The document provides an overview of respiratory physiology, including: - The mechanics of breathing involving contraction of respiratory muscles like the diaphragm and intercostal muscles to inhale and exhale air. - The control of respiration centered around respiratory centers in the brainstem that regulate breathing rhythm and can be modified by sensory inputs and other brain regions. - The transport and exchange of oxygen and carbon dioxide between the lungs, bloodstream, and tissues facilitated by diffusion gradients and partial pressures. Oxygen is carried by hemoglobin in red blood cells while carbon dioxide is transported as bicarbonate ion and bound to hemoglobin. - Factors like pH, temperature, and metabolic byproducts that can

1. AWALVAREZ NOVEMBER 2012

2. INTRODUCTION
• As they function, cells use O2 and produce
CO2.
• The respiratory system brings the needed
O2 into and eliminates CO2 from the body
by working closely with the cardiovascular
system.
• The blood transports these gases, carrying
O2 to the tissues and CO2 to the lungs

3. INTRODUCTION
• The blood transports these gases, carrying
O2 to the tissues and CO2 to the lungs.
• The basic rhythm of breathing is controlled
by respiratory centers located in the
brainstem.
• This rhythm is modified in response to
input from sensory receptors and from
other regions of the brain.

4. INTRODUCTION
• O2 and CO2 diffuse between the alveoli
and pulmonary capillaries in the lungs, and
between the systemic capillaries and cells
throughout the body.
• The diffusion of these gases, moving in
opposite directions, is called gas
exchange.

5. INTRODUCTION
• These gases are carried in several different forms:
1. dissolved in the plasma
2. chemically combined with hemoglobin (Hb)
3. converted into a different molecule
• Pulmonary ventilation, or breathing, is the
exchange of air between the atmosphere and the
lungs.
• As air moves into and out of the lungs, it travels from
regions of high air pressure to regions of low air
pressure
• Other animal species such as birds and fishes have a
unique respiratory features

6. MECHANICS OF BREATHING
• Breathing is an active process in most mammals -
requiring the contraction of skeletal muscles.
• The primary muscles of respiration include the
external intercostal muscles (located between the
ribs) and the diaphragm (a sheet of muscle located
between the thoracic & abdominal cavities).

7. MECHANICS OF BREATHING
 The external intercostals plus the diaphragm
contract to bring about inspiration:
 Contraction of external intercostal muscles > elevation of
ribs & sternum > increased front- to-back dimension of
thoracic cavity > lowers air pressure in lungs > air moves
into lungs
 Contraction of diaphragm > diaphragm moves downward
> increases vertical dimension of thoracic cavity > lowers
air pressure in lungs > air moves into lungs:

10. MECHANICS OF BREATHING
To exhale:
• relaxation of external intercostal muscles &
diaphragm > return of diaphragm, ribs, &
sternum to resting position > restores
thoracic cavity to pre-inspiratory volume >
increases pressure in lungs > air is exhaled

11. Intra-alveolar
pressure during
inspiration &
expiration

12. MECHANICS OF BREATHING
 As the external intercostals & diaphragm contract,
the lungs expand.
 The expansion of the lungs causes the pressure in
the lungs (and alveoli) to become slightly negative
relative to atmospheric pressure.
 As a result, air moves from an area of higher
pressure (the air) to an area of lower pressure (our
lungs & alveoli).
 During expiration, the respiration muscles relax &
lung volume decreases.

13. MECHANICS OF BREATHING
• This causes pressure in the lungs (and alveoli) to
become slight positive relative to atmospheric
pressure.
• As a result, air leaves the lungs.

14. CONTROL OF RESPIRATION
WE E K N O . 3

15. CONTROL OF RESPIRATION:
Respiratory Rate (RR) changes:
 When active, RR goes up; when less active, or
sleeping, it goes down.
 Even though the respiratory muscles are voluntary,
you can't consciously control them when you're
sleeping.
 So, how is respiratory rate altered & how is
respiration controlled when you're not consciously
thinking about respiration?

