The Composition and Function of Blood

Summary

This video script delves into the intricate nature of blood, a critical connective tissue in the human body. It discusses the composition of blood, including plasma, red and white blood cells, and platelets, and their roles in transporting oxygen, nutrients, and waste, as well as regulating body temperature and preventing infections. The script also touches on blood types and the importance of ABO and Rh factors in transfusions.

Takeaways

• 🩸 Blood is a connective tissue and the only fluid tissue in the body, composed of blood cells suspended in plasma.
• 🧬 Blood cells include erythrocytes (red blood cells), leukocytes (white blood cells), and platelets, each with specific functions for the body.
• 🌀 Blood's primary roles are to distribute oxygen, nutrients, and hormones, while also removing waste products like carbon dioxide.
• 🧬 Plasma is the liquid component of blood, rich in water, proteins, nutrients, ions, gases, and hormones, with albumin being the most abundant protein.
• 🔴 Erythrocytes are numerous and lack a nucleus, containing hemoglobin which binds and transports oxygen throughout the body.
• 🔬 Hemoglobin is a protein with iron that can reversibly bind to oxygen, with each red blood cell capable of transporting a billion oxygen molecules.
• 🌱 Hematopoietic stem cells in the bone marrow produce new red blood cells daily through a process called erythropoiesis.
• 🛡️ Leukocytes, part of the immune system, defend against pathogens with different types having specific roles, such as neutrophils killing bacteria and lymphocytes fighting viruses.
• 🩲 Platelets, derived from megakaryocytes, are crucial for blood clotting and the hemostasis process, plugging holes in damaged blood vessels.
• 🔄 The body maintains a constant number of blood cells, with old red blood cells being destroyed by macrophages and replaced by new ones.
• 🔄 Blood types (A, B, AB, O) and Rh factors are important for transfusions, with AB being the universal recipient and O the universal donor.

Q & A

What is the primary function of blood in the human body?

Blood's primary function is to distribute various substances around the body, including oxygen, nutrients, and hormones, and to remove waste products like carbon dioxide. It also helps regulate pH, maintain body temperature, and prevent infection.

How is blood classified in terms of body tissues?

Blood is technically considered a connective tissue and is the only fluid tissue in the body, containing fibrous proteins.

What are the main components of blood?

Blood is composed of formed elements, which include blood cells, suspended in a fluid called plasma. The formed elements consist of erythrocytes (red blood cells), leukocytes (white blood cells), and platelets.

What is plasma and what does it contain?

Plasma is a sticky fluid that is mostly water but also contains proteins, nutrients, ions, gases, and hormones. The most abundant plasma protein is albumin, followed by various globulins.

How does hemoglobin facilitate the transport of oxygen in the bloodstream?

Hemoglobin, contained within red blood cells, is a protein that can bind to oxygen molecules in a reversible fashion, allowing it to pick up oxygen in the lungs and release it to tissue cells throughout the body.

What is the structure of hemoglobin and how does it bind to oxygen?

Hemoglobin is made of a protein called globin, consisting of four polypeptides with two identical alpha chains and two identical beta chains, each bound to a heme group with iron at the center. The iron can bind to an oxygen molecule, allowing each hemoglobin molecule to bind four oxygen molecules.

How are red blood cells produced and what is their lifespan?

Red blood cells are produced through a process called erythropoiesis in the red bone marrow. They function properly for about three months before being destroyed by macrophages.

What is the role of white blood cells in the immune system?

White blood cells, or leukocytes, are part of the immune system and help defend against pathogens and harmful substances. They circulate in the blood and can also move into other connective tissues to perform their functions.

What are the two types of white blood cells and their functions?

There are granulocytes, which include neutrophils, eosinophils, and basophils, and agranulocytes, which include lymphocytes and monocytes. Granulocytes are involved in killing bacteria and parasites, while agranulocytes fight viruses, tumors, and produce antibodies or become macrophages to engulf intruders.

What is the importance of platelets in the blood clotting process?

Platelets are essential for blood clotting and hemostasis. When blood vessels are damaged, platelets plug the holes or tears to seal them off, preventing further blood loss.

What is the significance of blood types in blood transfusions?

Blood types, such as A, B, AB, and O, are determined by the presence of specific glycoproteins and glycolipids on red blood cells. These types are crucial for transfusions because incompatible blood types can cause a fatal immune response, leading to the destruction of the transfused blood cells.

