Components Common to Blood and Tissue Fluid

Steps:

• Blood contains dissolved CO2, circulating fatty acids, white blood cells, and plasma proteins.
• Tissue fluid, an ultrafiltrate of blood plasma, includes dissolved gases like CO2, nutrients such as fatty acids, and small amounts of proteins, but excludes cellular elements.
• Compare presence: CO2 diffuses freely into tissue fluid; fatty acids transport via blood and enter interstitial spaces; proteins leak slightly from capillaries; white blood cells remain in vessels unless migrating.
• Identify matching option: 1 (CO2), 2 (fatty acids), and 4 (proteins) are in both.

Why A is correct:

• Tissue fluid derives from blood plasma, retaining soluble components like CO2, fatty acids, and proteins per Starling's forces on capillary exchange.

Why the others are wrong:

• B: Includes white blood cells, absent from tissue fluid as it's acellular.
• C: Omits fatty acids and proteins, both present in tissue fluid for nutrient and osmotic roles.
• D: Includes white blood cells and excludes CO2 and fatty acids, key dissolved solutes in both.

Final answer: A