Physiology 🫁 Flashcards
What is the definition of respiration?
- It is the transport of O2 from atmosphere to the tissue.
What happens in the tissues? “Concerning respiration”
- In the tissues, oxidation of food stuffs occurs with liberation of energy & CO2.
What are the phases of respiration?
Respiration can be divided into:
I. External respiration which consists of:
1-Pulmonary ventilation or renewal of the air in the lungs from atmospheric air
2- Exchange of gases between the alveolar air and venous blood in the capillaries around the alveoli.
II. Respiratory function of the blood:
It is the carriage of O2 and CO2 by the blood.
III. Internal respiration:
- It is the utilization of the atmospheric oxygen in oxidation of food stuffs with production of the energy required for body activities.
What is a Physiological anatomy of the respiratory system?
The respiratory system consists of:
- The air passages and lungs. “Conducting zone and respiratory zone”
- Respiratory muscles which change the volume of the thoracic cavity and their nerve supply.
- Nerve center controlling respiration.
❖The air passages are divided into two functional zones, the conducting zone and the respiratory zone.
What is the conducting zone of the respiratory system?
This part includes the nose, nasopharynx, larynx, trachea and the two main bronchi (one for each lung), the smaller bronchioles till the respiratory bronchioles.
What are the characteristics of the wall of the conducting zone of the respiratory system?
The walls the conducting part are thick and do not allow gas exchange.
What are the functions of the conducting zone?
CC HF RN
- Conducting air into the respiratory zone
- Air conditioning
- Humidification
- Filtration
- Protective reflexes
- Non-respiratory function
What is the conditioning function of the conducting zone?
Inspired air reach the respiratory zone at a temperature of 37 °C to maintain a constant internal body temperature. The mucosa of the nose, mouth and pharynx has a large surface area and a rich blood supply. This adds heat to cold air or removes heat from hot air.
What is the humidification function of the conducting zone? “So as to avoid injury of the respiratory zone”
- Air is saturated with water vapour to protect delicate lung tissue from dryness.
- This humidification occurs by the trans-capillary fluid filtration in the mucous membrane.
What is the filtration function of the conducting zone?
- The air conducting part filters air from particles and bacteria.
- Large particles, larger than 4-6 microns are trapped by hairs at the entrance of the nose.
- Small particles are trapped by mucous secreted from the goblet cells in the epithelial lining of the passage.
What are the protective reflexes of the conducting zone?
- These reflexes remove foreign bodies & irritant substances from the respiratory passage. They include sneezing reflex and cough reflex.
What are the non-respiratory functions of the conducting zone?
- Smell: by olfactory epithelium of the nose.
- Phonation: the larynx is adapted to act as a vibrator; the vibrating element is the vocal cord. When air passes, it vibrates the vocal cord and produces sound.
What is a Respiratory zone and what are the characteristics of its walls?
- It consists of respiratory bronchioles “Belong to respiratory zone note conducting zone” , alveolar ducts, air sacs and alveoli.
- The membrane separating blood in pulmonary capillaries and air in alveoli is very thin. So, gas exchange occurs free and rapid.
- The alveoli are packed together by elastic connective tissue which makes them one unit.
What is pulmonary ventilation and in what way does it occur?
- It is renewal of air in the lung alveoli from the atmospheric air by movement of air in (inspiration) followed by its movement out (expiration).
- This occurs in cycles called “respiratory cycles”.
what does each respiratory cycle consist of?
Inspiration, expiration and expiratory pause
What is the definition of inspiration and what is its duration?
- It is an active process during which the thoracic cavity increases, lungs distend and air rushes in the lungs
- Its duration is l.3 sec. in normal quiet breathing.
What is the definition of expiration and what is its duration?
- It is a passive process during which the thoracic cavity decreases, lungs recoil and air rushes out of the lungs.
- It is slightly longer than inspiration. Its duration is about 1.7 seconds in normal quiet breathing.
what is the definition of the expiratory pause and what is its duration?
- A period of rest present after expiration in normal quiet breathing.
- Its duration is about 0.7 second.
- It is absent in rapid respiration as in muscular exercise.
What is the total duration of respiratory cycle?
1.3 + 1.7 + 0.7 = 3.7 sec.
What is the respiratory rate in adults and children?
- about 16/minute.
- In children respiratory rate is about 25/minute
What is the definition of normal inspiration?
- It is an active process that occurs as a result of contraction of the diaphragm and external intercostal muscles.
What is a muscle that is responsible for 75% of respiration?
