Endocrine System Quiz

Endocrine System Overview

• Composed of glands and specialized cells
• Secretes hormones
• Hormones diffuse into bloodstream to target tissues
• Hormones are chemical messengers
• Endocrine system functions
• Regulates metabolism
• Controls food intake and digestion
• Modulates tissue development
• Controls ion levels
• Controls water balance
• Regulates changes in heart rate and blood pressure
• Regulates blood glucose and nutrients
• Controls reproductive functions
• Stimulates uterine contractions and milk production
• Modulates immune function

Hormone Secretion Patterns

• Chronic: Relatively constant blood levels over long periods (e.g., thyroid hormones)
• Acute: Blood levels change suddenly and irregularly (e.g., epinephrine)
• Episodic: Secreted at predictable intervals and concentrations (e.g., reproductive hormones)

Control of Hormone Secretion

• Humoral stimuli: Stimulation by metabolites and molecules in the bloodstream (e.g., calcium, sodium, glucose)
• Neural stimuli: Following action potentials, neurotransmitters are released into synapses of hormone-producing cells (e.g., releasing hormones, inhibitory neurotransmitters)
• Hormonal stimuli: Hormones stimulate the secretion of other hormones (e.g., tropic hormones)

Hormone Characteristics

• Stability: Concept of half-life
• Communication: How hormones interact with their target cells
• Distribution: How hormones travel through the body

Chemical Composition of Hormones

• Lipid-soluble: Nonpolar (e.g., steroid hormones, thyroid hormones, fatty acid derivatives)
  • Travel in bloodstream bound to proteins
  • Removed from circulation through conjugation
• Water-soluble: Polar (e.g., proteins, peptides, most amino acid derivatives)
  • Usually free in the bloodstream
  • Have short half-lives

Hormone Receptors and Mechanisms of Action

• Hormones exert their actions by binding to target cell proteins called receptors
• Receptor site: Specific portion of each receptor molecule where a hormone binds to
• Specificity: tendency for each hormone to bind to one type of receptor

Agonists and Antagonists

• Agonist: Drug that binds to a receptor and activates it
• Antagonist: Drug that binds to a receptor but does not activate it, blocking the action of an agonist.

Receptor Number Regulation

• Decrease (Desensitization/Downregulation): Occurs when the number of receptors rapidly decreases after exposure to hormones
• Increase (Upregulation): Occurs when a target tissue increase receptor sensivity

Intracellular Receptors

• Lipid-soluble hormones bind to intracellular receptors
• The receptor-hormone complex activates genes
• mRNA is produced to translate new proteins and create response to the hormone
• Intracellular receptor mechanisms have slow responses compared to other mechanisms.

Water-soluble Hormones Mechanism

• After a water-soluble hormone binds to its receptor, the G protein is activated.
• The activated subunit binds to and activates adenylate cyclase.
• Adenylate cyclase converts ATP to cAMP.
• cAMP activates protein kinase enzymes.
• The activated enzymes produce the cell's response.
• Phosphodiesterase enzymes inactivate cAMP by converting cAMP to AMP

Cascade Effect

• A series of enzyme-catalyzed reactions
• Amplifies the initial signal to achieve a proportionally large effect in the cell

Endocrine Glands

• Hypothalamus
• Pituitary Gland (Anterior and Posterior)
• Thyroid Gland and its hormones (T3, T4, Calcitonin)
• Parathyroid Gland
• Adrenal Glands (Medulla & Cortex; Cortisol, Aldosterone)
• Pancreas
• Testes
• Ovaries, Progesterone
• Pineal Body
• Thymus

Other Endocrine Structures

• Gastrointestinal tract
• Kidneys
• Placenta and other endocrine structures

Hormone Regulation

• Regulation is either humoral, neural, or hormonal.
• Negative and positive feedback loops regulate hormone levels

Characteristics of different endocrine glands and their hormones

• Hypothalamus: Major roles in controlling the endocrine system, regulates water balance, hunger, and mood. It produces hormones that control the pituitary.
• Pituitary: Secretes many hormones that target multiple systems.
• Thyroid: Produces T3 and T4 which control metabolism and regulates growth.
• Adrenal: Produces various hormones such as cortisol, important during stress responses, and adrenaline and noradrenaline during immediate physical activity (fight response).