Physiology Flashcards
functions of the respiratory system
*Gas exchange
acid base balance
protection from infection
communication via speech
type 1 pneumocytes
cell type + function
simple squamous epithelium
for gas exchange
type 2 pneumocytes
cell type + function
Cuboidal epithelium
produce surfactant
muscles for inspiration
diaphragm (contracts + lowers)
external intercostal muscles (pull ribs up)
muscles for forced expiration
internal intercostal muscles (force ribs down)
abdominal muscles
Boyle’s law
+ relation to breathing
the pressure exerted by a gas is inversely proportional to its volume
*When you increase the volume in the lungs/ intrapleural cavity, the pressure decreases
steps of inspiration
- contraction of muscles
- decrease in intrapleural pressure
- lungs expand
- decrease in alveolar pressure
- air flows into lungs
Alveolar pressure (P (subscript)A)
pressure inside lungs
changes from slightly +ve to slightly -ve with breathing cycle
intrapleural pressure (P (subscript)ip)
pressure inside pleural cavity always negative (and less than alveolar pressure*) in health due to elastic recoil of lungs and chest wall away from each other
*If not, the lungs would collapse
transpulmonalry pressure (P (subscript)T)
alveolar pressure - intrapleural pressure
always positive in health. if negative, the lungs would collapse due to their elastic recoil.
respiratory minute volume/ pulmonary ventilation
the volume of air inhaled or exhaled from a persons lungs per minute
mechanical factors affecting respiratory minute volume
- difference between atmospheric and alveolar pressures
2. airway resistance (mostly determined by radii of airways)
Alveolar ventilation
volume of fresh air getting to the alveoli (and so available for gas exchange) per minute
alveolar PO2
100mgHg
13.3kPa
Arterial PO2
75mgHg
10kPa
Alveolar PCO2
40mgHg
5.3kPa
Arterial PCO2
46mgHg
6.1kPa
The role of pulmonary surfactant
reduces surface tension on the alveolar surface membrane which…
reduces tendency for alveoli to collapse
increases lung compliance (stretchability)
makes breathing easier
is more effective in smaller alveoli as is more concentrated
surface tension
the attraction between water molecules that occurs at any air-water interface
The law of Laplace
P = 2T/r
P = inwardly directed pressure T = surface tension (reduced by surfactant) r = radius of alveoli
significance of the law of laplace
inwardly directed pressure is equalised in differently sized alveoli
As inwardly directed pressure is greater in smaller alveoli but surfactant is more effective as it’s more concentrated
2,3-DPG
A sugar produced by RBCs in hypoxic conditions. This shifts the oxyhamoglobin dissociation curve to the right (decreases Hb affinity for O2) for more oxygen delivery
factors that affect gas exchange
the partial pressure gradient
gas solubility
available surface area
the thickness of the membrane
distance
the ventilation:perfusion ratio should be…
1 in a healthy lung
ventilation-perfusion ratio in the apex of the lung
ventilation > perfusion
because alveolar pressure is greater than arterial pressure so arterioles are compressed
alveolar dead space
Alveoli that are not perfused
ventilation > perfusion
shunt
ventilation < perfusion
response to ventilation > perfusion (alveolar dead space)
increase in alveolar PO2 –> pulmonary vasodilation (increases perfusion)
decrease in alveolar PCO2 –> mild bronchial constriction (decreases ventilation)
ratio balances
response to ventilation < perfusion (shunt)
decreased alveolar PO2
causes pulmonary vasoconstriction –> blood diverted to a better ventilated alveoli
increased alveolar PCO2 –> mild bronchial dilation (slight increase in ventilation)
anatomical dead space
air in the airways that does not reach the alveoli so is not available for gas exchange
physiological dead space
alveolar dead space + anatomical dead space
difference between partial pressure and gas content
partial pressure refers only to gas in solution.
gas content includes the gas in other forms, e.g. O2 bound to haemoglobin
concentration of oxygen in systemic arterial blood
200ml/L
static spirometry
measures the volume exhaled
dynamic spirometry
measures the time taken to exhale a certain volume
FEV1 / FVC
FEV1 = forced expiratory volume in 1 second FVC = forced vital capacity
= 80% in healthy males
Compliance in obstructive and restrictive lung diseases
obstructive = compliance normal restrictive = compliance decreased
FEV1 / FVC in obstructive and restrictive lung diseases
obstructive = lowered as rate of expiration is most affected
restrictive = normal/ higher as the volume of air in the lungs which can be exhaled is reduced
Tidal volume
volume usually breathed in/out
500ml
Residual volume
Volume of air that cannot be exhaled
1200ml
Inspiratory reserve volume
extra volume which can be inhaled on top of tidal volume
3000ml
expiratory reserve volume
volume which can be exhaled after tidal volume has been exhaled
1100ml
Total lung capacity
5800ml
inspiratory capacity
tidal volume + inspiratory reserve volume
3500ml
vital capacity
total volume that can be exhaled
4600ml
functional residual capacity
volume left in lungs after exhaling tidal volume.
