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Questions and Answers
What is the primary function of T3 and T4 hormones in adults?
What is the primary function of T3 and T4 hormones in adults?
Which cells in the thyroid gland are primarily responsible for producing triiodothyronine (T3) and thyroxine (T4)?
Which cells in the thyroid gland are primarily responsible for producing triiodothyronine (T3) and thyroxine (T4)?
How does calcitonin primarily function in the body?
How does calcitonin primarily function in the body?
Which axis regulates thyroid hormone production?
Which axis regulates thyroid hormone production?
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What type of hormones are T3 and T4 classified as?
What type of hormones are T3 and T4 classified as?
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What is the effect of calcitonin on renal function?
What is the effect of calcitonin on renal function?
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Which of the following best describes hypothyroidism?
Which of the following best describes hypothyroidism?
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Which hormones are involved in calcium homeostasis within the body?
Which hormones are involved in calcium homeostasis within the body?
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What is one of the main actions of parathyroid hormone (PTH) in promoting blood calcium levels?
What is one of the main actions of parathyroid hormone (PTH) in promoting blood calcium levels?
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How does PTH affect phosphate levels in the kidneys?
How does PTH affect phosphate levels in the kidneys?
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What mechanism prevents the release of PTH when blood calcium levels rise?
What mechanism prevents the release of PTH when blood calcium levels rise?
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What effect does calcitriol have on calcium in the intestines?
What effect does calcitriol have on calcium in the intestines?
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Which type of hormones are androgens and estrogens classified as?
Which type of hormones are androgens and estrogens classified as?
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What is the primary role of parathyroid hormone concerning bone health?
What is the primary role of parathyroid hormone concerning bone health?
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Which effect does PTH have on calcium reabsorption in the kidneys?
Which effect does PTH have on calcium reabsorption in the kidneys?
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What is the role of FSH in the female reproductive cycle?
What is the role of FSH in the female reproductive cycle?
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How does prolonged exposure to PTH ultimately affect blood calcium levels?
How does prolonged exposure to PTH ultimately affect blood calcium levels?
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How do estrogen levels affect the release of GnRH, FSH, and LH early in the ovarian cycle?
How do estrogen levels affect the release of GnRH, FSH, and LH early in the ovarian cycle?
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What event triggers ovulation according to the hormonal cycle described?
What event triggers ovulation according to the hormonal cycle described?
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What does progesterone primarily promote in the reproductive cycle?
What does progesterone primarily promote in the reproductive cycle?
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What happens to estrogen and progesterone levels if fertilization does not occur?
What happens to estrogen and progesterone levels if fertilization does not occur?
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What feedback mechanism does inhibin partake in during the ovarian cycle?
What feedback mechanism does inhibin partake in during the ovarian cycle?
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What is the duration of the ovarian and uterine cycles?
What is the duration of the ovarian and uterine cycles?
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During what stage in the ovarian cycle do high levels of estrogen promote the release of GnRH, FSH, and LH?
During what stage in the ovarian cycle do high levels of estrogen promote the release of GnRH, FSH, and LH?
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What is the primary action of adrenocorticotropic hormone (ACTH)?
What is the primary action of adrenocorticotropic hormone (ACTH)?
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Which hormone is responsible for stimulating uterine contractions?
Which hormone is responsible for stimulating uterine contractions?
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What triggers estrogen production and ovulation in females?
What triggers estrogen production and ovulation in females?
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Which hormone prevents prolactin production in the anterior pituitary?
Which hormone prevents prolactin production in the anterior pituitary?
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What is the function of growth hormone (GH)?
What is the function of growth hormone (GH)?
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What is the role of ghrelin in the body?
What is the role of ghrelin in the body?
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Which hormone increases in response to high adipose tissue stores?
Which hormone increases in response to high adipose tissue stores?
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What effect does somatostatin have on digestive function?
What effect does somatostatin have on digestive function?
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How is melatonin released in response to environmental light conditions?
How is melatonin released in response to environmental light conditions?
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Chronic excessive dietary intake may lead to which of the following conditions?
Chronic excessive dietary intake may lead to which of the following conditions?
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Which hormone is primarily responsible for the feeling of fullness after eating?
