Hypothalamus and Pituitary Gland Overview
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Questions and Answers

What is the main hormone secreted by somatotrophs in the anterior pituitary?

  • Adrenocorticotrophic hormone (ACTH)
  • Melanocyte stimulating hormone (MSH)
  • Growth hormone (GH) (correct)
  • Prolactin

    • Which hormone is primarily responsible for stimulating milk production in the breast?

  • Adrenocorticotrophic hormone (ACTH)
  • Luteinizing hormone (LH)
  • Prolactin (correct)
  • Growth hormone (GH)

    • What is the primary regulator of growth hormone (GH) secretion from the hypothalamus?

  • Corticotrophin releasing hormone (CRH)
  • Somatostatin (correct)
  • Adrenocorticotrophic hormone (ACTH)
  • Dopamine

    • What condition results from an excess of growth hormone in children?

    <p>Gigantism</p> Signup and view all the answers

    Which factor is known to inhibit the secretion of prolactin from the anterior pituitary?

    <p>Dopamine</p> Signup and view all the answers

    Which hormone is synthesized from pro-opiomelanocortin (POMC) in the anterior pituitary?

    <p>Melanocyte stimulating hormone (MSH)</p> Signup and view all the answers

    What effect does glucocorticoid negative feedback have on ACTH secretion?

    <p>Inhibits ACTH secretion</p> Signup and view all the answers

    What is the consequence of hyposecretion of prolactin in women?

    <p>Lactation failure</p> Signup and view all the answers

    What is the primary function of the hypothalamus?

    <p>Maintaining homeostasis in the body</p> Signup and view all the answers

    Which hormone is responsible for uterine contractions during labor?

    <p>Oxytocin</p> Signup and view all the answers

    Which type of hormones are released by the hypothalamus to regulate the anterior pituitary?

    <p>Releasing hormones and releasing hormones-inhibitory hormones</p> Signup and view all the answers

    What distinguishes the anterior pituitary from the posterior pituitary?

    <p>The anterior pituitary produces its own hormones.</p> Signup and view all the answers

    What is the primary characteristic of the pituitary gland's role in the endocrine system?

    <p>It is called the 'master control gland'.</p> Signup and view all the answers

    What are the two groups of hormones produced by the hypothalamus?

    <p>Peptides and regulatory hormones</p> Signup and view all the answers

    In what part of the brain is the hypothalamus located?

    <p>Above the pituitary gland</p> Signup and view all the answers

    Which hormone is also known as antidiuretic hormone?

    <p>Arginine-vasopressin</p> Signup and view all the answers

    What is the term used to describe the involvement of all pituitary hormones in deficiency?

    <p>Panhypopituitarism</p> Signup and view all the answers

    Which condition may result from a deficiency of growth hormone (GH) in children?

    <p>Growth retardation</p> Signup and view all the answers

    What might happen to plasma ACTH and/or TSH concentrations in the later stages of progressive pituitary damage?

    <p>They become deficient after a long time</p> Signup and view all the answers

    What symptom is associated with secondary hypogonadism due to gonadotrophin deficiency?

    <p>Amenorrhoea</p> Signup and view all the answers

    Which of the following conditions is NOT a consequence of pituitary hormone deficiencies?

    <p>Hypertension</p> Signup and view all the answers

    What is the primary function of antidiuretic hormone (ADH)?

    <p>Enhances water reabsorption in the kidneys</p> Signup and view all the answers

    Prolactin deficiency can lead to failure to lactate. What specific condition can this be associated with?

    <p>Sheehan’s syndrome</p> Signup and view all the answers

    What may occur as a result of a defect in antidiuretic hormone production?

    <p>Diabetes insipidus</p> Signup and view all the answers

    How does negative feedback control the secretion of pituitary hormones?

    <p>Decreased levels of target cell hormones suppress trophic hormone secretion</p> Signup and view all the answers

    What symptom is often seen with cortisol deficiency due to ACTH deficiency?

    <p>Hypotension</p> Signup and view all the answers

    Which neurotransmitter's action is affected by certain neuroleptic drugs, leading to changes in hormone secretion?

    <p>Dopamine</p> Signup and view all the answers

    What characterizes partial hypopituitarism compared to panhypopituitarism?

    <p>Involvement of only one or more hormones</p> Signup and view all the answers

    Which of the following hormones is used therapeutically to induce labor?

