Endocrine Physiology

Question 1

What are the functions of the endocrine system?

Answer 1

growth and development, thermoregulation, homeostatic regulation (use and storage of nutrients anabolism/catabolism, electrolytes and water), appetite and digestion, coping with diurnal variation and stress, reproductive functions.

Question 2

What are the general characteristics of hormones?

Answer 2

they are produced in response to a stimulus, frequently a derangement of homeostasis. they have specific rates and patterns of secretion (diurnal, pulsatile and cyclic patterns). they operate within feedback systems, either +ve (rare) or -ve to maintain an optimal internal environment. they affect only cells with appropriate receptors, specific cell functions initiated via normal cellular signalling mechanisms.

Question 3

Where are hormones released?

Answer 3

they are released from endocrine glands into the bloodstream, where they affect activity in cells at distant sites.

Question 4

What is an example of diurnal secretion with melatonin?

Answer 4

the pineal gland communicates information about environmental lighting to various parts of the body. this has an effect on sleep/awake cycles and other biological events connected to them, such as a lower production of gastric secretions at night.

Question 5

What is an example of diurnal secretion with cortisol.

Answer 5

HPA axis cortisol is low at night and increases before waking.

Question 6

Give an example of antagonistic hormones and blood calcium homeostasis.

Answer 6

rising blood ca2+ levels stimulates the thyroid gland to release calcitonin, which stimulates calcium salt deposit in the bone, causing the fall of ca2+ levels.

falling blood ca2+ levels causes the parathyroid gland to release PTH which stimulates osteoclasts to degrade the bone matrix and release ca2+ into the blood which raises ca2+ levels.

Question 7

Give an examples of antagonistic hormones and blood sugar levels.

Answer 7

if blood sugar is high, it triggers the pancreas to secrete insulin which causes the conversion of glucose to glycogen, decreasing blood sugar levels.

if blood sugar is low, it triggers the pancreas to secrete glucagon which causes breaks down glycogen to glucose, increasing blood sugar levels.

Question 8

Given example of negative feedback with thermoregulation.

Answer 8

decreased T3 or T4 concentrations in blood or low body temp triggers the hypothalamus to release TRH. this acts on the adenohypophysis which releases TSH. this stimulates the thyroid follicles to release T3 and T4 which supresses TRH and TSH productions.

Question 9

What is an example of positive feedback and oxytocin in contractions during birth?

Answer 9

oxytocin production is positively regulated by the production of prostaglandins.

contractions cause the release of prostoglandins, which causes more oxytocin to be secreted. the brain stimulates the pituitary gland to secrete oxytocin which induces contractions.

Question 10

What is the effect of hormones on target cells?

Answer 10

water soluble factors interact with membrane receptors to initiate signal transduction. lipid soluble diffuse across the membrane via carrier (thyroid hormones) and noncarrier (steroids) medicated mechanisms.

both thyroid hormones and steroid hormones are now appreciated to activate membrane and/or cytoplasmic receptors and induce physiological changes.

Question 11

What are the types of hormones?

Answer 11

amines which are amino acid derivatives, proteins/glycoproteins and steroids which are cholesterol derivatives.

Question 12

What are some examples of amines?

Answer 12

they include catecholamines and thyroid hormones. eg. epinephrine, norepinephrine, dopamine, T3 and T4

Question 13

What are some examples of protein and peptide hormones?

Answer 13

they include pituitary hormones, anterior which is GH, ACTH, TSH, FSH and posterior which is ADH and oxytocin. pancreas releasing hormones such as insulin and glucagon, and parathyoid hormone PTH

Question 14

What is the structure of a glycoprotein hormone?

Answer 14

they contain two subunits, a common alpha subunit and a distinct beta subunit. the B subunit is responsible for hormone specificity and high-affinity binding to the receptor. the a subunit maintains structural stability, dimerization and receptor binding. eg. TSH, LH, FSH, hCG

Question 15

What are examples of steroid hormones.

Answer 15

they include adrenal (cortex) hormones such as cortisol and aldosterone. kidney releasing hormones such as calcitrol which is an activce metabolite of Vit D. ovary releasing hormones such as estrogen and progesterone. teste releasing hormones such as testosterone.

Question 16

What is the function of the hypothalamus?

Answer 16

it is responsible for pain, smell, depression, excitation, nutrients, electrolytes, water and hormones.

