Wk 2 L18: misc hormones

The two main hormones released by the posterior pituitary are

Oxytocin

Anti-Diuretic Hormone (ADH)

Oxytocin and Anti-Diuretic Hormone (ADH)

small peptides produced in the hypothalamus → packaged in secretory granules → transported down the axon down the infundibular stalk

Stored in the posterior pituitary

Released posterior pituitary in response to stimuli detected in the hypothalamic nuclei.

Anti-Diuretic Hormone (ADH)(vasopressin)

acts through vasopressin type-2 (V 2 ) receptors

Main stimulus of ADH secretion

Increased plasma osmolarity(hypothalamic osmoreceptors)

Decreased blood pressure (aortic and carotid baroreceptors)

ADH expression and function

V₂ receptors are expressed in the distal and collecting ducts

regulates the kidneys’ ability to regulate urine volume and osmolarity → concentrated urine in a low volume

Stimulation and action of oxytocin

G protein-coupled receptors in the myometrium (uterus) and myoepithelial cells of the mammary alveoli

Main stimulus of OT secretion: Cervical dilation(parturition), Suckling of teats(lactation)

Oxytocin effects

stimulates the force and frequency of uterine contractions during parturition

stimulates the ejection of milk by contracting myoepithelial cells surrounding the

alveoli containing milk

The pineal gland is a small structure located?

at the caudal end of the roof of the third ventricle

Function of the pineal gland

neuroendocrine transducer, converting light-dark signals into hormonal responses that regulate reproductive cycles

Function of Pinealocytes

produce melatonin (MLT), a monoamine hormone derived from tryptophan

The central nervous system, pineal gland, hypothalamus, and pituitary gland work in

coordination to regulate seasonal breeding

Anatomy of the pineal gland

The pineal gland and relation to the suprachiasmatic nucleus (SCN)

The gland is innervated by the autonomic nervous system and closely linked to the

suprachiasmatic nucleus (SCN) of the hypothalamus.

The SCN, in response to light detected by the eyes, sends signals to the pineal gland to regulate melatonin production

Where is the SCN?

How does melatonin work?

Melatonin (MLT) is secreted at night and released into the cerebrospinal fluid,

signaling darkness to the body.

MLT has G protein-coupled receptors (MLT 1 and MLT 2) located in the hypothalamus.

MLT binds to these receptors to modulate GnRH secretion

Main functions and effects of melatonin in horses

helps regulate seasonal changes, especially reproduction.

As long-day breeders, horses are more likely to mate in spring and summer when daylight increases

Melatonin levels drop during longer days, which triggers reproductive hormones and promotes estrus (heat) and fertility