Hormones

The Hypothalamus Cell Types

Magnocellular neurons and Parvocellular neurons

Magnocellular Neurons

Neurons in the hypothalamus with their cell bodies located in the paraventricular nucleus and the supraoptic nucleus

What region does magnocellular neurons synapse onto?

The posterior pituitary

Parvocellular neurons

Neurons in the hypothalamus with their cell bodies located in the various hypothalamic nuclei

What region does parvocellular neurons synapse onto?

The median eminence

What neurohormones does the posterior pituitary release into the general circulation?

Oxytocin and Vasopressin

Oxytocin

A neurohormone involved in the milk let-down reflex and uterine contractions during labor

Vasopressin

A neurohormone important for water retention and vasoconstriction

Is Oxytocin a hormone or a neurotransmitter?

It can be either depending on where and how it’s released

What structure is arrow 1 pointing to?

The Parvocellular Neurons

What structure is arrow 2 pointing to?

The Magnocellular neurons

What structure is arrow 3 pointing to?

The Median Eminince

What structure is arrow 4 pointing to?

The portal system

What structure is arrow 5 pointing to?

The anterior pituitary

What structure is arrow 6 pointing to?

The posterior pituitary

What do the parvocellular neurons release onto the median eminence?

Neurohormones

What does the median eminence release into the portal system to the anterior pituitary?

Neurohormones

What does the anterior pituitary release into the circulation to the endocrine glands?

Tropic hormones

In the anterior pituitary pathway, what does the endocrine glands release to reach the target cells?

Effector hormones

What does the magnocellular neurons release onto the posterior pituitary?

Oxytocin and/or Vasopressin

What does the posterior pituitary release into the general circulation to the target cells?

Oxytocin and/or Vasopressin

How are peptide hormones released?

Via exocytosis through the vesicles

Are peptide hormones hydrophobic or hydrophilic?

Hydrophilic

Are peptide hormones lipophobic or lipophilic?

Lipophobic

The receptors for peptide hormones are located:

Within the cell membrane

Peptide hormones binding to their receptors results in:

Intracellular signaling cascades

Are steroid hormones hydrophobic or hydrophilic?

Hydrophobic

Are steroid hormones lipophobic or lipophilic?

Lipophilic

Where are the receptors for steroid hormones located?

Intracellularly

Steroid hormones binding to their receptors results in:

Changes in gene expression

Steroid hormones act as ____ when bound to their receptor.

Transcription factors

Hormones are regulated by

Negative Feedback

What can effector hormones released from endocrine cells regulate?

The release of its neurohormone and tropic hormone

What cells of the hypothalamus are integral to the Hypothalamo-Pituitary Gonadal (HPG) Axis?

Parvocellular neurons

In the HPG Axis, parvocellular neurons in the preoptic area release:

Gonadotropin Releasing Hormone (GnRH)

Is GnRH a peptide, amine, or steroid hormone?

Peptide

Where is GnRH released onto?

The median eminence

What receptors does GnRH bind to?

Gonadotrophs

Gonadotrophs are found in the:

Anterior Pituitary

What hormones do gonadotrophs produce & release?

Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH)

Is LH a peptide, amine, or steroid hormone?

Peptide

Is FSH a peptide, amine, or steroid hormone?

Peptide

What does FSH do in males?

Stimulates the production of sperm

What does LH do in males?

Stimulates the production and release of testosterone

What does LH & FSH do in females?

Stimulate the production and release of progesterone and the estrogen’s

Testosterone, estrogen, and progesterone are what kind of hormones?

Effector Hormones

Are testosterone, estrogen, and progesterone peptide, amine, or steroid hormones?

Steroid

In females, LH affects what structure and how does LH affect it?

LH cause the corpus luteum to produce & release estrogen and progesterone

In females, FSH affects what structure and how does FSH affect it?

FSH causes the follicles of the ovaries to produce & release estrogen

Estrus

The time of sexual receptivity in females (near ovulation)

Women have ____ estrus, which means?

Tonic/continuous estrus, meaning they are sexually receptive throughout their menstrual cycle (not just near ovulation)

What are follicles?

Structures within the ovary that contain the unfertilized egg

The 3 phases of the female ovulatory cycle

The menstrual phase, follicular phase, and luteal phase

Approximately what days of the female ovulatory cycle does the menstrual phase occur?

~Day 1-5 (though it varies widely)

Is LH high or low during the menstrual phase?

Low

Is FSH high or low during the menstrual phase?

Low

Is estrogen high or low during the menstrual phase?

Low

Is progesterone high or low during the menstrual phase?

Low

What occurs during the follicular phase of the female ovulatory cycle?

The follicles within the ovaries develop

Approximately what days of the female ovulatory cycle does the follicular phase occur?

~Day 6-12

During the follicular phase, the primary follicle:

Develops into a Graafian follicle (aka mature follicle)

Is LH high or low during the follicular phase?

Low

Is FSH high or low during the follicular phase?

Low

Is estrogen high or low during the follicular phase?

It is steadily increasing

Is progesterone high or low during the follicular phase?

Low

What is the LH surge?

When there is a sudden, rapid increase of LH during the follicular phase

The LH surge results in:

A sudden, rapid increase in estrogen

Approximately what day does the LH surge occur during the female ovulatory cycle?

~Day 13

What is ovulation?

When the graafian follicle ruptures and releases the egg during the follicular phase

Approximately what day does ovulation occur during the female ovulatory cycle?

~Day 14

What occurs during the luteal phase of the female ovulatory cycle?

The graafian follicle becomes the corpus luteum and produces estrogen and progesterone

Approximately what days of the female ovulatory cycle does the luteal phase occur?

~Day 15-21

Is LH high or low during the luteal phase?

Low

Is FSH high or low during the luteal phase?

Low

Is estrogen high or low during the luteal phase?

High

Is progesterone high or low during the luteal phase?

High

What happens when estrogen reaches a certain threshold during the female ovulatory cycle?

It switches from causing negative feedback to positive feedback

Estrogen causing positive feedback results in:

The LH surge