The respiratory system Flashcards
what is respiration
the process of supplying oxygen and removing carbon dioxide from the tissues
external, internal and cellular respiration
external- exchange of gases between lungs and blood
internal- exchange of gases between blood and cells
cellular- oxidation of glucose >energy
aerobic respiration
requires a constant supply of oxygen
glucose+oxygen=carbon dioxide+water+atp
what structures do the respiratory system consist of
the air conducting passages- nose, pharynx,larynx, bronchi and bronchioles
the respiratory surfaces (lungs)- respiratory bronchioles, alveolar ducts and alveoli
nasal cavity functions and adaptions
functions- filters, warms and moistens incoming air
adaptions- ciliated epithelium, mucus producing cells and surface area contact with blood supply
pharynx function and adaptions
function- continues to moisten and warm air
adaptions- mucous membrane - warm moist surface
larynx and epiglottis function and adaptions
functions- larynx- conducts air snd sound production, epiglottis- protects air passage
adaptions
larynx- contains vocal cords (epithelial flaps) which vibrate as air pass over them
epiglottis- flap of tissue closes over the larynx during swallowing, it prevents passage pf fluid into lungs
trachea, bronchi, bronchioles and terminal bronchioles functions and adaptions
functions- conducts air to respiratory surfaces, continues to filter air
adaptions- walls contain cartilage-maintains patency
smooth muscle- dilation of bronchioles
ciliated epithelium- continues to filter
respiratory bronchioles, alveolar ducts and alveoli functions and adaptions
functions- exchange of gases
production of surfactant-maintains patency of alveoli(prevents collapse)
adaptions- epithelial layer-one cell thick- surrounded by pulmonary capillaries- also one cell thick- facilitates diffusion
other epithelial cells produce surfactant-detergent action
structural and functional relationship with CVS
proximity of organs
- structural- main organs of both systems within the thoracic cavity
- functional- minimal distance for blood to travel
alveolar-capillary barrier:
-structural-capillary network wrapped closely round alveoli
-functional-adequate surface area for gaseous exchange and diffusion distance minimised
mechanism of breathing
the thorax is a closed cavity- sealed off from the outside air except for the trachea
thoracic cavity- lined by pleura-suction force
elastic lung tissue
stimulation by nerves from the respiratory centre-causes contraction of the respiratory muscle simultaneously
respiratory cycle
respiratory movements occur approx 12-14 times per minute. it is a cycle of events:
inspiration- active process, contraction of muscles
expiration- passive process, elastic recoil of lungs
pause
the pleura
double serous membrane-2 layers continuous- double back at helium of lung
between pleura-serous fluid (potential space)
exerts a negative pressure
inspiration
external intercostal muscles contract-ribs and sternum move up and put and diaphragm contracts
simultaneous action results in overall increase in capacity of thorax
pressure in pleural cavity reduced
increases suction pull on elastic lung tissue -stretched- expands to fill thoracic cavity
air pressure in alveoli- less than atmospheric pressure - air drawn in from atmosphere
expiration
external intercostal muscles relax, ribs and sternum go down and in and diaphragm relaxes, ascends to dome shale
simultaneous action results in overall decrease in capacity of thorax
pressure in pleural cavity increased
decreased suction pull on lung tissue elastic tissue recoils
air pressure in alveoli- greater than atmospheric pressure- air forced out into atmosphere
factors effecting efficiency of ventilation
compliance, airway resistance, surfactant
compliance-the ease which the lungs and thorax can be expanded
high compliance- expands easily (healthy tissue)
low- resistance to expansion
airway resistance
airflow depends on pressure diff between alveoli and atmosphere/ resistance of bronchi and bronchioles
degree of contraction of smooth muscle in walls of airways regulates diameter of airway-therefore resistance
increased sympathetic stimulation relaxes smooth muscle>bronchodilation (reduces resistance)
conditions causing narrowing of the airways> increased resistance
