Unit 6 Endocrine System Notes

Unit 6 Chapter 9


  • System of glands that secrete hormones (chemical messages) into the bloodstream.
  • Same functions as nervous system (communication and control) but much slower. Ex. Growth hormone


  1. Two Types of Glands
    1. Exocrine

1.  Make products (non-hormones)

Ex. Sweat, Tears, Digestive juices

2. Located next to their target organs

3. Release products into ducts

       b.  Endocrine

1.  Make and release hormones

2.  Not located next to target organs

3.  Release hormones into bloodstream

  • Hormone is then delivered to “target organ” where it binds to a receptor site (lock and key) in a process called the “Second Messenger Hypothesis”.
  • Hypersecretion – Production of too much hormone.
  • Hyposecretion – Production of too little hormone.


  1. Two Types of Hormones


  1. Protein hormones

1.  Provide communication between endocrine glands and target organs to affect cell activity (First Messenger)

  1. Steroid hormones

1.  Affect target organs cell activity by acting on genes.


  1. Second Messenger Hypothesis


  1. Attempts to explain why protein hormones cause effects on target organs but not other organs.
  2. First messengerDelivers chemical message from endocrine gland to target organ via the bloodstream.
  3. After attachment to receptor site, reactions take place which activate modules called second messengers which carry out effects of hormone.
  1. Regulation of Hormone
  1. Negative Feedback
  • Regulation of hormone levels in the blood. (Reverse the changes)

  • Ex. Blood sugar increases after meal, pancreas releases insulin, sugar transported to cells, blood sugar decreases, pancreas ceases release of insulin.

  1. Positive Feedback
  • Uncommon, but amplify changes rather than reverse changes.
  • Ex. Oxytocin increasing labor contractions.
  1. Prostaglandins (PG’s)
  1. Tissue Hormones which do not meet typical definition of hormone because it is made in an organ and stays within that organ (instead of being transported by bloodstream).
  2. Influence respiration, blood pressure, GI secretions, and the reproductive system.
  1. Hypothalamus  

  1. Produces ADH and Oxytocin
  • Stores ADH and Oxytocin in the posterior pituitary gland and nerve tissue signals the posterior pituitary to release these two hormones
  1. Contain releasing & inhibitory hormones, which travel to Anterior Pituitary Gland, where it will cause hormones to be released or inhibited.

7.  Anterior Pituitary Gland

a.      Controls thyroid gland, adrenal cortex, ovarian follicles, and corpus luteum.

b.      Stimulates 4 Tropic hormones (hormones that stimulate another gland to secrete hormones)

1) Thyroid Stimulating Hormone (TSH) "tropic hormone"

  • Secretion of thyroid hormones.

2) Adrenocorticotropic Hormone (ACTH) "tropic hormone"

  • Secretion of adrenal cortex hormones

3)  Follicle Stimulating Hormone (FSH) "tropic hormone"

  • Female – Development of ovarian follicles and secretion of estrogen.
  • Male – Sperm production

4) Lutenizing Hormone (LH) "tropic hormone"

  • Female – Maturation of ovarian follicles, ovulation, development of corpus luteum.
  • Male – Secrete testosterone.

5)  Melanocyte Stimulating Hormone (MSH) "non-tropic hormone"

  • Synthesis and distribution of melanin in skin.

6)  Growth Hormone (GH) "non-tropic hormone"

  • Growth in all organs.

7)  Prolactin "non-tropic hormone"

  • Breast development and milk secretion after pregnancy

8.  Posterior Pituitary Gland

1.  Releases 2 hormones

1) Anti-diuretic hormone (ADH)

  1.  Retention of water by kidneys (Urine production).
  2. To preserve water during times of dehydration

2) Oxytocin

  1. Uterine contraction during pregnancy and release of milk into breast ducts.
  2. Operates by positive feedback

9.  Pineal Gland

  • Small gland located in brain.
  • Produces melatonin which regulates the onset of puberty and menstrual cycle.
  • Responds to light levels and is thought to be body’s internal clock.


