Lecture 1 - 2017

Question 1

What is the HPO axis?

Answer 1

CNS -> Hypothalamus -> Pituitary -> Target Organs.

1. Hierarchical arrangement.
2. Neurosecretion.
3. Receptor specificity.
4. Feed-back loops.
5. Pulsatile secretion.

Question 2

How is reproduction controlled?

Answer 2

Hierarchical arrangement of endocrine glands with the hypothalamus as the master regulator.

Question 3

Where are hypothalmic hormones released into?

Answer 3

1. Posterior pituitary - general circulation (neural).

2. Anterior pituitary - hormones get released into portal system of veins for direct transport to ant.pit (humoral).

Question 4

What is the secretion of hormones from the hypothalamus?

Answer 4

Pulsatile - discrete bursts separated by periods (1-2hrs) of lower base line secretion and drive a correspondingly pituitary hormones. Basically hormones aren’t produced at steady levels.

Question 5

Describe the hierarchical arrangement?

Answer 5

The hypothalamus is under the control of the CNS. The result is a complex network of information transfer, and one which permits amplification, propagation and integration of signals throughout the body.

Question 6

Describe neurosecretion?

Answer 6

All neurons have secretory functions by which substances are made and act at sites away from where they are synthesised.

Question 7

Describe feedback loops?

Answer 7

Feedback may be negative or positive and by altering one component in the feedback loop it will lead to another component being affected. To limit the secretions of hormones you have a negative feedback loop - this comes from the target hormones or secretory product acting upon the gland supplying the trophic stimulus AND/OR hierarchical superior.

Question 8

Give an example of a feedback loop?

Answer 8

GnRH -> FSH + LH -> Estrogen. Estrogen acts as an inhibitor on GnRH to decrease the levels of FSH and LH.

Question 9

What are the inputs to the hypothalamus?

Answer 9

1. Light.
2. Smell.
3. Touch.
4. Sound.
5. Psychosocial.
6. Nutrition.

Question 10

Describe the light input to the hypothalamus?

Answer 10

Human reproduction is not affected by light, but what affects reproduction is seasonal breeding i.e. more babies are born in September due to breeding around Christmas and New years.

Question 11

Describe the smell input to the hypothalamus?

Answer 11

Smell has no influence on cycles, however it does have a huge behavioural influence - if you smell nice you’re more likely to find a partner for reproduction.

Question 12

Describe the touch input to the hypothalamus?

Answer 12

When a baby touches the nipple milk is released - oxytocin (released from post.pituitary).

Question 13

Describe the sound input to the hypothalamus?

Answer 13

If an experienced mother hears the baby cry, sometimes they will start to lactate - oxytocin.

Question 14

Describe the psychosocial input to the hypothalamus?

Answer 14

Pain can influence menstrual cycles as well as stress i.e. amenorrhea (being stressed can cause women to not have their periods).

Question 15

Describe the nutritional status input to the hypothalamus?

Answer 15

If a woman’s weight drops below 47kg, it can cause the HPO axis to shut down.

Question 16

What is the hypothalamus?

Answer 16

It is a 4g piece of tissue that is a funnel shaped structure leading to a downward extension in the brain. It developed from the hindmost part of the forebrain - diencephalon.

Question 17

What is the hypothalamus made of?

Answer 17

Cell bodies and axons. Cell bodies are clustered into distinct groups called nuclei (which are embedded in the funnel shaped wall of the hypothalamus).

Question 18

What are the type of hypothalmic nuclei?

Answer 18

1. Magnocellular - large cells.

2. Parvicellular - small cells.

Question 19

What are the type of magnocellular nuclei?

Answer 19

1. Paraventricular nuclei.

2. Supraoptic nuclei.

Question 20

Where do the magnocellular nuclei travel to?

Answer 20

Pars nervosa (post.pituitary) via long axons.

Question 21

Where does the paraventricular nuclei sit?

Answer 21

Alongside the third ventricle.

Question 22

Where does the supraoptic nuclei sit?

Answer 22

Above the optic tract.

Question 23

What does the magnocellular nuclei release at the posterior pituitary?

Answer 23

ADH (vasopressin) and OT (oxytocin).

Question 24

What are the parvicellular nuclei composed of?

Answer 24

Small cells:

1. Arcuate (infundibular).
2. Ventromedial.
3. Dorsomedial.
4. Preoptic.
5. Tuberals.
6. Posterior.

Question 25

What happens to the hormones synthesised in the parvicellular nuclei?

Answer 25

After travelling along the tuberoinfundibular tract of axons and into the intercellular space they go either into:
1. Capillaries in upper infundibular stem into a region known as median eminence (ME).
2. Capillaries in lower infundibular stem.
From there, the axons link indirectly to the ant.pituitary via the portal blood vessels.

Question 26

What does the parvicellular nuclei release at the anterior pituitary?

Answer 26

1. GnRH (gonadotrophin releasing hormone).
2. TRH (TSH release hormone).
3. GHRH (growth hormone releasing hormone).
4. Somatostatin (growth hormone inhibiting hormone).
5. Dopamine (prolactin inhibiting factor).
6. CRF (corticotrophin releasing factor).
7. PRH (prolactin releasing hormone).