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Dr RO Davies
Core Respiration lectures

handout: SUMMARY: Core Respiration

knowledge of anatomy is going to be helpful.
but physiology is more substantve. :)
physiology is "more important" [he's showing really wacky slides, her.]

this slide of the young dr washabau is pretty funny - and the "after" 
slide is abe lincoln....

hmmm. not sure where we're going with this. ah, ok, physio will give us 
integrity,character, and make us smart.

handout: two purposes. first 3 pages == CORE. we need to get it either 
from lectures or from textbook. second part starting w/R1-1 is a partial 
script for the lectures. one thing to know: MUST KNOW GRAPHS 
***dingdingding*** LEARN GRAPHS***IMPORTANT. and in background material 
is listing of laws...KNOW THOSE. (p 6)

physiology really deals with transport: movement of stuff from one place 
to another. transport can be stressed or unstressed as capacity of system 
reaches max limit.

note: dr davies will keep saying "as you remember" but he doesn't really 
think we remember anything from last semester, so just ignore when he 
says that. :)

respiration is not that clinically relevant, he says. some things are 
important. animals except horses and cats don't really get lung diseases 
that people do. but it's important to understand physio for anesthesia, 
critical care, sports medicine, and passing your second physio exam.

we need to gain an understanding of lung and gas delivery system. 
eventually, we should understand [slide: respiratory failure]

		respiratory failure
			/		\
lung failure		pump failure
	|					   |			
gas exch failure			ventilatory failure manifested by hypercapnia
	|							|			\			
manifested by hypoxemia		CNS depression or mechanical defect
              							\	  /	
	                          			fatigue

"if RO thinks CO2 is so damned important, he should say so right at the 
beginning of his lectures"- anon student, on course evaluation.

IT IS IMPORTANT!! CO2 IS IMPORTANT!!

"RO Sucks" - anon student on evaluation last year

Dr Davies says "suck" is not an intransitive verb; so he doesn't know 
what this means, so he reads it over and over again.

"no breathe, no live"  - mr miyage

so. ther is an exchange membrane exchanging gas between alveolus and 
capillary. it' sso thin you can't see it but there is blood, epithelium, 
basement membrane,alveolar cell, gas. in the horse, this is huge an it is 
very thin. relatively LITTLE blood is spread out over this...2.5 L spread 
over surface of courtyard, in horse. 

MECHANICS: must get gas through the complex airway system down into the 
exchange system (alveoli, resp bronchioles) = must get down there w/each 
breath.

terrible slide emphasizing point that blood gas chemistry is not simple. 
RO will try to make it easy; if he doesn't, blame him. it takes common 
sense and a lack of fear, mainly. 

exchange of gas between mammals and environment, is what we're going to 
discuss. we're going to consider how respiratory system provides nutrient 
environment for cells. the whole system is slave to cell respiration. 
mitochondria need O2, so we have to breathe. if mitochondria DON"T need 
oxygen, you don't have to breathe (but they do, to make ATP, so.)

FUNCTIONS OF RESPIRATORY SYSTEM:

- provide proper amount of oxygen to cells ** main thing resp sys does.
ENVIRONMENT is source of all oxygen in body - body only stores about 15 
seconds worth of oxygen. you MUST get it from the environment. this is 
something you are required to know. SOURCE of O2 is ENVIRONMENT. now, 
environment contains only 21% oxygen. it is NOT 100% oxygen. air is 
oxygen dissolved in nitrogen. air is 79% nitrogen. we would die in 4-5 
days if air was 100% oxygen. oxygen is a POISON. even at high altitude, 
air contains 21% oxygen, but pressure is reduced. so pO2 decreases with 
altitude, but PERCENT is the same.
-Cells are the sink, eg, site of oxygen utilization. all oxygen is used 
by mitochondria in the cells, to make ATP. to increase oxygen 
consumption, you need more mitochondria.
-Oxygen transport should be adapted to the needs of the cells. this is 
important. if you increase energy consumption via excercise, you must 
increase oxygen transport to the cells needing it. you don't want 
activity to be limited by a poor supply of oxygen. eg, factory output 
should be determined by demand for product, not by supply of raw 
ingredient. muscle activity should be determined by demand, not by oxygen 
supply.

-excrete the carbon dioxide produced: all CO2 comes from the cells as a 
product of oxidative metabolism. there is NO CO2 production without O2 
consumption. the body DOES NOT RUST. 
MUST MEMORIZE: there is NO CO2 in outside air, no matter HOW STUFFY the 
room is. when you increase ventilation, you get rid of CO2. you do not 
take in more CO2. unless it is an artificial situation, there is 
effectively no CO2 in outside air. so the lung EXCHANGES oxygen for CO2. 


RQ respiratory quotient = metabolic exchange ratio of CO2 produced/O2 
consumed. determined by tissue metabolism

R = respiratory exchange ratio: CO2 output/O2 uptake (determined by lung 
gas exchange)

in a steady state, RQ == R.

--maintain extracellular fluid pH. it does this by secreting an acid 
anhydride, CO2, carbon dioxide. 

