Endocrine System

PA 544: Clinical Anatomy

Tony Serino, Ph.D.

Biology Department

Misericordia Univ.

Endocrine System

• Controls and modifies the internal environment by releasing chemicals (hormones) into the blood

• Slower response time but longer duration of action compared to nervous system

Chemical Messengers (hormones)

• Hormone –secreted by cell into blood and acts on another cell some distance away

• Neurohormone –secreted by neuron into blood to affect a target cell some distance away

• Local hormones –secreted by cell into interstitial fluid to affects cells nearby– Paracrines –affect neighboring cells– Autocrines –affect the secreting cell

• Pheromones –secreted by cell onto body surface to affect cells of another individual

Hormones• Chemical Classification

– Amines –single or few amino acids, most water soluble• Epinephrine, Thyroxine (but water insoluble), Melatonin

– Proteins –short to long chains of amino acids; water soluble

• GH, FSH, LH, Insulin, Glucagon, ADH, etc.

– Steroids –derivatives of cholesterol; water insoluble• Estrogen, Testosterone, Progesterone, Cortisol, Aldosterone

Steroid Hormones

Characteristics Common to all Hormones

• Must have target cell with appropriate receptor molecules

• Receptor-hormone complex must trigger events in target cell that changes its physiology

• Mechanisms for deactivating the hormone response must be present

Controlling Hormone Response

• Half-life of the hormone• Physiological range• Modifying target cell response

– Up and down regulation

• Turning off secretion – Negative feedback– Control by other hormones, neurons and

metabolites

Control of Hormone Secretion

Mechanisms of Hormone Action

Water Soluble

WaterInsoluble

Carrier protein

2nd messengers

2nd Messengers: cAMP

2nd Messengers: IP3 and Ca++-Calmodulin

Steroid Hormone Transduction

Different Styles of Secretion• Prohormone –a hormone that is made as a

larger (inactive form) that must be changed prior to secretion (allows for storage of hormone in secreting cell)Ex.: proinsulin, pro-opiomelanocortin

• Prehormone –a hormone that is secreted in an inactive form that must be changed near or in the target cellEx.: Thyroxine, Angiotensinogen

Proinsulin

Types of Endocrine Disorders

• Hypersecretion– Too much secretion of the hormone

• Hyposecretion– Too little secretion of hormone

• Hyporesponsiveness– Normal secretion, but little to no response by

target cells

Endocrine Glands

Control of Growth

• Growth periods: prenatal and postnatal (consists of pre-puberal (especially the first 2 years –infancy) and puberty

• Several factors influence growth: genetics, diet, health, and hormonal balance

• Prenatal growth dominated by insulin secretion, post-natal dominated by GH, thyroxine, and sex hormones

GH secretion and effectsGH secretion stimulated by exercise, fasting, sleep (diurnal rhythm), stress on bones, decreased plasma glucose, increased plasma AA (such as after a high protein meal)

Increase differentiation

Increase protein synthesis

(increase mitosis)

GH interactions with other Hormones

• Thyroxine: essential and permissive for GH– Needed to maintain energy levels for growth– Increases sensitivity of target cells to GH effects

• Insulin: essential for GH effects– Dominant hormone for pre-natal growth

• Estrogen and Testosterone: surge at puberty stimulates GH release, synergistic with GH anabolism; also trigger epiphyseal closure

• Cortisol: anti-growth effects; decrease GH secretion, cell division, and increase catabolism

GH pathologies

• Hypersecretion:– Gigantism –in children

with responsive epiphyseal plates

– Acromegaly –in adults, with closed epiphyseal plates

GH pathologies• Hypofunction:

– Dwarfism –in children

• Pituitary –decreased GH secretion

• Laron –decreased responsiveness due to lack of GH receptors

Achondroplastic Dwarfism (genetic dwarf) due to failure of cartilage to form in epiphyseal plate

28 yo woman withpituitary dwarfism; 45” tall