Module 2 topic 3: respiratory physiology

Respiratory mechanics

the study of the mechanical principles behind the movement of air in and out of the body

• chest cavity get larger= air flows in and air pressure decreases

• Cavity gets smaller = air flows out and pressure increases

what does Respiration incompass

used to describe the combination of pulmonary ventilation (inhalation + exhalation) and internal and external respiration

Internal respiration

the exchange of gases between the blood and cells

• O2 to the cell

• CO2 to the blood

External respiration

The process of gas exchange between the lung and the blood that involves pulmonary ventilation, Gas exchange and gas transport

pulmonary ventilation

the process of bringing air into and out of the lungs that involves both inhalation and exhalation

• could be unconcious quiet breathing and conscious deep breathing

what drives pulmonary ventilation

Driven by the differences in pressure between two areas ( air flows to areas of low concentration from areas of high concentration)

• Atmospheric pressure, the pressure around us (750mmHg)

• Intrapulmonary pressure: alveolar pressure, aka the pressure inside the lungs

Pressure of air in lungs at rest

When at rest, the pressure in the lungs is equal to the atmospheric pressure at their is no net air movement

• 760mmHg

How does change in volume relate to chnage in pressure

Boyles law: their is an inverse relationshipe between volume and pressure

• An increase in volume of the lungs leads to a greater area through which air particles can move around, meaning their is less pressure (air goes into the lungs)

• a decrease in volume of the lung causes an increase in pressure as the air particles have less space to move around (air goes out of the lungs)

Boyles law: inhalation (quiet breathing)

• At rest, the pressure in the lungs is equal to the atmosphere at 760mmHg

• the diaphragm contracts down and the rib cage expands, causing an increase in thoracic cavity and lung volume (requires energy)

• An increase in volume causes a decrease in air pressure below the atmospheric pressure, which creates a pressure gradient

• air flows into the lungs

Boyles law exhalation

• air pressure = the same as the atmosphere at 750mmHg

• The diaphragm relaxes, and the rib cage muscle moves the rib cage down, causing a decrease in lung volume

• The decrease in lung volume causes an increase in lung pressure above the atmospheric pressure that creates a pressure gradient

• air flows into the lungs

How do fibres in the lungs asist exhalation

Exhalation requires no energy, as after the initial movement of the diaphragm and rib cage muscles, they will begin to recoil back to their original position using elastic fibres

• also assisted by the surface tension in alveolar by preventing collapse

Deep forceful breathing

caused by high O2 demand during stress, exercise or speaking for too long

• active breathing that requires energy

• movement is controlled by the accessory muscle that contracts the diaphragm and rib cage even more than usual

deep inhalation

requires a greater increase in volume of the lungs to take in more air, leading to even lower pressure compared to the atmosphere

• sternocleidomastoids - elevate the sternum

• scaleues - elevate the first two ribs

deep exhalation

requires a greater pressure in the atmosphere to exhale the CO2 in the lungs, leading to a greater increase in volume

• abdominal (push diaphragm up further)

• Internal intercostal muscle (pull the rib cage down further)

How do the lungs move in the chest

The movement of the lungs is controlled by the difference in pressure ( transpulmonary pressure gradient) between the pleura and the alveoli.

• the pressure difference in the sealed environment of the pleura causes the lungs to follow movements of the thoracic cavity while also preventing lung collapse

what happens in inhalation that cases the lungs to move

During inhalation, the pressure in the pleural cavity reaches -4 mmHg, causing the air in the lungs to follow the movement of the thoracic cavity to which the pleura is attached.

• holds the alveoli sacs open but counteracts recoil

Cohesion forces

the forces between water molecules in the fluid of the pleural cavity that forces the membrane to adhere to one another whilst being able to slide over one another freely

what are the factors that effect Pulmonary ventilation

• lung compliance

• Lung elasticity

• Surface tension in alveolar fluid

• airway resistance

Pulmonary ventilation: lung compliance

How much effort is required to stretch or distend the lungs

• high compliance: expands easily with less effort ( Emphysema causes higher compliance due to the breaking down of elastic fibres)

• Low compliance: lungs require greater force to expand and needs more pressure to bring air in (pulmonary fibrosis)

Pulmonary ventilation: Elastance

How well the lungs can recoil after stretching is due to the presence of elastic fibres and the surface tension of the alveolar fluid

• High elasticity: strong tendency for the lungs to return to their resting shape after inhalation (normal)

• Low elasticity:(emphysema causes the break of the fibres, making it more difficult for the lungs to recoil, leading to trapped air)

Pulmonary ventilation: surface tension

The tension of the layer of fluid that lines the alveoli is reduced by pulmonary surfactant

