21.4
Types of Hormones
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Q1: What are the four main classifications of hormones?
Hormones are classified into steroids, eicosanoids, amino acid-based derivatives, and peptide hormones based on their chemical structures. Steroids and eicosanoids are lipid-soluble hormones, while amines, peptides, and glycoproteins are water-soluble hormones. This classification reflects how hormones dissolve and travel through the bloodstream to reach target cells.
Q2: How are steroid hormones structured and what are examples?
Steroid hormones are derived from cholesterol and contain four connected carbon rings with different side chains attached. Estradiol, released from ovaries, and testosterone from testes are key examples. These lipid-soluble hormones play critical roles in reproductive physiology and other metabolic processes throughout the body.
Q3: What role does epinephrine play in the body?
Epinephrine, also known as adrenaline, is a tyrosine derivative and amine hormone synthesized from a single amino acid. It triggers the fight-or-flight response during stressful situations, preparing the body for rapid action. As a water-soluble hormone, it circulates quickly through the bloodstream to activate target cells.
Q4: How does melatonin differ from other amine hormones?
Melatonin is a tryptophan derivative, another type of amine hormone synthesized from a single amino acid. Unlike epinephrine, which triggers stress responses, melatonin regulates the sleep-wake cycle. Both are water-soluble hormones, but they have distinct physiological functions and target different processes.
Q5: What is the function of insulin as a peptide hormone?
Insulin is a peptide hormone produced by the pancreas after a meal. It comprises chains of amino acids and stimulates cells to absorb excess glucose from the blood, contributing to glucose homeostasis. Understanding insulin's role is essential for comprehending hormones regulating blood glucose and metabolic control.
Q6: What are eicosanoids and where do they originate?
Eicosanoids are lipid-soluble hormones derived from arachidonic acid and include prostaglandins and leukotrienes. They exert localized effects in various physiological processes, including responses to injury and infection. Unlike systemic hormones, eicosanoids typically act on nearby cells rather than distant targets.
Q7: What distinguishes glycoprotein hormones from other peptide hormones?
Glycoprotein hormones are peptide hormones with carbohydrate chains attached to the peptide structure. Thyroid-stimulating hormone is a notable example of this hormone type. These water-soluble hormones combine amino acid chains with sugar molecules, giving them unique structural and functional properties.