16. RESPIRATORY CENTERS

17. CHEMORECEPTORS
CENTRAL RECEPTORS
• Respiratory centers are not
directly affected by
changes in blood PCO2
and H+ concentration
instead there is
chemosensitive are beneath
the ventral surface of the
medulla

18. CHEMORECEPTORS
PERIPHERAL RECEPTORS
• Detects changes in PCO2 and PO2 in blood
• Located in aorta & carotid arteries

19. STRETCH RECEPTORS
• Stretch receptors in the walls of the bronchi and
bronchioles throughout the lungs
• When the lungs become overly inflated, these
receptors activate a feedback mechanism that
switches off the inspiratory ramp and thus stops
further inspiration  HERRING-BREUER REFLEX

20. FACTORS INVOLVED IN INCREASING
RESPIRATORY RATE:
Heavy exercise  greatly increases respiratory rate
 Mechanism?
 NOT increased CO2
 Possible factors:
 reflexes originating from body movements
(proprioceptors)
 increase in body temperature
 epinephrine release (during exercise)
 impulses from the cerebral cortex (may
simultaneously stimulate rhythmicity area & motor
neurons)

22. GAS EXCHANGE & TRANSPORT
WE E K N O . 3

23. GAS EXCHANGE
 The exchange of gases (O2 & CO2) between the
alveoli & the blood occurs by simple diffusion:
 O2 diffusing from the alveoli into the blood & CO2 from the
blood into the alveoli.
 Diffusion requires a concentration/pressure gradient. So,
the concentration/pressure of O2 in the alveoli must be
kept at a higher level than in the blood & the
concentration/pressure of CO2 in the alveoli must be kept
at a lower level than in the blood.
 We do this, of course, by breathing - continuously bringing
fresh air (with lots of O2 & little CO2) into the lungs & the
alveoli.

24. GAS EXCHANGE
 External respiration:
 exchange of O2 & CO2 between external
environment & the cells of the body
 efficient because alveoli and capillaries have
very thin walls & are very abundant (your
lungs have about 300 million alveoli with a
total surface area of about 75 square meters)
 Internal respiration - intracellular use of
O2 to make ATP
 occurs by simple diffusion along partial
pressure gradients

25. PARTIAL PRESSURE
 Individual pressure exerted independently by a
particular gas within a mixture of gasses.
 The air we breath is a mixture of gasses: primarily
nitrogen, oxygen, & carbon dioxide.
 So, the air you blow into a balloon creates pressure
that causes the balloon to expand (& this pressure
is generated as all the molecules of nitrogen,
oxygen, & carbon dioxide move about & collide
with the walls of the balloon).
 However, the total pressure generated by the air is
due in part to nitrogen, in part to oxygen, & in part
to carbon dioxide.

26. PARTIAL PRESSURE
 That part of the total pressure generated by O2 is the
'partial pressure' of O2 (PO2) while that generated by
CO2 is the PCO2.
 A gas's partial pressure, therefore, is a measure of how
much of that gas is present (e.g., in the blood or alveoli).
 the partial pressure exerted by each gas in a mixture
equals the total pressure times the fractional
composition of the gas in the mixture.
 So, given that total atmospheric pressure (at sea level) is
about 760 mm Hg and, further, that air is about 21%
oxygen, then the partial pressure of oxygen in the air is
0.21 X 760 mm Hg or 160 mm Hg.

27. PARTIAL PRESSURE:
Partial Pressures of O2 and CO2 in the body
(normal, resting conditions):
 Alveoli
 PO2 = 100 mm Hg
 PCO2 = 40 mm Hg
 Alveolar capillaries
 Entering the alveolar capillaries
○ PO2 = 40 mm Hg (relatively low because this blood has just returned
from the systemic circulation & has lost much of its oxygen)
○ PCO2 = 45 mm Hg (relatively high because the blood returning
from the systemic circulation has picked up carbon dioxide)

29. An Overview of the respiratory Process: (a) Partial pressures and diffusion
at the respiratory membrane (b) Partial pressure and diffusion at other
membranes

