Med-Surg Cardiovascular System, part 3: Hematologic System - Blood Components and Hemostasis

by Cathy Parkes September 01, 2021 Updated: March 20, 2022 5 min read

In this article, we explain the components of blood and how blood clotting works.

The Med-Surg Nursing video series follows along with our Medical-Surgical Nursing Flashcards, which are intended to help RN and PN nursing students study for nursing school exams, including the ATI, HESI, and NCLEX.

Blood components

Blood in the human body comprises plasma and formed elements, including red blood cells, white blood cells, and platelets. 

Plasma 

Plasma in blood contains water, ions, protein (albumin, globulin, fibrinogen, clotting factors), nutrients, wastes, and gasses.

Formed Elements

The formed elements in blood are red blood cells, white blood cells, and platelets. 

Red blood cells (erythrocytes) 

The body's red blood cells, or erythrocytes carry oxygen and remove carbon dioxide. This is also covered in our Respiratory overview.

White blood cells (leukocytes) 

The body's white blood cells, or leukocytes, are part of the body’s immune system, and their purpose is to detect and fight off pathogens.

Platelets (thrombocytes) 

Platelets in blood are instrumental in the blood clotting process. Thromboycytopenia is a condition wherein the blood doesn't have enough platelets which can put a patient at a high risk for bleeding. We'll cover the blood clotting process next!

Hemostasis

Hemostasis means blood clotting. In your med-surg classes, you'll need to be aware of both primary and secondary hemostasis. 

Primary Hemostasis 

The process of primary hemostasis begins when vascular injury causes vasoconstriction, platelet aggregation and formation of a platelet plug. This then triggers secondary hemostasis.

Secondary Hemostasis 

During secondary hemostasis, clotting factors 1-13 activate each other in a clotting cascade. As Cathy explains in the video, you may have to know all thirteen of these factors in a physiology class, but you may not need to in nursing school. Check with your program.

Within secondary hemostasis, there is the intrinsic pathway, extrinsic pathway, and a common pathway.

Intrinsic pathway 

The intrinsic pathway in secondary hemostasis is the activation of clotting factors inside the blood in response to blood vessel damage. The intrinsic pathway is measured as activated partial thromboplastin time (aPTT).

Extrinsic pathway 

The extrinsic pathway in secondary hemostasis is the activation of clotting factors outside the blood, in response to trauma to extravascular cells. The extrinsic pathway is measured as prothrombin time (PT).

Common pathway 

The common pathway in secondary hemostasis is when the Intrinsic and extrinsic pathways merge together.. Prothrombin is activated into thrombin, which activates fibrinogen into fibrin (clot).

The key takeaway from this information is that hemostasis involves platelets as well as clotting factors. So when we explore coagulation disorders later in this series, you'll see that some of those coagulation disorders are caused by a lack of platelets, and other coagulation disorders are caused by a lack of clotting factors.


Full Transcript

Hi, I am Cathy, with Level Up RN. In this video, we are going to continue our anatomy and physiology review of the cardiovascular system, focusing now on the hematologic system. So if you're following along with cards, definitely pull those out. We're going to talk about the components of the blood, and we're also going to talk about the steps involved in hemostasis. At the end of the video, I will be giving you guys a little quiz to test your knowledge of some of the concepts I'll be covering in this video. So definitely, stay tuned for that. Here's an illustration from our medical surgical nursing flashcard deck, and you could see that our blood is made up of plasma as well as formed elements. So within the plasma, plasma is comprised of water, ions, proteins such as albumin, globulin, fibrinogen and clotting factors. Nutrients are also contained within the plasma as well as waste and gases. Over here, we have our formed elements. So first of all, we have our red blood cells, which are erythrocytes. These are instrumental in carrying oxygen and removing carbon dioxide from the body. Our white blood cells are leukocytes, are part of the body's immune system and help to detect and fight off pathogens. And then lastly, we have our platelets, which are thrombocytes, and they are instrumental in the blood clotting process, which we are going to talk about next.

Now let's talk about the steps involved in hemostasis or blood clotting. So we have primary hemostasis and secondary hemostasis. With primary hemostasis, we have injury to a blood vessel. This triggers basal constriction, platelet aggregation, and the formation of a platelet plug. And formation of that plug then triggers secondary hemostasis. So during secondary hemostasis, we have all of these clotting factors. So clotting factors 1, 2, 3, all the way up to 13, and they activate each other in a very complicated clotting cascade. So when I was in physiology, I'm pretty sure I had to know a lot of the details of that cascade. But in nursing school, they did not expect me or anyone in my class to know that level of detail. So hopefully, you don't have to know that level of detail either. So within secondary hemostasis, we have the intrinsic pathway, extrinsic pathway, and a common pathway. So with the intrinsic pathway, we have activation of clotting factors inside the blood in response to blood vessel damage. And we measure this intrinsic pathway through activated partial thromboplastin time, so APTT.

Then we have our extrinsic pathway. This is where we have activation of clotting factors outside the blood in response to trauma to extravascular cells, so cells outside the blood. And we can measure the extrinsic pathway through prothrombin time, so PT. And then the intrinsic pathway and extrinsic pathway will come together into a common pathway. And during that time prothrombin is activated into thrombin, and this activates fibrinogen into fibrin, which is a clot. The key takeaway from this information is that hemostasis involves platelets as well as clotting factors. So when we talk about coagulation disorders later in this playlist, you'll see that some of those coagulation disorders are caused by a lack of platelets, and other coagulation disorders are caused by a lack of clotting factors. All right. You guys ready for your quiz? Question number one, what are the formed elements in the blood? The answer is red blood cells, white blood cells, and platelets. Question number two, where in the blood do you find clotting factors? If you said the plasma, you're correct. Question number three is a true/false question. Formation of a platelet plug occurs during primary hemostasis. The answer is true. Okay. I hope this video has been helpful. In my next video, we will start talking more about diagnostic tests related to the cardiovascular system. So definitely stay tuned for that.


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