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Questions and Answers
Which hormone is primarily released by the adrenal medulla during stressful situations?
Which type of stimuli involves the direct stimulation of glands by nerve fibers?
What is the primary function of cortisol in the body?
What role does the hypothalamus play in the endocrine system?
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In response to situations of fear or stress, which part of the adrenal gland is directly stimulated?
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Which type of hormone is aldosterone classified as?
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What is the primary method of hormone transportation within the endocrine system?
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Which statement best describes how hormonal secretion is initiated?
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What effect does androstenedione primarily have in the body?
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Which hormone is secreted by the parathyroid gland in response to low blood calcium levels?
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How does negative feedback affect hormone secretion within the endocrine system?
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In which scenario would humoral stimuli be activated?
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What characterizes a tropic hormone?
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Which hormone is primarily synthesized as a protein and is known to stimulate the thyroid gland?
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What is the main function of the antidiuretic hormone (ADH)?
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What type of hormone can easily pass through a cell membrane to reach its receptor?
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How does the anterior pituitary communicate with the hypothalamus?
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What triggers the hypothalamus to release antidiuretic hormone (ADH)?
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Negative feedback loops in the endocrine system serve what main purpose?
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Which of the following hormones is classified as a peptide hormone?
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Which hormone is primarily responsible for stimulating uterine contractions during labor?
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What is the significance of the hypothalamus concerning homeostasis?
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Which hormones are produced by the thyroid gland?
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What defines the release mechanism of protein hormones?
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What type of relationship exists between the hypothalamus and the anterior pituitary?
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What is the main function of the hormones produced by the posterior pituitary?
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In a positive feedback loop, the physiological response is aimed at what?
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Which hormone is regulated by its elimination through urine excretion and liver breakdown?
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What characterizes the anterior pituitary in relation to the hypothalamus?
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What is the primary function of T3 in the body?
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How do parathyroid glands respond when blood calcium levels are low?
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What role does calcitonin play in calcium metabolism?
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What are the two hormones produced by the pancreatic islets?
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Which type of hormones are produced by the adrenal cortex?
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What triggers the release of insulin from the pancreas?
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What is responsible for the regulation of calcium levels in the small intestine?
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Which gland plays a role in both endocrine and digestive systems?
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Study Notes
Hormones
- Thyroid hormones (T3 and T4), dopamine, epinephrine (adrenaline), norepinephrine, and melatonin can cross cell membranes, but some more easily than others
- Thyroid hormone can easily pass across a cell membrane to reach a receptor inside the cell, while epinephrine cannot
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Protein hormones are made of chains of amino acids and include:
- Insulin
- Thyroid-stimulating hormone (TSH)
- Follicle-stimulating hormone (FSH)
- Luteinizing hormone (LH)
- Growth hormone (GH, or human growth hormone HGH, or somatotropin)
- Parathyroid hormone (PTH)
- Antidiuretic hormone (ADH)
- Adrenocorticotropic hormone (ACTH)
- Glucagon
- Calcitonin
- Oxytocin
- Hormones from the hypothalamus
- Proteins are too large to pass through cell membranes
- Peptide and protein hormones are synthesized in stages, stored in secretory sacs, and only released when the hormone-secreting cell receives a proper stimulation
- After a hormone is secreted into the blood, three outcomes may take place:
- The hormone is either removed from the blood by the liver or kidney
- The hormone is converted to an inactive form.
- The hormone binds to its target cell and causes a change in its function
Homeostasis
- Homeostasis is a dynamic process of maintaining stable internal conditions
- The body constantly monitors variables and compares them to a set point, which is the ideal level stored for that variable.
- The hypothalamus stores the ideal set point for temperature
- Both endocrine and nervous systems work to maintain levels at or near the set point
Feedback Loops
- Negative feedback loops oppose the stimulus, helping to restore the variable to its set point
- Positive feedback loops increase the magnitude of a change, amplifying it further away from the set point
Hormonal Control
- Negative feedback is the primary mechanism controlling hormone secretion.
- As hormone levels rise, negative feedback inhibits further secretion.
- As hormone levels decrease, negative feedback triggers increased secretion.
- Negative feedback can be triggered by internal or external stimuli.
Types of Stimuli for Endocrine Gland Actions
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Humoral stimuli: Changes in blood levels of certain ions and nutrients.
- For example, parathyroid glands monitor blood calcium and secrete parathyroid hormone (PTH) when levels decrease.
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Neural stimuli: Nerve fibers directly stimulate certain glands.
- For example, the sympathetic nervous system stimulates the adrenal medulla to release norepinephrine and epinephrine in stressful situations.
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Hormonal stimuli: Hormone release due to the production of other hormones.
- For example, the hypothalamus regulates the secretion of pituitary hormones.
