Textbook of physiology
Ch 75 Introduction to endocrinology
Leerstof week 5 (p 925-939)
coordination of body functions
Types of chemical messenger systems:
1. Neurotransmitters: released by axon terminals, act locally to control nerve cell functions
2. Endocrine hormone: released by glands into circulating blood, influences the function of
target cells at another location in the body.
3. Neuroendocrine hormones: are secreted from neurons into circulating blood, influence
the function of target cells at another location in the body
4. Paracrines: secreted by cells into the extracellular fluid, affect neighbouring target cells of
a different type
5. Autocrines: secreted by cells into the extracellular fluid, affect the function of the same
cells that produced them
6. Cytokines: peptides secreted by cells into the extracellular fluid and can function as
autocrine, paracrine or endocrine hormones.
Zie ook table 75-1 op p 927 voor allemaal
belangrijke hormonen!
, Chemical structure and synthesis of hormones
Three general classes of hormones:
1. Proteins and polypeptides: including hormones secreted by the anterior and posterior
pituitary gland, the pancreas, the parathyroid gland, and many other (see table 75-1)
2. Steroid: secreted by adrenal cortex, the ovaries, the testes, the placenta
3. Derivatives of amino acid tyrosine: secreted by thyroid and adrenal medullae, there are no
know polysaccharides or nucleic acid hormones
polypeptide and protein hormones are stored in secretory vesicles until needed
- most hormones in the body are polypeptides and proteins
- in general polypeptides with 100 or more amino acids are called proteins, those with fewer are
referred to as peptides.
proteins are synthesized in the rough end of
the ER of the different endocrine cells.
They are usually synthesized as larger proteins
(pre-prohormones, non-active), then cleaved to
form prohomrones in the ER. These are
transferred to the Golgi apparatus for
packaging in vesicles.
In this process, enzymes in the vesicles cleave
the prohormones to produce smaller,
biologically active hormones and inactive
fragments.
Vesicles are stored in cytoplasm or are bound
the cell membrane.
Secretion occurs by exocytosis, the secretory
vesicles fuse with the cell membrane and the
granular contents are extruded into the
interstitial fluid or into the blood stream.
- The stimules for exocytosis:
1. Increased cytosolic calciu concentration caused by depolarization of the plasma
membrane
2. Stimulation of an endocrine cell surface receptor causes increased cAMP and subsequently
activation of protein kinase that initiate secretion of the hormone.
- peptide hormones are water solube -> allows them to enter circulatory system easily
Steroid hormones are usually synthesized from cholestrol and are not stored
- steroid hormones are lipid soluble and consist of three cyclohexyl rings and one cyclopentyl ring
combined into a single structure.
- Usually very little hormone storage in steroid-producing
endocrine cells, large stores of cholestrol ester in
cyotplasma can be rapidly mobilized for steroid synthesis
- much of cholesterol are produced,but there is also some
novo synthesis of cholesterol
Ch 75 Introduction to endocrinology
Leerstof week 5 (p 925-939)
coordination of body functions
Types of chemical messenger systems:
1. Neurotransmitters: released by axon terminals, act locally to control nerve cell functions
2. Endocrine hormone: released by glands into circulating blood, influences the function of
target cells at another location in the body.
3. Neuroendocrine hormones: are secreted from neurons into circulating blood, influence
the function of target cells at another location in the body
4. Paracrines: secreted by cells into the extracellular fluid, affect neighbouring target cells of
a different type
5. Autocrines: secreted by cells into the extracellular fluid, affect the function of the same
cells that produced them
6. Cytokines: peptides secreted by cells into the extracellular fluid and can function as
autocrine, paracrine or endocrine hormones.
Zie ook table 75-1 op p 927 voor allemaal
belangrijke hormonen!
, Chemical structure and synthesis of hormones
Three general classes of hormones:
1. Proteins and polypeptides: including hormones secreted by the anterior and posterior
pituitary gland, the pancreas, the parathyroid gland, and many other (see table 75-1)
2. Steroid: secreted by adrenal cortex, the ovaries, the testes, the placenta
3. Derivatives of amino acid tyrosine: secreted by thyroid and adrenal medullae, there are no
know polysaccharides or nucleic acid hormones
polypeptide and protein hormones are stored in secretory vesicles until needed
- most hormones in the body are polypeptides and proteins
- in general polypeptides with 100 or more amino acids are called proteins, those with fewer are
referred to as peptides.
proteins are synthesized in the rough end of
the ER of the different endocrine cells.
They are usually synthesized as larger proteins
(pre-prohormones, non-active), then cleaved to
form prohomrones in the ER. These are
transferred to the Golgi apparatus for
packaging in vesicles.
In this process, enzymes in the vesicles cleave
the prohormones to produce smaller,
biologically active hormones and inactive
fragments.
Vesicles are stored in cytoplasm or are bound
the cell membrane.
Secretion occurs by exocytosis, the secretory
vesicles fuse with the cell membrane and the
granular contents are extruded into the
interstitial fluid or into the blood stream.
- The stimules for exocytosis:
1. Increased cytosolic calciu concentration caused by depolarization of the plasma
membrane
2. Stimulation of an endocrine cell surface receptor causes increased cAMP and subsequently
activation of protein kinase that initiate secretion of the hormone.
- peptide hormones are water solube -> allows them to enter circulatory system easily
Steroid hormones are usually synthesized from cholestrol and are not stored
- steroid hormones are lipid soluble and consist of three cyclohexyl rings and one cyclopentyl ring
combined into a single structure.
- Usually very little hormone storage in steroid-producing
endocrine cells, large stores of cholestrol ester in
cyotplasma can be rapidly mobilized for steroid synthesis
- much of cholesterol are produced,but there is also some
novo synthesis of cholesterol
