Optional Endocrinology Reading 2025
NOTE: These Endocrinology notes are only optional.
ALL of the Exam questions from the Endocrinology Section will be taken ONLY
from the Dr. Hardy’s Powerpoint/Video Lectures.
,ENDO I: INTRODUCTION TO ENDOCRINOLOGY
D.B. Hardy
INTRODUCTION TO ENDOCRINOLOGY
Learning Objectives
At the end of this lecture you should be able to:
1. Explain how metabolism is regulated through both neural and endocrine mechanisms and that these
pathways are highly integrated
2. Define and compare the terms endocrine, paracrine and autocrine
3. Define and outline modes of endocrine feedback
4. Define the 3 major classes of hormones.
5. List factors affecting hormone action
6. Describe the functional anatomy of the hypothalamic-pituitary unit including the 3 types of
hypothalamic neurons and their functions.
7. Define the terms circadian, diurnal and ultradian.
8. Explain the generation and importance of episodic endocrine secretion.
9. Outline the 5 hypothalamic-anterior pituitary axes and 2 posterior pituitary axes.
1
,ENDO I: INTRODUCTION TO ENDOCRINOLOGY
D.B. Hardy
Introduction
Metabolic control and homeostasis is maintained through both neural (electrochemical) and endocrine
(chemical) mechanisms whereby the body’s sensory receptors (neuro-, mechano-, osmo-, baro- and
chemo-receptors) detect changes in both the external and internal environments and initiate an
appropriate response. The human neural and endocrine systems are highly integrated as elegantly
demonstrated by the location of the “master gland” or pituitary within the sella turica at the base of the
brain.
Endocrine hormones are chemical messengers synthesized in specialized (endocrine) cells and then
released into the circulation where they are available for uptake by and action on remote tissues. This is
the classic definition of endocrine. However, one should be aware that many of these same endocrine
hormones, and related cytokines and growth factors, can act in a paracrine (on a neighbouring cell or
cells in a tissue) or even autocrine (on the same cell that produces it) fashion. The fundamental concept
is that hormones are chemical mediators of metabolism.
Classes of Hormones
Peptide and polypeptide hormones
• strings of amino acids (aa)
• small monomers e.g. thyrotropin releasing hormone (TRH); 3 aa
• large multimeric proteins containing several subunits e.g. thyroid-stimulating hormone (TSH),
luteinizing hormone (LH) and insulin (Ins).
• polypeptide hormones can have upwards of 200 residues
• larger protein hormones can be very complex in both primary and secondary structure and are
often subject to post-translational modifications such as proteolytic processing and
glycosylation, necessary to produce a functional hormone.
• water-soluble; may or may not be associated with carrier/binding proteins
Steroid hormones are derived from the metabolism of cholesterol through a series of enzymatic steps
which take place in specific subcellular compartments.
• lipid-soluble
• serum carrier proteins (eg. CBG-Corticosteroid Binding Globulin; SHBG-Sex Hormone Binding
Globulin) help to regulate steroid bioactivity--only free steroid is available to the cell.
Amino acid derivatives
• as the name suggests, these hormones are derived from enzymatic modifications of an amino
acid
• catecholamines are derived from the metabolism of phenylalanine and tyrosine to produce L-
dopa, dopamine, norepinephrine and epinephrine all of which function as neurotransmitters
• of more interest to the endocrinologist are the thyroid hormones triiodothyronine (T3) and
thyroxine (T4) which are produced from the biological iodination of tyrosine residues in
thyroglobulin, which are then coupled and cleaved from the parent globulin.
2
, ENDO I: INTRODUCTION TO ENDOCRINOLOGY
D.B. Hardy
Regulation of Endocrine Secretion
• there are several schemas that are important in the regulation of hormone secretion from an
endocrine gland. Most hormone secretion is controlled through negative feedback much like a
thermostat
Negative Feedback
Antagonistic Pairs
“A
_
+
_ +
Compound X
_
+ “B + Compound Y
+
e.g. TSH and T4 e.g. PTH and Ca++ e.g. Insulin, glucose
and glucagon
Positive “Feed Forward”
rising levels of estrogen in the follicular
phase of the menstrual cycle result in the
preovulatory LH surge (green arrow)
the red arrow indicates the negative
feedback of estrogen on LH secretion
3
NOTE: These Endocrinology notes are only optional.
