Chapter 51: Endocrine System

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Chapter 51 Endocrine System
51-1 Hormones
51-2 Endocrine Glands
51-3 Feedback Mechanisms
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51-1 Hormones
I. Types of Glands (2 TYPES in our body)

• A GLAND secretes materials into BLOODSTREAM.

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(1) Exocrine Glands (e.g., sweat glands, mucous
glands, salivary glands)

• Secrete NON-hormonal substances into DUCTS
  ?transport these inside AND outside body.

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(2) Endocrine Glands (e.g., pituitary gland,
thyroid gland, adrenal gland)

• Ductless glands dump HORMONES directly into
  bloodstream.

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II. Types of Hormones (TWO classes)

• Chemicals that in SMALL amounts INFLUENCE
  activity of DISTANT cells (using our bloodstream
  as the MEDIUM).

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(1) Amino Acid (Peptide) Hormones (e.g.,
epinephrine, adrenaline)

• PROTEIN hormones that attach directly to cell
  membrane.

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(2) Steroid Hormones (e.g., estrogen,
testosterone)

• LIPID hormones derived from cholesterol (diffuse
  through cell membrane).

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III. Hormone Action

• When a hormone BINDS to a receptor on (or
  INSIDE) its TARGET CELL, it triggers a SERIES of
  events leading to CELL CHANGES.

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(1) Target Cells (e.g., testosterone works on
SKELETAL muscle cells)

• Cells that have receptors SPECIFIC to a SPECIFIC
  type of HORMONE.

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(2) Receptors

• Proteins BOTH INSIDE cytoplasm and ON SURFACE of
  a target cell.

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(A) Amino Acid Hormones (CANNOT diffuse ? needs a
MESSENGER)

• ID target cells by SURFACE RECEPTORS embedded in
  cell membrane.

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(1) First Messenger (i.e, the HORMONE)

• HORMONE ? 1ST messenger by BINDING to target
  cell receptor.

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(2) Hormone-Receptor Complex (HRC)

• Complex formed BETWEEN hormone and RECEPTOR
  proteinthe HRC activates a 2nd messenger INSIDE
  target cell.

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(3) Second Messenger (i.e., cyclic AMP or simply
cAMPgets ACTIVATED)

• cAMP initiates a SERIES of events that LEADS to
  CHANGES within target cell (NOTE Different
  ORGANS may respond differently to cAMP).

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(B) Steroid Hormones (fat soluble, easily PASS
THROUGH cell membrane)

• Diffuse THROUGH membrane, bind to a receptor
  INSIDE cellthe HRC then ENTERS nucleus and
  CHANGES cell activity.

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IV. Prostaglandins (stimulate LABOR contractions
blood CLOTTING)

• A group of LIPIDS (i.e., NOT hormones, NO
  glands) produced by cells ALL OVER the body, AND
  only act LOCALLY.

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51-2 Endocrine Glands
I. Pituitary Gland (i.e., MASTER gland, links
nervous WITH endocrine)

• Releases hormones that AFFECT other glands and
  organs (BUT is regulated by HYPOTHALAMUS).

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Critical Thinking
(1) Why might damage to the PITUITARY gland be
considered far MORE SERIOUS that damage to one of
the other endocrine glands?
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(1) Neurosecretory Cells (located in HYPOTHALAMUS)

• Makes hormones that REGULATE pituitarys
  activity. (releasing OR inhibiting hormones)

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(A) Posterior Pituitary (back of pituitary)

• Secretes OXYTOCIN and ADH.

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(1) Oxytocin (TARGETS mammary glands AND uterine
muscles)

• Initiates uterine CONTRACTIONS during
  childbirth stimulates SECRETION of breast milk.

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(2) Antidiuretic Hormone (ADHTARGETS kidney
nephrons)

• Stimulates REABSORPTION of WATER by kidneys,
  concentrates urine.

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(B) Anterior Pituitary (TOP of pituitary,
regulated by hypothalamus)

• Secretes GH, PROLACTIN, TSH, LH and ACTH.

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(1) Releasing Hormones (TARGET anterior pituitary)

• STIMULATES secretion of AP hormones.

(2) Release-Inhibiting Hormones (TARGET anterior
pituitary)

• INHIBITS secretion of AP hormones.

