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Link to UNIT GUIDE: *To be inserted*
(Feel free to skip the spiel if you're in a hurry!) We're used to common terms such as "left" and "right" and "up" and "down" to describe things both around and within us in our daily lives. For example, if you need to tell a physician that you injured yourself, you might say "I hurt my right arm," or if you're ever petting someone's dog, they might tell you that said dog likes to be scratched "behind their right ear."
Yet, things aren't always so simple, especially in the medical world. During a dissection, one will be exposed to a plethora of different organs, some that they might not even know the name of. And saying "the red blob to the right of the right of the blue tube" (based from personal experience) gets confusing pretty quickly. You might want to point out a certain direction on a certain animal. The meaning of "up" and "forwards" can have completely different meanings as the animals change (for instance, the "upper" part of a sheep would be its back/spine, while on a human, it would be their head/cranium), and in that case, it becomes vital to familiarlize oneself with specific directional terms that can better represent different regions on different organisms without sounding confusing.
Some of these (which are included on the unit guide) include:
Anterior
Posterior
Superior
Inferior
Superficial
Deep
Lateral
Medial
Proximal
Distal
Core
Extremities
Let's dive in!!
Essential Question #1: What are the major directional terms used in anatomy?
The diagram above shows the anatomical directional terms relative to the human body. Image Source: Medic Tests
Directional Terms
Anterior Vs. Posterior: Anterior refers to the "front" of an organism, while posterior refers to the "back." To put this in picture, if we look at ourselves, our anterior side (our face/chest/stomachs) is the side of us that faces forwards all the time. Meanwhile, posterior (our backside) refers to the side of us that faces backwards.
Example: "The intercostal muscles are anterior to the lungs," or "the cerebellum is posterior to the cerebrum."
Superior Vs. Inferior: When something is superior, it is at a "higher" elevation and when something is inferior, it is usually at a "lower" elevation. This applies to the human body, too. When part A is below part B another, it is inferior to part B. When part B is above part A, it is superior to part B.
Example: "The liver is inferior to the lungs," or "the pons is superior to the medulla oblongata."
Superficial Vs. Deep: Superficial refers to when something is closer to the surface of the body, while deep means something that is "deeper" within the body, or in other words, farther away from the surface.
Example: Visceral fat is a deep, endocrine active tissue and wraps around organs, while subcutaneous fat is superficial and exists underneath the dermis and epidermis (layers of skin).
Lateral Vs. Medial: On the diagram above, we can see a dashed blue line that cuts along the midline of the torso. Lateral means farther from the midline, while medial means closer to the midline.
Example: "The arms are lateral to the torso" or "the heart is medial to the lungs."
Distal Vs. Proximal: Proximal is when something is closer to its point of attachment (which is usually a joint). Distal is when something is farther from its point of attachment (and if there is no CLEAR point of attachment, you can also think of distal as being farther from the center of the body). A good analogy is to say: proximal = proximity and distal = distance.
Example: "The
Dorsal Vs. Ventral: At a first glance, dorsal and ventral might seem similar to Anterior and Posterior, and for humans, they usually are. Think of dorsal as
Core Vs. Extremities:
Want more practice? Check your comprehension here.
Essential Question #2: What is the structure and function of the heart?
Essential Question #3: What are the structures and functions of blood vessels?
Veins
(**To the right is a diagram/cross section of the human heart. Use this image for reference.)
The blue tubes are usually called veins (with the exception of the pulmonary artery, which will be discussed later!!), since they carry deoxygenated blood TOWARDS the heart. One such way that veins significantly differ from arteries is that arteries transport blood at high pressure, while the blood in veins is significantly slower moving.
To the very left (from our perspective) are two large blue veins labeled "superior vena cava" and "inferior vena cava". Use this image for reference to see all the veins in the body: Veins in the body (Wikipedia).
The superior vena cava brings deoxygenated blood from the upper half of the body (head, brain, neck and arms).
The inferior vena cava brings deoxygenated blood from the lower half of the body (pelvis, abdomen and lower extremities such as legs). You might be wondering how the inferior vena cava brings blood back towards the heart against the force of gravity. It does this using valves, which manually push the blood up towards the heart.