ALL of the Exam questions from the Endocrinology Section will be taken ONLY
from the Dr. Hardy’s Powerpoint/Video Lectures.
,ENDO I: INTRODUCTION TO ENDOCRINOLOGY
D.B. Hardy
INTRODUCTION TO ENDOCRINOLOGY
Learning Objectives
At the end of this lecture you should be able to:
1. Explain how metabolism is regulated through both neural and endocrine mechanisms and that these
pathways are highly integrated
2. Define and compare the terms endocrine, paracrine and autocrine
3. Define and outline modes of endocrine feedback
4. Define the 3 major classes of hormones.
5. List factors affecting hormone action
6. Describe the functional anatomy of the hypothalamic-pituitary unit including the 3 types of
hypothalamic neurons and their functions.
7. Define the terms circadian, diurnal and ultradian.
8. Explain the generation and importance of episodic endocrine secretion.
9. Outline the 5 hypothalamic-anterior pituitary axes and 2 posterior pituitary axes.
1
,ENDO I: INTRODUCTION TO ENDOCRINOLOGY
D.B. Hardy
Introduction
Metabolic control and homeostasis is maintained through both neural (electrochemical) and endocrine
(chemical) mechanisms whereby the body’s sensory receptors (neuro-, mechano-, osmo-, baro- and
chemo-receptors) detect changes in both the external and internal environments and initiate an
appropriate response. The human neural and endocrine systems are highly integrated as elegantly
demonstrated by the location of the “master gland” or pituitary within the sella turica at the base of the
brain.
Endocrine hormones are chemical messengers synthesized in specialized (endocrine) cells and then
released into the circulation where they are available for uptake by and action on remote tissues. This is
the classic definition of endocrine. However, one should be aware that many of these same endocrine
hormones, and related cytokines and growth factors, can act in a paracrine (on a neighbouring cell or
cells in a tissue) or even autocrine (on the same cell that produces it) fashion. The fundamental concept
is that hormones are chemical mediators of metabolism.
Classes of Hormones
Peptide and polypeptide hormones
• strings of amino acids (aa)
• small monomers e.g. thyrotropin releasing hormone (TRH); 3 aa
• large multimeric proteins containing several subunits e.g. thyroid-stimulating hormone (TSH),
luteinizing hormone (LH) and insulin (Ins).
• polypeptide hormones can have upwards of 200 residues
• larger protein hormones can be very complex in both primary and secondary structure and are
often subject to post-translational modifications such as proteolytic processing and
glycosylation, necessary to produce a functional hormone.
• water-soluble; may or may not be associated with carrier/binding proteins
Steroid hormones are derived from the metabolism of cholesterol through a series of enzymatic steps
which take place in specific subcellular compartments.
• lipid-soluble
• serum carrier proteins (eg. CBG-Corticosteroid Binding Globulin; SHBG-Sex Hormone Binding
Globulin) help to regulate steroid bioactivity--only free steroid is available to the cell.
Amino acid derivatives
• as the name suggests, these hormones are derived from enzymatic modifications of an amino
acid
• catecholamines are derived from the metabolism of phenylalanine and tyrosine to produce L-
dopa, dopamine, norepinephrine and epinephrine all of which function as neurotransmitters
• of more interest to the endocrinologist are the thyroid hormones triiodothyronine (T3) and
thyroxine (T4) which are produced from the biological iodination of tyrosine residues in
thyroglobulin, which are then coupled and cleaved from the parent globulin.
2
, ENDO I: INTRODUCTION TO ENDOCRINOLOGY
D.B. Hardy
Regulation of Endocrine Secretion
• there are several schemas that are important in the regulation of hormone secretion from an
endocrine gland. Most hormone secretion is controlled through negative feedback much like a
thermostat
Negative Feedback
Antagonistic Pairs
“A
_
+
_ +
Compound X
_
+ “B + Compound Y
+
e.g. TSH and T4 e.g. PTH and Ca++ e.g. Insulin, glucose
and glucagon
Positive “Feed Forward”
rising levels of estrogen in the follicular
phase of the menstrual cycle result in the
preovulatory LH surge (green arrow)
the red arrow indicates the negative
feedback of estrogen on LH secretion
3
