Respiratory System Flashcards
What are the 4 primary functions of the respiratory system?
1) Exchange of gases between the atmosphere and the blood - body brings in Oxygen for distribution to the tissues and eliminates Carbon dioxide waste produced by metabolism
2) Homeostatic regulation of body pH - the lungs can alter body pH by selectively retaining or excreting Carbon dioxide
3) Protection from inhaled pathogens and irritating substances
4) Vocalisation (speech) - air moving across the vocal cords creates vibrations used for speech
The respiratory system is only responsible for….
bringing gases in and out of the body - does’t transport oxygen or carbon dioxide - that’s the cardiovascular system
What are the two types of respiration? (1)
(1) Cellular Respiration: the intra-cellular reaction of oxygen with organic molecules to produce carbon dioxide, water, and energy (ATP)
What are the two types of respiration? (2)
(2) External Respiration: the movement of gases between the environment and the body’s cells
What are the 4 integrated processes of External Respiration? (1)
(1) Ventilation (breathing): exchange of air between the atmosphere and the lungs
Inspiration (inhalation): movement of air into the lungs
Expiration (exhalation): movement of air out of the lungs
What are the 4 integrated processes of External Respiration? (2)
(2) The exchange of Oxygen and Carbon dioxide between the lungs and the blood
What are the 4 integrated processes of External Respiration? (3)
(3) The transport of Oxygen and Carbon dioxide by the blood
What are the 4 integrated processes of External Respiration? (4)
(4) The exchange of gases between blood and the cells
What are the 2 parts of the respiratory system and what are their functions? (1)
(1) Upper Respiratory Tract (URT)
- Consists of the Mouth, Nasal Cavity, Pharynx and Larynx
Play an important role in conditioning (3) air before it reaches the alveoli.
(1) Warms air to 37oC, so that core body temperature doesn’t change and alveoli are not damaged by cold air
(2) Adding water vapour until the air reaches 100% humidity, so that moist exchange epithelium does not dry out (happens by the time air reaches the trachea)
(3) Filtering out foreign material, so that viruses, bacteria, and inorganic particles do not reach the alveoli
What are the 2 parts of the respiratory system and what are their functions? (2)
(2) Lower Respiratory Tract (LRT)
Trachea, Bronchi (primary & secondary), Bronchiole, Aveoli, Lungs
Mainly concerned with gas exchange
- Alveoli are clusters at the terminal bronchioles and make up the bulk of lung tissue; primary function = exchange of gases between themselves and the blood
What is the structure of the airways?
- Pharynx - air enters the URT though the mouth & nose and passes into the pharynx
- Larynx - air passes into the larynx; contains the vocal cords, connective tissue bands that vibrate and tighten to create sound when air moves past them
- Trachea - a semiflexible tube held open by 15-0 C-shaped cartilage rings and extends down into thorax. Divides into the a pair of primary bronchi
- The primary bronchi - one in each lung, they branch into progressively smaller bronchi. They are semi-rigid tubes supported by cartilage
- The secondary Bronchi - Primary bronchi branches into the secondary bronchi and this continues 21 more times resulting in the bronchioles
- The bronchiole - the smallest bronchi branch to become the bronchioles. Small collapsible passageways with walls of smooth muscle
How is air filtered in the trachea and bronchus’?
Via a watery saline layer.
The airways are lined with ciliated epithelium whose cilia secrete the saline (Cl ions are secreted into the lumen by apical anion channels causes Na uptake into the lumen - creates an osmotic gradient and water moves into the lumen)
Sticky layer of mucus floats over the cilia to trap most inhaled particles larger than 2μm. Secreted by goblet cells in the epithelium.
Imperative for there to be the saline layer underneath the mucus; aids functional mucocilary escalator
Cystic Fibrosis - no saline layer = mucus layer which can’t be moved easily and allows for bacterial colonisation
Whats the role of the alveoli?
