the process of obaining O2 from the environment and eliminating CO2 from the body.
What are the 4 steps of breathing?
Breathing- physical exchange of gas btwn the environment and the alveoli.
Alveolar gas exchange- exchange of O2 and CO2 btwn gas in the alveoli and blood in the pulmonary capillaries.
Gas transport- the transport of O2 and CO2 by the blood from the lungs to the tissues of the body.
Blood gas exchange- the exchange of O2 and CO2 btwn the blood and the tissues.
What are the steps of External Respiration?
Ventilation or gas exchange btwn the atmosphere and air sacs (alveoli) in the lungs.
Exchange of O2 and CO2 btwn air in the alveoli and the blood.
Transport of O2 and CO2 btwn the lungs and the tissues.
Exchange of O2 and CO2 btwn the blood and the tissues.
What is Internal (Cellular) Respiration?
Intracellular metabolic processes that take place w/in mitochondria.
Where the following reaction takes place:
Food + O2 -> CO2 + H2O + ATP
What is External Respiration?
Exchange of O and CO btwn the environment and the cells of the body.
The Anatomy of the Respiratory System.
(the system responsible for the first two stages of external respiration)
nasal passages- nose
pharynx- common passageway for the lungs and the stomach.
larynx- voice box located at the entrance to the trachea.
trachea- tube through which air is conducted to the lungs.
brochi- division of the trachea into 2 main branches.
What are Alveoli?
(Anatomy from Bronchi)
small, thin-walled sacs where gas exhcange takes place.
-tiny, air-filled chambers (~300um in diameter) w/in the lungs that serve as the site for the exchange of O2 and CO2 w/the blood.
Attached to brachioles: small branches of the respiratory airway.
Microscopic Anatomy of an Alveolus
Type I cell: form the walls of the alveoli.
Type II cells: secrete a pulmonary surfactant that acts to reduce the surface tension of the water inside the alveoli.
Each alveolus is in very close proximity to pulmonary capillaries.
The Lungs are...
a pair of organs consisting of the lower portion of the respiratory airways, the pulmonary circulation, and connective tissue.
Pleural Sacs- a pair of thin, fluid-filled, membranes that enclose the lungs. the space btwn the pair of membranes is referred to as the pleural cavity.
a gradient in pressure btwn the alveoli and the atmosphere provides the force to move air into and out of the lungs.
Pressures important in ventilation...
Atmospheric pressure- pressure exerted by the weight of the gas in the atmosphere on objects on Earth's surface (760 mm Hg at sea level)
Intra-alveolar pressure- the pressure w/in the alveoli (760 mm Hg when equilibrated with atmospheric pressure)
Intrapleural pressure- pressure w/in the pleural sac (the pressure exerted outside the lungs w/in the thoracic cavity 4mm Hg less than atmospheric pressure - 756 mm Hg)
Intra-pleural fluid cohesion- the force acting to attract two surfaces when they are separated by a layer of fluid.
Transmural pressure gradients
Transmural pressure gradients are...
differences in pressure btwn the intra-pleural space and the intra-alveolar and atmospheric spaces.
helps ensure that the lungs maintain close proximity to the thoracic wall.
An extremely dangerous condition that occurs when air is allowed to enter the plural cavity (either by a puncture wound in chest, or a hole in lung).
-As a result, the transmural pressure gradient is lost and the lungs and thorax separate and assume their own inherent dimensions (lungs collapse and thoracic wall expands).
At any constant temperature, the pressure exerted by a gas varies inversely with the volume of the gas.
decreased gas volume -> increased pressure exerted by gas
increased gas volume -> decreased pressure exerted by gas
Changes in lung volume and intra-alveolar pressure during inspiration and expiration.
Before inspiration- system is equilibrated; no net movement of air.
During inspiration- size of teh lungs increases as they are stretched to fill the expanded thorax.
as the lungs increase in volume, intra-alveolar pressure decreases creating a pressure gradient that favors the flow of air into the alveoli.
