MICROANATOMY

Detailed explanation-1: -Lipid insoluble hormones bind to receptors on the outer surface of the plasma membrane, via plasma membrane hormone receptors . Unlike steroid hormones, lipid insoluble hormones do not directly affect the target cell because they cannot enter the cell and act directly on DNA.

Detailed explanation-2: -The correct answer: The type of hormones that never enter the cell and are often called the first messengers are b) Peptide hormones. Peptide hormones are not able to enter the target cell directly to elicit the specific action in the cells.

Detailed explanation-3: -Non-steroid hormones are made of amino acids. They are not fat soluble, so they cannot diffuse across the plasma membrane of target cells. Instead, a non-steroid hormone binds to a receptor on the cell membrane (see Figure below). The binding of the hormone triggers an enzyme inside the cell membrane.

Detailed explanation-4: -Growth hormone, insulin, calcitriol, and secretin are examples of molecules that cannot pass the cell membrane.

Detailed explanation-5: -Amino acid-derived hormones and polypeptide hormones are not lipid-derived (lipid-soluble or fat-soluble); therefore, they cannot diffuse through the plasma membrane of cells.