Download Thyroid gland

Endocrine System
Part 2
Thyroid Gland
 Saddle bag shaped gland
 Largest endocrine gland in the body
 3 hormones
 Throxin
 Triiodothyronine
 Calcitonin
Thyroid hormone
Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
(on dorsal aspect
of thyroid gland)
Thymus
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
Copyright © 2010 Pearson Education, Inc.
Figure 16.1
Figure 16.8
Thyroid Hormone (TH)
 Actually two related compounds
 T4 (thyroxin)
 2 tyrosine molecules + 4 bound iodine atoms
 T3 (triiodothyronine)
 2 tyrosines + 3 bound iodine atoms
Thyroid Hormone (TH)
1)
2)
3)
4)
5)
6)
7)
Iodide enters body
Converted to iodine by thyroid gland
Iodine binds to thyroglobulin
Tyrosine added to iodized thyroglobulin, combined in vacuole
with lysosomes
Thyroglobulin freed and recycled while T3/T4 diffuses into
blood
T3/T4 bind to thyroxin-binding globulin in blood
At tissue receptor T4 converted to active T3 by tissue enzymes
Thyroid follicle cells
Colloid
1 Thyroglobulin is synthesized and
discharged into the follicle lumen.
Tyrosines (part of thyroglobulin
molecule)
Capillary
4 Iodine is attached to tyrosine
in colloid, forming DIT and MIT.
Golgi
apparatus
Rough
ER
Iodine
3 Iodide
is oxidized
to iodine.
2 Iodide (I–) is trapped
(actively transported in).
Iodide (I–)
Lysosome
T4
T3
DIT (T2) MIT (T1)
Thyroglobulin
colloid
5 Iodinated tyrosines are
linked together to form T3
and T4.
T4
T3
T4
T3
6 Thyroglobulin colloid is
endocytosed and combined
with a lysosome.
7 Lysosomal enzymes cleave
T4 and T3 from thyroglobulin
colloid and hormones diffuse
into bloodstream.
Colloid in
lumen of
follicle
To peripheral tissues
Figure 16.9
Thyroid Hormone (TH)
 Major metabolic hormone (catabolism)
 Regulates tissue growth and development
 Increases reactivity of mature nerve cells
 Regulates heart rate
 Regulates movement of gastrointestinal tract
Hypothalamus
TRH
Anterior pituitary
TSH
Thyroid gland
Thyroid
hormones
Target cells
Stimulates
Inhibits
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Figure 16.7
Imbalances of Thyroid Hormone
 Goiter
 Cretinism
 Myxedema
 Graves’ disease
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Figure 16.10
Calcitonin
 Lowers serum calcium
 Inhibits bone resorption
 Stimulates uptake by the bone matrix
 Antagonist to parathyroid hormone (PTH)
 Regulated by Ca2+ concentration in the blood
 Negative feedback mechanism
Parathyroid Glands
 Four tiny glands embedded in the posterior aspect of the thyroid
 Parathyroid hormone (PTH)
 Most important hormone in Ca2+ homeostasis
Pharynx
(posterior
aspect)
Thyroid
gland
Parathyroid
glands
Chief
cells
(secrete
parathyroid
hormone)
Oxyphil
cells
Esophagus
Trachea
(a)
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Capillary
(b)
Figure 16.11
Parathyroid Hormone
 Functions
 Stimulates osteoclasts to digest bone matrix
 Enhances reabsorption of Ca2+ by the kidneys
 Increases absorption of Ca2+ by intestinal mucosa
 Negative feedback
 Rising Ca2+ in the blood inhibits PTH release
Hypocalcemia (low blood Ca2+) stimulates
parathyroid glands to release PTH.
Rising Ca2+ in
blood inhibits
PTH release.
Bone
1 PTH activates
osteoclasts: Ca2+
and PO43S released
into blood.
Kidney
2 PTH increases
2+
Ca reabsorption
in kidney
tubules.
3 PTH promotes
kidney’s activation of vitamin D,
which increases Ca2+ absorption
from food.
