Endocrine Physiology - Part 2

Question 1

What is the Thyroid gland?

Answer 1

• A small gland located in the upper third of the neck, anterior to the trachea and just below the larynx in mammals
• 2 lobes connected by a narrow isthmus

Question 2

What hormones are secreted by the thyroid?

Answer 2

1. Thyroxine (T4)

2. Tri-iodothyronine (T3)

Question 3

Describe the basic histology of the thyroid?

Answer 3

• 2 types of endocrine cells: thyroid hormone secreting cells and clear cells/C cells/para-follicular cells.
• follicles filled with colloid store thyroid hormones

Question 4

What is required for the synthesis of Thyroid hormones?

Answer 4

iodine and tyrosine.

Question 5

What can enhance all aspects of thyroid hormone synthesis?

Answer 5

TSH

Question 6

How are thyroid hormones transported?

Answer 6

• 99% is bound with plasma proteins (released slowly to tissue cells by proteins)

Question 7

What % of hormones released from the thyroid are T3 and what % are T4?

Answer 7

93% = T4 
7% = T3

Question 8

What tissues are effected by thyroid hormones?

Answer 8

almost all

Question 9

Which thyroid hormones (T3 or T4) is more active than the other?

Answer 9

T3 is more active.

Question 10

What happens to most of the T4 that is secreted?

Answer 10

converted to T3 in peripheral tissues by de-iodination

Question 11

How do thyroid hormones work?

Answer 11

• activate nuclear transcription of a large number of genes resulting in the synthesis of many proteins
• this affects nearly all the cells in the body, which increases the functional activity of the whole body

Question 12

What is the function of thyroid hormones?

Answer 12

• increases cellular metabolic activity
• increases O2 consumption in most tissues
• produces heat (calorigenic effect)
• maintains level of metabolism in the body
• increases number and activity of mitochondria
• increases activity of Na+-K+ATPase throughout the body
• enhances cardiac output
• increases rate of utilisation of food

Question 13

What is the major factor that defines the body’s BMR?

Answer 13

plasma conc. of thyroid hormones

Question 14

Describe thyroid levels in endotherms compared to ectotherms

Answer 14

generally elevated in endotherms, but in ectotherms it is selectively elevated during periods of metabolically demanding activity

Question 15

What is the role of thyroid hormones in relation to body growth and the nervous system?

Answer 15

• increases GH secretion
• needed for development of CNS in foetus and after birth
• needed for normal CNS activity in adults
• needed for normal gonadal functions
• required for metamorphosis in frogs

Question 16

How are thyroid hormones regulated?

Answer 16

• by the hypothalamo-pituitary-thyroid axis
• cold exposure enhances secretion
• starvation reduces seretion

Question 17

What does euthyroid mean?

Answer 17

normal thyroid function

Question 18

What is hyperthyroidism?

Answer 18

excess thyroid activity

Question 19

What is the most common disorders in animals?

Answer 19

thyroid disporders

Question 20

What is hypothyroidism?

Answer 20

deficient thyroid activity

Question 21

What is one of the most common endocrine disorders in cats?

Answer 21

hyperthyroidism

Question 22

What is the function of the adrenal medulla?

Answer 22

• produces catecholamines: adrenaline and noradrenaline (aka epinephrine and norepinephrine)

Question 23

What stimulates the adrenal medulla?

Answer 23

• sympathetic nervous system, fight or flight response
• hypoglycaemia
• decreased BP
• cold exposure

Question 24

What is the target of adrenaline and noradrenaline?

Answer 24

heart, smooth muscle, pancreas, eyes

Question 25

What is Pheochromocytoma?

Answer 25

tumour of the adrenal medulla causing excessive secretion of catecholamines

Question 26

What is the function of the adrenal cortex?

Answer 26

secretion of steroid hormones

Question 27

What are the three layers of the adrenal cortex? (outside to inside)

Answer 27

1. zona glomerulosa 2. zona fasciculata 3. zona reticularis

Question 28

What is secreted by the zona glomerulosa?

Answer 28

mineralcorticoids

Question 29

What is secreted by the zona faciculata?

Answer 29

glucocorticoids

Question 30

What is secreted by the zona reticularis?

Answer 30

sex steroids (androgens)

Question 31

What is the main glucocorticoid in mammals?

Answer 31

cortisol

Question 32

What are the metabolic effects of glucocorticoids?

Answer 32

- increases blood sugar (needed during starvation) - enhances protein catabolism and lipid lipolysis - inhibits growth - adapts body to long term stress - anti-inflammatory and immunosuppressive effects

Question 33

What is the clinical use for glucocorticoids?

Answer 33

- used to suppress inflammatory response (inhibits production of substances that promote inflammation) - inhibit allergic reactions

Question 34

How are glucocorticoids regulated?

Answer 34

- by hypothalmic-pituitary-adrenal axis | - influenced by stress and circadian rhythm

Question 35

When are glucocorticoid levels highest in a normal animal?

Answer 35

- in diurnal animals: highest in the morning | - reverse in nocturnal animals

Question 36

What is the main mineralocorticoid?

Answer 36

aldostrone

Question 37

how are mineralocorticoids regulated/ stimulated?

Answer 37

- angiotensin II - elevated ECF K+ conc. - reduction of ECF Na+ conc. - renin

Question 38

What is the target tissue of mineralocorticoids?

Answer 38

renal tubules

Question 39

What is the effect of mineralocorticoids?

Answer 39

- stimulates Na+ reabsorption and excretion of K+ and H+ at the kidneys. - major role in regulating ECF volume and therefore BP

Question 40

What happens if there is no aldosterone?

Answer 40

- ECF K+ rises - sodium and chloride lost - ECF vol falls - cardiac output decreases - shock - death

Question 41

What is hyper-adrenocorticism (cushing's syndrome)?

Answer 41

- over secretion of CRH/ ACTH | - leads to excessive glucose (adrenal diabetes), protein shortage, fat deposition in abdomen

Question 42

What is primary adrenocortical insufficiency (addison's disease)?

Answer 42

- low BP, brady, weak pulse, prolonged CRT - lerthargy - lack of appetite, diarrhoea - syncope - hypoglycaemia - hyponatremia - hypokalemia

Question 43

What is hyperaldosteronism (Conn's disease)?

Answer 43

caused by eithr an adrenal tumour hypersecreting aldosterone, or bilateral adrenal hyperplasia

Question 44

What are the two main causes of Cushing's syndrome?

Answer 44

1. pituitary gland tumour | 1. adrenal gland tumour