Introduction to Endocrinology

Course Plan

1. Introduction2. Pituitary gland, Hypothalamus and their

disorders3. Hypothyroidism4. Hyperthyroidism5. Diabetes Mellitus6. Acute Complications of Diabetes Mellitus7. Chronic Complications of Diabetes Mellitus8. Disorders of the Adrenal Cortex9. Phaeochromocytoma10.Calcium and the Parathyroids

Introduction

• Endocrinology is the understanding of hormone secretion, hormone action, and principles of feedback control.

• The endocrine system is evaluated primarily by measuring hormone concentrations.

• Most disorders of the endocrine system are amenable to effective treatment once the correct diagnosis is determined.

Introduction

• The term endocrine was coined by Starling • Hormones secreted internally (endocrine) • Externally (exocrine) i.e. into a lumen, such as the

gastrointestinal tract. • The term hormone - derived from a Greek phrase meaning

“to set in motion,” aptly describes the dynamic actions of hormones as they elicit cellular responses and regulate physiologic processes through feedback mechanisms.

Introduction

The Endocrine organs

1. Hypothalamus2. Pituitary gland3. Thyroid gland4. Parathyroid glands5. Adrenal glands6. Pancreatic islet cells (Endocrine Pancreas) 7. Gonads8. Others – Eg. The gastrointestinal tract

The classic endocrine

organs

Introduction

Other hormones

Kidney (Erythropoietin, Renin)

Heart (ANP)

Lungs (PG, ACE)

GIT (Many GI hormones)

Placenta (Many hormones during Pregnancy)

Hormones

5 major classes

1. Amino acid derivatives dopamine, catecholamine, and thyroid hormone;

2. Small neuropeptides gonadotropin-releasing hormone (GnRH), thyrotropin-releasing hormone (TRH), somatostatin, and vasopressin;

3. Large proteins insulin, luteinizing hormone (LH), and PTH produced by classic endocrine glands;

4. Steroid hormones such as cortisol and estrogen;5. Vitamin derivatives such as retinoids (vitamin A) and

vitamin D.

Hormones

A variety of peptide growth factors , most of which act locally, share actions with hormones.

• As a rule – protein based hormones act on the ‘cell surface receptors’ and steroid based hormones act on ‘intracellular nuclear proteins’

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(a) Humoral: in response to changing levels of ions or nutrients in the blood

(b) Neural: stimulation by nerves

(c) Hormonal: stimulation received from other hormones

Mechanisms of hormone release

Endocrine glands

Sites of hormone action

Exocrine glands

Autocrine glands

Sites of hormone action

Neurotransmission

Functions

• Maintenance of growth & development – Growth hormone, Thyroxine, insulin, Glucocorticoid, & Gonadal hormones

• Maintenance of internal environment – ADH, Mineralocorticoids, PTH

• Regulation of energy balance and metabolism –Insulin, glucagon , Leptin & Ghrelin

• Reproduction & species propagation – Gonadal & Pituitary hormones

Interactions between

hormones

• When two or more hormones work together to produce particular result their effects are said to be synergistic.

• These effects may be additive or complementary.

• Additive: Same effect of the hormones on one target organ, for example, epinephrine and norepinephrine on heart rate

• Complementary: Work on different stages of a physiological procedure, for example, FSH (initiation) and testosterone (maintenance) on spermatogenesis

1. Synergistic effects

Interactions between

hormones 1. Synergistic effects

Interactions between

hormones

A hormone is said to have a permissive effect on the action of a second hormone when it enhances the responsiveness of a target organ to the second hormone or when it increases the activity of the second hormone.

• Estrogen – Expression of progesterone receptors on uterus – progesterone effect on the uterus.

• Glucocorticoids – effects of catecholamines on cardiovascular system

• Thyroid hormones- effects of catecholamines on cardiovascular system

2. Permissive effect

Interactions between

hormones

In some situations the actions of one hormone antagonize the effects of another.

Lactation during pregnancy is prevented because the high concentration of estrogen in the blood inhibits the action of prolactin and hence milk secretion.

2. Antagonistic effect

Example of an endocrinal axis

Regulation by negative feedback and direct control is shown, along with the equilibrium between active circulating free hormone and bound or metabolized hormone.

Endocrinal axes

Regulation

• Feedback control , both negative and positive, is a fundamental feature of endocrine systems.

• Each of the major hypothalamo-pituitary-hormone axes is governed by negative feedback, a process that maintains hormone levels within a relatively narrow range

Regulation

• As an example, a small reduction of thyroid hormone triggers a rapid increase of TRH and TSH secretion, thyroid gland stimulation and increased thyroid hormone production.

• When thyroid hormone reaches a normal level, it feeds back to suppress TRH and TSH.

• Feedback regulation also occurs for endocrine systems that do not involve the pituitary gland, Eg. glucose inhibition of insulin secretion

Overview of Endocrine disorders

Overview of Endocrine disorders

Presentation

Investigations