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Pengantar BiopsikologiMinggu ke-5

Endokrinologi ManusiaAti Harmoni

Sistem Endokrin dan Sistem Saraf

Two systems control all physiologic processes:The nervous system exerts point-to-point control through nerves, similar to sending

messages by conventional telephone. Nervous control is electrical in nature and fast.

The endocrine system broadcasts its hormonal messages to essentially all cells bysecretion into blood and extracellular fluid. Like a radio broadcast, it requires a receiver toget the message - in the case of endocrine messages, cells must bear a receptor for thehormone being broadcast in order to respond. As will be repeatedly demonstrated, thenervous and endocrine systems often act together to regulate physiology. Indeed, someneurons function as endocrine cells.

Sistem EndokrinSistem endokrin adalah sistem pada kelenjar endokrin atau kelenjar buntu yang

menghasilkan zat kimia yang disebut hormon.

Kelenjar endokrin merupakan kelenjar yang tidak mempunyai saluran sehingga sekresinyaakan masuk aliran darah dan mengikuti peredaran darah ke seluruh tubuh. Apabila sampaipada suatu organ target, maka hormon akan merangsang terjadinya perubahan.

Sistem endokrin bekerja paralel dengan sistem saraf mengontrol pertumbuhan, pematanganseksual dan homeostasis.

Pada umumnya pengaruh hormon berbeda dengan saraf. Perubahan yang dikontrol olehhormon biasanya merupakan perubahan yang memerlukan waktu panjang.

Tidak termasuk kelenjar eksokrin seperti kelenjar ludah, kelenjar keringat, dan kelenjar dalamsaluran pencernaan.

HormonHormon dikelompokkan kedalam 3 kelas berdasarkan strukturnya:

1. steroid

2. peptida3. amina

SteroidSteroid adalah lemak yang diturunkan dari kolesterol. Testosteron adalah hormon seks pria.Estradiol, yang mempunyai struktur seperti testosteron, bertanggung jawab atas beberapakarakteristik seks perempuan. Hormon steroid disekresikan oleh gonad, korteks adrenal, danplasenta.


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Peptida and AminaPeptida adalah rantai asam amino pendek; kebanyakan hormon adalah peptida. Hormontersebut disekresikan oleh pituitari, paratiroid, jantung, lambung, hati, dan ginjal.Amina diturunkan dari asam amino tirosin dan disekresikan oleh tiroid dan medula adrenalin.

Synthesis, Storage, and SecretionSteroid hormones are derived from cholesterol by a biochemical reaction series. Defects

along this series often lead to hormonal imbalances with serious consequences. Oncesynthesized, steroid hormones pass into the bloodstream; they are not stored by cells, andthe rate of synthesis controls them.

Gb. 1 dan 2Tujuh kelenjar endokrin yang penting, yang

membentuk sistem endokrin manusia, yaituhipofisis (pituitary gland), tiroid, paratiroid,

kelenjaradrenalin (anak ginjal), pankreas,ovarium, dan testis

Gb. 3

Kerja hormon dalam memilih sel target dan

mengantarkan pesanhormonal

1 2


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Peptide hormones are synthesized as precursor molecules and processed by theendoplasmic reticulum and Golgi where they are stored in secretory granules. Whenneeded, the granules are dumped into the bloodstream. Different hormones can often bemade from the same precursor molecule by cleaving it with a different enzyme.

Amine hormones (notablyepinephrine) are stored as granules in the cytoplasm until needed.

Sistem Endokrin dan Siklus Umpan BalikSistem endokrin menggunakan siklus dan umpan balik negatif (cycles and negative

feedback) untuk mengatur fungsi fisiologis.

Umpan balik negatif mengatur sekresi hampir setiap hormon.

Siklus sekresi menjaga kontrol fisiologis dan homeostatis. Durasi siklus ini bervariasi antarajam sampai bulanan.

Mechanisms of Hormone ActionThe endocrine system acts by releasing hormones that in turn trigger actions in specific target

cells.

Receptorson target cell membranes bind only to one type of hormone. More than fifty humanhormones have been identified; all act by binding to receptor molecules.

The binding hormone changes the shape of the receptor causing the response to thehormone. There are two mechanisms of hormone action on all target cells.

Nonsteroid HormonesNonsteroid hormones (water soluble) do not enter the cell but bind to plasma membrane

receptors, generating a chemical signal (second messenger) inside the target cell. Fivedifferent second messenger chemicals, including cyclic AMP have been identified. Secondmessengers activate other intracellular chemicals to produce the target cell response.

Gb.4

Negative feedback in the thyroxinerelease reflex

Gb.5The action of nonsteroid hormones
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Steroid HormonesThe second mechanism involves steroid hormones, which pass through the plasma

membrane and act in a two step process. Steroid hormones bind, once inside the cell, tothe nuclear membrane receptors, producing an activated hormone-receptor complex. Theactivated hormone-receptor complex binds to DNA and activates specific genes, increasingproduction of proteins.

Gb.6The action of steroid hormones

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