The diaphragm
What does the contraction of the diaphragm lead to and what supplies the diaphragm?
▪ Contraction of diaphragm leads to its descend from 1.5 cm.
▪ It is supplied by phrenic nerve (AHCs of cervical 3,4,5).
“C3,4,5 keep the diaphragm alive”
What does the contraction of external intercostal muscles lead to and what are they supplied by?
- Their contraction pushes the sternum outward causing increase the antero-posteriror diameter of the chest and elevates and everts the ribs causing increasing the transverse diameter. They are supplied by intercostals nerves (AHCs of thoracic 1-10).
What is the mechanism of normal inspiration?
- Contraction of the diaphragm and external intercostal muscles increases all diameters of the chest and the lungs follow the chest passively “pressure is distributed”. This causes increased volume of the lungs & decreased the intrapulmonary pressure by about -2mm Hg (below the atmospheric pressure) resulting in rush of 500 ml air into the lungs (Tidal volume).
What is the definition of normal expiration?
- It is a passive process that occurs as a result of relaxation of the diaphragm and external intercostal muscles.
What is the mechanism of normal expiration?
This relaxation decreases all diameters of the chest and lung recoils by its elasticity. This increases the intrapulmonary pressure to about + 2 mmHg (above the atmospheric pressure) resulting in rush out of 500 ml air (tidal volume).
What is forced inspiration?
It is an active process that occurs as a result of:
a) Forceful contraction of the diaphragm and external intercostal muscles.
b) Contraction of other thoracic muscles which are called (accessory muscles of respiration). They include: Sternocleiomastoid, serratus anterior, scaleni muscles, pectoralis minor and latismus dorssi muscles.
What is the mechanism of forced inspiration?
- Contraction of all these muscles causes marked increase of the dimensions of the chest & marked decrease in the intrapulmonary pressure to -20 mmHg causing rush of large volumes of air in.
What is forced Expiration?
It is an active process that occurs as a result of:
a) Relaxation of the diaphragm and external intercostal muscles.
b) Contraction of muscles of forced expiration (abdominal muscles and internal intercostal muscles)
What is the mechanism of forced expiration?
- This causes marked reduction of the dimensions of the chest & marked increase in the intrapulmonary pressure to + 30 mmHg causing rush of large volumes of air out.
What are the factors that affect pulmonary ventilation?
1) Resistance of the respiratory passage.
2) Pressure relationship in the thoracic cavity.
3) Surfactant.
4) Pulmonary compliance.
What describes the resistance of the respiratory passages?
Poiseuille’s law
What is poiseuille’s law?
where: R = 8 η l / πr 4
R = resistance η = viscosity of the inspired gas l = length of the airway r = radius of the airway
What are the factors that change airway resistance?
A. Contraction or relaxation of bronchial smooth muscle “Altering radius”
B. Lung volume “Altering radius”
C. Viscosity or density of inspired gas “Altering viscosity”
D- Bronchial Mucosa
How does contraction or relaxation of bronchial smooth muscles affect airway resistance?
■ Changes airway resistance by altering the radius of the airways.
(1) Parasympathetic stimulation, irritants, and the slow-reacting substance of anaphylaxis (asthma) constrict the airways, decrease the radius, and increase the resistance to airflow.
(2) Sympathetic stimulation and sympathetic agonists (isoproterenol) dilate the airways via β2 receptors, increase the radius, and decrease the resistance to airflow.
What is diurnal variation of the autonomic nervous system regarding airway resistance?
- The autonomic nervous activity shows “diurnal variation” in which the sympathetic activity reaches its maximum in the afternoon period whereas the parasympathetic activity is maximum in the late evening & early morning.
- This is why attacks of bronchial asthma are most common at late times of the day.
How does the lung volume affect the airway resistance?
■ alters airway resistance because of the radial traction exerted on the airways by surrounding lung tissue.
(1) High lung volumes are associated with greater traction and decreased airway resistance. Patients with increased airway resistance (e.g., asthma) “learn” to breathe at higher lung volumes to offset the high airway resistance associated with their disease.
(2) Low lung volumes are associated with less traction and increased airway resistance, even to the point of airway collapse.
How does viscosity or density of inspired gas affect airway resistance?
■ changes the resistance to airflow.
■ During a deep-sea dive, both air density and resistance to airflow are increased.
■ Breathing a low-density gas, such as helium, reduces the resistance to airflow.
How does bronchial mucosa affect airway resistance?
