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Lecture notes of endocrinology
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Almost all information given during the lectures of food and metabolism in 2021, all in one document. Including pictures from the slides for more clarification
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ENDOCRINOLOGYLECTURE 1. INTRODUCTION
Endocrinology is the medical specialty and biological science that deals with the endocrine system or
glands that have secretions in the body.
Exam material: lectures
Berthold was the first to do an endocrinology experiment. For this he used roosters. The conclusion
was that the testis produces something that conditions the blood. This conditioned blood caused
changes in the male. Years later this was showed to be the hormone of the testis: testosterone
In 1902 bayliss and starling discovered secreting. In 1889 a part of insulin was discovered, in 1922 the
Langerhans islets were discovered. In 1921 the neurotransmitters were discovered.
The development of new techniques helped in endocrinology research. One of these techniques is RIA
(radioimmunoassay): measuring hormone concentration in the plasma.
In principle the endocrine system is very simple, an endocrine cell produces a hormone into the
bloodstream. This hormone can bind to a receptor and sets in motion a response.
The exocrine gland: deliver products to a duct that leads to the lumen of another organ. Products do
not enter the blood stream.
• Endocrine: cell produces hormone which goes into the blood stream which affects to a distant
cell
• Neuroendocrine: neuron produces hormone which goes into the blood stream which affects
to a distant cell
• Paracrine: cell produces a hormone which affects neighbor cells
• Autocrine: cell produces a hormone which affects itself
• Neurocrine: neuron produces a factor that affects other neurons
Homeostasis is the regulation and maintenance of a balance, so that the
state of the internal environment in the body remains stable. As soon as a
certain value deviates from the norm, the body takes action.
The homeostasis in endocrinology is mainly regulated by negative feedback
systems.
There are also positive feedback
systems. Where metabolites are
increased, which increases a
hormone. (example is ovulation)
,There are two hormone categories:
• Protein hormones: amino acids
o 3- >180 aa
o Linear/ring structure
§ Linear: double/single chain
o Monomer/dimer
o Special adaptations:
§ Sulphation of tyrosine
§ Glutamate pyrrole structure
§ Carbohydrates (glycoproteins)
o Isoforms (gene level/post transcription level)
o Hydrophilic: cannot diffuse into the cell: extracellular receptor
Synthesis of protein hormones follows the standard
DNA-transcription/mRNA translation and formation
of hormone: proprohormone à prohormone à
hormone (chapter 7)
Hormone secretion of protein hormones: stimulus
à intracellular Ca2+ increase à fusion of secretory
granules (filled with hormones from pool of
hormones) with cell membrane à exocytosis
Protein hormones can be broken down into inactive metabolites. Because there are many of these
proteinases that can cut the protein hormones the half-life of those hormones is short
Protien hormones bind to extracellular receptors, this results to intracellular signaling which leads to
response of the cell. A receptor only binds 1 specific hormone which is called ligand binding specificity.
A receptor agonist is a factor that binds to a receptor, mimics a hormone. A receptor antagonist
occupies a receptor, and prevents activation of the receptor by the hormone
All protein hormones bind to extracellular receptors, the main
one is G-protein coupled receptor. >>>>
Different protein hormones are:
• Neurotransmitters: synthesized by neurons, released
and influences directly neighboring cells
• Neuropeptides: peptide hormone produced by nerve
cells
• Growth factors: peptide hormones that regulate growth activity
,Other big class of hormones are steroid hormones. Steroids: lipids with 4 characteristic carbon ring
structures. All steroid hormones are derived from cholesterol, they diffuse into a cell and have an
intracellular receptor. The mechanism of those steroid hormones is different from the protein
hormones. There is almost no storage in the cell, minimal storage in fat droplets. The hormones exit
cell by passive diffusion. The speed of production is the same as the speed of delivery, so the speed of
production is regulated instead of the speed of delivery.
A steroid hormone binds to an intracellular receptor.
Here the hormone-receptor complex moves to the
nucleus where it binds to binding domain promotor.
This leads to gene expression.
Steroid hormones are not able to dissolve into
water. So, they are coupled to transporter proteins.
Steroid hormones vs protein hormones
• Intracellular vs extracellular receptor
• Speed of production is speed of delivery to the circulation: slower delivery into the circulation
• Longer half-life, inactivated in the liver
• Bound to binding proteins
Another hormone category is amines: hormones made from tryptophan or tyrosine
• Melatonin: tryptophan
• Catecholamines: 1 tyrosine
• Thyroid hormone: 2 tyrosine’s
o Unique hormone: iodine needed for its functioning
o Just like steroid hormones: intracellular receptor
Other hormone categories:
• Eicosanoids and fatty acid derivates: prostaglandins, thromboxane, leukotrienes
• Pheromones: organic structures with carbon and hydrogen atoms. Is released by an animal
and causes a behavioral change in another animal
• Electrolytes and metabolites: hormone action: Na+ binds to osmoreceptors
Mechanisms of hormone effects are very simple. However, there are many mechanisms which can
make the endocrinology less simple. Those mechanisms are:
• A cell can only respond to a hormone if the cell has the receptor for that hormone
• A cell does not contain all receptors for all hormones
• But multiple types of cells can contain the same receptor
• The amount of receptors that a cell contains determines the response to a hormone
, Individual physiology is influence by the endocrine system, which in its turn is affected by external/
environmental factors and internal factors. Those factors can be the temperature, length of day, odors,
pain, changed electrolyte concentrations. The body must react to these changes, the endocrine system
does so by producing hormones, thereby inducing homeostasis. This is an interaction between the
nervous system and the endocrine system.
LECTURE 2. HUMAN MENSTRUAL CYCLE
Female genitals:
The ovarian and the menstrual cycle are not the same; the
ovarian cycle refers to the cycle within the ovary
(development of follicles), while the menstrual cycle
refers to the cycling of the endometrium myometrium
lining.
<<<< Different compartments of the regulation of
those cycles
Hormones that are involved are:
• GnRH: gonadotrophin releasing hormone
(LHRH: LH releasing hormone)
• LH: luteinizing hormone
• FSH: follicle stimulating hormone
• E2: estradiol
• P: progesterone
The ovarian cycle consists of two phases, the follicular
phase and the luteal phase, in the middle there is
ovulation. During the luteal phase (previous cycle),
follicles are recruited and grow into a dominant follicle,
within the follicle there is an oocyte, and during the
follicular phase the oocyte matures. During the ovulation
the oocyte is ovulated and the remaining of the follicle
goes into the corpus luteum.
The menstrual cycle also has two phases: the proliferative
phase and the secretory phase. The menstrual cycle starts
with menses which is the breakdown of the endometrial
lining in the myometrium wall. In the second part of the
proliferative phase, the wall is build up again, there is new
endometrial lining. During the secretory phase the
endometrial lining differentiates and it differentiates
making the wall ready for a fertilized oocyte.
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