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Questions and Answers
What is the primary function of the ribosome in hormone synthesis?
What is the primary function of the ribosome in hormone synthesis?
Where are steroid hormones primarily synthesized?
Where are steroid hormones primarily synthesized?
What is the role of enzymes in steroid hormone synthesis?
What is the role of enzymes in steroid hormone synthesis?
How are hormones typically stored within cells?
How are hormones typically stored within cells?
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What initiates the release of hormones from granules?
What initiates the release of hormones from granules?
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What is the primary purpose of carriers for hormones in the bloodstream?
What is the primary purpose of carriers for hormones in the bloodstream?
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What is the term for the time required for half of a hormone to be inactive or removed from circulation?
What is the term for the time required for half of a hormone to be inactive or removed from circulation?
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How do hormones interact with target cells?
How do hormones interact with target cells?
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Which hormone is derived from the amino acid phenylalanine?
Which hormone is derived from the amino acid phenylalanine?
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What characteristic of protein hormones makes them unable to pass through the cell membrane directly?
What characteristic of protein hormones makes them unable to pass through the cell membrane directly?
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What type of communication involves hormones being secreted directly into the bloodstream?
What type of communication involves hormones being secreted directly into the bloodstream?
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Which stage is NOT part of the hormone cycle?
Which stage is NOT part of the hormone cycle?
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Which hormone requires tyrosine and iodine for its synthesis?
Which hormone requires tyrosine and iodine for its synthesis?
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What is the role of neurotransmitters in paracrine communication?
What is the role of neurotransmitters in paracrine communication?
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What are pheromones primarily involved in?
What are pheromones primarily involved in?
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What is a common energy source required for hormone biosynthesis?
What is a common energy source required for hormone biosynthesis?
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What is the primary function of the endocrine system?
What is the primary function of the endocrine system?
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Which of the following best describes hormones?
Which of the following best describes hormones?
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How does neural regulation differ from hormonal regulation?
How does neural regulation differ from hormonal regulation?
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Which endocrine gland is considered particularly important for life?
Which endocrine gland is considered particularly important for life?
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Which of the following is NOT a characteristic of hormones?
Which of the following is NOT a characteristic of hormones?
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What is the nature of the secretion from endocrine glands?
What is the nature of the secretion from endocrine glands?
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Which hormone is produced by the kidneys?
Which hormone is produced by the kidneys?
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What defines homeostasis in the context of the endocrine system?
What defines homeostasis in the context of the endocrine system?
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Which neurotransmitters are involved in the control of somatotropin releasing hormone secretion?
Which neurotransmitters are involved in the control of somatotropin releasing hormone secretion?
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What role does norepinephrine play in the control of GnRH secretion?
What role does norepinephrine play in the control of GnRH secretion?
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What is the primary action of noradrenergic neurons regarding TRH secretion?
What is the primary action of noradrenergic neurons regarding TRH secretion?
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What is an example of a long-loop feedback system?
What is an example of a long-loop feedback system?
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How do neurohypophysial hormones differ in regulation compared to other hormones?
How do neurohypophysial hormones differ in regulation compared to other hormones?
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Which mechanism is associated with the inhibition of hypophysial hormones?
Which mechanism is associated with the inhibition of hypophysial hormones?
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Which hormones circulate to target organs to exert action from the pituitary gland?
Which hormones circulate to target organs to exert action from the pituitary gland?
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What effect does dopamine have on LH secretion?
What effect does dopamine have on LH secretion?
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What amino acids compose thyrotropin-releasing hormone (TRH)?
What amino acids compose thyrotropin-releasing hormone (TRH)?
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Which hormone does somatostatin primarily inhibit the release of?
Which hormone does somatostatin primarily inhibit the release of?
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What stimulates the secretion of somatostatin?
What stimulates the secretion of somatostatin?
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Which of the following hormones is not inhibited by somatostatin?
Which of the following hormones is not inhibited by somatostatin?
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What is the composition of somatocrinin?
What is the composition of somatocrinin?
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What physiological condition enhances the secretion of somatocrinin?
What physiological condition enhances the secretion of somatocrinin?
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Which hormone is regulated by gonadotropin releasing hormone (GnRH)?
Which hormone is regulated by gonadotropin releasing hormone (GnRH)?
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What characterizes the secretory ratio of FSH and LH during the estrus cycle?
What characterizes the secretory ratio of FSH and LH during the estrus cycle?
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Which hormone primarily stimulates the secretion of LH at the time of ovulation?
