Blood composition and functions

Blood is a connective tissue: cells scattered in an extracellular matrix. In blood the matrix is a fluid, the plasma.

• Epithelial tissue:
• Correct: Connective tissue:
• Muscle tissue:

Red bone marrow, in the flat bones and the ends of some long bones, is where hematopoiesis happens in adults. Yellow marrow is mostly fat.

• Correct: In the red bone marrow:
• In the yellow bone marrow:
• In the compact bone of the shaft:

Normal arterial blood pH is 7.35–7.45, slightly alkaline. Buffers hold it in this narrow range.

• 6.8 to 7.0:
• 7.0 to 7.2:
• Correct: 7.35 to 7.45:

Albumin makes up about 55–60% of plasma protein. It is made by the liver.

• Fibrinogen: Fibrinogen is the smallest of the three main groups, about 4–7% of plasma protein.
• Correct: Albumin: Correct. Albumin is more than half of all plasma protein.
• Gamma globulin: Gamma globulins are one part of the globulins, which together make up about 35–38%.
• Beta globulin: Beta globulins are another part of the globulins, and they are far less abundant than albumin.

Hematocrit = red column ÷ whole column × 100% = 20 ÷ 50 × 100% = 40%.

• 20%: 20 is the height of the red column in millimeters, not a percentage of the whole.
• 30%: 30 is the height of the plasma layer (50 − 20), not a percentage.
• Correct: 40%: Correct. 20 ÷ 50 = 0.40, which is 40%.
• 60%: 60% is the share of plasma (30 ÷ 50). The hematocrit is the share of red cells.

Losing plasma water leaves the cells and proteins in a smaller volume. Every concentration and ratio that has red cells or proteins on top rises, including the hematocrit, even though the body has not made a single extra red blood cell.

• Plasma volume: down. Sweat is made from water drawn out of the plasma, so plasma volume shrinks.
• Red blood cell volume: no change. No red cells leave the body in sweat, and new ones take days to make, so the red cell volume is unchanged.
• Hematocrit: up. The same red cell volume now sits in a smaller total blood volume, so red cells are a larger fraction of it.
• Plasma protein concentration: up. The proteins stay in the blood while water leaves, so the same amount of protein is dissolved in less water.
• Blood viscosity: up. Viscosity depends mostly on the hematocrit, which has risen, so the blood is thicker.

The first tube gives serum; the second gives plasma. Serum is plasma without its clotting proteins, because they were used up building the clot. Fibrinogen is the main one.

• Albumin: Albumin does not take part in clotting, so it is present in both serum and plasma.
• Alpha globulin: Alpha globulins are transport proteins, and they stay in serum.
• Correct: Fibrinogen: Correct. Fibrinogen is turned into the threads of the clot, so serum has none.
• Gamma globulin: Gamma globulins are immune proteins. They remain in serum, which is why many immune tests use serum.

Hematocrit is red cell volume divided by total blood volume. Dehydration had shrunk her plasma, raising the ratio. The drip restored plasma volume, so the same red cells became a smaller share of a larger total.

• Her marrow slowed red blood cell production overnight: Red blood cells circulate for about 120 days, so slowing production for a few hours would barely change their number.
• The salt solution destroyed some of her red blood cells: A salt solution given in the right concentration does not burst red blood cells. Her red cell volume is unchanged.
• Correct: Her plasma volume rose, diluting her red cells: Correct. The denominator of the ratio grew; the numerator stayed the same.
• Her kidneys removed the extra red blood cells: The kidneys filter plasma, not whole cells. They do not remove red blood cells from the blood.

Colony-stimulating factors drive marrow precursors to make white blood cells. Given as a drug after chemotherapy, one speeds the recovery of the white cell count.

• Erythropoietin, from the kidneys: Erythropoietin speeds red blood cell production, not white.
• Thrombopoietin: Thrombopoietin drives megakaryocytes and platelet production.
• Albumin: Albumin is a plasma protein that holds water in the blood. It is not a growth factor.
• Correct: A colony-stimulating factor: Correct. Colony-stimulating factors steer marrow cells toward white blood cells.

Blood is always red. Red blood cells full of oxygen make it bright scarlet; with less oxygen it is dark red. Veins look blue through skin because skin scatters and absorbs red and blue light differently, not because the blood is blue.

• She is right: venous blood is blue and turns red on contact with air: Blood drawn into a sealed tube, never meeting air, is still dark red. It is not blue inside the body.
• Correct: It is dark red; veins look blue because of how skin handles light: Correct. The color of a vein seen through skin is an effect of light in the skin.
• Venous blood is purple because it carries carbon dioxide: Carbon dioxide does not turn blood purple. Blood with less oxygen is darker red.
• Venous blood is blue in the limbs and red in the core: Blood in the limbs and the core is the same color for the same oxygen content. Blood is never blue.