• Low surface tension: Increases compliance and decrease elasticity to allow for easier breathing

• High surface tension: lungs colapse and fluid enters the alveoli

Pulmonary ventilation: resistance

The resistance of air flow in the airway is determined by the diameter of the airway

• Bronchiodilation: the relaxation of smooth muscle in airways that increases airway diameter but decreases the resistance of air flow

• Bronchoconstriction: the contraction of smooth muscle that decreases airway diameter and increases resistance ( excessive contraction leads to asthma

how is lung function measured

Spirometry measures the lung volume and lung function that allow us to determine lung capacity

• Some measurements can depend on the compliance of the patients

• tells us how much air we can hold and move in

Respiratory rate

The amount of air breathed in per minutes that can be changed based on O2 demand

• Healthy adult = 12-18 breaths per minutes

what are the lung volumes

• Inspiratory reserve volume ( the additional air we can breathe in after normal regulation = 3000ml)

• Expiratory reserve volume( the addition air we can breath out after normal exhalation = 1000ml)

• Tidal volume (amount of air moving in and out of the lungs in a single quiet breath = 500ml)

• Residual volume (air in the lungs after maximum exhalation, which is there to prevent lung collapse)

what are the measured lung capacities

• Inspiratory capacity - tidal volume + inspiratory reserve = 3500ml

• Functional residual capacity - expiratory reserve + residual = 2200ml

• Vital capacity - tidal + inspiratory + expiratory = 4500ml

• Total lung capacity - sum of all volumes = 3700ml

Forced expiratory volume

the volume of air that can be exhaled in 1 second of exhalation

• used to determine how well the lungs are functioning

Gas exchange

The exchange of O2 and CO2 across the blood-air barrier in the lungs and between cell and blood

• passive, so requires no energy

• moves allow the partial pressure gradient

air blood barrier

the layer (0.5 micrometers) between the lumen of the capillaries and the inside of the alveoli that contains

• Layer of the capillary = endothelium

• Middle = basement membrane

• layer of the alveoli = single layer of pneumocytes type 1

• surfactant to reduce surface tension of fluid in the alveoli

Gas exchange: fick’s law

• Diffusion is proportional to surface area, pressure gradient and the permeability of the membrane ( increase in surface area and pressure difference = quicker diffusion)

• Diffusion is inversely proportional to distance (the thicker the membrane or fluid build up slower the diffusion)

Gas exchange: Dalton’s law

Each gas in a mixture has its own partial pressure that is equal to its concentration

• This is why O2 and CO2 can move independently of one another

Gas exchange: henry’s law

Amout of gas dissolved in a liquid is equal to the partial pressure and solubility of a gas

Partial pressure

P(mmHg) describes the concentration of one gas in a mixture of gases

• PO2 or PCO2 = the partial pressure

• diffusion occurs down the concentration gradients, so the concentration of O2 in lungs has to be lower than the atmosphere to breath in

atmospheric composition/pressure

atmospheric pressure x the percentage of partial pressure = PO2

Air Lungs

• N (78.6% = 597mmHg) (7.54% 573mmHg)

• O (20.9% 159mmHg) (13.2% 100mmHg)

• CO2 (0.04% 0.3mmHg) (5.2% 40mmHg)

• H2O (0.46% 4.2mmHg) (6.2% 77mmHg)

diffusion in a liquid

The amount of gas dissolved in a liquid is equal to the partial pressure of a liquid

• can occur at any temp

• partial pressure of gas will increase until equilibrium is reached with the atmosphere

relationship between increase in volume and diffusion of gas

• decreased volume = increase in air partial pressure, causing the diffusion of gas into a liquid (closed and sealed soda can)

• Increased volume = decrease in air partial pressure that leads to the diffusion of gas out of the liquid (open a flat soda can)

what happens when liquid is expose to 2 gases

If they have an equal partial pressure, they will move in opposite directions until the equilibrise

• concentration of the gases won’t as CO2 is more soluble hence their would be a high concentration in blood while O2 needs to be carried by haemoglobin

Diffusion of O2 in lungs

During inhalation, the PO2 in the lungs is 100 mmHg, and the PO2 in the blood is 40mmHg

• air moves until equilibrium in partial pressure = 100mmHg in each

Diffusion of CO2 in lungs

the PCO2 of the lungs is 45mmHg and PCO2 = 40mmHg

• continues until Partial pressure = 45mmHg

diffusion of gas between blood and tissue

O2 and CO2 travel between the blood and the interstitial tissue

• PO2 = 95mmHg in capillary and 40mmHg in cell so O2 moves into cell

• PCO2 = 40mmHg in capillary and 45mmHG in cell so CO2 moves into blood

How is O2 transported through the blood

O2 is transported through the blood using haemoglobin, which contains a protein called globin with 1 iron molecule each

heme = red pigment in blood

procces of oxygen binding to haemoglobin

4 Oxygens bind to the 4 iron in haemoglobin (HbO2)

• 1 oxygen binds to 1 iron, causing the haemoglobin to change shape, allowing more oxygen to bind (binds sequentially

