Podcast
Questions and Answers
What distinguishes endocrine hormones from neurotransmitters?
What distinguishes endocrine hormones from neurotransmitters?
- Endocrine hormones are released into the circulating blood to affect target cells at a distance, whereas neurotransmitters act locally in the synaptic junctions. (correct)
- Endocrine hormones are fast-acting, while neurotransmitters have a slower, more prolonged effect.
- Neurotransmitters are synthesized from cholesterol, while endocrine hormones are derived from amino acids.
- Endocrine hormones act only on nerve cells, while neurotransmitters affect other tissues.
How do neuroendocrine hormones exert their effect?
How do neuroendocrine hormones exert their effect?
- By directly affecting the nervous system through ion channels.
- By being secreted by neurons into the circulating blood and affecting target cells at a distant location. (correct)
- By directly influencing gene transcription within the cells that produce them.
- By acting locally on adjacent cells through paracrine signaling.
What mechanism primarily prevents the oversecretion of a hormone or overactivity at the target tissue?
What mechanism primarily prevents the oversecretion of a hormone or overactivity at the target tissue?
- The degradation of receptors on the target tissue.
- Positive feedback loops that stimulate the gland to slow down production.
- Negative feedback mechanisms where the hormone or one of its products suppresses further release. (correct)
- The storage of hormones in intracellular vesicles until they are needed.
How does the action of steroid hormones in stimulating protein synthesis differ from that of peptide hormones?
How does the action of steroid hormones in stimulating protein synthesis differ from that of peptide hormones?
How does the pulsatile or cyclical release of hormones such as growth hormone contribute to their overall physiological effect?
How does the pulsatile or cyclical release of hormones such as growth hormone contribute to their overall physiological effect?
What role do plasma proteins play in the function of steroid and thyroid hormones?
What role do plasma proteins play in the function of steroid and thyroid hormones?
How does the metabolic clearance rate affect the concentration of a hormone in the blood?
How does the metabolic clearance rate affect the concentration of a hormone in the blood?
What is the significance of hormone receptors being located either on the cell membrane or inside the cell (cytoplasm/nucleus)?
What is the significance of hormone receptors being located either on the cell membrane or inside the cell (cytoplasm/nucleus)?
What is meant by 'down-regulation' of hormone receptors, and what effect does it have on target tissue responsiveness?
What is meant by 'down-regulation' of hormone receptors, and what effect does it have on target tissue responsiveness?
How do G protein-linked receptors mediate hormone actions?
How do G protein-linked receptors mediate hormone actions?
What is the role of second messengers like cAMP in hormone action?
What is the role of second messengers like cAMP in hormone action?
How does the activation of phospholipase C contribute to hormone action?
How does the activation of phospholipase C contribute to hormone action?
What role does the hormone-receptor complex play in genetic expression when steroid hormones, thyroid hormones, retinoid hormones or vitamin D, enter the cell?
What role does the hormone-receptor complex play in genetic expression when steroid hormones, thyroid hormones, retinoid hormones or vitamin D, enter the cell?
What is the main principle behind radioimmunoassay (RIA) in measuring hormone concentrations?
What is the main principle behind radioimmunoassay (RIA) in measuring hormone concentrations?
How does the Enzyme-Linked Immunosorbent Assay (ELISA) differ from radioimmunoassay (RIA) in measuring hormone concentrations?
How does the Enzyme-Linked Immunosorbent Assay (ELISA) differ from radioimmunoassay (RIA) in measuring hormone concentrations?
How do autocrine and paracrine signaling differ in their mechanisms of action?
How do autocrine and paracrine signaling differ in their mechanisms of action?
In the context of hormone action, what is the role of kinase enzymes, such as protein kinase A (PKA) or Janus kinase (JAK)?
In the context of hormone action, what is the role of kinase enzymes, such as protein kinase A (PKA) or Janus kinase (JAK)?
