The circulatory system

Now, the circulatory system awaits for us.

We need to learn 5 things here:
1. Function that it carries out, we already did it: nutrients, waste products...remember all that. Just think that our cells are immersed in a medium called interstitial fluid or interstitial plasma, which gives them all the nutrients they need and receives all the waste products released during metabolism. The circulatory system allows this medium to remain always the same.

2. Blood: components and functions.
Blood is a viscous fluid which flows inside vessels and is composed of blood plasma and 3 types of cells.
Give me a good definition of those four things...
OK, I'll do the first two:
a. Blood plasma is a yellowish substance made up of water and dissolve molecules (all kind of nutrients, waste products and hormones).
b. Erythrocytes or red blood cells (around 5 million per mm3 of blood) are disc-shaped, enucleated (with no nucleus) cells which contain haemoglobin, a red protein which transports O2 from the alveoli to the body's cells and CO2 back to the alveoli. Actually, most of the CO2 travels dissolved in the blood plasma and not attached to haemoglobin.
Erythrocytes are formed in the red bone marrow (connective tissue inside long and flat bones) and then destroyed, 80 to 120 days later, in the spleen.

Could you do something similar for leukocytes (white blood cells) and thrombocytes (platelets)?
What functions does the blood carry out? I would talk about 5 main functions: transportation of nutrients and residues, transportation of hormones around the body (you remember hormones,right?), defence of your body  against infections, regulation of our body temperature by moving heat from warmer areas to the cooler ones and, finally, protection from blood loss when blood vessels are broken.

3. Blood vessels.
Quite easy. You need to differentiate arteries, arterioles, capillaries, veins and venules.
Try something like this:
Veins are blood vessel which take blood back to the heart. Capillaries come together to form venules and these form veins. Their walls are thinner than artery walls because they have less muscle tissue (that's why they are different colours) and there are valves inside them which allow blood to flow towards the heart but not backwards.
Write down your paragraph about arteries and capillaries.

4. The heart.
I have posted three videos on our blog in which you'll find all you need to know. You will find 8 questions in one of them that I need you to answer.

1. Learn and practice the names of the cavities, vessels and valves.
2. Follow and describe the flow of blood through the heart.
3. Explain the meaning of the colour code. Why two colours? What does blue/red mean?
4. Imagine that you are an erythrocyte in the right atrium, how can you get to the left ventricle?
5. Draw and label a human heart. Your drawing must include: the names of the four chambers, names of the 2 atrioventricular valves and 2 semilunar valves, names of the 2 arteries exiting the heart and 6 veins entering it.
6. Can a human heart keep on pumping after being removed from the body? Why?
7. What causes the sound of a heartbeat? Hint: muscles do not sound when they contract.
8. After watching te video on Heart attacks, could you explain, using your own words, what a heart attack is?

Please, complete all these activities in your notebook, I promise I will check whether you did it or not.

5. Blood circulation.
Please, watch the video: "The heartbeat and blood circulation" available in www.anayadigital.com
Try to describe our double circuit (pulmonary and systemic circulation). Do not trust your memory too much, you'd rather write it down, just in case it could be a nice question in the test.


To start with, one tiny remark: printing out is not the same that writing down, I would say they are quite the opposite. I hope you are not printing out my posts and just gluing or glueing (both are correct) them in your notebooks, and I say it for two different reasons: first, because they have more directions than information, and second, because you learn more when you are active, deciding what is worth copying and what can be improved or completed. Actually, I am continuously asking you to do your part.

6. The cardiac cycle.
Each heartbeat has three phases. Yes, three and not two. Can you describe these 3 phases? 
I will give you a  hand: the first one is called "atrial systole" and in it, the atria (both of them) contract and the blood is pumped into the ventricles via the open atrioventricular valves.

Now is your turn.

After completing the three phases, could you locate the characteristic "lub-dub" sound of the heart in them?
Tricky question, 3 phases and two sounds (lub and dub). I will help you again: visualise the atrial systole (read the description I wrote), would you hear anything during this phase?

7. The decisive question to become a first-rate expert in circulation.
I need a long introduction. Here it goes: Ventricular systole pumps the blood into the major arteries. These arteries are elastic, so that they dilate when they receive blood, lowering blood pressure, and then contract back to their normal diameter, pushing the blood forward so that it flows through the arteries continuously, not intermittently as you may have thought.
Arteries branch out into arterioles and these into capillaries in turn. When the blood reaches the capillaries, the pressure is lower and the flow is slower which facilitates the exchange of substances between blood and cells (actually blood and interstitial plasma). 
We are almost there.
Now, the capillaries come together to form larger vessels, venules, and these will form veins. The problem is that all the pressure provided by the heart is now gone, so, and this is the question: how does the blood manage to complete the circuit and reach the atria of the heart?
Not an easy task, that's why 3 mechanisms cooperate to try to solve it.
Your answer:




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