MEH - Intro To Endocrinology

Question 1

What is the ‘biological clock’ in the brain?

Answer 1

A small group of neurones in suprachiasmatic nucleus which take cues from the environment to keep the body on a 24 hour cycle.

Question 2

What three things in the body change as a result of the circadian rhythm?

Answer 2

Core body temperature, cortisol and melatonin

Question 3

Which cues from the environment influence the circadian rhythm?

Answer 3

• light
• temperature
• social interaction
• exercise
• eating/drinking pattern

Question 4

Which hormone is mainly involved with setting the biological clock?

Answer 4

Melatonin from the pineal gland

Question 5

What is the difference between negative and positive feedback?

Answer 5

Negative feedback is a response in a way to reverse the direction of change, while positive feedback is response in a way so as to increase the magnitude of the change away from normal.

Question 6

Give some examples of positive feedback

Answer 6

Ovulation and blood clotting

Question 7

What is meant by short loop, long loop and ultrashort loop in negative feedback?

Answer 7

Ultrashort loop - hormone 1 is secreted by the hypothalamus and inhibits its own release
Short loop - hormone 1 triggers anterior pituitary to form hormone 2, which inhibits release of hormone 1 from the hypothalamus
Long loop - same as short loop, except hormone two causes release of hormone 3 from target gland, which inhibits release of hormone 1/2

Question 8

How is body water measured?

Answer 8

Osmotic pressure of blood plasma is monitored by osmoreceptors in hypothalamus

Question 9

What is osmolarity?

Answer 9

The number of osmoles per litre of solution

Question 10

What is osmolality?

Answer 10

The number of osmoles per Kg of solution

Question 11

What is an osmole?

Answer 11

The amount of a substance that dissociates in solution to form one mole of osmotically active particles, eg a 1 mM solution of NaCl corresponds to an osmolarity of 2 mOsmol/L (one mOsmol from Na+ ions and one from Cl- ions)

Question 12

What is the normal blood osmolality value?

Answer 12

Between 275 and 295 mOsm/kg

Question 13

What happens if the body detects high blood osmolality?

Answer 13

• body needs to conserve water
• detected by osmoreceptors in hypothalamus which cause posterior pituitary to secrete more ADH
• osmoreceptors also increase thirst
• increased reabsorption of H2O from urine into blood in collecting ducts in the kidney
• only small volume of concentrated urine is excreted so normal osmolality is restored

Question 14

What happens if low blood osmolality is detected?

Answer 14

• body needs to excrete water
• this is detected by the osmoreceptors in the hypothalamus
• posterior pituitary secretes less ADH causing decreased resorption of H2O from urine into blood in collecting ducts in the kidney
• a large volume of dilute urine is passed and normal blood osmolality is restored

Question 15

How is plasma glucose maintained at a steady level?

Answer 15

If glucose levels increase, pancreas releases insulin which stimulates glycogenesis in the liver and glucose uptake into tissues. Plasma glucose declines.
If glucose levels decrease, pancreas releases glucagon which stimulates glycogenolysis in the liver. Glucose is released into the blood and plasma glucose increases.

Question 16

Define ‘hormones’

Answer 16

Chemical signals produced in endocrine glands or tissues which travel in the bloodstream to cause an effect on other tissues

Question 17

What are the major endocrine glands?

Answer 17

Hypothalamus, pituitary gland, pineal gland, parathyroid gland, thyroid gland, thymus, adrenal gland, pancreas, ovary, testis

Question 18

True or false - only endocrine glands can release hormones?

Answer 18

False - the heart, liver, stomach, placenta, adipose and kidney all release important hormones too

Question 19

Give some similarities between the nervous system and the endocrine system

Answer 19

• both neurons and endocrine cells can secrete and be depolarised
• some molecules act as both neurotransmitter and hormone
• both require interaction with specific receptors in the target cells
• both work to control homeostasis

Question 20

What are the four classifications of hormones?

Answer 20

• peptide/polypeptide
• amino acid derivatives
• glycoproteins
• steroids

Question 21

Which protein classes are water soluble?

Answer 21

Peptide/polypeptide and glycoproteins are water soluble, while amino acid derivatives and steroids are lipid soluble.

Question 22

Give some examples of peptide/polypeptide hormones

Answer 22

• insulin
• glucagon
• growth hormone

These are all short chains of amino acids

Question 23

Give some examples of glycoprotein hormones

Answer 23

• luteinizing hormone
• follicle stimulating hormone
• thyroid stimulating hormone

All large protein molecules, often made up of subunits with a carbohydrate side chain

Question 24

Give some examples of steroid hormones

Answer 24

• cortisol
• aldosterone
• testosterone

These are all derived from cholesterol

Question 25

What are amino acid derivative hormones synthesised from?

Answer 25

Aromatic amino acids, eg. adrenaline, noradrenaline and thyroid hormones are all derived from tyrosine

Question 26

Why do some hormones bind to carrier proteins in blood?

Answer 26

• increase solubility of hormone in plasma
• increase half-life
• readily accessible reserve

Question 27

What are the three main factors that determine hormone levels in the blood?

Answer 27

• rate of PRODUCTION (this is the most highly regulated aspect of hormonal control)
• rate of DELIVERY (higher flow to a particular organ will deliver more hormone)
• rate of DEGRADATION (hormones are metabolised and excreted from the body)

Question 28

How do water soluble hormones influence the target cell?

Answer 28

They bind to cell surface receptors, eg. GPCRs or tyrosine kinase

Question 29

What are the two ways that lipid soluble hormones bind to the target cell?

Answer 29

1) cytoplasmic receptor binds hormone and receptor-hormone complex enters nucleus and binds to the DNA
2) hormone enters nucleus and binds to a pre-bound receptor on the DNA eg thyroid hormone. Binding relieves repression of gene transcription

In both cases, expression of new protein mediates the effects of the hormone

Question 30

In general terms, what causes obesity?

Answer 30

A chronic imbalance between energy intake and energy expenditure

Question 31

Where is the appetite control centre located?

Answer 31

In the hypothalamus

Question 32

What is the appetite control centre composed of?

Answer 32

Clusters of neurones called ‘nuclei’ which make up the arcuate nucleus

Question 33

What are the two types of primary neurone in the arcuate nucleus?

Answer 33

• stimulatory neurones, which contain neuropeptide Y (NPY) and Agoouti-related peptide (AgRP) and promote hunger
• inhibitory neurones, which contain pro-opiomelanocortin (POMC) which yields several neurotransmitters, including alpha-MSH and beta-endorphin and promote satiety

Question 34

What do primary neurones synapse with?

Answer 34

Secondary neurones in other regions of the hypothalamus, and the signals are integrated to alter feeding behaviour

Question 35

What is leptin released by?

Answer 35

Released into blood by adipocytes

Question 36

How does leptin suppress appetite?

Answer 36

• stimulates inhibitory (POMC) neurones
• inhibits excitatory (AgRP/NPY) neurones in the arcuate nucleus
• induces expression of uncoupling proteins in mitochondria, so energy is dissipated as heat

Question 37

What is the role of insulin in appetite regulation?

Answer 37

It suppresses appetite by similar mechanism as leptin

Question 38

Where is amylin released from?

Answer 38

Peptide hormone secreted by beta cells in the pancreas

Question 39

What are the roles of amylin?

Answer 39

Role not fully understood, but definitely suppresses appetite, decreases glucagon secretion and slows gastric emptying

Question 40

What is pramlintide?

Answer 40

An amylin analogue approved for treatment of type 2 diabetes