L15: HPA Axis & GH

Question 1

What is the hypothalamic pituitary axis?

Answer 1

Functional unit, compromising hypothalamus and pituitary gland, which serves as a major link between endocrine and nervous systems

Question 2

Where is the pituitary gland located?

Answer 2

Beneath hypothalamus in socket of the sella turcica bone at base of skull

Question 3

State the two parts of the pituitary gland and for each state its embryonic origin

Answer 3

• Anterior (adenohypophysis): evagination of oral ectoderm (Rathke’s pouch)- upward growth
• Posterior (neurohypophysis): neuroectoderm/primitive brain tissue- downward grwoth

Question 4

How do axons pass from hypothalamus to posterior pituitary?

Answer 4

Pituitary stalk (infundibulum)

Question 5

State another name for:

• Anterior pituitary
• Posterior pituitary

Answer 5

• Anterior: adenohypophysis
• Posterior: neurohypophysis

Question 6

State some processes modulated by hypothalamus and pituitary gland

Answer 6

Question 7

Describe the relationship between hypothalamus and anterior pituitary, include:

• What signals are sent
• How they are sent
• Consequences of signal

Answer 7

Hormones produced in hypothalamus control hormone production and secretion in anterior pituitary:

1. Hormones synthesised hypothalamus in neurosecretoy cells
2. Transported down axons and stored in median eminence
3. When ready, released into hypophyseal portal system
4. Hormones stimulate or inhibit endocrine cells in anterior pituitary by binding to GPCRs on surface
5. Anterior pituitary produces and secretes hormones to distal and neighbouring cells

Question 8

Striclty speaking, is the posterior pituitary a gland?

Answer 8

No, as it doesn’t produce the hormone it secretes

Question 9

Describe how ADH & oxytocin are produced and released

Answer 9

1. Produced in neurosecretory cells in supraoptic and paraventricular nuclei of hypothalamus
2. Transported down axons (via pituitary stalk/infundibulum) to posterior pituitary (axons merge with capillary bed)
3. Stored and released by posterior pituitary, when required, into general circulation to distant targets. Release is regulated by neuronal inputs to hypothalamus

Question 10

Posterior pituitary contains axons which originated in hypothalamus and some specialised glial cells called…?

Answer 10

Pituitcytes

Question 11

Describe the actions of ADH

Answer 11

• ADH: binds to receptors on epithelium of collecting ducts of kidneys and induces translocation of aquaporins to increase water reabsorption. Can also bind to receptors on smooth muscle cells in vasculature to cause vasoconstriction. Osmoreceptors in hypothalamus detect changes in plasma osmolality to control ADH release

Question 12

Describe the actions of oxytocin

Answer 12

• Oxytocin: suckling stimulates reflex in which signals from breast to hypothalamus cause release of oxytocin. Binds to receptors on myoepithelial cells in mammary glands causing contraction to squeeze milk out. Also released in childbirth due to pressure on cervix as can bind to smooth muscle cells in uterus causing contractions.

Question 13

State 2 hormones produced by hypothalamus but released by posterior pituitary

Answer 13

• ADH
• Oxytocin

Question 14

State 7 tropic hormones produced and released by hypothalamus into hypophyseal system to control release of anterior pituitary hormones

Answer 14

All are TROPIC hormones

• *RH= releasing/stimulating*
• *IH= inhibitory*

Question 15

State the name and role of 6 hormones produced and released by anterior pituitary

Answer 15

Question 16

Give a summary of effects of hormones involved in the hypothalamus & anterior pituitary system (think flow diagram)

Answer 16

Question 17

Does PRH (prolactin releasing hormone) play a major role in controling prolactin secretion?

Answer 17

No, its stimulatory effects don’t account for much of the regulation. A lot of the regultation comes from dopamine (PIH= prolactin release-inhibiting hormone); decrease levels to increase release and vice versa

Question 18

Define:

• Necrosis
• Apoptosis
• Atrophy
• Hyperplasia
• Hypertrophy

Answer 18

Question 19

Hormone production in both hypothalamus and anterior pituitary is regulated by negative feedback; describe the types of loops in this negative feedback

Answer 19

• Ultrashort: hormone released by hypothalamus feeds back
• Short: hormone produced by anterior pituitary feeds back
• Direct long: hormone produced by target endocrine tissue feeds back to anterior pituitary
• Indirect long loop: hormone produced by target endocrine tissue feeds back to hypothalamus

Question 20

Which cells, in anterior pituitary, produce growth hormone?

Answer 20

Somatotrope cells

Question 21

Describe the circadian rhythm of growth hormone

Answer 21

GH released in pulsatile fashion, with circadian rhythm, with maximal release at night

Question 22

Describe what is meant by direct and indirect effects of growth hormone

Answer 22

Exerts direct effects as GH; exerts indirect effects as it stimulates production of insulin-like growth factor (also called somatomedins, IGF1 & IGF2) in liver & skeletal muscle

Question 23

Describe the effects of growth hormone and IGFs in children and in adults

Answer 23

Question 24

Secretion of GH can be regulated by CNS (via inputs to hypothalamus) or metabolically. Describe some things that

a. ) Increase GH secretion
b. ) Decrease GH secretoin

Answer 24

Blue= CNS inputs

Green= metabolic

Question 26

Describe the negative feedback control of GH

Answer 26

* Short loop: GH stimulate or inhibit hormone release * Long loop: IGFs stimulate or inhibit hormone release from anterior pituitary (direct) or hypothalamus (indirect) *\*SAME AS DESCRIBED BEFORE*

Question 27

Explain what growth hormone deficiency in childhood can cause

Answer 27

**Pituitay dwarfism**: propotionate dwarfism. Can have complete or partial deficiency- both respond to GH therapy. Child will have slower growht rate and delayed or no sexual development in teen years

Question 28

Explain what growth hormone excess in childhood can lead to

Answer 28

**Gigantism:** rare and often caused by pituitary adenoma (above average height and girth)

Question 29

Whats another term for growth hormone?

Answer 29

Somatotropin

Question 30

Explain what growth hormone excess in adults can lead to?

Answer 30

**Acromegaly:** large extremeties e.g. hands, feet, lower jaw, broad nose, thickened lips, prominent supraorbital ridge, greasy skin)

Question 31

Describe how growth hormone (somatotropin) exerts its effects **indirectly** (4 step process)

Answer 31

1. GH binds to GH receptor 2. GH receptor coupled to **intracellular Janus Kinase enzyme** 3. Binding of GH causes **cross phosphorylation and activation of Janus Kinase** 4. JAK **activates transcription factor** and turns on **production of IGFs**

Question 32

State the two IGFs, produced mianly in liver and skeletal muscle, in mammals and what each does

Answer 32

* IGF1: fetal growth * IGF2: growth in adults

Question 33

How do IGFs travel in blood?

Answer 33

Bound to specific proteins whcih modulate their ability to activate IGF receptors

Question 34

State some actions of IGFs

Answer 34

* Hypertrophy * Hyperplasia * Increased rate of protein synthesis * Increased rate of lipolysis

Question 35

Growth hormone is not the only hormone which regulates growth; state some other hormones which can regulate growth and how

Answer 35