- Exchange of gases between themselves and the blood
- Cluster at the ends of terminal bronchioles & make up the bulk of lung tissue
- Each alveolus is composed of a single layer of epithelium - 2 types are present
1) Type II = smaller but thicker - synthesize and secrete surfactant - mixes with thin fluid lining alveolus to aid lungs as they expand during breathing
2) Type I = occupy about 95% of the alveolar surface area and are very thin so gases can diffuse rapidly
- Layer of basement membrane fuses the alveolar epithelium to the capillary endothelium
What’s Tidal Volume (TV)?
The volume of air breathed in and out of the lungs at each breath (around 500ml)
What’s Expiratory Reserve Volume (ERV)?
The maximum volume of air which can be expelled from the lungs at the end of a normal expiration (around 1100ml)
What’s Inspiratory Reserve Volume (IRV)?
The maximum volume of air which can be drawn into the lungs at the end of a normal inspiration (around 3000ml)
What’s Residual Volume (RV)?
The volume of gas in the lungs at the end of a maximal expiration (around 1200ml)
What’s Vital Capacity (VC)?
Tidal volume + inspiratory reserve volume + expiratory reserve volume (around 4600ml)
What’s Total Lung Capacity (TLC)?
Vital capacity + residual volume (around 5800ml)
What’s Inspiratory Capactiy (IC)?
Tidal volume + inspiratory reserve volume (around 3500ml)
What’s Functional Residual Capacity (FRC)?
Expiratory reserve volume + residual volume
What’s FEV1FVC?
Fraction of forced vital capacity expired in 1 second
Gas Laws: What’s Boyle’s Law?
The pressure exerted by a gas is inversely proportional to its volume
Gas Laws: What’s Dalton’s Law?
The total pressure of a mixture of gases is the sum of the pressures of the individual gases
The pressure of an individual gas in a mixture is known as the partial pressure of the gas
Partial pressure = atmospheric pressure (Patm) x gases relative contribution (%) to Patm
Gas Laws: What’s Henry’s Law?
The amount of gas dissolved in a liquid is determined by the pressure of the gas and its solubility in the liquid
What are the muscles of inspiration?
- Sternocleidomastoids
- Scalenes
- External Intercostals
- Diaphragm
What are the muscles of expiration?
- Internal intercostals
- Abdominal muscles
What’s the role of surfactant?
- Detergent like fluid produced by Type II alveolar cells
- Reduces surface tension on alveolar surface membrane thus reducing tendency for alveoli to collapse
- Increases lung compliance
- Reduces lung’s tendency to recoil
- Males work of breating easier
- More effective in small alveoli than large
What is “the Law of Laplace?
Describes the pressure-volume relationships of spheres
Pressure is greater in the smaller alveolus
P=2T/r
P = Pressure T = Surface tension r = Radius
Whats the difference between Pulmonary and Alveolar ventilation?
Pulmonary= total air movement into/out of lungs
Alveolar= FRESH air getting to alveoli and therefore available for gas exchange
What’s partial pressure?
Related to Dalton’s Law but:
- The pressure of a gas in a mixture of gases equivalent to the percentage of that particular gas in the entire mixture multiplied by the pressure of the whole gaseous mixture
E.g.
Atmospheric pressure: 760mmHg
21% of air we breath = O2
Partial pressure of O2 in air we breath = 0.21*760
=159.6mmHg
Why is partial pressure lower within the lungs compared to atmospheric?
Residual volume dilutes down the oxygen that we breath in and the air gets saturated by water vapour pressure
What’s compliance?
Change in volume relative to change in pressure
i.e. how much does volume change for any given change in pressure - represents the stretchability of the lungs
Tells us how easy it is to get oxygen into the lungs**
Healthy lungs are highly compliant (elastic fibres in tip top shape)
What’s high compliance?
Large increase in lung volume for small decrease in internal pressure
What’s low compliance?
Small increase in lung volume for large decrease in pressure
What does the pressure volume curve tell us about the apex and base of the lung?
