest cavity

Inhalation

• what is inhilation

• what happens to the intrathoracic vlume

• what happens to the pressure and volume of the intrapleural space

• describe what happens next in the process of inhalation and what is the primary mechanism referred to as

-When air enters the lungs

-it increases

-it increases in volume but decreases in pressure

-The gas in the lungs is initially at atmospheric pressure, which is now higher than the pressure in the intrapleural space.

The lungs will therefore expand into the intrapleural space, and the pressure in the lungs will drop.

Air will then be sucked in from a higher-pressure environment—the outside world.

This mechanism is referred to as negative-pressure breathing because the driving force is the lower (relatively negative) pressure in the intrapleural space compared with the lungs.

Negative-pressure breathing

Driving force for inhalation is the negative pressure in the intrapleural space compared to the lungs. When the diaphragm contracts, increase in volume lowers pressure, so air goes from high to low pressure

Exhalation

• what is it by definition

• how does it differ from inhalation

• how it operate

When air is pushed out of the lungs

Does not have to be an active process because muscles recoil

literally exact opposite process:

• As the diaphragm and external intercostals relax, the chest cavity decreases in volume.

• What will happen to pressure in the intrapleural space? It will go up, again explained by Boyle’s law.

• Now pressure in the intrapleural space is higher than in the lungs, which is still at atmospheric pressure.

• Thus, air will be pushed out, resulting in exhalation. During active tasks, we can speed this process up by using the internal intercostal muscles and abdominal muscles, which oppose the external intercostals and pull the rib cage down.

• This actively decreases the volume of the thoracic cavity. Finally, recall that surfactant prevents the complete collapse of the alveoli during exhalation by reducing surface tension at the alveolar surface.

Internal intercostal muscles

Layer of muscles beneath the ribs

Oppose the external intercostals and pull the rib cage down

Decrease volume of thoracic cavity to help with exhalation

Abdominal muscles

Can help with exhalation if needed

Spirometer

• what does it do]

• what are its limitations

Helps assess lung capacities and volumes

Cannot measure residual volume- amount of air remaining in the lungs are exhalation

Total lung capacity (TLC)

The maximum volume of air in the lungs when one inhales completely

Residual volume (RV)

The minimum volume of air in the lungs when one exhales completely

Cannot be measured by a spirometer

Vital capacity (VC) and equation

The difference between the minimum and maximum volume of air in the lungs

Total Lung Capacity - Residual Volume

(TLC - RV)

Tidal volume (TV)

The volume of air inhaled or exhaled in a normal breath

Expiratory reserve volume (ERV)

The volume of additional air that can be forcibly exhaled after a normal exhalation

Inspiratory reserve volume (IRV)

The volume of additional air that can be forcibly inhaled after a normal inhalation

Medulla oblongata

• what does it do

• what structure does it contain

Structure in the hindbrain that regulates ventilation

Ventilation center

• what is it/ what does it do

• what structure is contained here

• Collection of neurons in the medulla oblongata that fire rhythmically to cause regular contraction of respiratory muscles

• chemoceptor

Chemoreceptors in ventilation center

Ventilation center neurons use these to detect carbon dioxide concentration and act accordingly

Hypercarbia or hypercapnia

• what is it

• what does it cause

Too much CO2 in the blood

Causes respiratory rate to increase so more CO2 will be exhaled

Respiratory rate

Rate at which one breathes

Hypoxia

Low oxygen concentration in the blood

Ventilation center neurons respond to this as well but only when oxygen is very low in the blood

Cerebrum

The structure through which we can control our breathing

Overridden by medulla oblongata when we breathe too little for a time

Hypoventilation

Too little breathing

Causes CO2 concentration in blood to increase, causing pH to go down

Hyperventilation

• review bicarbonate buffer system and make a separate flashcard

Too much breathing

Causes CO2 concentration to decrease, making the bicarbonate buffer system shift to the left to compensate, causing alkalemia

Pulmonary arteries

alveloi are surrounded by capillaries

capillaries bring deoxygenated blood from the pulmonary arterier

the pulmonary arteries emerge from the right ventricle of the heart

Pulmonary veins

Bring newly oxygenated blood to the left atrium of the heart

1. Identify and describe the driving force for gas exchange in the aveoli

How would our respiratory systems adjust if we moved to higher altitudes where less oxygen is available?

1. The driving force for gas exchange is the pressure differential of the gases.

   When it initially arrives at the alveoli, blood has a relatively low partial pressure of oxygen and a relatively high partial pressure of carbon dioxide, facilitating transfer of each down its respective concentration gradient.

   O₂ in the alveoli flows down its partial pressure gradient from the alveoli into the pulmonary capillaries, where it can bind to hemoglobin for transport. Meanwhile, CO₂ flows down its partial pressure gradient from the capillaries into the alveoli for expiration. no energy needed for this gas transfer at the alveoli.

