Hypothalamus and pituitary gland

Question 1

what are the master controllers of the endocrine system?

Answer 1

hypothalamus and pituitary

Question 2

what is the hypothalamus?

Answer 2

Integration centre for endocrine systems

Question 3

what is the hypothalamus connected to the pituitary via?

Answer 3

a stalk (infundibulum)

Question 4

how is the hypothalamus connected to the anterior and posterior pituiary?

Answer 4

Hypothalamic axons and nerve terminals project to the posterior pituitary

Connection with anterior pituitary is via neurohormones

Question 5

where is the pituitary gland located?

Answer 5

in a pocket in the sphenoid bone, directly below the hypothalamus

Question 6

what two types of tissue does the pituitary gland contain?

Answer 6

anterior and posterior pituitary

Question 7

describe the anterior pituitary gland?

Answer 7

connected to hypothalamus via capillary portal system

true endocrine tissue

epithelial origin

also called adenohypophysis

makes up 2/3rds of the gland

Question 8

describe the posterior pituitary gland?

Answer 8

is a continuation of the hypothalmus

consists of axons and nerve terminals of hypothalamic neurons

secretes neurohormones made in hypothalamus

is neuroendocrine

is neural in origin

also called neurohypophysis

makes up 1/3rd of the gland

Question 9

what integrative functions do the hypothalamus and pituitary serve?

Answer 9

Question 10

what is released by both the hypothalamus and the anterior pituitary?

Answer 10

tropic and non-tropic hormones

Question 11

what are all hormones released by the hypothalamus?

Answer 11

neurohormones

Question 12

what are all hormones released by the posterior pituitary?

Answer 12

neurohormones (from the hypothalamus)

Question 13

what are all hormones released by the anterior pituitary?

Answer 13

classic endocrine hormones

Question 14

define non tropic hormones?

Answer 14

neurohormones produced in the hypothalamus and travel to posterior pituitary (via axons of hypothalamic neurons) where they are released into blood

Question 15

define tropic hormones?

Answer 15

neurohormones secreted into capillaries travelling to anterior pituitary. Govern release of anterior pituitary hormones

Question 16

what does the posterior pituitary contain?

Answer 16

magnocellular neurons

Question 17

where are the cell bodies of magnocellular neurons found?

Answer 17

hypothalamus

Question 18

what 2 peptide neurohormones do magnocellular neurons release?

Answer 18

vasopressin (aka anti-diuretic hormone; ADH)

Oxytocin

Question 19

what is the role of vasopressin (aka anti-diuretic hormone; ADH)?

Answer 19

maintains water balance

Question 20

what is the role of oxytocin?

Answer 20

stimulates uterine contraction at parturition, and aids expression of milk in lactating breast

Question 21

different subsets of neurons make…

Answer 21

EITHER vasopressin or oxytocin

Question 22

where are non tropic hormones synthesised?

Answer 22

in the hypothalamus and transported to the nerve terminal in posterior pituitary ready for release. Their terminals end directly on capillaries

Question 23

what does activity of magnocellular neurons result in?

Answer 23

release of the neurohormone directly into the blood stream at the posterior pituitary

Question 24

All hypothalamic neurohormones acting on anterior pituitary cells are what?

Answer 24

tropic hormones, i.e. stimulate/inhibit release of AP hormones

Question 25

what are the 5 different hypothelamix releasing hormones that stimulate release anterior pituitary?

Answer 25

Thyrotropin Releasing Hormone (TRH)
Corticotropin Releasing Hormone (CRH)
Growth Hormone Releasing Hormone (GHRH)
Gonadotropin Releasing Hormone (GnRH)
Prolactin Releasing Hormone (PRH)

Question 26

what are the 2 hypothalamic “inhibiting hormones” - stimulate posterior pituitary?

Answer 26

Growth Hormone Inhibiting Hormone (GHIH) aka somatostatin

Dopamine aka Prolactin Inhibiting Hormone (PIH)

Question 27

all hypothelamaic releasing and inhibiting hormones are what?

Answer 27

All are peptides, except dopamine

Question 28

what is the Hypothalamo-hypophyseal portal system?

Answer 28

Network of tiny vessels which transfer tropic hormones from hypothalamus to anterior pituitary

Hormones released from neurosecretory neurons at the median eminence

Very small amounts of hormones required

Short distance – very rapid and dynamic

Question 29

what is the production of anterior pituitary hormones controlled by?

Answer 29

hypothalamic “releasing” or “inhibiting” tropic hormones that stimulate or inhibit hormone production from the anterior pituitary e.g. Thyrotropin Releasing Hormone (TRH) from the hypothalamus stimulates the release of Thyroid Stimulating Hormone (TSH) from the anterior pituitary.

6 hormones are released from the anterior pituitary gland, all peptides;
5 of these are also tropic hormones

Question 30

what are the five anterior pituitary hormones?

Answer 30

Thyroid Stimulating Hormone (TSH) aka thyrotropin

Adrenocorticotropic Hormone (ACTH) aka corticotropin

Follicle Stimulating Hormone (FSH)

Luteinising Hormone (LH)

Growth Hormone (GH)

Prolactin

1-5 above control secretion of other endocrine glands = tropic hormones and also largely have direct or indirect effects in promoting growth = trophic action.

Question 31

what does prolactin directly stimulate?

Answer 31

directly stimulates milk production from the breast during lactation

Question 32

what is anterior pituitary feedback control?

Answer 32

complex, multi-tiered pathways involving up to 3 integration centres

Question 33

what three integration centres make up anterior pituitary feedback control?

Answer 33

hypothalamus

anterior pituitary

target endocrine cell

feedback from endocrine target = long-loop feedback
feedback from anterior pituitary to hypothalamus = short-loop feedback

Question 34

what is hyposecretion?

Answer 34

too little hormone secreted

Question 35

what is hypersecretion?

Answer 35

too much hormone secreted

Question 36

1* disorders?

Answer 36

are those in which the defect is in the cells that secrete the hormone

Question 37

2* disorders?

Answer 37

are those in which there is too little or too much tropic hormone from pituitary - over or understimylating

Question 38

3* disorders?

Answer 38

relate to hypothalamic defects - too little much released RARE

Question 39

hyporesponsiveness?

Answer 39

may be due to alterations in receptor for hormone, disordered post-receptor events, failure of metabolic activation of hormone, (where this is required for function) or antagonistic effects

Question 40

hyperresponsiveness?

Answer 40

could be due to permissive effects e.g. Thyroid hormone ++ adrenaline mediated lipolysis.

Question 41

Hypo/hyperresponsiveness origins:

Answer 41

When normal plasma hormone concentration is disrupted homeostatic responses are initiated to reduce impact on end function e.g.

- Prolonged exposure to low [hormone]plasma often 	leads to up-regulation of receptor number 	(increases tissue sensitivity/response to hormone). 

- Conversely, prolonged exposure to high 	[hormone]plasma typically leads to down-regulation of 	receptor number (decreases tissue 	sensitivity/response to hormone).

Question 42

what are permissive effects?

Answer 42

presence of one hormone enhances the effect of another eg epinephrine causes only modest lipolysis in adipose tissue, but when thyroid hormones are also present, greatly increased lipolysis occurs.

Question 43

what effect does TH have?

Answer 43

synthesis of receptors for epinephrine on adipocytes. TH itself has no effect on lipolysis but is permissive to epinephrine.
TH also permissive to GH.

The presence of one hormone reduces the effect of another e.g. Growth hormone impairs glucose uptake in response to insulin by decreasing the number of insulin receptors on muscle and adipose tissue.