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The Endocrine System
A. Introduction
pituitary gland
1. What is a hormone?
hypothalamus
thyroid gland
thymus gland
2. Main endocrine glands
a. Pituitary gland
b. Thyroid gland
c.
adrenal
glands
pancreas
(islets)
ovaries
Parathyroid glands
testes
d. Adrenal glands
e. Pancreatic islets
f.
Gonads
The Endocrine System
A. Introduction
3. Endocrine vs. exocrine
4. What is a target cell?
5. Negative feedback control
110 mg%
[glucose]
steady state
90 mg%
time
The Endocrine System
B. Review of structure and function
1. Pituitary gland
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
1. Pituitary gland
d. Anterior pituitary gland (adenohypophysis)
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)
The Endocrine System
B. Review of structure and function
2. Thyroid gland
a. Follicles
b. Follicular cells
c.
i.
Tetraiodothyronine (thyroxine, T4)
ii.
Triiodothyronine (T3)
Parafollicular cells
i.
Calcitonin
The Endocrine System
B. Review of structure and function
3. Parathyroid glands
a. Parathyroid hormone (PTH)
4. Adrenal glands
a. Adrenal medulla
i.
Norepinephrine and epinephrine
ii.
Fight-or-flight
b. Adrenal cortex
i.
Minheralocorticoids (aldosteorne)
ii.
Glucocorticoids (cortisol, hydrocortisone)
iii.
Gonadocorticoids (estrogens and androgens)
The Endocrine System
B. Review of structure and function
5. Pancreatic islets
a. Insulin
b. Glucagon
c.
Somatostatin
The Endocrine System
C. Age-related changes
1. Hormone secretion stays the same, but receptor
numbers on target cells tend to decrease
2. Pituitary gland – minimal changes
3. Thyroid gland
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
C. Age-related changes
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
The Endocrine System
C. Age-related changes
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)
D. Age-related dysfunctions
1. Endocrine disorders are infrequent in old age
2. Changes are pathologic rather than age-related
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
STRESS
ALARM
hypothalamus
C-RF secretion
ACTH
increased sympathetic activity
increased blood pressure
norepinephrine
epinephrine
----------------------------------------------------------------------------------------------------------------------------- ---RESISTANCE
glucocorticoids
increased blood pressure continued
decreased inflammatory response
increased blood glucose
altered protein and fat metaoblism
----------------------------------------------------------------------------------------------------------------------------- ---EXHAUSTION
decreased immune response + decreased energy reserves
decreased resistance to disease
hypertension
cardiac failure and renal failure
DEATH
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
end