The Endocrine System

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The Endocrine System
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Exocrine vs Endocrine

• Classified by location of secretion
• Exocrine- through tube or duct to a surface
• Endocrine- secrete into internal environment

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Endocrine Glands

• Can be cell, tissue, or organ (gland)
• Hormone- messenger secreted by gland
• Target cell- receives the message
• Receptor for hormone
• Hormone creates a response
• Tropic hormones- hormone whose target cell is
  another endocrine gland

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Other Messengers

• Local Hormones- never reach bloodstream
• Paracrine- affect neighboring cells
• Autocrine- affect secreting cell
• Prostaglandins- lipids messenger usually
  affecting organ secreted in

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Hormone Action

• Steroid Hormone (derivative of cholesterol)
• Must be carried by plasma proteins through
  bloodstream
• Diffuse into any cell
• Binds to receptor in cell
• Activates specific area of DNA
• Protein synthesis is end result
• Example

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Hormone Action (cont)

• Nonsteriod hormone (amines, peptides, proteins)
• Hormone (primary messenger) binds to receptor on
  outside of cell
• Binding causes activity center inside cell to
  activate a messenger (sometimes cAMP)
• This second messenger cause the change in the
  target cell

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Hormonal Control

• Stimulation of hormone release
• Hypothalamus
• Nervous system
• Changing internal environment
• Inhibition of hormone release
• Negative feedback loop

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Hypothalamus

• Located deep inside the brain
• Releasing and inhibiting hormone secretion to
  anterior pituitary
• Direct innervation to posterior pituitary

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Pituitary Gland

• Located deep within the brain
• Divided into two sections
• Anterior Pituitary- glandular epithelium with
  many blood vessels
• Posterior Pituitary- nerve fibers and neuroglial
  cells

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Tropic Hormones of the Anterior Pituitary

• Thyroid-stimulating hormone (TSH)
• Adrenocorticotropic hormone (ACTH)
• Gonadotropins
• Follicle-stimulating hormone (FSH)
• Lutenizing hormone (LH)

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Thyroid-stimulating hormone (TSH)

• Stimulation Thyrotropin-releasing hormone (TRH)
  from hypothalamus
• Inhibition Circulating thyroid hormones decrease
  TSH and TRH secretion
• Target Cell Thyroid
• Action Increase thyroid secretions

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Adrenocorticotropic hormone (ACTH)

• Stimulation Corticotropin-releasing hormone
  (CRH) from hypothalamus
• Target Cell Adrenal cortex
• Action Increase adrenal cortex secretions

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Follicle-stimulating hormone (FSH)

• Stimulation Gonadotropin-releasing hormone from
  hypothalamus
• Target Cell Gonads (testes in males and ovaries
  in females)
• Action
• Female- maturation of egg secretion of estrogen
• Male- development of sperm

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Lutenizing hormone (LH)

• Also called Interstitial cell stimulating hormone
  (ICSH)
• Stimulation Gonadotropin-releasing hormone from
  hypothalamus
• Target Cell Gonads (testes in males and ovaries
  in females)
• Action
• Female- release of mature egg from ovary
  (ovulation)
• Male- development of interstitial cell secretion
  of male sex hormones

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Other hormone of the Anterior Pituitary

• Growth Hormone (GH)
• Stimulation GH-releasing hormone from
  hypothalamus
• Inhibition GH release-inhibiting hormone
• Target Cell Somatic cells
• Action enhances movement of amino acids across
  cell membrane speeds up rate of carbohydrate
  utilization

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Other hormone of the Anterior Pituitary (cont)

• Prolactin (PRL)
• Stimulates breast development necessary for
  lactation
• Stimulates breast to secrete milk after birth

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Posterior Pituitary

• Antidiuretic hormone (ADH)
• Stimulation Nerve Impulse from hypothalamus when
  osmoreceptors sense dehydration
• Target Cell kidneys
• Action kidneys produce less urine to conserve
  water
• Oxytocin (OT)
• Stimulates contraction of the pregnant uterus
• Stimulates let-down of milk

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Thyroid

• Location attached to front of trachea
• Contains follicles
• Follicles have hollow center cavity filled with
  colloid

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Thyroid (cont)

• Follicular cells secrete two hormones
• Thyroxine (tetraiodothyronine)- T4
• Triiodothyronine- T3 (much more potent)
• Increases metabolism of carbohydrates, lipids,
  and proteins
• Extrafollicular cells secrete calcitonin
• Lowers blood calcium level by inhibiting
  osteoclasts and making kidney secrete more
  calcium in urine

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Parathyroid glands

• Located on the thyroid in four patches of highly
  dense secretory cells
• Secrete Parathyroid hormone (PTH)
• Raises blood calcium levels
• Inhibits osteoblasts, stimulates osteoclasts,
  makes kidneys conserve calcium, increase
  absorption of calcium in intestine

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Adrenal glands
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Adrenal Cortex

• Three layers outer, middle, and inner
• Closely packed masses of epithelial tissue

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Outer Layer of Cortex

• Outer (glomerulosa)
• Mineralocorticoid (MC)- regulate mineral
  electrolytes
• Aldosterone
• Stimulated by decrease in blood levels of sodium,
  increase in potassium in blood levels, or
  decrease in blood pressure
• Cause kidneys to retain sodium and secrete
  potassium into urine
• Indirectly water will be retained as well

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Adrenal Cortex (cont)

• Middle (fasciculata)
• Glucocorticoids- affects glucose metabolism
• Cortisol or hydrocortisone
• Increase gluconeogenisis
• Inhibition of protein synthesis
• Promotion of fatty acid release from adipose
  tissue
• Produce state of stress

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Adrenal Cortex (cont)

• Inner (reticularis)
• Sex hormones
• Produces androgen hormones
• Can be used to synthesize female sex hormones
  like estrogens

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Adrenal Medulla

• Composed of modified neurons
• Secrete epinephrine (adrenaline) and
  norepinephrine (noradrenaline)
• Fight or Flight response
• Directly innervated by sympathetic nervous system

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Pancreatic Islets (Islets of Langerhans)

• Alpha cells
• Glucagon
• Accelerates process of gylcogenolysis
• Beta cells
• Insulin
• Increeases movement of glucose inside of cells
  for metabolism
• Stimulates liver to produce glycogen

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Thymus

• Located in mediastinum cavity
• Hormones called thymosins
• Important function in development of immune
  system

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Pineal gland

• Releases melatonin
• Regulates body clock and sleep cycle

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Female Sex Glands

• Ovaries
• Ovarian follicles
• Corpus luteum

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Male sex glands

• Testes
• Interstitial cells produce testosterone
• Testosterone stimulates sperm production

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Placenta

• Chorionic gonadotropins
• Pregnancy tests test for this hormone
• Prevents dissolution of corpus luteum

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Other hormones

• Wall of Atria in Heart
• Atrial Natriuretic hormone- regulates fluid and
  electrolyte balance by increasing removal of
  sodium and water
• Various Digestive Glands
• Kidneys
• Erythropoietin- red blood cell growth hormone