Respiration (30-32) Flashcards
What is external respiration?
Exchange of oxygen and carbon dioxide between an organisms and external environment
What is the difference between breathing and ventilation?
Breathing → the physical act of muscle contraction/relaxation that move bones that change the volume of the lungs to move air in and out of the lung
Ventilation → movement of air from outside to inside the body for exchange of gas between air in the lungs and blood in capillaries within the alveoli - ventilating a patient: pushing air not breathing for them
What are the 3 aspects to the central control of breathing?
Reflex/automatic → generates respiratory rhythm coordinated in the ventral respiratory column
Voluntary/behavioural → control of breathing patterns
Emotional → can override respiratory patterning
What generates respiratory rhythm?
Reflexive/automatic control
Inspiratory rhythm → preBotzinger complex
Expiratory rhythm → parafacial respiratory group (pFRG)
Where does voluntary control of breathing originate?
Motor cortex
→ motor cortex neurones that modulate breathing synapse in the pons (part of your brainstem)
When can voluntary control of breathing not be maintained?
When stimuli, such as Pco2 or H+ become too intense → the breaking point
Can emotional control of breathing still occur in locked in syndrome?
Yes
→ volitional control does not occur
How does emotional control of breathing arise?
Through corticospinal projections
What feedback mechanisms pattern breathing?
Central/peripheral chemoreceptors (monitoring of blood gases)
Protective reflexes
Pulmonary stretch receptors
How does arterial Pco2 control breathing?
Arterial CO2 is the major chemical factor regulating minute breathing
→ excess CO2 (hypercapnia) leads to acidification
→ ability of Pco2 to control breathing associated with change in [H+]
→ central and peripheral chemoreceptors respond to high Pco2
How does hypoxia/hypercapnia modulate breathing?
Small increases in inhaled CO2 will stimulate breathing → 10% rise in CO2 - 100% rise in breathing, 20% rise more than trebles breathing
Hypoxia to a lesser degree → 35% drop in O2 - 20% increase in breathing, 55% drop in O2 - doubles breathing
What do peripheral chemoreceptors detect?
Alterations in blood gases - predominately oxygen (80% O2 detection, 20% CO2 detection)
→ carotid bodies, aortic bodies
→ respond to arterial blood changes (hypoxia, hypercapnia, acidosis)
What do central chemoreceptors detect?
Alterations in blood gases - predominantly CO2 (70% of CO2 detection, 30% of O2 detection)
→ mainly located in the medulla oblongata
→ respond to changes in cerebrospinal fluid (increased Pco2, changes in [H+]/pH)
What do slowly adapting pulmonary stretch receptors monitor?
Lung inflation
→ in smooth muscle on bronchi and trachea
→ signal lung volume to brain
→ inhibit inspiration and lengthen expiration (Hering-Breuer inflation reflex)
→ regulating respiratory rhythm e.g. exercise and sleep in neonates
What do rapidly adapting pulmonary stretch receptors monitor?
Irritants
→ in epithelial cells in larynx, trachea and airways
→ respond to mechanical stress: large inflation/deflation
→ respond to chemical environment of lung: noxious gases, dust, cold, histamine
→ constrict airway and promote rapid shallow breathing - responsible for ‘gasping inspirations of the newborn’
→ promote cough in trachea and larynx
→ promote signing due to gradual collapse of lungs (atelectasis) ~5 minutes
What are the two major determinants of lung compliance?
Lung compliance required so they can inflate and deflate - ability to expand lungs at any given change in trans pulmonary pressure
→ 1. stretchability of tissues
→ 2. surface tension within alveoli
How is surface tension within alveoli lowered?
By pulmonary surfactant
→ surface of alveoli is moist
→ surface tension at air-water interface resists stretching
→ pulmonary surfactant (lipids) lowers tension and increases compliance
What is pulmonary surfactant?
Lines the alveoli to lower surface tension
→ released from type II alveolar cells during sighing - prevents lungs collapsing
→ mixture of phospholipids and protein
→ makes lungs easier to expand
What are pulmonary protective reflexes?
Responses that protect the respiratory system from irritants
→ cough reflex: due to receptors in epithelial cells of upper airways
→ sneeze reflex: due to receptors in epithelial cells of nose of pharynx
What are the 3 phases of rhythmic breathing?
Breathing depends on the cyclical excitation of respiratory muscles
1. inspiration → active: initiated by activation of the nerves to the inspiratory muscles
2. post-inspiration → active: recruitment of post-inspiratory muscles
3. expiration → passive: inspiratory muscles relax and lungs recoil, active: activation of exploratory muscles
What happens when inspiratory muscles contract?
Contraction of inspiratory muscles draws air into the lungs
scalene → lift chest plate up
intercostals → open up rib cage
What is the function of the diaphragm?
