Endocrine System Flashcards
Sending Signals:
Nervous System
Who is involved? Neurons secreting neurotransmitters
Who are the targets? Other neurons, muscle, and glands
Methods of Communication
Action potentials cause Ca+2 influx that
trigger neurotransmitter release
Sending Signals: Endocrine System
Who is involved? Endocrine glands that secrete hormones into the bloodstream
Who are the targets? Any cell with hormone receptors
Methods of Communication
* Neural control: Nervous system triggers hormone
release
* Humoral control: Chemical levels in blood trigger
hormone release
* Hormonal control: Hormones trigger the release of
other hormones
Hormones: Lipid-Soluble
Example Steroids (like estrogen & testosterone)
How do they target cells?
Lipophilic hormones diffuse across the plasma membrane (hormone receptors are inside the cell)
Effects? Trigger protein synthesis to alter cell
structure changes and metabolic activity
changes
Hormones: Water-Soluble
Examples Insulin & Glucagon
How do they target cells?
Hormone receptors are located on the
plasma membrane. Water-soluble hormones
initiate signal transduction pathways.
Effects? Alter enzyme activity, ion permeability,
stimulate mitosis, stimulate muscle
contraction, trigger the release of other
hormones
Controlling Hormonal Release: Positive
Feedback
Loops that amplify with every cycle until desired effect is reached. (Rare)
Examples: Labor & delivery
Lactation
Controlling Hormonal Release: Negative
Feedback
- Response is opposite the
stimulus. - Low [hormones] = stimulate
glands - High [hormones] = inhibit
glands
Hypothalamus & Pituitary
Location: Hypothalamus is part of the diencephalon
Structure: Connects to the pituitary gland via the
infundibulum (stalk)
Hypothalamus
Anti-Diuretic Hormone (ADH):
o Causes the kidneys to conserve fluids to raise blood volume and BP
Oxytocin (OT): During labor and delivery, causes uterine contractions
During postpartum, causes mammary glands to contract to secrete milk
In all humans (regardless of sex), OT is the “love” hormone, for positive reinforcement of socio-emotional bonds
Pituitary: Anterior & Posterior Lobes
Location: Secured within the sella turcica of the cranium
Structure: Connects to the hypothalamus via the
infundibulum
Posterior Pituitary
Secretes the ADH & OT synthesized by the
hypothalamus
Growth Hormone (GH):
Stimulates growth and development (growth spurts in
infants & children)
Thyroid-Stimulating Hormone (TSH):
Stimulates the secretion of thyroid hormones
Adrenocorticotropic Hormone (ACTH):
Stimulates the secretion of adrenal cortex hormones
Prolactin (PRL):
Stimulates milk production in post-partum mothers
Follicle Stimulating Hormone (FSH) Luteinizing Hormone (LH):
Gonadotropins. In both sexes, FSH & LH stimulate sexual maturation and
Thyroid
Location: In the neck, inferior to the larynx and anterior to the trachea
Structure:
*Butterfly-shaped gland, has two lobes.
* Contains colloid-filled follicles.
* Follicular cells produce T3 and T4.
* Colloid stores T3 and T4.
