Additional Basic concepts

Question 1

Amine precursor uptake and decarboxylation (APUD) cells and the diffuse endocrine system

Answer 1

APUD cells are present in almost all tissues in the body. Hormones can be produced from any cells that possess APUD cells.

Question 2

How enzymes get cleared?

Answer 2

Kidneys
- Intratubular and intracellular degradation
- Uptake from peritubular blood
- Removed in urine

Liver and gut
- Also help eliminate hormones

Question 3

Enhancing hormone half-life

Answer 3

Hormones bind to plasma proteins called globulins

Ex. adrenal and gonadal steroids, thyroxine, and tri-iodothyronine are sulfated or conjugated with glucuronic acid in liver

Question 4

Globulins

Answer 4

• Present in circulation
• Secreted through kidneys
• Reabsorbed in the kidney and intestine

Question 5

Adrenal catecholamines and neurotransmitters inactivators

Answer 5

• Orthomethylation and oxidative deamination by catechol O-metyltransferase (COMT) and monoamine oxidase (MAO)
• NTs within synapses are rapidly terminated (by COMT) or taken back by the presynaptic axon and then inactivated by MAO
• Acetylcholinesterase inactivates acetylcholine in the synapse

Question 6

Receptors availability in cells is regulated

Answer 6

1. Receptor inactivation: When there is excess hormones acting on the cell, the receptor becomes desensitized and no signalling (uncoupling) occurs so pathway is halted
2. Receptor internalization: Ligand (agonist) binds and receptor is internalized in the cell. Hormone can be broken down or be used internally.
3. Receptor down-regulation: ligand binds, and receptor endocytosed into the cell and lysosome breaks it down/recycling

Question 7

Mechanisms that remove agonists

Answer 7

• bind to cell, released and received by receptor for removal
• degraded within the cell
• agonist reuptake and removal from cell