Lecture 2 Flashcards
Describe the probable chemical composition of any hormone that binds to a cytoplasmic or nuclear receptor. Also describe the manner of its secretion into the plasma, how it is transported in the blood, the length of its half-life, as well as how its message is conveyed in the effector cell
Half-life of hormones
the amount of time needed for half of the concentration of hormone to disappear from the blood.
Overall functions of the endocrine system? (6)
- Regulate organic metabolism and H2O and electrolyte balance.
- Induce adaptive changes to help body cope with stressful situations.
- Promote smooth, sequential growth and development.
- Control reproduction
- Regulate red blood cell production.
- (Along with autonomic nervous system)
Control and integrate both circulation and the digestion and absorption of food.
What do trophic hormones regulate?
They regulate hormone secretion by another endocrine gland
Another function of tropic hormones
Stimulates and maintains their endocrine target tissues
Example of a trophies hormone
TSH secreted from the anterior pituitary gland stimulates the thyroid hormone secretion by thyroid gland
- Also maintains structural integrity of thyroid gland
Pathway of thyroid hormone control
Tonic release stimulates the hypothalamus to secrete TRH (thyrotropin-releasing hormone)
Which then stimulates the ant pituitary gland to secrete TSH
Which in turn stimulates the thyroid gland to secrete thyroid hormone 4 and 3 which results in systemic metabolic effects which then triggers a negative feedback which results in a decrease in the secretion of TRH
Complexity of endocrine function: (7)
- Single endocrine gland may produce multiple hormones
- Single hormone may be secreted by more than one endocrine gland:
- Somatostatin —> Hypothalamus and pancreas - A single hormone has more than one type of target cell:
- ADH
> V2 receptors on distal and collecting tubules (for H2O reabsorption)
> V1 receptors on arterial smooth muscle cells (vasoconstriction) - Rate of secretion of some hormones varies considerably
- A single target cell may be influenced by more than one hormone
- Insulin - conversion of glucose to glycogen
- glucagon - conversion of glycogen to glucose - The same chem messenger may either be a hormone or a neurotransmitter.
- Some organs are exclusively endocrine and others perform other functions as well
- testis and pancreas
Factors that influence the [plasma] of a hormone (4)
- The hormones rate of secretion into the blood by endocrine gland
- The rate of metabolic activation or conversion:
Modification of a hormone at peripheral organs
> Thyroxine (T4) to tri-iodothyronine (T3)
(Liver and kidney) - Extent of binding of hormones to plasma proteins
- the rate of removal from blood by metabolic inactivation and excretion in urine:
Inactivation by enzymes in liver, kidneys, blood or target cells
Inactivation by enzymes in liver, kidneys, blood or target cells:
Peptide hormones
Hydrolysis of peptide bonds
Inactivation by enzymes in liver, kidneys, blood or target cells:
Insulin
Target cell engulfs hormone-receptor complex by endocytosis and degrades intra-cellularly
Inactivation by enzymes in liver, kidneys, blood or target cells:
Catecholamines
Enzymatically converted to biologically related inactive molecules
Inactivation by enzymes in liver, kidneys, blood or target cells:
Lypophilic steroid- and thyroid hormone
Inactivated by alterations of active portion of molecule
- liver added charge group to make them more water soluble
- freed from plasma protein-carrier and eliminated in urine
Hydrophilic peptides and catacholamines vs lipohylic hormones.
Which has the shortest half life and why?
Hormone secretion is tightly controlled, but inactivation and excretion are not regulated. What is the clinical implication of patients suffering from liver or kidney disease?