10.  Thyroid


  • Located in neck below larynx.
  • 3 Hormones stored in gland and released when needed.
    • Thyroxine (T4) - Release energy from food. “metabolism”
    • Iodothyronine (T3) - Release energy from food. “metabolism”
    • Calcitonin - Decreases concentration of calcium in blood from bone resorption.
    • Goiter -- Caused when the thyroid hyposecretes its hormones due to lack of iodine (common form in 3rd world countries) or an autoimmune problem (common form in U.S.) that stops the thyroid from releasing its hormones at normal levels.  The pituitary starts to release more TSH which causes the thyroid gland to grow in size to try and release the adequate amount of thyroid hormones into the blood stream.
      • Hyposecretion of T4 and T3
      • Hypersecretion of TSH (Thyroid Stimulating Hormone)

11.  Parathyroids

  • 4 Small glands on back of thyroid.
  • Parathyroid Hormone (PH)
    • increases concentrations of calcium by stimulating osteoclasts to break down bone tissue which enters bloodstream


12.  Thymus

  • Located in mediastinum
  • Made up largely of lymphocytes (white blood cells).
  • Only active in children
  • Creates hormone thymosin
    • important in the development and functioning of the immune system.
    • Myasthenia Gravis


13.  Adrenal Glands

  • Located on top of kidneys
  • Composed of 2 separate glands.
    • Adrenal Cortex  -  Made up of 3 layers secreting hormones called corticoids.
      • (Superficial layer)  Glomerulosa
        • a. Secrete mineralocorticoid(MC) containing hormone aldosterone.
          • 1)  Control amount of salts in blood.
          • 2)  Increases blood sodium and decreases blood potassium levels via the kidneys
      • (Middle layer)  Fasciculata
        1. a.  Secrete glucocorticoids (GC) containing cortisol and hydrocortisone.
          1. 1)  Maintain normal blood glucose levels
          2. 2)  Maintains normal blood pressure.
          3. 3)  Produce anti-inflammatory effects for injuries.
      • (Deep layer)  Reticularis
        1. Secrete sex hormones
          1. Testosterone
          2. Progesterone 
            1. Stimulate sex drive (weak testosterone in females).
    • Adrenal Medulla
      1. Inner portion of adrenals
      2. Secrete hormones epinephrine and norepinephrine.
        1. Relieve stress by increasing:
          1. heart-rate
          2. blood pressure
          3. blood supply to muscles
          4. secretion of more glucose for energy. “Fight or Flight”

14.  Pancreas (Islets of Langerhans)

  • Microscopic glands scattered throughout pancreas which secrete digestive juices (exocrine).
  • Also acts as an endocrine gland by changing blood glucose levels.
    • Alpha cells -- Secrete glucagon (increases blood glucose).
    • Beta cells – Secrete insulin (decreases blood glucose).
      1. Stimulates cells to uptake glucose from bloodstream
        1. 1)  Diabetes mellitus – Too little insulin
          1. a)  3 Major Symptoms
            1. Polyuria  excessive urination to flush out excess glucose and ketones
            2. Polydipsia excessive thirst due to excessive water loss from polyuria
            3. Polyphagia hunger caused by the inability to use sugars and loss of fat and protein by body
        2. 2)  Diabetes insipidus – Too much insulin


15.  Ovaries – Female Sex Glands

  • Primary sex glands are ovaries.
  • Ovarian follicles secrete estrogens.
  • Corpus luteum secretes progesterone and some estrogen.
    • Maintains menstrual cycle, increases width of hips, enlarges breasts
    • Decrease of hormones ends the cycle and causes breakdown of uterine wall

16.  Testes – Male Sex Glands

  • Primary sex organs are the testes.
  • Produce androgens
    • Testosterone – secondary male characteristic
      • Deepens voice
      • Enlarges muscles and bone
      • Increases body hair growth

17.  Placenta

  • Acts as temporary endocrine gland
  • Produces chorionic gonadotropins which are secreted by the chorion (membrane which surrounds developing baby).
    • Kidneys excrete large amounts in urine during pregnancy. (pregnancy tests)
    • Produces extra estrogens and progesterone to maintain uterine wall during pregnancy