The pulmonary veins are the little red tubes poking out from either side of the heart, and as you've probably noticed, red is used to mark vessels that carry oxygenated blood. So what is going on here??
The pulmonary veins, despite their name, are labeled this way because they participate in a process known as pulmonary circulation, which is the system the heart uses to re-oxygenate blood that it can pump back into our bodies. The role the pulmonary veins play in this whole process is simply bringing blood back to the left atrium after it has been oxygenated by the lungs.
Arteries
Arteries, on the other hand, are labeled in red, because they carry oxygenated blood AWAY from the heart (with the exception of the pulmonary veins, which were discussed earlier!). As mentioned earlier, the blood in the arteries travels at a much higher velocity and pressure than the blood in the veins, as shown in graph B and C: Vessel Comparison Graphs. This is also why arteries have a much thicker tunica media (the muscle that makes up the walls of arteries) than veins do.
On the cross section of the heart diagram above, you might notice the blue tube that crosses across the heart labeled as "pulmonary artery." In theory, it't true to its name because it does, in fact, carry blood AWAY from the heart. However, this blood is NOT oxygenated. The purpose of the pulmonary artery is to transfer the de-oxygenated blood it has recieved from the vena cavae and right ventrical to the lungs so it can be re-oxygenated and send back into the left atrium and eventually into the rest of the body! Here is a diagram of what the arteries look like in the body: Arteries in the body (Clevland Clinic).
Arteries to Veins
You might be wondering how oxygenated blood that comes out of the aorta finds it's way back into the superior and inferior vena cava. Or, in simpler terms, how blood from arteries finds its way into veins. Here is a flowchart:
Left atrium → Mitral/bicuspid valve → Left ventricle → Aortic valve → Aorta → Arteries (first, either the descending aorta or the carotid arteries) → Arterioles → Capillaries → Venules → Veins → Superior/Inferior Vena Cava → Right atrium
Capillaries are extrememly thin in diamater, and are the site of resource/nutrient transfer. They deliver things such as oxygen, nutrients and hormones to the surrounding tissue cells, while also accepting waste product from the same cells! This waste blood is then sent back to organs such as the heart and kidneys for "filtration" and "re-oxygenation". Here is a great diagram to visualize this: Veins to Arteries (Wikipedia Image) !!
Types of Circulation
As shown in the figure below the diagram of the cross-section of the heart, there are three main types of blood circulation you will need to know:
Pulmonary Circulation: The process of deoxygenated blood going from the right ventricle, through the pulmonary artery into the lungs, where carbon dioxide is released, and oxygen is picked up. The oxygenated blood is then sent back to the heart through the pulmonary veins into left atrium.
Systemic Circulation: The process of oxygenated blood traveling from the left ventricle, into the aorta, and down the descending aorta throughout the entire body into tissues, where oxygen and nutrients are delivered. The deoxygenated blood then enters back into the right atrium via the superior and inferior vena cava.
Coronary Circulation: The process of oxygenated blood circulating from the base of the aorta into the coronary arteries (arteries on the muscle of the heart) to supply blood to the heart. The reason the heart has it's own circulation system is because it's an organ that never stops beating. Therefore, to properly support the heart and ensure that it doesn't fail, it needs a constant flow of resources, hence, a blood supply of it's own. In the case that a coronary artery gets either blocked or hemorrhages, the part of the heart muscle it supplies can become deprived of oxygen and start to die off. This phenomenon is known as a heart attack, and is usually a side effect of other conditions such as Coronary Artery Disease (will be discussed more later!).
Want more practice? Check your comprehension here.
In this image, "Pulmonary trunk" means "Pulmonary Artery"
The Heartbeat
If you've ever used a stethoscope, you're probably familiar with the "lub-dub" sound that a regular, healthy human heart makes about 100,000 times a day! This is caused by the the atria constricting, pushing blood into the ventricles, and then the ventricles constricting, pushing blood into either the Pulmonary artery or the Aorta. The physical sound comes from the valves between those regions shutting and opening as blood gushes through them.
Link to Practice Questions: https://cardiovascularhealth.netlify.app/
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