Pituitary Gland I

Question 1

What is a hormone?

Answer 1

Chemical messenger transported to a target organ via the bloodstream

Question 2

What are the properties of peptide hormones? (3)

Answer 2

Synthesis:
Prohormone processed into hormone (eg. cleaved)

Storage:
In vesicles —> regulatatory secretion

Receptors:
Bind to membrane receptors —> effect via 2nd messenger model

Question 3

What are the properties of a steroid hormone

Answer 3

Synthesis:
Derived from cholesterol

Storage:
No storage (immediate release) —> constitutive secretion

Receptors:
Bind to intracellular receptors —> effect via directly changing gene expression

Question 4

What is the main anatomy of the pituitary gland?

Answer 4

Above:
1. Hypothalamus
2. Mammillary body
3. Optic chiasm

Top:
4. Median eminence
5. Infundibulum

Anterior:
6. Pars tuberalis, intermedia, distalis

Posterior:
7. Pars nervosa

Below:
8. Sella turcica of sphenoid bone (cavity)

Question 5

What are the properties of the anterior pituitary?

Answer 5

Adenohypohphysis

Cells:
Endocrine - somatotrophs, lactotrophs, corticotrophs, thyrotrophs, gonadotrophs

Origin:
Upgrowth from Rathke’s pouch (oral ectoderm) —> epithelial origin

Hypothalamus:
Separate —> hypothalami-pituitary portal circulation

Question 5

What are the properties of the posterior pituitary?

Answer 5

Neurohypohphysis

Cells:
Neural

Origin:
Downgrowth from diencephalon (3rd ventricle of brain)

Hypothalamus:
Extension —> magnocellular neurons

Question 5

What are the main differences between peptide and steroid hormoones? (4)

Answer 5

Synthesis:
Derived from prohormones vs cholesterol

Storage:
Stored in vesicle vs not stored

Secretion:
Regulatory vs constitutive

Receptors:
On membrane (2nd messenger) vs intracellular (gene expression)

Question 6

What are the main differences between the anterior and posterior pituitary?

Answer 6

Cells:
Endocrine vs neural

Origin:
Up from Rathke’s pouch vs down from diencephalon

Hypothalamus:
Separate so uses portal circulation vs continuation

Question 7

How does the hypothalamus communicate with the anterior pituitary? (4)

Answer 7

1. Hypothalamus sends nervous signals via short
   parvocellular neurons
2. Release hypothalamic releasing/inhibitory factors
   into capillary plexus of median eminence
3. Factors carried via hypothalamic-pituitary portal
   circulation to anterior pituitary
4. Factors stimulate/inhibit release of hormones into
   bloodstream

Question 8

What are the 6 hormones of the anterior pituitary?

Answer 8

1. Growth hormone
2. Prolactin
3. TSH (thyroid stimulating hormone)
4. LH (gonadotrophin)
5. FSH (gonadotrophin)
6. ACTH (adrenocorticotrophic hormone)

Question 9

How is growth hormone released and what are its effects?

Answer 9

Release:
Stimulated by - GHRH
Inhibited by - somatostatin
From - somatotrophs

Effects:
- Whole body —> growth
- Liver —> IGF-1 and IGF-2 —> body tissue —> growth

Question 10

How is prolactin released and what are its effects?

Answer 10

Release:
Inhibited by - dopamine (mechanical stimulation of breast inhibits dopamine release)
From - lactotrophs

Effects:
- Lactating breasts —> milk secretion

Question 11

How is TSH released and what are its effects?

Answer 11

Release:
Stimulated by - TRH
From - thyrotrophs

Effects:
- Thyroid gland —> triiodothyronine (T3) and
thyroxine (T4) release —> metabolic effects

Question 12

How are LH and FSH released and what are their effects?

Answer 12

Release:
Stimulated by - GRH
From - gonadotrophs

Effects:
- Testes
- Ovaries —> oestrogen and progesterone release —>
menstrual cycle

Question 13

How is ACTH released and what are its effects?

Answer 13

Release:
Stimulated by - CRH (corticotrophin releasing)
From - corticotrophs

Effects:
- Adrenal cortex —> cortisol release

Question 14

What can a pituitary tumour lead to regarding vision and why?

Answer 14

Bitemporal hemianopia
Tumour grows —> compresses optic chiasm —> prevents transmission from nasal retinae fibres to occipital lobe —> no lateral vision

Question 15

What is acromegaly?

Answer 15

Growth hormone hypersecretion
- After epiphysis fusion —> not gigantism

Symptoms:
- Face —> macroglossia, prominent nose,
prognathism
- Hands and feet larger
- Sweatiness
- Headaches

Question 16

How does the hypothalamus communicate with the posterior pituitary?

Answer 16

1. Hormones (AVP and oxytocin) made in
   hypothalamus
2. Hypothalamus sends nervous signals via long
   magnocellular neurons (supraoptic or
   paraventricular nuclei)
3. Stimulate release of hormone into posterior
   pituitary —> into bloodstream

Question 17

What are the 2 hormones of the posterior pituitary?

Answer 17

1. AVP (argenine vasopressin/ADH)
2. Oxytocin

Question 18

How is vasopressin released and what are its effect?

Answer 18

Release:
Stimulated by - low blood water potential
Supraoptic magnocellular neurons

Effects:
- Kidney —> V2 receptors (G coupled - adenylate
cyclase - cAMP - protein kinase A) —> aquaporin-2 to
membrane stimulates water reabsorption
- Blood vessels —> V1 receptors —> vasoconstriction
- Anterior pituitary —> ACTH release

Question 19

How is oxytocin released and what are its effect?

Answer 19

Release:
Stimulated by - mechanical nipple stimulation
- labour
Paraventricular magnocellular neurons

Effects:
- Uterus —> myometrial cell contraction —> deliver
baby
- Lactating breast —> myoepithelial cell contract —>
milk ejection

Question 20

How does lactation occur?

Answer 20

Mechanical stimulation of nipple:

• afferent signals to hypothalamus —> dopamine
  release from dopaminergic neurons inhibited —>
  less inhibition of lactorophs —> increased prolactin
  release —> mammary glands —> milk secretion
• afferent signals to hypothalamus —> paraventricular
  magnocellular neuron stimulation —> inc oxytocin
  released —> mammary glands —> milk ejection