residual volume + expiratory reserve volume
2300ml
significance of the plateau of the oxygen-haemoglobin dissociation curve
even at only 60mmHg, haemoglobin is still 90% saturated.
this allows for relatively normal O2 uptake when alveolar PO2 is reduced.
result of the oxygen-haemoglobin dissociation curve shifting LEFT
higher affinity = less O2 delivery
holds on tighter
result of the oxygen-haemoglobin dissociation curve shifting RIGHT
lower affinity = more O2 delivery
lets go easily
causes of the oxygen-haemoglobin dissociation curve shifting LEFT
low temperature
low PCO2
low 2,3-DPG
high pH
causes of the oxygen-haemoglobin dissociation curve shifting RIGHT
high temperature
high PCO2
high 2,3-DPG
low pH
foetal haemoglobin O2 affinity
higher than adult haemoglobin to be able to extract O2 from the mother
(oxygen-haemoglobin dissociation curve to the left)
myoglobin O2 affinity
higher than haemoglobin. as myoglobin exists in skeletal muscle, it must be able to extract O2 from arterial blood when exercising.
(oxygen-haemoglobin dissociation curve to the left)
forms in which CO2 is carried in the blood
7% dissolved in plasma
23% combines with deoxyhaemoglobin to form carbamino compounds
70% as bicarbonate ions in plasma or H ions bound to deoxyhaemoglobin (carbonic anhydrase)
the role of carbonic anhydrase
- 70% of CO2 enters RBCs
- it combines with water and forms carbonic acid - catalysed by CARBONIC ANHYDRASE
- carbonic acid dissociates into bicarbonate and H ions
CO2 + H2O H2CO3 HCO3- H+
- bicarbonate ions move into the plasma in exchange for Cl- ions. H+ ions bind to deoxyhaemoglobin
factors that influence ventilation*
*Respiratory drive, rate and depth of breathing
*chemoreceptor input
mechanosensory input (thorax stretch reflex)
voluntary over-ride via higher centres in the brain
Emotion via the limbic system
where are central chemoreceptors located?
the medulla
where are peripheral chemoreceptors located?
in the aorta and carotid arteries
what stimulus activates central chemoreceptors?
[H+] in the plasma
which directly reflects PCO2 as only CO2 can travel through the capillary wall into the CSF
Central chemoreceptors provide the primary ventilatory drive
equation determining plasma pH
CO2 + H2O H2CO3 H+ + HCO3-
activity of peripheral chemoreceptors
Fire APs in response to high [H+]* or significantly low PO2 in the plasma
Provide the secondary ventilatory drive
*H+ from any source - so regulates acid-base imbalance
VRG
Ventral Respiratory Group of neurons,
supplies the tongue, pharynx, larynx and expiratory muscles
DRG
Dorsal Respiratory Group of neurons
supplies the inspiratory muscles via the phrenic and intercostal nerves
Respiratory centres
e.g. VRG and DRG
groups of neurons that fire bursts of APs, setting an automatic rhythm of breathing which is ajusted in response to stimuli
response to acidosis
an increase in [H+]
stimulates an increase in ventilation to blow off CO2 and shift the equation:
CO2 + H2O H2CO3 H+ + HCO3-
to the left
response to alkalosis
a decrease in [H+]
stimulates a decrease in ventilation to retain CO2 and shift the equation:
CO2 + H2O H2CO3 H+ + HCO3-
to the right
response to hypoxia
significantly low [O2]
stimulates an increase in ventilation to increase O2 content in the blood
sperm formation
1 spermatogonium with 46 chromosomes forms 4 sperms with {22 + Y/X} chromosomes.
starts at adolescence and happens continuously
ovum formation
1 oogonium with 46 chromosomes forms 1 ovum with {22 + X} chromosomes.
Meiosis I is completed before birth. Meiosis II occurs once each month
stages of embryology
Pre-embryonic = 0-3 weeks Embryonic = 4-8 weeks Foetal = 9-40 weeks
Formation of the placenta and placental villi
process + timing
Can start by day 6
when the chorion is formed it forms villi which burrow into the endometrium and help implantation.
later the chorion forms the placenta and the villi provide maximum contact area with the maternal blood.
