In dit document van 20 pagina's staan aantekeningen van hoorcolleges en 1 werkcollege van Humane Fysiologie beschreven, inclusief afbeeldingen. De aantekeningen zijn gedeeltelijk in het Nederlands en gedeeltelijk in het Engels geschreven.
Hormones
Chemical mediators of intercullulair communication.
Substances produced by specialized tissues → secreted into the blood → carried to a target organ.
Gland: a group of cells that synthesizes substances such as hormones.
De adrenal gland (bijnier) is specialized for hormone production.
2 (working together) Major control systems in multicullulair organisms:
- Nervous sytem: parasympathisch & sympatisch
- Endocrine system: hormones
6 Groups of hormones:
- Endocrine hormones: endocrine cell → hormone molecules into the bloodstream → target
cell (long distance).
o Source: gland. Does not contribute to specificity of target. Syntheses and secretes
hormones.
o Distribution by: bloodstream. Distributed through body to reach target cell.
Importance of dilution.
o Received by: target cell. Has hormone binding receptors and bring message into the
cell. Responsiveness depends on: number of receptors, downstream pathways, other
ligands, metabolism of receptor cell.
- Autocrine hormones: autocrine cell releases hormone molecules altering its own behavior.
Releasing cel = target cell.
- Paracrine hormones: hormones are released into the intracellulair matrix (short distance) and
changes behavior of neighbour cells.
o Neurocrine hormones (synaptic transmission): paracrine function between brain cells.
▪ Source: adjacent cell. Determinant of target. Syntheses and secretes
hormones.
▪ Distrubution by: matrix.
▪ Received by: target cell. Has receptors
- Pheromone hormones: hormones are released to inform other organisms of the same
species.
- Allomone hormones: hormones are released to inform other organisms of different species.
2 types of glands (klieren):
- Exocrine glands: produces nonhormonal substances (sweat , saliva) and have ducts that carry
these substances to outsite the body.
- Endocrine glands: produces hormones and does not have ducts. Release hormones into
surrounding tissue fluid. Have rich vascular and lymphatic drainage that receives their
hormones.
De pancreas (alvleesklier) is an exocrine and endocrine gland.
- Exocrine function: Acinair cells produces enzymes into pancreatic duct for digestion.
- Endocrine function: Islets of Langerhans produces hormones into blood vessels to target cell.
, Chemical structure and behavior of hormones
Chemical structure determines solubility in water.
- Hydrophilic hormones: Water-soluble. Protein hormones and other mall molecules. Released
by endocrine cell → secreted by exocytosis → dissolved into blood circulation → target.
o Can not pass the membrane on it’s own, must interact with cell membrane receptors.
o Can be produced in advance and stored in vessels untill needed (for example
neurotransmitters).
o Amino acid based hormones are hydrophilic.
- Hydrophobic hormones: Water- insoluble. Mostly lipids / steroids. Released by endocrine
endocrine cell → secreted by diffusion → bound to carrier proteins to transport through
blood → target
o Can’t flow into the bloodstream vessels on it’s own because blood consists of water.
o Can pass the membrane on it’s own and interact with intracellulair receptor.
o Can not be stored in vessels. Go into circulation immediately after production.
o The mitochondria is central during steroid synthesis.
o Steroids (gonadal, adrenocortical) are hydrophoic. Synthesized from cholesterol.
- Eicosandoids: hormones derived from fatty acids (essentiele vetzuren). Biologically active,
modified. lipid made from arachidonic acid.
o Can not past cell membrane, bind to membrane receptors.
o Local effects: paracrine and autocrine function.
3 Types of cell membrane receptors:
Are bind by hydrophilic hormones.
- Channel-linked recepors: Ions pass these receptors.
- Enzyme-linked receptors: Hormone binds receptor → shape receptor changes → receptor
protein becomes enzyme to catalyse reactions.
- G-protein-coupled receptors: Hormone binds ligand → shape ligand changes → bind to G-
protein
Cell membrane receptors activated by hydrophilic hormones change the biochemistry of the target
cell by activating second messengers.
, Intracellulair receptors:
Are bind by hydrophobic hormones that pass though the plasma membrane in carrier proteins:
- Glucocorticoids
- Sex steroids (for example progesterone)
- Mineralocorticoids
- Thyroid hormones
- Retinoids.
Intracellulair receptors for steriod hormones are ligand induced transcription
factors.
Hormone = ligand. Intracellulair receptors activated by hydrophobic hormones
alter gene expression / DNA transcription / protein synthesis.
Comparison between hydrophobic hormones (lipid soluble) and hydrophilic hormones (water soluble)
Stimuli hormone release and responses to hormones
Stimuli causing hormone release:
- Humoral stimulus: hormone (for example PTH) released is caused by altered levels (mostly
low concentration) of certain critical ions or nurtriens (for example calcium)
- Neural stimulus: hormone release is caused by neural input (for example adrenaline,
noradrenaline).
- Hormonal stimulus: hormone release is caused by another hormone. Very common. For
example: releasing hormones from neuroendocrine gland (hypothalamus) → tropic
hormones from pituitary gland (hypofyse) → third hormone secretion from specialized gland.
o In hormonal stimulus, hormonal release is controlled by regulatory (negative)
feedback loops:
▪ Autocrine feedback: endocrine cell hormone → inhibits own hormone
production.
▪ Target cell feedback: endocrine cell hormone → activate target cell which
biological respons is releasing a signal → inhibits endocrine cell.
▪ Brain regulation: hypothalamus hormone → stimulates endocrine cell which
secretes hormones → target cell which biological respons is releasing a signal
→ inhibits hypothalamus hormone production.
▪ Brain and pituitary (hypofyse) regulation: hypothalamus releasing hormone →
pituitary gland tropic hormone → endocrine cells in gland produces third
hormone → reaches target cell & inhibits hypothalamus and pituitary hormone
production.
Releasing hormones produced by the hypothalamus: GHRH, CRH, TRH, GnRH.
Hormones are synthesized in enormous amounts because they’re secreted into the bloodstream.
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