1. THE ENDOCRINE SYSTEM
Regents Biology

2. OBJECTIVES
Upon completion of this unit students will be able to:
1. Compare the operations of the nervous and endocrine systems.
2. Differentiate exocrine, endocrine glands and hormones.
3. Explain the regulation of hormone secretion through negative
feedback.
4. Identify the two basic mechanisms of hormone action and
describe each.
5. Name the major endocrine glands of the body.
6. List the endocrine hormones and describe their functions.
7. Identify disorders caused by hyper/hypo-secretion of specific
hormones.
KEY WORDS
diabetes mellitus
glands
glucagons
hormones
hypersecretion
hyposecretion
insulin
negative feedback
positive feedback
thyroxin

3. I. INTRODUCTION
The endocrine system is the system which PRODUCES HORMONES FROM GLANDS TO REGULATE METABOLISM, HOMEOSTASIS, GROWTH AND REPRODUCTION
Endocrine glands DISCHARGE SECRETIONS DIRECTLY INTO THE BLOODSTREAM (DUCTLESS GLANDS) and exocrine glands DISCHARGE SECRETIONS INTO DUCTS (e.g., DIGESTIVE GLANDS)
Hormones are SECRETIONS THAT COME FROM GLANDS

4. II. REPRESENTATIVE ORGANISMS
A. Protozoans
Ameoba and paramecium have no endocrine system, but they do RESPOND TO STIMULI FROM THE ENVIRONMENT
B. Hydra
Also do not have an endocrine system, but do respond to stimuli in the environment.
C. Earthworm
Also do not have an endocrine system, but do respond to stimuli in the environment.
D. Grasshopper
Hormones regulate METAMORPHOSIS, color changes, and molting. Some insects have no metamorphosis, some have incomplete metamorphosis (egg larvae [nymph] adult), and some have complete metamorphosis (egg larva pupa adult).
Insects that undergo incomplete metamorphosis include grasshoppers, bugs and mantids. Insects that do not undergo metamorphosis include the SILVERFISH

5. E. Humans
Hormones are transported by the BLOODSTREAM to target organs.
The endocrine glands may undersecrete (HYPOSECRETION) or oversecrete (HYPERSECRETION)
There are 2 ways in which hormones may have an effect on an organ:
ONE-MESSENGER MODEL
TWO-MESSENGER MODEL
  (STEROID HORMONES)
HORMONE PASSES THROUGH CELL MEMBRANE AND ENTERS TARGET CELL TO COMBINE WITH RECEPTOR PROTEIN
ALTERS THE RATE OF REACTION
(PROTEIN HORMONES)
HORMONE CANNOT PASS THROUGH CELL MEMBRANE AND COMBINES WITH RECEPTOR MOLECULE ON MEMBRANE SURFACE
THIS CAUSES THE PRODUCTION OF ENZYMES (2ND MESSENGER)

6. The major endocrine glands are as follows:
1.  Thyroid Gland
o Located in the NECK and secretes THYROXIN, the hormone which regulates metabolic rate. Thyroxin contains IODINE.
o Undersecretion of thyroxin during childhood results in a condition called CRETINISM. The cretin dwarf is not only small but has reduced mental ability.

7. 2. Pituitary Gland
The major link between the endocrine system and the NERVOUS SYSTEM
Called the “MASTER GLAND” because it releases a variety of HORMONES which affect other glands; however, we now know that the secretions of other glands also influence the pituitary, thus, maintaining HOMEOSTASIS in the body by the NEGATIVE FEEDBACK MECHANISM
Example: Thyroid stimulating hormone (TSH) released from the PITUITARY GLAND stimulates the thyroid gland to release THROXIN. The thyroxin level in the blood increases and this affects the pituitary so that it decreases the release of TSH.

8. o Many other hormones are also released by the pituitary, and are often named by the gland or part of the body which the hormone affects. For example, follicle stimulating hormone (FSH), parathyroid stimulating hormone, adrenalcorticotropic hormone (ACTH), human growth hormone (HGH) etc.
o Giantism: HYPERSECRETION OF HGH; RESULTS IN VERY TALL HUMAN
Dwarfism: HYPOSECRETION OF HGH; RESULTS IN VERY SHORT HUMAN
o The HYPOTHALAMUS of the brain appears to produce hormones which influence the pituitary gland.