Which hormone primarily stimulates the secretion of LH at the time of ovulation?
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What is the effect of sex hormones on GnRH secretion?
What is the effect of sex hormones on GnRH secretion?
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What causes the surge of LH leading to ovulation in induced ovulators?
What causes the surge of LH leading to ovulation in induced ovulators?
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Which hormone is synthesized within the neurons of the hypothalamus and stimulates ACTH secretion?
Which hormone is synthesized within the neurons of the hypothalamus and stimulates ACTH secretion?
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What effect do stress and circadian light-dark cycles have on CRH?
What effect do stress and circadian light-dark cycles have on CRH?
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What is the primary action of Dopamine concerning prolactin secretion?
What is the primary action of Dopamine concerning prolactin secretion?
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What occurs if there is a lesion in the hypothalamus concerning prolactin levels?
What occurs if there is a lesion in the hypothalamus concerning prolactin levels?
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What effect does the damage of the hypothalamus have on melanocyte-stimulating hormone (MSH)?
What effect does the damage of the hypothalamus have on melanocyte-stimulating hormone (MSH)?
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Study Notes
Introduction to Endocrine System
- The endocrine system is a collection of organs with similar properties
- Endocrinology studies hormones, their receptors, intracellular pathways, and related diseases
- Endocrine glands are ductless glands that release hormones directly into the bloodstream
- Hormones are chemical substances that regulate cell and organ activity
- Homeostasis is crucial for life and involves maintaining a stable internal environment
- Regulation of the body's function occurs through both neural and hormonal methods
- Neural regulation is fast-acting and short-lived
- Hormonal regulation is slower but long-lasting
Regulation
- Neural regulation is fast-acting (seconds to minutes), and short-lived
- Hormonal regulation is slow-acting (delayed effect), and long-lasting
Common Endocrine Glands
- Hypothalamus
- Pituitary gland (anterior and posterior)
- Thyroid gland
- Parathyroid gland
- Adrenal gland
- Pancreas (islets of Langerhans)
- Pineal body
- Thymus
- Gonads
General Properties of Hormones
- Hormones do not directly affect the gland that secretes them
- Some hormones affect all body cells, while others affect specific organs
- Hormones trigger biochemical changes that may continue after they leave the bloodstream
- Hormones can have effects beyond their primary function (e.g., insulin stimulating protein synthesis)
- Stimuli that increase the release of some hormones may decrease the release of others with opposing effects (antagonistic hormones)
- Many hormones show cyclic changes in secretion rate (circadian rhythm)
- Hormones may be inactive when secreted and activated in target organs
- Hormones act at very low concentrations
- Unlike enzymes, hormones are constantly lost from circulation due to metabolism
Local Hormones
- Besides general hormones, local hormones act near their release site
- Examples include gastrointestinal hormones (e.g., gastrin, CCK) and neurotransmitters
Forms of Hormones in Blood
- Most hormones circulate in two forms:
- Free form (active form, small amount)
- Bound form (inactive form, reservoir for free form, bound to plasma proteins)
General Function of Hormones
- Regulate metabolic processes
- Control growth and metamorphosis
- Essential for homeostasis
- Important for resisting stress
- Crucial for reproduction, particularly through sex hormones
Chemical Nature of Hormones
-
Lipid-related:
- Derived from cholesterol (steroid hormones of adrenal cortex & sex hormones)
- Lipid-soluble (hydrophobic), easily pass cell membranes
- Examples include prostaglandins and leukotrienes
-
Nitrogen-related:
- Derived from single amino acids (catecholamines, thyroid hormones)
- Chain of peptides (3-200 amino acids)
- Protein hormones (carbohydrate attaches to peptide chain) - hydrophilic
- Cannot pass cell membranes without carriers
Communication of Hormones
- Endocrine: Hormones released into the bloodstream to affect distant target cells
- Paracrine: Hormones released into the extracellular space to affect nearby target cells
- Neuroendocrine: Hormones released directly into the bloodstream by specialized nerve cells. (e.g., norepinephrine and oxytocin, vasopressin)
Hormone Synthesis
- Requires raw materials (e.g., tyrosine, iodine for thyroid hormone, cholesterol for steroid hormones) and energy (ATP)
- Peptide hormones synthesized in ribosomes, processed through rough ER and Golgi apparatus to be packaged and secreted
- Steroid hormones synthesized in smooth ER and processed by enzymes within mitochondria and cytoplasm
Hormone Storage and Release
- Stored inside cells (pituitary gland, pancreas) or within gland follicles (thyroid gland)
- Stored in granules, released when granules fuse with cell membrane
- Release is stimulated by hormones, substances, and neural signals
Hormone Transport
- Transported via carrier proteins (mostly plasma globulins)
- Carrier proteins protect hormones from degradation & help transport across capillary membranes
- Hormone half-life is the time needed for half of the hormone molecules to be inactivated or removed from circulation (vary by hormone type)
Hormone Utilization (Hormone Receptors)
- Hormones bind to specific protein receptors on target cells to initiate action
- Intracellular receptors: Steroid hormones pass through membranes and bind to receptors inside the cytoplasm that migrate to nucleus
- Membrane receptors: Peptide hormones bind to membrane receptors, activating second messengers
- Thyroid hormones also affect cell function without entering cells directly
Receptors Number
- Number of receptors is not fixed, in response to hormone concentration
- Hormones can increase or decrease receptor quantities
- Hormone action is dependent on receptor type and quantity
- Receptor-mediated upregulation and downregulation due to high or low levels of specific hormones respectively
Downregulation/Desensitization
- Chronic exposure to high hormone concentrations leads to downregulation
- Reduced receptor numbers lead to decreased hormone action
- Presence of antibodies blocking receptors decrease signalling transmission
- Decrease in receptor synthesis or turnover.