Most important respiratory muscle (70% of tidal volume)
→ asymmetrically innervated
→ cruel diaphragm slows recoil
→ upon inhalation, the diaphragm contracts and flattens and the chest cavity enlarges
→ this contraction creates a vacuum, which pulls air into the lungs
What does contraction of the tongue support?
The airway and reduces resistance during inspiration
→ helps to move air efficiently
What is the thorax?
A closed compartment separated from the abdomen by the diaphragm
→ contained by spinal column, sternum, ribs and intercostal muscles
→ lungs and wall of the thorax are covered by thin membranes - pleurae
What are the different pleurae?
Visceral pleura → thin layer of epithelium covering each lung
Parietal pleura → lines inner surface of the walls of the thorax
Pleural cavity → maintains a partial vacuum which helps keep the lungs expanded
→ intra pleural fluid allows pleura to slide over one another - stops separation
How is pressure generated inside the plura?
Differential set points of muscles and lungs
→ lungs want to be further apart - fluid prevents it
What is transpulmonary pressure?
Ptp = Palv - Pip = 760 - 756 = 4mm Hg
(needs constant pressure so lungs don’t collapse)
Ptp → transpulmonary pressure: difference in pressure between the inside and outside of the lungs within the thorax
Pip → intra pleural pressure: the pressure outside the lungs in the thorax
Palv → alveoli pressure: the pressure inside the lungs
Palv > Pip - keeps the lungs inflated
What causes pneumothorax (collapsed lung)?
Air in the plural cavity
→ occurs when perforation of the lung or chest wall allows air to enter intrapleual space
→ trans pulmonary pressure decreases
→ elastic recoil collapses the lung
How does air move into the lung?
Air moves by bulk flow, from region of high pressure to one of low pressure
Ohms law: Q = (P1-P2)/R
Flow = (Patm-Palv)/R
Patm fixed to Palv must be altered to achieve air flow
How does alveolar pressure change?
By changes in volume of the lungs
Boyle’s law → P1V1 = P2V2
for a given volume there’s a certain amount of collisions
→ if volume inside lungs is changed, pressure inside lungs will also change
What happens to alveolar pressure during inspiration?
During inspiration
→ muscles of chest wall and diaphragm contract
→ ribs pulled upwards and diaphragm flattens
→ thorax enlarges Pip lowers, trans pulmonary pressure increases
→ chest volume increases to alveolar pressure decreases
Palv < Patm so air moves in
How do O2 and CO2 move between alveoli and blood?
By diffusion
→ occurs from a region where partial pressure is high to a region where it is low
What is the pressure of atmospheric air?
(total pressure is the sum of all the partial pressure of all the gases)
In atmospheric air: Patm = PN2 + PO2 + PCO2 = ~760mm Hg
How is partial pressure of gases in tissue determined?
By combustion of glucose - breaking something down with CO2
→ consumes 70-100% of oxygen, tissue PO2 = 30mm Hg
→ produces 45-70 mm Hg PCO2, tissue PCO2 = 45mm Hg
What are the two pulmonary dead spaces?
Anatomical dead space → volume of gas within the conducting airways, increases PCO2 in the alveoli
Physiological dead space → volume of gas not involved in gas exchange
→ two are almost equal in healthy lungs
→ dead space elevates CO2 levels within the body
How does gas exchange occur in alveoli?
O2 diffuses from alveoli into the lung capillaries → alveolar Po2 > pulmonary Po2
CO2 diffuses from the lung capillaries into the lung → alveolar Pco2 < pulmonary Pco2
How does gas exchange occur in tissues?
O2 diffuses from the tissue capillaries into the tissue → blood Po2 > tissue Po2
CO2 diffuses from the tissue into the tissue capillaries → blood Pco2 < tissue Pco2
What is the respiratory quotient (RQ)?
The ratio of CO2 production to O2 consumption
→ varies between 0.7-1.0, average 0.8
alveolar PO2 = inspires PO2 - (blood PO2/RQ)
How is oxygen primarily transported?
On haemoglobin
→ >98% of O2 reversibly combines with haemoglobin molecules in erythrocytes
→ <2% of O2 dissolved in the plasma and red blood cell water
What is the purpose of haemoglobin’s saturation curve?
Haemoglobin holds oxygen in a reversible combination so it can be released to tissues
→ when Po2 is high (in alveoli) haemoglobin binds O2
→ when Po2 is low (in tissues) haemoglobin releases its stored O2 reserves
What is the Bohr effect?
CO2 causes O2 to dissociate from haemoglobin, CO2 shifts the saturation curve to the right
→ CO2 causes haemoglobin to release more O2
→ CO2 diffuses from venous blood into alveolar space allowing more O2 to load onto haemoglobin
→ temperature and acidity promote O2 unloading
→ CO2 has a higher affinity for haemoglobin
How is CO2 transported in the blood?
