Which of the following statements about peptide or protein hormones is usually true?

Correct Answer: B

Rationale: The correct answer is B: Peptide or protein hormones have receptors on the cell membrane. These hormones are typically large molecules that cannot pass through the cell membrane, so they bind to receptors on the cell surface to initiate signal transduction pathways. This allows them to quickly and effectively communicate with target cells. A: They do not have longer half-lives than steroid hormones. Peptide hormones are usually rapidly degraded compared to steroid hormones. C: They do not have a slower onset of action than steroid and thyroid hormones. Peptide hormones can have rapid onset of action due to their signaling pathways. D: They can be stored in endocrine-producing glands, such as insulin being stored in pancreatic beta cells.

Correct Answer: C

Rationale: The correct answer is C: Spermatids are streamlined to form sperm via spermiogenesis. Spermiogenesis is the final stage of spermatogenesis where round spermatids mature into spermatozoa. During spermiogenesis, the spermatids undergo significant structural changes, including the formation of the acrosome, tail, and mitochondria, to become fully functional sperm cells. Choices A and B are incorrect because spermiogenesis does not involve building the stem cell line or producing type A cells. Choice D is incorrect because spermiogenesis does not result in the production of two sperm from one primary spermatocyte; rather, it is the process by which spermatids are transformed into mature sperm cells.

Correct Answer: D

Rationale: The correct answer is D: Bulbourethral fluid. Semen is composed of sperm, seminal fluid, and prostatic fluid. Bulbourethral fluid is not a component of semen but contributes to pre-ejaculatory fluid. This fluid is released from the Cowper's glands and serves to lubricate the urethra prior to ejaculation. The other choices (A, B, C) are all essential components of semen that play crucial roles in sperm transport, nourishment, and protection.

Correct Answer: D

Rationale: The correct answer is D because the innermost lining of the vagina does not slough off periodically like the uterine lining does during menstruation. The vaginal lining is composed of stratified squamous epithelium that does not undergo the shedding process seen in the endometrium. This is important for maintaining the integrity and functionality of the vagina. Choices A, B, and C are true statements about the vagina. A: The vagina serves as the birth canal. B: The distal end of the vagina is partially enclosed by the hymen. C: The vagina is the female organ of copulation.

Correct Answer: C

Rationale: The correct answer is C: round ligament. The round ligament holds the uterus in place laterally. It is a band of tissue that connects the uterus to the groin region. This ligament provides support and stability to the uterus during movements and changes in position. Choice A (8 place, laterally) and Choice D (100) are nonsensical and do not correspond to any anatomical structure or location. Choice B (25) is also incorrect as it does not exist as a ligament involved in supporting the uterus. In summary, the round ligament is the correct choice as it is the specific ligament responsible for holding the uterus in place laterally, providing essential support and stability.