What is the significance of hormone synthesis often starting with a preprohormone, which is then cleaved into a prohormone and ultimately the active hormone?
What is the significance of hormone synthesis often starting with a preprohormone, which is then cleaved into a prohormone and ultimately the active hormone?
How do endocrine glands and tissues maintain homeostasis through chemical messenger systems?
How do endocrine glands and tissues maintain homeostasis through chemical messenger systems?
How do local clock control in peripheral endocrine tissues and cyclical changes in tissue responsiveness impact hormonal regulation?
How do local clock control in peripheral endocrine tissues and cyclical changes in tissue responsiveness impact hormonal regulation?
How does understanding fluctuations in hormone concentrations relate to an individuals' stage of development and aging?
How does understanding fluctuations in hormone concentrations relate to an individuals' stage of development and aging?
Why might a pharmaceutical company target treatments that can up-regulate receptors and intracellular receptor tyrosine kinases for cell signalling?
Why might a pharmaceutical company target treatments that can up-regulate receptors and intracellular receptor tyrosine kinases for cell signalling?
What could happen in a disease situation if the body is only able to produce inhibitory G proteins (denoted G₁ proteins), which others produce stimulatory G proteins (denoted as G5 proteins)?
What could happen in a disease situation if the body is only able to produce inhibitory G proteins (denoted G₁ proteins), which others produce stimulatory G proteins (denoted as G5 proteins)?
How is the function of calmodulin related to troponin C in muscle contraction?
How is the function of calmodulin related to troponin C in muscle contraction?
How does Renin directly affect certain bodily functions?
How does Renin directly affect certain bodily functions?
How does Atrial Natriuretic Peptide (ANP) affect the body?
How does Atrial Natriuretic Peptide (ANP) affect the body?
What could be said about the function of Progesterone?
What could be said about the function of Progesterone?
What is the difference between Prohormones and Steroids?
What is the difference between Prohormones and Steroids?
Why can the body be affected dramatically even if there is the slightest amount of stimulus to the cell surface?
Why can the body be affected dramatically even if there is the slightest amount of stimulus to the cell surface?
How does decreased protein production affect the rates of chemical reactions in the body?
How does decreased protein production affect the rates of chemical reactions in the body?
What function does leptin serve?
What function does leptin serve?
Why have pharmaceutical companies started developing treatments for enzyme-linked receptor tyrosine kinases for cell signalling?
Why have pharmaceutical companies started developing treatments for enzyme-linked receptor tyrosine kinases for cell signalling?
Why are there no known hormones based from Polysaccharides or Nucleic Acid Hormones?
Why are there no known hormones based from Polysaccharides or Nucleic Acid Hormones?
What function does the Thymus Gland Provide to the body
What function does the Thymus Gland Provide to the body
How do thyroid hormone and adrenal medullary hormones differ in their synthesis and storage?
How do thyroid hormone and adrenal medullary hormones differ in their synthesis and storage?
What is the purpose of the suprachiasmatic nucleus (SCN) of the hypothalamus and what happens if it isn't functioning in a correct rhythm?
What is the purpose of the suprachiasmatic nucleus (SCN) of the hypothalamus and what happens if it isn't functioning in a correct rhythm?
How does the action of endocrine hormones differ fundamentally from that of paracrines?
How does the action of endocrine hormones differ fundamentally from that of paracrines?
What is the primary role of neuroendocrine hormones?
What is the primary role of neuroendocrine hormones?
Which characteristic distinguishes cytokines from traditional endocrine hormones?
Which characteristic distinguishes cytokines from traditional endocrine hormones?
How do neural stimuli primarily influence hormone secretion?
How do neural stimuli primarily influence hormone secretion?
What is the physiological significance of some hormones affecting multiple types of cells throughout the body?
What is the physiological significance of some hormones affecting multiple types of cells throughout the body?
How does the specificity of hormone action relate to hormone receptors?
How does the specificity of hormone action relate to hormone receptors?
