PHYSIOL [D] Flashcards
define respiration
process of burning of glucose for energy (cellular level)
define “breathing”:
process of getting gas in and out of your lungs
via what process do cells and tissues(cells) get nutrients?
diffusion
what is “Fick’s” law?
that gas moves from high -> low concentration
what does Fick’s law depend on?
- gradient (ΔC)
- permeability of membrane (P)
- area (A)
- molecular weight (MW)
- distance (D)
what is the equation for Fick’s law?
ΔC x P x A
net rate of diffusion = —————-
MW x D
problem with multi-cellular organism & nutrient diffusion?
cells in the middle(further away) too far from air, just diffusion process alone not sufficient
…solution? transfer system!
how long does it take for one RBS to go through your circulation?
1 minute
how many branches are there in the conducting airways?
28
within conducting pathways where does exchange actually occur?
end of branches in the alveolus
no exchange occurs along pathways - this is “dead” space
what part of the respiratory tract are reinforced with cartilage?
trachea
bronchi
what are the non-respiratory functions of the respiratory system?
- enhances venous return(cardiac suction pump)
- contributes to normal acid-base balance(CO2)
- enables vocalisations
- defends against inhaled foreign matter
- excretes some drugs(ethanol, anaestetics)
- route for water and heat eliminations
partial pressure:
in a mix of gases each component behaves separately
how do you calculate the partial pressure of one component of gas?
conc.(%) of that gas x total pressure
eg. AIR! oxygen = 21% nitrogen = 79%
total pressure @ sea level = 760mmHg
partial pressure of O2 = 0.21 x 760 = 150mmHg
how would the % composition change at everest?
% stays the same!
partial pressure is what changes
how to calculate transmural pressure across lung wall?
intra-alveolar pressure - intra-pleural pressure
how to calculate transmural pressure across thoracic wall?
atmospheric pressure - intra-pleural pressure
what is the intra-alveolar pressure @ rest?
760mmHg same as atmospheric!
what is the intra-pleural pressure?
slightly lower! 756mmHg
what nerve innervates the diaphragm?
phrenic nerve
what nerve innervates the external intercostal muscles?
intercostal nerve
what is enlargement of thoracic cavity during quiet respiration due to?
75% enlargement is due to contraction and flattening of the diaphragm
describe effects of thoracic expansion on pressures in lung:
decreases intra-pleural pressure (down to 754)
- > lungs drawn into area of low pressure
- > increase volume
- > decrease in intra-alveolar pressure
- > below atmospheric pressure => air enters lungs due to pressure differences
contraction of external intercostal muscles?
“bucket handle” elevation of ribs
=> increases side to side dimension of thoracic cavity
steps in onset of expiration?
1) relaxation of diaphragm & muscles of chest wall, elastic recoil of alveoli, decrease in size
2) intra-pleural and alveolar pressure increases
3) above atmospheric => air driven out
how can forced expiration occur?
contraction of expiratory muscles
what muscles?
skeletal muscles in abdominal wall and internal intercostal muscles
negative pressure ventilator?
atmospheric pressure reduced
=> inspiration
positive pressure ventilator?
air pumped in and out of trachea directly
major determination of resistance in respiratory tract?
- radius of conducting airways
- autonomic NS controls smooth muscle in walls of bronchioles
- > changing radii
diseases with increased resistance?
chronic obstructive pulmonary disease
asthma -> obstruction of airways
define compliance:
effort required to stretch or distend the lungs
=> high compliance
=> lung stretches further
what tends to COLLAPSE alveolus?
surface tension of water
and elasticity of membranes
why don’t alveoli collapse?
1) properties of surfactant (diagram 3 sperm pushing out to every one water pushing in)
reduces tension more as area decreases molecules are more crowded
2) alveolar inter-dependence “supports” individual alveoli
normal volume of quiet breathing cycle?
500ml inspired and expired
define Tidal Volume:
the air entering or leaving the lungs in a single breath
define inspiratory reserve volume?
extra air that can be maximally inspired over the typical resting TV
define inspiratory capacity?
max volume of air that can be inspired at the end of a normal quiet expiration
define expiratory reserve volume?
extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after a tidal volume
define vital capacity?
max volume of air that can be expired following a max inspiration
what is max and min volume of lungs?
lungs not completely emptied
max = 5,700ml
min = 1,200ml
normal volume of dead space?