    <p>Oxytocin</p> Signup and view all the answers

    What is indicated by a rise in plasma osmolality regarding antidiuretic hormone?

    <p>Increased ADH secretion</p> Signup and view all the answers

    What type of rhythms govern the release of hypothalamic and pituitary hormones?

    <p>Cyclic and circadian rhythms</p> Signup and view all the answers

    Which statement correctly describes the feedback mechanism of pituitary hormone secretion?

    <p>Rising concentrations of pituitary hormones suppress hypothalamic hormone secretion primarily through short feedback loops</p> Signup and view all the answers

    What is the purpose of measuring plasma concentrations after maximal stimulation of the target gland?

    <p>To evaluate the secretion of the pituitary hormones</p> Signup and view all the answers

    Which condition necessitates an insulin stimulation test?

    <p>To assess the growth hormone in growth deficiency</p> Signup and view all the answers

    If both target gland and trophic hormone concentrations are low or low-normal, what should be considered?

    <p>A pituitary stimulation test</p> Signup and view all the answers

    What is the required minimum increase in plasma cortisol concentrations after an adequate insulin stimulation test?

    <p>Exceeding 580 nmol/L</p> Signup and view all the answers

    Which hormone is primarily evaluated during the glucagon stimulation test?

    <p>Adrenocorticotropic hormone (ACTH)</p> Signup and view all the answers

    What immediate action should be taken before performing an insulin stimulation test?

    <p>Insert an indwelling intravenous cannula</p> Signup and view all the answers

    Which hormone's plasma concentration should be monitored specifically at 09.00 h to assess adrenocortical function?

    <p>Cortisol</p> Signup and view all the answers

    What is a common pituitary stimulation test combination used in evaluating pituitary hormones?

    <p>Insulin or glucagon plus TRH and GnRH</p> Signup and view all the answers

    Study Notes

    Hypothalamus

    • A brain structure responsible for maintaining body homeostasis
    • Regulates various bodily functions including endocrine functions, visceral functions, metabolic activities, hunger, thirst, sleep, wakefulness, emotion, sexual function, etc.
    • Produces two groups of hormones associated with the posterior and anterior pituitary glands.
    • The first group includes peptides transported to the posterior pituitary via nerve fibers for storage. These peptides are:
      • Arginine-vasopressin (ADH), also known as antidiuretic hormone
      • Oxytocin, a hormone with a structure similar to ADH, responsible for milk ejection from lactating breasts and initiating uterine contractions during labor.
    • The second group comprises regulatory hormones produced in the hypothalamus and transported through the bloodstream to the anterior pituitary. These hormones are:
      • Releasing hormones (RH) and releasing hormones-inhibitory hormones (RHIH)

    Pituitary Gland

    • A small gland located inside the skull, below the brain and above the nasal passages.
    • Connected directly to the hypothalamus.
    • Receives hormones released by the hypothalamus through tiny blood vessels, stimulating the pituitary to produce its own hormones.
    • Referred to as the “master control gland” because its hormones control the levels of hormones produced by other endocrine glands in the body.
    • Has two distinct parts: the anterior and posterior pituitary, each with unique functions.

    Anterior Pituitary Hormones

    • Cells in the anterior pituitary lobe are classified based on their staining properties as acidophils, basophils, and chromophobes.

    Acidophils

    • Two types of cells:
      • Somatotrophs: secrete growth hormone (GH) (somatotrophin), a polypeptide hormone.
        • Stimulates long bone and soft tissue growth.
        • Exerts complex actions on metabolism (amino acid, fatty acid, glucose).
        • Secretion is increased by hypoglycemia, stress, and exercise via the hypothalamus.
        • Regulated by growth hormone-releasing hormone (GHRH) from the hypothalamus, which stimulates GH release, and somatostatin, which inhibits GH release.
        • Systemic control via negative feedback by GH at the hypothalamus
        • GH insufficiency causes short stature (dwarfism), while GH excess causes gigantism in children and acromegaly in adults.
      • Lactotrophs: secrete prolactin, a polypeptide hormone.
        • Stimulates the development and growth of secretory alveoli in the breast and milk production.
        • Inhibits the reproductive system at the level of the gonads and pituitary (causes ‘lactational amenorrhea’ in women after delivery of a baby).
        • Secretion is increased by suckling.
        • Dopamine from the hypothalamus inhibits prolactin secretion.
        • Hypersecretion of prolactin can cause galactorrhoea, infertility, and amenorrhoea.
        • Hyposecretion of prolactin can cause lactation failure.

