Anatomy and Physiology I
Subtopic:
Blood and its Composition
Learning Objectives
- Define blood and describe its overall role in the human body.
- List the components of blood, including plasma, red blood cells (RBCs), white blood cells (WBCs), and platelets.
- Explain the functions of each blood component, such as oxygen transport, immune response, and clotting.
- Describe the physical and chemical properties of blood, including its pH, viscosity, and volume.
- Understand the importance of blood in homeostasis, such as regulation of temperature, pH, and fluid balance.
- Outline basic principles of blood typing, antigens, and compatibility.
Blood
Blood serves as a fluid form of connective tissue within the body. Its continuous movement throughout the organism enables ongoing communication between tissues regardless of their spatial separation.
Its roles involve:
oxygen from the lungs to the tissues, and carbon dioxide from the tissues to the lungs for excretion
nutrients from the alimentary tract to the tissues, and cell wastes to the excretory
hormones secreted by endocrine glands to their target glands and tissues,
heat produced in active tissues to other less active tissues,
protective substances, e.g. antibodies, to areas of infection clotting factors that coagulate blood, minimizing bleeding from ruptured blood vessels
Components of Blood
- Blood is made up of a clear, yellowish fluid termed plasma, where various types of blood cells are suspended.
- Plasma typically makes up 55% of the total volume of blood.
- The remaining 45% consists of the cellular components of blood.
- These two primary fractions, the blood cells and the plasma, can be separated through a process of spinning at high speeds (centrifugation) or by simply allowing a blood sample to rest. Due to their greater density, the blood cells will settle to the bottom of the sample.
In terms of body weight, blood accounts for roughly 7% – about 5.6 liters in an average 70 kg male. This proportion tends to be lower in females and notably higher in children, gradually decreasing until adulthood. The heart’s pumping action keeps blood in constant motion within blood vessels, ensuring a relatively stable internal environment for the body’s cells. Homeostatic mechanisms work to maintain blood volume and the concentrations of its numerous components within a narrow range.
Plasma
Plasma is primarily composed of water (between 90% and 92%) along with various dissolved and suspended substances, including:
Plasma Proteins
Constituting approximately 7% of the plasma, plasma proteins are generally confined within the bloodstream due to their large size, which prevents them from easily passing through the capillary walls into the tissues. They play a crucial role in establishing the osmotic pressure of the blood, which helps retain fluid within the circulatory system. If plasma protein levels decrease (due to reduced production or loss from blood vessels), osmotic pressure diminishes, causing fluid to move into the tissues (resulting in edema) and body cavities.
The thickness or viscosity of plasma is largely attributed to plasma proteins, particularly albumin and fibrinogen. With the exception of immunoglobulins, plasma proteins are synthesized in the liver.
Albumins
As the most abundant plasma proteins (making up about 60% of the total), their principal function is to uphold normal plasma osmotic pressure. Albumins also serve as transport molecules for unbound fatty acids, certain medications, and steroid hormones.
Globulins
Their primary functions include:
Antibodies (Immunoglobulins): These are complex proteins produced by lymphocytes that play an important part in immunity. They bind to and neutralize foreign materials (antigens) such as microorganisms.
Transportation: Globulins transport some hormones and mineral salts. For example, thyroglobulin carries the hormone thyroxine, and transferrin carries the mineral iron.
Inhibition of Proteolytic Enzymes: Some globulins inhibit proteolytic enzymes. For example, α2 macroglobulin inhibits trypsin activity.
Clotting Factors
These proteins are essential for the process of blood coagulation. Serum is essentially plasma from which the clotting factors have been removed. Fibrinogen is the most abundant clotting factor.
Electrolytes
These ions perform a variety of functions, including:The blood’s pH is maintained within a slightly alkaline range, specifically between 7.35 and 7.45, through a complex and ongoing series of chemical reactions involving buffering systems.
Nutrients
Digestion products, such as glucose, amino acids, fatty acids, and glycerol, are absorbed from the digestive tract.
Along with mineral salts and vitamins, these are utilized by body cells for:
Waste Products
Urea, creatinine, and uric acid are the byproducts of protein metabolism. They are produced in the liver and transported in the blood to the kidneys for excretion.
Hormones
These chemical messengers are synthesized by endocrine glands.
Hormones travel directly from the endocrine cells into the bloodstream, which carries them to their specific target tissues and organs throughout the body, where they exert their effects on cellular activity.
