Hypothalmic Axis

Question 1

the pituitary gland is also called the _____

Answer 1

hypophysis

Question 2

what is the significance of the hypothalamo-pituitary axis?

Answer 2

connection from brain to body: allow brain to maintain homeostasis (control center for endocrine system)

Question 3

What was believed to control/influence the body prior to discovery of hormones?

Answer 3

the 4 humours (choleric, phlegmatic, sanguine, melancholic)

Question 4

Who first described the parts of the pituitary?

Answer 4

Rathke (19th century)

Question 5

What did Aristotle identify the pituitary as?

Answer 5

connection between brain/body that 4 humours passes through

Question 6

What are the 2 parts of the pituitary?

Answer 6

adenohypophysis (anterior pit.)

neurohypophysis (posterior pit.)

Question 7

Who associated pituitary tumors with acromegaly? When?

Answer 7

Pierre Marie (1886)

Question 8

Who pioneered a method to improve acromegaly patients? How?

Answer 8

Harvey Cushing (1909); removed part of pituitary

Question 9

What experiment led to the discovery of growth hormone?

Answer 9

Evans & Long (1922) injected crude pituitary gland extract of animals -> increased growth

Question 10

How were most hormone functions discovered?

Answer 10

animal experiments

Question 11

What controls the pituitary?

Answer 11

Hypothalamus

Question 12

The hypothalamo-pituitary axis is also known as: _____

Answer 12

adenohypophysial axis

Question 13

What size is the pituitary? Where is it located?

Answer 13

0.5-1g (1cm diameter)

connected to hypothalamus stalk (under optic chiasm), within protective bone ‘saddle’ (sella turcica)

Question 14

What physical changes happen in the pituitary during pregnancy and why?

Answer 14

increased size (>30%)
need increased hormones for preg & lactation

Question 15

What are the anatomical parts of the anterior pituitary?

Answer 15

pars tuberalis
pars intermedia
pars distalis

Question 16

What are the anatomical parts of the posterior pituitary?

Answer 16

infundibular stalk

pars nervosa

Question 17

How does the hypothalamo-hypophyseal tract develop? (2)

Answer 17

Rathke’s pouch (outgrowth of buccal cavity) -> detach and become anterior pituitary

Neuroectoderm outgrowh (from third ventricle) -> form infundibulum, pituitary stalk, median eminence, posterior pituitary

Question 18

The anterior pituitary is formed from _____ cells, that develop from: ______.

Answer 18

ectodermal

Rathke’s pouch (outgrowth from buccal cavity/primitive mouth below)

Question 19

What cells form the posterior pituitary? Where is their origin, and what else do they form?

Answer 19

neuralectoderm cells
from neurohypophyseal bud (downgrowth from forebrain floor)
forms infundibulum, median eminence, pituitary stalk

Question 20

the pituitary is located below the ___ ____, encased in a cavity known as the ___ ___, within the ____ bone.

Answer 20

optic chiasma
turkish saddle
sphenoid

Question 21

Describe the blood flow pathway through the pituitary and hypothalamus:

Answer 21

from body -> hypophysial artery -> median eminence capillary bed -> portal blood vessel -> anterior pituitary capillary bed -> vein -> back to body

Question 22

Where are the major 2 capillary beds in the adenohypophysis located?

Answer 22

median eminence

anterior pituitary

Question 23

What carries blood from the median eminence down to the anterior pituitary?

Answer 23

portal hypophysial vessel

Question 24

There is some blood flow from the pituitary back to the hypothalamus, known as ___ flow. Why is this important?

Answer 24

retrograde flow

allow hormonal feedback from pit. to hypothalamus (short loop)

Question 25

How does the hypothalamus control the anterior pit.?

Answer 25

through releasing or inhibiting hormones -> passed through hypothalamic-hypophyseal portal system

Question 26

How does the hypothalamus control the posterior pituitary?

Answer 26

direct control (axons from hypothalamus extend down into posterior pit.)

Question 27

True/False: the posterior pituitary does not make any hormones

Answer 27

True; hormones made by neuron cells from above, released through axons

Question 28

True/False: posterior pituitary hormones cannot be stored

Answer 28

False; can be stored

Question 29

The specialized neurons that make the posterior pit. hormones are known as ____ neurons

Answer 29

neurosecretory

Question 30

What are the posterior pit. hormones?

Answer 30

vasopressin (ADH) | oxytocin

Question 31

Describe the production and release of the posterior pituitary hormones:

Answer 31

produced in cell bodies of neurosecretory hormones (in hypothalamus) -> packaged in granules -> migrate to axons (in posterior pit.) hypothalamus neurons stimulated -> trigger release from axon tips -> into capillaries/bloodstream

Question 32

_____ hormones are released from the hypothalamus into the _______, and flow through the ____ down to the anterior pituitary.

Answer 32

hypophysiotrophic median eminence HHPS (portal vein)

Question 33

True/False: a hypothalamic neurosecretory cell can produce a large variety of hormones

Answer 33

False: cells are highly specialized, can only produced 1 type of hormone

Question 34

How are the hypothalmic cells organized?

Answer 34

in bundles according to function (each section makes different hormone)

Question 35

what hypothalamic nuclei are responsible for the posterior pituitary? (2)

Answer 35

supraoptic nuclei | paraventricular nuclei

Question 36

Which hypothalamic nuclei are responsible for the anterior pituitary?

