BIOL 1011 Lecture Notes - Lecture 16: Autocrine Signalling, Pineal Gland, Paracrine Signalling
The Endocrine System and Hormones
March 31, 2015
Endocrine System:
• Chemical signalling system, works with nervous system
• Endocrine cells produce hormones for signals
Hormones – molecules secreted into extracellular fluid that are circulated around
the body and communicate with other tissues; have specific targets and receptors
Local Regulators:
• Paracrine signalling – affects nearby cells
• Autocrine signalling – affects itself
• Neuroendocrine – neurotransmitters pass signals from one nerve cell to
another across a synapse; neurohormones are released from nerve cells into
the blood
• Phermones – secreted into environment (behaviour/reproduction)
Classes of Hormones – the properties of hormones dictate how they are produced,
stored, transported and taken up by cells
1. Water- Soluble : signal transduction
• Packed in small vesicles which fuses with membrane and releases
them into blood
• Hormones are picked up by membrane of specific cell
• This signal receptor will act on the cell to produce a cytoplasmic
response or gene regulation
• Ex. Insulin
2. Lipid-Soluble: direct action
• Freely pass through membrane
Adrenal
glands
Hypothalamus
Pineal gland
Pituitary gland
Thyroid gland
Parathyroid glands
Pancreas
Kidney
Ovaries
Testes
Organs containing
endocrine cells:
Thymus
Heart
Liver
Stomach
Kidney
Small
intestine
Endocrine
Organsand
Tissues
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• Transport protein moves hormones to target cell
• It diffuses through membrane and binds to signal receptor inside the
cell
• When hormone binds, it completes a complex to initialize gene
regulation to produce cytoplasmic response
• Ex. Cortisol (steroid)
Hormones can cause different effects in different tissues if the signal transduction is
different.
Hormone Pathways
1. Simple Endocrine Pathway
• Endocrine cells are stimulated and release a hormone to the blood
• Hormones are picked up by their target cells
• Target cells elicit a response
• The response feeds back to the stimulus or endocrine cell
(positive/negative)
For example, Blood Glucose
• Very critical (70-110mg/100mL)
• Regulated by opposing hormones (insulin and
glucagon)
• Produced by 2 different cells of pancreas
Question: How do Type I and Type II diabetes
affect this pathway?
• Type I – stop producing insulin so blood
glucose becomes too high
• Type II – receptors fail and can not take up
glucose so blood glucose is high
Homeostasis:
Blood glucose level
(about 90 mg/100 mL)
Glucagon
STIMULUS:
Blood glucose level
falls.
Alpha cells of pancreas
release glucagon.
Liver breaks
down glycogen
and releases
glucose.
Blood glucose
level rises.
STIMULUS:
Blood glucose level
rises.
Beta cells of
pancreas
release insulin
into the blood.
Liver takes
up glucose
and stores it
as glycogen.
Blood glucose
level declines.
Body cells
take up more
glucose.
Insulin
Fig.45.13
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