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D.5 Hormones and Metabolism (Endocrine Gland (Types of Hormones (Lipid,…
D.5 Hormones and Metabolism
Endocrine Gland
Structure that secretes chemical messages called hormones directly into the blood
Types of Hormones
Lipid
Protein
Glycoprotein
Polypeptide
Amine
Tyrosine
Transported to specific target cells
most hormones are under negative feedback mechanism except Oxytocin
some occur
In pair: Adrenal Gland
single: Pancreas
Exocrine
Endocrine
Steroid Hormones
Function
Bind to receptor protein in cytoplasm of target cells
form receptor-hormone complex in cytoplasm of target cell
Property
Lipid Soluble
can cross directly through the target cell's plasma and nuclear membrane
e.g Estrogen
Mechanism of Action
1) Passes through plasma membrane of target cell
2) Binds with receptor protein in cytoplasm
3) Hormone-receptor complex pass through nuclear membrane
4) Hormone-receptor complex attach to DNA
5) Serves as a transcription factor
6) Instruction for synthesis of a polypeptide
7) Polypeptides synthesized by ribosome and mRNA
Receptor-Hormone Complex
affects expression of the calcium transport protein Calbindin
in small intestine
allow absorption of calcium in intestine
Promotes transcription of specific genes
Steroid Hormones
Steroid Hormones crosses the intestinal membrane
Binds to a receptor within the nucleus of cell
May have different effects in different cell
Promotion
Inhibition
Mechanism of Action of Peptide Hormones
dissolves in blood
hydrophilic and lipophobic
bind to surface receptor
triggers reaction mediated by second messenger
brief and reversible
Role of Second Messenger
Epinephrine
1) 'Fight or Flight' response
2) Under threat, organism need supply of blood glucose
3) Epinephrine reaches the liver binds to G-Protein couple receptor
4) G-Protein compose of three sub-units
5) activates G-Protein
Effect of an increased concentration of calcium ion
Muscle cell contraction
secretion of certain substances
cell division
cyclic cAMP - immediate effect is activation of protein kinase enzymes
Iodine Deficiency
Goitre Disease
Hypothalamus and pituitary continuously stimulate thyroid resulting in enlargement of thyroid
Goitre during pregnancy - fatal nervous development and mental retardation of infant
Thyroid Hormones: T3 and T4