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Questions and Answers
What is the primary function of the anterior pituitary gland?
What is the primary function of the anterior pituitary gland?
Which of the following is a hormone secreted by the posterior pituitary gland?
Which of the following is a hormone secreted by the posterior pituitary gland?
What connects the hypothalamus to the anterior pituitary gland?
What connects the hypothalamus to the anterior pituitary gland?
What is the primary structural feature between the anterior and posterior pituitary lobes?
What is the primary structural feature between the anterior and posterior pituitary lobes?
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How are anterior pituitary hormones delivered to the systemic circulation?
How are anterior pituitary hormones delivered to the systemic circulation?
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What type of blood supply primarily services the anterior pituitary gland?
What type of blood supply primarily services the anterior pituitary gland?
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Where are the hormones of the posterior pituitary gland synthesized?
Where are the hormones of the posterior pituitary gland synthesized?
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Which hormones are primarily transported via axoplasmic flow to the posterior pituitary?
Which hormones are primarily transported via axoplasmic flow to the posterior pituitary?
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What is the primary function of bromocriptine in relation to prolactin secretion?
What is the primary function of bromocriptine in relation to prolactin secretion?
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Which hormone is primarily synthesized in the supraoptic nuclei of the hypothalamus?
Which hormone is primarily synthesized in the supraoptic nuclei of the hypothalamus?
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How does antidiuretic hormone (ADH) affect the kidneys?
How does antidiuretic hormone (ADH) affect the kidneys?
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What effect does increased extracellular fluid osmolarity have on ADH secretion?
What effect does increased extracellular fluid osmolarity have on ADH secretion?
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What role do pituicytes play in the posterior pituitary gland?
What role do pituicytes play in the posterior pituitary gland?
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Which mechanism does ADH use to increase water permeability in renal cells?
Which mechanism does ADH use to increase water permeability in renal cells?
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What is a potential consequence of prolactin excess in women?
What is a potential consequence of prolactin excess in women?
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What is the effect of ADH on vascular smooth muscle?
What is the effect of ADH on vascular smooth muscle?
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Which hormone is secreted by somatotrophs in the anterior pituitary?
Which hormone is secreted by somatotrophs in the anterior pituitary?
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What is the primary function of the glycoprotein hormone human chorionic gonadotropin (HCG)?
What is the primary function of the glycoprotein hormone human chorionic gonadotropin (HCG)?
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Which of the following hormones is derived from the precursor pro-opiomelanocortin (POMC)?
Which of the following hormones is derived from the precursor pro-opiomelanocortin (POMC)?
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Which anterior pituitary hormone family includes thyroid-stimulating hormone (TSH)?
Which anterior pituitary hormone family includes thyroid-stimulating hormone (TSH)?
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What is the common factor among the hormones in the ACTH family?
What is the common factor among the hormones in the ACTH family?
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Which hormone is NOT secreted by the anterior pituitary?
Which hormone is NOT secreted by the anterior pituitary?
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In which condition is there an increase in POMC and ACTH levels due to negative feedback?
In which condition is there an increase in POMC and ACTH levels due to negative feedback?
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What percentage of anterior pituitary cells are responsible for secreting growth hormone?
What percentage of anterior pituitary cells are responsible for secreting growth hormone?
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Study Notes
Hypothalamic-Pituitary Relationships
- The pituitary gland, also known as the hypophysis, is connected to the hypothalamus by the pituitary stalk (infundibulum).
- The pituitary has two main distinct portions: the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis).
- A relatively avascular zone called the pars intermedia lies between these two portions.
Anterior Pituitary Hormones
- The anterior pituitary is primarily a collection of endocrine cells.
- Six peptide hormones are secreted: Thyroid-stimulating hormone (TSH), Follicle-stimulating hormone (FSH), Luteinizing hormone (LH), Growth hormone (GH), Prolactin (PRL), and Adrenocorticotropic hormone (ACTH).
- Hormones are stored in membrane-bound secretory granules.
- Release is stimulated by hypothalamic-releasing hormones or release-inhibiting hormones.
- Hormones are organized into families based on structural/functional homology.
- TSH, FSH, and LH form one family.
- ACTH forms a second family.
- GH and PRL constitute a third family.
