Respiratory System 1

• author "colorpencil1"
• tags "NPB101 "
• description "Midterm 3"
• fileName "NPB 101.txt"
• Respiration
• the process of obaining O₂ from the environment and eliminating CO_{2 from the body.}

• 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.

• 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.
• 

• Intracellular metabolic processes that take place w/in mitochondria.
• Where the following reaction takes place:
• Food + O₂ -> CO₂ + H₂O + ATP

Exchange of O and CO btwn the environment and the cells of the body.

• 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.

• 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.

• 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.

• 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.

• 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

• 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.
• Restated:
• decreased gas volume -> increased pressure exerted by gas
• increased gas volume -> decreased pressure exerted by gas

• 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.

• 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.
• (b) Lowering of diaphragm on contraction increases vertical dimension of thoracic cavity.
• (c) 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.
• Active expiration- 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.
• (b) Return of diaphragm, ribs, and sternum to resting position on relaxation of inspiratory muscles restores thoracic cavity to preinspiratory size.
• (c) Contraction of abdominal muscles causes diaphragm to be pushed upward, further reducing vertical dimension of thoracic cavity.

• influences airflow
• F= ΔP/R
• where...
• 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
• -allergies
• 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

• 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.

• 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.