Podcast Beta
Questions and Answers
When a hormone binds to an intracellular receptor, what is the subsequent effect on DNA?
What determines the responsiveness of a target cell to a hormone?
What is a characteristic of thyroid hormones?
What is the result of a hormone binding to a receptor?
Signup and view all the answers
What is a consequence of hyperthyroidism?
Signup and view all the answers
What is a characteristic of hormones with intracellular receptors?
Signup and view all the answers
What is necessary for a hormone to activate a gene response?
Signup and view all the answers
What is the result of a hormone binding to a receptor in a second messenger mechanism?
Signup and view all the answers
What is the characteristic of lipid-soluble hormones?
Signup and view all the answers
What is the function of plasma proteins in hormone transport?
Signup and view all the answers
What is the result of down-regulation of insulin receptors?
Signup and view all the answers
What determines the onset and duration of hormone action?
Signup and view all the answers
What is the characteristic of water-soluble hormones?
Signup and view all the answers
What is the result of cyclic variations in hormone release?
Signup and view all the answers
What is the function of receptors in hormone action?
Signup and view all the answers
What is the effect of prolonged stimulation on hormone receptors?
Signup and view all the answers
What is the fate of protein-bound hormones?
Signup and view all the answers
What is the term for the process of reducing the number of receptors?
Signup and view all the answers
What is the primary function of corticotropin-releasing hormone?
Signup and view all the answers
How does estrogen modulate prolactin secretion?
Signup and view all the answers
What is the role of the hypothalamus in the endocrine system?
Signup and view all the answers
How does thyroid hormone regulate metabolism?
Signup and view all the answers
What is the function of vasopressin in the body?
Signup and view all the answers
What is the mechanism of action of thyroid hormone?
Signup and view all the answers
What is the role of thyrotropin-releasing hormone (TRH) in thyroid hormone regulation?
Signup and view all the answers
What is the effect of low levels of thyroid hormone on the nervous system?
Signup and view all the answers
What is the role of the liver and kidney in thyroid hormone regulation?
Signup and view all the answers
What is the effect of high levels of thyroid hormone on the body?
Signup and view all the answers
Study Notes
The Hypothalamic-Pituitary Axis
- The final hormone in the chain acts on target tissues of the body, providing multiple input sites for other hormones and neurons to achieve fine control over the endocrine system.
- Corticotropin-releasing hormone (CRH) acts on the anterior pituitary to increase secretion of corticotropin, which in turn acts on the adrenal cortex to increase secretion of cortisol.
- Cortisol feeds back to both the anterior pituitary and the ventral hypothalamus to inhibit secretion of CRH and ACTH, respectively.
Negative Feedback Loops
- Negative feedback loops control circulating levels of target gland hormones.
- Negative feedback exerted by the target hormone can be directed at the anterior pituitary, the ventral hypothalamus, or both.
- Target hormones from one series can also influence the secretion of hypothalamic or anterior pituitary hormones from another series.
Prolactin
- Prolactin is secreted in small amounts in both males and females, with slightly higher levels in adult females due to estrogen modulation.
- Estrogen increases prolactin secretion but blocks its effect on milk production.
- High levels of estrogen during pregnancy cause large secretion of prolactin, promoting growth of the breast, but inhibiting milk production until after childbirth.
Neuroendocrine Reflexes
- Neuroendocrine reflexes, such as the milk ejection reflex, are mediated in the hypothalamus.
- Suckling induces release of oxytocin, causing myoepithelial cells of the mammary glands to contract and release milk.
Chemically-Sensitive Neurons
- The hypothalamus is the highest level integrating center for the autonomic nervous system and the coordinating center for neuroendocrine interactions.
- Fibers from many parts of the brain influence the endocrine system via hypothalamic neurons.
- The cerebral cortex is widely connected to the hypothalamus, both directly and indirectly.
Osmoreceptors
- Hypothalamic neurons, including neurosecretory cells, behave like osmoreceptors, detecting osmotic changes in body fluids.
- An increase in osmolarity in body fluids excites osmoreceptors, stimulating synthesis and release of vasopressin.
- Vasopressin acts on the kidney to promote water reabsorption, restoring normal osmolarity.
Circadian Rhythms
- Neurons of the hypothalamus generate circadian patterns of hormonal release by the hypothalamic-pituitary axis.
- Circadian rhythms are approximately 24 hours long and are synchronized to the 24-hour earth day by external signals.
- Thyroid hormone is the most important factor controlling basal metabolic rate, increasing oxygen consumption, and heat production.
Thyroid Hormone
- Thyroid hormone is essential for growth, metabolism, and normal development of the nervous system.
- Absence of thyroid hormone during the fetal period and immediate postnatal months produces a form of mental retardation called cretinism.
- Thyroid hormone is essential for normal function of the nervous system in adults, amplifying the activity of the sympathetic nervous system.
Cellular Mechanism of Action
- Thyroid hormones enter cells by diffusion and are transported through the circulatory system bound to carrier proteins.
- T3 is the active form of the hormone, binding to nuclear receptors that alter gene expression.
- Nearly every cell in the body requires thyroid hormone for normal function.
Symptoms of Thyroid Hormone Imbalance
- Hyposecretion: listlessness, low BMR, feeling of no energy, feeling cold, lethargy, sleepiness, mental sluggishness, slowed speech, and slowed reflexes.
- Hypersecretion: high BMR, restlessness, hyperexcitability, sweating, irritability, high heart rate, nervousness, and exaggerated responses to stimuli.### Thyroid Hormones
- Thyronine can bind to become triiodothyronine (T3) or thyroxine (T4)
- T3 has three iodine atoms, while T4 has four iodine atoms
Hormone Characteristics
- Each hormone has its own unique onset and duration of action
- Onset and duration depend on the stimulus and feedback
Hormone Transport and Clearance
- Lipid-soluble hormones are bound to plasma proteins, which slows down their clearance
- These hormones are only active when released from plasma proteins
- Water-soluble hormones, such as protein and peptide hormones, are not bound to plasma proteins and have a faster clearance
Mechanisms of Action of Hormones
- Binding to a specific cell receptor is the first step
- Receptors are present on the surface of the cell membrane or in the cell cytoplasm
- Lipid hormones, such as steroids, act in the cell nucleus
- The number of receptors can change through down-regulation or up-regulation
Cyclical Variations of Hormone Release
- Hormone release can vary depending on various factors, such as time of day, season, or stage of development
- Examples include menstruation and cortisol levels
- Cyclical variations can be influenced by emotions and superimposed on negative and positive feedback control
Regulation of Hormone Action
- Down-regulation occurs when there is too much hormone concentration and it's not cleared easily
- Down-regulation can lead to inactivation of receptors, inactivation of intracellular protein signaling molecules, or temporary sequestration of receptors
- Up-regulation is the opposite of down-regulation, leading to increased activation of receptors and signaling molecules
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Learn about the complex control system of the endocrine system, including the role of corticotropin-releasing hormone and corticotropin in regulating hormone secretion.
