Chapter 17 Audio

Main ideas / concepts covered

1) Hypothalamus–anterior pituitary control (general framework)

• The hypothalamus regulates the anterior pituitary by secreting regulatory hormones.
• Two categories:
  • Releasing hormones: increase anterior pituitary hormone secretion
  • Inhibiting hormones: decrease anterior pituitary hormone secretion
• Chemical nature
  • All listed releasing/inhibiting hormones are proteins, except:
  • Prolactin inhibiting hormone, which is a biogenic amine
• General signaling mechanism
  • Releasing/inhibiting hormones act via a second messenger pathway:
    • G-protein → adenylate cyclase → cyclic AMP (cAMP)

2) Anterior pituitary hormones: tropic vs non-tropic

• Anterior pituitary hormones are produced by glandular epithelial cells.
• Little hormone is stored in the anterior pituitary.
• General effects mechanism
  • Hormones affect target cells using G-protein/adenylate cyclase → cAMP
• Tropic hormones (5)
  • Stimulate another endocrine gland to release its own hormone.
• Non-tropic hormone (1)
  • Prolactin directly stimulates the mammary glands (not another endocrine gland).

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3) Releasing and inhibiting hormones (detailed list)

Releasing hormones (increase anterior pituitary secretion)

• TR (Thyrotropin-releasing hormone)
  • → anterior pituitary releases TSH
  • → thyroid gland releases thyroid hormones
• Prolactin-releasing hormone
  • → anterior pituitary releases prolactin
  • → milk production and mammary gland growth
• Gonadotropin-releasing hormone
  • → anterior pituitary releases:
    • LH (luteinizing hormone)
    • FSH (follicle-stimulating hormone)
  • Females: regulates ovarian development + secretion of estrogen and progesterone
  • Males: regulates sperm development + testosterone secretion
• Corticotropin-releasing hormone
  • → anterior pituitary releases ACTH
  • → adrenal cortex releases corticosteroids
• Growth hormone releasing hormone (GHRH)
  • → anterior pituitary releases GH (growth hormone)
  • → stimulates liver to release IGF-1 and IGF-2 (insulin-like growth factors)

Inhibiting hormones (decrease anterior pituitary secretion)

• Prolactin inhibiting hormone
  • → inhibits prolactin release
• Growth hormone inhibiting hormone
  • → inhibits growth hormone release

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4) Growth hormone (GH) pathway, actions, and regulation

Key pathway

• GHRH (from hypothalamus) controls GH release.
• GH stimulates hepatocytes (liver cells) to release IGFs (IGF-1, IGF-2).
• In circulation:
  • GH and IGFs act synergistically
  • IGFs last longer (longer half-life) → stronger/longer effects

Physiologic effects

• Increased protein synthesis
  • → increased amino acid uptake
• Increased cell division and cell differentiation
• Increased mobilization of stored fuels
  • release glucose, glycerol, fatty acids from storage

Negative feedback control

• When GH and IGF levels increase:
  • it inhibits further GH secretion
• Path described:
  • Increased GH/IGFs → inhibit GH-RH (GHRH) → reduces GH release from anterior pituitary

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5) Variables affecting GH release (especially for growth)

• Age
  • Highest in childhood, declines with age
  • Adolescents have nearly double the levels of young adults (as stated)
• Time of day
  • Peaks occur late evening before sleep
  • Growth occurs largely during sleep
• Nutrient levels
  • GH increases when:
    • amino acids increase (e.g., after a high-protein meal), or
    • glucose decreases
  • Rationale:
    • amino acids are needed for protein synthesis
    • GH increases blood glucose
• Stress/exercise
  • Can increase GH release
  • Severe emotional stress can decrease GH release in children
  • Rationale link: hypothalamus is connected to emotional control via limbic/ANS pathways

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6) Growth hormone disorders (general overview)

• Growth hormone deficiency

  • Cause: inadequate GH production (hypothalamic or pituitary issue)
  • Features:
    • short stature
    • low blood sugar
  • Treatment note:
    • GH can help, but “not to a normal state of height” (as stated)

