Thyroid Gland
Saddle bag shaped gland
Largest endocrine gland in the body
3 hormones Throxin
Triiodothyronine
Calcitonin
Thyroid hormone
Copyright © 2010 Pearson Education, Inc. Figure 16.1
Pineal gland
Hypothalamus
Pituitary gland
Parathyroid glands
(on dorsal aspect
of thyroid gland)
Thymus
Thyroid gland
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
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) Iodide enters body
2) Converted to iodine by thyroid gland
3) Iodine binds to thyroglobulin
4) Tyrosine added to iodized thyroglobulin, combined in vacuole
with lysosomes
5) Thyroglobulin freed and recycled while T3/T4 diffuses into
blood
6) T3/T4 bind to thyroxin-binding globulin in blood
7) At tissue receptor T4 converted to active T3 by tissue enzymes
Figure 16.9
To peripheral tissues
T3
T3
T3
T4
T4
Lysosome
Tyrosines (part of thyroglobulin
molecule)
T4
DIT (T2)
Iodine
MIT (T1)
Thyro-
globulin
colloid
Iodide (I–)
Rough
ER
Capillary
Colloid
Colloid in
lumen of
follicle
Thyroid follicle cells
Iodinated tyrosines are
linked together to form T3
and T4.
Iodide
is oxidized
to iodine.
Thyroglobulin colloid is
endocytosed and combined
with a lysosome. Lysosomal enzymes cleave
T4 and T3 from thyroglobulin
colloid and hormones diffuse
into bloodstream.
Iodide (I–) is trapped
(actively transported in).
Thyroglobulin is synthesized and
discharged into the follicle lumen.
Iodine is attached to tyrosine
in colloid, forming DIT and MIT.
Golgi
apparatus
1
2
3
4
5
6
7
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
Copyright © 2010 Pearson Education, Inc. Figure 16.7
Hypothalamus
Anterior pituitary
Thyroid gland
Thyroid
hormones
TSH
TRH
Target cells Stimulates
Inhibits
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
4-8 tiny glands embedded in the posterior aspect of the thyroid
Parathyroid hormone (PTH)
Most important hormone in Ca2+ homeostasis
Copyright © 2010 Pearson Education, Inc. Figure 16.11
(b)
Capillary
Chief
cells
(secrete
parathyroid
hormone)
Oxyphil
cells
Pharynx
(posterior
aspect)
Thyroid
gland
Parathyroid
glands
Trachea
Esophagus
(a)
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
Copyright © 2010 Pearson Education, Inc. Figure 16.12
Intestine
Kidney
Bloodstream
Hypocalcemia (low blood Ca2+) stimulates
parathyroid glands to release PTH.
Rising Ca2+ in
blood inhibits
PTH release.
1 PTH activates
osteoclasts: Ca2+
and PO43S released
into blood.
2 PTH increases
Ca2+ reabsorption
in kidney
tubules.
3 PTH promotes
kidney’s activation of vitamin D,
which increases Ca2+ absorption
from food.
Bone
Ca2+ ions
PTH Molecules
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
Figure 16.1
Pineal gland
Hypothalamus
Pituitary gland
Parathyroid glands
(on dorsal aspect
of thyroid gland)
Thymus
Thyroid gland
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
Adrenal Cortex
Three layers that produce corticosteroids
Outer layer = mineralocorticoids
Middle layer = glucocorticoids
Inner layer = sex hormones or gonadocorticoids
Figure 16.13a
• Cortex
Kidney
• Medulla
Adrenal gland
Capsule
Zona
glomerulosa
Zona
fasciculata
Zona
reticularis
Adrenal
medulla
(a) Drawing of the histology of the
adrenal cortex and a portion of
the adrenal medulla
Me
dulla
C
ortex
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
Figure 16.14
Primary regulators Other factors
Blood volume
and/or blood
pressure
Angiotensin II
Blood pressure
and/or blood
volume
K+ in blood
Direct
stimulating
effect Renin
Initiates
cascade
that
produces
Kidney
Hypo-
thalamus
Heart
CRH
Anterior
pituitary
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
Inhibitory
effect
Stress
ACTH Atrial natriuretic
peptide (ANP)
Secretion mainly
controlled by
blood pressure and
potassium levels
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
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
Figure 16.16
Short-term stress More prolonged stress
Stress
Hypothalamus
CRH (corticotropin-
releasing hormone)
Corticotroph cells
of anterior pituitary
To target in blood
Adrenal cortex
(secretes steroid
hormones)
Glucocorticoids Mineralocorticoids
ACTH
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
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
Adrenal medulla
(secretes amino acid-
based hormones)
Preganglionic
sympathetic
fibers
Spinal cord
Nerve impulses
Activities
Worksheet 3, Endocrine 24
Thyroid gland
Adrenal cortex
Worksheet 4, Endocrine 25
Hormone review, skip #6
Hormone origin matching
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
Figure 16.1
Pineal gland
Hypothalamus
Pituitary gland
Parathyroid glands
(on dorsal aspect
of thyroid gland)
Thymus
Thyroid gland
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
Insulin
Effects Lowers blood glucose levels
Enhances membrane transport of glucose
Inhibits glycogenolysis and gluconeogenesis
Figure 16.18
Liver
Liver
Tissue cells
Stimulates glucose uptake by cells
Stimulates
glycogen
formation Pancreas
Pancreas
Insulin
Blood
glucose
falls to
normal
range.
Stimulates
glycogen
breakdown
Blood
glucose
rises to
normal
range.
Glucagon
Stimulus
Blood
glucose level
Stimulus
Blood
glucose level
Glycogen Glucose
Glycogen Glucose
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
Insulin cont.
Other hormones affecting insulin levels
Growth hormone (GH)
Adrenocorticotropic hormone (ACTH)
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
Photoperiod
Physiological processes that show rhythmic variations
Body temperature, sleep, appetite
Not well understood in humans
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
Figure 16.16
Short-term stress More prolonged stress
Stress
Hypothalamus
CRH (corticotropin-
releasing hormone)
Corticotroph cells
of anterior pituitary
To target in blood
Adrenal cortex
(secretes steroid
hormones)
Glucocorticoids Mineralocorticoids
ACTH
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
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
Adrenal medulla
(secretes amino acid-
based hormones)
Preganglionic
sympathetic
fibers
Spinal cord
Nerve impulses Fight or Flight Resistance
Exhaustion
Stressor too strong K+ loss = cell death
Glucocorticoid depletion = cell starvation
Immune system failure
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