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Summary FLG222 Endocrinology
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FLG 222: ENDOCRINOLOGYIntro and hypothalamus
Endocrine System vs Nervous system
NERVOUS SYSTEM ENDOCRINE SYSTEM
Electrical communication Chemical communication
Transmission by Neurons Transported via Blood stream
Voluntary/involuntary Involuntary
Localised Often distant
Effect rapid Effect rapid or long-lasting
Endocrine System – organisation
The Endocrine System and Hormones
- Endocrine glands – Hormone secreting glands
- Hormones – Definition includes:
1. Chemicals - released in one part of the body
2. Travel through bloodstream and
3. Affect activities of cells – often distant parts of body (from where hormones where secreted)
4. Affected cells = target cells (have hormone-specific receptors)
, - Hormones are chemical messengers secreted into the bloodstream and exert their effects on target cells (i.e. cells with
receptors for the specific hormone).
- They are secreted by ductless glands known as endocrine glands.
- These glands make up the endocrine system.
- Hormones can be classified based on their chemical structures.
- The endocrine hormones are carried by the circulatory system to cells throughout the body, including the nervous system in
some cases, where they bind with receptors and initiate many cell reactions. Some endocrine hormones affect many
different types of cells of the body.
Hormone Classification
1. Amines
- small group of hormones derived from tyrosine
- made up of Catecholamines & Thyroid hormones
Catecholamines (example – Adrenaline):
- Are water-soluble
- Do not require carrier proteins in plasma (travel freely in the blood)
- Receptor are located on membrane surface (of cell) (not lipophilic and can therefore nor diffuse into
cell)
Thyroid hormones (Example – T3)
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2. Peptide & Protein Hormones
- Examples - Growth hormone, glucagon, prolactin (peptide), insulin (protein), etc
- Largest class of hormones
- Generally water soluble
- Do not require carrier molecules in the blood
- Receptors located on membrane surface
- synthesized on the rough end of the endoplasmic reticulum of the different endocrine cells
3. Steroid hormones
- Example - cortisol, aldosterone, oestrogen, progesterone etc.
- Synthesised from cholesterol
- Are not stored in vesicles
- Rapidly diffuse out of cell once synthesised (due to high lipid solubility)
- Require carrier proteins in blood (due to low water solubility)
- Free steroid hormones enter target cells primarily by passive diffusion
- Exert their effects through membrane surface receptors.
The locations for the different types of hormone receptors are generally the following:
1. In or on the surface of the cell membrane. The membrane receptors are specific mostly for the
protein, peptide, and catecholamine hormones.
2. In the cell cytoplasm. The primary receptors for the different steroid hormones are found mainly in
the cytoplasm.
3. In the cell nucleus. The receptors for the thyroid hormones are found in the nucleus and are believed
to be located in direct association with one or more of the chromosomes.
, Hypothalamus and pituitary
- Concerned with homeostasis
- Located in Brain - below thalamus
- Funnel-shaped stalk = infundibulum connects hypothalamus to pituitary
- Secretes Liberins & Statins (hormones) – regulate pituitary hormone secretion
- The hypothalamus and pituitary are located in the brain.
- The hypothalamus links the nervous and endocrine systems by way of the pituitary gland. Its function is to secrete releasing
hormones and inhibiting hormones that stimulate or inhibit of hormones in the anterior pituitary.
- The hypothalamus also synthesises oxytocin and anti-diuretic hormone (ADH or vasopressin), however, following their
synthesis, the two hormones are transported down the axons to the posterior pituitary.
- The two hormones, oxytocin and ADH, are secreted from the posterior pituitary into the bloodstream.
- Note that both ADH and oxytocin belong to the peptide/protein class of hormones.
Anatomical connection between the hypothalamus and pituitary
- The hypothalamus is connected to the anterior pituitary by the hypophyseal portal
system (a system of blood vessels).
- On the other hand, the hypothalamus is connected to the posterior pituitary by
means of a pituitary stalk, also known as the infundubulum, within which the
neurons are found.
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