ENDOCRINE SYSTEM
GLANDS 2 TYPES
1.Exocrine gland: Ducts, Lumen and Surfaces.
2.Endocrine gland : No ducts.
Secrete chemical messengers called hormones
directly into the blood stream into the plasma, where it
is dissolved and transported throughout entire body.
Hormones are substances that are secreted by one
group of cells that affects the physiology of another
group of cells (Organs).
Every cell is exposed to the hormone, but not every
cell responds to it. For a cell to respond to hormone,
the cell must have a functional hormone receptor.
Influences only specific tissues: Target cells that
have a receptor for that particular hormone.
ENDOCRINE GLANDS
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Hypothalamus
Pituitary Gland
Thyroid Gland
Parathyroid Glands
Adrenal Glands
Pancreas
Ovaries
Testes
Control of Hormone Secretion
• The endocrine system is controlled by the pituitary
gland and the hypothalamus.
• Always controlled by feedback loops.
• Concentration declines/reduces below a minimum:
more hormone is secreted.
• Concentration exceeds/increases maximum:
Hormone production is halted.
Control of Hormones Release
Three Mechanisms
• Humoral Trigger
 Blood
• Neuronal Trigger  Nervous system
• Hormonal Trigger  Hormones
Hypothalamus
• This is located at the base of the brain.
• The hypothalamus controls the endocrine system by
controlling the pituitary gland.
– Secretes releasing hormones to cause the pituitary to
release hormones.
– Secretes inhibiting hormones to turn off secretion of
pituitary hormones.
Hypothalamus Regulation
• The hypothalamus produces hormones which affect the
anterior pituitary, for example:
• Thyroid Stimulating Hormone Releasing Hormone (TSH-RH)
– Causes adeno-hypophysis to secrete TSH
– TSH affects thyroid gland to secrete TH
• Thyroid Stimulating Hormone Inhibiting Hormone (TSH-IH)
– Causes adeno-hypophysis to stop secreting TSH so thyroid
gland stops secreting thyroid hormone
• The hypothalamus affects the adeno-hypophysis, and that’s about it.
Some Hypothalamus Hormones
• Growth Hormone Releasing Hormone (GH-RH)
• Prolactin Releasing Hormone (PRL-RH)
• Thyroid Stimulating Hormone Releasing Hormone
(TSH-RH)
• Adrenocorticotropic Hormone Releasing Hormone
(ACTH-RH)
• Melanocyte Stimulating Hormone Releasing
Hormone (MSH-RH)
• Follicle Stimulating Hormone Releasing Hormone
(FSH-RH)
• Luteinizing Hormone Releasing Hormone (LH-RH)
Hypothalamus Hormones
• Growth Hormone Inhibiting Hormone (GH-IH)
• Pro-lactin Inhibiting Hormone (PRL-IH)
• Thyroid Stimulating Hormone Inhibiting Hormone
(TSH-IH)
• Adreno-corticotropic Hormone Inhibiting Hormone
(ACTH-IH)
• Melanocyte Stimulating Hormone Inhibiting
Hormone (MSH-IH)
• Follicle Stimulating Hormone Inhibiting Hormone
(FSH-IH)
• Luteinizing Hormone Inhibiting Hormone (LH-IH)
Pituitary Gland
• Secretes nine 9 major hormones
• Attached to the hypothalamus by the infundibulum
(stalk)
• Two basic divisions of the pituitary gland
– Adeno-hypophysis (anterior lobe)
– Neuro-hypophysis (posterior lobe)
HORMONES BY
ANTERIOR PITUITARY
TSH = Thyroid
stimulating hormone
ACTH = Adreno
corticotropin hormone
FSH = Follicle
stimulating hormone
LH = Luteinizing
hormone
MSH = Melanophore
stimulating hormone
GH = Growth Hormone
PRL = Prolactin
Two important
hormones secreted
by posterior pituitary
• ADH (Vasopressin)
• Oxytocin
Adeno-hypophysis
Growth hormone (GH)
–Causes the body to grow
Prolactin (PRL)
–Stimulates lactation (milk production) in females
–Stimulated lacrimation (desire to cry)
–Decreased in adolescent males so it decreases
desire to cry
Thyroid Stimulating Hormone (TSH)
–Causes the thyroid gland to release thyroid
hormone
Adeno-hypophysis
• Adrenocorticotropic hormone (ACTH)
– Acts on adrenal cortex to stimulate release of cortisol
– Helps to reduce when a person has stress
• Melanocyte-stimulating hormone (MSH)
– Darkens skin pigmentation
– Increases during pregnancy
– Also has effects on appetite and sexual arousal
• Follicle-stimulating hormone (FSH)
– Present in males and females, affects both
– Stimulates maturation of sex cells
• Luteinizing hormone (LH)
– Induces ovulation in females
– Induces testosterone in males
Neuro-hypophysis
• Oxytocin
– Childbirth contractions
• Anti-diuretic hormone (ADH)
– Signals kidneys to increase water reabsorption
• Di-Uresis : means more passage of urine.