How does the anatomical distribution of endocrine glands and tissues facilitate hormone action?
How does the anatomical distribution of endocrine glands and tissues facilitate hormone action?
What clinical outcome might be expected in an individual lacking insulin?
What clinical outcome might be expected in an individual lacking insulin?
What characteristic distinguishes steroid hormones from polypeptide hormones in terms of synthesis and storage?
What characteristic distinguishes steroid hormones from polypeptide hormones in terms of synthesis and storage?
How does the water solubility of peptide hormones affect their transport and action?
How does the water solubility of peptide hormones affect their transport and action?
What mechanisms are involved in the secretion of polypeptide hormones from endocrine cells?
What mechanisms are involved in the secretion of polypeptide hormones from endocrine cells?
Why are steroid hormones able to diffuse across the cell membrane?
Why are steroid hormones able to diffuse across the cell membrane?
How does hormone secretion occur when amine hormones are stored within thyroid follicles?
How does hormone secretion occur when amine hormones are stored within thyroid follicles?
What is the role of plasma proteins in the transport of steroid and thyroid hormones?
What is the role of plasma proteins in the transport of steroid and thyroid hormones?
How does metabolic clearance rate influence hormone concentration in the blood?
How does metabolic clearance rate influence hormone concentration in the blood?
What mechanism is responsible for the relatively long half-life of thyroid hormones compared to peptide hormones?
What mechanism is responsible for the relatively long half-life of thyroid hormones compared to peptide hormones?
What role does negative feedback play in hormone secretion?
What role does negative feedback play in hormone secretion?
How does positive feedback influence hormone secretion, and what is an example of this mechanism?
How does positive feedback influence hormone secretion, and what is an example of this mechanism?
What effect do cyclical variations in hormone release have on physiological functions?
What effect do cyclical variations in hormone release have on physiological functions?
How does the body regulate hormone action at the level of hormone receptors?
How does the body regulate hormone action at the level of hormone receptors?
How does the interaction between a hormone and its receptor typically initiate hormone effects at the cellular level?
How does the interaction between a hormone and its receptor typically initiate hormone effects at the cellular level?
Which type of hormone typically binds to receptors located on the cell membrane?
Which type of hormone typically binds to receptors located on the cell membrane?
What role does cAMP (cyclic adenosine monophosphate) play in hormone action?
What role does cAMP (cyclic adenosine monophosphate) play in hormone action?
How does the phospholipase C second messenger system contribute to hormone action?
How does the phospholipase C second messenger system contribute to hormone action?
What is the function of hormone response elements in the context of intracellular hormone receptors?
What is the function of hormone response elements in the context of intracellular hormone receptors?
Why can different tissues respond differently to the same hormone?
Why can different tissues respond differently to the same hormone?
How does leptin receptor activation lead to changes in cellular function?
How does leptin receptor activation lead to changes in cellular function?
What is the significance of the cascade of enzymatic reactions activated by cAMP?
What is the significance of the cascade of enzymatic reactions activated by cAMP?
How does the calcium-calmodulin system mediate hormone action?
How does the calcium-calmodulin system mediate hormone action?
What is the characteristic delay in the action of steroid hormones compared to peptide hormones, and why does it occur?
What is the characteristic delay in the action of steroid hormones compared to peptide hormones, and why does it occur?
Where do thyroid hormones primarily exert their effects at the cellular level?
Where do thyroid hormones primarily exert their effects at the cellular level?
Which step comes first in the measurement of hormone concentrations in the blood using radioimmunoassay?
Which step comes first in the measurement of hormone concentrations in the blood using radioimmunoassay?
Which of the following characterizes ELISA (Enzyme-Linked Immunosorbent Assay) methods for assessing hormones?
Which of the following characterizes ELISA (Enzyme-Linked Immunosorbent Assay) methods for assessing hormones?
