H O M E O S T A S I S T H R O U G H I N T E R C E L L U L A R C O M M U N I C A T I O N

THE ENDOCRINE SYSTEM

FUNCTIONS OF THE ENDOCRINE SYSTEM

• The endocrine system regulates long-term ongoing physiological process using hormones to preserve homeostasis in the body.• The endocrine system is made up of eight major

glands each of which produces chemicals that are used to regulate; metabolic processes, growth and development, tissue function, sexual function, reproduction, sleep and mood, among other things.• Just about every organ in the body is affected by

the functions of the endocrine system.

MAJOR STRUCTURES OF THE ENDOCRINE SYSTEM

• Hypothalamus• Pituitary Gland• Thyroid Gland• Adrenal Glands• Thymus• Suprarenal Glands• Pineal Gland• Parathyroid Gland• Adipose Tissue• Pancreas• Gonads• (Other related structures; Heart, Digestive Tract,

Kidney)

AN OVERVIEW OF THE ENDOCRINE SYSTEM

HORMONES

• Hormones: Chemical messengers used produces and released by the endocrine system to regulates physiologically processes of the human body.• Release and distributed to work on specific cells

(target cells) that respond to there presence.• The hormones of the endocrine system are

divided into three groups based on their chemical structure (Amino Acid Derivatives, Peptide Hormones, Lipid Derivatives).• There are 50+ different hormones in the human

body.

HORMONES OF THE BODY BY GROUP

• Peptide Hormones• The largest category of hormones• Consist of amino acid chains• Includes all of the hormones secreted by the

hypothalamus, pituitary gland, heart, kidney, thymus, digestive tract, and pancreas.

• Examples; Antidiuretic Hormone, Oxytocin, Growth Hormone, Prolactin, Insulin, etc.

HORMONES OF THE BODY BY GROUPLipid Derivative

Hormones• Steroids Versions• Androgens• Estrogens• Progestins• Mineralocorticoids• Glucocorticods

Lipid Derivative Hormones

• Eicosanoids Versions• Prostaglandins• Leukotrienes• Prostacyclin• Thromboxane

HORMONES OF THE BODY BY GROUP

• Amino Acid Derivative Hormones• Small chemicals that are structurally similar to amino

acids.• Examples of amino acid derived hormones would be;

epinephrine, norepinephrine, melatonin, and thyroid hormones.

HORMONE ACTION & TRANSPORT

• Hormone Transport:• Hormones can be • Freely circulating

• Rapidly removed from bloodstream• Bound to transport proteins e.g. albumin or globulin

HORMONE ACTION & TRANSPORT

• Each hormones’ shape is specific and can be recognized by the corresponding target cells (Lock & Key)

• The binding sites on the target cells are called hormone receptors. • Receptors for peptide hormones, are located on the

surface of cell membranes because they can not cross the membrane to enter the cell

• Thyroid and steroid hormones can cross the membrane and bind to receptors in the cytoplasm or nucleus

• Hormones that can not cross the membrane (e.g. Peptide hormones) bind to the receptor on the surface of the cell

• Binding of hormones to the receptor activate secondary messenger (in this figure binding of hormone activates G protein, and activated G protein activates adenylcyclase

• or activate PDE or activates PLC

• Hormones that can cross the membrane (e.g. steroid hormones) bind to the receptor inside the cell, at the cytoplasm, or they will enter the nucleus and bind to the receptor at the nucleus and initiate transcription)

CONTROLLING ENDOCRINE ACTIVITY

• Hypothalamus regulates the activity of the nervous and endocrine systems• Hypothalamus secrets regulatory hormones (releasing

hormones and inhibiting hormones) that control the activity of the pituitary gland

• Releasing/inhibiting hormones secreted by the hypothalamus either stimulate or inhibit activity of pituitary gland

THREE METHODS OF HYPOTHALAMIC CONTROL OVER THE ENDOCRINE SYSTEM

THE PITUITARY GLAND

• The pituitary gland is called the “master gland” but it is under the control of the hypothalamus. • Hypothalamus and pituitary gland control many

other endocrine functions. • Pituitary Gland releases nine important peptide

hormones.• All nine bind to membrane receptors and use

cyclic AMP as a second messenger.• Pituitary gland is divided into posterior and

anterior lobe.

ANTERIOR PITUITARY GLAND• Anterior lobe of pituitary gland produces 7 hormones (the

first four regulate the production of other hormones)• 1) Thyroid stimulating hormone (TSH)• TSH triggers the release of thyroid hormones by the thyroid glands.• Thyrotropin releasing hormone promotes the release of TSH.

• 2) Adrenocorticotropic hormone (ACTH)• ACTH stimulates the release of glucocorticoids by the adrenal gland.• Corticotrophin releasing hormone causes the secretion of ACTH.