150ml - will remain in dead space
volume/proportion of old/new air to reach alveoli each breath?
500ml total
350ml fresh air
150ml old air from dead space(left over from preceding expiration)
how is pulmonary ventilation calculated?
PV = TV x RR
how is alveolar volume calculated?
AV = (TV - DS) x RR
what is the PO2 in atmosphere?
21% x 760mmHg = 160mmHg
what is the PO2 in airways?
21% x (760 - 47) = 150mmHg
this is minus the water vapour pressure
what is the PO2 in alveoli?
around 100
PAO2 balance between addition from ventilation and removal by diffusion
At peak volume describe alveolar and atmospheric pressures:
alveolar pressure = atmospheric pressure
what does the bohr effect do to the O2 supply
increases the O2 supply to tissues
what is hyperventilation?
breathing too much!
-> blows off too much CO2, CO2 stimulates body to breath more
what happens to PAO2 and PACO2 during hyperventilation?
PAO2 = increases PACO2 = decreases (breath out more CO2 than take in)
what is the role of surfactant?
acts as detergent that reduces surface tension in the alveoli
what is the PAO2 and PACO2 composition of health air?
PAO2 = 100mmHg PACO2 = 40mmHg
how is the PAO2 of a person with anaemia(with reduced haem by 25%) affected?
PAO2 is normal, partial pressure not effected
O2 carrying capacity of blood will be reduced by about 25%
PO2 & PCO2 in atmosphere?
PO2 = 160 PCO2 = 0.03
PO2 & PCO2 in alveoli:
PO2 = 100 PCO2 = 40
what is the O2 and CO2 partial pressure gradient in the circulatory system?
O2 = 100-40 = 60 CO2 = 40-46 = 6
what is the amount of oxygen dissolved in plasma proportional to?
partial pressure
in dissolved form how much oxygen does normal arterial blood contain?
0.3ml O2/100ml
so 0.3%
how much O2 does 1g of Hb combine with?
1g Hg -> 1.39ml O2
how many g of Hg per 100ml of blood?
15g per 100ml
what is O2 capacity of normal blood?
15g(Hg per 100ml) x 1.39ml(O2 per g Hg) = 20.8ml O2/100ml blood
therefore 20.8%
what factors promote unloading of O2?
increase in CO2 from tissue
increase in acidity
higher temperature
what does the bohr effect do to the dissociation curve?
shifts curve to the right
difference between Hg affinity to CO and O2?
affinity of Hb for CO is 240 times its affinity of O2
what happens to the blood of someone who moves to high altitude for a few months?
chronic hypoxia -> erythropoietin release
= more blood cells
what is the blood content of an anaemic subject who has low [Hb] at sea level?
- normal PAO2
- normal Hb saturation (97.5%)
- decreased total O2 content
how is CO2 transported in blood(include percent):
physically dissolved: 10
bound to hemoglobin: 30
as bicarbonate (HCO3-): 60
what is the bicarbonate formula?
H+ + HCO3- <–> CO2 + H2O
increase in H+ increase in acidity
increase in
how does the plasma membrane of the erythrocyte facilitate diffusion of bicarbonate ions and chloride ions?
by the chloride shift passively facilitates diffusion
what us Hypercapnia?
excess of CO2 in the blood caused by hypoventilation
what is Hypocapnia?
below normal arterial level of CO2 in the blood, due to hyperventilation
what is Hyperpnea?
increased need for oxygen delivery and CO2 elimination during exercise
what provides rhythmic activity to breathing?
motor nerves innervating diaphragm
and external intercostal muscles
location of motorneurons innervating diaphragm?
in spinal cord receiving descending input from medulla
what are the neurons in medulla that connects to phrenic nerve?
DRG neurons - drive inspiration by firing
- drive expiration by not firing
where does the rhythm of breathing come from?
Boltzinger complex
role of higher control center in breathing?
pons
act to produce smooth coordinated breathing
what occurs if higher breathing control centers eg. pons are damaged?
breathing occurs in gasping pattern - rhythm fucks up
how are blood gas PCO2 and PO2 monitored?
