Friday, 21 March 2008

Revising heart and lungs

It's been physiology for the last day and a half: heart, circulation and lungs. Here are some of the more interesting things I am trying to commit to memory:
  • The vascular system is lined by endothelial cells. This is the only type of tissue that is actually in contact with the blood.
  • The heart consists of three distinct layers: endothelium (in contact with the blood), myocardium (the muscle cells), and epicardium (a thin external layer). The heart is contained in the pericardial sac, which is a double layer with fluid between the layers to reduce friction when the heart beats.
  • 99% of the heart is made up of contractile muscle cells, but there are also pacemaker cells that generate the rhythm of the heartbeat. Electrical activity within the heart is not carried by nerves, but by specialised muscle cells.
  • I've learned what the PQRST waves mean on an ECG trace, but it's too long to summarise in a bullet point. You can just about survive without your P wave, but if your QRS complex goes, you need help, fast.
  • At any time, most of your blood (64%) is in your veins. 7% is in your heart, and only 9% going round your lungs. The rest is in arteries, arterioles and capillaries.
  • In the 'fight or flight' reflex, the release of adrenaline restricts blood flow to all your organs, except the brain. Local effects like the reduction of oxygen and increase in carbon dioxide at the heart and skeletal muscles is what dilates those particular arterioles to increase blood flow so you can run away.
  • They used to think that endothelial cells didn't do much except line blood vessels, but now it's been found that they produce nitric oxide (a vasodilator) and endothelin (a vasoconstrictor).
  • The tissue lining the gas exchange surfaces in your lungs has two kinds of cells: type I (where the gas exchange takes place) and type II (which secrete the surfactant that keeps all the air pockets open). Parents of premature babies already know this.
  • Your Total Lung Capacity is the sum of your Residual Volume, your Expiratory Reserve Volume, your Tidal Volume and your Inspiratory Reserve Volume, usually about 6 litres in young healthy adults. It's more efficient to increase the depth of your breathing than the rate, but you know that from experience. It's to do with dead space.
  • Binding of oxygen to haemoglobin and dissociation curves - we did this at A level but it seems more secure in my head now. It's really clever, how oxygen is picked up in the lungs and dropped off where it's needed, all using the power of Chemistry.
This is like having online revision notes - I'm sure I will remember it better for writing it all out like this. Hope it's not too boring for any passing readers.


aims said...

I was thinking the same that you've written it down -

I thought at first - I can't read all this - but then I did - and it was very very interesting!

But - not interesting enough to make me want to do what you are doing! Good work girl!

Tina said...

OK, now I'm worried about my QRS complex. I think a gin would be medicinal, although you don't mention that. When do you do the bit about gin as medicine?