Which hormone is primarily responsible for the feeling of fullness after eating?
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What is a major function of the hormones released by the body regarding dietary intake?
What is a major function of the hormones released by the body regarding dietary intake?
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What occurs when dietary intake is chronically too low?
What occurs when dietary intake is chronically too low?
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What role does progesterone play during the ovarian cycle?
What role does progesterone play during the ovarian cycle?
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What initiates ovulation in the female reproductive cycle?
What initiates ovulation in the female reproductive cycle?
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What is the effect of low to moderate estrogen levels early in the ovarian cycle?
What is the effect of low to moderate estrogen levels early in the ovarian cycle?
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What happens to estrogen and progesterone levels if fertilization does occur?
What happens to estrogen and progesterone levels if fertilization does occur?
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What hormone is responsible for inhibiting FSH release during the ovarian cycle?
What hormone is responsible for inhibiting FSH release during the ovarian cycle?
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What is the primary role of the SRY gene during embryonic development?
What is the primary role of the SRY gene during embryonic development?
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Which hormone secreted by Sertoli cells plays a role in regulating spermatogenesis?
Which hormone secreted by Sertoli cells plays a role in regulating spermatogenesis?
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What feedback mechanism helps regulate testosterone levels in males?
What feedback mechanism helps regulate testosterone levels in males?
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At what stage does oogenesis begin in females, according to the information provided?
At what stage does oogenesis begin in females, according to the information provided?
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Which hormones are primarily regulated by the hypothalamic-pituitary-gonadal (HPG) axis in males?
Which hormones are primarily regulated by the hypothalamic-pituitary-gonadal (HPG) axis in males?
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What type of hormone are T3 and T4 classified as, based on their structure?
What type of hormone are T3 and T4 classified as, based on their structure?
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Which of the following actions does calcitonin NOT participate in?
Which of the following actions does calcitonin NOT participate in?
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What is the main consequence of thyroid hormones for metabolism?
What is the main consequence of thyroid hormones for metabolism?
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How does the body primarily regulate thyroid hormone production?
How does the body primarily regulate thyroid hormone production?
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What is the role of C cells in the thyroid gland?
What is the role of C cells in the thyroid gland?
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What is the role of calcitonin in regulating blood calcium levels?
What is the role of calcitonin in regulating blood calcium levels?
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Which type of cells in the thyroid gland are responsible for producing calcitonin?
Which type of cells in the thyroid gland are responsible for producing calcitonin?
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How does the hypothalamic-pituitary-thyroid (HPT) axis regulate thyroid hormone production?
How does the hypothalamic-pituitary-thyroid (HPT) axis regulate thyroid hormone production?
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What physiological effect does activation of nuclear thyroid hormone receptors have?
What physiological effect does activation of nuclear thyroid hormone receptors have?
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What is the predominant form of thyroid hormone found circulating in the bloodstream?
What is the predominant form of thyroid hormone found circulating in the bloodstream?
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Study Notes
Thyroid Gland
- Located in the neck, anterior to the trachea
- Contains two cell types: follicular cells and C (parafollicular) cells
- Follicular cells produce triiodothyronine (T3) and tetraiodothyronine (thyroxine, T4), collectively known as thyroid hormones
- Thyroid hormones are tyrosine derivatives and lipophilic, meaning they travel bound to plasma proteins
- Most circulating thyroid hormone is T4, but target tissues convert T4 to T3
- Thyroid hormones influence most cell functions and set the basal metabolic rate
- They increase cellular metabolism and body temperature through regulation of transcription