What is the role of fibrin in the blood clotting process?

Fibrin plays a key role in the final stages of blood clotting by forming a mesh that strengthens the platelet plug and helps patch up the damaged vessel.

How is a blood clot removed after the healing of a blood vessel?

A blood clot is removed through a process called fibrinolysis, which ensures that there is no blockage in the vessel once the healing is complete.

Outlines

00:00

🩸 Blood: The Fluid of Life

Professor Dave introduces the topic of blood, emphasizing its critical role in human life. Blood is a connective tissue, the only fluid tissue in the body, composed of blood cells suspended in plasma. The script explains that blood carries oxygen, nutrients, and hormones, while also removing waste products and regulating body temperature and pH. The paragraph delves into the components of blood, including erythrocytes (red blood cells), the buffy coat with platelets and leukocytes (white blood cells), and plasma, highlighting the function of hemoglobin in oxygen transport.

05:04

🛡️ Immunity and Hemostasis: The Protective Roles of Blood Cells

This paragraph focuses on the immune function of leukocytes, which are complete cells with nuclei and organelles, and their role in defending against pathogens. It differentiates between granulocytes, which include neutrophils, eosinophils, and basophils, and agranulocytes, which include lymphocytes and monocytes. The paragraph also discusses platelets, their origin from megakaryocytes, and their importance in blood clotting and hemostasis. The process of blood cell production through hematopoiesis and the significance of blood types in transfusions are also covered, concluding with an introduction to the circulatory system.

Keywords

💡Blood

Blood is a vital fluid in the human body that is responsible for transporting oxygen, nutrients, hormones, and waste products. It is technically a connective tissue and the only fluid tissue in the body. The video script emphasizes the importance of blood in maintaining life by highlighting its role in the circulatory system. For example, blood is described as being 'critical for human life' and is responsible for 'distributing various substances around the body.'

💡Circulatory System

The circulatory system is the network of organs and vessels that continuously pump blood throughout the body. It is central to the video's discussion on how blood functions and is maintained. The script mentions that the circulatory system's function is to 'continuously pump blood around the body,' which is essential for delivering oxygen and nutrients and removing waste products.

💡Plasma

Plasma is the liquid component of blood that contains water, proteins, nutrients, ions, gases, and hormones. It is described in the script as a 'sticky fluid' that is mostly water but also carries essential substances. Plasma plays a crucial role in maintaining osmotic pressure and transporting various molecules, as highlighted when the script discusses the 'abundant plasma protein called albumin'.

💡Erythrocytes

Erythrocytes, or red blood cells, are the most numerous cells in the bloodstream and are responsible for carrying oxygen. The script describes them as 'flattened discs with depressed centers' that contain hemoglobin, which binds to oxygen molecules. Their shape and function are critical for efficient oxygen transport, as noted when the script explains that 'each hemoglobin can bind four oxygen molecules.'

💡Hemoglobin

Hemoglobin is a protein in red blood cells that binds to oxygen, allowing for its transport throughout the body. The script details the structure of hemoglobin, which is made of a protein called globin and contains iron that binds reversibly to oxygen. This is crucial for oxygen transport, as the script illustrates by stating that 'one red blood cell can transport one billion oxygen molecules.'

💡Leukocytes

Leukocytes, or white blood cells, are part of the immune system and help defend against pathogens. The script differentiates them into granulocytes and agranulocytes, which have distinct functions. Leukocytes are essential for immune response, as shown in the script when it mentions that 'these help us defend against pathogens and other harmful things.'

💡Platelets

Platelets are fragments of large cells called megakaryocytes and play a crucial role in blood clotting. The script explains that they are essential during hemostasis, which is the process of stopping bleeding. Platelets plug holes in damaged blood vessels, as described in the script: 'platelets can plug up any holes or tears to seal things off.'

💡Hematopoiesis

Hematopoiesis is the process by which blood cells are produced, occurring in the red bone marrow. The script mentions that this process is responsible for the constant production of new red blood cells, which are essential for maintaining a nearly constant number in the bloodstream. This is highlighted when the script states that 'billions of new red blood cells are made every day to maintain a nearly constant number.'

💡Blood Types

Blood types refer to the classification of human blood based on the presence of specific antigens on the surface of red blood cells. The script discusses ABO blood groups (A, B, AB, O) and Rh blood groups (positive or negative), which are crucial for blood transfusions. The importance of matching blood types is emphasized in the script: 'if someone’s body only recognizes A and gets blood with B, the new blood cells will be recognized by antibodies as foreign, and destroyed.'

