Function of Endocrine System
-regulates and controls many metabolic processes
-helps maintain body homeostasis through "negative feedback"
-serves as one of the two major control systems of the body by synthesizing and secreting hormones (nervous system is other major control system)
composition of endocrine system
-endocrine glands located throughout the body
Endocrine and Nervous System
Common Features
1. both release chemical substances, ligands
(NS uses neurotransmitters/ES uses hormones)
2. both bind to cellular receptor on particular target cells
3. both initiate cellular change in target cells
Endocrine System features
NOT in common with nervous system
1. hormones transported within blood to target cells
2. causes metabolic changes in target cells
3. target any cells with receptors
4. exhibit longer reaction times
5. more widespread effects throughout the body
6. longer-lasting effects (minutes to days
Functions of the Endocrine System
1. maintaining homeostasis of blood composition and volume
2. controlling reproductive activities
3. regulating development, growth, and metabolism
4. controlling digestive processes
5 Major Endocrine Organs
(entirely endocrine in function)
1. pituitary gland
2. pineal gland
3. thyroid gland
4. parathyroid gland
5. adrenal gland
composition of endocrine glands
-secretory endocrine cells
-derived from epithelium with connective tissue framework
-have extensive blood supply (to be able to dump hormones into blood)
pineal gland
-major part of the epithalamus
-secretes melatonin
-regulates sleep/wake cycle
parathyroid gland
-four nodules on posterior thyroid gland
-secretes parathyroid hormone
-increases calcium level in blood
(PTH stimulates osteoclasts which break down bone and release calcium into the blood to increase blood calcium level)
Endocrine Cells within other organs
(secrete hormones but have other primary function)
-hypothalamus, skin, thymus
-heart, liver, stomach
-pancreas, small intestine
-kidneys, gonads
3 types of endocrine reflexes
(how hormone is released)
1. hormonal
2. humoral
3. nervous
Hormonal Stimulation
-hormone triggers release of another hormones
Humoral Stimulation
-changes in levels of nutrients or ions triggers release of hormones
Nervous System Stimulation
-nervous system triggers release of hormones
Steroid hormones
-lipid soluble
i.e. estrogen, progesterone, testosterone, corticosteroids
Protein hormones
-water soluble
-most hormones
i.e. insulin, glucagon, oxytocin, thyroid stimulating hormone, antidiuretic hormone, PTH, follicle stimulating hormone
Biogenic Amines
-water soluble (except thyroid hormone)
-modified amino acids
i.e. epinephrine, norepinephrine, thyroid hormone
Local hormones
-do not circulate within the blood
-released from cells that produce them, and bind with same cell or neighboring cells
Eicosanoids
-primary type of local hormone
-initiate smooth muscle contraction
-stimulate pain receptors
autocrine hormone stimulation
-cell releases a hormone that stimulates itself
paracrine hormone stimulation
-cell releases a hormone that stimulates its neighbor
Transport of water soluble hormones
-easy to transport TO cell bc blood is mostly water
-needs help crossing membrane---must bind to receptor to get INTO cell
Transport of lipid-soluble hormones
-harder to transport TO cell bc blood is mostly water
-easily diffuses across membrane INTO cell and binds to intracellular receptors
receptor fluctuations
- number of hormone receptors changes in order to regulate the level of response
- up-regulation (more receptors = more responsive)
- down regulation (less receptors = less responsive)
Synergistic hormone interactions
-hormones work together to produce a greater effect
Permissive hormone interactions
-a first hormone allows the action of a second hormone
Antagonistic hormone interactions
-one hormone causes the opposite effect of another
glycogenesis
-synthesis (making) of glucose from glycogen
glycogenolysis
-breakdown of stored glycogen into glucose
gluconeogenesis
-glucose made from something that is NOT sugar
hypothalamus functions
-main control center for endocrine function
-direct control over hormone release from pituitary gland
-indirect control over hormone release from thyroid, adrenal glands, lives, testes, and ovaries
pituitary gland
-anterior and posterior parts
-lies inferior to hypothalmus within sella truck of sphenoid bone (size of a pea)
-connected to hypothalamus by infundibulum
posterior pituitary
-"neural" part of pituitary gland
-DOES NOT produce hormones
-releases hormones produced in hypothalamus
*oxytocin and antidiuretic hormone
2 hormones released by pituitary gland
-oxytocin
-antidiuretic hormone
**
synthesized by hypothalamus but released by posterior pituitary gland
**
anterior pituitary
-hypothalamus releases hormones into blood vessels around the anterior pituitary (hypothalamo-hypophyseal portal system) which dumps them into the anterior pituitary and stimulates it to release hormones
Where does a "releasing hormone" originate from?
The hypothalamus-it sends releasing hormones to trigger the release of hormones from the anterior and posterior pituitary glands
list of releasing hormones from hypothalamus
1. thyrotropin-releasing hormone (TRH)
2. prolactin-releasing hormone (PRL)
3. gonadotropin-releasing hormone (GnRH)
4. corticotropin-releasing hormone (CRH)
5. growth-releasing hormone (GHRH)
oxytocin
(from posterior pituitary)
-stimulates labor contractions
antidiuretic hormone
(from posterior pituitary)
-holds onto water in blood (increases blood pressure)
thyroid stimulating hormone (TSH)
(from anterior pituitary)
-regulates release of thyroid hormone from thyroid gland
prolactin (PRL)
(from anterior pituitary)
-regulates mammary growth and breast milk production
gonadotropins (follicle-stimulating hormone FSH)
(from anterior pituitary)
-regulates hormone synthesis by gonads and production of gametes
adrenocorticotropic hormone (ACTH)
(from anterior pituitary)
-stimulates adrenal cortex to produce and secrete glucocorticoids
growth hormone (GH)
(from anterior pituitary)
-stimulates cell growth and cell division
-most cells in the body have this hormone
melanocyte-stimulating hormone (MSH)
(from anterior pituitary)
-stimulates rate of melanin synthesis by melanocytes in skin
-ceases prior to adulthood
thyrotropin-releasing hormone
-increases secretion of thyroid stimulating hormone
prolactin-releasing hormone
-increases secretion of prolactin
gonadotropin-releasing hormone
-increases secretion of follicle stimulating hormone and luteinizing hormone
corticotropin-releasing hormone
-increases secretion of adrenocorticotropic hormone`
growth-releasing hormone
-increases secretion of growth hormone
mineralocorticoids
(from adrenal cortex)
-regulates levels of electrolytes
glucocorticoids
(from adrenal cortex)
-regulates glucose
ex. cortisol - (stress hormone-most common)
gonadocorticoids
(from adrenal cortex)
-regulates sex homones
catecholamines
(from adrenal medulla)
-epinephrine or norepinephrine
-prolongs fight-or-flight response
thyroid gland in endocrine system
-largest structure in body devoted to endocrine activities
-has left and right lobes connected by isthmus
-releases thyroid hormone
-must have iodine to make thyroid hormone