Intestine
Ca2+ ions
PTH Molecules
Copyright © 2010 Pearson Education, Inc.
Bloodstream
Figure 16.12
Adrenal Glands
 Paired, pyramid-shaped glands atop the kidneys
 Essentially two glands in one
 Adrenal medulla
 Nervous tissue: part of the sympathetic nervous system
 NE and Epinephrine
 Adrenal cortex
 Three layers of glandular tissue
 Synthesize and secrete steroid hormones
Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
(on dorsal aspect
of thyroid gland)
Thymus
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
Figure 16.1
Adrenal Cortex
 Three layers that produce corticosteroids
 Outer layer = mineralocorticoids
 Middle layer = glucocorticoids
 Inner layer = sex hormones, or gonadocorticoids
Capsule
Zona
glomerulosa
• Medulla
• Cortex
Cortex
Adrenal gland
Zona
fasciculata
Zona
reticularis
Medulla
Kidney
Adrenal
medulla
(a) Drawing of the histology of the
adrenal cortex and a portion of
the adrenal medulla
Figure 16.13a
Mineralocorticoids
 Regulate extracellular Na+ and K+
 Na+: affects ECF volume, blood volume, blood pressure
 K+: sets resting membrane potential of cells
 Aldosterone is most important
 Stimulates Na+ reabsorption (and water retention) by kidneys
 Stimulates K+ secretion
Primary regulators
Secretion mainly
controlled by
blood pressure and
potassium levels
Blood volume
and/or blood
pressure
Other factors
K+ in blood
Stress
Blood pressure
and/or blood
volume
Hypothalamus
Kidney
Heart
CRH
Renin
Initiates
cascade
that
produces
Direct
stimulating
effect
Anterior
pituitary
Atrial natriuretic
peptide (ANP)
ACTH
Angiotensin II
Inhibitory
effect
Zona glomerulosa
of adrenal cortex
Enhanced
secretion
of aldosterone
Targets
kidney tubules
Absorption of Na+ and
water; increased K+ excretion
Blood volume
and/or blood pressure
Figure 16.14
Glucocorticoids
 Regulate carbohydrate metabolism
 Keep blood sugar levels relatively constant
 Gluconeogenesis
 Suppress inflammation
 Vasoconstriction
 Vessel permeability
 Stabilizing lysosomes
Imbalances of Glucocorticoids
 Cushing’s disease
 Addison’s disease
 Also involves deficits in mineralocorticoids
Figure 16.15
Gonadocorticoids (Sex Hormones)
 Most are androgens (male sex hormones)
 Converted to testosterone in tissue cells or estrogens in females
 Supplement hormones secreted by gonads
 May contribute to
 Onset of puberty
 Secondary sex characteristics
 Sex drive
Adrenal Medulla
 Epinephrine
 Affects the metabolic rate of all cells
 Bronchial dilation
 Increased blood flow to skeletal muscles and heart
 Norepinephrine
 Increased blood pressure
 Increased heart rate
 Increased stroke volume
Short-term stress
More prolonged stress
Stress
Nerve impulses
Hypothalamus
CRH (corticotropinreleasing hormone)
Spinal cord
Corticotroph cells
of anterior pituitary
To target in blood
Preganglionic
sympathetic
fibers
Adrenal medulla
(secretes amino acidbased hormones)
Catecholamines
(epinephrine and
norepinephrine)
Short-term stress response
1. Increased heart rate
2. Increased blood pressure
3. Liver converts glycogen to glucose and releases
glucose to blood
4. Dilation of bronchioles
5. Changes in blood flow patterns leading to decreased
digestive system activity and reduced urine output
6. Increased metabolic rate
Adrenal cortex
(secretes steroid
hormones)
ACTH
Mineralocorticoids
Glucocorticoids
Long-term stress response
1. Retention of sodium
and water by kidneys
2. Increased blood volume
and blood pressure
1. Proteins and fats converted
to glucose or broken down
for energy
2. Increased blood glucose
3. Suppression of immune
system
Figure 16.16
Imbalances in Adrenal Medulla
 Adrenal medullary hormones not essential for life
 Pheochromocytoma
Pancreas
 Long, flat gland near stomach
 Exocrine function
 Produces enzyme-rich juice for digestion
 Endocrine function
 Pancreatic islets (islets of Langerhans)
 Alpha () cells = glucagon
Hyperglycemic hormone
 Beta () cells = insulin
 Hypoglycemic hormone

Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
(on dorsal aspect
of thyroid gland)
Thymus
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
Figure 16.1
Glucagon
 Major target is the liver
 Release of glucose to the blood
 Hyperglycemic factor
Insulin
 Effects
 Lowers blood glucose levels
 Enhances membrane transport of glucose
 Inhibits glycogenolysis and gluconeogenesis
Stimulates glucose uptake by cells
Tissue cells
Insulin
Pancreas
Stimulates
glycogen
formation Glucose Glycogen
Blood
glucose
falls to
normal
range.
