Lecture 14- Respiratory 2 Flashcards

Question

How does the exachange of O2 and CO2 occur between the air and the blood?

Answer 1

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 gradient. So, the concentration (or pressure) of O2 in the alveoli must be kept at a higher level than in the blood & the concentration (or pressure) of CO2 in the alveoli must be kept at a lower lever 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.

Answer 2

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:

Answer 3

The walls of alveoli are coated with a thin film of water & this creates a potential problem. Water molecules, including those on the alveolar walls, are more attracted to each other than to air, and this attraction creates a force called surface tension. This surface tension increases as water molecules come closer together, which is what happens when we exhale & our alveoli become smaller (like air leaving a balloon). Potentially, surface tension could cause alveoli to collapse and, in addition, would make it more difficult to 're-expand' the alveoli (when you inhaled). Both of these would represent serious problems: if alveoli collapsed they'd contain no air & no oxygen to diffuse into the blood &, if 're-expansion' was more difficult, inhalation would be very, very difficult if not impossible. Fortunately, our alveoli do not collapse & inhalation is relatively easy because the lungs produce a substance called surfactant that reduces surface tension.

Answer 4

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) -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 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 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.

Answer 5

At body Temp. PH2O vapour = 47 mm Hg ␣ PO2 150 mm Hg ie. dead-space (functional residual capacity) ␣ O2 is continually moving down its partial pressure gradient ␣ ie across alveoli into blood -the air coming in is warmed and humidified so has larger vapor content= protection for the alevoli and also the partial pressure of this water is diluting the O2 and the dead space too the reulsting partial pressure= about 100

Answer 6

- Partial pressure gradient: Major determinant (PAO2 ␣ PcapO2)=Pcap 02= partial pressure in capillary - Surface area of alveolar membrane (A) : Constant at rest, rises during forced inspiration eg during exercise, decreases during some pathophysiological states(the larger the area the better it will be able to flow across also depends on how many alveoli participate= in big breaths =more) -Thickness of air blood barrier (x):Constant at rest rises during some pathophysiological states (the thicker it is the slower the movement of oxygen across when horses go hard. increas ein the intestitial space fluid= so thicker air blood barrier= point where the limit is reached ) -Diffusion coefficient of gas (D ) ␣ CO2 : 20x \> O2 Rate of O2 movement = D . A . (PAO2 - PcapO2)/x

Answer 7

-Oxygen is carried in blood: ## Footnote 1 - bound to hemoglobin (98.5% of all oxygen in the blood) 2 - dissolved in the plasma (1.5%) 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 diagram below 2 - carbaminohemoglobin - 30% formed when CO2 combines with hemoglobin (hemoglobin molecules that have given up their oxygen) 3 - dissolved in the plasma - 10%

Answer 8

extent to which the hemoglobin in blood is combined with O2 depends on PO2 of the blood:

Answer 9

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.' ## Footnote 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 you have 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 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.

Answer 10

- lower pH - increased temperature - more 2,3-diphosphoglycerate - increased levels of CO2 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+ & 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. 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 graph below). This means that at a given partial pressure of oxygen, the percent saturation for hemoglobin with be lower. For example, in the graph below, extrapolate up to the 'normal' curve (green curve) from a PO2 of 40, then over, & the hemoglobin saturation is about 75%. 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!

Answer 11

Haemoglobin forms unstable compound oxyHb - Disassociates in water - Blood P drives the reaction left or right O2 -Hb+O2 =HbO2(easy to dissociate not a time bind not that strong) capacity of plasma is limited in how much O2 it can carry= so it has RBCs full of haemoglobin that can bind to the oxygen and take it out of the solution Dissolved O2 is directly directly proprtional to the partial pressure of O2

Answer 12

carbon monoxide will bind to Hb strongly= dangerous, can't get oxygen if all Hb occupied

Answer 13

-increase in partial pressur eof O2 the increase in Hb saturation ## Footnote good that it isn't a straight line=even a modest rise of partial pressure= rapid filling up of the Hb in the end bit not as much as most are already occupied - Heme-heme interactions responsible for sigmoid shape of Oxy-Hb curve(special dissociation curve= if structure changed this changes) - type and sequence of Amino acids in protein chain of each heme subunit= alters O2 binding affinity, responsible for different types of mammalian Hb - small drop in O2 then release lot of O2 from Hb = bigger difference in the lower levels as ther emay be danger there the sigmoid curve is due to the nature of Hb

Answer 14

so most of the oxygen will be released at the low level when it's most needed in the active tissues

Answer 15

what can change the dissociation curve: chang in pH, increase in CO2 (tissues workinh hard more CO2 and increase in hydrogen ion= drop in pH and increase in temperature, biposphogylcerate increase) ## Footnote moving it to the right= so the steeper part comes earlier= so it will give more oxygen at lower levels still! around 20% difference in how much O2 delivered to the tissues that need it

Answer 16

- y measuring PO2 at 50% Hb saturation - different species have different Hb structures tha affect how the curve looks like - rabbit= more to the right, then gives out more O2 at lower level= smaller then have metabolic rate higher so need more O2 then larger animals who have lower metabolic rate

Answer 17

- hanged structure of fetal haemoglobin enhances binding affinity for O2 - fetal to the left, fetal haemoglobin hungruer for oxygen so oxygen is taken up from the maternal blood to the fetal cocn of Hb in fetal blood is higher and PCV is higher so more O2 taken up