Hypothalamus and Pituitary Gland

Question 1

describe where the third ventricle is

Answer 1

it is narrow vertical slit in the forebrain that runs antero-posteriorly along the midline above the midbrain is lies between the left and right thalamus, underneath the corpsu calosum

Question 2

what is either side of the third ventricle

Answer 2

right and left thalamus

Question 3

what connects the third and fourth ventricle

Answer 3

• Cerebral aqua duct connects third and fourth ventricle

Question 4

tissue from the third ventricle….

Answer 4

forms the stalk of the pituitary gland

Question 5

what does the hypothalamus consist of

Answer 5

The hypothalamus consists of a group of nuclei on the sides of the anterior most part of the third ventricle

Question 6

where is the optic nerves and optic chiasma in relation to the hypothalamus

Answer 6

the optic nerves and optic chiasm lie immediately below the hypothalamus

Question 7

how is the pituitary gland connected to the hypothalamus

Answer 7

• pituitary gland is a pea sized structure that lies along the midline in a bony recess below the hypothalamus
• it is connected to the hypothalamus by the pituitary stalk

Question 8

what does the hypothalamus do

Answer 8

• controls the glands in the body by the action of the pituitary

Question 9

what nervous system is the hypothalamus connected do

Answer 9

• the autonomic nervous system
• axons from the hypothalamus project to the cells in the lateral medulla of the brainstem that activate the sympathetic and parasympathetic systems

Question 10

describe how the fight or flight reflex works

Answer 10

• Visual or auditory information about a threat is detected by the cerebral cortex.
• The cortex sends an alerting message to the hypothalamus.
• The hypothalamus sends an alerting message to the medulla.
• The medullary cells project down the spinal cord to activate the sympathetic nervous system so you are ready for fight or flight.

Question 11

what does the grey matter of the hypothalamus contain

Answer 11

• it contains many small nucleic with separate functions

Question 12

where does the pituitary sit

Answer 12

• It sits in the pituitary fossa in the sphenoid bone

Question 13

describe the structure of the pituitary

Answer 13

• There is an anterior and posterior pituitary lobe
• There is also a small intermediate part
• The pituitary stalk is sometimes called infundibulum
• Laterally it is surrounded by a complex venous structure called the cavernous sinuses

Question 14

what are the two kinds of outputs to the pituitary from the hypothalamus

Answer 14

1. some hypothalamic cell bodies have axons that project down the pituitary stalk to the posterior lobe of the pituitary
   - they release peptides into the capillaries in the posterior pituitary
   - these betides then circulate in the blood to other organs
2. other hypothalamic cell bodies have shorter axons that release peptides onto a capillary plexus in the neck of the pituitary stalk
   - It is a connection from a nerve to a capillary therefore it is a secretory synapse
   - There are secretory endings of the axon which secrete peptides and enter the capillaries of the posterior pituitary and into the system

Question 15

describe what is the part fo the anterior and posterior pirtuiary part of the brain

Answer 15

• Anterior pituitary is an endocrine gland

- the posterior pituitary is part of the brain

Question 16

what does the anterior lobe develop from

Answer 16

• The anterior lobe develops from ectoderm in the roof of the mouth.
• This pouch of tissue eventually migrates upwards and separates from the oral cavity.

Question 17

what does the posterior lobe develop from

Answer 17

• The posterior pituitary develops from a downward pouch of brain tissue in the floor of the third ventricle.
• The upper part of the pouch remains connected to the hypothalamus and forms the pituitary stalk.
• The region where the stalk joins the hypothalamus is called the median eminence.

Question 18

what bone is the cavernous sinus in

Answer 18

sphenoid bone

Question 19

what is in the cavernous sinus and where are they in it

Answer 19

• The oculomotor nerves and V1 & V2 branches of the trigeminal, these run along the lower lateral border
• The final part of the internal carotid artery
• CN 3 & 4 run along the upper lateral border of the sinus and enter the bony orbit via the superior orbital fissure.
• CN 6 runs through the middle of the mesh below the carotid.

Question 20

what is special about the cavernous sinus

Answer 20

• There is an artery going through the vein, internal carotid goes through the vein

Question 21

where do veins leaving the pituitary drain

Answer 21

• Veins leaving the pituitary drain into the cavernous sinus

Question 22

what parts of homeostasis does the hypothalamus control

Answer 22

• temperature
• body water
• body weight
• sleep waking cycles
• reproduction
• it is also the link between your senses and activation of the autonomic nervous system

Question 23

what are the two classes of of sensors in the hypothalamus

Answer 23

• things that detect skin temperature

- things that detect pain

Question 24

describe how temperature is sensed

Answer 24

1, Blood temperature is detected through thermoreceptors within the anterior nucleus of the hypothalamus
2, Skin temperature is detected through cutaneous thermoreceptors (normally C fibre endings). Information passes up the lateral spinothalamic tract to the medulla and then hypothalamus
3, Information from these two sources is compared to the internal set point and either heat loss or heat gain mechanisms activated

Question 25

how is heat lost if body temperature is too high

Answer 25

1. Sweat glands under the skin secrete sweat. This causes heat loss by evaporation; however, a lot of essential water is lost.
2. Cutaneous vasodilation occurs. This redirects blood into the superficial capillaries in the skin increasing heat loss by convection and conduction.
3. The person becomes relatively inactive. Muscle activity generates heat, which increases core temperature.

