Endocrine system

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Endocrine system

• Al Mina, M.D.
• Erskine College

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Modified from

• Powerpoint Presentation for BG211 made by
• Dr. Nora Espinoza, Ph. D.
• Which was

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Modified from a PowerPoint Presentation made
to accompanyHoles Human Anatomy and
Physiology, 11/e byShier,
Butler, and LewisMcGraw-Hill - publisher
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Regulation of Hormones
Figure 13.8
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Pituitary Gland
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Pituitary Gland
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Regulation of Anterior Pituitary
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Anterior pituitary

• Utilizes portal system between hypothalamus and
  adenohypophysis
• Trophic hormones secreted into first capillary
  bed, delivered to pituitary
• Absorbed via 2nd capillary bed, pituitary
  hormones secreted
• Pituitary hormones act on other glands

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Growth hormone (GH)

• A.K.A. somatotropin
• Stimulated by Growth hormone releasing hormone
  (GHRH)
• Inhibited by somatostatin
• Stimulates cell growth, increases fat metabolism,
  promotes elongation of long bones

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GH contd

• Excess GH for prolonged period can lead to
  gigantism (if pre-puberty) or acromegaly
  (post-puberty)

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Thyroid Stimulating Hormone (TSH)

• Stimulated by Thyrotropin Releasing Hormone (TRH)
• TSH stimulated secretion of thyroid hormone from
  thyroid gland
• Also stimulates thyroid growth (excessgoiter)
• Thyroid hormone inhibits TSH and TRH secretion
  via negative feedback

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Adrenocorticotropic hormone (ACTH)

• Stimulates secretion of hormones fo adrenal
  cortex
• Regulated by corticotropin releasing hormone
  (CRH)
• Stress increases CRH, yielding increased ACTH
  secretion

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gonadotropins

• Follicle stimulating hormone (FSH)
• Leuteinizing hormone (LH)
• Regulated by gonatotropin Releasing hormone
  (GnRH)
• FSH female - stimulates follicle development,
  estrogen secretion
• Males sperm production
• LH egg release, secretion of sex hormones

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Prolactin

• Stimulates milk production
• Regulated by prolactin release inhibiting hormone
• Only ant. Pit. Hormone that has only inhibition
  from hypothalamus

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Posterior pituitary

• Hypothalamus communicates via neurons
• Bodies in hypothalamus, axons in neurohypophysis
• Activation leads to release of hormone in axon
  vesicles, secreted

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Antidiuretic hormone

• A.K.A. vasopressin
• Decreases urine formation (decrease water
  excretion)
• Also vasoconstricts vessels (both effects combine
  to raise blood pressure)
• Inhibited by BP elevation, alcohol
• Regulated by hypothalamus sensing osmotic
  concentration of body fluids

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Oxytocin

• Increases uterine contraction during childbirth
• Aids in lactation
• Both systems utilize a positive feedback system.

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Thyroid
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Thyroid Gland - Cell Types
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Parathyroid glands

• Set of four glands on posterior thyroid
• Secrete parathyroid hormone (protein)
• Regulate calcium/phospate ions
• Increase calcium
• Decrease phosphate

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Parathyroid Glands
Figure 13.22
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PTH contd

• PTH stimulates osteoclasts to increase resorption
  of bone (increase Ca/P)
• Signals kidneys to increase phosphate excretion
• Increases Vitamin D activity in intestine to
  increase calcium absorption

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PTH contd

• Serum calcium provides negative feedback
• PTH opposed by calcitonin (thyroid)

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Figure 13.25
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Adrenal Gland
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Adrenal glands

• Superior to kidneys
• Inner portion (medulla) and outer (cortex)

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Cortex

• Composed of 3 layers
• Each secretes different hormones

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Zona glomerulosa

• Outermost layer
• Aldosterone mineralocorticoid
• Regulates minerals sodium, potassium
• Retain sodium, excrete potassium
• End product of renin-angiotensin system
  (activated by decreased BP or sodium)
• Also vasoconstricts

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Zona fasciculata

• Glucocorticoids (glucose metabolism)
• Cortisol
• Maintains glucose levels between meals
• Inhibits protein synthesis (inc amino acids)
• Increase fatty acid release (inc energy)
• Increase glucose synthesis (gluconeogenesis)

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Figure 13.31
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• Regulated by CRH, ACTH
• Cortisol levels increase with stress
• Harmful over time

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Zona reticularis

• Sex hormones
• Start as androgens
• Some converted to estrogens in periphery
• Supplement gonadal hormones
• Stimulate development of reproductive organs

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Adrenal medulla

• Modified neurons
• Have direct connections to CNS (sympathetic
  nervous system)

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medulla

• Chromaffin cells
• Produce epinepherine/norepinepherine
• Stored in vesicles

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Epi/norepi

• Epinepherine synthesized from norepi
• Typically 80 epinepherine in gland
• Trigger fight or flight type responses

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Figure 13.32
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Pancreas

• Serves both exocrine and endocrine function
• Exocrine portion secretes digestive enzymes into
  intestine
• Endocrine cells located in pancreatic islets

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Glucagon

• Alpha cells of pancreatic islets
• Stimulated when glucose levels low
• Stimulates glycolysis liver
• Stimulates gluconeogenesis from non-carbs
• Negative feedback with glucose levels

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Insulin

• Formed in/secreted from beta cells
• Instrumental in glucose metabolism
• Stimulated when glucose levels increase
• Inhibits glycolysis/gluconeogenesis
• Promotes movement of glucose into many cell types
  (cardiac/resting skeletal muscle)

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Somatostatin

• Produced in delta cells
• Inhibits both insulin and glucagon

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Diabetes

• Elevated glucose levels
• Can be due to lack of insulin, or increased
  insulin resistance at cell receptors
• Chronic, long term problem
• Multitude of potential problems, many a result of
  damage to small vessels.

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Types of diabetes

• Type I (juvenile)
• Autoimmune disorder
• Immune system attacks own beta cells
• No insulin produced
• Insulin supplementation mandatory for treatment

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Type II

• Develops over many years
• Genetic, but also lifestyle plays large role
• Starts with resistance of insulin receptors
• May lead to beta cell burnout
• Variety of medicines available to target problem
  at different stages
• Insulin may be needed

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Pineal gland

• Small gland in brain attached to thalamus
• Secretes melatonin in response to light/absence
• Aids in maintaining circadian rhythm
• Melatonin induces sleepiness
• Some treatments for insomnia target melatonin

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Stress

• Physical and psychological components
• Activates hypothalamus
• Activates sympathetic NS fight or flight
• Chain of events leading to response to stress

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Figure 13.35
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Cortisol actions

• Increases amino acid supply
• Diverts glucose to brain
• Trigger release of other hormones
• Glucagon (increase glucose level)
• Growth hormone (repair?)
• Anti-diuretic hormone (conserve H2O, sodium,
  increase pressure)

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Figure 13.34