• Pituitary gigantism

  • Cause: over-secretion of GH in childhood
  • Often due to a pituitary adenoma (benign tumor)
  • Features:
    • abnormally tall (up to ~8 ft stated)
    • enlarged internal organs
    • protruding tongue
    • blood glucose management problems
  • Treatment:
    • removal of pituitary adenoma (often eliminates over-secretion)
  • If untreated:
    • can lead to early death (as stated)

• Acromegaly

  • Cause: excessive GH in adults
  • Features:
    • overgrowth of bones that are still responsive (face, hands, feet)
    • protruding jaw
    • enlarged internal organs (e.g., liver)
    • increased glucose release → may progress toward diabetes
  • Mechanism described:
    • loss of negative feedback control
  • Treatment described:
    • growth hormone inhibiting hormone to inhibit GH release

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7) Thyroid: structure, transport, synthesis, regulation, and effects

Thyroid structure and cell types

• Thyroid follicles filled with colloid
  • colloid is protein-rich, jelly-like fluid
• Follicular cells (simple cuboidal epithelium)
  • surround follicles
  • make thyroglobulin and help produce T3 and T4
• Parafollicular (C) cells
  • produce calcitonin
  • stimulated by high blood calcium
  • also mentioned as associated with stress/exercise

Hormone transport

• T3/T4 travel in blood bound to carrier proteins:
  • albumin or TBG (thyroxine-binding globulin)
• Thyroid hormone is lipid soluble
  • emphasized as enabling “direct gene activation”

Calcitonin effects

• Decreases blood calcium by:
  • inhibiting osteoclast activity
  • increasing kidney calcium excretion in urine

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Thyroid hormone synthesis, storage, and release (stepwise)

1. Iodide is taken from blood and moved into the colloid.
2. Thyroglobulin is synthesized in follicular cells and released into colloid via exocytosis.
3. In the colloid:
   • thyroglobulin binds to tyrosine
   • tyrosine becomes iodinated:
     • attaches to one or two iodides
   • forms pre-T3 or pre-T4 while still bound to thyroglobulin
4. Pre-T3/pre-T4 + thyroglobulin are internalized back into follicular cells via endocytosis.
5. Inside follicular cells:
   • enzymes cleave thyroglobulin to release T3 and T4
6. T3/T4 enter blood by simple diffusion.
7. Carrier proteins are already available in blood.
8. Remaining thyroglobulin is reprocessed/rebuilt in follicular cells, restarting the cycle.

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Thyroid regulation (hypothalamus → anterior pituitary → thyroid)

• Hypothalamus releases TR
• TR stimulates anterior pituitary to release TSH
• TSH binds receptors on thyroid → stimulates follicular cells to release thyroid hormones

Factors that stimulate TR release (as listed)

• low/high thyroid hormone blood levels (TR depends on levels)
• cold temperatures
• pregnancy
• high altitude
• hypoglycemia

Negative feedback

• When thyroid hormone levels rise:
  • it inhibits TR and TSH release

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Thyroid hormone effects on body systems (main effects)

• In all cells
  • increased metabolic rate
  • increased synthesis of sodium/potassium pumps → heat production → increased temperature
  • increased amino acid and glucose uptake
  • increased protein synthesis
  • increased glucose use → increased ATP production
  • increased numbers of cellular respiration enzymes in mitochondria
• Liver
  • increased glycogenolysis and gluconeogenesis
• Fat cells
  • increased lipolysis
  • release glycerol and fatty acids
  • “glucose sparing effect” to save glucose for the brain
• Lungs and heart
  • increased respiration rate (more oxygen demand)
  • increased blood flow
  • increased heart rate and force of contraction

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Thyroid disorders (overview)

• Hypothyroidism (low thyroid hormone)