💡Connective Tissue

Connective tissue is a category of tissue that serves various functions in the body, including support and connection. Blood is described in the script as a type of connective tissue, being the only fluid tissue in the body. This classification is significant as it highlights blood's role in binding and supporting other tissues, as well as its unique properties among body tissues.

💡Hemostasis

Hemostasis is the process by which the body stops bleeding, involving vascular spasm, platelet plug formation, and coagulation. The script explains that this process is crucial for preventing excessive blood loss when blood vessels are damaged. The script describes hemostasis as involving 'vascular spasm, platelet plug formation, and then coagulation, or blood clotting,' which is essential for maintaining blood vessel integrity.

Highlights

Blood is a familiar substance in the human body, but its exact nature and functions were not well-understood for a long time.

Blood is now recognized as a connective tissue and the only fluid tissue in the body, consisting of formed elements suspended in plasma.

Plasma, the liquid component of blood, is made mostly of water and contains proteins, nutrients, ions, gases, and hormones.

Erythrocytes or red blood cells are the densest formed element in blood and are responsible for transporting oxygen.

Red blood cells contain hemoglobin, a protein that binds oxygen and allows for its transport throughout the body.

Hemoglobin's structure consists of four polypeptides bound to heme groups with iron, enabling reversible oxygen binding.

Each red blood cell can transport one billion oxygen molecules due to the presence of numerous hemoglobin molecules.

Blood cells are produced through the process of hematopoiesis, occurring in the red bone marrow.

Leukocytes or white blood cells are part of the immune system, helping defend against pathogens and harmful substances.

There are two types of white blood cells: granulocytes, which have granules and perform various immune functions, and agranulocytes, which include lymphocytes and monocytes.

Platelets are fragments of megakaryocytes and play a crucial role in blood clotting and hemostasis.

Blood clotting involves platelet plugs, vascular spasm, and the formation of a fibrin mesh to seal off damaged vessels.

Blood types, such as A, B, AB, and O, are determined by the presence of specific glycoproteins and glycolipids on red blood cell membranes.

The Rh blood group, either positive or negative, is another important factor in blood transfusions and compatibility.

Understanding blood types is crucial for safe blood transfusions, as incompatible blood can lead to severe reactions.

The circulatory system is responsible for continuously pumping blood throughout the body, distributing substances and maintaining homeostasis.

Transcripts

Professor Dave here, let’s learn about blood.

Of all the substances within the human body, blood is one of the more familiar ones, as

we’ve all had an injury that involves bleeding.

For a long time it was not well-understood exactly what blood is, or what it does, we

just knew that if you lose enough of it, you die.

But we now have an intimate understanding of this fluid, as well as the circulatory

system whose function it is to continuously pump blood around the body.

We will get to this system in a moment, first let’s examine blood itself, what it’s

made of, and why it is so critical for human life.

First let’s mention that blood is technically considered a connective tissue, and as such

it is the only fluid tissue in the body, full of fibrous proteins.

It is comprised of formed elements, which are blood cells, suspended in a fluid called plasma.

If we place blood in a centrifuge, it will separate into its components.

The densest section is comprised of erythrocytes, or red blood cells, and the least dense section

will be the yellowish plasma.

They are separated by the buffy coat, a white layer containing platelets as well as leukocytes,

otherwise known as white blood cells.

As a whole, blood is responsible for distributing various substances around the body, most notably

oxygen, which we can’t survive very long without.

But it also carries nutrients absorbed from the digestive tract, and hormones secreted

by endocrine organs.

Blood also delivers waste products to the organs that will dispose of them, like the

carbon dioxide that we exhale.

Beyond this, blood serves to regulate pH in various tissues, maintain body temperature,

and prevent infection.

Let’s discuss each component of blood now, beginning with plasma.

This is a sticky fluid made mostly of water, but also containing a variety of proteins,

nutrients, ions, gases and hormones.

The most abundant plasma protein is called albumin, which contributes significantly to

plasma’s osmotic pressure, and this is followed by a variety of globulins, which bind to certain

molecules for transport.

Moving to the formed elements, these are erythrocytes, or red blood cells, leukocytes, or white blood

cells, and platelets.

