Pituitary Gland

Question 1

What is a hormone

Answer 1

A message carried from the organ where they are produced to the organ which they affect by means of bloodstream

Question 2

Types of hormones

Answer 2

Peptide and steroid

Question 3

Peptide hormones:

Synthesis, storage and receptors

Answer 3

Synthesised as prohormones requiring further processing to activate
Stored in vesicles (regulatory secretion)
Bind receptors in cell membrane and transducer signal using 2nd messenger systems

Question 4

Steroid hormones:

Synthesis, storage and receptors

Answer 4

Synthesised in a series of reactions from cholesterol
Released immediately (constitutive secretion)
Bind to intracellular receptors to change gene expression directly

Question 5

Describe function and pathway of Hypothalamic parvocellular neurons

Answer 5

Regulate anterior pituitary function
Neurones are short and terminate on median eminence
Release hypothalamic releasing/inhibitory factors into capillary plexus in median eminence
These hypothalamic regulatory factors carried by portal circulation to anterior pituitary

Question 6

Anterior Pituitary - adenohypophysis

Answer 6

Anatomically distinct from hypothalamus
Made up of endocrine cells:
Somatotrphs, Lactotrophs, Corticotrophs, Thyrotrophs and Gonadotrophs
Regulated by hypothalamic releasing/inhibiting factors via hypophyseal-pituitary portal system

Question 7

How does the Hypothalamo-pituitary portal system work?

Answer 7

Axon terminals of hypothalamic neurosecretory cells release hormones into the system
The RHs and IHs travel in the portal system to the anterior pituitary
The RHs and IHs stimulate or inhibit the release of hormones from anterior pituitary cells
Anterior pituitary hormones leave the gland via the blood
These blood vessels constitute the hypothalamic-pituitary portal system

Question 8

Describe regulation of thyroid hormone production

Answer 8

Axon terminals of hypothalamic neurosecretory cells release Thyrotrophin Releasing Hormone (TRH) into hypothalamo-hypophysial portal system
TRH travels in the portal system to the anterior pituitary
TRH stimulates the release of Thyroid Stimulating Horomone (Thyrotrophin) from anterior pituitary thyrotrophs
TSH leaves the gland via the blood to travel to the thyroid gland to stimulate thyroid hormone release (thyroxine)

Question 9

Somatotrophs

Answer 9

Growth hormone (somatotrophin) - releasing
Somatostatin- inhibiting
Receptor: general body tissues (particularly liver)

Question 10

Lactotrophs

Answer 10

Prolactin (dopamine) - inhibiting

Receptor: breasts (lactating women)

Question 11

Thyrotrophs

Answer 11

Thyroid stimulating hormone (TSH)
Thyrotrophin
-releasing
Receptor: thyroid

Question 12

Gonadotrophs

Answer 12

Luteinising hormone (LH) [receptor: testes]
Follicle Stimulating Hormone (FSH) [receptor: ovaries]
- releasing

Question 13

Corticotrophs

Answer 13

Adrenocorticotrophic hormone (ACTH, corticotrophin)
-releasing
Receptor: adrenal cortex

Question 14

Assessing a bitemporal hemianopia

Answer 14

Normal vision - full view

Pituitary tumour - only see middle section of normal view

Question 15

Describe bitemporal hemianopia

Answer 15

Fibres from the nasal retinae cross at the optic chiasm
Compression of the optic chiasm by a pituitary/ suprasellar tumour prevents transmission of sensory information from lateral visual fields to the occipital lobe

Question 16

Name bony dish the pituitary gland sits in

Answer 16

Sella turcica of sphenoid bone

Question 17

Describe the neuroendocrine reflex arc: milk production

Answer 17

Mechanical stimulation of nipple and surrounding area activated afferent pathways
Afferent signals integrated in the hypothalamus and inhibit dopamine release from dopaminergic neurons
Less dopamine in the hypothalamic-pituitary portal system causes less inhibition of anterior pituitary lactotrophs
Increased plasma prolactin increases milk secretion in mammary glands

Question 18

Mechanism of growth hormone action

Answer 18

Growth hormone (somatotrophin) released from anterior pituitary
Travels directly to body tissues causing metabolic actions that increase growth and development
Also reaches the liver which releases insulin like growth factor (somatomedin) which then travels to body tissues causing growth and development

Question 19

Acromegaly

Answer 19

Excess growth hormone 
Coarsening of facial features (macroglossia/ prominent nose)
Large jaw - prognathism
Increased hand and feet size 
Sweatiness
Headache 
Does not result in increased height

Question 20

The posterior pituitary gland (neurohypophysis) hormones

Answer 20

Arginine vasopressin (anti-diuretic hormone)
Oxytocin

Question 21

Describe the hypothalamic magnocellular neurons

Answer 21

Posterior pituitary is anatomically continuous with hypothalamus
Neurons are long, originating in supraoptic (AVP) and paraventricular (oxytocin) hypothalamic nuclei
From Nuclei down the stalk into the posterior pituitary

Question 22

Regulation of the posterior pituitary gland

Answer 22

Two sets of hypothalamic neurosecretory cells produce AVP and oxytocin and transport the. To the posterior pituitary
Excitation of these hypothalamic magnocellular neurons stimulates release of AVP or oxytocin into the posterior pituitary where they leave via blood and diffuse into blood capillaries

Question 23

Physiological action of vasopressin

Answer 23

Diuresis= production of urine
Main physiological action is stimulation of water reabsorption in the renal collecting duct, this concentrates urine. Acts through the V2 receptor in the kidneys
Also a vasoconstrictor via V1 receptor stimulating ACTH release from anterior pituitary

Question 24

Physiological actions of oxytocin

Answer 24

1. Uterus at parturition, myometrial cells - Contraction for delivery of baby
2. Great during lactation, myoepithelial cells - Contraction for milk ejection

Question 25

Neuroendocrine reflex arc - milk ejection

Answer 25

Mechanical stimulation of nipple and surrounding area activates afferent pathways
Afferent signals integrated in the hypothalamus and stimulate oxytocin-releasing neuron activity
APs travel down oxytocin neurones and oxytocin is secreted into the bloodstream
Increased plasma oxytocin increases milk ejection in mammary glands