ENDOCRINE GLANDS

Endocrine glands, (Figure 51-3), are located throughout the body and regulate many of its vital processes.  This section discusses the Hormones that each endocrine gland produces and their effects on the Body.

OBJECTIVES:  List the major endocrine glands and hormones found in the body.  Discuss the relationship between the hypothalamus and the pituitary gland.  Describe the function of each endocrine gland.

THE RELATIONSHIP BETWEEN THE HYPOTHALAMUS AND THE PITUITARY GLAND

THE HYPOTHALAMUS

1. The Hypothalamus is the part of the Brain and Nervous System that regulates body temperature, breathing, hunger and thirst.  Located beneath the Thalamus in the Brain, it Regulates Our Body's Internal Environment.

2. The Hypothalamus can also be considered the Master Switchboard for the Endocrine System. The Hypothalamus REGULATES the Two Lobes Pituitary Gland. By Releasing - Releasing or Releasing-Inhibiting Hormones.

3. The Hypothalamus LINKS the Nervous System to the Endocrine System.

4. NEUROSECRETORY CELLS of the Hypothalamus Produce hormones that EITHER are STORED in the Pituitary Gland or REGULATE the Pituitary's Activity.

5. The Hypothalamus is continuously checking (monitoring) conditions inside your body.

6. If your Internal Environment (Homeostasis) starts to get out of balance, The Hypothalamus has several ways to set things right again.

    A. Send out a Nerve Signal to another part of the Brain – the Medulla – to speed up or slow down your heart rate.

    B.  Send out commands in the form of Hormones, thus acting like an Endocrine Gland.

7. THE HYPOTHALAMUS AND THE PITUITARY GLAND ARE THE PRIMARY REGULATORS OF THE ENDOCRINE SYSTEM.

THE PITUITARY GLAND - TWO LOBES - POSTERIOR AND ANTERIOR

1. A small gland about 1 cm in diameter is connected to the Hypothalamus by a Stalk-like Structure.

2. The Pituitary has TWO portions called the Posterior and the Anterior Pituitary. (Figure 41-4)

3. The Posterior Pituitary Stores Two Hormones, Vasopressin or ADH and Oxytocin, both which are Produced By and Released from the Hypothalamus.

    A. ANTIDIURETIC HORMONE - (ADH) OR VASOPRESSIN  – Causes the kidneys to form more concentrated urine, conserving water. Thus, the kidneys produce urine with a High Solute Concentration.

    B. OXYTOCIN – Stimulates Contractions of the Uterus during Labor, also causes the release of milk from the breast of a nursing mother.

ANTERIOR PITUITARY GLAND

1.  Neurosecretory Cells in the hypothalamus also produce and secrete RELEASING HORMONES, which STIMULATE Endocrine Cells of the Anterior Pituitary Lobe to Produce and Secrete Hormones.

2. Other Hypothalamic Cells which Produce RELEASE-INHIBITING HORMONES,  which INHIBIT Production and Secretion of the Anterior Pituitary Hormones

3.  Releasing Hormones and Release-Inhibiting Hormones are produced in response to various stimuli that are processed by the Nervous system.

4. There is at Least ONE Releasing Hormone for each Anterior Pituitary Hormone.

5. The Anterior Pituitary Produces at least 7 different Hormones:

    A.  GROWTH HORMONE (GH) (SOMATOTROPIN) – Promotes cell division, protein synthesis, and Bone and Muscle Growth.

    B.  PROLACTIN (PRL) – It causes mammary gland in breast to develop and produce milk.  It also plays a role in carbohydrate and fat metabolism.

    C.  MELANOCYTE-STIMULATING HORMONE - stimulates the Melanocytes of the Skin, increasing their production of the dark pigment melanin.

6. The Anterior Pituitary (Hypophysis) is sometimes called the Master Gland because it Controls the Secretion of other Endocrine Glands.

