Hormones can be chemically classified
into four groups:
- Amino acid-derived: Hormones that are modified amino acids.
- Polypeptide and proteins: Hormones that are chains of amino acids of less than or more than about 100 amino acids, respectively. Some protein hormones are actually glycoproteins, containing glucose or other carbohydrate groups.
- Steroids: Hormones that are lipids synthesized from cholesterol. Steroids are characterized by four interlocking carbohydrate rings.
- Eicosanoids: Are lipids synthesized from the fatty acid chains of phospholipids found in plasma membrane.
Endocrine
glands release hormones in response to one or more of the following stimuli:
- Hormones from other endocrine glands.
- Chemical characteristics of the blood (other than hormones).
- Neural stimulation.
Most hormone production is managed by a
negative feedback system.
The
nervous system and certain endocrine tissues monitor various internal
conditions of the body. If action is required to maintain homeostasis, hormones
are released, either directly by an endocrine gland or indirectly through the
action of the hypothalamus of the brain, which stimulates other endocrine
glands to release hormones.
The
hormones activate target cells, which initiate physiological changes that
adjust the body conditions. When normal conditions have been recovered, the
corrective action - the production of hormones - is discontinued.
Thus, in negative feedback, when the original (abnormal)
condition has been repaired, or negated, corrective actions decrease or
discontinue. For example, the amount of glucose in the blood controls the
secretion of insulin and glucagons via negative feedback.
Sumber : Bpk. Dr. Iskandar Zulkarnain
#posting tugas cyberprenership
ahmad baihaqi
NIM 1112503964
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