Intro and Hypothalamus

Question 1

The _______ is a slave to the hypothalamus, and the ____ is a slave to the ____

Answer 1

The pituitary is a slave to the hypothalamus, and the hypothalamus is a slave to the CNS

Question 2

Draw and describe the Hypo/pituitary/target organ axis

Answer 2

The Hypothalamus sends inputs to the small pituitary.

The blue lines: Hormones flowing through the blood vascular system to target organs

Target Hormones: Release hormones once activated

Question 3

Memorise this table

Answer 3

…

Question 4

Summarise step-by-step this axis

Answer 4

GNRH+ : Important hormone in reproduction. Travels ~1cm to the Pituitary

Pituitary: Has certain cells that responds to GNRH. Releases FSH(follicle stimulating hormone) and LH (luitenizing hormone)

Ovaries/testes: These have certain cells with receptors that will respond to LH and FSH, stimulating hormone production (both oestrogen and testosterone!)

Question 5

What occurs in the Hieracheal arrangment of the endocrine glands, what does this allow?

Answer 5

Amplification: start with tiny hormone in the hypothalamus → huge amounts in bloodstream

Propagation

Integration: Hormones are reliant on feedback from the other systems when producing (‘dampen down or produce more’)

Question 6

What is special about the connection of the Hypothalamus to the differing parts of the Pituitary?

Answer 6

The Pituitary is made from an anterior and a posterior lobe, which is each connected to the hypothalamusin different ways.

Hypothalamus→ anterior: Humoral connectionvia a very special portal blood system

Hypothalamus → posterior: Neural connections via ‘long’ axons

Question 7

Draw this diagram out

Answer 7

Question 8

The hypothalamus has what types of input from the sensory systems, and does that affect reproduction?

Answer 8

• Light: seasonal breeding due to # of daylight hours, so ovaries/testes only develop at certain times of the year. DOESN’T AFFECT HUMAN REPRODUCTION. Elective caesarian has a big impact on days of birth!
• Smell: phermones are actually unrelated to our breeding, and cycle coordination is unfounded
• Touch: big effect on hormone release (oxytocin)
• Sound (oxytocin)
• Psycho-social: pain (severe pain) and stress → amenorrhea
• Nutritional Status <47kg

Question 9

Whats Oxytocin?

Answer 9

Hormone released from post. pituitary → contraction of smooth muscles or myoepithelial cells in myosin

Involved in the milk response when breast feeding, released to the sound of a baby crying or the sucking touch sensation on the nipple.

Question 10

What’s Neurosecretion?

Answer 10

The process of neurons producing hormones (they don’t just send signals!)

Manufactured in the cell body → transported down the nucleus → released into blood stream

Question 11

Receptor Specificity to hormones

Answer 11

Ensure that when the large amount of hormones are released in the BS, only certain organs can respond

Question 12

WHat’s the purpose of reproductive feedback loops

Answer 12

So components of the heirachy know whats happening at each level, quite complicated. There are short loops and long loops for feedback, integrating the components at every level!

Question 13

What’s Pulsatile Secretion?

Answer 13

Hormones are produced in ‘bumps’. Eg; growth hormones after midnight. More importantly LH is released in a pulsitile fashion every two hours!

These circhorial (~1hr) pulses are characteristic to the Reproductive System, and info is contained in both amplitude and frequency!!

Big pulse: big hormone release
High frequency of pulses: Lots of hormone released

Question 14

Describe the Pulsatile release

Answer 14

Characteristic feature of hypothalamic secretions is that they are released ub discrete bursts, seperate by periods (1-2hrs) of lower base-line secretion.

This corresponds to pulsatile release of pituitary hormones.

Feed-back mechanisms modulate freq. and/or amplitude

Question 15

Where’s the origin of the Hypothalamus, and where’s it now located?

Answer 15

The hindmost part of the forebrain, the diencephalon.
Now in the base of the forebrain in the dicephalon.

The hypothalamus is shaped like a funnel, with a ‘neural-tissue’ wall, with a CSF-filled hole = the 3^rd ventricle!!

Leads to a downward extension; solid stalk of neural tissue (**part of pituitary), so not a real funnel

Question 16

W

Answer 16

Hard to find a sample where the pituitary stalk and two bulges (ant/post) are still preserved. As they are usually enclosed in bone these will just shear off with dissection

Question 17

What anatomically surrounds the hypothalamus?

Answer 17

Hypothalamic Sulcus: surrounds the hypothalamus and the thalamus.

Mamillary Body: little bulges involved in the limbic system

Optic Chiasm: Nerve fibres from the eyes that have crossed over

Question 18

Draw a diagram of the ‘funnel’ hypothalamus

Answer 18

Tuber cinereum: Surface of the funnel is lumpy

Question 19

Composition of the Hypothalamus

Answer 19

• Cell bodies + axons of hypothalamic neurons
• Axons and terminals of other neurones whose cell bodies are outside the hypothalamus
• Axons passing through: only using it as a transit route
• Glial Cells
• Blood Vessels; especially in median eminence

Question 20

What are Hypothalamic Nuclei and why are they so special?

Answer 20

Cell bodies of the hypothalamic neurons are clustered into distinct groups called ‘nuclei’, embedded in the funnel shaped wall of the hypothalamus.

“Each hypothalamic nucleus is composed of 100’s-1000’s of cell bodies, each of which have its own nucleus.

These are the bilateral sites where hormones are released.

Question 21

What are the hypothalamic Nuclei we do need to worry about?

Answer 21

Magnocellular Nuclei: composed of quite large cells

Make Vasopressin and Oxytocin!

1. Supraoptic (paired): above the optic tracts on each side
2. Paraventricular (paired): alongside the 3^rd ventricle

Axons travel to pars nervosa of the posterior pituitary, bottom of the stalk, lots of capillaries here for release!

Question 22

How is Oxtocin and VP released from the hypothalamus

Answer 22

1. PVN and SON send axons down the pituitary stalk
2. At the pars Nervosa, Oxytocin and vasopressin are directly released.

Question 23

What’s the Parvocellular Nuclei?

Answer 23

Composed, unlike the magnocellular, with quite small cells.

Know that they contain the
Arcuate (infundibular) nuclei, two of them that sit at the top of the stalk, like a doughnut around the stalk. This prduces GnRH.

Axons link to the anterior pituitary via the PORTAL blood vessels.

Question 24

Describe the process of hormones being released by the anterior pituitary

Answer 24

1. Arcuate and pre-optic produce axons that run down to the upper-indundibulum stalk and longer ones that run to the lower infundibulum stalk (containing GnRH etc)
2. From those two capillary beds we have two sets of blood vessels that come across and feed into the pars distalis (*only blood supply it gets!)
3. These vessels open up into leaky sinusoids and go out into cells of the PD→ hormone release

Question 25

What hormones are released by parivcellular nuclei?

Answer 25

• LH-FSH (gonadotrophin) releasing hormone (GnRH)
• Thyroid Stiulating Hormone releasing hormone (TRH)
• GH releasing hormone (GHRH- somatoliberin): stimulate GH in pit.
• GH inhibiting hormone (somatostatin): also produced elsewhere in the body
• Prolactin Inhibitin Factor (PIF- dopamine)
• Corticotrophin releasing factor (CRF): goes down to adrenal glands

*Each nucleus produces more than one hormone although one usually dominants