2 receptor systems
1) peripheral chemoreceptors
2) central chemoreceptors
where are the peripheral chemoreceptors located?
carotid bodies and aortic arch
where are the central chemoreceptors located?
in the medulla
what are peripheral chemoreceptors sensitive to and why?
PCO2 - “life-savers” NOT PO2
as there is a large safety margin for O2 binding to Hb
small drop would not be noticeable
what are the central chemoreceptors sensitive to?
depressed by severe lack of oxygen
VERY sensitive to to PCO2
what is the relationship between partial pressure of CO2 in alveoli(PAO2) and ventilation?
inversely proportional
so if persons breathing is suppressed PAO2 will rise in precise relation to the depression of their ventilation
what are central chemoreceptors actually sensing?
actually sensing pH change
H+ + HCO3- <–> CO2 + H2O
SENSING THE H+ ACIDITY LEVELS
what do peripheral chemoreceptors do?
respond to pH(H+ concentration) of blood
regulate acid-base balance by altering amount of CO2 “blown off”
why does ventilation increase during exercise??
temperature?
reflexes from body movements?
adrenaline response?
input from higher brain centres? motor cortex?
why is it vital to maintain clean lungs?
blood is only a micron away from alveoli => most lung diseases are result of breakdown/by-pass of lung defences
where do inhaled particles end up?
- deposited in respiratory tract => disease process begins
- exhaled in next breath
- large particles lodged in nose
- smaller particles that make it through the nose/mouth settle out in small-diameter bronchioles => trapped by mucus lining
what is the main factor affecting movement of smallest particles?
diffusion, may carry them into the alveoli
why isn’t rate of air flow affecting movement of smallest particles?
rate of airflow decreases as gas moves closer to alveoli
after what part of the respiratory tract does the cross sectional area dramatically decrease?
terminal bronchioles
what is sneezing caused by?
irritation of mechanoreceptors in nasal mucosa
steps in sneezing reflex?
- deep inspiration
- glottis closed, expiratory muscles contract forcefully against closed glottis
- open -> pressure(intra-thoracic) forces air out
what is coughing caused by?
presence of foreign particle or liquid in larynx
steps in coughing reflex?
- forced expiration against closed glottis, collapse of medium airways, sides touch - mucus meniscus stretches across airways
- as you cough, mucus and other particles are blown towards mouth
what drugs suppress the cough reflex?
alcohol @ blood conc. 0.08%
narcotics eg. codeine & morhine => increase risk of vom in intoxicated people
what are some non-neural defence mechanisms?
muco-cilary system
thickness of mucus film in healthy humans = 5-10 um thick
how much mucus do healthy people secrete every day?
7-21ml/day
what does secreted mucus bind?
large quantities of water
forms stringy fibres
elastic recoil
what are the 2 layers of broncial mucosa?
- sticky layer
2. fluid layer (containing beating cilia)
difference between beating cilia in airway tubes and nasal?
airway = beat "UPWARDS" nasal = beat "backwards" towards pharynx
how often is bronchial mucosa cleared?
every 24 hours
how often is nasal mucosa cleared?
every 10-15 mins
why is clearing of mucosa important?
as inflammation of mucosa may kill cilia
what is chronic bronchitis?
number of cilia greatly reduced
rate of mucus production greatly increased => overloading of muco-cilary “escalator => risk of pneumonia
describe cellular defense:
lungs = macrophages and leukocytes
engulf particulate matter and carry it to the muco-cilary excalator for removal from lungs
what happens when one particular part of the lungs decreases ventilation?
- > decrease of alveolar O2
- > vasoconstriction (reduce blood flow to that part of lung and redirects flow to parts that work better)
- > increase CO2 relaxes bronchioles attempt to increase circulation
describe distribution of blood flow in lung:
APEX = low blood flow BASE = high blood flow
why? gravitational - this can change with posture & exercise
describe ventilation in lung?
more ventilation lower and less ventilation in the upper area
as top cannot stretch as much…think of slinky diagram
what would save your life when oxygen is low?
peripheral receptors
what would be the effect on the dissociation curve on everast?
same shape, stops at around 50 PO2
changes in partial pressure gradients in circulation?
PO2: 100 -> 40
PCO2: 40 -> 46