    Basophils

    • Three types of cells:
      • Corticotrophs: synthesize pro-opiomelanocortin (POMC), a large polypeptide that serves as a precursor for adrenocorticotrophic hormone (ACTH; corticotrophin), melanocyte-stimulating hormone (MSH), and β-lipotrophin.
        • ACTH stimulates the synthesis and secretion of steroids from the adrenal cortex and maintains adrenal cortical growth.
        • Secretion of ACTH is increased by stress, follows a pulsatile pattern with a diurnal rhythm.
        • Release of ACTH is stimulated by corticotrophin-releasing hormone (CRH) from the hypothalamus.
        • ACTH release is inhibited by glucocorticoid negative feedback.
        • Excess ACTH from pituitary tumors causes excess glucocorticoid secretion (Cushing’s disease), while deficiency of ACTH causes glucocorticoid deficiency (Addison's disease.)
      • Thyrotrophs: Secrete thyroid-stimulating hormone (TSH).
        • TSH stimulates the synthesis and secretion of thyroid hormones from the thyroid gland.
        • Release is stimulated by thyrotrophin-releasing hormone (TRH) from the hypothalamus.
        • Negative feedback control by thyroid hormones at the hypothalamus.
        • TSH deficiency causes hypothyroidism, while TSH excess causes hyperthyroidism.
      • Gonadotrophs: Secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
        • FSH and LH are involved in the development and function of the gonads.
        • Regulated by gonadotropin-releasing hormone (GnRH) from the hypothalamus.
        • Negative feedback control by gonadal hormones (testosterone in males and estrogen and progesterone in females).
        • Deficiency of gonadotropins leads to hypogonadism (failure of sexual maturation and reproductive function).

    Posterior Pituitary Hormones

    • Derived from neurons in the hypothalamus.
    • Synthesized in the hypothalamus and transported to the pituitary via specific carrier proteins called neurophysins.   - Hormones are stored in the posterior pituitary gland and released independently, under hypothalamic control.
    • Two main hormones:
      • Antidiuretic hormone (ADH) (Arginine vasopressin): a peptide of nine amino acids.
        • Enhances water reabsorption from the collecting ducts in the kidney.
        • Increased plasma osmolality stimulates hypothalamic osmoreceptors, leading to ADH secretion.
        • ADH enhances water reabsorption, normalizing plasma osmolality.
        • Defects in ADH lead to diabetes insipidus (hypothalamic or cranial vs renal or nephrogenic). This occurs due to a lack of ADH production or action, respectively.
      • Oxytocin: Responsible for the ejection of milk from the lactating breast and plays a role in initiating uterine contractions.
        • May be used therapeutically to induce labor.
        • Generic names: Pitocin®, Syntocinon®

    Control of Pituitary Hormone Secretion

    • Four main mechanisms:
      • Extra hypothalamic neural stimuli modify, and sometimes override, other control mechanisms.
        • Physical or emotional stress and mental illness may mimic or even trigger endocrine disease.
      • Feedback control is mediated by circulating target cell hormones.
        • A rising concentration typically suppresses trophic hormone secretion.
        • This negative feedback may directly suppress hypothalamic hormone secretion or modify its effect on pituitary cells (long feedback loop).
        • Secretion of hypothalamic hormones may also be suppressed by rising concentrations of pituitary hormone in a short feedback loop.
      • Inherent rhythms.
        • Hypothalamic, and consequently pituitary, hormones are released intermittently, either in pulses or in a regular circadian rhythm.
      • Drugs can stimulate or block the action of neurotransmitters.
        • Certain neuroleptic drugs, such as chlorpromazine and haloperidol, interfere with the action of dopamine, resulting in reduced GH secretion (reduced effect of releasing factor) and increased prolactin secretion (reduced inhibition).
        • Bromocriptine, which has a dopamine-like action, and levodopa, which is converted to dopamine, decrease prolactin secretion.

    Hypopituitarism

    • A syndrome of deficiency in pituitary hormone production that can result from disorders of the hypothalamus, pituitary, or surrounding structures.
    • Clinical features are typically absent until at least 70% of the gland is destroyed, unless there is associated hyperprolactinemia.
      • Amenorrhea and infertility may be early symptoms in this case.
    • Panhypopituitarism refers to involvement of all pituitary hormones, while partial hypopituitarism affects only one or more hormones.
    • Isolated hormone deficiencies, particularly of GH, can occur, but several hormones are usually affected.
    • Causes include tumors, infections (tuberculosis, meningitis, and syphilis), infiltrations, head injury, and more.

