Hypothalamus and Pituitary Gland

Question 1

Hypothalamus

Answer 1

A part of the BRAIN
Hypothalamic nuclei control and integrate various functions including homeostasis, some somatic functions and a great deal of endocrine activity

Question 2

Anatomy of Hypothalamus

Answer 2

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)

Question 3

Pituitary Stalk

Answer 3

Extends between brain and the pituitary body
“Suspends” pituitary body from the brain
2 Distinct but connected parts: infundibular stalk and pars tuberalis

Question 4

Infundibular Stalk

Answer 4

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

Question 5

Pars Tuberalis

Answer 5

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

Question 6

Pituitary Body

Answer 6

Lies in a bony space (sella turcica) in ventral most part of cranial vault
3 Lobes: anterior, intermediate (smallest) and posterior

Question 7

Pituitary Gland Jargon

Answer 7

1. Pituitary Gland= Hypophysis
2. Anterior Lobe= Adenohypophysis= distal part= pars distalis
3. Posterior Lobe= Neurohypophysis=Neural part=pars nervosa
4. Intermediate Lobe= Pars Intermedia

Question 8

Hypothalamus and Pituitary Gland Relations

Answer 8

1. Together, control most endocrine organs/tissues
2. 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
3. Hypothalamus controls the other part of the pituitary gland and is composed of entirely different tissue than the part related to the brain
4. Therefore they are intimately related in both structure and function

Question 9

Hypophyseal Embryology Origins

Answer 9

1. Infundibulum: Nervous origin (neural tissue)- a ventral outpocketing from the BRAIN into infundibular stalk (definitive structure)
2. Oral Diverticulum: Oral origin (oral surface tissue)- a dorsal outpouching from the roof of the oral cavity

Question 10

Hypophyseal Embryology Progression

Answer 10

Both parts grow toward each other, contact and form pituitary gland:

1. Infindibulum retains its connection to the brain and forms the infidibular stalk (part of the pituitary stalk) and all of the posterior pituitary gland
2. 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

Question 11

Regional Arterial Supply to Pituitary Gland and Hypothalamic Region

Answer 11

1. Median eminence and infidibulum/infindibular stalk= direct supply, has its own dedicated arterial supply (“Artery A”)
2. Posterior Pituitary= direct supply (has its own blood supply) (“Artery B”)
3. Anterior Pituitary= No direct arterial supply, works through hypophyseal portal system

Question 12

Hypophyseal Portal System

Answer 12

Vascular supply to the anterior pituitary

1. “Artery A” forms a capillary network in median eminence and infundibular stalk
2. Capillary bed from artery A forms venules that travel to anterior pituitary
3. Venules re-arborize within the anterior pituitary into second capillary bed
4. Forms a hypophyseal portal system
5. Blood from median eminence passes through infundibular stalk and into anterior pituitary
6. Therefore, substances can be transported directly from the median eminence to the anterior pituitary gland
7. This is how the hypothalamus communicates with and controls the adenohypophyseal part of the pituitary gland

Question 13

Venous Drainage from Pituitary Gland

Answer 13

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

Question 14

Hypothalamic-Posterior Pituitary Hormones General

Answer 14

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)

Question 15

Hypothalamic-Anterior Pituitary Hormones General

Answer 15

Those hormones related to the anterior pituitary are released into the PITUITARY CIRCULATION
Target ENDOCRINE cells in the ANTERIOR PITUITARY GLAND (topic)

Question 16

Hypothalamus-Posterior Pituitary Interactions

Answer 16

1. Hypothalamus communicates DIRECTLY with the neurohypophysis
2. 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
3. Thus, the posterior pituitary gland is a DIRECT hypothalamic extension
4. Hormones made by these two hypothalamic nuclei travel to the posterior pituitary and are stored there (made in hypothalamus)
5. 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
6. The posterior pituitary gland itself makes NO hormones, rather it stores and later releases those made by the hypothalamus

Question 17

Hypothalamus-Anterior Pituitary Interactions

Answer 17

1. Hypothalamus communicates INDIRECTLY with the adenohypophysis
2. These two came from different developmental tissues and no direct TISSUE connection exists between the two so we employ the hypophyseal portal system
3. Therefore, the only connection between these two is only VASCULAR

Question 18

Process from Hypothalamus to Anterior Pituitary

Answer 18

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)

Question 19

Hypothalamic Hormones

Answer 19

All Peptide Hormones

2 Sets: those related to anterior pit and those related to posterior pit

Question 20

Hypothalamic Hormones Related to Posterior Pituitary Gland

Answer 20

1. Oxytocin

2. Vasopressin/ADH

Question 21

Hypothalamic Hormones Related to Anterior Pituitary Gland

Answer 21

1. Factors- a tropic hormone made by the hypothalamus that affects the anterior pituitary (factor=hormone)
2. 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
3. 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

Question 22

Releasing Hormones of the Hypothalamus

Answer 22

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)

Question 23

Thyrotropin Releasing Hormone

Answer 23

(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)

Question 24

Corticotropin Releasing Hormone

Answer 24

CRH/CRF- stimulates corticotropin release (adrenocorticotropic hme- ACTH) from anterior pituitary
ACTH stimulates adrenal glands release of cortisol

Question 25

Growth Hormone Releasing Hormone

Answer 25

GHRH/GHRF-Stimulates growth hormone release/secretion from anterior pituitary

Question 26

Gonadotropin-Releasing Hormone

Answer 26

GnRH/GnRF- regulates release of BOTH FSH (follicle-stimulating hormone) and LH (luteinizing hormone) from anterior pituitary

Question 27

Prolactin Releasing Hormone

Answer 27

PRH/PRF
Not entirely well characterized
Promotes release of prolactin from the anterior pituitary

Question 28

Inhibiting Hormones/Factors of the Hypothalamus

Answer 28

1. Growth hormone inhibiting hormone (GHIH/F) or Somatostatin (SS)
2. Prolactin Inhibiting Hormone (PIH/PIF)

Question 29

Prolactin Inhibiting Hormone/Factor

Answer 29

PIH/PIF

Inhibits release of prolactin from the anterior pituitary gland

Question 30

Growth Hormone Inhibiting Hormone

Answer 30

GHIH/GHIF
AKA Somatostatin
Inhibits growth hormone release from anterior pituitary gland