Gases
Oxygen, carbon dioxide, and nitrogen are transported throughout the body while dissolved in the plasma. Oxygen and carbon dioxide are also carried in combination with hemoglobin within red blood cells.
The majority of oxygen is transported bound to hemoglobin, and most carbon dioxide is carried as bicarbonate ions dissolved in the plasma. Nitrogen from the atmosphere enters the body in the same manner as other gases and is present in the plasma but has no known physiological role.
Cellular Components of Blood
There are three main categories of blood cells:
Red Blood Cells (Erythrocytes)
White Blood Cells (Leukocytes)
Platelets (Thrombocytes)
Blood cells are primarily produced in the red bone marrow. Some lymphocytes are also produced in lymphoid tissues.
Within the bone marrow, all blood cells originate from pluripotent stem cells (meaning they have the capacity to develop into various cell types) and undergo a series of developmental stages before entering the bloodstream. Different types of blood cells follow distinct developmental pathways. The process of blood cell formation is known as hemopoiesis.
image here depicting the stages of blood cell development
Red Blood Cells
Red blood cells, also known as erythrocytes, are shaped like biconcave discs, lack a nucleus, and have a diameter of approximately 7.5 micrometers.
Their primary role is the transport of gases, mainly oxygen, but they also carry some carbon dioxide. Their unique biconcave shape is well-suited for their function, as it increases the surface area available for gas exchange, and the thin central region facilitates rapid entry and exit of gases. These cells are flexible, allowing them to navigate through narrow capillaries, and lack internal organelles to maximize space for hemoglobin, the major pigment responsible for gas transport
Lifespan and Function of Erythrocytes
Erythrocytes are produced in the red bone marrow, which is located at the ends of long bones and within flat and irregular bones. They progress through several developmental stages before entering circulation. Their lifespan within the bloodstream is approximately 120 days. The development of red blood cells from stem cells takes about 7 days, a process called erythropoiesis. Immature red blood cells, called reticulocytes, are released into the circulation and mature into erythrocytes within a day or two. During this maturation process, they lose their nucleus and thus lose the ability to divide.
Both vitamin B12 and folic acid are necessary for the synthesis of red blood cells. They are absorbed in the intestines, although the absorption of vitamin B12 requires binding to intrinsic factor. Both of these vitamins are found in dairy products, meat, and green vegetables. The liver typically stores a supply of vitamin B12 that can last for several years, but signs of folic acid deficiency can appear within a few months.
Hemoglobin
Hemoglobin is a large, complex protein composed of a globular protein component (globin) and an iron-containing pigment complex called heme.
Each hemoglobin molecule contains four globin chains and four heme units, with each heme unit containing one atom of iron. Since each iron atom can bind with one oxygen molecule, a single hemoglobin molecule can transport up to four oxygen molecules. An average red blood cell contains roughly 280 million hemoglobin molecules, giving each cell a theoretical capacity to carry over a billion oxygen molecules.
Iron is transported in the bloodstream bound to the protein transferrin and is stored in the liver. Normal red blood cell production requires a continuous supply of iron. The absorption of iron from the digestive tract is a slow process, even with an iron-rich diet, meaning that iron deficiency can easily occur if losses exceed intake.
Questions on Blood and its Composition
What is the primary function of blood in the body?
a) Transport oxygen and nutrients
b) Store energy
c) Produce hormones
d) Regulate body temperature
Answer: a) Transport oxygen and nutrients
Rationale: Blood serves as a fluid form of connective tissue that transports oxygen, nutrients, and other substances throughout the body.
True or False: Plasma makes up 55% of the total volume of blood.
Answer: True
Rationale: Plasma typically makes up 55% of the total volume of blood, with the remaining 45% consisting of cellular components.
What is the main component of plasma?
a) Proteins
b) Water
c) Electrolytes
d) Hormones
Answer: b) Water
Rationale: Plasma is primarily composed of water (between 90% and 92%), along with various dissolved and suspended substances.
Which plasma protein is the most abundant?
a) Globulins
b) Fibrinogen
c) Albumins
d) Clotting factors
Answer: c) Albumins
Rationale: Albumins are the most abundant plasma proteins, making up about 60% of the total plasma proteins.
True or False: Plasma proteins play a crucial role in establishing the osmotic pressure of the blood.
Answer: True
Rationale: Plasma proteins help establish the osmotic pressure of the blood, which helps retain fluid within the circulatory system.
