Endocrinology Chapter on Inhibin and Oestradiol

Questions and Answers

At what age do foals begin to develop a pattern of melatonin secretion?

3 weeks

7 weeks (correct)

5 weeks

9 weeks

Which gland is primarily responsible for controlling the release of gonadotrophins?

Adrenal gland

Pineal gland

Hypothalamus (correct)

Thyroid gland

What type of biological signals have a role in the hypothalamic-pituitary-ovarian axis?

A combination of hormonal and neuronal signals (correct)

Neuronal signals only

Electrical signals only

Hormonal signals only

Which of the following substances is responsible for the release of FSH and LH in vivo?

GnRH Signup and view all the answers

What is currently unknown regarding gonadotrophins?

Specific inhibitory factors related to their release Signup and view all the answers

Which substance, secreted by the hypothalamus, influences the release of pituitary hormones?

Arginine vasotocin Signup and view all the answers

Which external factors can influence the hypothalamic-pituitary-ovarian axis?

Light, olfaction, and touch Signup and view all the answers

What is the primary function of inhibin in the reproductive system?

Acts as a negative feedback mechanism on FSH secretion. Signup and view all the answers

What was determined to be the molecular structure of porcine GnRH in 1971?

A deca-peptide Signup and view all the answers

Which hormone is primarily responsible for the day-to-day fluctuations in the reproductive cycle?

Oestradiol Signup and view all the answers

What specific role do activin and follistatin play in the context provided?

Activin stimulates FSH secretion, while follistatin suppresses it. Signup and view all the answers

Which hormone produced by the corpus luteum is mentioned as having a modulating effect on the release center?

Progesterone Signup and view all the answers

What effect does the preovulatory surge of oestradiol have on the anterior pituitary?

Triggers the release of LH. Signup and view all the answers

What is the source of inhibin in the reproductive system?

Granulosa cells of large antral follicles Signup and view all the answers

What happens to the response of the anterior pituitary to GnRH after the decline in progesterone levels?

It increases due to rising oestradiol levels. Signup and view all the answers

Which hormone is mentioned as having a longer half-life compared to others in the hormonal feedback mechanism?

Inhibin Signup and view all the answers

What is the primary factor responsible for luteal regression in species such as the ewe and cow?

PGF2α activity Signup and view all the answers

Where is PGF2α primarily synthesized in mammals?

Endometrium Signup and view all the answers

What characterizes the cyclic activity of mares compared to other equine species?

Seasonal breeding pattern Signup and view all the answers

Which of the following describes the process of functional regression of the corpus luteum?

Secretion of progesterone declines rapidly. Signup and view all the answers

What is the typical reproductive behavior of native pony breed mares?

They may cycle throughout the year. Signup and view all the answers

What effect can environmental conditions have on mare reproductive cycles?

They can enhance cycling with proper feeding and lighting. Signup and view all the answers

In regards to luteal regression, what does the term 'structural regression' refer to?

The physical reduction in size of the corpus luteum. Signup and view all the answers

What is the significance of PGF2α having been first isolated from semen?

It highlights its potential link to prostaglandins. Signup and view all the answers

What role does noradrenaline play in ovarian cyclicity?

It stimulates the release of FSH and LH. Signup and view all the answers

How does serotonin affect LH secretion?

It inhibits the basal secretion of LH. Signup and view all the answers

What occurs when the conversion of dopamine to noradrenaline is inhibited?

LH release is inhibited, blocking ovulation. Signup and view all the answers

Which system contributes to the secretion of FSH and LH in domestic species?

Two separate but interrelated systems. Signup and view all the answers

What hormone's release is primarily regulated by dopamine?

Prolactin Signup and view all the answers

Which hormone is responsible for the 'oestradiol-induced' release of LH?

Noradrenaline Signup and view all the answers

What effect does the inhibition of serotonin have on ovarian cyclicity?

Increases LH secretion. Signup and view all the answers

Where is GnRH secreted in the context of ovarian cyclicity regulation?

Hypothalamic centers Signup and view all the answers

What is the approximate maximum size of the larger ovary in heifers and young cows?

3.5 cm x 3 cm x 2.8 cm Signup and view all the answers

Which characteristic describes the smaller ovary?

Flat from side to side Signup and view all the answers

During what phase will there be little variation in ovarian size due to the bulk of the developing corpus luteum (CL)?

Interoestrus phase Signup and view all the answers

What is a notable feature of the larger ovary during examinations of heifers and young cows?

It is distinctly larger than the smaller ovary. Signup and view all the answers

What dimensions characterize the smaller ovary?

2.5 cm x 1.5 cm x 1.2 cm Signup and view all the answers

When will the corpus luteum start to significantly influence the size of the ovary?

After the sixth day of the dioestrous period Signup and view all the answers

What is the primary reason for the little size difference observed during oestrus?

The regressing CL has lost its significant bulk. Signup and view all the answers

What measurement represents the dimensions of the larger ovary from side to side?

2.8 cm Signup and view all the answers

Study Notes

Hormonal Regulation of Reproduction

Inhibin produced by antral follicles impacts the hypothalamus and anterior pituitary.
Oestradiol from maturing follicles and progesterone from the corpus luteum provide negative feedback for hormonal regulation.
Episodic and tonic releases from the hypothalamus are adjusted by oestradiol and progesterone levels.
Low progesterone levels play a modulating role in the hypothalamic release center, particularly in ruminants.

Peptide Hormones' Role

Activin stimulates FSH secretion, while follistatin suppresses it; both are isolated from ovarian follicular fluid.
The exact roles of activin and follistatin in follicular growth control remain unclear in domestic species.

Gonadotropin Release Mechanism

Inhibin, released by granulosa cells of large antral follicles, regulates the anterior pituitary's response to GnRH, influencing ovulation and corpus luteum formation.
High oestradiol levels trigger the preovulatory surge of LH necessary for ovulation.

Seasonal Reproduction Control

The pineal gland assists in regulating reproduction in seasonal breeders, affecting puberty timing and gonadotropin release via melatonin.
Seasonal breeders, like mares, display cyclic activity primarily in spring to autumn, becoming anoestrous during winter.

Ovarian Size and Luteal Changes

Functional luteal regression occurs rapidly, leading to a swift decline in progesterone levels.
Structural regression of the corpus luteum is slower, impacting ovarian size changes over time.

Follicular Dynamics in Ovaries

Ovarian size difference is notable in heifers and young cows; one ovary typically larger than the other (larger: ~3.5cm; smaller: ~2.5cm).
Limited size variation occurs during the interoestrus phase due to the developing or regressing corpus luteum.

Neurotransmitter and Hormonal Interactions

Noradrenaline facilitates FSH and LH release, while dopamine inhibits LH release.
Serotonin suppresses basal LH secretion, and dopaminergic regulation is crucial for prolactin control.

Anatomic and Physiological Considerations

GnRH, released from the hypothalamus, drives FSH and LH secretion in the anterior pituitary.
PGF2α, a luteolysin, exhibits activity across multiple species in luteal regression processes.

Impact of External Factors

External stimuli such as light and touch affect the hormonal release mechanisms tied to the hypothalamic-pituitary-ovarian axis.
Increased food intake and artificial lighting can enhance cyclic activity in seasonal breeders during unfavorable conditions.

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Description

This quiz focuses on the role of inhibin and oestradiol in the regulation of the hypothalamus and anterior pituitary. It covers the feedback mechanisms and the effects of progesterone produced by the corpus luteum. Test your understanding of these vital hormones in the reproductive system.