Pituitary Anatomy and Physiology

Question 1

Describe the anatomical position of the pituitary gland

Answer 1

In the pituitary fossa (sella turcica) in the sphenoid bone.

Question 2

What connects the pituitary to the hypothalamus

Answer 2

The pituitary stalk

Question 3

How does venous blood drain from the pituitary gland

Answer 3

By a number of veins into the cavernous sinus

Question 4

What is the anterior pituitary gland derived from

Answer 4

An upward growth of the ectoderm of the roof of the oropharynx (Rathke’s pouch) which becomes pinched off

Question 5

What is the posterior pituitary gland derived from

Answer 5

Down growth of neuroectoderm of the floor of the third ventricle

Question 6

Name the hormones secreted by the anterior pituitary

Answer 6

Growth hormone (GH) 
Prolactin 
Adrenocorticotrophin hormone (ACTH) 
Thyroid stimulating hormone (TSH) 
Luteinizing hormone (LH) and follicle stimulating hormone (FSH)

Question 7

What is the most abundant hormone secreted by the anterior pituitary gland

Answer 7

Growth hormone

Question 8

What does GH stimulate

Answer 8

hepatic synthesis and secretion of insulin-like growth factor 1
Epiphyseal prechondrocyte differentiation and linear bone growth in children
lipolysis
increases protein synthesis
antagonises insulin action
phosphate, water and sodium retention

Question 9

How does GH work

Answer 9

It binds to its plasma membrane receptor (usually in the liver) which leads to receptor dimerisation

Question 10

What happens after receptor dimerisation ?

Answer 10

It is followed by a phosphorylation cascade mediated by Janus kinds (JAK) and components of the signal transduction and activators of transcription (STAT) family, which translocate to the nucleus and regulate target gene expression

Question 11

How is the secretion of GH stimulated

Answer 11

BY hypothalamic GH releasing hormone

Question 12

How does hypothalamic GH releasing hormone work

Answer 12

It acts via a G-protein coupled receptor and increases cyclic AMP leaves

Question 13

What factors may stimulate GH release

Answer 13

stress
exercise
sleep
prolonged fasting

Question 14

What inhibits GH secretion

Answer 14

IGF-1 and hypothalamic somatostatin

Question 15

Describe the release of GH

Answer 15

pulsatile

Question 16

What does prolactin stimulate

Answer 16

the proliferation of the breast lobule-alveolar epithelium and lactation

Question 17

What does prolactin suppress

Answer 17

Gonadotrophin-releasing hormone (GnRH)

Pituitary gonadotrophin secretion

Question 18

How does prolactin work

Answer 18

In the same way as GH - It binds to its plasma membrane receptor which leads to receptor dimerisation which is followed by a phosphorylation cascade

Question 19

What inhibits prolactin secretion

Answer 19

Hypothalamic dopamine binding to D2 receptors

Question 20

What stimulates prolactin secretion

Answer 20

hypothalamic thyrotrophin releasing hormone (TRH) and others including oestrogen, opiates, serotonin and ACh

Question 21

When might prolactin levels be high

Answer 21

in stress
during sleep 
following a suckling stimulus 
exercise 
meals 
sex 
epileptic fit

Question 22

When are the prolactin secretory peaks

Answer 22

during rapid eye movement sleep (between 4 and 6am)

Question 23

What does ACTH do

Answer 23

It stimulates the conversion of cholesterol to pregnenolone in the zone fasciculate and reticular
therefore stimulates the production of cortisol and adrenal androgens

Question 24

How does ACTH work

Answer 24

It binds to its plasma membrane receptor in the zone fasciculata of the adrenal gland which results in the activation of adenylate cyclase

Question 25

What does the activation of adenylate cyclase result in

Answer 25

an increased cyclic AMP production which then results in stimulation of steroidogenic acute regulatory protein

Question 26

what does steroidogenic acute regulatory protein do

Answer 26

It mediates the transport of cholesterol through the cytosol to the inner mitochondrial membrane where it is converted to pregnenolone

Question 27

What is the rate limiting step in cortisol synthesis

Answer 27

the transport of cholesterol through the cytosol to the inner mitochondrial membrane, where it is converted to pregnenolone