7. The Anterior Pituitary Secretes the following Hormones, which have an Affects on other Endocrine Glands:

    A. THYROID-STIMULATING HORMONE (TSH) – Regulates the Thyroid to Produce and Release Thyroxin and Triiodothyronine.

    B. ADRENOCORTICOTROPIC HORMONE (ACTH) – Which stimulates the Adrenal Cortex. Causes the Adrenal Cortex to Produce and Release Cortisol and Aldosterone.

    C. GONADOTROPIC HORMONES (FOLLICLE-STIMULATING HORMONE - FSH and LUTEINIZING HORMONE - LH) - Which stimulate the gonads - the Testes in Males and the Ovaries in Females.  Causes the Gonads to Secrete Sex Hormones and Stimulates Gamete (Sperm and Egg) Production.

THYROID GLAND

1. LOCATED AT THE BASE OF THE NECK JUST BELOW THE LARYNX. (Figure 51-5)

2. THYROID-STIMULATING HORMONE (TSH) REGULATES THE THYROID GLAND.

3. PRODUCES THYROXIN, TRIIODOTHYRONINE, AND CALCITONIN

    A. THYROXIN AND TRIIODOTHYRONINE STIMULATES AND MAINTAINS METABOLIC ACTIVITIES, NORMAL HEART RATE, BLOOD PRESSURE, AND BODY TEMPERATURE.  THEY ALSO PROMOTE CARBOHYDRATE USAGE OVER FAT USAGE FOR ENERGY.

    B. CALCITONIN  (C CELLS) INHIBITS RELEASE OF CALCIUM FROM BONES. OR REGULATES THE LEVEL OF CALCIUM IN THE BLOOD.

4. IN ORDER TO PRODUCE THYROXIN AND TRIIODOTHYRONINE, THE THYROID GLAND REQUIRES IODINE.  IODIZED SALT.

5. GOITER THE SWELLING OF THE THYROID GLAND IS A RESULT OF IODINE DEFICIENCY.

6. DECREASED LEVELS OF THYROXIN CAUSES A DECREASE IN THE CELLULAR RESPIRATION RATE.  CELLS PRODUCE LESS ENERGY AND BECOME LESS ACTIVE.

7. HYPERTHYROIDISM - TOO MUCH THYROXIN RESULTS IN NERVOUSNESS, ELEVATED BODY TEMPERATURE, INCREASED HEART AND METABOLIC RATES, INCREASED BLOOD PRESSURE, AND WEIGHT LOSS. HYPERTHYROIDISM CAN BE TREATED WITH MEDICATION OR BY SURGICAL REMOVAL OF PART OF THE THYROID GLAND.

8. HYPOTHYROIDISM - NOT ENOUGH THYROXIN RESULTS IN LOWER METABOLIC RATES (LETHARGY) AND BODY  TEMPERATURE, LACK OF ENERGY, AND WEIGHT GAIN.  IN SOME CASES, IS ASSOCIATED WITH GOITER, OR ENLARGEMENT OF THE THYROID GLAND.  HYPOTHYROIDISM CAN BE TREATED WITH SUPPLEMENTARY THYROXIN.

9. HYPOTHYROIDISM IN INFANTS AFFECTS NORMAL DEVELOPMENT OF THE SKELETON, MUSCULAR, AND NERVOUS SYSTEMS AND RESULTS IN A CONDITION CALLED CRETINISM.

10.  CRETINISM IS CHARACTERIZED BY DWARFISM AND MENTAL RETARDATION.

PARATHYROID GLANDS (4)

1. ATTACHED TO OR EMBEDDED IN THE BACK SURFACE OF THE THYROID GLAND, TWO IN EACH LOBE. (Figure 51-9)

2. PRODUCES PARATHYROID HORMONE (PTH) REGULATES THE CALCIUM LEVELS IN THE BLOOD BY INCREASING THE REABSORPTION OF CALCIUM IN THE KIDNEYS AND BY INCREASING THE UPTAKE OF CALCIUM FROM THE DIGESTIVE SYSTEM.