How did scientists like Rosalyn Yalow and Solomon Berson revolutionize the measurement of hormones in the blood?
How did scientists like Rosalyn Yalow and Solomon Berson revolutionize the measurement of hormones in the blood?
In what scenario would an individual have excessively high levels of steroid hormones in their system?
In what scenario would an individual have excessively high levels of steroid hormones in their system?
Why have researchers and doctors begun using radioimmunoassay?
Why have researchers and doctors begun using radioimmunoassay?
How would some molecules travel to reach a target tissue?
How would some molecules travel to reach a target tissue?
How do most steroid receptors commonly found in the cell?
How do most steroid receptors commonly found in the cell?
What accounts for the relatively long duration of thyroid hormone action compared to epinephrine?
What accounts for the relatively long duration of thyroid hormone action compared to epinephrine?
How does the activation of G protein-coupled receptors contribute to the diversity of cellular responses?
How does the activation of G protein-coupled receptors contribute to the diversity of cellular responses?
How does the presence of hormone receptors inside the cell (cytoplasm or nucleus) affect the time course of hormone action?
How does the presence of hormone receptors inside the cell (cytoplasm or nucleus) affect the time course of hormone action?
What is the underlying principle behind the cyclical variations observed in hormone release?
What is the underlying principle behind the cyclical variations observed in hormone release?
How does the metabolic clearance rate (MCR) influence hormone concentration, and what factors affect MCR?
How does the metabolic clearance rate (MCR) influence hormone concentration, and what factors affect MCR?
What determines tissue-specific responses to hormones that utilize intracellular receptors?
What determines tissue-specific responses to hormones that utilize intracellular receptors?
In what ways do the protein and steroid hormones differ in their mechanisms of synthesis and storage?
In what ways do the protein and steroid hormones differ in their mechanisms of synthesis and storage?
How does the interplay between hormone secretion and target tissue activity maintain hormonal control?
How does the interplay between hormone secretion and target tissue activity maintain hormonal control?
In the context of hormone action, what roles do protein kinases serve?
In the context of hormone action, what roles do protein kinases serve?
What is the significance of the radioactive isotope in radioimmunoassay (RIA)?
What is the significance of the radioactive isotope in radioimmunoassay (RIA)?
How does the water solubility of hormones (e.g., peptide vs. steroid hormones) affect their transport in the blood?
How does the water solubility of hormones (e.g., peptide vs. steroid hormones) affect their transport in the blood?
How does hormone binding to plasma proteins influence the hormone's availability and clearance?
How does hormone binding to plasma proteins influence the hormone's availability and clearance?
Hormones can be formed from the modification of what?
Hormones can be formed from the modification of what?
What occurs to hormone receptors that causes them to be inactivated or destroyed over time?
What occurs to hormone receptors that causes them to be inactivated or destroyed over time?
What is the purpose of leptin, a hormone secreted by fat cells?
What is the purpose of leptin, a hormone secreted by fat cells?
How does the Enzyme-Linked Immunosorbent Assay (ELISA) affect hormone molecule detection based on prior methods?
How does the Enzyme-Linked Immunosorbent Assay (ELISA) affect hormone molecule detection based on prior methods?
How does the action of hormones that bind to cell surface receptors differ from those that bind to intracellular receptors?
How does the action of hormones that bind to cell surface receptors differ from those that bind to intracellular receptors?
Which mechanism best describes the means action for steroid hormones upon entering a target cell?
Which mechanism best describes the means action for steroid hormones upon entering a target cell?
How does the action of phospholipase C lead increased mobilization effect bodily function?
How does the action of phospholipase C lead increased mobilization effect bodily function?
What function does Atrial Natriuretic Peptide perform within the structure of the body?
What function does Atrial Natriuretic Peptide perform within the structure of the body?
Within a cell, certain parts regulate cell functions, such as cAMP, what occurs if these parts are abnormally situated?
Within a cell, certain parts regulate cell functions, such as cAMP, what occurs if these parts are abnormally situated?
