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Questions and Answers
What type of response duration is characteristic of the endocrine system?
How do hormones exert their effects on target tissues?
In the endocrine system, what determines the strength of the hormonal response?
What does the amplitude-modulated system in the endocrine system refer to?
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Which of the following correctly contrasts the nervous system and the endocrine system?
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What is the role of inhibitory hormones released by the hypothalamus?
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What is specificity in the context of hormone-receptor interaction?
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Which of the following statements about neurotransmitters is correct?
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What is the function of receptors in hormone action?
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Which pairs correctly represent an agonist and antagonist in hormone actions?
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What is the primary role of the rostral/preoptic area of the hypothalamus?
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Which statement accurately describes the anterior pituitary gland?
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How does the hypothalamus regulate the anterior pituitary gland?
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What defines the function of the posterior pituitary gland?
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What is the main role of the infundibulum in the context of the pituitary gland and hypothalamus?
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Which hormone signaling type can communicate only within a localized area?
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What is primarily responsible for the removal of lipid-soluble hormones from circulation?
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Which type of hormone typically circulates as free hormones in the bloodstream?
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What defines an acute hormone secretion pattern?
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Which of the following is NOT a characteristic of water-soluble hormones?
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What is the role of proteases in relation to water-soluble hormones?
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Which of the following hormones would exhibit chronic secretion patterns?
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What type of stimuli causes hormonal secretion as a direct response to blood metabolites?
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What is the primary role of growth hormone (GH) in the body?
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Which hormone is produced by parafollicular cells of the thyroid gland?
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What effect do T3 and T4 hormones have on metabolism?
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Which factor stimulates secretion of aldosterone from the adrenal cortex?
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What is the primary function of parathyroid hormone (PTH)?
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How does insulin primarily affect blood glucose levels?
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Which hormone is primarily secreted by the adrenal medulla during stress?
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What triggers the secretion of calcitonin?
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What role do gonadocorticoids play in the body?
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How does glucagon primarily function within the body?
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What effect does cortisol have on the body during stress?
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Which gland is responsible for producing melatonin?
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What hormone has the primary role in stimulating the reabsorption of sodium (Na+) in the kidneys?
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Study Notes
Endocrine System Characteristics
- Composed of endocrine glands and specialized endocrine cells
- Secrete hormones, which are chemical messengers that diffuse into the bloodstream
- Hormones travel to their target tissues or effectors
Nervous System vs. Endocrine System
- Nervous System: Uses neurotransmitters for short-duration responses, released directly onto target cells
- Endocrine System: Uses hormones for long-duration responses, circulate in the blood, affect receptors through G proteins