9.  3.  Parathyroid Glands
o Four glands which are embedded in the THYROID gland
o They secrete parathormone which regulates the amount of the element Ca++ in the blood. It, therefore, affects nerve transmission, bone and teeth formation, and muscle contraction.

10. 4.  Islets of Langerhans (in the Pancreas)
o The Islets of Langerhans are groups of cells embedded in the PANCREAS and secrete the hormones INSULIN and GLUCAGON
o Insulin helps sugar get INTO the body cells as well as stimulating the conversion of excess sugars into animal starch called GLYCOGEN
o Glycogen is stored in the muscles and LIVER
o GLUCAGON acts antagonistically to insulin in that it RAISES BLOOD GLUCOSE LEVEL

11. 5. Adrenal Glands
o Located at the top of each KIDNEY
o Each has an outer region called the CORTEX (for long-term stress) and the MEDULLA (for sudden stress).
o The cortex releases STEROID hormones which influence the conversion of fat and protein to glucose as well as regulating water balance and salts in the blood.
The medulla releases the hormone ADRENALINE during times of emergency. This hormone stimulates the release of glucose into the blood and faster breathing rate and heartbeat. It is often referred to as the “FIGHT OR FLIGHT“ hormone.

12. 6. Thymus Gland
Releases THYMOSIN which is thought to stimulate development of T-LYMPHOCYTES during childhood T-lymphocytes are important in immunity.
7. Gonads (ORGANS)
o     In addition to producing GAMETES, these organs also release hormones which influence the development of the male and female secondary sexual characteristics.
o     At puberty, in the male, release of TESTOSTERONE promotes development of a deeper VOICE, greater growth of body hair, and muscle development.
For the female, ESTROGEN is the main hormone. The menstrual cycle begins at PUBERTY and the female is now releasing EGGS and therefore capable of becoming pregnant. Breast development and rounding out of the female contours (shape) takes place.

13. 8. Stomach and Small Intestine (ORGANS)
o These organs also release hormones which cause them to release digestive juices.
The stomach releases GASTRIN which stimulates the release of juices from the walls of the STOMACH, and the small intestine releases several hormones, one of which is SECRETIN which stimulates the flow of PANCREATRIC JUICE

14. PITUITARY GLAND
HYPOTHALAMUS
THYROID GLAND
PARATHYROID GLAND
THYMUS GLAND
ADRENAL GLANDS
PANCREAS
OVARIES
TESTES

15. (ISLETS OF LANGERHANS)
GLAND
HORMONE
FUNCTIONS
PITUITARY
·       TSH
·       ACTH
·       HGH
·       FSH
·       LH
·       PROLACTIN
·       OXYTOCIN
·       VASOPRESSIN
·       THYROID STIMULATING HORMONE
·       ADRENAL STIMULATING HORMONE
·       STIMULATES GROWTH IN BONES
·       FOLLICLE STIMULATING HORMONE
·       LUTEINIZING HORMONE
·       SECRETION OF BREAST MILK
·       UTERINE CONTRACTION DURING LABOR
·       ANTIDIURETIC
 THYROID
·      THYROXIN
·      REGULATES RATE OF METABOLISM
 PARATHYROID
·       PARATHORMONE
·      REGULATES CALCIUM AND PHOSPHATE METABOLISM
ADRENAL
·      ADRENALINE
·        CORTICOSTERIODS
·      FIGHT OR FLIGHT
·      AFFECT METABOLISM OF CARBS,
PROTEINS AND FATS
PANCREAS
(ISLETS OF LANGERHANS)
·      INSULIN
·      GLUCAGON
·      PUTS GLUCOSE IN CELLS
·      PUTS GLUCOSE IN BLOOD   
GONADS
·     ESTROGEN
·     PROGESTERONE
·     TESTSOSTERONE
·      SECONDARY SEX CHARACTERISTICS; EGGS
·      MENSTRUATION
·      SECONDARY SEX CHARACTERISTICS AND
SPERM PRODUCTION
 THYMUS
 ·      THYMOSIN
 ·      DEVELOPMENT OF T-LYMPHOCYTES