Neurotransmitters influence target cells at distant locations by travelling through the blood stream.
Neurotransmitters influence target cells at distant locations by travelling through the blood stream.
Paracrines affect the function of the same cells from which they are secreted.
Paracrines affect the function of the same cells from which they are secreted.
The adrenal medullae and the pituitary gland primarily secrete hormones in response to stimulation from other hormones.
The adrenal medullae and the pituitary gland primarily secrete hormones in response to stimulation from other hormones.
Growth hormone from the adrenal gland affects many different types of cells throughout the body.
Growth hormone from the adrenal gland affects many different types of cells throughout the body.
Hormones like adrenocorticotropic hormone affect only specific target tissues because these tissues have abundant receptors for the hormone.
Hormones like adrenocorticotropic hormone affect only specific target tissues because these tissues have abundant receptors for the hormone.
Without insulin, the body's cells can efficiently use food carbohydrates for energy.
Without insulin, the body's cells can efficiently use food carbohydrates for energy.
Steroid hormones are synthesized from amino acids.
Steroid hormones are synthesized from amino acids.
The anterior pituitary gland secretes protein and polypeptide hormones.
The anterior pituitary gland secretes protein and polypeptide hormones.
Preprohormones are smaller, biologically active forms of hormones that are synthesized in the Golgi apparatus.
Preprohormones are smaller, biologically active forms of hormones that are synthesized in the Golgi apparatus.
Steroid hormones are stored in large quantities within the cytoplasm of endocrine cells.
Steroid hormones are stored in large quantities within the cytoplasm of endocrine cells.
Hormones derived from tyrosine include thyroid hormones and adrenal medullary hormones and are synthesized by the actions of ribosomes.
Hormones derived from tyrosine include thyroid hormones and adrenal medullary hormones and are synthesized by the actions of ribosomes.
The concentrations of hormones required to control metabolic and endocrine functions can be relatively high.
The concentrations of hormones required to control metabolic and endocrine functions can be relatively high.
Positive feedback mechanisms always prevent overactivity in hormone systems.
Positive feedback mechanisms always prevent overactivity in hormone systems.
The secretion of growth hormone stays constant throughout the day.
The secretion of growth hormone stays constant throughout the day.
Plasma proteins increase the clearance of hormones from the blood.
Plasma proteins increase the clearance of hormones from the blood.
Steroid and thyroid hormones primarily circulate freely in the blood.
Steroid and thyroid hormones primarily circulate freely in the blood.
Hormone receptors are small molecules and each cell that is to be stimulated usually has the same 100 receptors or less.
Hormone receptors are small molecules and each cell that is to be stimulated usually has the same 100 receptors or less.
Down-regulation of receptors increases the target tissue's responsiveness to a hormone.
Down-regulation of receptors increases the target tissue's responsiveness to a hormone.
G proteins are named for their ability to bind to cyclic AMP (cAMP).
G proteins are named for their ability to bind to cyclic AMP (cAMP).
Lipophilic hormones, like steroids, are not able to pass through the cell membrane.
Lipophilic hormones, like steroids, are not able to pass through the cell membrane.
Match the type of chemical messenger with its method of action:
Match the type of chemical messenger with its method of action:
Match the hormone with its effect on the body:
Match the hormone with its effect on the body:
Match each hormone class with its general chemical structure:
Match each hormone class with its general chemical structure:
Match each hormone with its effect on hormone secretion:
Match each hormone with its effect on hormone secretion:
Match the factor that increases or decreases hormone concentration in the blood:
Match the factor that increases or decreases hormone concentration in the blood:
Match the hormone receptor location with the hormone type that binds there:
Match the hormone receptor location with the hormone type that binds there:
Match the intracellular signaling mechanism with its description:
Match the intracellular signaling mechanism with its description:
Match the second messenger with its description:
Match the second messenger with its description:
Match the method for blood measurements to what it measures:
Match the method for blood measurements to what it measures:
Match the function with function or process that steroid hormones have on cells:
Match the function with function or process that steroid hormones have on cells:
Flashcards
Neurotransmitters
Neurotransmitters
Released by axon terminals; control nerve cell functions locally.
