Lecture 2: The Hypothalamus and Pituitary

Question 1

describe the difference between the anterior and posterior pituitary gland

Answer 1

anterior pituitary:
- connected to hypothalamus via capillary portal system
- true endocrine tissue
- epithelial origin
- makes up 2/3 rds of the gland

posterior pituitary:
- is a continuation of the hypothalamus
- consists of axons and nerve terminals of hypothalamic neurons
- secreted neurohomrones made in hypothalamus
- is neuroendocrine and neural in origin
- makes up 1/3rd of the gland

Question 2

what is the anterior pituitary gland also called?

Answer 2

adenohypophysis

Question 3

what is the posterior pituitary gland also called?

Answer 3

neurohypophysis

Question 4

all hormones released the posterior pituitary and hypothalamus are classed as what>

Answer 4

neurohormones

Question 5

all hormones released by the anterior pituitary are classed as what?

Answer 5

classic endocrine hormones

Question 6

what are the two forms of hypothalamic neurohormones?

Answer 6

• non-tropic
• tropic

Question 7

what is the difference between tropic and non-tropic hormones?

Answer 7

• non-tropic: neurohormones produced in the hypothalamus and travel to posterior pituitary (via axons of hypothalamic neurons) where they are released into blood.
• tropic: neurohormones secreted into capillaries travelling to anterior pituitary. Govern the release of anterior pituitary hormones.

Question 8

posterior pituitary contains magnocellular neurons which have their cell bodies in the?

Answer 8

hypothalamus

Question 9

magnocellular neurons store and release which two peptide neurohormones?

what are their function?

Answer 9

• vasopressin (aka ADH) = maintains water balance
• oxytocin = stimulates uterine contraction at parturition, and aids expression of milk in lactating breast

Question 10

do magnocellular hormones secrete tropic or non-tropic hormones?

Answer 10

non-tropic

Question 11

are vasopressin and oxytocin tropic or non-tropic hormones?

Answer 11

non-tropic

Question 12

Answer 12

Question 13

what are the 5 hypothalamic releasing hormones called? (tropic hormones which stimulate release of anterior pituitary hormones)

Answer 13

• thyrotropin releasing hormone (TRH)
• corticotropin releasing hormone (CRH)
• growth hormone releasing hormone (GHRH)
• gonadotropin releasing hormone (GnRH)
• prolactin releasing hormone (PRH)

Question 14

what are the two hypothalmic ‘inhibiting’ hormones called? (tropic hormones which inhibit the release of anterior pituitary hormones)

Answer 14

• growth hormone inhibiting hormone (GHIH) aka somatostatin
• dopamine aka prolactin inhibiting hormone (PIH)

Question 15

describe the hypothalamo-hypophyseal portal system

Answer 15

• 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 16

what controls the production of anterior pituitary hormones?

Answer 16

controlled by the hypothalamic ‘releasing’ or ‘inhibiting’ tropic hormones that stimulate or inhibit hormone production from the anterior pituitary

Question 17

what are the 6 hormones released from the anterior pituitary gland classified as?

Answer 17

all peptide hormes, 6 of these are also tropic hormones

Question 18

what are the 6 anterior pituitary hormones called?

Answer 18

1. thyroid stimulating horome (TSH) aka thyrotropin
2. adrenocorticotropic hormone (ACTH) aka corticotropin
3. follice stimulating hormone (FSH)
4. lutenising hormone (LH) aka gonadotropins
5. growth hormone (GH)
6. prolactin

1-5 are tropic hormones

Question 19

which of the 6 anterior pituitary hormones is non-tropic?

Answer 19

prolactin > directly stimulates milk production from the breast during lactation.

Question 20

anterior pituitary feedback control involves complex, multi-tiered pathways involving up to which 3 integration centres:

Answer 20

1. hypothalamus
2. anterior pituitary
3. target endocrinecell

each hormone feeds back to inhibit hormone secretion by integrating centres earlier in the reflex

Question 21

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what is feedback from the endocrine target called?

anterior pituitary feedback control

Answer 21

long-loop feedback

Question 22

what is feedback from anterior pituitary to hypothalamus called?

anterior pituitary feedback control

Answer 22

short-loop feedback

Question 23

what are primary endocrine disorders?

Answer 23

those in which the defect (hyposecretion or hypersecretion) is in the cells that secrete the hormone

Question 24

what are secondary endocrine disorders?

Answer 24

those in which there is too little or too much tropic hormone from pituitary

Question 25

what are tertiary endocrine disorders related to?

Answer 25

hypothalamic defects

Question 26

what may cause hyporesponsiveness?

Answer 26

may be due to alteration in receptor for hormone, disordered post-receptor events, failure of metabolic activation of hormone, or antagonistic effects.

Question 27

what may cause hyperresponsiveness?

Answer 27

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

Question 28

prolonged exposure to low [hormone]plasma often leads to….

Answer 28

up-regulation of receptor number (increases tissue sensitivity/response to hormone) > hypersensitivity

Question 29

prolonged exposure to high [hormone] plasma typically leads to…

Answer 29

down-regulation of receptor number (decreases tissue sensitivity/response to hormone) > hyporesponsiveness

Question 30

describe permissive effects of hormones

Answer 30

• the presence of one hormone enhances the effect of another e.g. epinephrine causes only modest lipolysis in adipose tissue, but when thyroid hormones are also present, greatly increased lipolysis occurs.
• TH increases synthesis of receptors for epinephrine on adipocytes.

Question 31

describe antagonstic effects of hormones and give an example

Answer 31

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.