- pressure volume curve varies between apex and base of the lung - base the volume change is greater for a given change in pressure
- Alveolar ventilation declines with height from base to apex
- Compliance is lower at the apex due to being more inflated at FRC… at the base, the lungs are slightly compressed by the diaphragm hence more compliant on inspiration
How is O2 transported from the lungs to tissue?
Blood transports oxygen from the the lungs to tissues; also transports the waste product of this process (carbon dioxide) from tissues to lungs for removal
How is the bulk of oxygen transported within blood?
Oxygen is quite insoluble in water (only 3ml oxygen dissolve per litre of plasma)
Haemoglobin in RBC increases oxygen carrying capacity to 200ml/L
Pulmonary circulation: Pulmonary artery carries?
Deoxygenated blood AWAY from the heart to the lungs
Pulmonary circulation: Pulmonary vein carries?
Oxygenated blood TOWARDS the heart from the lungs
How does gas exchange occur between the alveoli and blood?
Simple diffusion - gas moves across a membrane that is permeable to that gas, down its partial pressure gradient and will continue until equilibrium is reached
Directly proportional to the partial pressure gradient
Directly proportional to the solubility of the gas
Alveoli conditions: What’s the pathology of Emphysema?
Breakdown of alveoli wall and elastic fibres - reduces elasticity of the lungs - increasing compliance but they cant contract and reduces surface area for gaseous exchange
What’s the structure of haemoglobin?
- Complex quaternary structure
- X2 Alpha & X2 Beta chains of polypeptides
- Each chain is a globular protein subunit
- Each chain contains a single heme molecule which hold a single iron ion
What’s the function of haemoglobin?
Transport oxygen to tissue and removal of carbon dioxide
Amount of oxygen bound to haemoglobin depends mostly on oxygen content of the blood (PP of oxygen)
When plasma oxygen levels are low - haemoglobin releases oxygen (typically in the peripheral capillaries - plasma carbon dioxide is high)
Haemoglobin has a higher affinity to carbon dioxide so readily unloads oxygen in its presence
How does haemoglobin maintain the partial pressure gradient for oxygen in the alveoli and capillaries?
Haemoglobin sequesters oxygen from the plasma - maintaining a partial pressure gradient that continues to suck oxygen out of the alveoli - until haemoglobin becomes saturated with oxygen
A high affinity to oxygen draws oxygen out of the plasma and causes a drop in plasma oxygen concentration and PP - causing more oxygen to diffuse from the alveoli
Oxygen-haemoglobin dissociation curve: How does haemoglobin saturation vary with changes in PO2?
- Haemoglobin is nearly 100% saturated at normal systemic arterial PO2 of 100mmHg
- Saturation reduces by only 10% when P02 drops by 40% (60mmHg) - suggesting haemoglobin permits a relatively normal uptake of oxygen by blood even when alveolar PO2 is moderately reduced
- Venous blood is actually oxygenated - holds a reserve of oxygen
What 4 factors can alter haemoglobin’s affinity for oxygen?
1) pH
2) Carbon dioxide partial pressure (reduces saturation)
3) Temperature
4) DPG
Affinity for oxygen is decreased by a decrease in pH or an increase in PCO2 or temp. These conditions exist locally in actively metabolising tissues and facilitate the dissociation of oxygen from haemoglobin
A rise in pH or fall PCO2 or temp increases the affinity of haemoglobin for oxygen - these conditions make oxygen unloading more difficult but aid collection of oxygen in the pulmonary circulation
Carbon dioxide transport: How is carbon dioxide transported in the blood?
- CO2 is more soluble than O2
- 7% dissolves directly into the plasma and is transported in simple solution
- 93% moves into the RBC’s where 23% forms carbamino-compounds with the now de-saturated haemoglobin - the remainder is converted to bicarbonate ions
Bi-carbonate and carbamino compounds are converted back into dissolved carbon dioxide and leave the capillary via the lumen of alveolus
What’s the relationship between ventilation and perfusion?