Endocrine hormones
Endocrine hormones
Released by glands into the blood; influence target cells elsewhere.
Neuroendocrine hormones
Neuroendocrine hormones
Secreted by neurons into blood, affects target cells elsewhere.
Paracrines
Paracrines
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Autocrines
Autocrines
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Cytokines
Cytokines
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Widespread Hormones
Widespread Hormones
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Hormone classes
Hormone classes
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Protein/polypeptide hormones
Protein/polypeptide hormones
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Steroid hormones
Steroid hormones
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Amine hormones
Amine hormones
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Polypeptide/protein hormones storage
Polypeptide/protein hormones storage
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Steroid hormones secretion
Steroid hormones secretion
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Thyroid hormones transport
Thyroid hormones transport
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Hormone Clearance
Hormone Clearance
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Metabolic clearance rate
Metabolic clearance rate
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Hormone Clearance Ways
Hormone Clearance Ways
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Hormone Action
Hormone Action
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Hormone receptors
Hormone receptors
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Receptor Down-regulation
Receptor Down-regulation
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Receptor Up-regulation
Receptor Up-regulation
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Ion Channel Receptors
Ion Channel Receptors
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G Protein-Linked Receptors
G Protein-Linked Receptors
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Enzyme-Linked Receptors
Enzyme-Linked Receptors
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Cortisol
Cortisol
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Aldosterone
Aldosterone
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Testosterone
Testosterone
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Estrogens
Estrogens
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Intracellular Receptors
Intracellular Receptors
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Adenylyl Cyclase
Adenylyl Cyclase
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Other Secondary Messengers
Other Secondary Messengers
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Cell Membrane Phospholipid 2nd Messenger System
Cell Membrane Phospholipid 2nd Messenger System
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Calcium-Calmodulin Second Messenger System
Calcium-Calmodulin Second Messenger System
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Steroid Hormones
Steroid Hormones
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Thyroid Hormones
Thyroid Hormones
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Radioimmunoassay
Radioimmunoassay
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ELISA Method
ELISA Method
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Homeostasis via Messengers
Homeostasis via Messengers
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Hypophysiotropic Hormones
Hypophysiotropic Hormones
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Target Tissue Specificity
Target Tissue Specificity
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Hormone Role Example
Hormone Role Example
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Preprohormones
Preprohormones
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Prohormones
Prohormones
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Negative Feedback
Negative Feedback
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Positive Feedback
Positive Feedback
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Cyclical Variations
Cyclical Variations
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Circadian Clocks
Circadian Clocks
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Thyroid Hormone Control
Thyroid Hormone Control
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Multiple hormone systems' role
Multiple hormone systems' role
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Endocrine glands loci
Endocrine glands loci
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Amine hormone formed by
Amine hormone formed by
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Growth hormone
Growth hormone
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Parathyroid hormone
Parathyroid hormone
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Thyroxine and Triiodothyronine
Thyroxine and Triiodothyronine
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Thyroid-stimulating hormone
Thyroid-stimulating hormone
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Adrenocorticotropic hormone
Adrenocorticotropic hormone
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Gonadotropin-releasing hormone
Gonadotropin-releasing hormone
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Neural-endocrine interactions
Neural-endocrine interactions
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Follicle-stimulating hormone
Follicle-stimulating hormone
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Luteinizing hormone
Luteinizing hormone
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Antidiuretic hormone
Antidiuretic hormone
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Oxytocin
Oxytocin
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Hormone Concentrations
Hormone Concentrations
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Steroid Action
Steroid Action
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Study Notes
Types of Chemical Messengers
- The multiple activities of cells, tissues, and organs are coordinated by chemical messenger systems.