3. PARATHYROID HORMONE IS IMPORTANT IN PROMOTING PROPER NERVE AND MUSCLE FUNCTION AS WELL AS MAINTAINING BONE STRUCTURE.

4. LOSS OF PARATHYROIDS CAUSES A DROP IN THE LEVEL OF CALCIUM IN THE BLOOD, WHICH MAY RESULT IN VIOLENT MUSCULAR SPASMS KNOWN AS TETANY.

5. CAN BE RELIEVED BY THE ADMINISTRATION OF LARGE AMOUNTS OF PTH AND INJECTIONS OF CALCIUM.

ADRENAL GLANDS (CORTEX AND MEDULLA)

1. ONE GLAND IS LOCATED ON TOP OF EACH KIDNEY. (Figure 51-6)

2. COMPOSE OF TWO VERY DIFFERENT TYPES OF TISSUE SO IT IS DIVIDED INTO TWO PARTS.

    A. OUTER - THE ADRENAL CORTEX

    B. INNER - THE ADRENAL MEDULLA

ADRENAL CORTEX

1. THE OUTER PORTION, MAKES UP 80 PERCENT OF THE MASS OF THE GLAND.

2. THE ADRENAL CORTEX RESPONDS TO ADRENOCORTICOTROPIC HORMONE (ACTH), WHICH IS SECRETED BY THE ANTERIOR PITUITARY GLAND.

3. PRODUCES MORE THAN TWO DOZEN HORMONES CALLED CORTICOSTEROIDS, WHICH ARE STEROID HORMONES AND ESSENTIAL FOR NORMAL BODY FUNCTION.

4. ALDOSTERONE REGULATES THE REABSORPTION OF SODIUM AND THE EXCRETION OF POTASSIUM BY THE KIDNEYS.  THIS AFFECTS WATER AND SALT BALANCE IN THE BODY.

5. CORTISOL AFFECTS CARBOHYDRATE, PROTEIN AND FAT METABOLISM.  IT ALSO HELPS PEOPLE COPE WITH STRESS.

6. DECREASE ACTIVITY OF THE ADRENAL CORTEX CAN RESULT IN ADDISON'S DISEASE - WEIGHT LOSS, LOW BLOOD PRESSURE, AND GENERAL WEAKNESS, DEATH MAY OCCUR BECAUSE OF HEART FAILURE.

7. PEOPLE WITH ADDISONS DISEASE RECEIVE REGULAR DOSES OF ADRENAL CORTICAL HORMONES.

8. INCREASE ACTIVITY OF THE ADRENAL CORTEX CAN RESULT IN CUSHING SYNDROME - OBESITY, INCREASE BLOOD SUGAR LEVELS, HIGH BLOOD PRESSURE, AND WEAKENING OF BONES.

9. TREATMENT INVOLVES DECREASING THE SECRETION OF HYPERACTIVE HORMONE, IF POSSIBLE.

ADRENAL MEDULLA

1. THE INNER PORTION, IS A SPECIALIZED PART OF THE SYMPATHETIC NERVOUS SYSTEM.

2. SECRETS TWO AMINO ACID BASED HORMONES CALLED NEUROHORMONES - ADRENALINE (EPINEPHRINE) AND NORADRENALINE (NOREPINEPHRINE).

3. ADRENALINE IS MORE POWERFUL IN ITS ACTIONS AND MAKES UP 80 PERCENT OF THE TOTAL SECRETIONS.

4. "FIGHT OR FLIGHT" HORMONES - NERVE IMPULSES FROM THE SYMPATHETIC NERVOUS SYSTEM RESULTS IN THE SECRETION OF ADRENALINE AND NORADRENALINE.

5. ADRENALINE INCREASES HEART RATE, BLOOD PRESSURE, AND BLOOD SUPPLY TO SKELETON MUSCLES, INCREASES THE CONVERSION OF GLYCOGEN TO GLUCOSE AND STIMULATES THE RATE OF METABOLISM.