- Thyroid hormones are essential for development in children
- Production is regulated by the hypothalamic-pituitary-thyroid (HPT) axis
- C cells produce calcitonin, a peptide hormone involved in calcium homeostasis
- Calcitonin is secreted in response to increased plasma calcium concentration
- It decreases bone resorption by osteoclasts, promotes bone calcium storage, increases renal excretion of calcium, and decreases intestinal absorption of calcium
Parathyroid Glands
- Located on the posterior surface of the thyroid gland
- Contain chief cells that produce parathyroid hormone (PTH)
- PTH is a peptide hormone that increases plasma calcium levels
- It has three main effects:
- Promotes bone resorption, increasing blood calcium levels
- Increases calcium reabsorption in the kidneys
- Increases the activity of the enzyme that converts inactive vitamin D to its active form, calcitriol, in the kidneys, which promotes calcium and phosphate absorption in the intestines
- PTH release is regulated by a negative feedback mechanism, where high blood calcium levels inhibit PTH release
Sex Hormones
- Steroid hormones involved in sexual development and reproduction
- Androgens are involved in masculine characteristics
- Estrogens are involved in feminine characteristics
- At puberty, estrogens (like estradiol) and progesterone contribute to the menstrual cycle, oogenesis, and development of secondary sexual characteristics
- The ovarian and uterine cycles occur concurrently and last approximately 28 days
- The HPG axis regulates these cycles through FSH and LH
- FSH stimulates oogenesis and estrogen release from ovarian follicles
- An LH surge triggers ovulation
- Early in the cycle, low estrogen levels inhibit the release of GnRH, FSH, and LH
- Later, high estrogen levels promote the release of these hormones
- Progesterone, released by the corpus luteum, promotes thickening of the endometrium
- It also inhibits GnRH, FSH, and LH release
- Inhibin, produced by the dominant ovarian follicle, inhibits FSH release
- If fertilization doesn't occur, estrogen and progesterone levels drop, restarting the cycle
- If fertilization occurs, estrogen and progesterone levels remain high to support the uterine environment
Appetite Hormones
- Regulate energy intake and utilization
- Ghrelin is released from stomach cells and stimulates appetite prior to a meal
- Leptin is released from adipose tissue after a meal
- It triggers feelings of satiety, suppressing appetite
- Leptin levels are proportional to adipose tissue stores
- Somatostatin, produced by delta cells in the pancreas, has a general inhibitory effect on digestion
Other Hormones
- Melatonin is produced by the pineal gland
- It influences circadian rhythms, promoting sleep
- Melatonin secretion is stimulated by low light levels detected by retinal photoreceptors
Thyroid Gland
- Thyroid gland is located in the neck, anterior to the trachea.
- Follicular cells produce triiodothyronine (T3) and tetraiodothyronine (thyroxine, T4), collectively known as thyroid hormones.
- Both thyroid hormones are lipophilic and travel in the bloodstream bound to plasma proteins.
- T4 is the predominant form of thyroid hormone in circulation, but target tissues increase circulating T3 levels by converting T4 to T3.
- Thyroid hormones influence function of most body cells and help set the basal rate of metabolism.
- C cells of the thyroid gland produce calcitonin, a peptide hormone involved in calcium homeostasis
- Calcitonin is secreted in response to increased plasma calcium concentration and is thought to reduce plasma calcium.
- Calcitonin decreases bone resorption by osteoclasts and promotes bone calcium storage.
- Calcitonin also increases renal excretion of calcium and decreases intestinal absorption of calcium.
Sex Hormones
- In an XY embryo, expression of the SRY gene on the Y chromosome promotes sex determination and development of the testes, which produce testosterone.
- Testosterone promotes the development of male sex organs.
- XX embryos do not express the SRY gene, resulting in the development of female sex organs.
- Spermatogenesis and development of secondary sexual characteristics are regulated by the hypothalamic-pituitary-gonadal (HPG) axis.
- LH promotes secretion of testosterone by Leydig cells in the testes.
- FSH promotes and maintains spermatogenesis by stimulating Sertoli cells.
- Testosterone inhibits GnRH and LH, limiting excessive testosterone production.
- Sertoli cells secrete inhibin, which inhibits FSH and controls spermatogenesis.
- Oogenesis (egg cell production) begins during the fetal stage, but is arrested during infancy and childhood due to low sex hormone levels.
- Estrogens and progesterone promote the uterine (menstrual) cycle, the resumption of oogenesis during the ovarian cycle, and the development of secondary sexual characteristics.
- Ovarian and uterine cycles occur concurrently, lasting approximately 28 days.
- FSH promotes oogenesis by stimulating estrogen release from ovarian follicles.
- An LH surge stimulates ovulation.
- Estrogens inhibit GnRH, FSH, and LH early in the ovarian cycle.
- High levels of estrogen promote GnRH, FSH, and LH release later in the cycle.
