Human Anatomy and Physiology

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Human Anatomy and Physiology

• Endocrinology

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Overview

• Nervous system
• electrochemical impulses regulate muscles and
  glands
• quick response
• Endocrine system
• influences metabolism via chemical messages
• prolonged response
• Endocrine versus exocrine glands

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Endocrine glands

• Major glands
• Pituitary, thyroid, parathyroid, adrenal, pineal
  and thymus glands
• Other glands
• Pancreas, gonads
• Organs/tissues producing hormones
• Adipose tissue, intestine, stomach, kidneys, heart

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Hormones

• Steroidal
• Gonads, adrenal glands
• Amino acid based
• Works by a secondary messenger system
• Cyclic AMP cAMP signaling mechanism
• PIP-Calcium signaling mechanism
• cAMP components
• Receptor, G protein, adenylate cyclase, cAMP,
  protein kinase

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Cyclic AMP signaling
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Cyclic AMP signaling

• Steps
• First messenger
• GDP displaced by GTP
• Activation of G-protein
• Activation of adenylate cyclase
• Hydrolysis of GTP to GDP
• Inactivation of G-protein
• Second messenger cAMP from ATP
• Activation of protein kinase
• Activation of metabolism

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PIP calcium signaling
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PIP calcium signaling

• Steps
• First messenger
• GDP displaced by GTP
• Activation of G-protein
• Activation of phospholipase
• Hydrolysis of GTP to GDP
• Inactivation of G-protein
• Phospholipase splits PIP2 into DAG and IP3
• DAG and IP3 act as secondary messengers
• DAG activates protein kinases, IP3 triggers Ca
  release from ER
• Ca activates channels on plasma membrane or
  binds to calmodulin which activates metabolism

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Steroidal hormones
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Steroidal hormones

• Steps
• Diffuse into cell and enter nucleus
• Bind to receptors to form receptor complexes
• Complexes bind to DNA
• Production of mRNA
• mRNA ribosomes make proteins
• Proteins include enzymes that stimulate
  metabolism

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Hormones

• Hormones travel in blood free or bound to protein
  carriers
• Blood hormone concentration decreases
• Degraded by target organs
• Removal by kidneys and liver
• Half-life (seconds to 30 min.)

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Hormone release

• Three major stimuli
• 1. Humoral
• Ca lowering causes PTH release
• 2. Neural
• SNS stimulates adrenal gland to release
  epinephrine
• 3. Hormonal (common)
• Hypothalamus releases hormones that cause
  pituitary to release other hormones (e.g. GnRH to
  FSH)

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Growth hormone

• Site of release
• Anterior pituitary
• Target organ
• All body organs especially bones and skeletal
  muscle
• Stimulation
• Primarily in adolescence, low levels of GH
• Feedback mechanism
• High levels of GH, hyperglycemia, obesity

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Thyroid hormone precursors

• Hypothermia

TRH
TSH
T3 T4
Increase in metabolism body temperature
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Thyroid hormone

• Stimulation
• Falling levels of T3 (triiodothyronine) and T4
  (thyroxine). TH raise BMR and heat production
• Feedback mechanism
• Increase in BMR and body heat (i.e., exercise)

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Parathyroid hormone

• Site of release
• Parathyroid glands
• Target organ
• Bone, intestine, kidneys
• Stimulation
• Falling Ca blood levels
• Feedback mechanism
• Increase in Ca blood levels

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Parathyroid hormone

• Ca needed for nerve impulses, muscle
  contraction and blood clotting

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Adrenocorticotropic hormone

• Site of release
• Anterior pituitary
• Target organ
• Adrenal cortex (glucocorticoids)
• Stimulation
• Stress (i.e., fever, hypoglycemia)
• cortisol
• Feedback mechanism
• Increase levels of blood glucocorticoids

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Adrenal gland hormones

• Mineralocorticoids (aldosterone)
• Site of release
• Adrenal cortex
• Target organ
• Kidneys
• Stimulation
• Decrease in blood volume, pressure, Na level
• Feedback mechanism
• Increase in blood volume, pressure, Na level

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Adrenal gland hormones

• Epinephrine and norepinephrine
• Site of release
• Adrenal medulla
• Target organ
• Heart, vasculature, bronchioles
• Stimulation
• Sympathetic nervous system (SNS)
• Feedback mechanism
• None. SNS stimulation decreases when needed

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Pancreatic hormones

• Insulin and glucagon

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Other hormones

• Renal
• Arginine vasopressin (antidiuretic hormone - ADH)
• Reproduction
• Follicle-stimulating hormone (FSH)
• Luteinizing hormone (LH)
• Oxytocin