    Consequences of Pituitary Hormone Deficiencies

    • Progressive pituitary damage typically presents with evidence of gonadotropin and GH deficiencies.
    • Plasma ACTH and/or TSH concentrations may remain normal or become deficient months or even years later.
    • Clinical and biochemical consequences of target gland failure include:
      • Growth retardation in children due to GH deficiency.
      • Secondary hypogonadism due to gonadotropin deficiency, presenting as amenorrhea, infertility, atrophy of secondary sexual characteristics with loss of axillary and pubic hair, impotence, and/or loss of libido. Puberty is delayed in children.
      • Secondary adrenocortical hypofunction (ACTH deficiency).
        • Cortisol is critical for maintaining normal blood pressure. Hypotension may be associated with ACTH deficiency.
        • Cortisol and/or GH deficiency may cause increased insulin sensitivity with fasting hypoglycemia.
      • Secondary hypothyroidism (TSH deficiency).
        • May sometimes be clinically indistinguishable from primary hypothyroidism.
      • Prolactin deficiency, associated with failure to lactate.
        • May occur after postpartum pituitary infarction (Sheehan’s syndrome).
        • However, in hypopituitarism due to a tumor, plasma prolactin concentrations are often elevated, potentially causing galactorrhoea.

    Investigation of Suspected Hypopituitarism

    • Deficiency of pituitary hormones causes hypofunction of the target endocrine glands.
    • Investigation aims to confirm this deficiency, exclude disease of the target gland, and test pituitary hormone secretion after maximal stimulation of the gland.
    • Measurement should be made of the plasma concentrations of:
      • LH, FSH, and oestradiol (female) or testosterone (male).
      • Total or free T4 and TSH.
      • Prolactin.
      • Cortisol at 09.00 h, to assess the risk of adrenocortical insufficiency.
    • If the plasma concentration of the target gland hormone is low and the concentration of trophic hormone is raised, the affected target gland should be investigated.
    • Conversely, if the plasma concentrations of both the target gland and trophic hormones are low or low-normal, consider a pituitary stimulation test.
    • Investigation of the pituitary region using imaging techniques such as CT or MRI scanning may help elucidate the cause of hypopituitarism.
    • Combined pituitary stimulation tests (insulin or glucagon plus TRH and GnRH given as one test) are sometimes used to evaluate pituitary hormones.

    Insulin Stimulation Test

    • This test is potentially dangerous and must be conducted under direct medical supervision.
    • Indications of the insulin stimulation test include:
      • Assessment of GH in growth deficiency.
      • Assessment of ACTH/cortisol reserve.
      • Differentiation of Cushing's syndrome from pseudo-Cushing's syndrome (e.g., depression or alcohol excess).
    • After an overnight fast, an indwelling intravenous cannula is inserted.
    • After at least 30 minutes, basal samples for cortisol, GH, and glucose are collected at time 0 minute.
    • Soluble insulin is injected in a dose sufficient to lower plasma glucose concentration to less than 2.5 mmol/L and evoke symptomatic hypoglycemia.
    • Blood samples are collected at 30, 45, 60, 90, and 120 minutes after the injection for cortisol, GH, and glucose assays.
    • If hypoglycemia has been adequate, plasma cortisol concentrations should rise by more than 200 nmol/L and exceed 580 nmol/L.
    • An adequate GH response occurs with an absolute response of greater than 20 mU/L (7 µg/L).

    Glucagon Stimulation Test

    • This test is useful if the insulin hypoglycemic test is contraindicated.
    • It is essential that the test is carried out in a specialist unit by experienced staff.
    • Glucagon stimulates GH and ACTH release, likely via a hypothalamic route.
    • Patients should fast overnight.
    • An indwelling intravenous cannula should be inserted.

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    Clinical Chemistry Lecture 1: Hypothalamus & Pituitary Gland PDF

    Description

    Explore the intricate functions of the hypothalamus and pituitary gland in this quiz. Learn about their roles in regulating body homeostasis, hormone production, and various physiological processes. Test your understanding of these essential components of the endocrine system.

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