Endocrine System

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Endocrine System

• Chapter 10

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Endocrine Glands

• Endocrine glands are ductless glands and tissues
  that secrete hormones directly into the
  bloodstream.
• Hormone
• Hormon- gr. to excite.
• Chemical messengers.
• Released in small amounts.
• Affect target cells.

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General Functions of Hormones

• Growth and development
• Reproduction
• Metabolism
• Biological clock
• Contraction of cardiac and smooth muscle
• Glandular secretion

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Feedback mechanisms regulate the secretion of
hormones

• Negative feedback- the outcome of a process feeds
  back on the system, shutting down the process.
• Antagonistic feedback- one hormone has an
  opposite effect of another hormone on the system.
• Positive feedback- the outcome of a process feeds
  back on the system, further stimulating the
  process.

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Negative Feedback
Antagonistic Feedback
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Positive Feedback

• Im good enough, Im smart enough, and doggone
  it, people like me!

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Positive Feedback- Oxytocin (OCT)

• Sucking by the infant stimulates nerve receptors
  in the nipple.
• The resulting impulses travel along nerves to the
  hypothalamus.
• The hypothalamus signals the posterior pituitary
  to release OCT.
• OCT travels via the bloodstream to the mammary
  glands.
• Milk is ejected from the mammary glands.

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Hypothalamus

• Anatomy
• Part of the diencephalon, inferior to the
  thalamus.
• Functions
• Regulates the internal environment through the
  autonomic nervous system.
• Controls glandular secretions of the pituitary
  gland.

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Pituitary Gland- anatomy

• Anatomy
• Pea-shaped structure.
• ½ inch in diameter.
• Lies in the sella turcica of the sphenoid bone.
• 2 anatomically and functionally different
  portions.

Posterior
Anterior
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Anterior Pituitary
Posterior Pituitary
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Pineal Gland

• Anatomy
• Pine cone shape.
• In the epithalamus.
• Covered by a capsule made of pia mater.
• Function
• Secretes melatonin that targets the brain
  involved in regulating daily sleep-wake cycle.

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Thyroid Gland

• Anatomy
• Inferior to the larynx.
• 2 lobes, shield-shaped and deep red in color.
• Isthmus connects the lobes.
• 30g in weight (1 oz.).
• Functions
• Increases metabolic rate.
• Regulate growth and development.

Isthmus
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The Thyroid Gland Secretes Thyroid Hormone (TH)

• Hypothyroidism- undersecretion of the thyroid
  hormone.
• Fetus or infant- cretinism.
• Dwarfism and mental retardation.
• Adult- myxedema.
• Weight gain.
• Lethargy.
• Loss of hair.
• Lowered body temperature.

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• Hyperthyroidism- oversecretion of thyroid
  hormone.
• Adult- Graves disease
• Increased metabolic rate.
• Enlargement of the thyroid gland.
• Rapid heart rate.
• High blood pressure.
• Exophthalmos.
• Treatment for Graves disease
• Surgery.
• Ingestion of radioactive iodine.

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Parathyroid Glands

• Anatomy- 4 small masses at the back of the
  thyroid gland.
• Hormones- parathyroid hormones.
• Target- bones, kidneys, intestines.
• Hormone Functions
• Increase blood calcium level.
• Antagonistic action between calcitonin and
  parathyroid hormone maintains blood calcium
  levels.

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Thymus Gland

• Anatomy
• Upper mediastinum.
• Large in infants (70 g), atrophied in adult (3
  g).
• 2 lobed organ.
• Hormones- thymosins.
• Target- T lymphocytes (white blood cells).
• Hormone Functions
• Promote production and maturation of T
  lymphocytes.

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Adrenal Glands

• Anatomy
• Almond-shaped, located at the tops of the
  kidneys.
• Consists of adrenal medulla and adrenal cortex.
• Hormones and Functions
• Adrenal Medulla
• Epinephrine- adrenaline. Fight or flight.
• Norepinephrine- noradrenaline.
• Adrenal Cortex
• Sex Hormones. Development.
• Mineralocorticoids. Salt water balance.
• Glucocorticoids. Regulate glucose levels.
• Targets- all tissues.

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Pancreas

• Anatomy
• 5-6 inches long, 1 inch thick.
• Attached to the duodenum, posterior to the
  stomach.
• Two tissue types.
• Exocrine tissue- produce and secrete digestive
  juices.
• Endocrine tissue- produce and secrete insulin and
  glucagon directly into the blood.
• Target- liver, muscles, adipose tissue.
• Hormones and Functions
• Insulin- lowers blood sugar.
• Glucagon- increases blood sugar.

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Testes

• Anatomy
• Scrotum of male.
• 2 oval glands.
• 2 inches long, 1 inch in width.
• Hormone- testosterone.
• Target- gonads, skin, muscles, bones.
• Hormone Function
• Stimulate male sex characteristics.

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Ovaries

• Anatomy
• Abdomen of female
• 5 cm X 2.5 cm (2 X 1 inch).
• Hormones
• Estrogens.
• Progesterone.
• Targets
• Gonads, skin, muscles, bones.
• Hormone Function
• Stimulate female sex characteristics.