Question 26

Describe how heat can be gained

Answer 26

1) Sweat stops being produced.
2) The erector pili muscles attached to hair follicles contract, lifting the hair follicle upright (piloerection). This makes hairs stand on end which acts as an insulating layer, trapping heat.
3) Arterioles carrying blood to superficial capillaries under the surface of the skin constrict, thereby rerouting blood away from the skin and towards the warmer core of the body. This prevents blood from losing heat to the surroundings. In extremely cold conditions excessive vasoconstriction leads to numbness and pale skin.
4) Shivering is triggered. This increases heat production as activity generates heat in muscle cells. Shivering is more effective than exercise at producing heat because the animal remains still. In man shivering uses glucose as a fuel source. When the readily available glucose is used up shivering stops and the person becomes hypothermic

Question 27

How can we adapt to hot or cold climates

Answer 27

On the longer term, we can adapt to hot or cold climates. Adaptation to heat involves increasing the number and activity of sweat glands, and increasing cutaneous capillaries. Adaptation to cold involves increased secretion of thyroid stimulating hormone, and deposition of body fat

Question 28

How is water balance controlled

Answer 28

• it is controlled by hypothalamus
• Axons from the cells in the paraventricular nucleus and the supraoptic nucleus of the hypothalamus send axons down to the posterior pituitary.
• Here they end as secretory terminals on capillaries within the posterior pituitary.
• The terminals secrete ANTIDIURETIC HORMONE
• ADH reduces water loss in urine by increasing water reabsorbtion in the kidney collecting ducts.

Question 29

what is produced by the posterior pituitary

Answer 29

oxytocin

Question 30

what is the role of oxytocin

Answer 30

• This releases stored milk from the breast during the milk let down reflex, the sucking action on the breast is transmitted in the hypothalamus which releases oxytocin and this makes smooth muscle in the milk ducts contract to expel milk - this is a neuro-hormonal reflex
• Can also be released during childbirth, causes the uterus to expand, it acts on the smooth muscle to produce the persteal contraction which push the baby out

Question 31

where does the oxytocin nerves go

Answer 31

• they branch and go back into other parts of the hypothalamus
• go into the limbic system

Question 32

why is the oxytocin important

Answer 32

• The oxytocin released when your baby is suckling makes the mother feel good
• This helps the mother baby bond
• Makes mother less prone to post natal depression

Question 33

why are ADH and oxytocin released in the posterior pituitary

Answer 33

• They have a fast response
• They are released rapidly on demand
• They are not under complex negative feedback control

Question 34

what is the blood supply to the anterior pituitary

Answer 34

• portal system

Question 35

describe the blood supply to the anterior pituitary

Answer 35

• there are two sets of capillaries in series
• first set are in the neck infundibulum) of the pituitary stalk. T
• the second set are in the anterior pituitary body, with a portal venin connecting the two

Question 36

how do axons act on the anterior pituitary

Answer 36

• Axons from hypothalamic nuclei such as the arcuate, suprachiasmatic and preoptic nuclei have short axons that end on capillaries in the first part of the portal system.
• They secrete ‘releasing hormones’ into these capillaries, which then pass down from the capillaries and are released on to the cells of the anterior pituitary

Question 37

what is the difference between the anterior pituitary and posterior pituitary

Answer 37

In the anterior pituitary there is hormone secreting cells compared to the posterior pituitary
- anterior pituitary releases hormones cyclically whereas posterior are released on demand

Question 38

what are the 6 hypothalamic releasing hormones from the anterior pituitary

Answer 38

1. CRH
2. GnRH
3. TRH
4. GHRH
5. GHIH
6. PIH

Question 39

what are the 6 hypothalamic releasing hormones and what do they do from the anterior pituitary

Answer 39

1) CRH (corticotrophin releasing hormone) releases Adrenocorticotrophic hormone (ACTH)
2) GnRH (gonadotrophin releasing hormone) releases both Luteinising Hormone (LH) & Follicle stimulating hormone (FSH)
3) TRH (thyrotropin releasing hormone) releases Thyroid Stimulating Hormone (TSH)
4) GHRH (growth hormone releasing hormone) releases Growth Hormone (GH)
5) GHIH (growth hormone inhibiting hormone: somatostatin) inhibits release of Growth Hormone (GH)
6) PIF (prolactin inhibiting factor, i.e. dopamine) inhibits Prolactin release – most tumours of the pituitary are prolactinomas as these cells tend to be toncially active and downregulated by an inhibitor mechanism

Question 40

describe the cyclic control of cortisol in the anterior pituitary

Answer 40

• For example CRH acts on the anterior pituiry which releases ACTH which acts on the drneal cortex to release cortisol
• Cortisol can inhibit the release of ACTH from the anterior pituitary and can pass through the cells in the hypothalamus and inhibit the cells releasing CRH
  Done to enable a dual negative feedback control for the anterior pituitary hormones

Question 41

describe the cyclic control of thyroid hormones in the anterior pituitary

Answer 41

• Thyroid hromones, T3 and T4 inhibit the release of both TRH and TSH

Question 42

describe the cyclic hormones of the anterior pituitary

Answer 42

• In a woman, LH & FSH are released in a monthly cycle.
• In both sexes GH is released mainly at night
• TSH is secreted mainly during the day.
• There are daily rhythms of ACTH, with a peak in the morning
• In contrast, feedback inhibition does NOT control the release of ADH and OXY from the posterior pituitary