• each oxygen binds with a greater affinity than the last and that affinity is lost and oxygen is lost to cells

oxyhaemoglobin curve

an S-shaped curve that shows the relationship between the percentage of haemoglobin saturation and PO2

• higher saturation = High PO2

• Saturation and alveoli = 100% and reduces to only 75% at the resting state

• saturation never drops below 40% to be used just in case metabolic demand dramatically increases

Factors that alter the affinity of O2

An increase in affinity leads to a stronger binding that makes it more difficult for oxygen to unbind from haemoglobin and enter cells

• pH

• Temp

• PCO2

affect of pH on O2 affinity

• decrease in pH leads to a decrease in saturation to 60% at rest (increased O2 unloading - decreased affinity)

• Increase in pH leads to an increase in saturation to 80% at rest (decreased O2 unloading - increased affinity)

pH can increase or decrease depending on CO2 saturation or due to lactic acid concentration that is produced during anaerobic respiration due to low O2 levels

effect of increased CO2 on O2 affinity

saturation reaches 75% at an increase in CO2 leads to decreased affinity, that make oxygen unloading easier

effect of temp on O2 affinity

• A decrease in Temp leads to 50% saturation at rest causing a decrease in affinity and an increase in O2 unloading (maybe in an attempt to keep warm)

• increase in temp leads to 100% saturation at rest causing a increase of O2 affinity that make it more difficult for oxygen to unload

what is the Bohr effect

the process at which High CO2 concentrations and High H+ concentrations promote the production of Carbonic acid that lower pH and decreases O2 affinity

• increase in H+ leads to an increase in pH that leads to an increase in O2 saturation as the H_ ions bind to haemoglobin, allowing them to more easily release O2 into tissues

How is CO2 transported through the blood stream

• 7% of CO2 is dissolved in the blood

• 23% is bound to haemoglobin, forming carbaminohaemoglobin

• 70% as bicarbonate ions (bicarbonate ions in haemoglobin are replaced with chloride ions, and then they dissociate)

How is the diffusion of gases regulated locally

the diffusion of gases and the direction at which they move is regulated locally by pressure differences and by the presence of gases

• and increase in CO2 leads to a decrease in O2 due to metabolic conversion

• and increase in CO2 also causes vasodilation and more blood flows to capillaries to remove the CO2

Ventilation perfusion

the relationship between airflow in teh alveoli and blood flow in the capillaries

• air flow = alveoli ventilation(V)

• blood flow = Lung perfusion (Q)

• need to be equal to one another

how is ventilation perfusion regulated locally

maintained via the adjustment of of vessel diameter called V/Q matching

• capillaries constrict when alveoli O2 decreases causing it to be redirected to a more efficient alveoli

• bronchioles dilate when increase in CO2 to increase gas removal

what is Involuntary Neural regulation

the involuntary breathing pattern that is set by 3 pairs of nuclei in a retangular shape of the medulla oblongata and the pons

• in brain stem

• 3 pairs of nuclei make the respiratory rhythmicity center

Involuntary Neural regulation: respiratory rhythmicity centre

Contains 2 neuron groups called the dorsal respiratory group (DRG) and the ventral respiratory group (VRG) and is responsible fir

• basic respiratory rate (breaths per minutes)

• rhythm

• depth of respiration (Inhalation = 2 sec + exhalation = 3 sec)

Dorsal respiratory group function

A cluster of neurons that control inspiration during normal quite breathing by sending out signals that contract the necessary muscles (diaphragm and intercostal)

• when active: inhalation occurs

• when inactive: passive exhalation occurs due to recoil of elastic fibres

Ventral respiratory group

group of neurons that control inspiration and expiration that lead to forceful breathing

• stimulated by a decrease in DRG activity

• Activates accessory muscles

Ventral respiratory group when active

Both the inspiratory and expiratory neurons are active causing the rhythmic contraction of muscle nescersary for forceful inhalation and exhalation

• DRG is also active and all inhalation

Ventral respiratory group when inactive

when not active the DRG is active and undergoes normal respiration

what are the centres that make up the pons

work together to adjust the output of respiratory centres and modify rate and depth of breathing to match metabolic rate

• Apneustic centre: stimulates DRG continuously to respond to sensory input in inhalation (facilitates inhalation)

• Pneumotoxic centre: Inhibits the other centres to trigger passive or active exhalation

Voluntray Neural regulation

the temporary override of involuntary neural respiratory control required for speaking, singing or holding your breath

• will eventually be taken over by involuntary neural regulation

factors that affect voluntary neural regulation

• strong emotion: stimulates areas of the hypothalamus

• emotional state: can activate the sympathetic or parasympathetic nervous system in the automatic NS (causes bronchodilation/ contracting impacting airflow)

• anticipation of exercise: stimulates the sympathetic nervous system and increase cardiac output and respiratory rate

Chemical regulation

the regulation of the respiratory system that involves the use of chemoreceptors that detect change in blood gas composition and pH.