Respiratory system also helps regulate temperature eg panting. Water 
balance is regulated by the respiratory system. it's used in balance, and 
communication (vocalization) as well. but we're concentrating on the main 
three functions listed above.

resp sys is SERIES OF TRANSPORT SYSTEMS linking outside AIR (source of 
O2) to the CELL (where O2 is used by mitochondria). Then biochemistry 
takes over.

we're going to start with the last link in the chain...O2 delivery to the 
cell. cell delivery is KEY to all this. the amount of O2 used by cell 
determines how hard the lung has to work. we can say:

Despite varying requirements(rest, exercise) and despite varying 
availability (lung dz, altitude), oxygen MUST be delivered in adequate 
amount (molecules/min) equal to oxygen consumption, AND it must be 
delivered at high enough pressure - pO2 in capillaries - high enough to 
drive the diffusion transport.

eg, putting out fire; need ENOUGH water, and it must be at high enough 
PRESSURE To reach fire. if pressure too low, water spills onto sidewalk, 
doesn't reach roof. if not enough water, fire will keep burning. see?

so. what determines O2 delivery to tissues?

1. capillary pO2. the capillary partial pressure of oxygen = driving 
force, concentration gradient. a difference in pressure drives flow. 
difference in concentration drives diffusion.

so, pressure. what are the pressures in capillary? in arterial blood, pO2 
= approx 100 mmHg (learn that) and in veins, pO2 = about 40 mmHg.(learn 
that too)
so as blood traverses capillary bed, cells are picking up O2 and using 
it, so pO2 is dropping, because oxygen is leaving blood and going to the 
cells. that seems like it makes sense. so pO2 is 100 going into the bed, 
and 40 coming out of the bed, so it drops as it goes through. 

2. blood flow: the more flow, the more O2 delivery. if more blood is 
delivered, you can keep capillary pO2 high. the more blood delivered, the 
higher will be the pO2.

3. distance of a cell from a capillary. the farther a cell is from a 
capillary, the longer the diffusion distance, and as distance increases, 
resistance increases, so it's harder for oxygen to diffuse to that cell. 
cells next to the capillary consume oxygen, and so less is available for 
cells farther away. the farther away the cell, the more it is at risk for 
low O2. so you can change distance by opening new capillaries. this is a 
very important adaptation to exercise! if RO hands out As, the people in 
the front row will grab them all, and none will be left for those in the 
back row. [candy demo. not FAIR. people in back row do not get candy, it 
doesn't diffuse down here. but if we open more beds...hey! he's handing 
out a whole bunch of candy! *sigh* this diet sucks.]

4. metabolic rate itself...how much oxygen are mitochondria using? 
metabolic rate determines oxygen utilization. also determines how much 
system has to work.

slide: capillaries, each w/mean pO2 of 50. close to capillary, O2 
concentration is high, and farthest away - eg, dead between the two - the 
tissue pO2 is lower, more like 35 or so. these slides are in handout. 
farther from arteriole, lower pO2 as well. 

you can lower pO2 at farthest distance from capillary by lowering pO2 in 
capillary, or by increasing metabolic rate of tissue, or increasing 
distance between open capillaries. so you can't let capillary pO2 fall 
below a certain level, or there will be cells in the middle not getting 
any oxygen which would suck (HA!). those cells won't be able to carry out 
respiration, will have lactic acid build up, will die if no oxygen is 
brought in. so it can't fall below a certain critical level below which 
there will be tissue hypoxia and anaerobic metabolism. what is this 
level?

experiment: take an animal and measure the pO2 in arterial blood of 
animal, and then lower O2 concentration in gas it breathes. as you do 
that, you lower arterial pO2. O2 consumption stays constant until you 
reach critical point. cells don't get enough, so can't consume, so oxygen 
use falls. this happens at about paO2 = 60 mmHg. then, if you have 
working animal, this critical level drops down to 40 mmHg. this is 
somewhat counter intuitive for me. even though oxygen consumption is 
higher, why is critical threshold lower? AH! because there are MORE open 
capillaries, so the distance has been decreased, so critical pO2 doesn't 
have to be as high. ok, that makes sense. there are more open capillaries 
in exercising muscle. 

if you think about that capillary bed, what is lowest possible 
concentration to which cells are exposed? 100 mmHg at beginning, and 40 
mmHg at the venous side. so cells on venous side are MOST at risk to 
hypoxia. so VENOUS critical pO2 is less than 10. how much oxygen must be 
extracted to satisfy metabolic needs, is what this measures...eg, 
requirements of tissue vs supply. venous pO2 tests this..how adequate the 
oxygen supply is.need right heart sample...yuck.

how can you tell if your cat has had enough food? well, you feed it. it 
stops eating. look at how much food is left over. you fed it enough if 
there is food left over. so, if there is a lot of oxygen coming OUT of 
venous side of cap bed, then there is enough oxygen supplying tissue. if 
you go below 25 mmHg you will build up lactic acid. system tries to keep 
venous pO2 at 35 or higher to ensure adequate oxygen to the tissues. to 
assess patient's oxygenation status, check venous pO2...if 35 or more, is 
ok.


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