4/12 Lecture E1 Flashcards
Approximately how many alveoli are in each lung?
150 million
What type of cells make up 95% of alveoli surface area?
Squamous (type 1) alveolar cells
What type of cells make up 5% of alveolar surface?
Round to cuboidal cells (type II)
What is the role of type II alveolar cells?
repair the alveolar epithelium when type I cells are damaged.
What do type II cells secrete and why?
pulmonary surfactant: a mix of phospholipids and proteins that coats the alveoli and prevents them from collapsing during exhalation.
What is the most numerous of all cells in the lung?
Alveolar macrophages (dust cells)
What do alveolar macrophages do?
wander lumens and keep alveoli free from debris by phagocytizing dust particles
What separates alveolar air from blood?
respiratory membrane
What does the respiratory membrane consist of?
squamous alveolar cells, endothelial cells of blood capillary, and their shared basement membrane
What is the membrane that closely covers the lungs?
visceral pleura
What adheres to the mediastinum, inner surface of the rib cage and the superior surface of the diaphragm?
Parietal pleura
What is the function of the pleurae and pleural fluid?
1) reduce friction
2) create pressure gradient: assists lung inflation
3) compartmentalization: prevents the spread of infection
What does the diaphragm do?
Prime mover of respiration: contraction pulls air into the lungs, relaxation bulges the muscle and compresses the lungs and expelling the air.
What is the purpose of internal and external intercostal muscles?
synergists to diaphragm. stiffen the thoracic cage during respiration. Prevents rib cage from caving inward when diaphragm descends. Add about 1/3 of the air that ventilates the lungs
what do the scalenes do?
synergist to diaphragm, fix or elevate ribs 1 and 2
What does muscle relaxation during normal respiration do?
recoils structures and results in airflow out of the lungs.
During forced expiration, what does the rectus abdominis do?
pulls down on sternum and ribs
What causes increased thoracic pressure?
increased abdominal pressure pushing viscera up against diaphragm. This forces air out.
Automatic, unconscious cycle of breathing is controlled by what?
three hairs of respiratory centers in the reticular formation of the medulla oblongata and the pons
What are the two respiratory groups in the MEDULLA?
Ventral respiratory group and the Dorsal respiratory group
What is another word for quiet unlabored breathing?
eupnea
What is the primary generator of the respiratory rhythm?
Ventral respiratory group
What nerve do inspiratory neurons fire to the diaphragm through and for how long?
Phrenic nerve, two seconds
how long do expiratory neurons fire in eupnea?
3 seconds
What is the respiratory rhythm produced by the VRG?
12 breaths per minute
which respiratory network in the medulla modifies the rate and depth of breathing?
Dorsal respiratory group
What is the respiratory network in the pons?
Pontine respiratory group
What does the pontine respiratory group do?
1) modifies rhythm of the VRG by outputs to both the VRG and DRG
2) adapts breathing to special circumstances
What happens during hyperventilation?
1) CO2 levels drop and pH rises causing cerebral arteries to constrict, reducing cerebral perfusion
What are central chemoreceptors?
brainstem neurons that respond to changes in pH of cerebrospinal fluid
What does the pH of cerebrospinal fluid reflect?
CO2 level in the blood
Where are peripheral chemoreceptors located?
carotid and aortic bodies of the large arteries above the heart
What do peripheral chemoreceptors respond to?
O2, CO2, and pH of the blood
Where are stretch receptors found?
smooth muscles of bronchi and bronchioles, and in the visceral pleura
What do stretch receptors respond to and which nerve do they use?
inflation of the lungs via the vagus nerve
What is the inflation reflex also called?
Hering-Breuer reflex
What is the inflation reflex triggered by?
excessive inflation
What does the inflation reflex do?
its a reflective reflex that inhibits inspiratory neurons and stops inspiration.
What are the irritant receptors?
nerve endings amid the epithelial cells of the airway
What do irritant receptors respond to?
smoke, dust, pollen, chemical fumes, cold air and excess mucous
What do irritant receptors trigger?