Ventilation (air getting to alveoli) and perfusion (local blood flow) compliment each other
If ventilation decreases in a group of alveoli PCO2 increases and PO2 decreases. Blood flowing past these alveoli doesn’t get oxygenated = SHUNT
Decreased tissue PO2 around under-ventilated alveoli caues artery constriction and diverts blood to better ventilated alveoli
Alveolar dead space?
Alveoli that are ventilated but not perfused - opposite of shunt
How does the distribution of blood flow vary throughout the lungs?
The distribution of blood flow in the lung is influenced by HYDROSTATIC (BLOOD) PRESSURE & ALVEOLAR PRESSURE
At the base of the lungs blood flow is high since perfusion pressure exceeds alveolar pressure and hence vascular resistance is low
At the apex of the lungs blood flow is low because perfusion pressure is less than alveolar pressure - compresses the arterioles and vascular resistance is increased
How is ventilation controlled?
Required stimulation of the skeletal muscles of inspiration via the phrenic (to diaphragm) and intercostal nerves (to external intercostal muscles)
Control resides within centres in the pons and medulla (respiratory centres)
- normally subconscious
- can be subject to voluntary modulation
- entirely dependent on signalling from the brain (spinal cord C3-5 CRUCIAL FOR BREATHING)
Breathing depends upon..
cyclical activation of the phrenic and intercostals nerves stimulating contraction of the inspiratory muscles
Neural activity triggered by the medullary inspiratory nerurones but with voluntary override
How can the respiratory rhythm be modulated?
1) Emotion (limbic system)
2) Voluntary over-ride
3) Mechano-sensory input from the thorax (stretch reflex)
4) Chemical comp. of the blood - detected by the chemoreceptors
What’s the most significant respiratory control mechanism?
Chemoreceptor input:
Central chemoreceptors
- Medulla
- Responds directly to H+ (directly reflects PCO2)
- Primary ventilatory drive
Peripheral chemoreceptors
- Carotid & aortic bodies
- Respond primarily to plasma H+ and PO2
- Secondary ventilatory drive (30% of ventilatory drive)
How do the central chemoreceptors in the medulla work?
- Detect changes in H+ ions in CSF around the brain
- Cause reflex stimulation of ventilation following rise in H+ ions (driven by raised PO2 = Hypercapnea)
Ventilation is reflexly inhibited by a decrease in arterial PCO2 (reduces CSF H+ ions)
How do central chemoreceptors work?
- When arterial PCO2 increases CO2 crosses the BBB not H+
- Central chemoreceptors monitor the PCO2 indirectly in the CSF
- Bicarbonate and H+ ions are formed and the receptors respond to the H+ ions
- Feedback via the respiratory centres increases ventilation in response to increased arterial PCO2
- Decreased arterial PCO2 slows ventilation rate
What happens to individuals with chronic respiratory conditions?
They are reliant on their peripheral chemo-receptors but they only account for 30% of respiratory control
PCO2 is chronically elevated in these individuals and their central chemoreceptros become desensitised to PCO2 and instead rely on changes in PO2 to stimulate ventilation
“Hypoxic drive”
How do the peripheral chemoreceptors work?
- Carotid and aortic bodies detect changes in arterial PO2 and H+ ions
- Causes reflex stimulation of ventilation following significant fall in arterial PO2 or rise in H+ ions
Sedation: How do Barbiturates work?
Inhibit phrenic nerve activity, decrease depth of breathing
Sedation: How do Opioids work?
(morphine) decreases the sensitivity to pH and therefore response to PCO2 - decreases peripheral chemoreceptor response to PO2
Sedation: How do Benzodiazepines work?
(diazepam) similar to opioids but less severe
Sedation: How does Nitrous oxide work?
Little effect on response to PCO2 but significantly depresses response to falling PO2
Caution with COPD patients as they lack central chemoreceptor responses (PCO2) - if both are suppressed them they have no involuntary control over breathing
