Hypothalamus & Pituitary Gland

Question 1

Hypothalamo-Pituitary Axis (what are the main functions + how do they communicate w/ each other)

Answer 1

HYOTHALAMUS & PITUITARY = MAIN ORGANISERS OF ENDORINE SYSTEM

• HYPOTHALAMUS COMMUNICATION W/ PITUITARY IS BOTH:

	○ NEURAL = POSTERIOR PITUITARY
	○ ENDOCRINE = ANTERIOR PITUITARY

	○ So, has a NEUROENDOCRINE FUNCTION

Question 2

Inputs for Hypothalamus

Answer 2

• HYPOTHALAMUS RECEIVES VARIETY OF STIMULI
  
  • MUST MAINTAIN HOMEOSTASIS + CO-ORDINATE APPROPRIATE RESPONSE BY STIMULATING VARIOUS OTHER TISSUES TO RELEASE APPROPRIATE HORMONES

Inputs: cold, stress, metabolic demands, hydrations status, exercise, day/night, menstrual cycle, sleep, breastfeeding, pregnancy, puberty

Outputs: adrenal function, thyroid function, gonadal function, lactation, parturition, growth, H2O balance, metabolism

Question 3

Hypothalamic-Pituitary Hormones (trophic hormones, what types of hormones does hypothalamus & pituitaries release)

Answer 3

• HYPOTHALAMUS + ANTERIOR PITUITARY RELEASE TROPIC & NON-TROPIC HORMONES

	○ TROPIC HORMONES = GOVERN RELEASE OF OTHER HORMONES

* HYPOTHALMIC HORMONES = NEUROHORMONES
* POSTERIOR PITUITARY HORMONES (from hypothalamus) = NEUROHORMONES
* ANTERIOR PITUITARY HORMONES = CLASSIC ENDOCRINE HORMONES

Question 4

Hypothalamic Tropic Neurohormones

Answer 4

Govern release of anterior pituitary hormones by binding to receptors

5 HYPOTHALAMIC STIMULATING HORMONES:

* Thyrotropin Releasing Hormone (TRH)
* Corticotropin Releasing Hormone (CRH)
* Growth Hormone Releasing Hormone (GHRH)
* Gonadotropin Releasing Hormone (GnRH)
* Prolactin Releasing Hormone (PRH)

2 HYPOTHALAMIC INHIBITING HORMONES:

* Growth Hormone Inhibiting Hormone (GHIH) aka Somatostatin
* Dopamine aka Prolactin Inhibiting Hormone (PIH)

Question 5

Hypothalamic-Hypophyseal Portal System

Answer 5

• NETWORK OF TINY VESSELS TRANSFERRING TROPIC HORMONE FROM HYPOTHALAMUS TO ANTERIOR PITUITARY

	○ SMALL NO. of NEUROSECRETORY NEURONS SUFFICIENT FOR CONTROL

	○ NEUROSECRETORY NEURONES RELEASE HORMONES AT MEDIAN EMINENCE

• V. SMALL AMOUNT OF HORMONES REQ. + SHORT DISTANCE = V. RAPID & DYNAMIC

Question 6

Anterior Pituitary Hormones

Answer 6

ALL ARE PEPTIDES

Thyroid Stimulating Hormone (TSH) aka thyrotropin

Adrenocorticotrophic Hormone (ACTH) aka corticotropin

Follicle Stimulating Hormone (FSH)

Luteinising Hormone (LH)

Growth Hormone (GH)

Prolactin

Question 7

What do the Anterior Pituitary Hormones Do?

Answer 7

PROLACTIN = stimulates breast to lactate (direct)

TSH = stimulated thyroid to release thyroid hormones (tropic)

ACTH = stimulated adrenal cortex to release cortisol (tropic)

GH = stimulates liver to release IGF-1 (tropic) & tissue metabolism (direct)

FSH & LH = stimulates gonads to regulate reproductive function (direct) & sex hormone release (tropic)

Question 8

Anterior Pituitary Feedback Control

Answer 8

Involves 3 integration centres: hypothalamus, anterior pituitary, target endocrine cell

Hormones themselves act as -ve feedback signal to integration systems

LONG FEEDBACK LOOP = FEEDBACK FROM ENDOCRINE TARGET to anterior pituitary & hypothalamus

SHORT FEEDBACK LOOP = FEEDBACK FROM ANTERIOT PITUITARY to hypothalamus

Question 9

Difference bwtn Anterior & Posterior Pituitary

Answer 9

Anterior/Adenohypophysis:

True endocrine tissue + Epithelial origin

Connected to hypothalamus by capillary portal system

2/3 of gland

Posterior/Neurohypophysis:

Neuroendocrine tissue + Neural origin

Neural connection to hypothalamus via infundibulum + secretes neurohormones made by hypothalamus

1/3 of gland

Question 10

Posterior Pituitary (purpose + what hormones do they release + how)

Answer 10

• STORES + RELEASES 2 PEPTIDE NEUROHORMONES: VASOPRESSIN/ANTI-DIURETIC HORMONE & OXYTOCIN

	○ Both behave as typical peptide hormones (synthesis & storage in vesicles, cell surface receptors etc.)

• SYNTHESISED IN MAGNOCELLULAR NEURONES (whose cell bodies are located in specific areas of the hypothalamus)

	○ DIFF. SUBSETS MAKE EITHER VASOPRESSIN/OXYTOCIN

• AXONS PROJECT DOWN INFUNDIBULUM TO POSTERIOR PITUITARY + TERMINAL ENDS DIRECTLY ON CAPILLARIES (don’t synapse w/ other neurones)

Question 11

Classification of Endocrine Disorders:

Answer 11

hyposecretion: too little hormone secreted
hypersecretion: too much hormone secreted
hyporesponsiveness: reduced response of the target cell
hyperreponsiveness: increased response of the target cell

1° disorders = defect is in the cells that secrete the hormone

2° disorders = too little or too much trophic hormone from pituitary

3° disorders relate to hypothalamic defects = least common

Hyporesponsiveness = alterations in receptor for hormone, disordered post-receptor events or failure of metabolic activation of hormone, (where this is required for function)

Hyperresponsiveness: could be due to permissive effects e.g. Thyroid hormone ++ adrenaline mediated lipolysis.