• Anti- : means reduces urine production by
absorbing more water from the kidneys.
THYROID GLAND
Largest endocrine gland
in the body.
Weight about 20 – 25gm.
– Located along the
midline of the neck
– Secretes two
hormones.
• Thyroid hormone
• Calcitonin
Thyroid Hormones
• Thyroid hormone (TH)  T3,T4
– Acts on most cells of the body
– Increases metabolic rate
– Controlled by hormonal mechanism
– Iodine is needed to make TH
• Calcitonin
– Lowers blood calcium levels in children
– Slows osteoclasts to allow for bone deposition
– Regulates metabolism
• Increases protein synthesis
• Promotes glycolysis, gluconeogenesis, glucose uptake
• Calcitonin: calcium metabolism
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Thyroglobin
If a segment has two iodines, it is called T2.
If there are 3 iodines attached, it is called T3
(Tri-iodothyronine).
If it has 4 iodines, it is T4 (thyroxine).
The T3 and T4 are then released into
the bloodstream. Those thyroglobulin segments that
have only 1-2 iodines are recycled for parts and are
not released.
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• T4 is the most abundant form, but it is inert (inactive).
T3 has more activity on the cells. So, T3 gets used first
by the body cells. T4 takes longer to be ready; one iodine
has to drop off. As T3 is used up, T4 is being converted to
more T3.
• To make thyroid hormone, you need iodine in your body.
Iodized salt has enough to meet this need. Without enough
iodine in the diet, thyroid hormone cannot be made, no
matter how much TSH is present.
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ACTIONS OF THYROID HORMONE
• Increases GI motility
• Increases mental activity
• Increases endocrine activity
• Promotes growth and brain development in the
fetus and young children
• Stimulates fat metabolism
• Excites CNS
• Causes sleep difficulty
Thyroid Hormone Effects
• All cells respond to thyroid hormone, increasing their
metabolic rate (heart rate speeds up, beats with greater
force, more nutrients are used, etc).
• Too much thyroid hormone is hyperthyroidism; these
people are thin and active.
• When levels of TH are too low, it is called
hypothyroidism; these people are overweight, move
slowly, have no energy.
• TH also stimulates neurons; the person feels more alert,
observing their environment with more interest. When
there is too much TH, they get muscles tremors and
increased blood glucose levels (hyperglycemia).
• With not enough TH, they lose interest, become sluggish,
they get low blood glucose levels (hypoglycemia).
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Hypothalamus
TSH-RH
Hypothalamus makes TSH-RH
(Thyroid stimulating hormone
releasing hormone)
Pituitary
Pituitary makes TSH
(Thyroid stimulating hormone)
TSH
Thyroid
TH
Thyroid gland makes TH
(Thyroid hormone)