- Neurotransmitters are released by the axon terminals of neurons into the synaptic junctions to control nerve cell functions.
- Endocrine hormones are released by glands or specialized cells into the circulating blood to influence the function of target cells elsewhere in the body.
- Neuroendocrine hormones are secreted by neurons into the circulating blood to influence the function of target cells elsewhere in the body.
- Paracrines are secreted by cells into the extracellular fluid to affect neighboring target cells of a different type.
- Autocrines are secreted by cells into the extracellular fluid and affect the function of the same cells that produced them.
- Cytokines are peptides secreted by cells into the extracellular fluid that can function as autocrines, paracrines, or endocrine hormones.
- Examples of cytokines include interleukins and lymphokines.
- Cytokine hormones produced by adipocytes are called adipokines.
- The adrenal medullae and the pituitary gland release hormones primarily in response to neural stimuli.
- Neuroendocrine cells in the hypothalamus release neurohormones like antidiuretic hormone, oxytocin, and hypophysiotropic hormones, controlling anterior pituitary hormone secretion.
Endocrine Hormone Transportation and Function
- Endocrine hormones are carried by the circulatory system.
- Hormones bind with receptors in the nervous system and initiate cell reactions.
- Adrenocorticotropic hormone specifically stimulates the adrenal cortex to secrete adrenocortical hormones.
- Ovarian hormones mainly affect female sex organs and secondary sexual characteristics
- Growth hormone from the anterior pituitary gland causes growth in most parts of the body.
- Thyroxine from the thyroid gland increases the rate of many chemical reactions in almost all the body’s cells.
- Without growth hormone, a person would be very short.
- Without thyroxine and triiodothyronine, the body’s chemical reactions would become sluggish.
- Without insulin, the body's cells could use little food carbohydrates for energy.
- Without sex hormones, sexual development and functions would be absent.
Chemical Structure and Synthesis of Hormones
- Three general classes of hormones: proteins and polypeptides, steroids, and derivatives of the amino acid tyrosine.
- Proteins and polypeptides are secreted by the anterior and posterior pituitary gland, the pancreas, and the parathyroid.
- Polypeptides with 100+ amino acids are proteins; fewer than 100 amino acids, peptides.
- Protein and peptide hormones are synthesized on the rough endoplasmic reticulum, then cleaved into prohormones.
- Enzymes in the Golgi apparatus cleave prohormones into active hormones and inactive fragments, stored in secretory vesicles.
- Secretion occurs through exocytosis when vesicles fuse with the cell membrane, triggered by increased cytosolic calcium or cAMP.
- Peptide hormones are water-soluble for easy entry into the circulatory system.
- Steroid hormones have a cholesterol-like structure and synthesized from cholesterol.
- Little steroid hormone storage occurs in endocrine cells, but cholesterol esters are rapidly mobilized from cytoplasmic vacuoles synthesis after stimulation
- Steroids are lipid-soluble, so they diffuse across the cell membrane.
- Amine hormones are thyroid and adrenal medullary hormones, synthesized by enzymes in cytoplasmic compartments.
- Thyroid hormones are stored in the thyroid gland, incorporated into thyroglobulin inside follicles.
- Hormone secretion occurs when amines are split from thyroglobulin.
Steroid Hormones
- Steroid hormones include cortisol and aldosterone, estrogen and progesterone, and testosterone.
- Figure 75-1 shows the anatomical locations of the major endocrine glands and tissues.
- Table 75-1 provides a summary of endocrine glands, hormones, functions and structures.
Feedback control of hormone secretion
- Negative feedback ensures proper hormone activity.
- Positive feedback occurs when a hormone's biological action causes additional hormone secretion, such as estrogen's effect on LH before ovulation.
- Hormone release varies cyclically due to seasonal changes, development stages, daily cycles, and sleep.
- Secretion of growth hormone increases during early sleep, reduced later.