surfactant
a detergent like substance secreted by type 2 alveolar cells
a complex mixture of phospholipids and lipoproteins
reduces the surface tension in the alveoli
effort of inspiration to overcome surface tension reduced
eupnea, apnoea, hyperpnoea and hypopnea definitions
euponea- normal breathing
apnoea- absence of breathing
hyperpnoea- over breathing/ hyperventilation
hypopnoea- under breathing/ hypoventilation
what is tidal volume
tidal volume is the volume of air entering or leaving the lungs with each breath
resting Vt is about 500ml male and 375ml female
increases during exercise
vital capacity
max volume of air that can be moved in or out the lungs with a single breath
residual volume
volume of air left in the lungs after maximal respiration
anatomical dead space
includes air from regions where no has exchange occurs (airways and unperfused alveoli)
part of tidal volume, since air must flow through these dead spaces with each breath to reach alveoli
pulmonary circulation
deoxygenated blood in arteries and oxygenated blood in veins
lower pressure than systemic circulation
blood vessels constrict in response to lack of oxygen
this diverts blood to better oxygenated parts of the lung
allows for ventilation/perfusion matching
blood vessel structure and function
regulation of tone dependent on vasodilator /vasoconstrictor stimuli:circulating hormones, neurotransmitters, EDF, blood pressure
all help determine contractile state hence vessel diameter and hydraulic resistance
-contractility is major determinant of resistance to blood flow
-contractile state known as vascular tone
- tone helps regulate blood pressure and blood flow distribution, ion channels fundamental to this process
ion movement across the plasma membrane determines membrane potential
MP and calcium conc. regulates influx and release
influences sensitivity of contractile apparatus
calcium triggers contraction
ion channels expressed by vascular smooth muscle
potassium channel(Katp, BKca, Kv, Kir) calcium channel( l type amd t type) chlorine channels(Clca, Clvol) non specific cation channels
unique features of pulmonary circulation
8x lower pressure, thinner walls, collapsible capillaries and very low resistance to blood flow
gas exchange
gas exchange is optimal at both low and high cardiac output, takes place at alveolar level. the capillaries are densely packed in a continuous sheet of blood flow around the alveoli, giving a maximal contact surface to enhance gas exchange
each alveoli is perfused proportionally to its ventilation, when oxygen partial pressure is low in a region of the lungs, adjacent vessels contract and divert the blood away to better ventilated areas. by actively regulating local perfusion, acute HPV optimises conditions for gas exchange
hypoxic pulmonary vasoconstriction (HPV)
unique feature of the pulmonary circulation (in the systemic circulation low O2 results in dilation)
HPV is an important physiological function
optimises ventilation/perfusion match. potential to increase arterial blood PO2
segmental hypoxia in some diseases e.g. pneumonia diverts blood away from hypoxic lobe.
global hypoxia results in elevated pulmonary pressure
pulmonary vein constriction resulting in oedema formation
observed at all levels (isolated lung to single cells) appears to nr intrinsic to smooth muscle
driven primarily by pulmonary arteries (but veins also important)
ventilation/perfusion ratio
0.8 ideal ratio to provide optimal gas exchange
oxygen transport
99% combined with haemoglobin to form oxyhemoglobin minute amount (1%) dissolved in plasma
haemoglobin
4 haem-porphyrin ring structures containing iron that binds to oxygen
4 globin polypeptide chains(2 alpha, 2 beta)
many different genetic variants, some of which have diminished oxygen biding capacity
conditions that effect association of oxygen and hb
pH
temp
2,3-DPG (an intermediate in glucose breakdown)
how is CO2 utilised around the body
7% dissolved in plasma
combined with haemoglobin to form carbaminohaemoglobin 23%
buffered as bicarbonate ion 70%
carbonic anhydrase
important enzyme found in red blood cells (and elsewhere eg kidney)
catalyses conversion of CO2 to carbonic acid H2CO3
how is CO2 transported around the body
buffering by Hb facilitates production of plasma Na HCO3. this in turn modulates CO2 dissociation in plasma. Hb therefore modulates plasma pH by modulating [HCO3]