• 3) Follicle stimulating hormone (FSH)• FSH stimulates follicle development and estrogen secretion in

females and sperm production in males.• 4) Leutinizing hormone (LH)• LH causes ovulation and progestin (progesterone) production in

females and androgen (testosterone) production in males• Gonadotropin releasing hormone (GNRH) promotes the secretion of

FSH and LH

ANTERIOR PITUITARY GLAND• 5) Prolactin (PH)• PH stimulates the development of mammary glands

and milk production.• 6) Growth hormone (GH or somatotropin)• GH stimulates cell growth and replication through

release of somatomedins or IGF.• Growth-hormone releasing hormone

(GH-RH)• Growth-hormone inhibiting hormone

(GH-IH)• 7) Melanocyte stimulating hormone (MSH)• Stimulates melanocytes to produce melanin.

PITUITARY GLAND

POSTERIOR PITUITARY GLAND

• The posterior lobe of the pituitary gland secretes two hormones: Antiduretic Hormone and Oxytocin. • 1) Antidiuretic hormone (ADH) • Decreases the amount of water lost at the kidneys• Elevates blood pressure

• 2) Oxytocin• Stimulates contractile cells in mammary glands• Stimulates smooth muscle cells in uterus

THYROID GLAND• Thyroid gland is located near the thyroid cartilage of the larynx.• The two lobes of thyroid gland are connected by an isthmus.• It has 2 distinct population of cells: Flicular Cell (produce thyroid

hormone) and C cell (produce calcitonin).• Thyroid gland release several hormones such as thyroxine (T4)

and triiodothyronine (T3)• Functions of Thyroid hormones include:• Increasing ATP production, when bound to mitochondria.• Activating genes that control energy utilization, when bound to

receptors • Exert a calorigenic effect

• C cells of thyroid gland produce calcitonin• Calcitonin helps to regulate calcium concentration in body

fluids

THYROID

PARATHYROID

• Four parathyroid glands embedded in the posterior surface of the thyroid gland.• Chief cells produce parathyroid hormone (PTH)

in response to lower than normal calcium concentrations.• Parathyroid hormones plus calcitonin are

primary regulators of calcium levels in healthy adults.

PARATHYROID GLAND

ADRENAL GLAND

• Adrenal Cortex• Manufactures steroid hormones derived from cholesterol

(corticosteroids).• Corticosterioid hormones are divided into 3 functional groups

• Mineralocorticoids (Aldosterone)• Regulate mineral and salt balance by renin-angiotensis-aldosterone

system• Glucocorticoids (cortisol and cortisone)

• Regulate glucose levels i.e. they increase gluconeogenesis and decrease protein synthesis

• Decrease inflammation response• Androgens also called sex hormones

• Adrenal Medulla• Responsible for flight-or-fight response • Produces epinephrine and norepinephrine

ADRENAL GLAND

PINEAL GLAND

• Contains pinealocytes• Synthesize melatonin• Suggested functions include inhibiting

reproductive function, protecting against damage by free radicals, setting circadian rhythms (biological clock)

PANCREAS

• Pancreatic Islets• Clusters of endocrine cells within the pancreas called

Islets of Langerhans or pancreatic islets• Alpha cells secrete glucagons• Glucagon raises blood glucose by increasing the

rates of glycogen breakdown and glucose manufacture by the liver

• Beta cells secrete insulin• Insulin lowers blood glucose by increasing the

rate of glucose uptake and utilization• Delta cells secrete GH-IH• F cells secrete pancreatic polypeptide

PANCREAS

KIDNEY• Produce calcitriol and erythropoietin (EPO) and the enzyme

rennin• Calcitriol = stimulates calcium and phosphate ion

absorption along the digestive tract• EPO stimulates red blood cell production by bone marrow• Renin converts angiotensinogen to angiotensin I• Angiotensin I is converted to angiotensin II at the lungs• Agiotensin II:

1. Stimulates production of aldosterone by the adrenal glands

2. Stimulates release of ADH by the pituitary gland3. Promotes thirst4. Elevates blood pressure

ENDOCRINE ACTIVITY

• The Heart• Specialized muscle cells produce natriuretic peptides

in response to high blood pressure• Natriuretic peptide generally has the opposite

actions of angiotensin II • The Intestine• Produce hormones important to the coordination of

digestive activities• The Thymus• Produces thymosins• Help develop and maintain normal immune

defenses

GONADS

• Interstitial cells of the testes produce testosterone• Most important sex hormone in males

• In females, oocytes develop in follicles• Follicle cells produce estrogens

• After ovulation, the follicle cells form corpus luteum. Corpus luteum releases a mixture of estrogens and progesterone

ADIPOSE TISSUE

• Leptin, a feedback control for appetite• Resistin, which reduces insulin sensitivity

HORMONE GROWTH & BEHAVIOR

• Behavior• Many hormones affect the CNS• Changes in the normal mixture of hormones significantly alters

intellectual capabilities, memory, learning and emotional states• Growth• Normal growth requires the interaction of several endocrine

organs• Six hormones are important• GH• Thyroid hormones• Insulin• PTH• Calcitriol• Reproductive hormones