Blood and Gas Exchanage ppt Flashcards
What are the 3 histologic layers of blood vessels?
- Tunica: intima
- Tunica media
- Tunica adventitia
Describe the structure of arteries
Large diameter, thick muscular walls (thick Tunica media)
When do arteries stretch and recoil?
Stretch during ventricular ejection & recoil during diastole
What do arteries act as?
Pressure reservoirs
What happens to the arterial blood pressure and pulse during the cardiac cycle?
It fluctuates
What causes the stiffness of arteries? **
- Age
- Atherosclerosis
- Rise in arterial BP
Describe the structure of veins
Thin walled, larger lumen than arteries, thin tunica media
What structure in veins prevents backflow?
Valves
How is blood flow mostly achieved in veins?
By the contraction of surrounding musculature or respiratory movements
What do veins function as?
Major blood reservoir
What are the 4 main descriptive measures of arterial pressure?
- Systolic pressure (highest during one cycle)
- Diastolic pressure (lowest during one cycle)
- Pulse pressure (systolic pressure – diastolic pressure)
- Mean arterial pressure (diastolic pressure = 1/3 pulse pressure
Name the 4 palpable pulses in the upper body
- Temporal
- Cartoid - side of neck
- Brachial - inner biceps
- Radial - inner wrist under thumb line
Name the 4 palpable pulses in the lower body
- Femoral - near pelvic bone
- Popliteal - behind knee
- Anterior & Posterior tibialis - lower limb
- Dorsal Pedis - over instep of foot
How does blood pressure change with age?
Systolic blood pressure rises throughout life
Diastolic blood pressure rises until the 6th decade and then becomes constant.
Is blood pressure higher in men or women?
Blood pressure is generally higher in men
What factors are associated with raised blood pressure?
-Dietary fats and salt
- Obesity
- Physical inactivity
- Psychological stress
- Excess alcohol intake.
What is the conventional unit for measuring blood pressure?
Millimeters of mercury (mmHg)
How is blood pressure typically expressed?
systolic pressure / diastolic pressure
Normal value is around 120 / 80
What is the mean arterial pressure?
The average pressure in the arteries over a cardiac cycle
Typically around 93 mmHg
What is the normal blood pressure range?
Systolic - less than 120
Diastolic - less than 80
What is the elevated blood pressure range?
Systolic - 120-129
Diastolic - Less than 80
What is the stage 1 high blood pressure range?
Systolic - 130-139
OR
Diastolic - 80-89
What is the stage 2 high blood pressure range?
Systolic - 140+
OR
Diastolic - 90+
Hypertensive crisis is when….?
Systolic - 180+
AND/OR
Diastolic - 120+
What are the principles of gas exchange?
Gas molecules move randomly, but in a net direction from regions of high concentration to regions of low concentration
What is partial pressure?
The pressure exerted by a specific gas in a mixture of gases, expressed as a percentage of the total pressure
What is the atmospheric pressure and composition of air?
Atmospheric pressure = 760mmHg
Dry air is composed of 79% nitrogen, 21% oxygen, and 0.04% carbon dioxide
How is partial pressure of a gas calculated?
By multiplying the percentage of the gas in the mixture by the total pressure of the mixture
Eg. partial pressure of oxygen (PO2) in air is 0.21 x 760 mmHg = 159.5 mmHg
What happens to air as it enters the respiratory tract?
Air is humidified>Oxygen diffuses from alveoli into blood>CO2 diffuses from blood into alveoli
This air is then partially replaced by the next inspiration
What is the partial pressure of oxygen and CO2 in air?
PO2 = 159mmHg
PCO2 = 0.3mmHg
What is the partial pressure of oxygen and CO2 in the alveolar air?
PO2 = 104mmHg
PCO2 = 40mmHg
O2 diffuses into blood until it has PO2 of 104mmHg
Blood has PCO2 of 45mmHg so CO2 diffuses into alveoli
What is the partial pressure of oxygen and CO2 in the oxygenated blood in the left atrium?
PO2 = 95mmHg
PCO2 = 40mmHg
Slight loss of PO2 from alveoli to end the of pulmonary vein - pulmonary vein receives some deoxygenated blood from bronchial veins
What is the partial pressure of oxygen and CO2 in systemic tissue cells?
PO2 = 40mmHg
PCO2 = 45mmHg
CO2 diffuses into the capillaries that have a PCO2 of 40mmHg
What is the partial pressure of oxygen and CO2 in the deoxygenated blood in the right atrium?
PO2 = 40mmHg
PCO2 = 45mmHg
(same as in tissue cells)
What percentage of blood is plasma and formed elements?
Plasma = 46-63%
Formed Elements = 37-54%
What makes up formed elements of blood and in what percentage?
Platelets + white blood cells = 0.1%
Red blood cells = 99.9%
What are the 5 types of white blood cells are what are their percentage quantities?
Neutrophils = 50-70%
Lymphocytes = 20-30%
Monocytes = 2-8%
Eosinophils = 2-4%
Basophils = <1%
What is the lifespan of an erythrocyte?
120 days in men and 110 days in women.
How many erythrocytes are destroyed every second?
About 2.5 million or 1/10000% of the total 25 trillion erythrocytes are destroyed every second.
Where does erythropoiesis occur and how long does it take?
In the bone marrow and takes about 4 days.
How does low PO2 stimulate erythropoiesis?
By increasing the formation of the glycoprotein erythropoietin in the kidneys
This induces the bone marrow to make more erythrocytes
What is the ratio of erythrocytes to white blood cells?
