Respiratory System

nose

During breathing, air enters the nose by passing through the nares. The interior of the nose consists of the nasal cavity which is lined by mucosa (respiratory mucosa). The mucosa rests on a network of veins that warm the air as it flows past.

How is oxygen carried in the bloodstream?

Most attach to hemoglobin molecules inside RBCs to form oxyhemoglobin. A very small amount is carried dissolved in the plasma.

How is carbon dioxide carried in the bloodstream?

Most is transported in plasma as the bicarbonate ion. A smaller amount (20-30% of the transported CO2) is carried inside RBCs, bound to hemoglobin.

dead space volume

Much of the air that enters the respiratory tract remains in the conducting zone passageways and never reaches the alveoli.

What part of the brain controls breathing?

Neural centers that control respiratory rhythm and depth are located mainly in the medulla oblongata and pons.

respiratory gas transport

Oxygen and carbon dioxide must be transported to and from the lungs and tissue cells of the body via the bloodstream.

vocal folds (true vocal cords)

Part of the mucous membrane (of the larynx) forms a pair of folds which vibrate with expelled air so we can speak.

epiglottis

Protects the superior opening of the larynx; keeps food from entering the windpipe and the lungs.

Why is residual volume important?

RV allows gas exchanges to go on continuously even between breaths and helps to keep the alveoli open (inflated).

alveoli

air sacs of the lungs in which the exchange of oxygen and carbon dioxide takes place

tidal volume (TV)

amount of air per breath in relaxation ~ 500 ml

expiratory reserve volume (ERV)

amount of air that can be forcibly exhaled after a tidal expiration ~ 1200 ml

inspiratory reserve volume (IRV)

amount of air that can be taken in forcibly over the tidal volume ~ 2100 to 3200 ml

What two zones is the respiratory system divided into?

conducting zone (nose, pharynx, larynx, trachea, bronchi, and bronchioles) and respiratory zone

alveolar pores

connect neighboring air sacs and provide alternative routes for air to reach alveoli whose feeder bronchioles have been clogged by mucus or otherwise blocked

Which bronchi is a more common site for an inhaled foreign object to become lodged?

right main bronchus

What factors affect respiratory capacity?

size, sex, age, physical condition

terminal bronchioles

smallest bronchioles (no cartilage in their walls); lead into the respiratory zone structures, even smaller conduits that eventually terminate in alveoli

functions of the respiratory system

supplying the body with oxygen and disposing of carbon dioxide

respiratory (bronchial) tree

the continuous branching of the respiratory passageways in the lungs

conchae

3 mucosa-covered projections (lobes) which greatly increase the surface area of the mucosa exposed to the air. They also increase the air turbulence in the nasal cavity. As the air swirls through twists and turns, inhaled particles are deflected onto the mucus-coated surfaces, where they are trapped.

internal respiration (blood cell level)

At systemic capillaries, gas exchanges must be made between the blood and tissue cells. Gas exchanges occur between the blood and cells *inside* the body.

thyroid cartilage

Adam's apple; the largest of the hyaline cartilages, shield-shaped

bronchioles

After entering the lungs, the main bronchi subdivide into smaller and smaller branches (secondary and tertiary bronchi, etc.), finally ending in the smallest of the conducting passageways.

residual volume (RV)

After maximum exhalation, 1200 ml of air still remains in the lungs and cannot be voluntarily expelled.

pharynx

Also known as the throat. A muscular passageway (about 5 inches long) for food and air. Air enters the nasopharynx from the nasal cavity and then descends through the oropharynx and laryngopharynx.

larynx

Also known as the voice box. This organ routes air and food into the proper channels and plays a role in speech. Formed by 8 rigid hyaline cartilages and a flap of elastic cartilage, the *epiglottis*. It is also the location of the vocal folds, glottis, and thyroid cartilage.

expiration (exhalation)

As the inspiratory muscles relax and resume their initial resting length, the rib cage descends and the lungs recoil. Both the thoracic and intrapulmonary pressure decrease. As the intrapulmonary pressure decreases, the gases inside the lungs are forced more closely together and the intrapulmonary pressure rises to a point higher than atmospheric pressure. This causes the gases to flow out to equalize the pressure inside and outside the lungs.

alkalosis

Body fluids have excess base (alkali). *Decreased carbon dioxide* (an acid) or increased bicarbonate (a base) levels make the body too alkaline.

pulmonary ventilation

Breathing: the process of air flowing into the lungs during inspiration and out of the lungs during expiration. Air must move into and out of the lungs so that the gases in the alveoli of the lungs are continuously refreshed.

pleura

Each of a pair of serous membranes lining the thorax and enveloping the lungs. They produce pleural fluid, a slippery serous secretion which allows the lungs to glide easily over the thorax wall during breathing movements and causes the two pleural layers to cling together. The pleurae can slide easily from side to side across one another, but they strongly resist being pulled apart. Consequently, the lungs are held tightly to the thorax wall.