Question 17

What are releasing and inhibiting factors of the hypothalamus?

Answer 17

it secretes releasing and inhibiting factors to direct the production of hormones by the anterior pituitary gland.

releasing factors include TRH, CRH, GnRH, GHRH.

inhibiting factors include PIH, GHIH

Question 18

What is the anatomy of the pituitary gland?

Answer 18

there are two lobes, the anterior and posterior. the anterior (adenohypophysis) is glandular and produces and secretes 6 hormones. the posterior (neurohypophysis) is made of neural tissues and stores and secretes 2 hormones ADH and oxytocin.

Question 19

How does the hypothalamic anterior pituitary axis regulate hormone release?

Answer 19

APG produces tropin hormones that stimulate distal endocrine tissues to synthesise and release their hormones.

negative feedback mechanisms inhibit further production of associated releasing hormone or tropin by hypothalamus or anterior pituitary respectively.

Question 20

What is the function of the hormones produced by the AP?

Answer 20

GH - body growth and metabolism
TSH - thyroid gland function
ACTH - glucocorticoid hormone levels
prolactin - breast growth and milk production
FSH and LH - gonad function

Question 21

How is GH regulated?

Answer 21

through somatomedians and ghrelin.

somatomedins are a group of polypeptide hormones (IGF), plasma concentrations are governed by GH secretion. IGF-1 mediates anabolic linear growth-promoting effect of pituitary GH protein, and provides negative feedback which results in the production of somatostatin.

ghrelin is involved in the regulation of apetite, GH secretion and energy balance. it is a GH secretagogue, stimulates release of GH from PG through a specific receptor in hypothalamus.

Question 22

What are factors that stimulate GH?

Answer 22

dec in blood glucose, free fatty acids and protein (starvation/chronic illness).

inc stress (trauma, excitement), exercise, testosterone, estrogen, deep sleep.

Question 23

What are the metabolic actions of GH?

Answer 23

it helps to support glucose homeostasis by conservation of carbs (indirectly via IGF-1) and catabolism of stored fat (directly).

it promotes the use of amino acids to grow and repair tissues (indirectly via IGF-1)

Question 24

What is the function of the thyroid gland?

Answer 24

it is the largest gland and releases the thyroid hormone. the functions of the thyroid hormone are they increase metabolism (heat production is a symptom) and protein synthesis, and it influences growth and development in children.

Question 25

What is the action of T3?

Answer 25

it is actively transported across the cell membrane and diffuses to the nucleus. in the nucleus, it binds to the thyroid hormone receptor to activate transcription of genes containing a thyroid hormone response element THRE. T4 is also transported into the cell but it must be converted into T3.

Question 26

How are glucocorticoid hormone levels regulated?

Answer 26

in the adrenal cortex, they are stimulated by ACTH. aldosterone regulates sodium and potassium levels. cortisol regulates the genetic expression of key enzymes in carbohydrate metabolism. androgens, estrogen and progesterone regulate secondary sexual characteristics.

ACTH stimulates the zona fasciculata to produce glucocorticods (cortisol), and the zona reticularis to produce androgens.

angiostensin 2 stimulates the zona glomerulosa to produce mineralocorticoid (aldosterone)

in the adrenal medulla, it is stimulated by the sympathetic NS. epinephrine and norepinephrine is released.

Question 27

What is the purpose of cortisol?

Answer 27

it supports a wide range of bodily functions such as regulation of blood sugar, blood pressure, bone health, weight, metabolism, inflammation, vision and balance, and mood and depression

Question 28

What is the behaviour and patterns of ACTH levels?

Answer 28

they exhibit both circadian and pulsatile behaviour. the pattern of ACTH production results in predictable patterns of cortisol production by the adrenal cortex in the early morning and mid afternoon. cortisol production follows a natural rhythm with low levels at night and high levels in the morning. people who sleep at night and are awake during the day should have peak cortisol levels between 6-9am, and lowest points between 11pm and 1am

Question 29

What is the role of prolactin in breast growth and milk production?

Answer 29

plays an important role in normal development of mammary tissue and milk production. prolactin release in predominantely under negative control by hypothalamic dopamine. sucking stimulates the release of prolactin, which inhibits its own release by stimulating dopamine release from hypothalamus. males have low levels of prolactin, high levels are pathalogical and associated with infertility.