Download Endocrine system II

Section 3 Thyroid Gland
I. Biological Actions of Thyroid
Hormones




T3 and T4 bind with nuclear receptor,
activate and initiate genetic transcription. ---mRNA
protein synthesis in cytoplasmic ribosomes ---general increase in functional activity throughout
the body.
1. On Metabolism
 Calorigenic
action of thyroid
hormones
 Effect on metabolism of
 protein
 carbohydrate
 fat
Calorigenic action

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increase O2 consumption of most tissues in
the body, increasing heat production and BMR.
mechanism

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A: Enhances Na+-K+ ATPase activity
B: Causes the cell membrane of most cells to
become leaky to Na+ ions
on metabolism of protein
•
Physiological level: stimulates synthesis
of proteins and enzymes,
•
Hyperthyroidism: catabolism of
protein, leads weigh-loss and muscle
weakness
•
Hypothyroidism: myxedema (粘液性
水肿） develops because of deposition
of mucoprotein binding with positive
ions and water molecules in the
interstitial spaces while protein synthesis
decreases
On carbohydrate metabolism
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Increase absorption of glucose from the
gastrointestinal tract
Enhance glycogenolysis, and even enhanced
diabetogenic effect of glucagon, cortisol and
growth hormone.
Enhancement of glucose utilization of
peripheral tissues.
On fat metabolism

Fatty acids:
accelerate the oxidation of free fatty acids
 increase the effect of catecholamine on
decomposition of fat.

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decrease plasma cholesterol concentration
promote synthesis
 increase decomposition
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2. on Growth and Development

essential for normal growth and development
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especially skeletal growth and development.
stimulate formation of dendrites, axons, myelin
and neuroglia.
Critinism
A child without a thyroid gland
 growth and mental retardation.
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3. Effects on Nervous System

increase excitability of
central nervous system
 sympathetic nervous system

.

Hyperthyroidism:
extreme nervousness,
 many psychoneurotic
tendencies including anxiety
complexes, extreme worry,
paranoia （妄想）and
muscle tremor

Hyperthyroidism
Effects on Nervous System

Hypothyroidism
fatigue
 extreme somnolence
 poor memory
 slow mentation （精神状态）

4. Other Effects

on cardiovascular system

increase heart rate and stroke volume,


(may through enhance calcium release from
sarcoplasmic reticulum)
on gastrointestinal tract

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increase the appetite and food intake by metabolic
rate increased.
increase both the rate of secretion of the digestive
juices and the motility of the gastrointestinal tract.
Lack of thyroid hormone can cause constipation.
II Regulation of Thyroid
Hormone Secretion
 Hypothalamic
Pituitary Thyroid Axis
 Feedback Mechanisms
 Autoregulation
 Effect of Autonomic Nervous System
Hypothalamic Pituitary Thyroid Axis

TSH (throid-stimulating
hormone):


Increase secretion of T4
and T3
Stimulate thyroid gland to
growth, increasing size and
number of thyroid cells
Hypothalamic Pituitary Thyroid Axis

TRH（thyrotropinreleasing hormone)
causes the anterior
pituitary to produce and
release of TSH.
 Cold and various
emotional reactions can
increase TRH secretion
through nervous system

Feedback Mechanisms of Thyroid
Hormones

T3 and T4
pituitary
inhibitory protein in anterior
reduces production and secretion of TSH
 decrease response of pituitary to TRH


Negative feedback
(Inhibitory Protein)
In the absence of sufficient dietary iodide the thyroid cannot
produce adequate amounts of T4 and T3.
causes abnormally high level of the TSH secretion, which in
turn stimulate the abnormal growth of the thyroid (a goiter).
Autoregulation of Thyroid Hormone
Secretion


thyroid gland adapt itself function to iodide uptake,
 When iodine is insufficient, the thyroid gland
increases formation of hormones
 large doses of iodide act directly on the thyroid gland
to produce a mild and transit inhibition of hormone
synthesis.
In patients with hyperthyroidism

iodides cause the vascularity of hyperplastic gland to
decrease (Wolff-Chaikoff effect)

making iodide treatment considerable in preparing patients for
surgery.
Effect of Autonomic Nervous System
on Thyroid Activity

The thyroid gland is innervated by both
sympathetic nerve and parasympathetic
nerve.
sympathetic nerve increases formation of thyroid
hormones
 cholinergic fibers (vagus nerve) inhibits secretion of
thyroid hormone