What is the primary function of red blood cells (erythrocytes)?
a) Fight infections
b) Transport gases
c) Produce antibodies
d) Clot blood
Answer: b) Transport gases
Rationale: Red blood cells (erythrocytes) primarily transport gases, mainly oxygen, and some carbon dioxide.
Which component of blood is responsible for clotting?
a) Red blood cells
b) White blood cells
c) Platelets
d) Plasma
Answer: c) Platelets
Rationale: Platelets (thrombocytes) are responsible for blood clotting, helping to minimize bleeding from ruptured blood vessels.
True or False: Hemoglobin is a protein found in red blood cells that binds to oxygen.
Answer: True
Rationale: Hemoglobin is a large, complex protein in red blood cells that binds to oxygen, allowing for its transport throughout the body.
What is the lifespan of a red blood cell?
a) 30 days
b) 60 days
c) 90 days
d) 120 days
Answer: d) 120 days
Rationale: The lifespan of a red blood cell is approximately 120 days.
Which vitamins are necessary for the synthesis of red blood cells?
a) Vitamin C and Vitamin D
b) Vitamin A and Vitamin E
c) Vitamin B12 and Folic Acid
d) Vitamin K and Vitamin B6
Answer: c) Vitamin B12 and Folic Acid
Rationale: Both Vitamin B12 and Folic Acid are necessary for the synthesis of red blood cells.
True or False: White blood cells (leukocytes) are primarily involved in the immune response.
Answer: True
Rationale: White blood cells (leukocytes) are primarily involved in the immune response, helping to fight infections and protect the body.
What is the primary function of plasma proteins?
a) Transport oxygen
b) Establish osmotic pressure
c) Produce hormones
d) Store energy
Answer: b) Establish osmotic pressure
Rationale: Plasma proteins play a crucial role in establishing the osmotic pressure of the blood, helping to retain fluid within the circulatory system.
Which component of blood is responsible for carrying hormones to target tissues?
a) Red blood cells
b) White blood cells
c) Platelets
d) Plasma
Answer: d) Plasma
Rationale: Plasma carries hormones synthesized by endocrine glands to their specific target tissues and organs throughout the body.
True or False: Electrolytes in the blood help maintain the body’s pH within a slightly alkaline range.
Answer: True
Rationale: Electrolytes in the blood help maintain the body’s pH within a slightly alkaline range, specifically between 7.35 and 7.45.
What is the primary function of white blood cells (leukocytes)?
a) Transport gases
b) Fight infections
c) Clot blood
d) Produce hormones
Answer: b) Fight infections
Rationale: White blood cells (leukocytes) are primarily involved in the immune response, helping to fight infections and protect the body.
Which component of blood is responsible for transporting nutrients from the digestive tract to the tissues?
a) Red blood cells
b) White blood cells
c) Platelets
d) Plasma
Answer: d) Plasma
Rationale: Plasma transports digestion products, such as glucose, amino acids, fatty acids, and glycerol, from the digestive tract to the tissues.
True or False: Hemopoiesis is the process of blood cell formation.
Answer: True
Rationale: Hemopoiesis is the process of blood cell formation, where blood cells originate from pluripotent stem cells in the red bone marrow.
What is the primary function of hemoglobin in red blood cells?
a) Produce energy
b) Bind to oxygen
c) Fight infections
d) Clot blood
Answer: b) Bind to oxygen
Rationale: Hemoglobin in red blood cells binds to oxygen, allowing for its transport throughout the body.
Which component of blood carries waste products to the kidneys for excretion?
a) Red blood cells
b) White blood cells
c) Platelets
d) Plasma
Answer: d) Plasma
Rationale: Plasma carries waste products, such as urea, creatinine, and uric acid, to the kidneys for excretion.
True or False: Nitrogen in the blood has no known physiological role.
Answer: True
Rationale
Join Our WhatsApp Groups!
Are you a nursing or midwifery student looking for a space to connect, ask questions, share notes, and learn from peers?
Join our WhatsApp discussion groups today!
Join Now
We are a supportive platform dedicated to empowering student nurses and midwives through quality educational resources, career guidance, and a vibrant community. Join us to connect, learn, and grow in your healthcare journey
Get in Touch
(+256) 790 036 252
(+256) 748 324 644
Info@nursesonlinediscussion.com
Kampala ,Uganda
© 2025 Nurses online discussion. All Rights Reserved Design & Developed by Opensigma.co