6. NORADRENALINE STIMULATES THE HEART MUSCLE - INCREASES RATE AND STRENGTH OF HEARTBEAT.

REPRODUCTIVE GLANDS - GONADS

1. GONADS - THE OVARIES IN FEMALES AND THE TESTES IN MALES - ARE GAMETE-PRODUCING ORGANS THAT ALSO PRODUCE A GROUP OF STEROID SEX HORMONES.

2. SEX HORMONES REGULATE BODY CHANGES THAT BEGIN WITH PUBERTY.

3. PUBERTY IS THE ADOLESCENT STAGE DURING WHICH THE SEX ORGANS MATURE AND SECONDARY SEX CHARACTERISTICS, SUCH AS FACIAL HAIR, APPEAR.

4. WHEN SECRETED BY THE ANTERIOR PITUITARY GLAND, LUTEINIZING HORMONE (LH) AND FOLLICLE-STIMULATING HORMONE (FSH) STIMULATE SECRETION OF SEX HORMONES FROM THE GONADS.

5. THE FEMALE GONADS, OR OVARIES PRODUCE EGGS (OVA) AND ALSO PRODUCE SEX HORMONES THAT AFFECT CELLS THROUGHOUT THE BODY.

6. THE OVARIES PRODUCE THE FEMALE SEX HORMONES, THE ESTROGENS AND PROGESTERONE.

7. ESTROGENS ARE REQUIRED FOR THE DEVELOPMENT OF OVA AND FOR THE FORMATION OF THE PHYSICAL CHARACTERISTICS (SECONDARY SEX CHARACTERISTICS) ASSOCIATED WITH THE FEMALE.

8. THESE CHARACTERISTICS INCLUDE THE DEVELOPMENT OF THE FEMALE REPRODUCTIVE SYSTEM, THE MENSTRUAL CYCLE BEGINS, WIDENING OF THE HIPS, AND DEVELOPMENT OF THE BREAST. PUBERTY.

9. PROGESTERONE PREPARES THE UTERUS FOR THE ARRIVAL OF A DEVELOPING EMBRYO - OR CONTROLS THE MENSTRUAL CYCLE.

10. MALE GONADS OR TESTES PRODUCE SPERM, AND SEX HORMONES THAT AFFECT CELLS THROUGHOUT THE BODY.

11. TESTES PRODUCE ANDROGENS OR THE MALE SEX HORMONE. TESTOSTERONE IS AN ANDROGEN THAT REGULATES MALE SECONDARY SEX CHARACTERISTICS.

12. ANDROGENS ARE REQUIRED FOR NORMAL SPERM PRODUCTION AND THE DEVELOPMENT OF PHYSICAL CHARACTERISTICS (SECONDARY SEX CHARACTERISTICS) ASSOCIATED WITH THE MALE. PUBERTY.

13. THESE CHARACTERISTICS INCLUDE THE GROWTH OF FACIAL HAIR, INCREASE IN BODY SIZE, AND DEEPENING OF THE VOICE.

PANCREAS

1. LOCATED JUST BEHIND THE STOMACH.

2. PANCREAS IS BOTH AN EXOCRINE (DUCTS) AND ENDOCRINE GLAND.

3. THE HORMONE PRODUCING PORTION OF THE PANCREAS CONSISTS OF CLUSTERS OF CELLS THAT RESEMBLE ISLANDS, CALLED ISLETS OF LANGERHANS.