- The presence of secretion (mucus) or an increase in the thickness of the mucosa (mucosal edema) increases the airway resistance as in bronchial asthma.
what are the pressures in the thoracic cavity?
A. Intra pulmonary pressure.
B. Intra pleural pressure.
C. Intrathorathic pressure.
What is the definition of intrapulmonary alveolar pressure? And what is it connected with?
- It is the pressure inside the lung alveoli, with the atmosphere
What are the values of the intra- pulmonary alveolar pressure?
- Before the start of inspiration, it equals zero (i.e., equal to atmospheric pressure).
- During normal inspiration, It is equals -2 mmHg (i.e., 2 mmHg below the atmospheric pressure). This is due to contraction of the diaphragm and external intercostal muscles that increases all dimensions of the chest.
- At the end of inspiration, pressure becomes atmospheric (zero) again. This is due to rush of about 500 ml air (tidal air) air that fills the lungs at the end of inspiration.
- During normal expiration: the intrapulmonary pressure increases to about +2 mmHg (i.e., 2 mmHg above the atmospheric pressure). This is due to relaxation of the diaphragm and external intercostal muscles that decreases all dimensions of the chest cavity. This forces 500 ml of air out of the lungs helped by its elasticity. Thus, pressure returns zero again at the end of expiration.
N.B.: in forced respiration, the alveolar pressure follows the same course of change BUT at different values during forced inspiration (where it reaches -20 mmHg) and during forced expiration (where it reaches +20 mmHg).
“كلام فاضي كله”
What is the anatomy of pleura?
- Each lung is enclosed in a double-walled sac called “pleura”. Both layers of the pleura are formed of serous membrane.
- The part of the pleura that lines the thoracic cavity is called “parietal pleura”. It is reflected at the hilum of the lung to cover firmly the outer surface of the lung as “visceral pleura”.
- Between the two layers of pleura, there is an extremely narrow “pleural cavity” or “pleural sac”.
What is the pleural cavity filled with and what is its function?
- This cavity (sac) is filled with “pleural fluid”, which is serous fluid secreted by pleura. This fluid acts as lubricant to reduce friction between the two layers during respiratory movements. So, it causes lung to slide on the chest wall & resists their separation. Thus, lungs follow passively movement of chest wall.
What is intrapleural pressure?
It is the pressure in the pleural cavity (sac).
What are the values of intrapleural pressure?
Normal values of I.P.P. (usually a negative pressure):
▪ - 3 mmHg at the end of normal expiration.
▪ - 6 mmHg at the end of normal inspiration.
▪ -30 mmHg in forced inspiration with closed glottis (Muller’s experiment).
▪ +40 mmHg in forced expiration with closed glottis (Valsalva’s maneuver).
What are the causes of negativity of intrapleural pressure? “Lack of air tendency”
- Lack of air in the pleural cavity.
- Continuous tendency of the lung to recoil AGAINST tendency of chest wall to expand. Both lungs and chest wall have a “relaxation volume” at which they are neither stretched nor compressed. This relaxation volume is 0.6 L for the lungs and 3.5 L for the chest wall. However, at the end of normal expiration (when respiratory muscles are relaxed), the volume of both lung and chest wall equals 2.2 L (functional residual capacity). Thus, lungs continuously tend to recoil (from 2.2 to 0.6) and chest wall tends continuously to expand (from 2.2 to 3.5).
“Easy”
What happens of air is introduced into the intrapleural cavity?
- If air is introduced into the pleural sac (in pneumothorax), the negativity of I.P.P. is lost, the lung collapses and the chest is expanded.
What is responsible for the elastic properties of the lungs?
- The elastic tissue in the bronchial wall and the interstitial tissues of the lungs.
- The arrangement of the muscle fibers of the bronchi and bronchioles in a network. So that, on contraction, the bronchial tree not only becomes constricted but also shortened in length (recoils).
- The surface tension of the fluid lining the alveolar walls.
What is the significance of the negativity of intrapleural pressure?
Negative pressure is a suction force so:
- It helps expansion of the lung during inspiration and prevents its collapse during expiration.
- Responsible for the negativity of intrathorathic pressure which helps:
a. Expansion of the lung.
b. Venous return to the heart: This is called “respiratory pump”. During normal and more during forced inspiration; the intrathorathic pressure becomes negative lead to suction of more blood from the extrathorathic vein increasing venous return and cardiac output.
c. The negative intrathorathic pressure helps lymphatic flow in the thoracic duct through the thoracic cavity.
d. Helps pulmonary blood flow.
what does a surfactant line and what is its function in brief?
