Endocrine System Overview

Endocrine System Overview

• The neuroendocrine system is a communication system.
  • The nervous system uses electrical signals and neurotransmitters.
  • The endocrine system uses chemical messengers called hormones.
• Hormones are slower to respond but have longer-lasting effects than the nervous system.
• Hormones are chemical messengers synthesized, stored, and released by endocrine glands and certain other cells.
• The endocrine system consists of a host organ, small concentrations of chemical messengers, and a target/receptor organ.
• Hormones are chemical substances synthesized by specific host glands.

Hormone Half-Life

• Half-life is the time required to reduce a hormone's blood concentration by half.
• It indicates how long the hormonal effect lasts.
• Most hormones circulate in the blood, affecting distant tissues.
• Some hormones affect local areas of synthesis.
• Many hormones need transport proteins for transport (e.g., sex hormone-binding globulin).
• Hormone effects depend on receptor location. Only unbound (free) hormones interact with their receptors.

Endocrine System Function

• The endocrine system constantly monitors the internal environment and coordinates integration of physiological systems during rest and exercise.
• It maintains homeostasis via hormones, controlling and regulating cell and organ activity.
• During exercise it maintains homeostasis, controls substrate metabolism, and regulates fluid and electrolyte balance.

Hormone Release Patterns

• Most hormones respond to peripheral stimuli as needed.
• Hormones are released in bursts (pulsatile).
• Plasma hormone concentrations fluctuate over minutes, hours and days.
• Concentrations fluctuate over days/weeks.
• Hormone release is regulated by homeostasis. This includes negative feedback (like a thermostat) and positive feedback loops (e.g., oxytocin).
• Hormones are released at regular intervals following diurnal patterns or cycles.

Hormone Receptors

• Hormone binds to receptors to create a hormone-receptor complex (H-RC).
• Receptors can be on the cell surface or inside the cell.
• Hormones only affect tissues with specific receptors.
• Hormone effects occur after receptor binding.
• A typical cell has 2,000 to 10,000 receptors.

Hormone-Receptor Binding

• The "lock and key" mechanism is the first step in hormone action.
• The extent of target cell activation depends on:
  • Hormone concentration in the blood.
  • Available receptors on the target cell. (Receptors can be upregulated, downregulated, or saturated.)
  • Affinity (or sensitivity) of hormone-receptor binding.
  • Other chemical inhibitors (e.g., beta blockers).

Hormone-Target Cell Reactions

• Hormones alter cellular reactions in specific target cells by:

  • Changing enzyme activity rates.
  • Modifying intracellular protein synthesis rates.
  • Activating second-messenger systems (e.g., G-proteins, cAMP, and kinase reactions).
  • Inducing secretory activity (e.g., growth hormone and insulin-like growth factors).

• The same hormone can have different effects depending on the target organ.

• Steroid hormones migrate into their target cells. Example include testosterone in skeletal muscle or dihydrotestosterone in sex-linked tissues.

Explore the complex interactions within the endocrine system, focusing on how hormones function as chemical messengers. Learn about the role of the neuroendocrine system and the significance of hormone half-life in physiological responses. This quiz covers the key concepts and components of the endocrine system, enhancing your understanding of its dynamics.