4. EACH ISLET IS COMPOSED OF BETA CELLS WHICH SECRETES INSULIN, AND ALPHA CELLS WHICH SECRETES GLUCAGON.

5. THESE TWO HORMONES, INSULIN AND GLUCAGON REGULATE THE METABOLISM OF BLOOD GLUCOSE (SUGAR) AND THE HORMONES HAVE OPPOSITE EFFECTS. (ANTAGONISTIC HORMONES - FIGURE 51-10)

6. INSULIN STIMULATES ITS TARGET CELLS TO TAKE UP AND USE GLUCOSE. THIS ACTION LOWERS BLOOD GLUCOSE LEVELS.  "USE OR STORE"

7. GLUCAGON STIMULATES ITS CELLS TO BREAKDOWN STORED GLYCOGEN AND INCREASE GLUCOSE LEVELS IN THE BLOOD.

8. WHEN THERE IS AN UNDER SECRETION OF INSULIN, A CONDITION CALLED DIABETES MELLITUS OCCURS.

9. TYPE I OR JUVENILE ONSET - BEFORE AGE 25, LITTLE OR NO INSULIN PRODUCTION, REQUIRES A STRICT DIET AND DAILY INJECTIONS OF INSULIN.

10.  TYPE II OR ADULT ONSET - AFTER AGE 40, PRODUCE NORMAL AMOUNTS OF INSULIN, BUT CELLS ARE UNABLE TO RESPOND PROPERLY BECAUSE OF LACK OF INSULIN RECEPTORS, CAN BE CONTROLLED BY DIET.

11. HYPOGLYCEMIA CAUSED BY EXCESS (HIGH) INSULIN OR LOW BLOOD SUGAR, a Disorder in which Glucose is Stored rather than being properly delivered to the cells of the body – causing cells to starve to death. This leads to a lower blood glucose concentration and subsequent release of Glucagon and Epinephrine (Adrenaline). Symptoms of hypoglycemia include Lethargy, Dizziness, Nervousness, Overactivity, and in extreme cases, Unconsciousness (Ketoacidosis or Diabetic Coma) and DEATH. To assist someone with this problem, provide them some Sugar, such as Soda (6 oz).

12. HYPERGLYCEMIA CAUSED BY LOW INSULIN OR HIGH BLOOD SUGAR. Can cause Nausea and Rapid Breathing, possibly leading to Oxygen Deficiency, Circulatory and Nervous System Failure, Diabetic Coma, or even Death.
 

THE THYMUS GLAND

1. THE THYMUS GLAND IS LOCATED BENEATH THE STERNUM (BREASTBONE) AND BETWEEN THE LUNGS.

2. THE THYMUS CONSISTS MOSTLY OF T-CELLS AND PLAYS A ROLE IN THE DEVELOPMENT OF THE IMMUNE SYSTEM.

3. THE THYMUS GLAND SECRETES THYMOSIN, AN AMINO ACID BASED HORMONE THAT STIMULATES THE FORMATION OF T-CELLS, WHICH HELP DEFEND THE FROM PATHOGENS.

THE PINEAL GLAND

1. THE PINEAL GLAND IS LOCATED NEAR THE BASE OF THE BRAIN. (Figure 51-8)

2. THE PINEAL GLAND SECRETES THE HORMONE MELATONIN.

3. MELATONIN CONCENTRATIONS INCREASE SHARPLY AT NIGHT AND DECREASE DRAMATICALLY DURING THE DAY.

4. THIS CYCLIC RELEASE OF MELATONIN INDICATES THAT IT HELPS REGULATE SLEEP.

DIGESTIVE ORGANS

1. ENDOCRINE CELLS WITHIN THE WALLS OF SOME DIGESTIVE ORGANS ALSO SECRETE A VARIETY OF HORMONES THAT HELP DIGEST FOOD.

2. WHEN FOOD IS EATEN, ENDOCRINE CELLS IN THE STOMACH LINING SECRETE GASTRIN, A HORMONE THAT STIMULATES OTHER STOMACH CELLS TO RELEASE DIGESTIVE ENZYMES AND HYDROCHLORIC ACID.

3. ENDOCRINE CELLS OF THE SMALL INTESTINE RELEASE SECRETIN, A HORMONE THAT STIMULATES THE RELEASE OF VARIOUS DIGESTIVE FLUIDS FROM THE PANCREAS AND BILE FROM THE LIVER.