■ lines the alveoli and reduces surface tension by disrupting the intermolecular forces between liquid molecules. This reduction in surface tension prevents small alveoli from collapsing and increases compliance.
What synthesizes the surfactant and what is it primarily consisting of?
■ is synthesized by type II alveolar cells and consists primarily of the phospholipid dipalmitoyl phosphatidylcholine (DPPC).
When is surfactant synthesized in the fetus?
■ In the fetus, surfactant synthesis is variable. Surfactant may be present as early as gestational week 24 and is almost always present by gestational week 35.
What reflects mature levels of surfactant?
■ Generally, a lecithin:sphingomyelin ratio greater than 2:1 in amniotic fluid reflects mature levels of surfactant.
What causes neonatal respiratory distress syndrome and what does the infant experience during it?
■ Neonatal respiratory distress syndrome can occur in premature infants because of the lack of surfactant. The infant exhibits atelectasis (lungs collapse), difficulty reinflatingthe lungs (as a result of decreased compliance), and hypoxemia (as a result of decreased V/Q).
What are the functions of surfactant? “Immunity and decreasing surface tension”
- It decreases the surface tension of the fluid lining the alveoli through:
a) It scatters among the fluid molecule decreasing the attraction between them.
b) It also spreads over the fluid preventing air-fluid interface.
This decreased surface tension:
▪ Helps lung expansion during inspiration esp.
▪ Protects against pulmonary edema as it decreases the filtration forces for the fluid from pulmonary
capillaries into alveoli.
▪ Prevents lung collapse during expiration.
▪ Decreases the work of breathing needed.
- Surfactant activates alveolar macrophages.
- It has a bacteriolytic effect, making the bacteria susceptible to alveolar macrophages.
- The phospholipids of surfactant may act directly on T-lymphocytes cell membrane to prevent excess immune response.
- It assists ciliary movement in upper respiratory tract (so, helps to remove any particles and mucus away from air passage).
What is the types of respiratory distress syndrome?
Infant RDS (hyaline membrane disease)
Adult respiratory distress syndrome (ARDS)
What is the definition of infant RDS?
is a deficiency of surfactant in infants
Why does infant RDS happen?
- In fetal life, surfactant is not produced in sufficient amounts until about the eighth month. Thus, premature babies lacking sufficient surfactant are born with collapse alveoli.
- Because of the high surface tension, plasma fluid leaks into the alveoli producing pulmonary edema.
- Due to “glistening membrane” appearance, the condition is also called “hyaline membrane disease”.
What are the characteristics of RDS in infants?
- RDS is a fatal condition. It is more sever and more common in infants with low plasma level of thyroid hormone. Thyroid hormone increases the size and number of lamellar bodies in type II alveolar cells.
How is RDS in infants treated?
“Ready O2 or surfactant or helping in the synthesis of the surfactant”
- RDS babies can be saved by mechanical ventilators that keep them alive until their lung can manufacture sufficient surfactant. Otherwise, bovine or synthetic surfactant can be administrated.
- When premature delivery (before 8 months) is life-saving for the mother, elective caesarean section may result in baby with collapsed lungs. It is better in this condition to inject the mother with cortisol hormone which is essential for surfactant formation.
What is adult RDS?
Acute lung injury.
What causes acute RDS?
A- Bloodstream (sepsis): develops from injury to the pulmonary capillary endothelium, leading to interstitial edema and increased lymph flow.
B- Airway (gastric aspirations): direct acute injury to the lung epithelium increases permeability of the epithelium followed by edema.
C- Cigarette smoking decreases surfactant. It leads to destruction of type II alveolar cells.
D- After cardiac surgery during which the pulmonary circulation is interrupted, alveolar epithelium fails to secrete surfactant.
E- Long-term inhalation of 100% O2.
what are the harmful effects of respiratory distress syndrome?
In respiratory distress syndrome, the lung becomes stiffer and compliance decreases. This greatly increases the work of breathing. Also, a more negative pressure is required to maintain a given lung volume.
What is the equation that describes compliance?
C = Δ V/P
C = compliance (mL/mm Hg) ,V = volume (mL), P = pressure (mm Hg)
What is compliance?
- the extent to which the lung expands for each unit increase in its transmural pressure.
What is transmural pressure?
- For the lungs, transmural pressure = intrapulmonary pressure – intrapleural pressure. It is called “transpulmonary pressure”.
What is the normal compliance of the lungs in the average adult human?
