HYPOTHALAMUS AND APG

• Hypothalamus

  Portion of the brain located in the walls and floors of the third ventricle
• Hypothalamus

  • It is located just above the pituitary gland
  • It is connected to the pituitary gland by a structure called the "Infundibulum"
• 3 Zones of Hypothalamus

  • Periventricular Nuclei/Zone
  • Medial Nuclei
  • Lateral Nuclei
• Periventricular Nuclei/Zone

  Regulates the hormone levels and other messages carried in the blood
• Medial Nuclei

  Responsible for Autonomic and Somatic behavior
• Lateral Nuclei

  Responsible for Autonomic and Somatic behavior
• The hypothalamus can secrete 2 groups of hormones: releasing and inhibiting hormones
• Hypothalamic Releasing Hormones

  • Corticotropin-Releasing Hormone (CRH)
  • Thyrotropin Releasing Hormone (TRH)
  • Growth Hormone Releasing Hormone (GHRH)
  • Gonadotropin Releasing Hormone (GnRH)
  • Prolactin Releasing Factor
• Corticotropin-Releasing Hormone (CRH)

  Stimulates the secretion of ACTH (Adrenocorticotropic Hormone) in the Anterior Pituitary Gland
• Thyrotropin Releasing Hormone (TRH)

  Stimulates the secretion of TSH (Thyroid Stimulating Hormone) and PRL (Prolactin) in the Anterior Pituitary Gland
• Growth Hormone Releasing Hormone (GHRH)

  Stimulates the secretion of GH (Growth Hormone) by the Anterior Pituitary Gland
• Gonadotropin Releasing Hormone (GnRH)

  Stimulates the secretion of FSH (Follicle Stimulating Hormone) and LH (Luteinizing Hormone) in the Anterior Pituitary Gland
• Prolactin Releasing Factor

  Stimulates the secretion of Prolactin
• Tropic

  Hormone that is turning towards another gland or tissue
• Trophic

  Hormone for the enhancement of neural growth (nerve tissues)
• Hypothalamic Inhibiting Hormones

  • Growth Hormone Inhibiting Hormone (GHIH)
  • Prolactin Inhibiting Factor (PIF)
• Growth Hormone Inhibiting Hormone (GHIH)

  Inhibits the secretion of GH, TSH, PRL, ACTH
• Prolactin Inhibiting Factor (PIF)

  Inhibits the secretion of PRL, TSH, GH
• Hypothalamus would control the activity of pituitary gland that is why it is discussed first before hypothalamus
• Pituitary Gland

  Also known as Hypophysis, located within the Sella turcica, divided into anterior and posterior lobes
• Anterior Pituitary Gland

  Also known as Adenohypophysis, communicates with the hypothalamus to secrete trophic hormones
• 5 Groups of Cells in Anterior Pituitary Gland

  • Somatotrophs
  • Corticotrophs
  • Thyrotrophs
  • Gonadotrophs
  • Lactotrophs
• Somatotrophs

  Cells that produce and synthesize Growth Hormone, target organ is the liver to stimulate IGF-1 production
• Corticotrophs

  Cells that promote the synthesis of POMC, which is the precursor of ACTH, β-endorphin & β-LPH, targets the adrenal cortex
• Thyrotrophs

  Cells that promote the synthesis of TSH, targets the thyroid gland
• Gonadotrophs

  Cells responsible for the production of α & β subunits of FSH and LH, target organs are the ovaries and testes
• Lactotrophs

  Cells responsible for the formation of Prolactin, target tissue is the breast
• Somatotrophs are the predominant cell type in the anterior pituitary gland, so growth hormone is the predominant hormone
• Growth Hormone

  A single chain polypeptide consisting of 191 amino acids, structurally similar to Prolactin and Human Placental Lactogen, synthesized and secreted by somatotrophs in response to GHRH from the hypothalamus
• Growth Hormone

  • Promotes growth through stimulation of Insulin-like Growth Factors
  • Has several anabolic metabolic effects
• How Growth Hormone Exerts its Anabolic Functions

  1. Increases lipolysis to use energy from fats

  2. Increases hepatic glucose production
• Somatotrophs

  Cells of the pituitary gland that synthesize and secrete growth hormone
• Synthesis and secretion of GH by the somatotrophs

  1. In response to the secretion of GHRH by the hypothalamus

  2. Stimulated by GHRH

  3. Inhibited by somatostatin
• Growth hormone (GH)

  • Promotes growth through the stimulation of insulin-like growth factors
  • Has several metabolic effects, specifically anabolic (building up and formation)
• How GH exerts its anabolic metabolic effects

  1. Increases lipolysis (usage of energy from fats)

  2. Increases hepatic glucose production (conversion of glycogen to glucose)

  3. Decreases tissue glucose uptake

  4. Increases protein synthesis
• GH is considered a hyperglycemic agent as it can increase plasma glucose level by promoting glycogenolysis
• Secretion of GH

  • Secreted in pulsatile fashion
  • Peaks during puberty stage
  • Steady decline with increasing age
  • Increased during the first 2 hours of deep sleep
  • Mediated by GHRH (promotes release) and somatostatin (inhibits release)
• Factors that can stimulate GH secretion

  • Stress (surgery, sepsis, blood infection)
  • Exercise (physical activity)
  • Hypoglycemia (fall in blood glucose level)
  • Fasting and ingestion of certain amino acids
  • High protein intake
• Estrogen

  Can sensitize the hypothalamus to release more GHRH, leading to higher GH secretion in women compared to men
• Abnormalities of GH secretion

  • Hypopituitarism (decreased pituitary function)
  • Hyperpituitarism (excessive GH secretion)