12.1 Introduction to Blood

12.1 Introduction to Blood

by Nikki Chenevert

​12.1 Introduction

Blood signifies life, and for good reason—it has many vital functions. This complex mixture of cells, cell fragments, and dissolved biochemicals transports nutrients, oxygen, wastes, and hormones; helps maintain the stability of the interstitial fluid; and distributes heat. The blood, heart, and blood vessels form the cardiovascular system and link the body’s internal and external environments.

Multiple Choice

What does blood transport?

• Nutrients
• Oxygen 
• Carbon Dioxide
• All of the above

Multiple Choice

Which of the following is not a function of blood?

• help fight disease
• transports nutrients, oxygen, wastes, and hormones
• to distribute neorotransmitters
• distributes heat

Multiple Choice

What is the main function of the circulatory system?

• Provides oxygen to the body's cells, while moving carbon dioxide
• Responsible for control of the body and communication among body parts
• Transports materials throughout body via the blood (oxygen, carbon dioxide, nutrients, wastes)
• Breaks down food, allows for nutrient absorption into blood, and eliminates indigestible material

​Blood is a type of connective tissue whose cells are suspended in a liquid extracellular matrix.

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Blood is vital in transporting substances between body cells and the external environment, thereby promoting homeostasis.

​Whole blood is slightly heavier and three to four times more viscous than water. Its cells, which form mostly in red bone marrow, include red blood cells that transport gases and white blood cells that fight disease. Blood also contains cellular fragments called blood platelets that help control blood loss. Together, the cells and platelets are termed “formed elements” of the blood, in contrast to the liquid portion called plasma (plaz′mah).

Multiple Choice

I am the 'liquid' portion of blood.

• Erythrocytes
• Thrombocytes
• Leukocytes
• Plasma

​Blood consists of a liquid portion called plasma and a solid portion (the formed elements) that includes red blood cells, white blood cells, and platelets.

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(Note: When blood components are separated by centrifugation, the white blood cells and platelets form a thin layer, called the “buffy coat,” between the plasma and the red blood cells, which accounts for about 1% of the total blood volume.)

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Blood cells and platelets can be seen under a light microscope when a blood sample is smeared onto a glass slide.

​A blood sample is usually about 45% red blood cells by volume. This percentage is called the hematocrit (HCT). The white blood cells and platelets account for less than 1%.

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The remaining blood sample, about 55%, is the plasma, a clear, straw-colored liquid. Plasma is a complex mixture of water, amino acids, proteins, carbohydrates, lipids, vitamins, hormones, electrolytes, and cellular wastes (fig. 12.1).

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​90% of plasma is made of water.

Multiple Choice

What percentage of plasma is made up of water?

• 98-100%

• 90-92%

• 43-45%

• 53-55%

​Men have more blood than women. Men have 5–6 liters (1.500 gallons), compared to 4–5 liters (0.875 gallons) for women.

Multiple Choice

The blood volume in an average adult is approximately

• 1-2 liters

• 2-4 liters

• 4-6 liters

• 6-8 liters

​Check Your Recall page 319

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1. What are the major components of blood?

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2. What factors affect blood volume?