Hormones and Cell Communication

Hypothalamic Hormones and Pituitary Hormones

• The hypothalamus produces releasing and inhibiting hormones that regulate the anterior pituitary.
• The anterior pituitary produces hormones that stimulate target organs.
• GnRH, CRH, TRH, PRH, Dopamine, and GHRH are hypothalamic hormones.
• FSH/LH, ACTH, TSH, Prolactin, and GH are anterior pituitary hormones.
• Target organs include gonads, adrenal cortex, thyroid, and mammary glands (and all other parts of body)
• The posterior pituitary releases ADH and oxytocin.

Cell-Cell Communication

• Multicellular organisms require long-range signaling mechanisms to coordinate cell behavior.
• Specialized cell types evolved to enable intercellular communication over large distances.
• Major communication systems include the nervous system, endocrine system, and immune cells.
• These systems use neurotransmitters, hormones, and cytokines to integrate stimuli and respond to environmental changes.

Autocrine Signaling

• Cells release signals that have a localized effect on the same cell type.
• The signals are rapidly inactivated.
• Prostaglandins are an example.

Prostaglandin Autocrine Control

• Prostaglandins are autocrine signals.
• COX-2 upregulates prostaglandin synthesis.
• Prostaglandins stimulate cell growth.

Paracrine Signaling

• Cells release signals that affect nearby cells.
• The signals are not transported via the bloodstream.
• Paracrine signaling in the pancreas regulates the release of hormones like insulin, glucagon, and somatostatin, from different cells.

Endocrine Signaling

• Hormones produced by endocrine glands enter the bloodstream and affect distant target cells with specific receptors.
• Endocrine hormones cause a longer-lasting response than neurotransmitters.

Neuro-Endocrine Signaling

• Stimuli sensed by the nervous system lead to specialized neuroendocrine cells producing hormones.
• Neuroendocrine cells signal an appropriate response.

Pheromones

• Chemicals secreted in sweat and other bodily fluids.
• Thought to influence behavior in the same species.

Nervous and Endocrine Communication - Similarities

• Both systems have an association with the brain—specifically the hypothalamus.
• Both involve common messengers like epinephrine, which can act as a neurotransmitter and hormone.
• The systems are cooperative, with the nervous system releasing neurohormones into the bloodstream and the endocrine system innervated directly by the nervous system.

Nervous and Endocrine Communication - Differences

• Mode of transport: Axonal (unidirectional) for the nervous system and via the bloodstream or interstitial fluid for the endocrine system.
• Speed of response: Instantaneous (milliseconds) for the nervous system and delayed (seconds) for the endocrine system.
• Duration of response: Brief (milliseconds to seconds) for the nervous system and sustained (minutes to days) for the endocrine system.

Amplitude vs. Frequency Modulation

• Amplitude modulation: Hormone concentration changes over time and affects the strength of the signal.
• Frequency modulation: Changes in the frequency of hormone release, rather than the amount, affect the signal's overall strength.

Controlling Hormone Secretion

• The rate of hormone production (synthesis and secretion), the rate of delivery via blood flow, and the rate of degradation and elimination are essential aspects in controlling hormone secretion.

Free Hormone

• The unbound hormone is considered the active form.
• Feedback inhibition is regulated by free hormone concentrations.
• Clinically relevant to hormone excess or deficiency.

Bound Hormone

• Hormone bound to plasma proteins is inactive.
• Increases the serum half-life of the hormone.
• The rate of delivery to target cells is controlled by the bound hormone concentration.

Synthesis and Secretion of Hormones

• Hormone synthesis and secretion are tightly regulated by negative and positive feedback loops.
• This regulation is a major aspect of endocrine control.

Negative Feedback Loops

• The hormone negatively regulates its own production.
• For example, the thyroid hormone (T4 and T3) release is regulated by the hypothalamus and pituitary, with a negative feedback mechanism.

Positive Feedback Loops

• The hormone's release stimulates further release.
• Example is the release of oxytocin during childbirth and breastfeeding

Humoral Stimuli- Blood Chemistry

• Blood chemical concentrations trigger hormone release.
• For instance, low calcium levels stimulate parathyroid hormone (PTH) release.

Humoral Stimuli - Glucose Insulin

• High blood glucose levels stimulate insulin secretion.

Neural Stimuli Control

• Electrical signals from the nervous system can trigger hormone release.

Control by Hormonal Stimuli

• Hormone production is controlled by higher factors(regulatory hormones) from the hypothalamus.
• These induce production of tropic hormones from the anterior pituitary, which act on their target organ to release a hormone. (e.g. the anterior pituitary produces TSH, which stimulates the thyroid gland to produce hormone T4/3).

Hormone Interaction

• Synergism: Two or more hormones acting together have an amplified effect.
• Permissiveness: One hormone is necessary for another to exert its full effect

Agonists and Antagonists

• Agonists mimic the action of a hormone.
• Antagonists block or reduce the action of a hormone.

Agonists Mimic Response

• Mimic natural hormones, binding to their receptors.
• Trigger similar cellular responses to the natural hormone.

Antagonists Inhibit Response

• Compete with natural hormones for similar receptor sites.
• Prevent the activation of the receptor, blocking hormone action.

Receptors

• Muscarinic receptors: Bind acetylcholine in the autonomic nervous system.
• Nicotinic receptors: Bind acetylcholine at neuromuscular junctions and are blocked by curare.

Explore the intricate roles of hypothalamic and pituitary hormones in regulating bodily functions. This quiz also covers the significance of cell-cell communication mechanisms, including autocrine and long-range signaling systems in multicellular organisms. Test your knowledge on how these processes integrate and respond to environmental changes.