Which cell type is primarily responsible for the production of antibodies in the immune system?

A. Facilitating gas exchange:Gas exchange occurs in the respiratory system (alveoli), not the lymphatic system.
B. Returning excess fluid to the bloodstream:The lymphatic system collects interstitial fluid (lymph) and returns it to the venous circulation, preventing edema.
C. Digesting proteins:Protein digestion is performed by the gastrointestinal tract and its enzymes, not the lymphatic system.
D. Producing red blood cells:Hematopoiesis (red blood cell production) occurs in bone marrow, not the lymphatic system.

A. Catecholamines:Catecholamines (such as epinephrine and norepinephrine) are derived from amino acids like tyrosine and act mainly through cell surface receptors, not by entering the cell to affect gene transcription.
B. Peptide hormones:Peptide hormones are chains of amino acids that bind to receptors on the cell surface because they are not lipid-soluble; they act via secondary messenger systems rather than directly influencing DNA transcription.
C. Thyroid hormones:Thyroid hormones are amino acid–derived but are lipid-soluble; they can enter cells and influence gene expression, although they are not cholesterol-derived.
D. Steroid hormones:Steroid hormones (e.g., cortisol, estrogen, testosterone) are synthesized from cholesterol and are lipid-soluble, allowing them to cross the cell membrane, bind intracellular receptors, and regulate gene transcription in the nucleus.