Answer 36

hypothalamic-hypophysiotropic nuclei

Question 37

What controls the hypothalamus?

Answer 37

signals from all other parts of brain -> neurotransmitters

Question 38

What are the main neurotransmitters? (5)

Answer 38

``` norepinephrine epinephrine dopamine serotonin acetylcholine ```

Question 39

What happens to hormone production if the hypothalamus is removed?

Answer 39

no posterior pit. hormones most anterior pit. hormones stop GH, FSH, LH fall to basal levels (very low) PRL increases

Question 40

What anterior pituitary hormones show some degree of autonomy in secretion?

Answer 40

GH, FSH, LH (will still have some low levels without hypothalamus)

Question 41

How is PRL control different from the other pit. hormones?

Answer 41

hypothalamus does INHIBITORY control, not stimulatory

Question 42

What are the subgroups of cells in the anterior pituitary gland? What do they produce?

Answer 42

1. somatotrophs (GH) 2. mammotrophs (PRL) 3. thyrotrophs (TSH) 4. gonadotrophs (LH, FSH) 5. corticotrophs (ACTH, beta lipotropin)

Question 43

What is the target(s) of ACTH?

Answer 43

adrenal gland adipocytes melanocytes

Question 44

What anterior pit. hormone causes responses in almost all cells?

Answer 44

GH

Question 45

What antierior pit. hormone targets the breasts and gonads?

Answer 45

PRL

Question 46

Classify the anterior pit. cells based on their cell type (2 types)

Answer 46

1. basophils: thyrotrophs, gonadotrophs, corticotrophs | 2. acidophils: somatotrophs, mammotrophs

Question 47

How are basophil hormones and acidophil hormones different?

Answer 47

basophil hormones more heavily glycosylated; protected from degradation (longer half life)

Question 48

What hormone would have a longer half life: GH or FSH?

Answer 48

FSH

Question 49

What is TRH and its role?

Answer 49

thyrotrophin releasing hormone (from hypothalamus) | stimulate release of TSH & PRL minor stimulation of FSH release

Question 50

What is GnRH and its role?

Answer 50

gonadotrophin releasing hormone (from hypothalamus) stimulate release of LH, FSH

Question 51

What hypthalmic hormone stimulates release of GH? What is its counterpart?

Answer 51

GHRH somatostatin (SMS) will inhibit GH

Question 52

What hormone works counterpart to TRH?

Answer 52

somatostatin (will inhibit TSH and PRL)

Question 53

How is PRL controlled (primary control)

Answer 53

inhibited by dopamine from hypothalamus

Question 54

___ and ____ promote FSH release

Answer 54

GnRH | TRH (minor)

Question 55

Characteristics of hypothalmic hormones affecting anterior pituitary:

Answer 55

fast action short half-life bind to GPCR

Question 56

What type of G proteins are used by trophic vs. inhibitory hypothalmic hormones?

Answer 56

trophic (stimulatory): Gas, Gaq | inhibitory: Gai

Question 57

What are the different feedback loop types in the hypothalmic-pituitary axis?

Answer 57

1. short feedback loop: AP hormones -> hypothalamus 2. Fast feedback loop: from ultimate hormone -> hypothalamus & adenohypophysis 3. Long feedback loop: ultimate hormone -> CNS, hypothalamus, adenohypophysis

Question 58

What is the general release pattern of hypothalmic hormones, and why is this important? (2)

Answer 58

pulsatile release - synchronized with target tissue - must keep renewing stimulus (short half life of signals)

Question 59

Role of the pineal gland:

Answer 59

take info from light signals -> help set biological rhythm

Question 60

Major hormone of pineal gland:

Answer 60

melatonin (made from Trp)

Question 61

How do melatonin levels change throughout the day, and throughout life stages?

Answer 61

production begin in evening -> peak at night -> fall low in day highest in youth -> decline with age

Question 62

Why does melatonin secretion decrease with age?

Answer 62

sleep is less crucial (no more development) calcification of pineal gland

Question 63

Describe the pathway controlling circadian rhythm from light stimulus

Answer 63

light -> retina -> SCN -> b-adrenergic receptor on pinealocyte -> activate cAMP pathway -> convert Trp to melatonin -> body (and also back to SCN for feedback)

Question 64

What acts as the circadian pacemaker 'clock?'

Answer 64

SCN (suprachiasmatic nucleus)

Question 65

What is the effect of darkness on melatonin?

Answer 65

levels increase (up to 10-fold)

Question 66

functions of melatonin:

Answer 66

core body temp induce sleep depress reproductive activity in animals

Question 67

additional melatonin functions (possible)

Answer 67

antioxidant (anti-aging properties?) enhance immunity (correlation, not necessarily causation) help adjust jet-lag sleeping aid in elderly

Question 68

possible side effects of melatonin supplements:

Answer 68

daytime sleepiness hypothermia desensitized receptors adverse effects in those with seizure disorders adverse interaction with coumadin/warfarin

Question 69

What is 'chronotherapy?'

Answer 69

optimatl timing of medication, surgery, chemotherapy to align with hormone levels for maximum effectiveness

Question 70

examples of chronotherapy:

Answer 70

asthma meds in morning (when attacks are the worst) arthritis meds at night (when pain is worst) breast cancer surgery after ovulation (when estrogen is low; to prevent tissue regrowth from estrogen acting as mitogen)