Liver
Stimulus
Blood
glucose level
Stimulus
Blood
glucose level
Blood
glucose
rises to
normal
range.
Pancreas
Liver
Glucose Glycogen
Stimulates
glycogen Glucagon
breakdown
Figure 16.18
Imbalances of Insulin
 Diabetes mellitus (DM)
 Due to hyposecretion or hypoactivity of insulin
 Vascular component
 Three cardinal signs of DM
 Polyuria = copious urine output
 Polydipsia = excessive thirst
 Polyphagia = excessive hunger and food consumption
Table 16.4
Diabetes Mellitus
 Type I
 Type II
 Gestational
Insulin cont.
 Other hormones affecting insulin levels
 Growth hormone (GH)
 Adrenocorticotropic hormone (ACTH)
Minor Endocrine Glands
 Thymus
 Pineal gland
Thymus
 2 lobed organ high in chest
 Thymosins = lymphocytes
 Active during fetal development and for first two
years after birth
Pineal Gland
 Small gland hanging from the roof of the third ventricle
 Melatonin
 Timing of sexual maturation and puberty
 Photoperios
 Physiological processes that show rhythmic variations
 Body temperature, sleep, appetite
Not well understood in humans
Stress
 Physical
 Psychological
Strong emotional reactions
Individual reactions vary
The Stress Response
 Changes largely mediated by hypothalamus
 Three stages
 Alarm (acute, sympathetic)
 Resistance (chronic, endocrine)
 Exhaustion
Temporary change in homeostasis =
General Adaptation Syndrome (GAS)
Alarm Reaction
 Immediate
 Hypothalamus
 Sympathetic nervous system
 Adrenal medulla
 Increased serum glucose
 Increased circulation
Resistance Reaction
 Long-term modification
 Hypothalamus
 Pituitary gland
 Many effects…
 Increases energy availability
 Produces new proteins
 Improves circulation
Short-term stress
More prolonged stress
Stress
Fight or Flight
Nerve impulses
Resistance
Hypothalamus
CRH (corticotropinreleasing hormone)
Spinal cord
Corticotroph cells
of anterior pituitary
To target in blood
Preganglionic
sympathetic
fibers
Adrenal medulla
(secretes amino acidbased hormones)
Catecholamines
(epinephrine and
norepinephrine)
Short-term stress response
1. Increased heart rate
2. Increased blood pressure
3. Liver converts glycogen to glucose and releases
glucose to blood
4. Dilation of bronchioles
5. Changes in blood flow patterns leading to decreased
digestive system activity and reduced urine output
6. Increased metabolic rate
Adrenal cortex
(secretes steroid
hormones)
ACTH
Mineralocorticoids
Glucocorticoids
Long-term stress response
1. Retention of sodium
and water by kidneys
2. Increased blood volume
and blood pressure
1. Proteins and fats converted
to glucose or broken down
for energy
2. Increased blood glucose
3. Suppression of immune
system
Figure 16.16
Exhaustion
 Stressor too strong
 K+ loss = cell death
 Glucocorticoid depletion = cell starvation
 Immune system failure
General Adaptation Syndrome
(or Stress Response)
Questions?