chapter 15 the endocrine system

The Endocrine System

1. What is a hormone?

2. Main endocrine glands

A. Introduction

a. Pituitary gland

b. Thyroid gland

c. Parathyroid glands

d. Adrenal glands

e. Pancreatic islets

f. Gonads

thyroid gland

pancreas (islets)

testes

pituitary gland

thymus gland

adrenal glands

ovaries

hypothalamus


3. Endocrine vs. exocrine

4. What is a target cell?

5. Negative feedback control

A. Introduction

time

[glucose]

110 mg%

90 mg%

steady state


1. Pituitary gland

B. Review of structure and function

a. Controlled by the hypothalamus

b. Infundibulum

c. Posterior pituitary gland (neurohypophysis)

i. Oxytocin

ii. Anti-diuretic hormone (ADH)



i. Growth hormone (GH)

ii. Thyroid-stimulating hormone (TSH)

iii. Adrenocorticotrophic hormone (ACTH)

iv. Follicle-stimulating hormone (FSH)

v. Luteinizing hormone (LH)

vi. Prolactin (PRL)

1. Pituitary gland

d. Anterior pituitary gland (adenohypophysis)


2. Thyroid gland


a. Follicles

b. Follicular cells

i. Tetraiodothyronine (thyroxine, T4)

ii. Triiodothyronine (T3)

c. Parafollicular cells

i. Calcitonin


3. Parathyroid glands


a. Parathyroid hormone (PTH)

i. Norepinephrine and epinephrine

ii. Fight-or-flight

4. Adrenal glands

a. Adrenal medulla

i. Minheralocorticoids (aldosteorne)

ii. Glucocorticoids (cortisol, hydrocortisone)

iii. Gonadocorticoids (estrogens and androgens)

b. Adrenal cortex


5. Pancreatic islets


a. Insulin

b. Glucagon

c. Somatostatin


1. Hormone secretion stays the same, but receptor numbers on target cells tend to decrease

2. Pituitary gland – minimal changes

3. Thyroid gland

C. Age-related changes

a. T4 production declines by 50% with very old age, but blood levels of thyroxine remain normal

b. Gland atrophies with increased nodule formation

c. Basal metabolic rate (BMR) decreases


4. Parathyroid glands


a. No atrophy of glands; some fat deposition

b. Post-40, PTH levels in women increase, adding to bone loss problems

5. Adrenal glands

a. No atrophy of glands; increased fibrous tissue

b. Functional capacity isn’t loss, but there is a moderate decline in adrenocortical hormone secretion

c. Secretions of adrenal medulla increase with aging


6. Pancreatic islets


a. Generally, no decline in insulin

b. Decline in function occurs at target cell level (reduced response time in glucose tolerance tests)

1. Endocrine disorders are infrequent in old age

2. Changes are pathologic rather than age-related

D. Age-related dysfunctions



3. Diabetes mellitus

a. Essential problem = glucose does enter body cells; blood become hyperglycemia

b. Type I (insulin-dependent) = deficient secretion of insulin by islet cells

c. Type II (noninsulin-dependent) = decreased sensitivity of target cells to insulin (insulin resistance)

d. Clinical features

i. Ketosis as a result of excessive lipid use for energy production

ii. Skin ulcers, glaucoma, cataracts, poor peripheral circulation, retinopathy, neuropathy



4. Hypothyroidism

a. 5% over age 65 have thyroid hypofunction

b. Causes = TSH deficiency, radiation therapy, chronic autoimmune inflammation of the gland, removal of the gland

c. Clinical features difficult to diagnose

i. Fatigue, depression, mental confusion

ii. Dry skin, weight gain, constipation



5. Stress responses

a. What is stress?

b. Subtle stresses for the elderly could be social isolation, loss of spouse, decreased community status

c. Activation of the hypothalamo-pituitary-adrenal axis and sympathetic nervous system leads to …

d. General adaptation syndrome

i. Alarm stage

ii. Resistance stage

iii. Exhaustion stage

GENERAL ADAPTATION SYNDROME

ALARM

RESISTANCE

EXHAUSTION

STRESS

hypothalamus

C-RF secretion increased sympathetic activity

increased blood pressure

ACTH norepinephrineepinephrine

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glucocorticoids increased blood pressure continued

decreased inflammatory responseincreased blood glucosealtered protein and fat metaoblism

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decreased immune response + decreased energy reserves

decreased resistance to disease

hypertension

cardiac failure and renal failure

DEATH

end


E. Take home messages

1. Structural changes include atrophy, fibrous and fatty deposition, but nothing major

2. Blood levels remain within normal ranges, except for gonadal hormones

3. Demand for various hormones changes and target cell receptors decrease, altering rates of secretion

4. No convincing evidence that age-related changes in endocrine function promote aging

5. Plenty of evidence that stress promotes aging

chapter 15 the endocrine system

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