Hormone Communication & Distribution
- Hormones are able to communicate with their target cells
- Stability of hormones is defined by their half-life (exponential decrease)
- Hormones are distributed throughout the body via the bloodstream
Chemical Composition of Hormones
-
Lipid-Soluble Hormones: Nonpolar, including steroid hormones, thyroid hormones, and fatty acid derivative hormones
- Travel bound to proteins in the bloodstream
- Removed from circulation through conjugation (enzymes attach water-soluble molecules)
-
Water-Soluble Hormones: Polar molecules, including protein hormones, peptide hormones, and most amino acid derivative hormones
- Travel as free hormones in the bloodstream
- Have shorter half-lives due to proteases (hydrolytic enzymes)
- Some modifications occur to protect them from destruction (glycoproteins, modified terminal end, binding proteins)
Hormone Secretion Patterns
- Chronic: Relatively constant blood levels over long periods (e.g., thyroid hormones)
- Acute: Concentrations change suddenly and irregularly (e.g., epinephrine)
- Episodic: Secreted at predictable intervals and concentrations (e.g., reproductive hormones)
Regulation of Hormone Secretion
- Humoral Stimuli: Stimulation by metabolites and molecules in the bloodstream (e.g., calcium, sodium, glucose)
- Neural Stimuli: Action potentials release neurotransmitters into synapses of hormone-producing cells (e.g., releasing hormones from the hypothalamus)
- Hormonal Stimuli: Hormones stimulate the secretion of other hormones (e.g., tropic hormones from the anterior pituitary)
Hormone Receptors & Mechanisms of Action
- Hormones exert their actions by binding to receptors on target cells
- Receptor Site: Specific portion of each receptor molecule where a hormone binds
- Specificity: Each type of hormone tends to bind to one type of receptor
Hypothalamus
- Rostral/Preoptic Area: Involved in thermoregulation, fever, electrolyte balance, sleep-wake cycles, and sexual behavior
- Tuberal Hypothalamus: Involved in feeding, sexual behavior, aggression, and autonomic/endocrine responses
- Posterior Area: Regulates wakefulness and the stress response
Pituitary Gland/Hypophysis
- Pea-sized gland located in the sella turcica of the sphenoid bone
- Posterior Pituitary (Neurohypophysis): Continuous with the hypothalamus, stores and releases neuropeptides
- Anterior Pituitary (Adenohypophysis): Develops from the embryonic oral cavity, produces traditional hormones
Pituitary Gland & Hypothalamus Interaction
-
Anterior Pituitary Regulation: Hypothalamohypophyseal portal system (specialized blood vessels)
- Releasing hormones: Stimulate hormone secretion
- Inhibiting hormones: Decrease hormone secretion
-
Posterior Pituitary Regulation: Hypothalamohypophyseal tract (neural pathway)
- Posterior pituitary stores and releases hormones produced in the hypothalamus
Growth Hormone (GH)
- Stimulates growth in most tissues & regulates metabolism
- Promotes protein synthesis, fat breakdown, and glucose synthesis
- GH secretion increases in response to low blood glucose, stress, and increased amino acids
- Regulated by hypothalamic hormones: GHRH (releasing) and GHIH (inhibiting)
Thyroid Gland
- Largest endocrine gland located in the anterior neck
- Composed of follicles that produce thyroglobulin
- Parafollicular cells produce calcitonin
Thyroid Hormones
- Triiodothyronine (T3): Two tyrosines with three bound iodine atoms (90%)
- Tetraiodothyronine (T4): Two tyrosines with four bound iodine atoms (10%)
Effects of Thyroid Hormones
- Increase metabolic rate (glucose, fat, and protein metabolism)
- Increase body temperature
- Regulate blood pressure, tissue growth, skeletal/nervous system development, maturation, and reproductive capabilities
Regulation of Thyroid Hormone Secretion
- Regulated by TRH (hypothalamus) and TSH (anterior pituitary)
- TRH increases TSH secretion
- TSH increases T3 and T4 secretion
- T3 and T4 negatively feedback to inhibit TSH and TRH secretion
Calcitonin
- Produced by parafollicular cells of the thyroid gland
- Directly regulated by blood Ca2+ levels
- Low Ca2+ = Low Calcitonin
- High Ca2+ = High Calcitonin
- Targets skeleton to inhibit osteoclast activity and stimulate calcium uptake
Parathyroid Gland
- Tiny glands embedded in the posterior aspect of the thyroid
- Secrete parathyroid hormone (PTH)
- Plays a crucial role in regulating blood calcium balance (more important than calcitonin)
Parathyroid Hormone (PTH)
- Increases release of Ca2+ from bones into the blood (increased osteoclast activity)
- Promotes calcium reabsorption in kidneys and active vitamin D formation
- Active vitamin D increases calcium absorption in the intestine