- approximately 200 ml/cm of water pressure. That is every time, the transpulmonary pressure increase by one centimeter of water, the lungs expand 200 milliliters.
What are the types of pulmonary compliance?
Two types of pulmonary compliance can be measured:
1- Static pulmonary compliance.
2- Dynamic lung compliance.
How is static pulmonary compliance estimated?
- Can be estimated from static (relaxation) pressure – volume curve of the whole respiratory system (pressure is recorded after the muscles of respiration are relaxed).
Describe the relaxation pressure - volume curve at FRC
- The relaxation pressure of the lung and chest wall equals zero when the lung volume is equal to functional residual capacity (FRC) which is the volume of the lung and chest wall at the end of normal expiration. Thus, FRC is the relaxation volume of the total respiratory system. At this volume, lung tendency to recoil and chest tendency to expand balance.
- At the FRC volume, the curve of the lung alone shows +ve pressure (as the lung tends to collapse to reach its relaxation volume which is about 0.6 L) whereas the curve of chest wall alone shows –ve pressure (as the chest wall tends to expand to reach its relaxation volume which is about 3.5 L).
Describe the relaxation pressure-volume curve at volumes higher than FRC.
- At volumes higher than FRC, the relaxation pressure of total respiratory system is positive “instead of zero” mainly due to recoil tendency of the lung “strong” (as chest wall is approaching its relaxation volume). “Weaker”
Describe the relaxation pressure-volume curve at volumes lower than FRC.
- At volumes lower than FRC, the relaxation pressure of total respiratory system is negative mainly due to expansion tendency of the chest wall (as lungs are approaching their relaxation volume).
How can dynamic lung compliance be estimated?
- Can be estimated from pressure – volume curve of the lungs recorded during the respiratory cycle (pressure is recorded in steps during inspiration and expiration).
what can be concluded from the dynamic lung compliance curve?
- The compliance of the lung is more during expiration (BZA) than during inspiration (AXB).
- This is known as “hysteresis” (i.e., forward path is different from the reverse path).
What determines the lung compliance?
“Only lung compliance not the whole respiratory system”
- The compliance of the lung is determined by the diagonal line (BYA) connecting the two ends of the curve (average lung compliance).
What are the factors affecting compliance?
- Factors in the lung:
- It is affected by elastic forces of the lung (1/3 of compliance) and surface tension of the fluid lining the alveoli (2/3 of the compliance).
- Lung compliance is decreased in pulmonary congestion, pulmonary fibrosis and pulmonary edema whereas it is increased in emphysema. (CFE - E)
- Factors in the chest wall:
- It is affected by the elastic properties of the thorax caused by elasticity of the muscles, tendons and connective tissues in the chest wall.
- Chest wall compliance is decreased in case of:
- Deformities of spine
- Arthritis of vertebra.
- Skeletal muscle disease e.g. poliomyelitis
- Obesity.
What are the changes in lung compliance?
Emphysema and fibrosis
How does emphysema change lung compliance?
- often caused by smoking, results in destruction of the alveolar septa and capillaries. Therefore, lung compliance is increased and the tendency of the lungs to collapse is decreased. Therefore, at the original FRC, the tendency of the lungs to collapse is less than the tendency of the chest wall to expand. The lung–chest wall system will seek a new, higher FRC so that the two opposing forces can be balanced; the patient’s chest becomes barrel-shaped, reflecting this higher volume. “Easy”
How does fibrosis change lung compliance?
- Fibrosis has increased collagen fiber deposition, which increases the tissue component of elastic recoil. Therefore, lung compliance is decreased and the tendency of the lungs to collapse is increased. Therefore, at the original FRC, the tendency of the lungs to collapse is greater than the tendency of the chest wall to expand. The lung–chest wall system will seek a new, lower FRC so that the two opposing forces can be balance. “Easy”
What is work of breathing and what is its value?
- During normal quiet respiration, work is done only during inspiration whereas expiration is entirely a passive process. At rest, work of breathing is about 1-2% of the total body energy expenditure. Even during heavy exercise, work is only about 3-5% of the total energy expenditure of the body.
What is the work of breathing divided into?
1- Compliance work (elastic work) (65% of total work)
2- Tissue resistance work (7% of total work)
3- Airway resistance work (28% of total work)
What is compliance work? And how could it be calculated?
- It is the work required to expand the lung against its elastic force.
- This can be calculated as follow:
Compliance work = volume x pressure needed to inflate this volume
What is tissue resistance work?
- It is the work required to overcome the resistance of non-elastic tissue of the lungs and thoracic cage.
