L4 Pituitary Gland

Question 1

What are endocrine glands?

Answer 1

Oragns that secrete hormones directly into the blood stream.

Question 2

What levels can hormones act on?

Answer 2

• Cellular level (e.g. mitosis, apoptosis, secretion)
• Molecular level (e.g. protein synthesis, enzyme activity)
• Whole body level (e.g. growth and development)

Question 3

What is the difference between autocrine and paracrine signalling?

Answer 3

Autocrine: cell which produces a hormone and is influenced by that hormone itself
Paracrine: hormone has an effect on neighbouring cells, it’s not released into circulation

Question 4

What type of chemical nature can hormones be of?

Answer 4

• Steroid
• Peptide
• Single amino acid derived hormones

Question 5

Do hormones travel free in plasma?

Answer 5

Yes, some do.

Others are bound to a carrier protein to prolong the half-life of the hormone.

Question 6

Where is the pituitary gland located?

Answer 6

Close to the optic chiasm, inferior to the hypothalamus.

Question 7

Describe the stucture of the pituitary gland.

Answer 7

• Anterior lobe: connected to hypothalamus by blood vessels
• Posterior lobe: connected to nerve fibres which originate in the hypothalamus, these nerve fibres transport hormones to the posterior pituitary (intra-axonal transport)

Question 8

What is the overall function of the pituitary gland?

Answer 8

“The master gland” which secretes hormones that carry out important bodily functions and also controls the activity of other hormone glands

Question 9

Which 2 hormones does the posterior pituitary release?

Answer 9

• Oxytocin

- Vasopressin (anti-diuretic hormone)

Question 10

What is the function of oxytocin?

Answer 10

• Controls uterine contraction during labour

- Controls milk release from lactating breasts

Question 11

Explain the action of oxytocin.

Answer 11

• Child attaches to breast, sends nerve impulses to hypothalamus
• Hypothalamus produces and releases oxytocin through nerve fibres to posterior pituitary which releases oxytocin to general circulation
• Oxytocin binds to receptors on myoepithelial cells
• Intracellular calcium increases, milk is forced out

Neuro-endocrine reflex

Question 12

What is the function of vasopressin/ADH?

Answer 12

Acts on kidneys to resorb water.

Regulates blood osmolarity and urine output.

Question 13

Explain the action of vasopressin.

Answer 13

• Increased plasma osmolarity stimulates osmoreceptors in the hypothalamus to produce ADH
• Posterior pituitary releases ADH and water is selectively resorbed in distal tubule of kidney
• Urine becomes more concentrated and lower volume
• Decreases plasma osmolarity

Neuro-endocrine reflex

Question 14

Which 6 hormones does the anteiror pituitary release?

Answer 14

• Growth hormone
• Prolactin
• Adrenocorticotropic hormone
• Follicle stimulating hormone
• Lutenising hormone
• Thyroid stimulating hormone

Question 15

What type of hormones does the anterior putuitary secrete?

Answer 15

Tropic hormones: regulate secretions of other endocrine organs.
Prolactin and growth hormones are exceptions, they are not tropic hormones.

Question 16

What is the function of prolactin?

Answer 16

Stimulates milk production.

Question 17

Explain the release of hormones from the anterior pituitary.

Answer 17

• Stimulatory hormones are produced and released from the hypothalamus to control the secretory activity of the anterior pituitary (inhibit or stimulate).
  e. g. dopamine, somatostatin, corticotrophin releasing hormone

Question 18

Which hormones from the hypothalamus inhibit and stimulate secretion of growth hormone?

Answer 18

Inhibit: somatostatin
Stimulate: growth hormone releasing hormone

Question 19

Extent of growth is not entirely dependent on growth hormone, which other hormones play a role?

Answer 19

• Thyroxine inhibits growth
• Cortisol inhibits growth in excess
• Insulin stimulates growth in excess

Question 20

Which cells synthesise and store growth hormone?

Answer 20

Somatotrophs

Question 21

Which tissues does growth hormone target?

Answer 21

Bone and skeletal muscle

Question 22

What are the direct metabolic effects of growth hormone?

Answer 22

• Decreases glucose uptake in muscles
• Stimulates AA uptake and protein synthesis in muscles, inhibits protein breakdown therefore increasing muscle mass
• Decreases glucose uptake in adipose tissue and increases lipolysis so there’s a decrease in fat deposits
• Increases gluconeogenesis, protein synthesis and IgF production in the liver

GH is important in protecting against hypoglycaemia.

Question 23

Which factors increase and decrease GH release?

Answer 23

Decrease: somatostatin

Increase: exercise, stress, sleep, fasting, hypoglycaemia, GHRH

Question 24

Describe gigantism.

Answer 24

• Usually seen in children with pituitary tumours
• Excess GH secreted
• High IgF makes them abnormally tall as growth plates are still open until age 18
• Normal body proportions also affected

Question 25

Describe acromegaly.

Answer 25

• Pituitary tumour causing increased GH in adulthood when growth plates have already fused
• Causes enlarged hands and feet, unusual facial features, protruding jaw, seperation of teeth, enlarged tongue, thickened lips, diabetes, cardiomegaly

Question 26

Describe GH insufficiency.

Answer 26

• No major impact on adults
• Causes pituitary dwarfism in children
• Slow growth rate, normal body proportions, poor muscle development
• GH injections used as treatment

Question 27

Describe oral manifestattions of GH disorders.

Answer 27

• Hypo and hyper pituitarism
• Decreased facial and cranial base growth
• Gaps between teeth, delayed eruption, incomplete root formation
• Overgrown gum tissue
• Missing teeth