Endocrine System Overview

Endocrine System

• Endocrine and nervous systems communicate in the body
• Nervous system is faster, but endocrine response is not always slower
• Norepinephrine and insulin produce fast responses; some hormones have fast responses
• Functions of the endocrine system include homeostasis, growth regulation, reproduction regulation, and maturation regulation

Hormone Classification

• Hormones are chemical substances produced by endocrine glands
• Steroid hormones are derived from cholesterol and are not soluble in blood; they need transporters
• Protein hormones are soluble in blood and do not require transporters
• Steroid hormones cross cell membranes and act on intracellular receptors
• Protein hormones do not cross cell membranes and act on extracellular receptors

Hormone Receptors types

• Hormone receptors are glycoprotein structures that bind with hormones
• Hormone quality, quantity, and sensitivity may be impacted by physiological conditions
• Other hormones or hormones acting on receptors can also affect hormone actions

Hormone Regulation

• Hormone-level changes may affect receptor number (upregulation or down regulation)
• Example: During parturition (childbirth), oxytocin receptor number increases in uterus, and estrogen increases receptor sensitivity
• Insulin levels, when high, trigger down-regulation of receptors to decrease insulin synthesis

Thyroid Hormone

• Thyroid hormone is stored in follicles and transported in the blood with proteins
• Thyroid hormone acts on intracellular receptors
• Thyroid hormone has a long half-life

Catecholamines

• Catecholamines do not cross cell membranes
• They are stored in granules and transported in blood, often without protein carriers
• Catecholamines act on extracellular receptors
• Catecholamines have a short half-life

Hormones: Site of Action

• Autocrine action: hormones act within the organ where they are produced
• Paracrine action: hormones act on nearby cells
• Endocrine action: hormones released into the blood and act on distant target organs

Mechanism of Action of Protein Hormones

• Protein hormones work through a cascade of biochemical reactions
• cAMP (cyclic AMP) is a second messenger often involved
• Other second messengers like protein kinases, calcium-calmodulin systems, and phosphatidyl inositol systems also exist
• Second messengers influence cellular functions, often activating or inactivating enzymes through phosphorylation

Mechanism of Action of Steroid and Thyroid Hormones

• Steroid and thyroid hormones bind to intracellular receptors
• The hormone-receptor complex acts on DNA sequences, regulating gene transcription
• Binding alters DNA-binding domain conformation causing a downstream effect in the cell

Explore the functions and classifications of hormones in the endocrine system. Understand how the endocrine and nervous systems communicate, the differences between steroid and protein hormones, and the role of hormone receptors. This quiz will enhance your comprehension of regulation in growth, reproduction, and homeostasis.