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Lecture notes HUB2019F - Introduction to Endocrinology
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Introduction to Endocrinology
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ENDOCRINOLOGYWhat is the Endocrine system?
= a system which uses chemical messengers/hormones which are released into the blood
- These are regulated by negative feedback
What types of processed do hormones control?
• Reproduction
• Growth and development
• Mobilization of body defenses
• Maintenance of much of homeostasis
• Regulation of metabolism
The Endocrine System is also very important in Intercellular Communication.
- Together with the nervous system’s communication, the two are NB for homeostasis
(thus = Referring to the Neural and Endocrine Signaling)
Hormones = the signals.
Are transported via
bloodstream to the target
cells
At the target cells, they will
bind to receptors thus
leading to a certain response
Therefore NS/ neurotransmitters act locally and rapidly (target cells response quickly and
response ends quickly) = NS responds quickly to rapid changes in the env
While Endocrine system can respond quickly but usually slower acting (their duration of action
varies) to ensure maintenance of homeostasis. Thus, the distance the hormones travel can be
long or short depending on hormone, and don’t necessarily act locally.
, Different types of cell communication
AUTOCRINE = Cell targets itself / The signal/chemical is released by the cell, and specific
receptors on the same cell bind the chemical which has an effect on the cell itself. EG:
PARACRINE = The chemical;/signal = paracrine factors = released by the cell, cant travel far as
too low in concentration, thus have an effect on a neighboring cell
Composition of the Endocrine System
- Endocrine glands (secrete the hormones):
1. Pituitary
2. Thyroid
3. Parathyroid
4. Adrenal
5. Pineal
- Organs with endocrine function (also secrete hormones, used for intercellular
communication):
a) Hypothalamus
b) Thymus
c) Heart
d) Kidneys
e) Stomach
f) Small Intestine
g) Liver
h) Skin
i) Ovaries, Testes
j) Pancreas
k) Adipose Tissue
, • SOME GLANDS ARE PURELY ENDOCRINE / ONLY HAVE ENDOCRINE FUNTIONS
• SOME GLANDS ARE MIXED AND HAVE BOTH ENDOCRINE AND EXOCRINE FUNCTIONS
ENDOCRINE FUNC = insulin and
glucagon hormones secreted by
the pancreas into the blood
stream
EXOCRINE FUNC = enzymes
delivered to small intestine are
released through ducts
, HORMONES
❖ Secreted into the blood
❖ Act ONLY on target cells by binding to the specific receptors of those target cells
❖ Potent, and needed in very small amounts
❖ Produce long-lasting effects in the target cells
❖ Maintain homeostasis by regulating metabolic processes
❖ Action MUST be terminated
❖ Regulated by negative feedback mechanisms
How do we Classify Hormones?
1. WATER-SOLUBLE / HYDROPHILLIC / POLAR HORMONES
o Highly water soluble, low lipid solubility
o Amino acid based
o Size varies [amines = smallest etc]
o Freely circulating in the blood thus don’t need to be bound to carrier protein
o Have a short half-life which can vary from seconds to minutes
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