- dissolved in plasma (5%)
- in red blood cells (bound to Hb or dissolved in cytoplasm)
→ most CO2 is converted into carbonic acid by enzyme carbonic anhydrase
→ carbonic acid immediately dissociates into H+ and HCO3-
→ HCO3- ions are transported out of red blood cells in exchange for Cl- ions (70%) - chloride shift - Cl- allows for greater unbinding of CO2
Why does carbon monoxide poisoning occur?
Because CO has a higher binding affinity for Hb
→ CO displaces O2 from Hb to form carboxyhaemoglobin, thus decreasing the amount of O2 that combines with haemoglobin in pulmonary capillaries
→ Hb saturation curve shifted to the left, thus decreasing the unloading of O2 from haemoglobin in the tissues
How is the respiratory system organised?
Air is delivered to the lungs via the trachea → from the mouth and nose
There are two lungs, each divided into lobes → 3 lobes in right lung, 2 lobes in left lung
Bronchi and bronchioles distribute air throughout the lungs → respiratory bronchioles give rise to alveoli (site of gas exchange)
Respiratory tree → comprises the branching structures from the trachea to the alveoli
What are the divisions of the respiratory system?
The upper/lower airways → anatomical divisions
The conducting zone
The respiratory zone
What is the upper airways?
aka upper respiratory tract
→ mouth, nose, pharynx, larynx
→ infection symptoms: sneezing, nasal discharge, runny nose, nasal congestion, fever, sore throat - non
→ obstruction of the upper airways causes snoring during sleep
What is the lower airways?
aka the lower respiratory
→ extends from the top of the trachea to the alveoli
→ infection symptoms: bronchitis, oedema, shortness of breath, weakness, fever, coughing, fatigue - affect gas exchange
What is the conducting zone?
Extends from mouth and nose to terminal bronchioles
→ conducts air but does not exchange gas
→ provides low-resistance pathway for airflow
→ warms (or cools) and moistens the air
→ defends against microbes, toxic chemicals and other foreign matter
→ airway resistance decreases from bronchi to terminal bronchiole
What defence mechanisms does the airway have?
Contraction of bronchioles via smooth muscle
Cilia → hair-like projecting from epithelial cells that line airways, constantly beat upward toward the larynx, immobilised by many noxious agents, smokers damage cilia - lots of mucus
Mucus → secreted by glands and epithelial cells lining the airways, particulate matter and bacteria in sipped air sticks to mucus, continuously moved by cilia, swallowed every 30s
Macrophages → phagocytic cells that are present in airways and alveoli, engulf and destroy inhaled particles and bacteria, injured by noxious agents (air pollutants, cig smoke)
What is asthma?
Disorder of the conducting zone
→ chronic inflammation - causes airway smooth muscle to be hyper-sensitive to triggers
→ intermittent episodes of smooth muscle contraction increases airway resistance
→ reduced airway diameter increases work of breathing
→ reversible: short-acting beta2 adrenergic receptor agonist e.g. salbutamol (ventolin)
What is bronchitis?
Disorder of the conducting zone
→ persistent inflammation of the bronchial walls, airways are inflamed and thickened
→ increase in mucus-secreting cells and loss of ciliated cells
→ obstruction of the airways, hindering both breathing and oxygenation of the blood
What is the respiratory zone?
Extends from respiratory bronchioles to alveolar sacs
→ provides O2, eliminated CO2
→ regulates blood pH in coordination with the kidneys
→ influences arterial concentrations of chemical messengers
→ traps and dissolves blood clots arising from systemic veins
What is the pulmonary circulation?
Includes blood pumped from the right ventricle through the lungs to the left atrium
→ large network of capillaries in the alveolar walls
→ low pressure (15mm Hg), 70ml blood
→ high-flow (5L blood/min) system, blood cells spend 0.75s in lung
How is blood supplied to the respiratory zone?
Each alveoli associated with many pulmonary capillaries
→ inhaled air is brought close proximity to pulmonary blood
→ allows efficient gas exchange between air and blood, alveolar walls very thin
How is gas exchange in alveoli optimised?
Thinness of barrier between blood within the alveolar wall capillary and the air within the alveolus
→ the vast surface area of alveoli in contact with capillaries
→ the moist surface of the alveolar cells
What is emphysema?
Disorder of the respiratory zone
→ lungs undergo self-destruction by proteolytic enzymes secreted by leukocytes
→ adjacent alveoli fuse to form fewer but larger alveoli - reduces SA available for gas exchange
→ destruction of alveolar walls and collapse of lower airways
→ increased airway resistance due to inflammation - greatly increases the work of breathing
What is chronic pulmonary disease?
Chronic bronchitis and emphysema
COPD 2011 4th leading worldwide cause od death
→ ~65mil suffered worldwide, ~ 3mil deaths per annum