respiration

Entails 4 distinct events: 1. Pulmonary ventilation 2. External respiration 3. Respiratory gas transport 4. Internal respiration

acidosis

Excessive blood acidity caused by a loss of bicarbonate from the blood (metabolic acidosis) or by *an overabundance* of acid (*carbon dioxide*) in the blood (a result of poor lung function or slow breathing).

external respiration (lung level)

Exchange of oxygen and carbon dioxide between the pulmonary blood and alveoli must take place. Gas exchanges are being made between the blood and the body *exterior*.

main (primary) bronchi

Formed buy the division of the trachea. Both run obliquely before plunging into the hilum of the lung on its own side. The right one is wider, shorter, and straighter than the left. By the time incoming air reaches the bronchi, it is warm, cleansed of most impurities, and well humidified.

How does gas exchange occur in the alveoli?

Simple diffusion through the respiratory membrane. Oxygen passes from the alveolar air into the capillary blood and carbon dioxide leaves the blood to enter the gas-filled alveoli.

What happens to the trachea if you smoke too much?

Smoking destroys the cilia and mucus will accumulate in the lungs. The mucus is loaded with dust particles, other debris, and bacteria. The presence and buildup of these can cause all sorts of maladies such as cancer.

lungs

Soft and spongy organs that occupy the entire thoracic cavity except the most central area (the mediastinum). The apex is just deep to the clavicle. The broad lung area resting on the diaphragm is the base. Each lung is divided into lobes by fissures (2 lobes on the left, 3 lobes on the right).

functions of nasal mucosa

Sticky mucus moistens the air and traps incoming bacteria and foreign debris, and lysozyme enzymes in the mucus destroy bacteria chemically. The ciliated cells of the nasal mucosa create a gentle current that moves the sheet of contaminated mucus posteriorly toward the pharynx (throat) where it is swallowed and digested by stomach juices.

vital capacity (VC)

TV + IRV + ERV; the total amount of exchangeable air (4800 ml in healthy young men); exhaling as much air as possible after maximum inhalation

trachea

The "windpipe" is rigid because its walls are reinforced with C-shaped rings of hyaline cartilage. These rings serve a double purpose. The open parts of the rings abut the esophagus and allow it to expand anteriorly when we swallow a large piece of food. The solid portions support the trachea walls and keep it open in spite of the pressure changes that occur during breathing.

pulmonary capillaries

The external surfaces of the alveoli are covered with a "cobweb" of capillaries.

inspiration (short)

The movement of air from the external environment, through the air ways, and into the alveoli. Intrapulmonary volume increases, the gases within the lungs spread out to fill the larger space. This results in a decrease in gas pressure in the lungs.

expiration (short)

The movement of air out of the bronchial tubes, through the airways, to the external environment. Intrapulmonary volume decreases, the gases inside the lungs are forced more closely together, and intrapulmonary pressure rises.

intrapleural pressure

The normal pressure within the pleural space is always negative and this is the major factor preventing collapse of the lungs.

pleural space

The potential space between the parietal pleura and the visceral pleura. It is described as "potential" because under normal conditions, the space does not exist since the lungs are held so tightly to the thorax wall.

cellular respiration

The process by which cells use oxygen to produce energy (ATP) from nutrients, and then release waste products such as carbon dioxide.

glottis

The slitlike passageway between the vocal folds.

cilia of the trachea

The trachea is lined with a ciliated mucosa. The cilia beat continuously in a direction opposite to that of the incoming air. They propel mucus, loaded with dust particles and other debris, away from the lungs to the throat, where it can be swallowed or spit out.

What is it about the structure of the alveoli that make them so good at diffusion?

Their walls are composed largely of a single, thin layer of squamous epithelial cells. The thinness of their walls is hard to even imagine.

sinuses

These cavities lighten the skull and act as resonance chambers for speech. They also produce mucus, which drains into the nasal cavities.

respiratory membrane (air-blood barrier)

Together, the alveolar and capillary walls, their fused basement membranes, and occasional elastic fibers construct this. Gas (air) flows past on one side and blood flows past on the other.

inspiration (inhalation)

When the diaphragm and external intercostals contract, the size of the thoracic cavity increases. The lungs adhere tightly to the thorax walls so they are stretched to the new, larger size of the thorax. As the intrapulmonary volume increase, the gases within the lungs spread out to fill the larger space. The resulting decrease in the gas pressure in the lungs produces a partial vacuum (pressure less than atmospheric pressure) which sucks air into the lungs until the intrapulmonary pressure equals atmospheric pressure.

organs of the respiratory system

nose, pharynx, larynx, trachea, bronchi, bronchioles, lungs, alveoli

respiratory zone structures

the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli

visceral (pulmonary) pleura

the surface of each lung is covered by this pleura

parietal pleura

the walls of the thoracic cavity are lined by this pleura