The Endocrine System

Dr. Anderson GCIT

Endocrine System

• A collection of glands that work together to maintain the homeostasis of the body by:

• Coordinating ____________________________and activity via chemical communication

The Theory of Communication

• All communication has at least three parts

• Sender – entity that releases information• Message – the forms of the information itself• Receiver – the entity that collects and

interprets the information contained in the message

Hormones

• Hormones are chemicals released by glands that control the function/activity of cells generally far from the source of production

Body Communication

• Sender?

• Message?

• Receiver?

Tissue that creates the hormone

The hormone itself

The target tissue

Autocrines vs. Paracrines

Autocrines – cells produce hormones that effect themselves

Paracrines – cells produce hormones that effect other nearby cells

How can chemicals alter cellular function?

Hormones can…

• 1. Alter cell membrane permeability• 2. Stimulate synthesis of proteins or enzymes• 3. Activates or deactivates enzymes• 4. Induces exocytosis• 5. Stimulates mitosis

Human Growth Hormone – Normal Amounts

Examples – HGHAbnormally High Amounts

Testosterone – Normal Amounts

Testosterone – Abnormal Amounts/ Gender Differences

Hormone Classification

• 3 Chemical classes– Amino acid based– Steroid-based (sterols)– Eicosanoid (lipid-based)

• What is the most important functional difference between these molecules?

Amino acid-Based Hormones

• Water soluble, so can diffuse through blood and body fluids easily

• However, they are generally fat-insoluble• How do they enter and affect cells?

Receptor Proteins

• Target cells have receptors for each hormone– Not every cell has all receptors

• Receptors bind with hormones to start a series of events, ultimately changing cell function

Water Soluble (Amino acid-based) Hormones

Fat-Soluble Hormones

• Can go right through the cell membrane!

• Bond with receptor proteins in the cytoplasm instead of the cell membrane

• Receptor-hormone complex can bond to DNA to initiate gene expression

Fat-Soluble Hormones

Hormone Life (Half-life)

• Presence of a hormone in the blood is limited by:

1.

2.

3.

Hormone Release• What controls the release/retention of

hormones?

1. Humoral Stimulus – Blood levels of certain ions/nutrients

2. Neural Stimulus- Nerve fibers stimulate hormone release

3. Hormonal Stimuli – hormones tell glands to release/retain hormones

Regulation

• Hypothalamus – regulates most hormonal release in the body– Monitors body

homeostasis (blood sugar, wastes, hormone levels)

– Direct link to pituitary gland

Pituitary gland

Hypothalamus Hormones

• The hypothalamus makes two hormones that are stored in the posterior pituitary gland– ADH– Oxytocin

• These hormones travel down the infundibulum ( nerve extensions) into the posterior pituitary where they are stored

Pituitary Gland• Bi-lobed structure that stores and produces

hormone• Under the direct control of the hypothalamus!

Pituitary Gland (Hypophysis)

Posterior Pituitary

• Does not create, but rather stores hormones that are made in the hypothalamus

• Derived from nervous tissue– Anti-diuretic hormone (ADH) -

– Oxytocin

Anterior vs. Posterior Pituitary

Anterior Pituitary• Derived from epithelial tissue (secretory cells)

• Creates MANY hormones de novo– Human growth hormone (HGH)– Thyroid Stimulating Hormone (TSH)– Adrenocorticotropic Hormone– Prolactin– Leutinizing Hormone– Follicle Stimulating Hormone

• Released or inhibited as directed by hormones from hypothalamus (stimulates or inhibits AP hormone production and release)

Pituitary Perfusion (Posterior)

• Posterior Pituitary (PP) is perfused with one major artery and vein

• Carries PP hormones out to body

Pituitary Perfusion (Anterior)

• Capillaries are “split” (form plexi) twice!– Primary capillary

plexus– Secondary capillary

plexus

• Why???

Primary plexus

Secondary plexus

Thyroid Gland• Surrounds the

trachea (bilateral lobes)

• Produces the hormone thyroxin

• Why is this not considered to be an exocrine gland?