CO2 dissociation in RBC principally affected by Hb
CO2 in plasma dependent only on PCO2
what regulates PCO2 and [HCO3]
lungs, kidney
how may pH be maintained
kidney activity/respiratory activity
what happens as Hb loses O2
H affinity increases
respiratory acidosis
primarily increase in pCO2 (carbon dioxide retention) e.g. respiratory depression. increase in PCO2 causes decrease in pH. kidney compensates by excreting H+ producing highly acidic urine
respiratory alkalosis
primarily decrease in PCO2 e.g. voluntary over-breathing, chronic oxygen decrease. decrease in PCO2 causes increase in pH. kidney compensates by excreting HCO3
metabolic acidosis
primarily H level too high in the blood e.g. starvation
decreased pH blood registered by central chemoreceptors which:
stimulates respiration, more CO2 lost from lungs, dec PCO2, dec [H], inc pH
respiratory changes (hyperventilation) compensate for changes in pH
metabolic alkalosis
primarily increase HCO3 in blood e.g. excessive vomiting, ingestion of HCO3:
inc HCO3, dec [H], inc H
registered in chemoreceptors
inhibits respiration, less CO2 lost in lungs, inc PCO2, inc [H], dec
pH
respiratory change (hypoventilation) compensate change in pH
control of respiration
generally an involuntary automatic event but under certain conditions may become voluntary,
respiratory centre- groups of specialised neurones in the medulla oblongata and the pons, responsible for involuntary control.
areas in the cerebral cortex responsible for voluntary control
alveolar PCO2 normally held constant, effects of excess H in blood is combated, PO2 is raised when it falls to a potentially dangerous level.
breath to breath control is achieved by regulation of CO2 levels through central chemoreceptors. haemoglobin is highly saturated with oxygen- even in venous blood at rest still 75% saturated
‘alarm’ must be triggered if O2 levels fall to extent that saturation of hb is compromised- achieved through peripheral chemoreceptors.
central chemoreceptors
located in the medulla of the brain, sensitive to pH and pCO2 but not PO2, actual stimulus is change in pH which results from change in pCO2
peripheral chemoreceptors
aortic body- located in the wall of the aorta
, carotid bodies- located at the bifurcation of the carotid arteries (main supply to the head). sensitive to changes in PO2 (facilitated by very high blood flow to the bodies)
effect of changes in blood oxygen level on respiration
INCREASE IN PO2:
registered by peripheral chemoreceptors, inhibits respiration, pO2 will fall back to normal
DECREASE IN PO2:
registered by peripheral chemoreceptors, stimulates respiration, chemoreceptors particularly sensitive when pO2 in the range of the steep portion of the oxygen: haemoglobin saturation curve, stimulation of respiration facilitates oxygen uptake in the lungs increasing PO2 back to normal.
effect of changes in blood CO2 level on respiration
INCREASE IN PCO2;
registered as decrease in pH in central chemoreceptors, stimulates respiration, more CO2 lost out of lungs during expiration, so PCO2 falls back to normal
DECREASE IN PCO2;
registered as increase pH central chemoreceptors, inhibits respiration, less CO2 lost from lungs during expiration, pCO2 increases back to normal
CNS control of respiration-medullary control centres
inspiratory centre: sends stimulus to inspiratory muscles, resting discharge rate approx 12/min, this occurs automatically in the inspiratory centre, does not require input from elsewhere in CNS, but firing rate can be modified by other inputs
expiratory centre: discrete area, located near inspiratory centre, not active during passive expiration, during active expiration sends impulses to expiratory muscles, reinforcing respiratory effort. neural connections exist linking inspiratory Nd expiratory centres.
cough centre (does it exist) ; receives input from the irritant receptors in the lungs, triggering cough reflex. considered a reflex essential to life aa it serves to remove foreign bodies from the airways
apnoeustic centre; stimulates the medullary inspiratory centre, prolongs inspiration, must be inhibited for inspiration to terminate and expiration to commence
pneumotaxic centre: inhibits apnoeustic centre and inspiratory centre, facilitates expiration
