Hypothalamic and pituitary
hormones
Tuesday, 16 November 2021 2:11 PM
Hypothalamus and pituitary
- Hypothalamus
○ Portion of the brain located below the thalamus and just above
the brainstem
○ Links the nervous system to the endocrine system via the
pituitary gland
- Pituitary
○ Protrusion of the bottom of the hypothalamus and is enclosed in
the bony cavity
§ Sella turcica
○ Dual embryonic origin
§ Anterior from glandular tissue
§ Posterior from neural tissue
- The hypothalamus / pituitary or hypophysis form a unit that exerts
control over many functions of endocrine glands and other
physiological functions
- Connected by
○ Blood flow in hypophyseal portal system
§ Begins in hypothalamus and drains into anterior pituitary
gland
○ Nerve axons connecting supraoptic and paraventricular nuclei of
hypothalamus with posterior pituitary gland
Control of anterior pituitary gland
- Hypothalamus synthesizes and secretes releasing / inhibiting factors
○ Regulate secretion of pituitary hormones
1. Stimuli from higher center activates endocrine secreting neurons to
release hypothalamic inhibiting/releasing factors to capillaries at the
median eminence
2. They travel down to anterior pituitary through hypothalamic pituitary
portal system
3. They act on endocrine secreting cells and regulate the
synthesis/secretion of anterior pituitary hormones
4. Anterior pituitary hormones are released into the capillaries and
delivered to target tissue
, 3. They act on endocrine secreting cells and regulate the
synthesis/secretion of anterior pituitary hormones
4. Anterior pituitary hormones are released into the capillaries and
delivered to target tissue
Hormones of anterior pituitary
- Many are trophic hormones that affect the morphology and secretory
activity of other endocrine glands
- Excess trophic hormone can cause hypertrophy of target gland
- Insufficient can cause atrophy of target gland
- Hormones released by hypothalamus to ATG
○ Prolactin inhibiting hormone
§ Inhibits secretion of prolactin from anterior
□ Targets mammary gland development and milk
production
□ Stimulates milk production in the alveoli of the
mammary glands and maintains lactation
® Baby suckling stimulates mechanoreceptors in
the nipple
® Stimulation sent to higher brain centers
® PIH releases from hypothalamus is inhibited
and thus stimulating the secretion of prolactin
from anterior pituitary
○ Thyrotropin releasing hormone
§ Stimulates thyroid stimulating hormone
□ Stimulates secretion of thyroid hormones by thyroid
gland
□ Stimulates the synthesis and secretion of thyroid
hormones (T3/4) from the thyroid glands
○ Corticotropin releasing hormone
§ Stimulates secretion of adrenocorticotropic hormone
(ACTH)
□ Targets secretion of glucocorticoids by the adrenal
gland
□ Stimulates the synthesis and secretion of
glucocorticoids (cortisol) from the adrenal cortex,
zona fasciculata (middle layer)
○ Growth hormone releasing hormone
§ Stimulates growth hormone (somatotroph) release
□ Promotes growth, carbohydrate and lipid
metabolism and secretion of IGFs by liver
® Insulin like growth factor
□ Indirect effect through the actions of insulin like
growth factors which is produced by the liver
® IGF has growth promoting effects e.g. cell
division on almost all cells in the body,
hormones
Tuesday, 16 November 2021 2:11 PM
Hypothalamus and pituitary
- Hypothalamus
○ Portion of the brain located below the thalamus and just above
the brainstem
○ Links the nervous system to the endocrine system via the
pituitary gland
- Pituitary
○ Protrusion of the bottom of the hypothalamus and is enclosed in
the bony cavity
§ Sella turcica
○ Dual embryonic origin
§ Anterior from glandular tissue
§ Posterior from neural tissue
- The hypothalamus / pituitary or hypophysis form a unit that exerts
control over many functions of endocrine glands and other
physiological functions
- Connected by
○ Blood flow in hypophyseal portal system
§ Begins in hypothalamus and drains into anterior pituitary
gland
○ Nerve axons connecting supraoptic and paraventricular nuclei of
hypothalamus with posterior pituitary gland
Control of anterior pituitary gland
- Hypothalamus synthesizes and secretes releasing / inhibiting factors
○ Regulate secretion of pituitary hormones
1. Stimuli from higher center activates endocrine secreting neurons to
release hypothalamic inhibiting/releasing factors to capillaries at the
median eminence
2. They travel down to anterior pituitary through hypothalamic pituitary
portal system
3. They act on endocrine secreting cells and regulate the
synthesis/secretion of anterior pituitary hormones
4. Anterior pituitary hormones are released into the capillaries and
delivered to target tissue
, 3. They act on endocrine secreting cells and regulate the
synthesis/secretion of anterior pituitary hormones
4. Anterior pituitary hormones are released into the capillaries and
delivered to target tissue
Hormones of anterior pituitary
- Many are trophic hormones that affect the morphology and secretory
activity of other endocrine glands
- Excess trophic hormone can cause hypertrophy of target gland
- Insufficient can cause atrophy of target gland
- Hormones released by hypothalamus to ATG
○ Prolactin inhibiting hormone
§ Inhibits secretion of prolactin from anterior
□ Targets mammary gland development and milk
production
□ Stimulates milk production in the alveoli of the
mammary glands and maintains lactation
® Baby suckling stimulates mechanoreceptors in
the nipple
® Stimulation sent to higher brain centers
® PIH releases from hypothalamus is inhibited
and thus stimulating the secretion of prolactin
from anterior pituitary
○ Thyrotropin releasing hormone
§ Stimulates thyroid stimulating hormone
□ Stimulates secretion of thyroid hormones by thyroid
gland
□ Stimulates the synthesis and secretion of thyroid
hormones (T3/4) from the thyroid glands
○ Corticotropin releasing hormone
§ Stimulates secretion of adrenocorticotropic hormone
(ACTH)
□ Targets secretion of glucocorticoids by the adrenal
gland
□ Stimulates the synthesis and secretion of
glucocorticoids (cortisol) from the adrenal cortex,
zona fasciculata (middle layer)
○ Growth hormone releasing hormone
§ Stimulates growth hormone (somatotroph) release
□ Promotes growth, carbohydrate and lipid
metabolism and secretion of IGFs by liver
® Insulin like growth factor
□ Indirect effect through the actions of insulin like
growth factors which is produced by the liver
® IGF has growth promoting effects e.g. cell
division on almost all cells in the body,