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Critical Thinking
(2) Severe structural abnormalities result from
gigantism, a condition of extremely rapid growth,
and from pituitary dwarfism, a condition of
slowed growth. Based on your understanding of
the endocrine system, suggest what causes these
inherited disorders.
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(3) Growth Hormone (GH, targets growth tissue)

• Regulates GROWTH of muscle AND bone tissue.

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(4) Prolactin (TARGETS mammary glands)

• Stimulates and sustains MILK PRODUCTION in
  breasts before AND during lactation.

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II. Thyroid Gland (TWO lobes, near larynx)

• Regulated by TSH secretes thyroxine,
  triiodothyronine, and calcitonin.

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(1) Thyroid-Stimulating Hormone (TSH, TARGETS
thyroid gland)

• Secreted by AP, REGULATES thyroid gland.

(2) Thyroxine and Triiodothyronine (TARGETS
various tissues)

• MAINTAIN heart rate, blood pressure,
  temperature, and metabolism.

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(3) Calcitonin (TARGETS osteoblasts of BONE
tissue)

• Stimulates DEPOSIT of CALCIUM IONS (Ca ) from
  BLOOD TO BONE.

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(4) Hyperthyroidism (OVER-production of thyroid
hormones)

• OVER-activity, weight LOSS, HIGH blood pressure,
  an ELEVATED heart rate and temp. (treated
  w/medicine)

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(5) Hypothyroidism (UNDER-production of thyroid
hormones)

• SLOWED-growth, lethargy, weight GAIN, DECREASED
  heart rate AND temp. (treated with thyroxine)

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(6) Cretinism (can result from a HYPOthyroidism,
a DEFICIENCY)

• A form of mental IMPAIRMENT during fetal and
  childhood development.

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(7) Goiter (if there is an IODINE deficiency, a
NUTRIENT for thyroid)

• A SWELLING of thyroid gland ?treated with IODINE
  and THYROXINE.

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III. Adrenal Glands (above EACH kidney, two
regionsmedulla cortex)

• Medulla (controlled by NS) and cortex
  (controlled by AP) ? function as TWO separate
  glands.

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(A) Adrenal Medulla (e.g., work with SYMPATHETIC
nervous system)

• Produce EPINEPHRINE (adrenaline) and
  NOREPINEPHRINE.

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(1) Epinephrine and Norepinephrine (released
under STRESS or danger)

• Blood-glucose levels are RAISED (liver), bronchi
  ENLARGE, pupils/blood vessels DILATE, and heart
  rate INCREASES.

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(B) Adrenal Cortex (CENTER region of adrenal
gland)

• Responds to adrenocorticotropic hormone (ACTH)
  in order to secrete 2 hormones (1) Cortisone,
  (2) Aldosterone

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(1) Adrenocorticotropic Hormone (ACTH, TARGETS
adrenal cortex)

• Secreted by AP under STRESS, forces secretion of
  STEROID hormones cortisol and aldosterone.

(2) Cortisol (Cortisone) (e.g., the STRESS
hormone)

• Regulates METABOLISM of carbs and proteins.

(3) Aldosterone (TARGETS the kidneys)

• Helps to regulate your SALT-AND-WATER balance in
  blood.

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IV. Gonads

• ALSO supply steroid SEX HORMONES.

(1) Sex Hormones and Puberty

• Changes in body PREPARE for reproductive
  behaviors.

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(2) Luteinizing Hormone (LH, TARGETS ovaries AND
testes)

• Stimulates P AND E initiates OVULATION
  (females) stimulates TESTOSTERONE (males) (made
  by AP).

(3) Follicle-Stimulating Hormone (FSH, TARGETS
ovaries and testes)

• Stimulates oogenesis AND spermatogenesis (made
  by AP).

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(4) Estrogen (stimulated by LH in females)

• Female SEX hormone, prepares for features NEEDED
  for reproduction (made in ovaries).

(5) Progesterone (stimulated by LH in females)

• Works with E to maintain OR shed UTERINE LINING
  during ovulation (also made in ovaries).

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(6) Androgens (stimulated by LH in males)

• SEX hormones testosterone ? driving agent in
  BOTH sexes.

(7) Testosterone

• Responsible for sex drive, and muscle-building
  features.

