KIN 105 Lecture Notes - Fick'S Laws Of Diffusion, Abdomen, Bronchiole
Lecture 5 – Fick Equation and Determinant of VO2
Ventilation and Gas Transport in the Blood
VO2 = HR X SV X (CaO2 – CvO2)
Ca = arterial O2 content is determined by ventilation, respiration, hemoglobin (Hb)
concentration and Hb saturation.
Cv = dependent on metabolic rate of the tissues and blood flow of tissue
Respiratory Musculature
Diaphragm is the primary respiratory muscle in inspiration and expiration
At rest, expiration is passive
During exercise, muscles are recruited to enhance expiration
- Internal intercostalis
- External abdominal oblique
- Internal abdominal oblique
- Transversus abdominis
- Rectus abdominus
Mechanics- Changes in Volume and Pressure Drive Ventilation
Breathing in
- Chest expands
- Diaphragm contracts
- Increase in thoracic volume
- 740 mmHg atmospheric pressure in KW > 737 mmHg intrapulmonary pressure
- ∴ air flows into the lungs
Breathing out
- Chest contracts
- Diaphragm relaxes
- Decrease in thoracic volume
- 740 mmHg atmospheric pressure in KW < 743 mmHg Intrapulmonary pressure
- ∴ air flows out of the lungs
NOTE: do not need a huge pressure gradient, really only need 4 mmHG difference
Pulmonary – Structure and Function
Conducting Zone – serve to conduct, clean, warm and moisten the air. This portion is composed
of the nose, pharynx, larynx, trachea, bronchi, and bronchioles.
- Trachea and Bronchi are rigid tubes
• Cartilage for protection since it is exposed as well as keeping it open
- Bronchioles are soft, dynamic tubes
• smooth muscle which dilate during expiration because of SNS stimulation:
decreases resistance to air flow
- 4 primary functions:
1. Filters the air (dirt and pathogens)
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2. Warms the air up (core temperature)
• Lungs do not have heat exchange
• Helps to maintain homeostasis
3. Humidifies the air
• Alveoli are wet area
• If the air is dry, it will dry out the wet areas in the body
4. Conducts or conveys air
Respiratory Zone – facilitate gas exchange. These are located entirely within the
lung and are represented by respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.
- Respiratory bronchioles have sporadic alveoli
- Alveoli – site of gas exchange
Uptake of O2 from the Air in the Lung by the Pulmonary Capillary Blood
PATM = 760 mmHg
FATM O2 = 0.209 (20.9%)
∴PATM O2 = 159 mmHg
Mixing of inspired air in the respiratory system creates PAO2 (alveolar
PO2) = 104 mmHg
Alveolar-capillary unit – close proximity pulmonary capillary and an
alveolus
Mixed venous blood coming from the right ventricle/pulmonary
artery
- PO2 = 40 mmHg
Diffusion is facilitated by pressure gradient and surface area.
Capillaries wrap around the alveoli, which allows rapid exchange
Venous end with concentrated PO2 (of 104 mmHg) heads to the left atrium to become systemic
arterial blood
Equilibration – point where pressure at the alveolus and capillary at the same
- Equilibration of alveolar air and blood PO2 occurs at 1/3 of the distance along the
pulmonary capillary at normal cardiac output
As CO2 increases:
1) The equilibration point moves further down the pulmonary capillary (towards the right)
due to a derease i RBC trasit tie the aout of tie it takes, the distae does’t
change. Less time for diffusion.
2) More alveolar capillary units are recruited to ensure full equilibration between alveolar
air and blood PO2
- They are kept under diffused at rest to allow for an increase in recruitment in exercise
3) when equilibration is not 100% (ex. during heavy exercise). On the graph, it prolongs
and plateaus very late – typically in elite athletes
Changes in PO2 Throughout the Pulmonary and Systemic Circulations
As blood flows through systemic capillaries, PO2 in the blood equilibrates (by diffusion) with the
tissue PO2 (PTO2; normally 40 mmHg, but can be decreased in active muscle during exercise)
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PTO2 is a function of:
1) Metabolic rate
2) Blood flow –
normally will match
with metabolic
reai, if it does’t
the PTO2 will drop
The graph shows the
changes in PO2 in blood as
the unit of blood moves
through the body
Components of Blood
Plasma – liquid portion of the blood (i.e. no cells). Contains ion, proteins, glucose, fatty
acids, etc. 2-3% of the O2 carried in the blood is dissolved in the plasma
White blood cells (WBC) – important for immunity
Platelets – blood clotting
Red blood cells (RBC) or erythrocytes – O2 transport
Hematocrit - % of the total blood volume that is occupied by RBC
Hemoglobin content of healthy blood:
- Males: 15 g Hb/100 mL blood (150 g Hb/L blood)
- Females: 12.5 g Hb/100 mL blood (125 g Hb/L blood)
Hemoglobin content of diseased (anemic) blood:
- Females and Males: 8-11 g Hb/100 mL blood
97-98% of the O2 in the blood is carried bound to Hb in RBCs
How do Hb and PO2 Actually Affect How Much O2 is in the Blood?
Hemoglobin (Hb) - is an O2-binding protein
- Hb is like an O2 buffer
This allows the amount of O2 in the blood to be much higher than it would be without
Hb
97-98% of the O2 in the blood is carried in association with Hb with the remaining 2-3%
dissolved in plasma
Free [Hb] - amount of Hb in a RBC is constant, so total Hb in the blood depends on the
hematocrit, which on an acute timescale, is also constant
Hb + O2 HbO2
Free O2 is determined by local PO2
Changes in PO2 in different locations is the acute method of loading/off-loading O2 onto/off of
Hb via the equilibrium reaction, since Hb does not change
- High PO2 = increase in loading (HbO2)
- Low PO2 = decrease in unloading (HbO2)
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