Endocrine System. Endocrine vs Exocrine Endo = within Exo = outCrine = to secrete Exocrine glands (sweat, sebaceous, digestive) secrete products through.

Endocrine System

Endocrine vs Exocrine

Endo = within Exo = out Crine = to secrete

Exocrine glands (sweat, sebaceous, digestive) secrete products through ducts into body cavities or onto body surfaces

Endocrine glands are small, inconspicuous, ductless tissues that deposit products into the interstitial tissues that bathe the cells.

Hormonal Actions

Reproduction Growth and Development Mobility of body defenses Maintenance of blood electrolyte,

water and nutrient balance Regulation of cellular metabolism Energy balance

Regulate the metabolic function of other cells in the body

Chemistry of Hormones Body produces a large variety of hormones Classified chemically as:

A) Amino acid based 1) Makes up the majority

2) Can be simple AA derivatives or long polymers

B) Steroids1) derived from cholesterol

2) only gonadal and adrenocortical hormones

C) Prostaglandins/Eicosanoids1) Derived from lipids

2) Leukotrienes

3) Protaglandins

Endocrine System Focuses on the hormonal control of the body Integrates with nervous system to maintain

homeostasis

Nerves stimulus receivedmillis

econdsMuscle/Gland

Activity

EndocrineGland

Stimulus received

Increase in metabolic

activity in most body cellsSeconds to

Days

Endocrine Hormones

Steroid Hormone Signaling

Amino Acid-Based Hormone Action: cAMP Second Messenger

Second Messenger Mechanisms

Cyclic AMP

Activated G-protein moves along the

membrane; binds and activates the enzyme

Adenylate Cyclase

Receptor changes shape

and binds to an inactive

G-protein

GTP in the cytoplasm

binds to and “turns

on” the G-protein

ActivatedAdenylate Cyclase

generates the second messenger cAMP

from ATP

Hormone binds to its receptor on

the Target cell membrane

cAMP now triggers cascade reactions to

activate protein kinase,which can catalyze

hundreds of reactions

ATP = Adenocine Triphosphate

How Hormones work?

1. Hormones signal a cell by binding to specific receptors on or in the cell

2. lock and key

3. alter chemical rxns in target cell (ex. Initiate synthesis of new protein)

4. different hormones can work together- synergism

5. different hormones can have opposite effect- antagonism

Prostaglandins

lipid molecules that are similar to, but do not meet usually definition of, a hormone

A through I secreted by seminal vesicles, kidneys,

lungs, iris, brain, thymus varied functions. Ex:

– PGE- regulate HCL secretion in stomach– PGF- cause uterus contractions; induce labor

Prostaglandins

Hormone Interaction at Target Cells

Multiple hormones acting upon target cells simultaneously = varied resultsPermissiveness = one hormone depends upon

another in order to have full effect (reproductive hormones need thyroid hormones)

Synergism = More than one hormone amplifies the desired effect (glucagon and epinephrine cause liver to release glucose)

Anatgonism = One hormone opposes the action of another(insulin and glucagon produce opposite effects on blood glucose levels)

Control of Hormone Release Humoral Stimuli

– Respond to blood levels of ions and nutrients• Aldosterone (Kidney)

• Insulin (Pancreas)

Neural Stimuli– Respond to innervation

• Sympathetic nervous system releases Epinephrine and Norepinephrine during stress

Hormonal Stimuli– Respond to release of other hormones

Endocrine Organs & Hormones

Overview of the hypothalamic-pituitary system

The pituitary gland (Hypophysis)1. “master gland”2. stalk- infundibulum3. 2 parts:

1. adenohypophysis (anterior pituitary)- secretes GH, TSH, PRL, LH, FSH, MSH- actually controlled by hypothalamus’ releasing hormones (ex. GnRH)

2. neurohypophysis (posterior pituitary)- secretes ADH and OT

hangs from diencephalon

Pituitary Gland

Posterior pituitary: axons from hypothalamusOxytocin & ADH

Pineal Body

Pineal Body- part of diencephalon

– biological clock- sleeping; female reproductive cycle

– secretes melatonin- induces sleep; secretion inhibited by sunlight

Thyroid Gland: Master of metabolism

below larynx secretes Thyroid

hormones– T4

– T3

– Calcitonin, CT

Thyroid GlandsCell Type Follicular cells Parafollicular cells

Hormone Thyroid Hormones (T3,T4) Calcitonin

Regulator TSH Calcitonin

Target Tissue all tissues Bone

Function Regulates basal metabolic rate Regulates blood Ca++ levels in

and has important influences concert with parathyroid hormone.

on growth and maturation. Calcitonin lowers Ca++ by inhibiting

decalcification of bone.

Parathyroid Gland

Acts on:  Bone:  increases blood calcium by inhibiting osteoblast

deposition of calcium and stimulating osteoclast removal of calcium. 

Kidney:  increases blood calcium by increasing calcium ion reabsorption by kidney tubular cells; inhibits reabsorption of phosphate ion from the glomerular filtrate

Small intestine:  increases the absorption of calcium from the small intestine

Parathyroid Glands- 4 or 5; posterior surface of thyroid; secrete PTH

Calcium regulation

PTH - increases blood calcium by taking in out of bones, kidney, and small intestine

Calcitonin - decreases blood calcium by stimulating uptake into bone

Parathyroid Hormone & Ca2+

Adrenal Glands (aka suprarenal)

top of kidneys; secrete corticosteroids

which are divided into:

1. Mineralocorticoid- aldosterone

2. glucocorticoids- cortisol; cortisone

3. gonadocorticoids- androgens

What’s this stress mess?

The Endocrine Pancreas The endocrine pancreas is

formed by the Islets of Langerhans that are scattered throughout the exocrine tissue.

Secretes the following:– glucagon– Insulin– Somatostatin– pancreatic polypeptide

Islets of Langerhans

A sweet battle: Insulin vs. Glucagon

What happens when there is no insulin?

Miscellaneous structures that produce hormones

1. Placenta- secretes hCG

2. thymus- thymosin and thymopoietin

3. gastric & intestinal mucosa- gastrin, secretin

4. heart- ANH