31. PARTIAL PRESSURE:
• While in the alveolar capillaries, the diffusion of
gasses occurs: oxygen diffuses from the alveoli into
the blood & carbon dioxide from the blood into the
alveoli.
• Leaving the alveolar capillaries
• PO2 = 100 mm Hg
• PCO2 = 40 mm Hg

32. PARTIAL PRESSURES:
 Blood leaving the alveolar capillaries returns
to the left atrium & is pumped by the left
ventricle into the systemic circulation.
 This blood travels through arteries & arterioles
and into the systemic, or body, capillaries.
 As blood travels through arteries & arterioles,
no gas exchange occurs.
 Entering the systemic capillaries
○ PO2 = 100 mm Hg
○ PCO2 = 40 mm Hg
 Body cells (resting conditions)
○ PO2 = 40 mm Hg
○ PCO2 = 45 mm Hg

33. PARTIAL PRESSURES:
 Because of the differences in partial pressures of
oxygen & carbon dioxide in the systemic
capillaries & the body cells, oxygen diffuses from
the blood & into the cells, while carbon dioxide
diffuses from the cells into the blood.
 Leaving the systemic capillaries
○ PO2 = 40 mm Hg
○ PCO2 = 45 mm Hg
 Blood leaving the systemic capillaries returns to
the heart (right atrium) via venules & veins (and
no gas exchange occurs while blood is in venules
& veins).
 This blood is then pumped to the lungs (and the
alveolar capillaries) by the right ventricle.

34. GAS TRANSPORT
How are oxygen & carbon dioxide transported in the
blood?
 Oxygen is carried in blood:
1. bound to hemoglobin (98.5% of all oxygen in the blood)
2. dissolved in the plasma (1.5%)
 Because almost all oxygen in the blood is
transported by hemoglobin, the relationship
between the concentration (partial pressure) of
oxygen and hemoglobin saturation (the % of
hemoglobin molecules carrying oxygen) is an
important one.

36. O2 CONCENTRATION VS. HEMOGLOBIN
SATURATION:
Hemoglobin saturation:
• extent to which the hemoglobin in blood is
combined with O2
• depends on PO2 of the blood:

38. O2 CONCENTRATION VS. HEMOGLOBIN
SATURATION:
 The relationship between oxygen levels and
hemoglobin saturation is indicated by the oxygen-
hemoglobin dissociation (saturation) curve (in the
previous graph).
 At high partial pressures of O2 (above about 40 mm
Hg), hemoglobin saturation remains rather high
(typically about 75 - 80%).
 This rather flat section of the oxygen-hemoglobin
dissociation curve is called the 'plateau.'

39. HEMOGLOBIN
 Recall that 40 mm Hg is the typical partial pressure of
oxygen in the cells of the body.
 Examination of the oxygen-hemoglobin dissociation
curve reveals that, under resting conditions, only about
20 - 25% of hemoglobin molecules give up oxygen in the
systemic capillaries.
 This is significant (in other words, the 'plateau' is
significant) because it means that there is a substantial
reserve of oxygen.
 In other words, if you become more active, & your cells
need more oxygen, the blood (hemoglobin molecules)
has lots of oxygen to provide

40. HEMOGLOBIN:
 When you do become more active, partial
pressures of oxygen in your (active) cells may drop
well below 40 mm Hg.
 A look at the oxygen-hemoglobin dissociation
curve reveals that as oxygen levels decline,
hemoglobin saturation also declines - and declines
precipitously.
 This means that the blood (hemoglobin) 'unloads'
lots of oxygen to active cells - cells that, of course,
need more oxygen.

42. FACTORS THAT AFFECT THE O2-HB
DISSOCIATION CURVE:
• The oxygen-hemoglobin dissociation curve 'shifts'
under certain conditions.
• These factors can cause such a shift:
• lower pH
• increased temperature
• more 2,3-diphosphoglycerate
• increased levels of CO2

43. FACTORS THAT AFFECT THE O2-HB
DISSOCIATION CURVE:
 These factors change when tissues become more
active.
 For example, when a skeletal muscle starts contracting,
the cells in that muscle use more oxygen, make more
ATP, & produce more waste products (CO2).
 Making more ATP means releasing more heat; so the
temperature in active tissues increases.
 More CO2 translates into a lower pH.
 That is so because this reaction occurs when CO2 is
released:
CO2 + H20  H2CO3  HCO3- + H+

