THE ENDOCRINE SYSTEM

Endocrinology – the study of the biological effects of hormones released by ENDOCRINE GLANDS and

the diseases caused by their dysfunction.

ENDOCRINE GLANDS – ductless glands the release chemical regulators called HORMONES directly into

the extracellular fluid ( interstitial fluid and blood).

What is the difference between hormones and neurotransmitters?

Figure 16.1

The “Major” Endocrine Glands

Release of Hormones• Hormones are released in response to

homeostatic imbalances referred to as STIMULI.

• Hormones work via NEGATIVE FEEDBACK to maintain homeostasis

• Negative Feedback Mechanism – the biological effects of hormones negate/eliminate the stimuli that caused the release of the hormones

General Stimuli for the release of Hormones

• Humoral stimuli – changes in the levels of chemicals in the body’s humors ( bodily fluids) stimulate endocrine glands to release hormones.

• Neural stimuli – activation of the nervous system stimulates endocrine glands to release hormones

• Hormonal stimuli - released hormones stimulate endocrine glands to release other hormones

Figure 16.5

STIMULI FOR THE RELEASE OF HORMONES

Nomenclature• Hormones are named based on:• Organ of Origin – the endocrine gland releasing

the hormone• Ex. Parathyroid hormone

• Function – the major biological effect of the hormone

• Ex. Follicle stimulating hormone

• Chemical Structure – unique feature of the chemical structure

• Ex. Triiodothyronine(T3)

3 Chemical Structures of Hormones• Biogenic amine hormones – hormones

derived from the amino acid TYROSINE

Biogenic hormones are generally polar chemicals

• Peptide/protein/glycoproteins hormones– hormones composed of a sequence of amino acids: attain structural complexity; protein with carbohydrate moiety attached.

These hormones are polar

• Steroid hormones – hormones derived from cholesterol.

Steroid hormones are non polar

Target Cells/Tissues for a Hormone• Express ACCESSIBLE, FUNCTIONAL

receptors that the hormone binds to on or inside the cells.

• A cell may act as a target for several hormones.

• A target cell that possess different types of receptors may be bound to more than one hormone simultaneously.

Hormonal Interactions – How hormones interact with their target cells

• Classical Endocrine Interaction- hormones are released into the bloodstream to reach their target cells

• Paracrine Interaction – hormones are released into interstitial fluid to reach their target cells located nearby.

• Juxtacrine Interaction – hormones bind to their target cells as they are being released from the endocrine cells which are in close contact with the target cells.

• Autocrine Interaction – the endocrine cells releasing the hormone also act as target cells for the hormone

Hormone Receptors

• Characteristics:• All hormone receptors are Proteins (globular proteins)• Hormones bind to their cognate receptors REVERSIBLY

H + R <--------HR• Hormone receptors bind with high affinity and specificity to their

cognate (specific) hormone• Hormone receptors are located on the plasma membrane or inside

the target cells –

2 types of Hormone Receptors:

Membrane or cell surface receptors – bind polar hormones = biogenic amine hormones; peptide/protein/glycoprotein

hormones

Intracellular receptors – cytoplasmic and nuclear receptors

- bind non polar hormones = steroid hormones and the

thyroid hormones

Figure 16.2

Figure 16.3

Figure 16.4

Hormonal Interrelationships – How hormones affect the biological actions of other hormones

• Agonism – a hormone binds to the receptors of another hormone and mimics the biological effects of that hormone

• Antagonism – a hormone binds to the receptors of another hormone blocking the hormone from binding to its own receptors; No biological effects of that hormone observed

• Permissiveness – the biological effects of a hormone ( bound to its own receptors), increases the levels of another hormone and/or increases the number of receptors of that hormone resulting in the overall increase in the biological effects of that hormone

• Cooperativity – hormones work in in tandem on the same target tissue to bring about a desired biological effect.

• Synergism – a group of hormones affects a target tissue simultaneously to bring about a biological response greater than the sum of the individual hormonal effects

Figure 16.6

HYPOTHALAMIC-PITUITARY AXIS

Table 16.1.4

Table 16.1.2

Table 16.1.3

Table 16.1.1

Figure 16.7

Figure 16.8

THE THYROID GLAND

Figure 16.9

BIOSYNTHESIS OF THE THYROID HORMONES = T3 & T4

Table 16.2.1

Table 16.2.2

Figure 16.10

GOITER

EXOPHTHALMOS OF GRAVES’ DISEASE

Figure 16.11

PARATHYROID GLANDS

Figure 16.12

THE BIOLOGICALACTIONS OF PTH

Figure 16.13

THE ADRENAL GLANDS

The Adrenocorticosteroids• Gluccocorticoids – CortisolFunctions: Cortisol stimulates gluconeogenesis, lipolysis,

protein catabolism

Pharmacological uses of cortisol: as anti-inflammatory drugs and as immunosuppressive drugs

Hyper function- Cushing’s syndrome

Hypofunction – Adrenocortical insufficiency

• Adrenal Androgens – DHEA and Androstenedione:

Function: substrates for testosterone• Mineralocorticoids – Aldosterone

Function: Aldosterone stimulates NaCl and water reabsorption

Table 16.3.1

Table 16.3.2

Figure 16.15

Cushing’s syndrome : Buffalo hump; Moon face

Buffalohump

Figure 16.16

THE CATECHOLAMINES = EPINEPHRINE & NOREPINEPHRINE

Table 16.3.2

Figure 16.1

The Major Endocrine Glands

Figure 16.17

THE PANCREAS:

Alpha cells – produce glucagon

Beta cells – produce insulin

Figure 16.18

Figure 16.18 top

Figure 16.18 bottom

Figure 16.19

SYMPTOMS OF DIABETES MELLITUS - due to insulin deficiency or dysfunctional insulin receptors