Lect 26 - hypothalamus, pituitary, and GH

Flashcards covering the hypothalamus, pituitary gland, and growth hormone.

Hypothalamus

Lower part of the brain that secretes hormones controlling pituitary function.

Pituitary Gland

Gland hanging off the base of the hypothalamus that secretes hormones controlling other endocrine glands.

Hormones secreted by the anterior pituitary lobe

• thyroid stimulating hormone (TSH)

• adrenocorticotropic hormone (ACTH)

• growth hormone (GH)

• prolactin (PRL)

• gonadotropins

  • follicle stimulating hormone (FSH)

  • luteinizing hormone (LH)

• melanocyte stimulating hormone (MSH)

Hormones secreted by the posterior pituitary lobe

• antidiuretic hormone (ADH)

• oxytocin (OXT)

Anterior Pituitary (Adenohypophysis)

• Derived from epithelial tissue,

• makes up 75% of the pituitary gland;

• includes pars distalis (big part) and pars tuberalis (wraps around infundibulum)

Posterior Pituitary (Neurohypophysis)

• Derived from neuroectoderm,

• mostly composed of pituicytes;

• includes pars nervosa (large part) and infundibulum (connects with hypothalamus)

Hormones that control secretion of anterior pituitary.

Releasing Hormones (RH) and Release Inhibiting Hormones (RIH)

Neurosecretory Neurons

Synthesise hormones secreted by posterior pituitary.

Median Eminence

The region where RH and RIH are secreted from neurosecretory neurons to diffuse into the 1° capillary network.

Supraoptic and Paraventricular Nuclei

Neurosecretory cells that produce ADH and OXT.

Stimuli for oxytocin (OXT) release

Stretching of the cervix and infant suckling.

Results of oxytocin (OXT) release

Contraction of uterine smooth muscle and milk letdown reflex.

Stimulus for ADH release

Increased ECF osmolarity.

Effects of ADH

Increases water reabsorption in the kidneys and constricts arterioles.

Neurogenic Diabetes Insipidus + potential causes

Insufficient ADH secretion

• occur due to trauma, injury, infection of region of hypothalamus and posterior pituitary

Nephrogenic Diabetes Insipidus+ potential causes

Kidneys don't respond to ADH.

• genetic, medication induced, secondary to renal disease

Syndrome of Inappropriate ADH Secretion (SIADH)

Inappropriate release of ADH, when paired with MDMA can lead to overhydration and low ECF sodium.

Anterior Pituitary Hormone Producing Cells

• somatotrophs: GH

• thyrotrophs: TSH

• gonadotrophs: FSH & LH

• lactotrophs: PRL

• corticotrophs: ACTH

Hypothalamic Releasing Hormones

• thyrotropin releasing hormone (TRH)

• corticotropin-releasing hormone (CRH)

• growth hormone releasing hormone (GHRH)

• prolactin releasing hormone (PRL)

Hypothalamic Inhibiting Hormones

• growth hormone inhibitory hormone (GHIH/somatostatin)

• prolactin inhibitory hormone (PIH/dopamine)

Human Growth Hormone (GH)

Protein hormone produced by somatotrophs of anterior pituitary that promotes growth.

Somatomedins (IGFs)

Proteins formed by the liver in response to GH, mediating GH's effects.

• most important: somatomedin C (IGF-1)

Metabolic Effects of GH (8)

• increases amino acid transport into cells —> promotes protein synthesis

• increases cartilage, muscle, bone growth

• increases metabolism of fatty acids from adipose tissue

• increases use of fatty acids as energy source for cells

• glucose in blood available for cells more dependent on it

• weakens some of insulin’s actions

  • less glucose taken up from blood by muscle and adipose tissue

  • increase glucoe released into blood by liver

Factors stimulating GHRH release (8)

Deep sleep, low blood glucose, strenuous exercise, fasting, trauma, stress, testosterone, estrogen

Factors reducing GH secretion (4)

Increased blood glucose, increased fatty acids, increased somatomedins, aging

Dwarfism

Lack of GH during childhood.

Gigantism

Excess GH prior to closure of epiphyseal plates.

Acromegaly

Excess GH secretion after epiphyseal plates fuse.

Symptoms of Acromegaly

Increased muscle, bone and internal organ mass, large hands, thickened frontal bone, humpback, large tongue, large mandible, arthritis, carpal tunnel syndrome, enlarged heart, high BP, hyperglycemia, visual disturbances

Pars intermedius

• intermediate lobe

• between anterior and posterior

• mostly inactive in adult life (may produce MSH)

capillary network associated with anterior pituitary

1. Releasing RH and/or RIH secreted from neurosecretory neurons in region of median eminence at the base of hypothalamus

2. RH and RIH diffuse into 1° capillary network (plexus) 

   • The network is supplied by the superior hypophyseal artery

3. RH and RIH travel through portal vessels to 2° capillary network in anterior pituitary

4. RH and RIH diffuse out of 2° capillary network and stimulate the secretion of hormone from anterior pituitary cells

5. Blood containing ant. pituitary hormone drains into anterior hypophyseal veins to enter systemic circulation and around the body

capillary network associated with the posterior pituitary

1. Supraoptic nuclei and paraventricular nuclei which are neurosecretory cells produce ADH and OXT

2. ADH and OXT are packaged into secretory vesicles and move along axons to terminals in posterior pituitary to be stored

3. Hormones are released via. exocytosis when action potentials arrive at terminals and diffuse into capillary plexus of posterior pituitary

   • Capillary network is supplied by inferior hypophyseal arteries

   • Capillary network is drained by posterior hypophyseal veins

how does stretching of the cervix work?

1. Afferent sensory impulses from cervix conducted to hypothalamus

2. Action potentials generated in neurons of paraventricular nuclei triggering release of oxytocin from terminals in posterior pituitary

3. Results in contraction of uterine smooth muscle (positive feedback)

how does infant suckling during breastfeeding work?

1. Afferent sensory impulses from nipples conducted to hypothalamus

2. Action potentials in neurons of paraventricular nuclei triggering release of oxytocin from terminals

3. Myoepithelial cells in mammary glands → milk letdown reflex

4. Around breast tissue there are exocrine glands

   • Exocrine glands secrete product into a duct (produces milk)

   • Myoepithelial cells surround the epithelial cells and contract causing the milk in the glands to move through duct to the baby

secretion of ADH in response to increased ECF osmolarity

1. Osmoreceptors signal neurosecretory cells triggering action potentials and release of ADH from terminals in posterior pituitary

2. ADH diffused into capitally plexus and travels in blood to kidney

3. Binds to receptors on collecting duct cells in kidney and increases water reabsorption

4. Restores ECF osmolarity (negative feedback)