Question 28

What else does the activation of adenylate cycles result in

Answer 28

the unregulated gene expression of other enzymes involved in steroid synthesis

Question 29

What stimulates ACTH

Answer 29

hypothalamic corticotrophin-releasing hormone (CRH) as well as other factors, including stress

Question 30

What inhibits ACTH

Answer 30

cortisol

Question 31

When is there a peak of cortisol

Answer 31

8am

Question 32

What does TSH stimulate

Answer 32

Every step in thyroid hormone synthesis | also stimulates the expression of many genes in thyroid tissue and causes thyroid hyperplasia and hypertrophy

Question 33

What inhibits TSH synthesis

Answer 33

T4 and T3

Question 34

What are some other factors that may reduce TSH secretion

Answer 34

dopamine somatostatin acute non-thyroidal illness increased human chorionic gonadotrophin (early pregnancy

Question 35

What do LH and FSH do in males

Answer 35

LH stimulates the production of testosterone | FSH stimulates spermatogenesis (alongside testosterone)

Question 36

How do the gonadotrophin work in males

Answer 36

Binding of LH and FSH to their plasma membrane receptors results in a stimulation of adenylate cyclese and increased cAMP production LH stimulates testosterone synthesis by acting on the StAR protein which delivers cholesterol to the inner mitochondrial membrane where it is converted to pregnenolone

Question 37

What stimulates the release of LH and FSH

Answer 37

pulsatile release of hypothalamic GnRH

Question 38

What does testosterone inhibit

Answer 38

hypothalamic GNRH and pituitary LH production

Question 39

How does LH and FSH work in females

Answer 39

LH stimulates the early steps in steroidogenesis and the production of androgens in ovarian theca cells

Question 40

What does the LH surge induce

Answer 40

ovulation and thereafter maintains the secretory function of the corpus luteum

Question 41

What does FSH stimulate

Answer 41

the recruitment and growth of ovarian follicles and their secretion of estradiol

Question 42

What does FSH stimulate

Answer 42

The aromatase enzyme that converts androgens to oestrogen

Question 43

What is the secretion of FSH and LH fundamentally under the control of

Answer 43

negative feedback control by ovarian steroids (oestradiol) and by inhibin

Question 44

What does the oestrogen peak cause

Answer 44

the LH surge

Question 45

What are the hormones secreted by the posterior pituitary

Answer 45

Oxytocin | vasopressin (ADH)

Question 46

How are vasopressin and oxytocin synthesised and packaged

Answer 46

In granules in the cell bodies of specific magnocellular neurones in the supraoptic and paraventricular nuclei of the hypothalamus

Question 47

What stimulates vasopressin secretion

Answer 47

an increase in serum osmolality decreased extracullar volume decreased BP stress

Question 48

What inhibits vasopressin secretion

Answer 48

alcohol and cold

Question 49

How does Vasopressin cause generation of cyclic AMP and activation of intracellular protein kinases

Answer 49

It binds to the VR2 membrane receptors on the distal renal tubular cells (in the collecting duct) causing activation of adenylate cyclase

Question 50

How does vasopressin cause urine to become concentrated

Answer 50

Insertion of water channel proteins into the tubular membrane, allowing a flow of solute free water from the hypotonic luminal fluid into the hypertonic renal interstitium

Question 51

What happens at high concentrations

Answer 51

Vasopressin binds to VR1 receptors on vascular smooth muscle and causes vasoconstriction

Question 52

Where else is vasopressin secreted into

Answer 52

the portal circulation

Question 53

What does vasopressin stimulate

Answer 53

ACTH release from the pituitary

Question 54

What stimulates oxytocin release

Answer 54

vaginal stimulation caused by the fetus during parturition, sex or nipple stimulation during lactation

Question 55

What is oxytocin released inhibited

Answer 55

Stress

Question 56

What does oxytocin stimulate

Answer 56

contractions of the uterine muscle which helps deliver the foetus and the placenta

Question 57

What is another function of oxytocin

Answer 57

Stimulate the contraction of the myoepithelial cells that surround the alveoli in the breast to aid milk ejection