During expiration- as the lungs recoil to their pre-inpiratory size, intra-alveolar pressure increases, establishing a pressure gradient that favors the flow of air out of the alveoli into the atmosphere.
Intra-alveolar & intrapleural pressures during respiration...
Throughout the respiratory cycle, intra-pleural pressure is always less than intra-alveolar pressure. Thus, a transmural pressure gradient always exists that serves to stretch the lungs to fill the available thoracic space.
When intra-alveolar pressure is less than atmospheric pressure, air enters the lungs. When intra-alveolar pressure is greater than atmospheric pressure, air exits the lungs.
Accessory muscles of inspiration- contract only during forceful inspiration.
Major muscles of inspiration- contract every inspiration; relaxation causes passive expiration.
Muscles of active expiration- contract only during active expiration.
Diaphragm- contracts increasing the vertical dimensions of the thoracic cavity.
External intercostal muscles- contract elevating the rib cage and increasing the thoracic cavity form side-to-side and front-to-back.
(a) Elevation of ribs causes sternum to move upward and outward, which increases front-to-back dimension of thoracic cavity.
Lowering of diaphragm on contraction increases vertical dimension of thoracic cavity.
Contraction of external intercostal muscles causes elevation of ribs, which increases side-to-side dimension of thoracic cavity.
Passive expiration- the ribs, sternum, and diaphragm return to resting position upon relaxation of the inspiratory muscles.
- contraction of abdominal muscles causes the diaphragm to be pushed upward, further reducing the vertical dimension of thoracic cavity.
Also, contraction of internal intercostal muscles flattens the ribs and sternum further reducing the size of the thoracic cavity.
(a) Contraction of internal intercostal muscles flattens ribs and sternum, further reducing side-to-side and front-to-back dimensions of thoracic cavity.
Return of diaphragm, ribs, and sternum to resting position on relaxation of inspiratory muscles restores thoracic cavity to preinspiratory size.
Contraction of abdominal muscles causes diaphragm to be pushed upward, further reducing vertical dimension of thoracic cavity.
F= airflow rate
ΔP= difference btwn atmospheric and intra-alveolar pressure.
R= resistance of the airways, determined by their radius.
A decrease in the radius of bronchioles.
resistance due to a ↓ in radius
caused by:contraction of airway smooth muscle
- ↑ parasympathetic nervous stimulation
- ↓ CO2 concentrations
physical factors such as mucous, edema, airway collapse
An increase in bronchiolar radius.
resistance due to ↑ radius
caused by:relaxation of airway smooth muscle
- ↑sympathetic nervous stimulation
- hormonal control: epinephrine
- ↑ CO2 concentrations
Chronic Obstructive Pulmonary Disease (COPD) is...
What are the the 3?
a group of lung diseases characterized by increased airway resistance resulting from narrowing of the lumen of the lower airways. (pathalogical increase in airway resistance)
1) Chronic Bronchitis: long-term inflammatory responses to irritants, pathogens or allergens lead to thickening and edema of the airway walls and overproduction of thick mucus.
2) Asthma: long-term inflammatory responses to irritants, pathogens or allergens lead to thickening and edema of the airway walls, overproduction of thick mucous, and hyper-resonsiveness of airway smooth muscle.
3) Emphysema: macrophage enzynes released in response to irritants cause collapse of airways and breakdown of alveolar walls. Many alveoli can burst and then enlarge.
Elastic recoil is the...
force that restores the lungs to their preinspiratory volume after the inspiratory muscles relax at the end of inspiration.
Due to:elastic properties of pulmonary tissue- elastin fibers are arranged in a meshwork that provides the tissue with a high degree of elasticity.
alveolar surface tension- force due to the attraction of water molecules to each other; opposes expansion of the alveoli.
Alveolar surface tension is reduced by a pulmonary surfactant (mixture of lipids and proteins) synthesized by type II alveolar cells.
plays a major role in preventing the collapse of small alveoli.