Endocrine Signaling Overview

Endocrine Signaling

• Five types of communication between animal cells are described; 5-8 slides.
• Endocrine signaling: Hormones secreted into extracellular fluids by endocrine cells reach target cells via the bloodstream.
• Homeostasis is maintained.
• Responses to stimuli are mediated.
• Growth and development are regulated.
• Triggers changes underlying sexual maturity and reproduction.

Paracrine/Autocrine Signaling

• Paracrine: Target cells lie near the secreted cells.
• Autocrine: Target cell is also the secreting cell.
• These two play roles in blood pressure regulation and nervous system/reproductive function.

Synaptic Signaling

• Neurons communicate with target cells via specialized junctions (synapses).
• Neurotransmitters diffuse short distances, binding to receptors on target cells.

Neuroendocrine Signaling

• Specialized neurosecretory cells release neurohormones.
• Neurohormones diffuse into bloodstream from nerve endings.

Hypothalamus

• Located at the base of the brain.
• Coordinates endocrine signaling.
• Signals travel to the pituitary gland (posterior and anterior).
• Makes gonadotropin-releasing hormone (GnRH).

Pituitary Gland

• Composed of posterior and anterior pituitary.
• Posterior Pituitary: Stores and secretes hormones made in the hypothalamus.
• Anterior Pituitary: Makes and releases hormones, regulated by the hypothalamus.

Thyroid Gland

• Located in the neck.
• Regulates body metabolism (converts food to energy).
• Regulated through a hormone cascade pathway:
  • Low thyroid hormone levels trigger the hypothalamus to release TRH.
  • TRH stimulates the anterior pituitary to release TSH.
  • TSH stimulates the thyroid to release thyroid hormone.

Parathyroid Glands

• Located near the thyroid glands in the neck.
• Regulates blood calcium levels.
• Makes parathyroid hormone (PTH):
  • Released when calcium levels are low.
  • Raises calcium levels by releasing calcium from bones and stimulating reabsorption in kidneys.
• Makes calcitonin:
  • Lowers blood calcium levels.
  • Stimulates calcium deposition in bones.