Peripheral chemoreceptors - location + function

Location: aorta and carotid arteries

functions: responds strongly to pH changes in plasma (caused by CO2) and weakly to O2 level when they are low (40% saturation)

Central chemoreceptors - location + function

Location: medulla

Function: pH changes in the cerebrospinal fluid caused by increased CO2 diffusion across the blood brain barrier

process of regulation: hypercapnia

Hypercapnia: arterial PCO2 increase via abnormal respiratory rate in hypoventilation ( doesn’t remove enough CO2)

Receptor: chemoreceptors triggered by PCO2 increase and pH decrease

Effector: stimulates respiratory muscle to increase that rate and depth or respiration ( increase CO2 removal)

process of regulation Hypocapnia

Hypocapnia: decrease in arterial pressure due to hyperventilation

Receptor: chemoreceptors are inhibited by decrease in CO2 and increase in pH

Effector: respiratory muscle are inhibited causing a fall in respiratory rate and CO2 removal

Respiratory defuse system

consists of respiratory endothelium that is responsible for removing dusts, pathogens, pollutants or bacteria

• goblet cells make mucous to trap foreign objects and the cilia move it up to be coughed out or swallowed

• can breakdown due to the overactivity of the immune system

what can stimulate the over activity of the immune system

• irritants

• agressive pathogens

• genetic diseases

Irritants - types + causes

irritants include cigarette smoke, asbestos that rigger inflammatory responses that can damage the lungs in the long-term and increase mucous production.

• causes Lung cancer or COPD (astma, emphysema, chronic bronchitus)

how can irritant causes overactivity of immune system

Macrophages and WBCs produce protase to break down the particles that when made in excess can begin to breakdown the lung tissue

• can also damage the kung repair system and DNA repair systems leading to cancer

Aggressive pathogens

causes bacterial infections that can spread from the lungs but can remain dormant for a long time before infection occurs if it does at all

• Infections often triggered by immunocompromisation via other diseases or poor hygiene/nourishment

• able to evade and destroy macrophages causing excessive macrophage production

genetic diseases

leads to the failure of respiratory endothelium in the removal or mucous that can lead to chronic infections or death

• cystic fibrosis. primary ciliary dyskinesia or COPD

• cystic fibrosis due to mutation in the chloride ion channel in mucous production causing it to become too thick for removal.

Obstructive lung diseases

includes emphysema, asthma and bronchitus that lead to a decreased in expiratory reserve volume and an increase in airway resistance leading to difficulty exhaling

Restrictive lung diseases

includes lung fibrosis that leads to tissue scaring that reduced elasticity and compliance or lung distress syndrome

• leads to decrease in total lung capacity and inspiratory reserve volume

asthma + symptoms

overactive narrowed airways that are excessively triggered by allergens, cold air, smoke or exercise

• chronic inflammation of airway walls (swelling, irritation or thickening)

• bronchioconstriction ( smooth muscle contracts and narrows airways)

• wheezing, shortness or breath, tightness inc hest and air trapping

asthma treatment

reversible with bronco dilatory or anti-inflammatory medications that reduce airflow resistance, increase diameter and mucous production

Emphysema

caused by the overinflamatory responce to irritants such as cigarette smoke that s progressive and only reversible in the short-term

• excessive protase that causes the breaking down of lung tissue lead to reduced compliance

• causes air trapping that causes a barrel chest

emphysema + symptoms and treatment

• increase in residual volume of air left in lefts that makes it more difficult to exhala efficiently

• Damages alveoli walls leading to a decrease in surface area for gass excahnge( also decreases elasticity

• protase breaks down CT anchors an bronchioles that hold the opn leading to increased chance of collapse

can be reduced through supplemental oxygen

The structure of the respiratory tract

Mucousa(innermost)- layer of epithelial tissue + basement emenrane with lamin propris (thin lamina

Submucosa - dense irregular CT and smooth muscles with glands

Hyoline cartilage - dence ECM embedded with chondrocytes

adventitia (outermost) - CT