Protective reflexes such as bronchoconstriction, shallower breathing, breath-holding (apnea), or coughing
Where does voluntary control of breathing originate?
in the motor cortex of frontal lobe of the cerebrum.
How does voluntary control happen?
Impulses are send from the motor cortex of the frontal lobe of the cerebrum down corticospinal tracts to respiratory neurons in spinal cord, bypassing brainstem
What is the limit to voluntary control?
The breaking point is when CO2 levels rise to a point where automatic controls override one’s will.
True or false: respiratory airflow is governed by the same principles of flow, pressure, and resistance as blood flow.
True
What are the principles of respiratory airflow?
1) the flow of a fluid is directly proportional to the pressure difference between two points
2) the flow of a fluid is inversely proportional to the resistance.
What type of pressure drives respiration?
atmospheric pressure
What is atmospheric pressure?
the weight of the air above us
What is atmospheric pressure at sea level?
760 mmHg at sea level or 1 atm. Pressure is lower at hight elevations
What is Boyle’s Law?
at a constant temperature, the pressure of a given quantity of gas is inversely proportional to its volume
If the lungs contain a quantity of a gas and the lung volume increases, their internal pressure (intrapulmonary pressure) ___.
falls
if the pressure falls below atmospheric pressure, air moves ___ the lungs.
into
If the lung volume decreases, intrapulmonary pressure ____.
rises
if the pressure of the lungs rises above atmospheric pressure, air moves ___ of the lungs.
out
What is the unit of pressure used by respiratory physiologists?
cm H2O
which is more sensitive: mmHg or cm H2O?
cm H2O
What is intrapleural pressure?
the slightly negative pressure that exists between the two pleural layers
what causes intrapleural pressure?
the recoil of lung tissue and tissues of thoracic cage causes lungs and chest wall to be pulling in opposite directions. the small space between the parietal and visceral pleura is filled with watery fluid, and they cling together. A negative 5 sm H2O pressure results.
What happens to the alveoli during inspiration?
They stretch within the lungs
As the thoracic cage increases in volume, what happens to the internal pressure?
The pressure drops and air flows in.
What is Charles’ Law?
volume of a gas is directly proportional to its absolute temperature
Specific to anatomy, what is Charles’ Law?
warming of the air expands the lungs. The air is warmed as it moves through the tubing to the alveoli.
How is relaxed expiration mainly achieved?
Elastic recoil of the thoracic cage
What is the intrapulmonary pressure during relaxed expiration?
about 1 cm H2O
Why does air flow out during relaxed expiration?
Air flows down the pressure gradient
During forced breathing, what happens to the intrapulmonary pressure?
Accessory muscles raise the pressure as high as +40 cm H2O
What is Pneumothorax?
The presence of air in pleural cavity
What does a pneumothorax result in?
loss of negative intrapleural pressure allows lungs to recoil and collapse
What is atelectasis?
Collapse of part or all of a lung
What can atelectasis result from?
An airway obstruction as blood absorbs gases from blood
What two factors influence airway resistance?
1) bronchiole diameter
2) pulmonary compliance
What stimulates bronchodilation?
Epinephrine and sympathetics stimulate dilation
What does bronchodilation result in?
increased airflow
What stimulates bronchoconstriction?
Histamine, parasympathetic nerves, cold air, and chemical irritants
What does bronchoconstriction result in?
decreased airflow
What does extreme bronchoconstriction result in and what is a potential cause?
Extreme constriction can cause suffocation. This can be caused by anaphylactic shock of asthma
What is pulmonary compliance?
Ease with which the lungs can expand
What can reduce pulmonary compliance?
degenerative lung diseases in which the lungs are stiffened by scar tissue
What is compliance limited by?
the surface tension of the water film inside alveoli
What causes infant respiratory distress syndrome?
premature babies lacking surfactant
RX for infant respiratory distress syndrome
artificial surfactant until they can make their own
