All MCQs

Photoperiod can influence melatonin and reproductive hormone pathways. Many animals use seasonal cues to time reproduction.

Steroid and thyroid hormone receptors often function inside cells and regulate gene expression. Many peptide hormone receptors are on the membrane.

High thyroid hormone feeds back to reduce hypothalamic and pituitary stimulation, including TSH. This prevents excessive thyroid activity.

Exocrine glands release secretions through ducts to surfaces or cavities. Endocrine glands release hormones directly into internal fluids without ducts.

Endocrine hormones are commonly transported through blood, so blood levels provide useful information about endocrine function and feedback status.

Target-cell specificity is central to endocrine function. Hormone molecules can circulate widely, but only receptor-bearing cells respond.

Adrenaline prepares the body for rapid action by increasing heart rate, blood flow to muscles, and energy availability.

Cnidarians have simple nervous systems and chemical communication. They lack vertebrate endocrine glands but still coordinate feeding, movement, and reproduction.

Sponges do not possess true organs or endocrine glands, but cells can communicate chemically to coordinate basic activities.

Hormone action depends partly on how long the hormone remains active in circulation. Rapid degradation shortens the response.

Animal development often depends on hormonal signals integrated with environmental cues. In invertebrates, molting and metamorphosis are classic examples.

Negative feedback normally limits secretion when hormone levels are adequate. Failure of feedback can produce excessive hormone action.