Matures by 18-20 weeks
functions of the placenta
foetal nutrition
transport of waste and gas
immune function
structures derived from the ectoderm
epidermis of skin
neural tube
structures derived from the mesoderm
PARAXIAL: dermis of skin, muscles, bone
INTERMEDIATE PLATE: urogenital system
LATERAL PLATE: peritoneum, pleura, body cavities
structures derived from the endoderm
gut
respiratory system
steps of fertilization
- several sperms surround the ovum
- one penetrates
- the pronucleus of the sperm fuses with the pronucleus of the ovum forming a diploid cell = ZYGOTE
the laryngotracheal groove grows out of the…
foregut
the oesophagus and trachea are separated by the…
oesophagotracheal septum
outer cells of the blastocyst
trophoblast
layers of the bilaminar disc
top = epiblast bottom = hypoblast
Formed from the inner cell mass of the blastocyst
cavities around the bilaminar disc
top = amniotic cavity bottom = yolk sac
morula
a solid mass of cells formed by mitotic division of the zygote
the axis of the embryo is formed by the…
primitive streak (in the midline of the epiblast)
formation of the trilaminar disc
epiblast cells…
- migrate between the epiblast and hypoblast forming the mesoderm.
- displace the hypoderm forming the endoderm
The epiblast is now called the ectoderm:
ECTOderm
MESOderm
ENDOderm
notochord formation
ectoderm cells sink to between the mesoderm and endoderm to form a solid tube
neural tube formation
the notochord induces ectoderm cells to sink to between the ectoderm and mesoderm and form the neural tube
3 sections of the mesoderm
(outside to inside:)
lateral plate mesoderm
intermediate plate mesoderm
paraxial mesoderm
somites
bilaterally paired sections of the paraxial mesoderm, each is innervated by a spinal nerve pair.
they subdivide into a dermatome, myotome and sclerotome.
space between the slanchnic and somatic lateral plate mesoderms
intra-embryonic coelom
Week 1 embryo development
blastocyst formation
blastocyst moves to uterine cavity
Week 2 embryo development
bilaminar disc formed
implantation
placenta formation
Week 3 embryo development
gastrulation
nurulation
somite formation
Lateral folding begins
Week 4 embryo development
lateral folding completes (gut tube forms)
Head + Tail folding
organogenesis
gastrulation
formation of germ layers
nurulation
formation of neural tube
Pneumocytes
Alveolar cells
Conducting airways
Trachea
Primary bronchi
Smaller bronchi
Respiratory airways
Bronchioles
Alveoli
Function of pleural fluid
“sticks” the pleura together. This sticks the lungs to the rib cage and diaphragm so the lungs inflate when the chest expands
Compliance definition
Stretchability
NOT elasticity
Transport of O2 in the blood
O2 dissolves into the plasma and then binds to Hb, this maintains the partial pressure gradient that continues to “suck” O2 out of the alveoli.
Hb + O2 HbO2
At normal PO2, Hb becomes ~98% saturated, this saturation is reduced when PO2 is reduced
Significance of the shape of the oxyhaemoglobin dissociation curve for O2 unloading in the tissues
At 40mmHg (a resting cell) only 25% O2 is extracted from haemoglobin
However as PO2 falls in an exercising cell, the % saturation of Hb rapidly falls to greatly increase O2 delivery
Blastocyst development
As the morula grows, getting nutrition to the central core of cells becomes difficult do a blastocystic cavity develops.
This forms a blastocyst consisting of an inner cell mass inside an outer lining of cells (trophoblast)
Blastocyst implantation
at ~7 days the blastocyst begins to burrow into the endometrium (uterine wall)
The trophoblast forms the chorion which develops villi which help to burrow
Development of the lung bud
- The laryngotracheal groove grows from the anterior foregut (at 4 weeks)
- This diverticulum grows out into the splanchnic mesoderm and enlarges forming lung buds
Development of the bronchial tree
- the oesophagotracheal septum separates the oesophagus and trachea
- Lung buds “punch” into the splanchnic mesoderm forming airways
- Lung buds expand, pushing the splanchnic and somatic mesoderms together
Formation of alveoli
Alveolar sacs form at the end of terminal bronchioles
They progressively divide into smaller subunits leading to alveoli.
~95% of alveoli are formed post-natally
Pericardialperitoneal canals
Gap between the splanchnic and somatic mesoderm (Visceral and parietal pleura)
Will form the pleural cavity