- Oscillations in endocrine signaling are often drive by circadian clocks, with the suprachiasmatic nucleus (SCN) of the hypothalamus serving as the master clock.
- There is local clock control in peripheral endocrine tissues, such as the adrenal gland and pancreas, which have cyclical changes in sensitivity.
Hormone Transport
- Water-soluble hormones (peptides and catecholamines) dissolve in plasma.
- Steroid and thyroid hormones are mainly bound to plasma proteins.
- Protein-bound hormones cannot easily diffuse across capillaries.
- Binding to plasma proteins slows hormone clearance and provides a reservoir.
- Metabolic clearance rate influences hormone concentrations and is expressed as the volume of plasma cleared per minute.
- Hormones are cleared through metabolic destruction by tissues, by binding with tissues, through excretion by the liver into the bile, or excretion by the kidneys into the urine.
Hormone Receptors and Activation
- First step of a hormone action is to bind to specific receptors at the target cell
- Cells lacking receptors do not respond
- Hormone receptors located on target cell membrane, in the cytoplasm or the nucleus
- Hormone-receptor combination initiates cascade of reactions in the cell
- Hormone receptors are large proteins, each cell has up to 100,000
- Also highly specific for a single hormone
- The locations for the different types of hormone receptors are generally 1. On the surface of the cell membrane. 2. In the cell cytoplasm. 3. In the cell nucleus.
G Protein-Linked Hormone Receptors
- All known G protein-coupled receptors (~1000) have seven transmembrane segments.
- Inactive G proteins bind guanosine diphosphate (GDP), active proteins bind guanosine triphosphate (GTP).
- Ligand binding causes a conformational change, activating G proteins and triggering intracellular signals.
- The G proteins (trimeric) include α, β, and γ subunits when hormone bind the receptor
- Some hormones are coupled to inhibitory G proteins (denoted as G₁ proteins), whereas others are coupled to stimulatory G proteins (denoted as G5 proteins)
- This mechanism causes phosphorylation of signal transducer and activator of transcription (STAT) proteins.
Enzyme-Linked Hormone Receptors
- Enzyme-linked receptors function directly as enzymes or are closely associated with enzymes that they activate.
- When activated, enzyme-linked receptors function directly as enzymes or activate other enzymes. One exception is the leptin receptor.
- Table 75-2 lists peptide growth factors, cytokines, and hormones that use enzyme-linked receptor tyrosine kinases for cell signaling.
Intracellular Signalling
- Adenylyl cyclase catalyzes the formation of cAMP, a second messenger that controls cell activity.
- Receptors, when activated, will stimulate, cause inhibitory or stimulatory on G proteins
- Other important second messengers include calcium ions, calmodulin, and membrane phospholipid breakdown products.
- Table 75-3 shows a few of the many hormones that use the adenylyl cyclase-cAMP mechanism to stimulate their target tissues
- Table 75-4 Hormones That Use the Phospholipase C Second Messenger System
Hormones That Act on the Genetic Machinery of the Cell
- The steroid hormones increase protein synthesis in target cells.
- After proteins enter the cells, the sequence enters follows these steps: 1. The steroid hormone diffuses across the cell membrane and enters the cytoplasm of the cell. 2. The combined receptor protein. 3. The combination binds at specific points on the DNA strands in the chromosomes, which activates the transcription process of specific genes to form mRNA. 4. That mRNA diffuses into the cytoplasm.
Measurement of Hormone Concentrations in the Blood
- The method of performing ELISA is where each well is coated with an antibody that is highly specific for the hormone being assayed.
- Samples or standards are added to each of the wells, followed by a second antibody.
- In contrast to competitive radioimmunoassay methods, ELISA methods use excess antibodies so that all hormone molecules are captured in antibody-hormone complexes.
- Rosalyn Yalow and Solomon Berson developed radioimmunoassay in 1959 and revolutionized hormone measurement
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