  • Features: low metabolic rate, weight gain, feeling cold, lethargy, photophobia (as stated)
  • Causes mentioned:
    • decreased iodine uptake
    • reduced pituitary stimulation
    • immune destruction of thyroid
    • post-therapy hypothyroidism (thyroid removal or radioactive iodine)
  • Treatment:
    • oral replacement of thyroid hormone
  • Possible associated issue:
    • goiter from insufficient dietary iodine

• Hyperthyroidism (high thyroid hormone)

  • Features: increased metabolic rate, weight loss, hyperactivity, heat intolerance
  • Causes mentioned:
    • excessive T4 ingestion
    • overly active thyroid nodules
    • Graves disease

• Graves disease

  • Autoimmune condition: antibodies mimic TSH
  • Bind TSH receptors → abnormally high thyroid hormone release
  • Hallmark mentioned:
    • bulging/protruding eyes (exophthalmos)
  • Treatment approach mentioned:
    • remove thyroid; then take hormone supplements

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8) Adrenal glands: anatomy, hormones, cortisol regulation, and disorders

Anatomy

• Adrenal glands sit on top of kidneys.
• Two main parts:

Adrenal cortex (outer yellow region due to lipids)

• Zona glomerulosa
  • makes mineralocorticoids (main: aldosterone)
  • regulates sodium/potassium balance
  • increases sodium and water retention + potassium secretion
  • severe imbalance can cause death (as stated)
• Zona fasciculata (referred to as zona vasculada in subtitles)
  • makes glucocorticoids including cortisol
  • released in response to ACTH
• Zona reticularis
  • makes gonadocorticoids / adrenal androgens
  • male hormone production is secondary (testes are primary)

Adrenal medulla (inner red-brown, vascular)

• Releases catecholamines:
  • epinephrine and norepinephrine
• Controlled by the sympathetic nervous system
• Response to emotional/physical stress
• Prolongs fight-or-flight response

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Cortisol regulation (CR → ACTH → cortisol) and daily rhythm

Cortisol release stimulation

• Hypothalamus releases CR when detectors sense cortisol changes (e.g., low cortisol).
• Cortisol fluctuates daily:
  • peaks just before waking
  • high levels occur late in the sleep cycle
• Light/dark cycles influence rhythm:
  • retina → signals hypothalamus
• Emotional and physical stress increases:
  • CR, ACTH, and cortisol
• Therefore cortisol is called the stress hormone

Stepwise pathway described

• Hypothalamus releases CR
• CR stimulates anterior pituitary to release ACT
• ACT stimulates adrenal cortex to release cortisol
• Transport:
  • cortisol binds transport proteins (e.g., corticosteroid binding globulin or albumin)
• Action:
  • cortisol unbinds and leaves circulation to act on target cells

Cortisol effects (metabolic shifts)

• Increases blood nutrient availability:
  • Liver: increased glucose release via glycogenolysis and gluconeogenesis
  • Adipose: increased lipolysis → fatty acids + glycerol
  • Body cells:
    • increased protein catabolism → amino acids released for liver
    • decreased glucose uptake by body cells
• Result: “glucose sparing effect” to spare glucose for the brain

Negative feedback

• Rising cortisol inhibits CR release (reduces upstream signal)

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Adrenal cortex disorders (overview)

• Addison’s disease (low glucocorticoids)

  • Cause: hypo-secretion of glucocorticoids
    • malformed adrenal glands
    • impaired steroid synthesis enzymes
    • autoimmune destruction
  • Mechanism described:
    • lack of cortisol → no inhibition of ACT release
    • ACT becomes high due to lack of negative feedback
  • Symptoms:
    • weight loss
    • fatigue/weakness
    • hypotension (low blood pressure)
    • skin darkening
  • Treatment: oral corticosteroids

• Cushing syndrome (high glucocorticoids)

  • Cause:
    • chronic excess glucocorticoids via therapy, or
    • overproduction from adrenal gland
  • Side effects listed:
    • osteoporosis
    • muscle weakness
    • salt retention
    • redistribution of body fat (face/back mention)
    • kidney stones
    • female menstrual irregularities

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Speakers / Sources featured

• None explicitly identified (the subtitles present a single instructor/lecturer voice without naming).