Transcript Table 13-2

Stress (cont.)
During stress, the priorities of the secretions of the
hypothalamo-pituitary peripheral-endocrine axes
are shifted in favor of the
hypothalamo-pituitary-adrenocortical (HPA) axis.
During stress:
HPA
GHRH
GH
GnRH
FSH
LH
Hypothalmo-Pituitary-Thyroid
System
Figure 13-1: Diagrammatic representation of the thyroid gland
Figure 13-2
Table 13.3
Major Actions of Thyroid Hormones
• Calorigenesis
• Metabolism
• Brain maturation
• Behavior
• Growth & development
Figure 1 3- 3
(-)
CNS

HYPOTHALAMUS
TRH

(-)
PITUITAR Y

TSH
CLE ARANCE

THYROID GLAND



T3
T4
r T3
FREE &
BOUND
TA RGET CELLS

T4

T3
INTRACELLULAR (N UCLEAR) BINDING

METABOLIC RESPONSE
3, 5, 3’, 5’ Tetraiodothyronine (thyroxine, T4)
3, 5, 3’ Triiodothyroine (T3)
Table 13-2: Some MORPHOLOGIC Changes
in the Thyroid Gland with Aging
FOLLICLES:
- Are distended
- Change in color
- Epithelium flattened w/
reduced secretion
Fewer mitoses
Increased
connective tissue;
Fibrosis
Atherosclerotic
changes
Table 13-2 (con’t.): Some SECRETORY Changes
in the Thyroid Gland with Aging
circulating T3 levels
but generally within
the normal (lower) range
Simultaneously decreased
secretion and metabolic
clearance of T4 with resulting
essentially normal levels
TSH levels in 10%
of the elderly, associated
peripheral
conversion of T4 to T3
Failure of up-regulation
of
T3 nuclear receptors
in antithyroid antibodies,
present even in the absence of
manifestations of hypothyroidism
Table 13-1: Some Critical Aspects of Thyroid Hormone Regulation
1. Major source of circulating T3 from peripheral deiodination of
T4 (NOT from thyroid gland secretion)
2. The negative feedback at the pituitary anterior lobe is mainly
through T4 (taken from circulation & converted into T3)
3. The peripheral deiodination of T4 depends on the physiological
state of the organism. It allows an autonomy of response of the
tissues to the hormones.
4. Deiodination can convert T4 (a less biologically active hormone)
to T3 (a more active hormone). This conversion depends on the
activity of the various deiodinating enzymes.
Figure 13-4
Basal Metabolic Rate
from
birth to 70
years old
Basal
Metabolic
Rate
Table 13-5 In the Elderly,
Thermoregulatory Insufficiency
Results from:
heat production,
body mass,
muscle activity,
shivering,
sweating response,
vasomotor responses,
temperature perception.
Table 13-6 Autoimmune Diseases of the Thyroid Gland
Characteristics
Graves’ Disease
Hashimoto’s Thyroiditis
Thyroid Status
Hyperthyroid
Hypothyroid
TSH
Generally undetectable Normal to elevated
T4, T3 (serum)
Above normal
Below normal
Antibodies(ABs)
Stimulatory ABs
compete with TSH at
receptor sites
Loss of TSH control
over thyroid function
Some ABs block TSH
actions
Autoantibodies against Generally present
thyroglobulin, T3, T4,
thyroid destroy thyroid
microsomal and nuclear
components
Generally present
Lymphocytic Invasion
Limited
Marked
Female:Male Ratio
As high as 10:1
As high as 10:1