The Endocrine System
Overview of the Endocrine System
▪ System of ductless glands that secrete hormones
▪ Hormones are “messenger molecules”
▪ Circulate in the blood
▪ Act on distant target cells
▪ Target cells
...
The Endocrine System
Overview of the Endocrine System
▪ System of ductless glands that secrete hormones
▪ Hormones are “messenger molecules”
▪ Circulate in the blood
▪ Act on distant target cells
▪ Target cells respond to the hormones for which they have receptors
▪ The effects are dependent on the programmed response of the target cells
▪ Hormones are just molecular triggers
▪ Basic categories of hormones
▪ Amino acid based: modified amino acids (or amines), peptides (short chains of amino acids), and proteins (long chains of amino acids)
▪ Steroids: lipid molecules derived from cholesterol
2
Endocrine Organs
▪ Purely endocrine organs
▪ Pituitary gland
▪ Pineal gland
▪ Thyroid gland
▪ Parathyroid glands
▪ Adrenal: 2 glands
▪ Cortex
▪ Medulla
▪ Endocrine cells in other organs
▪ Pancreas
▪ Thymus
▪ Gonads
▪ Hypothalamus
Mechanisms of hormone release
(a) Humoral: in response to changing levels of ions or nutrients in the blood
(b) Neural: stimulation by nerves
(c) Hormonal: stimulation received from other hormones
Learn the 3 endocrine organs on this slide: Hypothalamus
Pituitary (hyophysis) Pineal
Hypothalamus
Anterior pituitary Posterior pituitary
(adenohypophysis)
(neurohypophysis)
Hypothalamus
Pituitary
(hypophysis)
The Pituitary
Sits in hypophyseal fossa: depression in sella turcica of sphenoid bone
Pituitary secretes 9 hormones
Two divisions:
▪ Anterior pituitary
(adenohypophysis)
1. TSH
2. ACTH
3. FSH
4. LH
5. GH
6. PRL
7. MSH
The first four are “tropic” hormones, they regulate the function of other hormones
▪ Posterior pituitary
(neurohypophysis)
8. ADH (antidiuretic hormone), or vasopressin
9. Oxytocin
What the letters stand for…
▪ TSH: thyroid-stimulating hormone
▪ ACTH: adrenocorticotropic hormone
▪ FSH: follicle-stimulating hormone
▪ LH: luteinizing hormone
▪ GH: growth hormone
▪ PRL: prolactin
▪ MSH: melanocyte-stimulating hormone
▪ ADH: antidiuretic hormone
▪ Oxytocin
Hypothalamus controls anterior pituitary hormone release
▪ Releasing hormones (releasing factors) Secreted like neurotransmitters from neuronal axons into capillaries and veins to anterior pituitary
(adenohypophysis)
TRH-----turns on TSH
CRH-----turns on ACTH
GnRH (=LHRH)---turns on FSH and LH
PRF-----turns on PRL
GHRH----turns on GH
▪ Inhibiting hormones
PIF-----turns off PRL
GH inhibiting hormone ---turns off GH
...........................................................................continued............................................................................
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