Pakistan MCQs

Cells can reduce receptor number or signaling after prolonged stimulation. This decreases sensitivity and helps prevent overstimulation.

The lymphatic system returns excess tissue fluid to the bloodstream and also participates in immune defense through lymph nodes and lymphocytes.

Endocrine disruptors can interfere with normal signaling by mimicking, blocking, or altering hormone pathways. This can affect development, reproduction, and metabolism.

Thyroid hormones increase metabolic activity in many tissues. This can help regulate energy use, growth, and heat production.

Paracrine signals act locally on nearby cells, unlike classical endocrine hormones that travel through circulation to distant targets.

Blocked lymph drainage prevents interstitial fluid from returning to blood, causing edema or swelling in tissues.

Chemical regulation is widespread across animal groups. Invertebrates use endocrine and neuroendocrine signals for molting, growth, reproduction, and metabolism.

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

Autocrine signaling occurs when a cell releases a messenger that binds receptors on the same cell. It is common in growth and immune regulation.

Physical and chemical barriers are innate defenses. They act broadly and immediately against many pathogens before specific immune responses develop.

Ecdysone triggers molting, while juvenile hormone determines the character of the molt. High juvenile hormone favors larval traits.

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