- The major systems of the human body are as follows
- The endocrine system is an integration system influencing the metabolic activities of cells. It functions through hormones – chemical messengers synthesized by endocrine glands namely – hypothalamus, pineal, pituitary, parathyroid, thyroid, gonads, and adrenals.
- Hormones :They are the chemical substances produced by the endocrine glands that control the metabolic functions of other cells.
- Steroid based hormones – cholesterol derivatives.
- Amino acid-based hormones: single modified amino acids, amino acid derivatives, proteins, peptides, glycoproteins.
- Eicosanoids derivatives of arachidonic acid, 20-carbon polyunsaturated fatty acid
- Mechanisms of Hormone Action
- Synthesised hormones affect on target cells by:
- Changing in membrane permeability as a result of the closing and opening of the channels.
- Deactivation or activation of regulatory molecules covalent modification.
- Synthesis of regulatory molecules involves changes in gene expression. All these effects result in physiological changes, including :
- Mitotic stimulation
- Contraction or relaxation
- Induction of secretory activity.
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