44. FACTORS THAT AFFECT THE O2-HB
DISSOCIATION CURVE:
 More hydrogen ions = a lower (more acidic) pH.
 So, in active tissues, there are higher levels of CO2,
a lower pH, and higher temperatures.
 In addition, at lower PO2 levels, red blood cells
increase production of a substance called 2,3-
diphosphoglycerate.
 These changing conditions (more CO2, lower pH,
higher temperature, & more 2,3-
diphosphoglycerate) in active tissues cause an
alteration in the structure of hemoglobin, which, in
turn, causes hemoglobin to give up its oxygen.

45. FACTORS THAT AFFECT THE O2-HB
DISSOCIATION CURVE:
 In other words, in active tissues, more hemoglobin
molecules give up their oxygen.
 Another way of saying this is that the oxygen-
hemoglobin dissociation curve 'shifts to the right' (as
shown with the light blue curve in the next graph).
 This means that at a given partial pressure of
oxygen, the percent saturation for hemoglobin with
be lower.
 For example, in the next graph, extrapolate up to
the 'normal' curve (green curve) from a PO2 of 40,
then over, & the hemoglobin saturation is about
75%.

46. FACTORS THAT AFFECT THE O2-HB
DISSOCIATION CURVE:
 Then, extrapolate up to the 'right-shifted' (light blue)
curve from a PO2 of 40, then over, & the
hemoglobin saturation is about 60%.
 So, a 'shift to the right' in the oxygen-hemoglobin
dissociation curve (shown above) means that more
oxygen is being released by hemoglobin - just
what's needed by the cells in an active tissue!

47. CARBON DIOXIDE TRANSPORT
Carbon dioxide - transported from the body
cells back to the lungs as:
1. bicarbonate (HCO3) - 60%
 formed when CO2 (released by cells making
ATP) combines with H2O (due to the enzyme in
red blood cells called carbonic anhydrase) as
shown in the following diagram
2. carbaminohemoglobin - 30%
 formed when CO2 combines with hemoglobin
(hemoglobin molecules that have given up
their oxygen)
 dissolved in the plasma - 10%

49. AVIAN RESPIRATORY
PHYSIOLOGY

50. OUTLINE
• Functions
• Distinct Features
• Movement of Gases
• Gas Exchange
• Clinical Aspects
The avian respiratory system is different from that of
other vertebrates, with birds having relatively small
lungs plus nine air sacs that play an important role in
respiration

51. FUNCTIONS
• Gas Exchange
• Heat Elimination (Thermoregulation)
• Vocalization

52. DISTINCT FEATURES
• Dead space: tracheal length and dead space
volume in birds is typically 4.5 times or more greater
than that of comparably sized mammals. They
compensate for this by increasing tidal volume and
reducing respiratory frequency see alveolar
ventilation equation.
• Lungs: non-collapsing parenchyma with distinctive
pattern of air passages arranged in an open system
birds lungs do not have blind-sac alveoli as do
mammals.
• Additionally, birds have no diaphragm.
• It is impossible for them to develop a pneumothorax

54. DISTINCT FEATURES
• permit a unidirectional flow of air through the lungs.
• Unidirectional flow means that air moving through
bird lungs is largely 'fresh' air & has a higher oxygen
content.
• In contrast, air flow is 'bidirectional' in mammals,
moving back and forth into and out of the lungs.
• As a result, air coming into a mammal's lungs is
mixed with 'old' air (air that has been in the lungs for
a while) & this 'mixed air' has less oxygen.
• So, in bird lungs, more oxygen is available to diffuse
into the blood.

57. AIR SACS
Most birds have 9 air
sacs:
• one interclavicular sac
• two cervical sacs
• two anterior thoracic
sacs
• two posterior thoracic
sacs
• two abdominal sacs

58. AIR FLOW

59. AIR FLOW

60. AIR FLOW

61. GAS EXCHANGE
• Cross-Current Exchange System