There are 700 times more Erythrocytes, than white blood cells.
What property allows erythrocytes to exchange quickly with surrounding plasma?
A large volume to surface ratio
How do erythrocytes pass through narrow capillaries?
They form stacks and bend/flex
This allows them to pass through capillaries as narrow as 4 um
What is haemoglobin made up of?
4 polypeptides (called globins) which each bind one heme molecule
What is the colour of each heme molecule and what does it bind to?
Red
Binds to 1 iron molecule - this then binds with oxygen
What does adult haemoglobin consist of?
2 alpha chains, and 2 beta chains
What is oxygen rich haemoglobin called?
Oxyhaemoglobin
What is oxygen-deficient haemoglobin called?
Deoxyhaemoglobin
What percentage of oxygen in the blood is carried by haemoglobin?
97%
How is the remaining 3% of oxygen carried in the blood?
It is carried in solution in the blood plasma
What type of binding does O2 have with haemoglobin?
Reversible
Where does O2 bind to haemoglobin?
In the lungs
Where does O2 dissociate from haemoglobin?
In the tissue
What describes the relationship between O2 and haemoglobin?
The oxygen dissociation curve
At what PO2 is haemoglobin in erythrocytes nearly 100% saturated with oxygen?
PO2 of 80 mm Hg and above
thus the blood in the alveolar capillaries is saturated
At what PO2 is haemoglobin 75% saturated?
40mmHg
About 25% of O2 carried by erythrocytes can dissociate into the interstitial fluid
When, and at what PO2, does haemoglobin give up 75% of its O2?
During moderate exercise when interstitial fluid in skeletal muscle can drop to 15 mm Hg
What is the Haldane response?
The decline in haemoglobin’s affinity for O2 with increasing CO2 concentrations
How is carbonic acid formed?
CO2 combining with water
What does carbonic acid dissociates into?
H ions and bicarbonate ions
This further decreases the affinity of haemoglobin for O2
What is the Bohr effect?
The shift in the oxygen dissociation curve to the right
Caused by a decrease in pH and an increase in CO2 concentration
Leads to a greater PO2 being required to saturate haemoglobin
How does increased temperature affect the oxygen dissociation curve?
It shifts the oxygen dissociation curve to the right
What effect does the accumulation of lactic acid have on the oxygen dissociation curve?
It shifts the oxygen dissociation curve to the right
In what conditions can haemoglobin release around 95% of its bound O2?
In heavy exercise - CO2 and lactic acid accumulates, temperature increases
Opposite in lungs
How is lactic acid important in the cardiovascular system?
It is transported to the heart and used by the cardiomyocytes to generate ATP
What 3 major tasks does physical exercise impose on the cardiovascular system?
- Increase pulmonary blood flow - along with gas exchange and ventilation
- Increase blood flow through the working muscles
- Maintain a stable blood pressure
What is the most important respiratory adjustment to exercise?
Ventilation-perfusion matching
What is Ventilation-perfusion matching?
Matching the increase in pulmonary blood flow with an increase in alveolar ventilation
How is ventilation-perfusion matching achieved?
By increasing both the rate and depth of breathing
Cardiac Output (CO) equation?
Cardiac Output (CO) = Heart Rate (HR) x Stroke Volume (SV)
How much can O2 consumption increase during exercise?
About 13 times its resting level
How is a 13-fold increase in O2 absorption by the pulmonary circulation is typically achieved?
a 1.5X increase in Stroke Volume
a 3X increase in Heart Rate
a 3X increase in Arteriovenous O2 difference
How does heart rate increase with work rate in adults and what is the maximum?
Rises Linearly
Maximum of 180-200bpm
What 2 factors increase heart rate and O2 uptake?
- Decreased vagal (parasympathetic) inhibition
- Increased sympathetic stimulation of the pacemaker cells in the sinoatrial node
How is an increase in stroke volume achieved?
-Increased filling pressure (which increases ventricular EDV)
- Increased ventricular contractility (which increases ejection fraction and decreases ventricular ESV)
What compromises ventricular end diastolic volume?
Reduced ventricular filling at higher work loads
How does cardiac output increase with O2 consumption?
In a virtually linear relationship
How does rest cardiac output change during exercise in an untrained adult?
From around 5 L.min-1 at rest to a maximum of 20-25 L.min-1 (a 4-5 fold increase)
What is the initial anticipatory respiratory response to exercise?
Inhalation and breath holding
What does the Initial anticipatory response do?
Forces more blood from the lungs back to the heart This increases heart stroke volume
What does increased PCO2 do to blood pH, and what detects change??
Decreases
Detected by chemoreceptive area in the medulla oblongata
What follows detection of pH change by the chemoreceptive area?
Increased respiratory rate
Increased tidal volume
What is respiratory rate in exercise measured as?
The ventilatory equivalent for oxygen (Ve/Vo2) - ratio between minute ventilation arte and oxygen consumption
What is the (Ve/Vo2) maintained at in a normal health individual?
25 up up to about 55% the maximum O2 consuption (Vo2 max)
When does the minute ventilation start to increase disproportionately during exercise?
When O2 consumption (Vo2) exceeds 2.5L/min
Ve can increase from 25 to 35-40 during maximal exercise (oxygen uptake efficiency from lungs can almost half)
What is the point at which there is a disproportionate increase in ventilation called?
Ventilatory threshold (VT)
What buffers the onset of blood lactate accumulation (OBLA) and increased lactic acid during exercise?
A reaction with sodium bicarbonate
Lactate + NaHCO3 —–> Na lactate + H2CO3 ——> H20+ CO2
