The Endocrine System

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The Endocrine System
A. Introduction
hypothalamus

• What is a hormone?
• Main endocrine glands

• Pituitary gland
• Thyroid gland
• Parathyroid glands
• Adrenal glands
• Pancreatic islets
• Gonads

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The Endocrine System
A. Introduction

• Endocrine vs. exocrine
• What is a target cell?
• Negative feedback control

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The Endocrine System
B. Review of structure and function

• Pituitary gland

• Controlled by the hypothalamus
• Infundibulum
• Posterior pituitary gland (neurohypophysis)

• Oxytocin
• Anti-diuretic hormone (ADH)

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The Endocrine System
B. Review of structure and function

• Pituitary gland

d. Anterior pituitary gland (adenohypophysis)

• Growth hormone (GH)
• Thyroid-stimulating hormone (TSH)
• Adrenocorticotrophic hormone (ACTH)
• Follicle-stimulating hormone (FSH)
• Luteinizing hormone (LH)
• Prolactin (PRL)

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The Endocrine System
B. Review of structure and function
2. Thyroid gland

• Follicles
• Follicular cells

• Tetraiodothyronine (thyroxine, T4)
• Triiodothyronine (T3)

c. Parafollicular cells

• Calcitonin

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The Endocrine System
B. Review of structure and function
3. Parathyroid glands

• Parathyroid hormone (PTH)

4. Adrenal glands

• Adrenal medulla

• Norepinephrine and epinephrine
• Fight-or-flight

b. Adrenal cortex

• Minheralocorticoids (aldosteorne)
• Glucocorticoids (cortisol, hydrocortisone)
• Gonadocorticoids (estrogens and androgens)

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The Endocrine System
B. Review of structure and function
5. Pancreatic islets

• Insulin
• Glucagon
• Somatostatin

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The Endocrine System
C. Age-related changes

• Hormone secretion stays the same, but receptor
  numbers on target cells tend to decrease
• Pituitary gland minimal changes
• Thyroid gland

• T4 production declines by 50 with very old age,
  but blood levels of thyroxine remain normal
• Gland atrophies with increased nodule formation
• Basal metabolic rate (BMR) decreases

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The Endocrine System
C. Age-related changes
4. Parathyroid glands

• No atrophy of glands some fat deposition
• Post-40, PTH levels in women increase, adding to
  bone loss problems

5. Adrenal glands

• No atrophy of glands increased fibrous tissue
• Functional capacity isnt loss, but there is a
  moderate decline in adrenocortical hormone
  secretion
• Secretions of adrenal medulla increase with aging

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The Endocrine System
C. Age-related changes
6. Pancreatic islets

• Generally, no decline in insulin
• Decline in function occurs at target cell level
  (reduced response time in glucose tolerance tests)

D. Age-related dysfunctions

• Endocrine disorders are infrequent in old age
• Changes are pathologic rather than age-related

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The Endocrine System
D. Age-related dysfunctions
3. Diabetes mellitus

• Essential problem glucose does enter body
  cells blood become hyperglycemia
• Type I (insulin-dependent) deficient secretion
  of insulin by islet cells
• Type II (noninsulin-dependent) decreased
  sensitivity of target cells to insulin (insulin
  resistance)
• Clinical features

• Ketosis as a result of excessive lipid use for
  energy production
• Skin ulcers, glaucoma, cataracts, poor peripheral
  circulation, retinopathy, neuropathy

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The Endocrine System
D. Age-related dysfunctions
4. Hypothyroidism

• 5 over age 65 have thyroid hypofunction
• Causes TSH deficiency, radiation therapy,
  chronic autoimmune inflammation of the gland,
  removal of the gland
• Clinical features difficult to diagnose

• Fatigue, depression, mental confusion
• Dry skin, weight gain, constipation

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The Endocrine System
D. Age-related dysfunctions
5. Stress responses

• What is stress?
• Subtle stresses for the elderly could be social
  isolation, loss of spouse, decreased community
  status
• Activation of the hypothalamo-pituitary-adrenal
  axis and sympathetic nervous system leads to
• General adaptation syndrome

• Alarm stage
• Resistance stage
• Exhaustion stage

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GENERAL ADAPTATION SYNDROME
ALARM
RESISTANCE
EXHAUSTION
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The Endocrine System
E. Take home messages

• Structural changes include atrophy, fibrous and
  fatty deposition, but nothing major
• Blood levels remain within normal ranges, except
  for gonadal hormones
• Demand for various hormones changes and target
  cell receptors decrease, altering rates of
  secretion
• No convincing evidence that age-related changes
  in endocrine function promote aging
• Plenty of evidence that stress promotes aging

end