2.First, we would breathe more rapidly to try to avoid hypoxia; second, the binding dynamics of hemoglobin to oxygen would be altered to facilitate the unloading of oxygen at the tissues.

the natural response of hemoglobin to the decreased carbon dioxide concentration in the environment would actually be to decrease the unloading of oxygen to tissues, so other mechanisms can counteract and override this phenomenon to allow adequate delivery of oxygen.

In the short term, the body can make more red blood cells to ensure the adequate delivery of oxygen. In the long term, the body could develop more blood vessels (vascularization), which would facilitate the distribution of oxygen to tissues.

Thermoregulation

• what is it

• through what mechanisms does it occur

• describe the mechanisms

• other mechanisms of heat regulation

• the regulation of body temperature

• vasodilation and vasoconstriction

• As capillaries expand, more blood can pass through these vessels, and a larger amount of thermal energy can be dissipated. As capillaries contract, less blood can pass through them, conserving thermal energy

• While these capillary beds provide a mechanism for thermoregulation, humans predominantly regulate temperature using capillaries and sweat glands in the skin, or rapid muscle contraction (shivering). The respiratory system can also transfer heat to the environment through evaporation of water in mucous secretions. Other animals, such as dogs, take advantage of this cooling mechanism by panting.

Vasodilation

Expansion of capillaries in the nasal cavity and trachea to dissipate thermal energy

Vasoconstriction

Contraction of capillaries in the nasal cavity and trachea to conserve thermal energy

how does the respiratory system fight off pathogens

The nasal cavity also contains an enzyme called lysozyme. Also found in tears and saliva, lysozyme is able to attack the peptidoglycan walls of gram-positive bacteria.

The internal airways are lined with mucus, which traps particulate matter and larger invaders. Underlying cilia then propel the mucus up the respiratory tract to the oral cavity, where it can be expelled or swallowed; this mechanism is called the mucociliary escalator.

Macrophages can engulf and digest pathogens and signal to the rest of the immune system that there is an invader. Mucosal surfaces also contain IgA antibodies that help to protect against pathogens that contact the mucous membranes.

Finally, mast cells also populate the lungs. These cells have preformed antibodies on their surfaces. When the right substance attaches to the antibody, the mast cell releases inflammatory chemicals into the surrounding area to promote an immune response. Unfortunately, these antibodies are often reactive to substances such as pollen and molds, so mast cells also provide the inflammatory chemicals that mediate allergic reactions.

Mucociliary escalator

Internal airways are lined with mucus which traps particulate matter and larger invaders

Underlying cilia propel the mucus up the respiratory tract to the oral cavity, where it is expelled or swallowed

Macrophages

Seen in the lungs, especially alvoeli. Engulf and digest pathogens and signal to the rest of the immune system that there is an invader

IgA antibodies

Contained on mucosal surfaces

Help protect against pathogens that contact mucous membranes

Mast cells

can also be seen in lungs. Release inflammatory chemicals to promote an immune response upon contact with an antigen

Can Cause allergic reactions

what does the bicarbonate buffer system do

what is the equation

plays a role in pH balance in blood -

CO2 (g) + H2O (l) <-> H2CO3 (aq) <-> HCO3- (aq) + H+ (aq)

Physiological pH

7.35-7.45

what happens when ph is too low

pH of blood is too low and H+ concentration is high- acidemia

acid-sensing chemoreceptors just outside the blood-brain barrier send signals to the brain to increase the respiratory rate.

Further, an increasing hydrogen ion concentration will cause a shift in the bicarbonate buffer system, generating additional carbon dioxide.

Effects of acidemia

CO2 concentration increases due to excess of H+

Ventilation center senses this and increases respiratory rate to blow off more CO2

Decreased CO2 pushes bicarbonate buffer equation to left until H+ concentration is normal again

As the respiratory rate increases, more carbon dioxide is blown off. This will also push the buffer equation to the left, but notice the difference: the shift to the left in the previous paragraph was caused by an increase in hydrogen ion concentration, which elevated the concentration of carbon dioxide. Here, the removal of carbon dioxide causes a shift to the left that allows the hydrogen ion concentration to drop back to normal.

what happens when pH is too high

pH of blood is too high- alkalemia

then the body will seek to increase acidity.

If the respiratory rate is slowed, then more carbon dioxide will be retained, shifting the buffer equation to the right and producing more hydrogen ions and bicarbonate ions. This results in a lower pH.

Effects of alkalemia

Respiratory rate is slowed to increase CO2 concentration and shift bicarbonate buffer equation to right to decrease pH

If H+ is an acid and HCO⁻3 is a base, then why doesn't increasing both of them maintain a constant pH?

The reason is because H+ is a strong acid, while HCO⁻3 is a weak base. (buffer system!)

Difference between lung response and kidney response to pH imbalances

Lung response is faster

Kidney response is slower, more long-term