Endocrine Organs
- The endocrine system is a network of glands that secrete hormones into the bloodstream, affecting various bodily functions.
- The major functions of the endocrine system include:
- Regulating metabolism
- Controlling chemical reactions
- Transporting substances
- Regulating water and electrolyte balance
- Aiding in reproduction, growth, and development
- Organs that secrete hormones include:
- Hypothalamus
- Pituitary gland
- Thyroid gland
- Parathyroid glands
- Pancreas
- Adrenal glands
- Stomach, small intestine, kidneys, and heart may also secrete hormones.
Hypothalamus and Pituitary Gland
- The pituitary gland is divided into the anterior and posterior pituitary
- Often called the “master gland” due to its role in controlling other endocrine glands.
- The pituitary gland acts under orders from the hypothalamus, with which it is directly connected.
- The hypothalamus secretes hypophysiotropic hormones that regulate the anterior pituitary, while the posterior pituitary secretes tropic hormones
- The anterior pituitary is connected to the hypothalamus through blood vessels.
- The posterior pituitary is connected to the hypothalamus through neurons that secrete antidiuretic hormone (ADH) and oxytocin hormone, which are synthesized in the hypothalamus.
Antidiuretic Hormone (ADH)
- Also known as vasopressin, ADH is involved in regulating water balance and osmolarity.
- Secreted by the hypothalamus when it senses decreased blood volume or increased blood osmolarity, triggering the kidneys to reabsorb more water.
- Crucial in long-term blood pressure control, especially during dehydration.
Oxytocin
- Plays a vital role in:
- Maintaining uterine contractions during labor
- Milk ejection from the breasts during breastfeeding
- Its function in males is not fully understood
Anterior Pituitary Hormones
- Human Growth Hormone (hGH): Promotes growth and development, especially in children.
- Thyroid-stimulating hormone (TSH): Stimulates the thyroid gland to produce thyroid hormone (T3 and T4).
- Adrenocorticotropic hormone (ACTH): Stimulates the adrenal cortex to produce cortisol and other corticosteroids.
- Follicle-stimulating hormone (FSH): In females, it stimulates the growth and development of follicles in the ovaries. In males, it stimulates the production of sperm cells.
- Luteinizing hormone (LH) : In females, it triggers ovulation and production of estrogen and progesterone. In males, it stimulates the production of testosterone.
- Prolactin: Stimulates the mammary glands to produce milk.
Thyroid Gland
- Located anterior and lateral to the trachea, just inferior to the larynx.
- Secretes T3 (triiodothyronine) and T4 (thyroxine), collectively called thyroid hormone.
- Produced from tyrosine and iodide.
- T4 is secreted in larger amounts, but T3 is more active.
- Regulates metabolic rate, growth, brain development, and function
- Also secretes calcitonin, which stimulates the deposition of calcium in bones, more relevant for children than adults.
Parathyroid Glands
- Four small glands embedded in the posterior surface of the thyroid gland.
- Produce parathyroid hormone (PTH), which regulates blood calcium levels by:
- Stimulating the reabsorption of calcium from bones
- Increasing the absorption of calcium in the small intestine
Pancreas
- Part of both the endocrine and digestive systems.
- Located inferior and posterior to the stomach.
- Contains pancreatic islets (islets of Langerhans), which produce insulin and glucagon.
Insulin and Glucagon
- Insulin is released when blood glucose levels rise, helping glucose enter cells and storing excess glucose as glycogen in the liver.
- Glucagon is released when blood glucose levels fall, causing the liver to release glucose into the bloodstream.
Adrenal Glands
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Situated superior and medial to the kidneys.
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Composed of two parts:
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Adrenal cortex:
- Outer layer of the adrenal gland
- Produces over 30 steroid hormones (adrenocorticosteroids) divided into three categories:
- Mineralocorticoids: Primarily aldosterone, which regulates sodium and potassium balance.
- Glucocorticoids: Primarily cortisol, which regulates stress response and glucose metabolism.
- Androgens: Sex hormones, including testosterone, produced in smaller amounts in the adrenal cortex.
- Production is stimulated by the anterior pituitary.
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Adrenal medulla:
- Middle layer of the adrenal gland
- Stimulated by the sympathetic nervous system during stress, fear, and pain.
- Releases epinephrine (adrenaline) and norepinephrine (noradrenaline) to enhance the body's “fight-or-flight” response.
- Medulla cells can stimulate the cortex to secrete cortisol during times of stress.
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Description
This quiz covers various hormones including thyroid hormones, protein hormones, and their characteristics. Explore how these hormones interact with cell membranes and the differences between peptide and protein hormones. Test your understanding of hormonal functions and synthesis as highlighted in this section.
