chapter 15 the endocrine system
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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
The Endocrine System
3. Endocrine vs. exocrine
4. What is a target cell?
5. Negative feedback control
A. Introduction
time
[glucose]
110 mg%
90 mg%
steady state
The Endocrine System
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)
The Endocrine System
B. Review of structure and function
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)
The Endocrine System
2. Thyroid gland
B. Review of structure and function
a. Follicles
b. Follicular cells
i. Tetraiodothyronine (thyroxine, T4)
ii. Triiodothyronine (T3)
c. Parafollicular cells
i. Calcitonin
The Endocrine System
3. Parathyroid glands
B. Review of structure and function
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
The Endocrine System
5. Pancreatic islets
B. Review of structure and function
a. Insulin
b. Glucagon
c. Somatostatin
The Endocrine System
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
The Endocrine System
4. Parathyroid glands
C. Age-related changes
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
The Endocrine System
6. Pancreatic islets
C. Age-related changes
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
The Endocrine System
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
The Endocrine System
D. Age-related dysfunctions
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
The Endocrine System
D. Age-related dysfunctions
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
The Endocrine System
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
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