Puberty (Repro 1) Flashcards
The hypothalamus consists of…
clusters of neuronal bodies called hypothalamic nuclei.
What do the surge center and tonic center of the hypothalamus produce?
Gonadotropin releasing hormone (GnRH)
GnRH
Gonadotropin releasing hormone.
A neurohormone with 10 amino acids.
What is the adenohypophysis?
Anterior lobe of the pituitary.
What is the neurohypophysis?
Posterior lobe of the pituitary.
What do the surge center and tonic centers communicate with?
The adenohypophysis.
What is the system of communication between the serge and tonic centers with the anterior lobe of the pituitary?
Hypothalamo-hypophyseal portal system
What is the primary portal plexus (PPP)?
A capillary network at the pituitary stalk formed by the superior hypophyseal artery.
What is the secondary portal plexus (SPP)?
A continuation of the capillary network from PPP into the anterior lobe of the pituitary.
How does the hypothalamo-hypophyseal portal system work?
- Axons from the surge and tonic centers extend to the primary portal plexus and release GnRH.
- The GnRH (now in the portal system) reaches the anterior lobe of the pituitary.
- The pituitary releases gonadotropins under the influence of GnRH.
What is the functional significance of the hypothalamo-hypophyseal portal system?
It allows small quantities of GnRH to act directly on the anterior lobe of the pituitary without being diluted through the general circulation.
It is also involved in the transport of other hormones from the hypothalamus to the AL of pituitary.
What do neurons in the paraventricular nucleus and supraoptic nuclei synthesize?
Oxytocin
Where do PVN axons extend to?
Capillary network in the posterior pituitary.
Describe the communication between the hypothalamus and posterior pituitary.
- Neurons in the PVN and supraoptic nuclei synthesize oxytocin.
- The axons from these neurons extend to the capillary network in the posterior pituitary.
- Oxytocin is transported through these axons and deposited directly into the capillary network in the posterior pituitary.
What is the main function of oxytocin?
Initiation of contractions for parturition and milk secretion.
What does the adenohypophysis produce?
Gonadotropins
- FSH
- LH
- Prolactin
What is the function of follicle stimulating hormone?
Stimulates follicular development in the ovary.
What is the function of luteinizing hormone?
Induces the ovulation of mature follicles from the ovary and luteinizes the follicular cells of an ovulated follicle, leading to the formation of a CL.
What is the function of a corpus luteum?
Secretes progesterone to maintain pregnancy.
What are the functions of ovaries?
- Oogenesis and folliculogenesis
- Hormone synthesis (estrogen/estradiol 17-B, progesterone)
What are the functions of testes?
- Spermatogenesis
- Testosterone synthesis
What are the different areas of the ovary?
Cortex and medulla
Where do follicles develop?
In the ovarian cortex.
What are primordial follicles?
A primary oocyte surrounded by a single layer of squamous epithelial cells.
Where do primordial follicles come from?
During embryogenesis, primordial germ cells migrate to the ovary and are surrounded by squamous epithelium. The primordial germ cells become primary oocytes after undergoing mitotic division but remain in mitotic prophase.
What are primary follicles?
A primary oocyte surrounded by a single layer of cuboidal follicular (granulosa) cells.
What is a secondary follicle?
An enlarged primary oocyte surrounded by several layers of follicular cells (granulosa cells). A zona pellucida is present and there are two layer types of follicular cells (theca interna and theca granulosa).
What is the function of a zona pellucida?
It forms a protective coat around the developing oocyte.
What can the fluid aspirated from an antral follicle be used for in animals and humans?
In vitro fertilization
What is a tertiary follicle?
A developing antral follicle.
What is an antral follicle?
A blister-like structure with a follicular cavity containing follicular fluid. The oocyte which is surrounded by multiple cell layers is surrounded by the fluid cavity.
What cells are transformed into luteal cells after ovulation?
Theca interna and granulosa cells.
What is luteolysis?
The process of regression/death of a CL.
How do gonadotropins exert their effects?
By interacting with plasma membrane protein receptors.
They interact with G proteins which activate adenylate cyclase. Adenylate cyclase activates protein kinases to perform various cell functions.
Are steroid hormones all similar?
Yuh
What is the parent compound of all steroid hormones?
Cholesterol
What are the steps/enzymatic conversions to produce steroid hormones?
- Starts as cholesterol
- Pregnenolone
- Progesterone
- Testosterone
- Estradiol
How many carbons are in progesterone, estrogen, and testosterone?
P = 21
E = 18
T = 19
What cells and receptors does FSH act on?
Granulosa cells through FSH receptors
What cells and receptors does LH act on?
Theca interna cells through LH receptors.
What do theca interna cells produce?
Testosterone from cholesterol under the influence of LH
Where is testosterone produced and where is it converted to estradiol?
Produced by theca interna cells.
Testosterone then diffuses to granulosa cells where it is converted to estradiol.
What is the mechanism of action of steroid hormones?
Steroid hormones are able to diffuse into the cell and into the nucleus. Steroid receptors are located within the nucleus.
Where does estradiol act on?
Brain and reproductive tract, transported through the blood.
What are the main classes of steroid hormones?
- Androgens
- Estrogens
- Progestins
How does the tonic center release GnRH?
It releases a small, maintenance level of GnRH in a pulsatile manner.
What exerts a negative feedback on the tonic center to keep GnRH secretion minimal?
Estrogen and P4 in combination.
What frequency and amplitude characterize the tonic release of GnRH?
Low frequency and amplitude.
How does the surge center release GnRH?
Only at a specific time in the cycle when there is no or low amounts of progesterone. When progesterone is low, a threshold amount of estradiol exerts a positive feedback effect on the surge center. This leads to a massive “surge” release of GnRH.
What is the release of GnRH by the serge center characterized by?
High frequency and high amplitude.
What follows the surge release of GnRH?
A surge release of LH, which is a pre-requisite for ovulation.
Which nuclei are part of the tonic center?
- Ventromedial nucleus
- Arcuate nucleus
What nuclei are part of the surge center?
- Preoptic
- Anterior hypothalamic
- Suprachiasmatic
What does the molecular binding of estrogen involve?
Binding to a nuclear receptor.
Describe the hormones present in the early follicular phase.
Low P4 and low E2
Describe the hormones present in the preovulatory follicle phase.
High E2
What causes the surge center to regress in males?
Exposure to E2 in embryo
Why does E2 not affect the female surge center?
Alpha-fetoprotein and estradiol can occur within the blood which prevents estradiol from entering the blood brain barrier.
Estradiol is not bound to E2 in males and enters the brain where it is converted to E2.
What defines age at puberty in females?
The age at which she shows first estrus accompanied by an ovulation.
What are the start of pubertal events?
An increase in GnRH secretion (tonic center becomes more active)
Why is the first ovulation “silent”?
Estrus behaviours require progesterone exposure and therefore the first ovulation is not accompanied with any estrus symptoms
What is the definition of puberty in males?
There are many different definitions:
- Age at first ejaculation
- Age at which sperm first appear in the ejaculate
- Changes in behavioural traits
How is puberty defined in bulls?
The age when ejaculate contains a threshold number of sperm (over 50 million) and 10% of sperm show progressive motility (moving forward).
