Hormone action

Question 1

What is the endocrine system and what does it do?

Answer 1

System of ductless glands that secrete hormones

Regulates many physiological processes e.g. metabolism, homeostasis and reproduction

Question 2

Which organs are part of the endocrine system?

Answer 2

Hypothalamus
Pituitary gland
Thyroid gland
Thymus
Adrenal glands
Gonads
Pancreatic islets
Digestive tract 
Adipose tissue 
Kidney 
Heart
Parathyroid gland 
Pineal gland

Question 3

Define: endocrine glands

Answer 3

Release secretions (hormones) into blood directly from cells = ductless glands

Question 4

Define: exocrine glands

Answer 4

NOT PART OF THE ENDOCRINE SYSTEM

Release their secretions outside the organ/body and may be ducted e.g. gut secretions, sweat glands

Question 5

Define: mixed glands

Answer 5

Both endocrine and exocrine glands

e.g. pancreas produces digestive juice + insulin, glucagon and somatostatin

Question 6

What are the different types f signalling molecules?

Answer 6

Hormones - steroids and related compounds e.g. thyroid and sex steroids
Neurotransmitters - noradrenaline
Growth factors and cytokines - epidermal growth factor

Question 7

What are the major regulatory systems?

Answer 7

Endocrine and nervous systems

Question 8

What are the differences between the endocrine and nervous system in terms of regulatory functions?

Answer 8

Endocrine= uses hormone, effect is generally slow, effects tend to be long-lasting and the effects are localised to secretions into the blood (widespread)

Nervous = uses neurotransmitters, effect is rapid, effects tend to be short-lived and effects are localised to target cells (localised)

Question 9

What are neuro-endocrine hormones?

Answer 9

Boundaries blurred because some hormones are secreted from nerve endings

Question 10

How do hormones work?

Answer 10

Secreted directly into the blood by specialised cells and then they are carried in the blood to receptors on target organs (endocrine, autocrine, paracrine)
Present in only minute concentrations in the blood and bind to specific receptors to influence cellular reactions

Question 11

What is the difference between autocrine, paracrine and endocrine?

Answer 11

Autocrine= same cell
Paracrine= neighbouring cell
Endocrine= released into the blood 

Hormone may have several sites of action simultaneously

Question 12

How is the control of hormone release regulated?

Answer 12

Feedback mechanisms

• feedback:process by which body senses changes and responds to it
• negative feedback: process by which body senses change and activates mechanisms to reduce it - final product of endocrine cascade acts to inhibit the release of hormones higher up the cascade
• Positive feedback: process by which body senses change and activates mechanism to amplify it

Question 13

What is a tropic hormone?

Answer 13

A hormone that stimulates another endocrine gland

Question 14

What factors govern the concentration of hormone seen by the cell?

Answer 14

Rate of production: synthesis and secretion - control mediated by positive and negative feedback circuits
Rate of delivery: high blood flow delivers more hormone than low blood flow
Rate of degradation and elimination: hormones have characteristic rates of decay and are metabolised and excreted from the body through several routes

Question 15

What are the 2 pathways in which hormone receptor interaction can take?

Answer 15

1) altered protein function leading to altered cytoplasmic machinery leading to altered cell behaviour = fast (

Question 16

What are the three main groups of hormones?

Answer 16

Protein/peptide hormones - TRH
Steroid hormones = Cortisol
Amine hormones = adrenaline

Question 17

What are peptide hormones like?

Answer 17

Large, hydrophilic molecules - made of chains of amino acids
E.g. ACTH, GH and insulin
Bind receptor proteins on the cell surface = second messenger system
Most common type
Preformed and stored in membrane bound vesicles ready for release by exocytosis - produced on RER as pre-prohomrones

Question 18

How are peptide hormones produced?

Answer 18

Transcription of gene exported from the nucleus as mRNA to RER for translation of protein from mRNA
Then it can undergo post-translational modifications (glycosylation) in the golgi apparatus
Then its packaged into secretory granule ready for excretion by exocytosis

Question 19

What is common and what is unique with regards to TSH, LH, hCG and FSH?

Answer 19

Glycoproteins with common alpha subunits but their beta subunits are unique and confer specificity
- each subunit starts off as a larger molecule

Question 20

What are steroid hormones like?

Answer 20

Lipophilic and easily pass through plasma membrane -made from cholesterol / acetate
Glucocorticoids (from adrenal cortex) and sex hormones
Receptors are found within the target cells
- e.g. cytoplasm: glucorticoid, androgen. Nucleus: thryoid, vitamin D
Activates/repress gene expression
Synthesised as required and diffuse out
Produced in the SER

Question 21

What are amine hormones like?

Answer 21

Thyroid hormones - made from tyrosine in the thyroid gland
T4 contains iodine residues - metabolised to more active T3

Vitamin D3 regulates Ca metabolism and bone growth (VDR)

Question 22

What are the differences between peptide and steroid hormones?

Answer 22

• chemistry
• virtually all cells in body are targets for steroid/thyroid hormones
• all steroids binds to some extent to plasma proteins e.g. albumin
• Some steroids transported by specific binding proteins, which affect their half life and elimination
• most peptide hormones circulate uncomplexed to serum proteins

Question 23

Why do steroid and thyroid hormones need to be transported in blood by carrier proteins?

Answer 23

• increase solubility in blood
• increase half-life
• create readily accessible reserve in blood

Question 24

What are some examples of specific and non specific binding proteins?

Answer 24

Specific: Thyroid binding globulin and cortisol binding globulin
Non-specific: albumin - loose binding

Question 25

What are the steps of hormone - receptor interaction?

Answer 25

Hormone receptor detects and binds hormone specifically
Binds hormone with high affinity - hormones tend to be present in low concentrations
Present in specific tissues
Saturable with limited number of binding sites
Mediates a biological response

Question 26

What are the two types of hormone receptors?

Answer 26

Cell surface - peptide
- activates second messenger cascade leading to phosphorylation within the cell and then the activated proteins bring about a change in the cellular function
- some steroid hormones bind to membrane receptors and can activate 2nd messenger system
Intracellular - steroid

Question 27

What is tyrosine kinase?

Answer 27

Enzyme that transfers a phosphate from ATP to a tyrosine residue in a protein
- phosphorylation induces conformation changes
- tyrosine kinase activity can be either intrinsic or recruited
Intrinsic= epidermal growth factor receptor or insulin receptor

Question 28

What happens when TSH binds to its receptor?

Answer 28

It causes substitution of GTP for GDP on the alpha subunit of the heterotrimeric G protein = dissociation from the beta and gamma subunits

Question 29

What are the cellular actions of steroid/thyroid hormones?

Answer 29

Bind intracellular receptor which binds to specific hormone response elements within the promoter region of specific genes = modification of gene transcription and protein synthesis
Receptors = ligand inducible transcriptional factors

Question 30

What is interesting about steroid hormone receptors?

Answer 30

Many receptors have been identified that have no known ligand = orphan receptors