Thyroid Structure• Principal (Follicle)

Cells – produce thyroglobulin

• Colloid – stores thyroglobulin and iodine molecules

• Parafollicular cells – produce calcitonin

Thyroid Synthesis1. Thyroglobulin made by follicular cells and goes

into follicle2. Iodine trapped from the blood (active

transport)3. Iodide converted to iodine4. Iodine attached to tyrosine5. Iodinated tyrosines are linked6. Thyroglobulin is endocytosed7. Thyroid hormone is processed by enzymes

and diffuse from the cell into the blood stream

Thyroid Production

Calcitonin• Produced by the

parafollicular cells in the thyroid

• Release of calcitonin results in lowered blood Calcium– 1. Inhibits osteoclast activity– 2. Enhances bone absorption

of Ca.

The Parathyroid Glands

• Paired glands located on the posterior aspect of the thyroid

• They produce parathyroid hormone which control Calcium levels in the blood– Antagonist of calcitonin (inhibited by rising Ca

levels)

The Adrenal Glands

• Divided into two sections– Adrenal Medulla (the

core of the gland)

– Adrenal Cortex (the outermost layer of tissue)• Zona glomerulosa• Zona fasciculate• Zona reticularis

Adrenal Cortex

• Produces corticosteroids (derived from cholesterol!)

• Each zone of the cortex produces its own suite of hormones that are functionally specific

Adrenal Cortex – Zona glomerulosa

• Produce mineralocorticoids– Regulate ion concentration in blood and interstitial

fluid

– Aldosterone reduces excretion of Na + from the body and enhances resorption • Production triggered by low blood volume, low blood

pressure and increases in K+ ion concentration.

• Why is this important?

Glucocorticoids

• Synthesized in zona fasciculata

• Cortisol – steroid-based hormone– Release of cortisol promoted

by ACTH release– Depresses inflammation,

increases blood sugar by provoking gluconeogenesis

Gluconeogenesis

• Where do sugars normally come from?

• Gluconeogenesis -

Gonadocorticoids

• Secreted in the zona fascicularis/reticularis

• Most are weak androgens (precursors to testosterone and estrogen)– Not really (anabolic) steroids?

• Play a large role during puberty (both sexes) and female sex drive

The Adrenal Medulla• Chromaffin cells produce

catecholamines – Epinephrine– Norepinephine

• Released during fight-or-flight stress– Increases heart rate,

constricts blood vessels (increasing blood pressure) for a short time

Pineal Gland

• Located in the diencephalon

• Produces melatonin, which causes drowsiness

• Decreased light, received by the eyes (to brain) stimulate the release of melatonin

Pancreas

• Organ most directly related in regulating blood sugar

• Two hormones produced– Glucagon – produced by alpha cells when blood

sugar is low (hypoglycemia)– Insulin – produced when blood sugar is high

(hyperglycemia)

Pancreas

Glucagon

• When released from the pancreas, 1. causes the breakdown of glycogen (liver starch)

into sugar2. Gluconeogenesis3. Release of glucose from liver cells into the blood

Insulin

• When released from the pancreas, insulin…

1. Enhances cellular uptake of blood glucose2. Inhibits gluconeogenesis3. Inhibits the breakdown of glycogen to

glucose

Diabetes mellitus• Due to low or non-functional insulin

• Since sugar cannot be absorbed into body cells:– Blood sugar levels rise (hyperglycemia)– This stress causes the body to release MORE

glucose into the blood!• Gluconeogenesis from fat and protein conversion, the

waste products of which lead to ketoacidosis (nail polish breath)

Diabetes Symptoms

• In the kidneys, sugar lost in urine pulls water from the blood at excessive rates (polyuria)

• Dehydration leads to excessive thirst (polydipsia)

• Excessive hunger (polyphagia) results as fat stores are used in a effort to get sugar into body cells

Ovaries

• Ovaries – produce estrogen and progesterone

– Estrogen – regulates monthly menstrual cycle

– Progesterone – support pregnancy and menstruation

Menstrual Cycle

Testes

• Produce testosterone leading to puberty (secondary sex characteristics), aggression, muscle growth