Hormone Action
- Hormones bind to receptors, initiating intracellular effects
- Different actions depend on receptor location
Cell Membrane Receptors
- Hormones bind to receptors on the cell surface which start a signalling cascade.
- G-protein coupled receptors (GPCR) are common for peptide hormones.
Messengers
- Hormones are the first messengers, causing a response in target cells.
- Second messengers, such as cyclic AMP (cAMP), Inositol Triphosphate (IP3) and Diacylglycerol (DAG), lead to enzymatic cascades and cellular responses
Inactivation and Excretion
- Hormones are inactivated after their action or response
- Peptide hormones are inactivated by enzymes (peptidases), primarily in the liver and kidneys.
- Thyroid hormones are deiodinized
- Steroid hormones metabolized in the liver, conjugated to be water-soluble, excreted in urine or bile
Pathway of IP3 and DAG
- Phospholipase C is activated by hormones; cleaving PIP2 into IP3 and DAG.
- IP3 release Ca++ into cytoplasm; triggering effects
- DAG activates protein kinase C
Mechanisms of Feedback Control
- Long-loop: Peripheral target tissue hormones act on the hypothalamus and pituitary
- Short-loop: Hormones from the pituitary inhibit their own release from the hypothalamus
Control of Posterior Pituitary Hormones
- Neurohypophysial hormones are regulated by reflex pathways, not hormonal feedback
- Reflexes triggered by sensory input (e.g., suckling leads to oxytocin release)
- Blood volume/electrolyte changes lead to vasopressin release
Hypothalamus
- Part of the diencephalon, lies below thalamus, forms part of the third ventricle walls.
- Surrounded by optic chiasma, mammillary bodies, and thalamus
- Involved in regulating various physiological functions and endocrine control
Hypothalamic Nuclei
- Supraoptic and paraventricular nuclei control posterior pituitary secretions
- Paraventricular & Supraoptic nuclei synthesize oxytocin & vasopressin and control their secretion from the posterior pituitary.
Anatomical Considerations (hypothalamic-hypophysial portal system)
- Vascular connection between median eminence and pituitary
Magnocellular System
- Supraoptic and paraventricular neurons synthesize and secrete oxytocin and vasopressin
Hypothalamic Hormones
- Hypophysiotropic hormones regulate anterior pituitary function
Feedback Mechanisms
- Peripheral hormones, via hormone concentrations, affect hypothalamic and pituitary release mechanisms
Control of Hypothalamic Hormones
- Various factors (neurotransmitters, organic substances) regulate hypothalamic hormone release
- Stress, neurotransmitters, etc. are examples of stimulating factors, and negative feedback from hormones themselves are examples of inhibitory factors.
Pathophysiological Correlates of Hormone Action
- Hormone depletion/excess can cause an increase/decrease in specific receptor numbers, modifying target cell response
- Example is hyperthyroidism leading to enhanced sympathetic nervous system activity due to the modification of receptors
Some Hormones Receptors Issues
- Autoimmune diseases can create antibodies that interfere with cell function
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Description
This quiz explores the fundamental concepts of the endocrine system, focusing on the regulatory roles of hormones and the glands involved. Learn about the differences between neural and hormonal regulation, and the significance of homeostasis in maintaining bodily functions.