Section 4 Adrenal Gland
I. Adrenal Cortical
Hormones
 The mineralocorticoids
are secreted by zona
glomerulosa
 regulates the
concentration of the
extracellular fluid.
 Aldosterone is the
principal
mineralocorticoid.
 The glucocorticoids are
secreted by both zona
fasciculata and zona
reticularis,
 exhibiting an important
effect on increasing
blood glucose
concentration
 Cortisol is the principal
glucocorticoid
 Small amounts of sex
hormones are secreted by
the zona reticularis.
1. Biological Effects of Adrenocortical Hormones
CBD, corticosteroid-binding globulin; GR, glucocorticoid receptor
(1) On metabolism
1) On carbohydrate metabolism.
A, Stimulation of gluconeogenesis by the liver cell
----activates DNA transcription in the liver cell nuclei and
increase the synthesis of enzymes required for
gluconeogenesis.
----causes mobilization of amino acids from extrahepatic
tissues, mainly from muscle.
Result: a marked increase in glycogen storage in the liver cells.
B, Reduction of glucose utilization by the cells.
by inhibition of response of cells to insulin.
Elevate blood glucose concentration
2) On protein metabolism
A. mobilizes amino acids from the nonhepatic tissues
and diminishes the tissue stores of protein.
B. decreases protein synthesis and increases
catabolism of protein in many extrahepatic tissues
especially in muscle and lymphoid tissue
In the presence of great excesses of cortisol, the
muscles become weak and the immunity functions of
lymphoid tissue decrease.
3) On fat metabolism
A. Promote mobilization of fatty acids from adipose tissue
and increases the concentration of free acids in the plasma
B. Increases oxidation of fatty acids in the liver cells for
energy.
Cushing’s Syndrome
People with excess cortisol
secretion
develop a peculiar type of
obesity
excess deposition of fat in
the chest and head regions
of the body
a buffalo-like torso and a
rounded “moon-face”.
Cushing’s Syndrome
“moon face”
striae
4) Effects on water and electrolytes
slight enhancement of sodium reabsorption and
potassium excretion by distal tubules and colleting
ducts in kidney.
increases the rate of renal blood flow and then
glomerular filtration rates, facilitating water excretion
In patients with adrenal insufficiency, excretion of
water is so slow that there is a danger of water
intoxication and only glococorticoids can repair this
deficit.
(2) On blood cells
increase the production of red cells and platelets by
stimulating bone marrow.
decrease the number of lymphocytes and
eosinocytes (嗜酸性粒细胞）
causes atrophy of the all lymphoid tissues and
promotion of destruction of lymphocytes and
eosinocytes.
(3) On cardiovascular system
necessary for maintenance of normal blood pressure.
1) Cause permissive action, enhancing the response of
vascular muscle to catecholamines.
2) Inhibit synthesis of prostaglandins that have
vasodilator effect.
3) Reduces the permeability of capillaries, which is
useful to maintenance of blood volume.
(4) Effect on stress.
Almost any type of stress
cause increase in ACTH
secretion, and consequent
cortisol secretion.
essential for survival.
(5) Other effects.
increase in production of HCl and pepsin,
promotion of synthesis of fetal surfactant.
pharmacological effects including antiinflammatory, antiallergic and antishock effect.
2. Regulation of Secretion of Adrenocortical Hormone
Hypothalamus –
Anterior Pituitary
– Adrenocortical
Axis
(1) Action of ACTH
(adrenocorticotropin
hormone)
control of cortisol
secretion
ACTH causes
formation of adrenocortical
adrenocortical secretion.
hypertrophy and proliferation of the adrenocorticol cells.
(2) CRH (corticotropin releasing
hormone)
A, Action of CRH
promote synthesis and release of
ACTH
B, Regulation of CRH secretion
Fluctuations in plasma ACTH and glucotorticoids
throughout the day in a normal girl (age 16).
The
circadian
rhythm is
driven by
impulses
from the
suprachiasmatic
nuclei
11-OHCS (11-hydroxycorticosteroids, １１－羟皮质类醇 )
(3) Feedback
mechanism
Cortisol has direct
negative feedbacks on
the hypothalamus to
decrease formation of
CRH
High circulating
levels of cortisol
inhibit secretion and
formation of ACTH,
decreasing response
of anterior pituitary
gland to CRH.
High levels of ACTH
also inhibit CRH
secretion by a negative
feedback mechanism.
These feedbacks help
regulate the plasma
concentration of
cortisol toward a
normal control level.
Clinical treatment of cortisol (large does and long time)
always cause the atrophy of the adrenal gland.