- Progesterone, released by the corpus luteum, promotes thickening of the endometrium.
- Progesterone also inhibits GnRH, FSH, and LH release.
- Inhibin produced by the ovarian follicle inhibits FSH release.
- If fertilization does not occur, estrogen and progesterone levels drop, initiating a new ovarian cycle.
- If fertilization occurs,estrogen and progesterone levels remain high to support embryonic and fetal development.
Appetite Hormones
- Ghrelin is released by stomach cells and stimulates appetite by acting on the hypothalamus.
- Leptin, released by adipose tissue, triggers feeling of satiety and suppresses appetite.
- Somatostatin, produced by delta cells in the pancreas, has a generalized inhibitory effect on digestive function.
- Retinal photoreceptors detect low light levels, which stimulates the pineal gland to secrete melatonin.
- Melatonin influences circadian rhythms and promotes drowsiness and sleep.
Other Hormones
- Glucocorticoids (cortisol, cortisone) are steroid hormones that increase blood glucose during the stress response.
- Mineralocorticoids (aldosterone) are steroid hormones that increase blood volume and pressure by promoting water and salt reabsorption in the kidney.
- Cortical sex hormones are steroid hormones that stimulate sperm cell differentiation and development of male/female sexual traits.
- Catecholamines (epinephrine, norepinephrine) are amino acid-derived hormones produced by the adrenal medulla. They increase blood glucose levels, heart rate, and blood flow to critical organs during the stress response.
- Glucagon, a peptide hormone produced by the pancreas, increases blood glucose levels.
- Insulin, also a peptide hormone produced by the pancreas, decreases blood glucose levels.
- Somatostatin, a peptide hormone produced by the pancreas and the hypothalamus, has a general inhibitory effect on digestion.
- Parathyroid hormone (PTH) is a peptide hormone that increases blood calcium levels.
- Testosterone, a steroid hormone, promotes spermatogenesis and development of male sexual characteristics.
- Estrogens (estradiol, estrone, estriol), steroid hormones, promote oogenesis and the development of female sexual characteristics.
- Progesterone, a steroid hormone, promotes thickening of the endometrium.
- Inhibin, a peptide hormone, inhibits FSH release.
Thyroid Gland
- The thyroid gland is located in the neck, anterior to the trachea.
- The thyroid gland is composed of follicular cells and C (parafollicular) cells.
- Follicular cells produce triiodothyronine (T3) and thyroxine (T4), collectively known as thyroid hormones.
- Thyroid hormones are tyrosine derivatives that contain iodine atoms.
- Thyroid hormones are lipophilic (water-insoluble) and travel in the bloodstream bound to plasma proteins.
- T4 is the most abundant circulating thyroid hormone, but target tissues convert T4 to T3 to increase circulating T3 levels.
- In adults, T3 and T4 influence the function of most cells, setting the basal rate of metabolism.
- Thyroid hormone receptors have a general stimulatory effect on many processes, increasing cellular metabolism and body temperature by regulating transcription in target cells.
- In children, thyroid hormones are crucial for development.
- Thyroid hormone production is regulated by the hypothalamus, pituitary, and thyroid gland (hypothalamic-pituitary-thyroid [HPT] axis).
- The C cells of the thyroid gland produce calcitonin.
- Calcitonin is a peptide hormone involved in calcium homeostasis.
- Calcitonin is secreted in response to high plasma calcium concentration.
- Calcitonin is thought to reduce plasma calcium by:
- Decreasing bone resorption by osteoclasts and promoting bone calcium storage.
- Increasing renal excretion of calcium.
- Decreasing intestinal absorption of calcium.
Parathyroid Hormones
- The parathyroid glands are four small endocrine glands located in the neck on the posterior surface of the thyroid gland.
- Parathyroid glands produce parathyroid hormone (PTH).
- PTH is important for regulating calcium homeostasis and phosphate homeostasis.
- PTH actions are antagonistic to those of calcitonin.
- PTH is released in response to decreased plasma calcium and acts to increase calcium levels in three ways:
- Stimulates bone resorption by indirectly acting on osteoclasts.
- Increases calcium reabsorption in the kidneys.
