Hypothalamus and Pituitary Gland Flashcards
Hypothalamus
A part of the BRAIN
Hypothalamic nuclei control and integrate various functions including homeostasis, some somatic functions and a great deal of endocrine activity
Anatomy of Hypothalamus
Body- Forms the floor of the third ventricle of the brain (way up in the brain)
Median Eminence- Neck of a “funnel”, ventral extension of the hypothalamus extending toward but not quite reaching the pituitary gland (not a part of the pituitary gland)
Pituitary Stalk
Extends between brain and the pituitary body
“Suspends” pituitary body from the brain
2 Distinct but connected parts: infundibular stalk and pars tuberalis
Infundibular Stalk
NEURAL tissue
connects hypothalamus to posterior pituitary
Ventral extension from the median eminence that suspends the posterior pituitary from the brain
Largest part of pituitary stalk
Pars Tuberalis
GLANDULAR tissue
Doesn’t get into brain
Dorsal extension from the anterior pituitary that wraps around the infundibular stalk and holds the two together
Helps hold anterior pituitary to posterior pituitary
Pituitary Body
Lies in a bony space (sella turcica) in ventral most part of cranial vault
3 Lobes: anterior, intermediate (smallest) and posterior
Pituitary Gland Jargon
- Pituitary Gland= Hypophysis
- Anterior Lobe= Adenohypophysis= distal part= pars distalis
- Posterior Lobe= Neurohypophysis=Neural part=pars nervosa
- Intermediate Lobe= Pars Intermedia
Hypothalamus and Pituitary Gland Relations
- Together, control most endocrine organs/tissues
- Hypothalamus extends ventrally into and forms PART of pituitary gland
- This part of the pituitary gland behaves very differently from the rest of the gland - Hypothalamus controls the other part of the pituitary gland and is composed of entirely different tissue than the part related to the brain
- Therefore they are intimately related in both structure and function
Hypophyseal Embryology Origins
- Infundibulum: Nervous origin (neural tissue)- a ventral outpocketing from the BRAIN into infundibular stalk (definitive structure)
- Oral Diverticulum: Oral origin (oral surface tissue)- a dorsal outpouching from the roof of the oral cavity
Hypophyseal Embryology Progression
Both parts grow toward each other, contact and form pituitary gland:
- Infindibulum retains its connection to the brain and forms the infidibular stalk (part of the pituitary stalk) and all of the posterior pituitary gland
- Oral diverticulum loses its connection to oral cavity and forms the pars tuberalis (part of the pituitary stalk), the intermediate lobe of the pituitary gland and the anterior pituitary gland
Regional Arterial Supply to Pituitary Gland and Hypothalamic Region
- Median eminence and infidibulum/infindibular stalk= direct supply, has its own dedicated arterial supply (“Artery A”)
- Posterior Pituitary= direct supply (has its own blood supply) (“Artery B”)
- Anterior Pituitary= No direct arterial supply, works through hypophyseal portal system
Hypophyseal Portal System
Vascular supply to the anterior pituitary
- “Artery A” forms a capillary network in median eminence and infundibular stalk
- Capillary bed from artery A forms venules that travel to anterior pituitary
- Venules re-arborize within the anterior pituitary into second capillary bed
- Forms a hypophyseal portal system
- Blood from median eminence passes through infundibular stalk and into anterior pituitary
- Therefore, substances can be transported directly from the median eminence to the anterior pituitary gland
- This is how the hypothalamus communicates with and controls the adenohypophyseal part of the pituitary gland
Venous Drainage from Pituitary Gland
Both regions drain by their own veins into the systemic circulation
Therefore, whatever has been released by either the anterior or posterior pituitary gland eventually attains the systemic circulation
Hypothalamic-Posterior Pituitary Hormones General
Those hormones released into the posterior pituitary are released into the SYSTEMIC circulation at the posterior pituitary
Target NON ENDOCRINE cells in the peripheral BODY (non-tropic)
Hypothalamic-Anterior Pituitary Hormones General
Those hormones related to the anterior pituitary are released into the PITUITARY CIRCULATION
Target ENDOCRINE cells in the ANTERIOR PITUITARY GLAND (topic)
Hypothalamus-Posterior Pituitary Interactions
- Hypothalamus communicates DIRECTLY with the neurohypophysis
- Axons of neurons whose cell bodies are in two particular hypothalamic nuclei extend ventrally through the infundibular stalk and expand to form the body of the posterior pituitary gland
- Thus, the posterior pituitary gland is a DIRECT hypothalamic extension
- Hormones made by these two hypothalamic nuclei travel to the posterior pituitary and are stored there (made in hypothalamus)
- Under stimulation, these hormones are released directly into the systemic circulation at the posterior pit. and travel to have their effect on their targets in the peripheral body
- The posterior pituitary gland itself makes NO hormones, rather it stores and later releases those made by the hypothalamus
Hypothalamus-Anterior Pituitary Interactions
- Hypothalamus communicates INDIRECTLY with the adenohypophysis
- These two came from different developmental tissues and no direct TISSUE connection exists between the two so we employ the hypophyseal portal system
- Therefore, the only connection between these two is only VASCULAR
Process from Hypothalamus to Anterior Pituitary
Hypothalamus makes the appropriate hormones and releases them at the median eminence where they travel through the hypophyseal portal system to the adenohypophysis where they affect anterior pituitary function
(Hypothalamic hormones target cell of anterior pituitary gland which then makes hormones to target the body)
Hypothalamic Hormones
All Peptide Hormones
2 Sets: those related to anterior pit and those related to posterior pit
Hypothalamic Hormones Related to Posterior Pituitary Gland
- Oxytocin
2. Vasopressin/ADH
Hypothalamic Hormones Related to Anterior Pituitary Gland
- Factors- a tropic hormone made by the hypothalamus that affects the anterior pituitary (factor=hormone)
- Releasing Hormones- peptides made by the hypothalamus to control the anterior pituitary and cause it to PRODUCE and/or RELEASE a particular stimulating hormone (ex. thyroid releasing hormone- target=anterior pituitary)
Releasing- Always from hypothalamus - Inhibiting Hormones- Peptides made by the hypothalamus to control the anterior pituitary to INHIBIT production/release a specific stimulating hormone
Stimulating- always from anterior pituitary
Releasing Hormones of the Hypothalamus
All target Anterior Pituitary
TRH/TRF (thryrotropin releasing hormone/factor), CRH (corticotropin releasing hormone/factor), GnRH (gonadotropin-releasing hormone/factor), PRH (prolactin releasing hormone/factor), GHRH/GHRF (growth hormone releasing hormone/factor)
Thyrotropin Releasing Hormone
(TRH/TRF)- stimulates release of thyroid stimulating hormone (TSH) from anterior pituitary
(TRH/TRF from hypothalamus, go to anterior pituitary, release TSH, goes to thyroid gland)
Corticotropin Releasing Hormone
CRH/CRF- stimulates corticotropin release (adrenocorticotropic hme- ACTH) from anterior pituitary
ACTH stimulates adrenal glands release of cortisol