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Critical Thinking
(3) A number of different hormones secreted by
various endocrine glands help regulate the blood
glucose concentration. Based on your knowledge
of the importance of glucose, hypothesize why
glucose should be controlled by several hormones
rather than just one hormone.
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V. Pancreas (digestive AND endocrine organ)

• Contains endocrine cells known as Islets of
  Langerhans.

(1) Islets of Langerhans (REGULATE BLOOD SUGAR)

• Secretes 2 hormones, insulin AND glucagon.

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(2) Insulin (i.e., LOWERS blood sugar)

• Brings glucose FROM bloodstream INTO cells for
  glycolysis.

(3) Glucagon (i.e., ELEVATES blood sugar)

• Stimulates CONVERSION of glycogen (from LIVER)
  into blood glucose.

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(4) Diabetes Mellitus (results from insulin
deficiency, Types I and II)

• Condition of abnormally HIGH blood glucose
  concentration
• NOTE In diabetics, excess glucose INHIBITS water
  reabsorption by kidneys, producing DILUTE
  urinepossibly dehydration, kidney damage, rapid
  breathing, or even DIABETIC COMA.

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Critical Thinking
(4) Suppose a friend tells you that he or she has
recently experienced some of the warning signs of
diabetes mellitus. What other conditions could
cause symptoms that are similar to those of
diabetes?
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(5) Hypoglycemia (results from EXCESSIVE insulin
in bloodstream)

• Glucose is rapidly STORED, leaving starving
  cells LOOKING for glucose
• ? Leads to LOWER blood-glucose levels and release
  of glucagon and epinephrine (symptoms may include
  LETHARGY or DISORIENTATION).

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VI. Other Endocrine Glands

• Thymus gland, pineal gland, parathyroid glands,
  and endocrine cells within walls of digestive
  organs (e.g., stomach and small intestine).

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(1) Thymus Gland

• Between lungs, holds T-cells as a
  glandsecretes THYMOSIN.

(2) Thymosin

• PEPTIDE hormone stimulates development of
  T-cells (in thymus gland).

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(3) Pineal Gland (sunlight influenced)

• Base of brain ? secretes MELATONIN into blood
  during NIGHTFALL.

(4) Melatonin

• Cyclic RELEASE helps to regulate SLEEP patterns.

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(5) Parathyroid Glands

• 4 glands in back of thyroid gland, secrete
  PARATHYROID hormone.

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(6) Parathyroid Hormone (works with OSTEOCLASTS
of bone tissue)

• INCREASES Ca in BLOOD ? bone growth, muscle
  and nerve impulses.

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Critical Thinking
(5) Why might OVERACTIVE parathyroid glands cause
BONE problems?
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(7) Gastrin (secreted by endocrine cells of
STOMACH after a meal)

• Stimulates stomach cells (in gastric pits) to
  release DIGESTIVE ENZYMES (pepsin) and HCl.

(8) Secretin (secreted by endocrine cells of
SMALL INTESTINE)

• Stimulates release of enzymes from PANCREAS and
  bile from LIVER.

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51-3 Feedback Mechanisms
I. Homeostasis (requires a COORDINATION of
cellstissuesorgans)

• FEEDBACK mechanisms ? regulate HORMONE within
  a SAFE RANGE.

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Critical Thinking
(2) Why might it be important to CAREFULLY
control the dose of supplemental THYROXINE
administered to a person with hypothyroidism?
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(1) Antagonistic Hormones (e.g., Insulin
Glucagon)

• Exert OPPOSITE effects in body (a tightly
  regulated SYSTEM)

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(2) Feedback Mechanisms (i.e., positive OR
negative)

• A series of EVENTS in which the LAST step
  controls the FIRST.

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(3) Negative Feedback (LAST step INHIBITS FIRST
step)

• Release of X stimulates production of Y that
  subsequently INHIBITS FURTHER release of X.

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(4) Positive Feedback (LAST step STIMULATES FIRST
step)

• Release of X stimulates production of OTHER
  hormones which INCREASE FURTHER RELEASE of X.

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II. Negative Feedback Mechanisms (inhibits signal
products build up)

• Original signal is INHIBITED as PRODUCTS begin
  to BUILD UP.

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