A closer look at the heart and how it works

We spent most of class this week focused on the heart and circulatory system.  First, we watched this video, which illustrates how the heart works.  We talked about how hearts of mammals, which are four chambered.  See the illustration to the right to the right, to see what we discussed.

• The bottom line is that the heart from the body comes to the Superior vena cava at the top of the heart and then fills the right atrium.  
• At the right moment, the tricuspid valve opens and lets the deoxygenated blood go into the right ventricle.  
• The heart contracts and pumps the blood up to the lungs by going through the pulmonary valve and the pulmonary artery.  
• In the lungs, oxygen is added to the blood.
• Then, it comes back to the heart, through the pulmonary veins and into the left atrium.
• It gets dumped into the left ventricle by passing through the mitral valve.
• The heart contracts and pumps the oxygenated blood through the aortic valve, then the aorta and onto the body to bring oxygen and nutrients to our brain and other organs.
• The valves prevent blood from flowing backwards.

One cool thing we learned is that a fetal heart has a hole between the left and right atrium called the foramen ovale.  Because the fetus doesn't get its oxygen from breathing air into its lungs, there is no need to separate the blood flowing from the lungs from the blood flowing from the body.  The fetus gets its oxygen from the mom's blood, across the placenta.  

The hole normally closes shortly after birth, which is when the baby begins to breathe air and needs to keep the oxygenated and deoxygenated blood separate.  We looks at our fetal pig hearts and could not find the foramen ovale.

Actually, mammalian fetuses have their own form of hemoglobin, the molecule in blood that attracts oxygen.  Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin, which allows the fetus to take oxygen out of the mom's blood and into its own.  Pregnant women have to expand their lungs and breathe in more oxygen to make up for this, and it all happens automatically.  This curve below shows that fetal hemoglobin attracts oxygen better than adult hemoglobin.

We dissected the adult pig heart too, which was very large compared to the fetal pig hearts.  We weighed the adult heart, and found it was about 1.3 lbs, which was less than we predicted.  Then we weighed all 8 of the fetal hearts and found they were also less than we predicted, a total of about 70 grams, when we thought they would add up to about 150 grams.  

Lungs and Heart, Thymus and Thyroid

This week, we took apart some of the organs that we dissected in a block last week.  First, we examined the trachea and esophagus.  They were two tubes at the top, the trachea firm and the esophagus soft.  We tried blowing into the trachea to inflate the lungs, but it didn't work.  Later, we used the eye droppers to inflate the lungs, and that was pretty cool!

Here on the right is a photo of what the organs we looked at this week would look like if we were very skilled dissectors.  The organs did pretty much look like this, but we generally had more damaged and missing pieces, because we are not yet very skilled at this dissection.  That's ok, we're just learning!

On the sides of the trachea, we all tried to find the thymus, which is an immune organ.  Most could find it.  It turns out the thymus is proportionately larger in a fetus compared to an adult.  See this picture to the left, and you see that in a fetus, the thymus is almost as big as a lobe of the lung, but in the adult, the thymus looks about a tenth the size of a lobe of the lung.

Then, we looked for the thyroid gland, which was a small, brownish organ also above the heart and near the trachea.  Most of us could not find that, probably due to not properly dissecting it out with the other organs.

We weighed each of the organs we dissected out today, which included the thymus, thyroid, lungs, and heart.  Each one was about 20 grams.  We also measured each of these organs with our rulers and noted all the measurements for our autopsy reports.

We discussed the lungs a bit, and wondered if it was possible to pop the lungs.  I thought that a normal human or animal could not pop their lungs simply by taking in a huge breath.  The lungs are designed to handle any size breath you can do.  But by blowing from an outside source (using the straws or medicine droppers to push air into the lungs) you could possibly pop them.  Also, some people get lung diseases when they are older that can cause their lungs to get brittle and the tiny air sacs can in fact pop.  Here is a picture showing how the airways get smaller and smaller in the lungs down to tiny little air sacs, called alveoli.  The largest tube is called the trachea, then there are two bronchi that come off.  Smaller than that is the bronchioles.  The diaphragm at the bottom moves down to cause the lungs to fill and up to make us breathe out and empty the air out of the lungs.  We need to discuss lung diseases such as asthma, smoker's lung, emphysema, lung cancer, pulmonary embolism, and bronchitis in class.  We also looked a bit at the hearts but need to discuss more about how the heart works.

hmm

i am an intelegent person. i say something smart using big werds about pigs and there guts .....the end


i cant wate to kepe on dissection

Forensic pigs - the first incisions

This week, we finally began the actual dissection of the pigs.  First, we reviewed what we had learned about skin, and talked a bit about scientific language.

• The prefix derm- relates to the skin, as in the layers of the skin called epidermis, dermis, and hypodermis.  Dermatology is the study of skin and its diseases and disorders.
• Stratum is a term that means layer.  There are five layers of epidermis, and four of them have the word stratum in them.  The word stratum is not only used in the skin and the body but also in geology when talking about rock layers.
• The innermost skin layer, called the subcutis (or hypodermis) is related to the term subcutaneous, which means just below the outer skin layer but still within the skin.  When people receive injections, often they are IM or intramuscular, which is when the needle is stuck through the skin and into the muscle.  Many vaccinations are done like this, in the thighs of babies but usually in the arms of older kids and adults.  But sometimes the injections are subcutaneous, often called SubQ, when they want the liquid to be absorbed from within the skin.  A third way of injecting is called IV, or intravenous, and that is when the liquid is injected directly into the bloodstream.  This gets it circulated throughout the body very quickly.  I didn't actually talk about intradermal injections, which are illustrated above.

Next, we went over some important anatomical terms.

• Medial -- toward the midline or middle.  
• Lateral -- opposite of medial, away from the midline or middle
• Anterior -- toward the head
• Posterior -- toward the butt
• Dorsal -- toward the back (spine)
• Ventral -- toward the stomach
• Proximal -- close to a specific point
• Distal -- far from a specific point

We practiced moving a point on another person's back in the medial, lateral, anterior and posterior directions.  What is a bit confusing is that with pigs and other animals that walk on all fours, anterior is toward the head and posterior is toward the butt.  For humans, anterior is towards the stomach (like ventral) and posterior is towards the back (like dorsal).  Also for humans, superior is toward the head and inferior is towards the feet.  We're focusing on the terms we'll use as we dissect our pig.

We began our autopsies by completing our observations of the external features of our pigs.  We used the terms to describe where birthmarks were, and determined the gender of our pigs.  Nearly all the girls have male pigs and all the boys have female pigs, ironically.

Our first incisions were the Y incision used in a typical autopsy.  We cut all the way down so that we could get all of the major internal organs out together.  I thought it was neat to see the trachea and esophagus right next to each other, and to see how big the lungs are.  Next week, we'll examine each of the organs, one by one, and hopefully take some samples to look at under the microscope.