- Increases the activity of the enzyme that converts inactive vitamin D to its active form, calcitriol, in the kidneys.
- PTH promotes phosphate excretion in the kidneys.
- Calcitriol promotes calcium and phosphate absorption in the intestinal lumen and reabsorption of calcium in the kidneys.
Sex Hormones
- Sex hormones are steroid hormones involved in sexual development and reproduction.
- Androgens are hormones involved in developing and maintaining masculine sexual characteristics.
- Estrogens are hormones involved in developing and maintaining feminine sexual characteristics.
Hormones and Appetite
- Ghrelin is a hormone released by stomach cells that stimulates appetite.
- Leptin is a hormone released by adipose tissue that triggers feelings of satiety.
- Somatostatin, produced by delta cells of the pancreas, has a generalized inhibitory effect on digestive function.
Melatonin
- Melatonin is an amino acid-derived hormone produced by the pineal gland.
- Melatonin is thought to influence circadian rhythms and promote sleep.
- Melatonin is secreted when retinal photoreceptors detect low light levels.
Hypothalamic and Pituitary Hormones
- The hypothalamus and pituitary gland produce a variety of hormones that regulate various functions throughout the body.
- Antidiuretic hormone (ADH) (peptide) increases blood volume and pressure by increasing nephron water reabsorption (produced by the hypothalamus, released by the posterior pituitary).
- Oxytocin (peptide) stimulates uterine contractions and milk ejection from mammary glands (produced by the hypothalamus, released by the posterior pituitary).
- Adrenocorticotropic hormone (ACTH) (peptide) promotes glucocorticoid synthesis and secretion in the adrenal cortex (released by the anterior pituitary).
- Follicle-stimulating hormone (FSH) (peptide) stimulates ovarian follicle maturation and spermatogenesis (released by the anterior pituitary).
- Luteinizing hormone (LH) (peptide) stimulates estrogen production, triggers ovulation, and promotes testosterone synthesis (released by the anterior pituitary).
- Thyroid-stimulating hormone (TSH) (peptide) promotes thyroid hormone synthesis and secretion in the thyroid gland (released by the anterior pituitary).
- β-endorphins (peptide) decrease pain perception and cause feelings of euphoria (released by the anterior pituitary).
- Growth hormone (GH) (peptide) regulates growth by promoting protein synthesis and fat utilization (released by the anterior pituitary).
- Prolactin (peptide) promotes production and secretion of milk by mammary glands (released by the anterior pituitary).
- Corticotropin-releasing hormone (CRH) (peptide) stimulates ACTH production in the anterior pituitary (released by the hypothalamus).
- Gonadotropin-releasing hormone (GnRH) (peptide) stimulates FSH and LH production in the anterior pituitary (released by the hypothalamus).
- Thyrotropin-releasing hormone (TRH) (peptide) stimulates TSH production in the anterior pituitary (released by the hypothalamus).
- Prolactin-inhibiting factor (PIF, dopamine) (amino acid-derived) prevents prolactin production in the anterior pituitary (released by the hypothalamus).
Other Important Endocrine Hormones
- Glucagon (peptide) stimulates glucose release from the liver.
- Insulin (peptide) promotes glucose uptake into cells.
- Epinephrine (amine) stimulates the "fight or flight" response.
- Norepinephrine (amine) stimulates the "fight or flight" response.
- Cortisol (steroid) regulates stress response.
- Aldosterone (steroid) regulates electrolyte balance.
- Testosterone (steroid) promotes masculine characteristics.
- Estrogen (steroid) promotes feminine characteristics.
- Progesterone (steroid) supports pregnancy.
- Vitamin D (steroid) regulates blood calcium levels.
- Gastrin (peptide) stimulates gastric acid secretion.
- Secretin (peptide) stimulates pancreatic secretion.
- Cholecystokinin (peptide) stimulates gallbladder contraction.
- Renin (enzyme) regulates blood pressure.
- Erythropoietin (peptide) stimulates red blood cell production.
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This quiz explores the anatomy and functions of the thyroid gland, including its cell types, hormone production, and regulation. You'll learn about the essential roles of thyroid hormones in metabolism, development, and calcium homeostasis. Perfect for students and enthusiasts of human biology.
