Section 48.4 (Exam 4) Blood

Question 1

What is blood?

Answer 1

connective tissue—cells in an extracellular fluid matrix, the blood plasma

Question 2

What is hematocrit?

Answer 2

Hematocrit is the percent of blood that is red blood cells (RBCs)

Question 3

What is the normal human hematocrit range?

Answer 3

Normal hematocrit is 42–46%; higher in people who live at high altitudes

Low O2 levels stimulate production of more RBCs

Question 4

What are the scientific names for red blood cells (RBCs) and white blood cells (WBCs)?

Answer 4

Erythrocytes (RBCs)

Leukocytes (WBCs)

Question 5

What are the three cellular components of blood and what are their functions?

Answer 5

Erythrocytes (RBCs) are used to transport oxygen and carbon dioxide

Leukocytes (WBCs) are used to destroy foreign cells, produce antibodies, and play roles in the allergic response

Platelets are used for blood clotting

Question 6

What are some features of mature erythrocytes (RBCs)?

Answer 6

Biconcave for a larger surface area

Flexible so they can squeeze through narrow capillaries

Packed with hemoglobin so they can transport many gases

Lack nuclei so they can carry more hemoglobin

Question 7

What are some features that arteries have and veins do not?

Answer 7

Thicker walls with more elastic fiber (elastin) due to higher pressure

Thicker smooth muscles in order to constrict or dilate the vessels for thermoregulation

Question 8

What is one feature that veins have that arteries do not?

Answer 8

One-way valves to prevent backflow that can occur due to low pressure

Question 9

Where do capillary beds lie?

Answer 9

Between arterioles and venules

Question 10

Describe capillary walls.

Answer 10

Thin, only a single layer of endothelial cells

Permeable to water, ions, and small molecules (not large proteins and RBCs)

Question 11

What happens to the pressure of the arterial blood once it reaches the capillaries?

Answer 11

When it reaches the capillaries, pressure and flow rate drop, allowing time for exchange of materials

Question 12

Why is the total cross-sectional area of the capillaries greater than that of any other class of blood vessel?

Answer 12

Greater surface area means more efficient exchange of materials

Question 13

What are Starling’s forces?

Answer 13

Opposing forces that maintain water balance in the capillaries:

Blood pressure—forces water and small solutes out

Osmotic pressure—pulls water back into the capillaries

Question 14

While blood pressure is actual pressure from the heart, osmotic pressure is not. What causes osmotic pressure to pull water back into the capillaries?

Answer 14

Osmotic pressure is caused by the difference in the concentration of solutes (like blood proteins) inside and outside the blood vessels

Water moves toward the area with a higher concentration of solutes (back into the capillary) to balance things out

Question 15

What happens if blood pressure is greater than osmotic pressure? What about the opposite case?

Answer 15

Where blood pressure is higher than osmotic pressure, fluid leaves the capillary; where blood pressure is lower, fluid returns to the capillary

Question 16

Where is blood pressure higher and osmotic pressure higher?

Answer 16

Blood pressure is higher at the arterial end of the capillary bed and drops at the venous end

Osmotic pressure is lower and the arterial end and increases at the venous end

Question 17

What are fenestrations?

Answer 17

Small holes in the endothelial cells that make up the capillary wall

Water and small solutes like oxygen, carbon dioxide, and small ions can pass through these fenestrations or through small gaps between the endothelial cells that make up the capillary wall

Question 18

Why are veins considered capacitance vessels?

Answer 18

Veins are capacitance vessels due to their capacity to stretch and store blood

Their walls are expandable and blood can accumulate

Question 19

Blood pressure in veins is low. How does blood in the veins return to the heart?

Answer 19

Blood returning from the upper body is assisted by gravity

Blood returning from below the heart is assisted by skeletal muscle contractions that squeeze the veins

One-way valves in the veins prevent backflow