Thyroid Hormones
Triiodothyronine (T3 ) and Thyroxine (T4)
*Major metabolic hormones
*Stimulate nervous system activity
Parathyroid
Location: Posteriorly embedded within the lobes of
the thyroid gland
Structure: Contains chief or principal cells that secrete
PTH
Parathyroid Hormone
- During hypocalcemia, stimulates
osteoclasts to degrade bone - Causes kidneys to conserve calcium
- Stimulates vitamin D activation within
kidneys - Indirectly causes intestines to absorb
calcium
Adrenal Gland
Location: Adrenal glands are located on top of each kidney (suprarenal glands)
Structure:
* Cortex = Bark
Composed of zona (layers) that
secrete mineralocorticoids,
glucocorticoids, and androgens
* Medulla = Middle
At the core of the adrenal
gland, secretes catecholamines
Adrenal Medulla Hormones
- Secretes catecholamines
- Same EPI and NE covered in A&P 1 for the fight-or-flight response (sympathetic drive)
Adrenal Cortex Hormones
- Zona glomerulosa: Secrete mineralocorticoids
Mainly aldosterone for salt retention - Zona fasciculata: Secrete glucocorticoids
Mainly cortisol, a major stress hormone - Zona reticularis: Secrete androgens
Supplemental sex hormones (Not responsible
for fertility. Just secondary sex
characteristics)
Pancreas
Location: Within the curve of the duodenum, connected to the small intestine
Structure: Contains alpha and beta cells within pancreatic islets or islets of Langerhans
Pancreatic Islets: Alpha Cells
- Secrete glucagon (“glucαgon”) = raises blood sugar levels
- Release glucagon when blood sugar levels are low
(hypoglycemia) - Triggers the liver to break stored glycogen down and release glucose into the bloodstream
Pancreatic Islets: Beta Cells
Secrete insulin (“βinsulin”)= lowers blood sugar levels
* Release insulin when blood sugar levels are high
(hyperglycemia)
* Triggers cells to uptake glucose
* Stimulates liver to store glucose in the form of glycogen
* Stimulates storage into adipocytes
Hypoglycemia
α cells will secrete glucagon. Liver breaks
stored glycogen down to release glucose.
Hyperglycemia:
β cells will secrete insulin to:
1. Signal glucose uptake by cells
2. Signal glucose storage into liver as glycogen
3. Signal lipogenesis
The HPT Axis and TSH
- Hypothalamic-Pituitary-Thyroid Axis
- Stimulating the HPT axis: Low blood [T3/T4], Hypoglycemia, Cold weather, High altitude, or Pregnancy
- Response: Hypothalamus releases Thyrotropin Releasing Hormone (TRH)
TRH causes anterior pituitary to release TSH
TSH causes thyroid gland to release T3/T4 - Inhibiting the HPT axis: When T3/T4 levels normalize, there is no need for more TRH or TSH
The HPA Axis and Stress
- Hypothalamic-Pituitary-Adrenal Axis
- What is Short-Term Stress?
oFirst stage of the stress response.
oStimulates the body’s resources to prepare for immediate activity. - What is Long-Term-Stress?
oSecond stage in the stress response (how we cope with prolonged stress)
oInvolves ACTH triggering the adrenal cortex
Short-Term Stress Response
Who responds: Adrenal medulla
is triggered by the sympathetic nervous system
* Hormones secreted: Catecholamines (EPI & NE)
* Effects: Fight-or-Flight
o raises HR, BP, breathing rate,
bronchodilation, raises [blood
glucose] and metabolic rate
Long-Term Stress Response
- Who responds: Adrenal cortex is triggered by ACTH
- Hormones secreted: Mineralocorticoids (aldosterone)
and glucocorticoids (cortisol) - Effects:
o raises BP (salt and water retention)
o raises [blood glucose], protein and fat breakdown
o Immunosuppression(!)
Hormones and Aging
- Lowered GH levels: Leads to loss of body weight and
muscle mass. In women, Low GH + loss of
estrogen leads to osteoporosis - Lowered estrogen and
testosterone levels: Also affects body weight and muscle mass. In women, loss of estrogen = loss of
fertility
Pituitary Disorders
- Pituitary gigantism = hyperpituitarism (elevated GH)
- Pituitary dwarfism = hypopituitarism (low GH)
- Inappropriate lactation = hyperpituitarism (elevated PRL and/or OT)
Thyroid Disorders
- Cretinism = congenital hypothyroidism, impaired mental development
- Goiter = thyroid swelling
- Grave’s Disease = autoimmune hyperthyroidism
- Hashimoto’s Disease = autoimmune hypothyroidism
Parathyroid Disorder
- Hyperparathyroidism = causes hypercalcemia and osteoporotic symptoms
Adrenal Disorders
Cushing’s Disease = Hypercortisolism, a pituitary tumor causes elevated ACTH secretion
* Addison’s Disease = Adrenal insufficiency