Red blood cells and platelets are interesting in that they don’t possess all the typical

organelles and they don’t divide, they are replaced by stem cells in the bone marrow.

Red blood cells are very numerous in the bloodstream, and they are shaped like flattened discs with

depressed centers.

There is no nucleus, not much of anything inside other than lots of hemoglobin.

This is the protein that allows for the transport of oxygen throughout the bloodstream, which

is picked up in the lungs and then released for tissue cells throughout the body.

There are other proteins as well that have structural or protective functions, but hemoglobin

will be the focus here.

This is the structure of hemoglobin, it is made of a protein called globin, consisting

of four polypeptides, two identical alpha chains and two identical beta chains, each

of which is bound to a heme group with iron at the center.

The iron in this heme is able to bind to an oxygen molecule in reversible fashion, so

that it can bind and then release when necessary, so each hemoglobin can bind four oxygen molecules,

and there are around two hundred fifty million hemoglobins per red blood cell, so one red

blood cell can transport one billion oxygen molecules.

Blood cells are produced through a process called hematopoiesis, and this occurs in the

red bone marrow, which is a soft network of connective tissue found on certain blood capillaries,

and which contains hematopoietic stem cells.

For erythrocytes, this is more specifically called erythropoiesis, and billions of new

red blood cells are made every day to maintain a nearly constant number, given that red blood

cells function properly for only about three months, only to be destroyed by macrophages,

which are a phagocytic type of white blood cell.

Next let’s look at leukocytes, or white blood cells, which unlike the far more abundant

red blood cells, are complete cells with nuclei and organelles.

These are part of the immune system, which we will discuss in greater detail later, but

for now, we will just understand that these help us defend against pathogens and other

harmful things.

These use the circulatory system to get around the body, but they can also slip out into

other connective tissues to do their work.

There are two types of white blood cells, granulocytes and agranulocytes, which differ

in the presence or absence of granules.

The three types of granulocytes are neutrophils, which kill bacteria, eosinophils, which kill

parasitic worms, and basophils, which contain histamine that attracts other white blood

cells to a site of inflammation.

Agranulocytes, on the other hand, can be lymphocytes, which fight viruses and tumors, and also give

rise to plasma cells, which produce antibodies, which we will discuss later, or they can be

monocytes, which become macrophages that can eat up intruders.

Leukocytes are produced by leukopoiesis, which is stimulated by certain chemical messengers.

Lastly we get to the platelets.

These are fragments of large cells called megakaryocytes.

These fragments are essential during blood clotting, which happens when blood vessels

are damaged, as platelets can plug up any holes or tears to seal things off.

They flow through the bloodstream in an inactive state unless needed, dying every ten days

or so and constantly regenerated.

Megakaryocytes form due to repeated mitotic cycles that do not perform cytokinesis, so

the result is one huge cell with a multilobed nucleus.

This then presses against a sinusoid, and its extensions burst to release the platelets.

These platelets are important during hemostasis, which is the process by which the body will

stop bleeding through vascular spasm, platelet plug formation, and then coagulation, or blood clotting.

This essentially means that where there is damage to a vessel, smooth muscle will contract,

platelets will plug the tear, and a protein called fibrin will form a mesh to patch everything up.

Once the vessel has healed, the clot is removed through a process called fibrinolysis, so

that there is no blockage in the vessel.

So those are the components of blood.

We can look at a diagram like this one to see how these arise during hematopoiesis.

We can also briefly mention the different blood types that humans can exhibit.

These are A, B, AB, and O.

These have to do with glycoproteins and glycolipids found in the plasma membranes of red blood cells.

A and B refer to two different agglutinogens that can be found in these membranes, so blood

group A has one of them, B has the other, AB has both, and O has neither.

This is important for blood transfusions, because if someone’s body only recognizes

A and gets blood with B, the new blood cells will be recognized by antibodies as foreign

and destroyed, which can be fatal, so someone with AB blood can receive any blood, since

both A and B will be recognized, hence they are universal recipients, and someone with

O blood can give blood to anyone, since there are no markers to be recognized, hence they

are universal donors.

There are also Rh blood groups which refer to agglutinogens called Rh factors, and for

these a person is either positive or negative.

This is reported along with the ABO blood group by tacking on positive or negative to

the end, giving us groups like O positive, A negative, and so on.

And with that, we are familiar enough with the structure and function of blood that we

can begin to examine the circulatory system as a whole, so let’s move forward and do just that.