- Secreted in response to decreased blood Ca2+ levels
Adrenal Glands
- Paired, pyramid-shaped organs located on top of the kidneys
- Adrenal Medulla (Inner Area): Arises from sympathetic nervous system cells, secretes epinephrine and norepinephrine
-
Adrenal Cortex (Outer Area): Glandular tissue derived from mesoderm, composed of three layers:
- Zona glomerulosa
- Zona fasciculata
- Zona reticularis
Adrenal Medulla Hormones
- Epinephrine (Adrenaline): 80% of hormones released
- Norepinephrine: 20% of hormones released
- Prepare the body for physical activity by:
- Increasing blood glucose levels
- Increasing glycogen and glucose use in muscle
- Increasing heart rate and force of contraction
- Causing vasoconstriction in skin and viscera
- Causing vasodilation in skeletal and cardiac muscle
- Released in response to emotions, injury, and stress by the sympathetic nervous system
Adrenal Cortex Hormones
- Corticosteroids: Steroid hormones
-
Zona Glomerulosa: Mineralocorticoids (Aldosterone)
- Regulates electrolytes in extracellular fluids
- Maintains Na+ balance and decreases K+ and H+ levels in the blood
- Secreted in response to high K+, low Na+, or decreased blood volume/pressure
-
Zona Fasciculata: Glucocorticoids (Cortisol)
- Help the body resist stress by maintaining blood sugar, blood volume, and preventing water shifts
- Provoke gluconeogenesis, increase blood glucose, fatty acids, and amino acids
- Excessive levels can suppress immune function and cause other adverse effects
-
Zona Reticularis: Gonadocorticoids (Androgens)
- Primarily testosterone, contributes to puberty, secondary sex characteristics, and sex drive in females
Pancreas
- Triangular gland located behind the stomach with exocrine and endocrine functions
- Acinar Cells: Produce digestive enzymes (exocrine)
-
Pancreatic Islets (Islets of Langerhans): Produce hormones (endocrine)
- Alpha (α) Cells: Produce glucagon
- Beta (β) Cells: Produce insulin
Insulin
- Target tissues: Liver, adipose tissue, muscle, satiety center in the hypothalamus
- Increases glucose and amino acid uptake by cells
- Glucose used for energy, stored as glycogen, or converted into fat
- Amino acids used for protein synthesis
- Low insulin levels promote ketone body formation by the liver
Glucagon
- Target tissue primarily the liver
- Promotes glycogen breakdown to glucose
- Stimulates glucose synthesis from amino acids
- Liver releases glucose into the blood
Hormonal Regulation of Nutrients
-
After a meal:
- High glucose stimulates insulin and inhibits glucagon, cortisol, GH, and epinephrine
- Insulin increases glucose, amino acid, and fat uptake
- Blood glucose drops: Insulin decreases, other hormones increase, glucose released
-
During Exercise:
- Sympathetic activity increases epinephrine and glucagon secretion, leading to glucose release
- Low blood sugar stimulates epinephrine, glucagon, GH, and cortisol secretion, increasing fatty acids and ketones for energy
Testes & Ovaries
-
Testes: Secrete testosterone
- Initiates male reproductive organ maturation
- Causes secondary sex characteristics and sex drive
- Necessary for sperm production
-
Ovaries: Secrete estrogen and progesterone
- Maturation of female reproductive organs
- Appearance of secondary sex characteristics
- Breast development and uterine cycle
Pineal Body
- Small, pine cone-shaped structure located superior and posterior to the thalamus
- Secretes melatonin
- May inhibit reproductive maturation and regulate sleep-wake cycles
Thymus
- Lobulated gland located deep to the sternum
- Produces thymopoietins and thymosins
- Essential for T-lymphocyte development in the immune system
Other Endocrine Glands
- Gastrointestinal Tract: Produces gastrin, secretin, and cholecystokinin (regulate digestion)
- Kidneys: Produce erythropoietin (stimulates red blood cell production)
- Placenta: Secretes human chorionic gonadotropin (maintains pregnancy)
Hormone-Like Substances
- Autocrine Agents: Local effects on cells of the same type (e.g., prostaglandins, thromboxanes)
- Paracrine Agents: Local effects on cells of a different type (e.g., growth factors, clotting factors)
- Key differences from hormones: Not secreted from discrete glands, local effects, functions not always fully understood
Developmental Aspects of the Endocrine System
- Endocrine glands derive from all three germ layers: ectoderm, mesoderm, and endoderm
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Description
Explore the fundamental characteristics and functions of the endocrine system. Learn how hormones are secreted and distributed throughout the body, and understand the differences between the nervous and endocrine systems. This quiz covers hormone communication, stability, and chemical composition.
