OUTLINE 18

I. OXYGEN TRANSPORT

A. Dissolved in the Blood
1. 1.5%: dissolved

B. Oxyhemoglobin
1. 98.5%: bound to hemoglobin
2. Without oxygen, deoxyhemoglobin

C. O2 Carrying capacity of Blood and Resting O2 Extraction
1. Carrying capacity = gm Hb/dl x 1.34 ml O2/gm Hb
a. 15 g/dl x 1.34 ml O2/gm Hb = 20.1 ml O2/dl or 20 vol %

2. Resting O2 extraction
a. Of the 20 ml being transported, each 100 ml of blood delivers only 5 ml of O2
b. At rest, body requires 250 ml O2/min
1. So what must flow be to deliver sufficient oxygen??

c. 5 ml O2 delivered x 250 ml O2 required 100 ml blood x ml

x = 5000 ml/min (Systemic Flow??? 5 L/min)

Oxygen delivery is neither constant nor arbitrary. Active tissues receive more O2; inactive tissues receive less O2.

D. Oxyhemoglobin Dissociation Curve
Graph: PO2 vs. % Saturation Hb

1. Hemoglobin delivers only 20-30% of its supply.
a. At PO2 of 100 mm Hg in arterial blood
(pulmonary venous blood), :Hb is 98% saturated
b. At PO2 of 40 mm Hg in venous blood after O2 is delivered: Hb is 70% saturated

2. Active tissue receives more O2: curve shifts right
a. Active tissue has the following:
1. Increase in PCO2
2. Increase in H+ ion concentration
3. Decrease in pH, more acidic
4. Increase in temperature

3. Inactive tissue receives less O2; curve shifts left
a. Inactive tissue has the following:
1. Decrease in PCO2
2. Decrease in H+ ion concentration
3. Increase in pH, more alkaline
4. Decrease in temperature

II. CARBON DIOXIDE TRANSPORT

A. Dissolved in the blood (10%)

B. Carbaminohemoglobin (20%)

C. Bicarbonate (70%)

1. Define:
a. Carbonic anhydrase:

b. Chloride shift:
1. In tissues:

2. In lungs, process is reversed

____________________________________________________________

D. Role of Hemoglobin as a Buffer

a. Globin: Carries H+ and CO2
1. CO2 and H+ levels increase together
a. Globin binds increase in H+ so H+ doesn't enter the plasma and cause pH to decrease (become acidic)
b. As H+ is loaded onto Hb, O2 is bumped off
1) Bohr Effect

2. Increase in CO2 production, Hb accepts even more
a. Limits the amount of CO2 dumped into the blood
b. Haldane Effect

III. REGULATION OF ALVEOLAR VENTILATION

A. Medullary Centers (Primary)
0. Controls the rate and rhythm of breathing

1. Inspiratory Centers: Dorsal respiratory group (DRG)and Ventral Respiratory Group (VRG)
a. Innervation
1. Phrenic nerves to diaphragm
2. Intercostal nerves to external intercostal muscles

c. DRG integrates information from peripheral stretch and chemoreceptors

d. VRG inititates an impulse or signal
1. Impulse causes muscle contraction;
a. Inspiratory phase lasts about 2 sec

e. VRG expiratory neurons fire; impulses stop

a. Passive expiration occurs
1. Muscles relax, thoracic cavity decreases,
lungs recoil
2. Expiratory phase lasts about 3 sec
f. Result: Resp rate of 12-15: normal
a. Eupnea: good breath

2. Expiratory Center: Ventral Respiratory Group (VRG)
a. Active during forced expiration
1. Stimulates contraction of internal intercostals

B. Pontine Centers (Secondary)(Regions in the pons)

1. Pontine respiratory group transmits impulses to the VRG
2. Basic effects
a. Influences and modifies the activity of medullary neurons;
b. Smooths out the transitions from inspiration to expiration


C. Hering-Breuer Reflex (Inspiro-inhibitory reflex):
Prevents overstretch by inhibiting further inspiration

1. Stretch receptors in the wall of the lung, sense stretch
2. High degree of stretch: receptors fire
3. Info is carried via afferent vagal fibers to DRG
4. Inhibits respiration; expiration occurs; lungs recoil
5. Prevents overstretch by inhibiting further inspiration

D. Chemoreceptor Reflexes
Arterial PCO2 is most important stimulus for respiration!!!
***Chemoreceptors respond to PCO2, H+, and O2***

1. PCO2
a. Direct effect on respiration
1. Chemoreceptors (ARTERIAL!!)
a. Central: In medulla
b. Peripheral: Aortic arch and carotid sinus
2. Increase in PCO2, DRG is stimulated, respiration increases
b. Indirect effect on respiration
1. Increase in CO2, diffuses into CSF
2. Combines with H2O,then dissociates
3. Forms HCO3- and H+, decreasing pH of CSF
4. Central receptors are excited
5. DRG is stimulated, increasing respiration

2. pH
a. Increase in H+, peripheral receptors are activated
b. Stimulate DRG, increase in respiration

3. PO2
a. Must be a big decrease in O2 to serve as a stimulus
1. Resevoir of O2 on Hb
2. Only 20-30% reduction in %HB saturation at rest
b. Increase in PCO2 stimulates respiration first
1. Decrease in PO2 increases sensitivity to CO2 levels
c. In patients with pulmonary disease, CO2 may be chronically elevated
1. Receptors become less sensitive
2. Decrease in PO2 then becomes important
a. Produces the hypoxic drive for respiration