- Hormones of the ACTH family are derived from a single precursor, pro-opiomelanocortin (POMC).
Growth Hormone (GH)
- GH is synthesized in somatotrophs of the anterior pituitary. Also called somatotropin or somatotropic hormone.
- GH secretion follows a pulsatile pattern, with bursts occurring approximately every 2 hours, with the largest burst occurring within 1 hour of falling asleep.
- During childhood GH secretion is relatively stable.
- A significant surge occurs during puberty due to estrogen in females and testosterone in males.
- Secretion is controlled by two pathways from hypothalamus.
- Stimulatory - GHRH.
- Inhibitory - Somatostatin (SRIF)
- Regulation by negative feedback loops:
- GHRH inhibits its own secretion (ultrashort-loop).
- Somatomedins (IGFs) from target tissues inhibit GH secretion
- GH and somatomedins stimulate somatostatin secretion from the hypothalamus.
Actions of GH
- Some of GH’s effects are direct on target tissues (skeletal muscle, liver, and adipose tissue).
- These direct actions are mediated by tyrosine kinase-associated receptors.
- Other actions are mediated indirectly through the production of somatomedins in the liver (e.g., somatomedin C).
- Somatomedins act through IGF receptors.
- GH has a diabetogenic effect (impairing insulin's effects).
- GH stimulates protein synthesis, and increases linear growth.
Pathophysiology of GH
- GH deficiency results in short stature, mild obesity, and delayed puberty in children.
- GH excess results in acromegaly (before puberty it causes gigantism.)
- Treatments for GH disorders involve using somatostatin analogs like octreotide.
Prolactin (PRL)
- PRL is the major hormone responsible for lactogenesis (milk production).
- It participates in breast development along with estrogen.
- PRL secretion is tonically inhibited by dopamine (also called prolactin-inhibiting factor [PIF]).
- TRH increases PRL secretion
- PRL inhibits its own secretion (negative feedback) by stimulating dopamine release from the hypothalamus.
- Pregnancy and breast-feeding are significant stimuli for PRL secretion.
Actions of PRL
- PRL stimulates milk production in the breast (in cases such as casein and lactalbumin).
- PRL is necessary for breast development from estrogens.
- PRL inhibits ovulation by decreasing synthesis and release of GnRH.
- PRL inhibits spermatogenesis by decreasing the synthesis of GnRH.
Posterior Pituitary Hormones
- ADH is made in the supraoptic nuclei.
- Oxytocin is made in the paraventricular nuclei.
- ADH (also called vasopressin) affects kidneys and blood vessels.
- Oxytocin influences the breast and uterus.
ADH (Antidiuretic Hormone)
- ADH causes the kidneys to decrease water excretion (antidiuresis.
- ADH increases H2O permeability in the late distal tubule and collecting duct (via V2 receptor).
- ADH causes vascular smooth muscle contraction (via V1 receptor).
- Factors affecting ADH secretion include increased serum osmolarity, decreased ECF volume, pain, nausea, and more.
Central Diabetes Insipidus
- Caused by failure of the posterior pituitary to secrete ADH.
- Results in large volumes of dilute urine, and serum that is too concentrated (e.g., increased Na+ concentration).
- Treated with ADH analogues.
Nephrogenic Diabetes Insipidus
- Defect in the ability of the collecting ducts' principal cells to respond to ADH.
- Results in large volumes of dilute urine, and increased serum osmolarity.
- Treated with thiazide diuretics.
Syndrome of Inappropriate ADH (SIADH)
- Autonomous secretion of ADH not regulated appropriately from an autonomous site.
- Results in excess water reabsorption and too much diluted body fluid.
- Urine is inappropriately concentrated.
- Treatable with antagonists of ADH or water restriction.
Oxytocin
- Oxytocin stimulates milk expression from breast alveoli into ducts.
- Oxytocin causes contraction of the myoepithelial cells in the breast.
- Oxytocin causes uterine contraction during pregnancy.
- Oxytocin can be used to induce labor.
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Description
Explore the intricate relationships between the hypothalamus and the pituitary gland. This quiz focuses on the anatomy and functions of the anterior and posterior pituitary, including the various hormones they release. Test your understanding of endocrine signaling and hormone interaction mechanisms.
