Outline-1, BIO 2320, Endocrine System

IV. Endocrine System

A. Overall functions

1. Regulatory System

2. Maintains homeostasis internally

3. Responds to help cope with environmental changes

4. Growth & development

5. Reproduction

B. Exocrine vs Endocrine glands

Exocrine releases contents into ducts or skin surface, endocrine glands are ductless and release contents into blood

C. Hormone

1. Definition – Chemical messenger carried by bloodstream, made by endocrine glands

2. Structure

Organic, amino acids, cholesterol derivatives

3. Transport

Many are bound to specific carrier proteins

4. Action

a. Target cell

b. Receptors

1. Plasma membrane

2. Within target cell

c. Second messenger cAMP

1. Stimulatory

2. Inhibitory

d. Activation of genes

5. Hormonal interrelationships

6. N.S. & Endocrine relationships

D. Controls

1. Negative feedback

2. Releasing or inhibiting hormones- Hypothalamus

E. Pituitary Gland {Hypophysis}

1. Location

Sella turcica of sphenoid bone

2. Adenohypophysis

Anterior lobe of pituitary gland

a. Gonadotropins

 Stimulates gonads

FSH – Follicle stimulating hormone, stimulates follicle development in ovaries, stimulates sperm production and maturation in male

LH / ICSH Luteinizing hormone results in ovulation in female, Interstitial cell stimulating hormone results in testosterone production in male

b. TSH -Thyroid stimulating hormone

c. ACTH -Adrenocorticotropic hormone

d. GH -Growth hormone

e. Prolactin– Initiates and maintains milk production in female

f. MSH – Melanocyte stimulating hormonestimulates skin melanin (pigment)

g. Endorphins – Peptides made by Adenohypophysis in addition to the hormones that has opiate-like effects

3. Controls

a. Inhibiting/releasing hormones (GnRH Gondadotropin releasing hormone, TRH Thyrotropin releasing hormone, PIF Prolactin inhibiting factor, CRF Corticotropin releasing factor, Somatostatin Growth hormone inhibiting hormone)

b. Brain (Emotions)

c. Feedback

Negative feedback mechanisms prevail

4. Neurohypophysis

Posterior lobe of pituitary gland

a. Infundibulum (Hypothalamic-hypophyseal tract)

b. ADH (vasopressin) – Antidiuretic hormone causes water reabsorption from kidney to bloodstream

c. Oxytocin

Uterine contractions for childbirth and milk letdown

F. Thyroid Gland

1. Location

Inferior larynx

2. Histology (follicle cells, colloid)

3. Thyroid hormones

a. Iodine

b. T4 (thyroxine) 90%

c. T3(triiodothyronine) 10%

d. TBG – Most thyroid hormones are carried in plasma bound to thyroid binding globulin

e. Regulates metabolic rate

f. Controls

TSH, TRH, negative feedback

4. Calcitonin

a. Parafollicular = C cells

b. Decreases Ca & P

c. Controls

If blood calcium levels are high, Calcitonin is secreted

G. Parathyroid glands

1. Location

4 – embedded in posterior surface of thyroid gland

2. PTH (=Parathormone)function (increases Ca; decreases P)

3. Controls

If blood calcium levels are low, PTH is secreted

H. Adrenal gland

1. Location

Superior to kidney

2. Adrenal medulla – Inner portion

a. Chromaffin cells

b. Epinephrine(80%), Norepinephrine (20%)

c. Action (glucose, ht, bl. vessels, bl. pressure, airways)

d. Release (Pregang. neurons, excitement, injury)

3. Adrenal cortex – Outer portion

a. Mineralocorticoids

1. Zona glomerulosa – Outermost layer

2. Aldosterone(90%)

3. Na reabsorption, K excretion – In kidneys

4. Release/controls

a. Renin/Angiotensinogen

Renin is an enzyme made by the kidneys in response to low blood pressure. It causes inactive angiotensinogen to activate into Angiotensin, which stimulates Aldosterone release.

b. High K, Low Na


b. Glucocorticoids

1. Zona fasciculata – Very thick middle layer

2. Conserves & supplements energy

3. Anti-inflammatory

4. Release/controls


b. Stress

c. Sex hormones

1. Zona reticularis – Innermost layer

I. Pancreas

1. Location

Behind stomach and along duodenum (first part of small intestine)

2. Exocrine & endocrine

3. Pancreatic islets (of Langerhans) – ENDOCRINE portion

4. Insulin(beta cells, lowers blood glucose)

5. Glucagon(alpha cells, raises blood glucose)

6. Somatostatin(delta cells, inhibits growth hormone release)

7. Release/Controls

a. Blood glucose level

b. GI hormones – meals/between meals

c. ANS

J. Gonads

Testes make androgens to be discussed later, Ovaries make estrogens and progesterones to be discussed later.

K. Pineal gland

1. Location

Roof of third ventricle in brain

2. Melatonin(decreases repro. activity)

L. Thymus

1. Location

Within mediastinum above heart

2. Puberty

Decreases in size as we mature

3. Immunity

Thymic hormone stimulates T cells after they leave the thymus

M. Prostaglandins

1. Fatty acids

2. Localized

3. Functions vary

Useful Videos:

Crash Course A&P Endocrine System Part 1

Crash Course A&P Endocrine System Part 2

Hormonal Communication Video

Negative and Positive Feedback Mechanisms Video