The pituitary gland

Question 1

Peptide hormones:

Synthesis, storage and receptors

Answer 1

synthesised as prohormones
stored in vesicles
bind to cell membrane receptors and pass signal using 2nd messenger systems

Question 2

Steroid hormones:

Synthesis, storage and receptors

Answer 2

synthesised in series of reactions from cholesterol
released immediately
bind to intracellular receptors - change gene expression directly.

Question 3

Method of regulation of anterior pituitary (adenohypophysis) function is by

Answer 3

hypothalamic parvocellular neurons. Terminate on median eminence, release factors carried in hypophysial portal system to anterior pituitary

Question 4

Anterior pituitary endocrine cell types and the hormones they produce

Answer 4

Somatotrophs - Growth hormone (Somatotrophin)
Lactotrophs - Prolactin
Corticotrophs - Adrendocorticotrophic hormone (ACTH, corticotrophin)
Thyrotrophs - Thyroid stimulating hormone (TSH, Thyrotrophin)
Gonadotrophs - Luteinising hormone (LH), Follicle stimulating hormone (FSH)

Question 5

Hypothalamo-pituitary regulation hormones

Answer 5

Growth hormone + Growth hormone releasing hormone
- Somatostatin
Prolactin - Dopamine
Thyroid stimulating hormone + Thyrotrophin releasing hormone
Luteinising hormone and Follicle stimulating hormone + Gonadotrophin releasing hormone
Adrendocorticotrophic hormone + Corticotrophin releasing hormone

Question 6

Anterior pituitary hormones and their main target cells

Answer 6

Growth hormone - general body tissues, particularly liver
Prolactin - Breasts 
Thryotrophin - Thyroid 
Gonadotrophins - Testes M, Ovaries F
Corticotrophin - Adrenal cortex

Question 7

Bitemporal hemianopia

Answer 7

Pituitary tumour compressing optic chiasm. (fibres from nasal retinae cross here, Nasal part of retina gives temporal (lateral) visual field.)

Question 8

Neuroendocrine reflex arc : milk production

Answer 8

1. Mechanical stimulation of nipple activates afferent pathways
2. Afferent signals inhibit dopamine release from dopaminergic neurones in hypothalamus
3. Less dopamine in hypothalamic-pituitary portal system causes less inhibition of anterior pituitary lactotrophs, more prolactin production, secreted into blood
4. Increased plasma prolactin increases milk secretion in mammary glands

Question 9

Mechanism of growth hormone action

Answer 9

Can act directly on muscle bone GH receptors etc, or acts on liver and IGF - 1 acts on bone and muscle IGF - 1 receptors

Question 10

Too much growth hormone

Answer 10

Child - Gigantism
Adult - Acromegaly, bone epiphyseal plates fuse therefore no height growth but coarsening of facial features, growth in hands feet, headaches from tumour pressure

Question 11

Regulation of posterior pituitary gland - neurohypophysis

Answer 11

Made of neural tissue, continuous with hypothalamus.
Hypothalamic magnocellular neurons originate in supraoptic (AVP) and paraventricular (oxytocin) hypothalamic nuclei.
Excitation of these neurones stimulates release of Arginine vasopressin (ADH) / oxytocin into posterior pituitayr where they diffuse into blood capillaries.

Question 12

Physiological action of vasopressin

Answer 12

Diuresis - production of urine, AVP = ADH.
Acts through V2 receptor in kidney - stimulates water reabsorption (via aquaporin 2 insertion into tubular membrane) - concentrates urine. Also stimulates ACTH from anterior pituitary. (cortisol from adrenal gland)

Question 13

Physiological action of oxytocin

Answer 13

Parturition - myometrial cells in uterus - contraction - deliver baby
Lactation - myoepithelial cells in breast - contraction - milk ejection