Chapter 16: The Endocrine System Flashcards
Sending a message: Nervous System
-via neurons- fast and precise. “crisis management”
Sending a message” Endocrine system
- via hormones- slower, last longer, target most cells of body.
- > “controls ongoing metabolic processes”
Endocrine system: overview
- > acts with the nervous system to coordinate and integrate the activity of body cells
- > influences metabolic activities via hormones through blood
- > system is slower but lasts longer than NS
- endocrine glands: pituitary, thyroid, parathyroid, adrenal, and pineal
slide 4
picture of all glands and functions
chemistry of hormones
2 main classes:
-> Amino acid-based hormones (water based)
-> Steroids (lipid based)
- Amino acid-based hormones (water based)
- Amines, thyroxine, peptides, and proteins
- cannot cross cell membrane, binds to receptors on membrane
- Steroids (lipid based)
- synthesized from cholesterol
- gonadal and adrenocortical hormones
- since they are lipids can cross the cell membrane
Mechanisms of hormone action
- > Hormone action on target cells has receptor for that hormone
1. alter plasma membrane permeability of membrane potential by opening or closing ion channels
2. stimulate synthesis of proteins or regulatory molecules
3. activate or deactivate enzyme systems
4. induce secretory activity
5. stimulate mitosis
Amino-acids hormones (except thyroid hormones)
- > usually water soluble
- > binds to receptors on cell membrane- extracellular receptors
- > activates an enzyme inside cell
- > activates secondary messengers (ex. cyclic AMP)
Steroid hormones
- > Enters the cell by passing directly across membrane
- > binds to receptor to form hormone-receptor complex- intracellular receptors
- > complex enters nucleus, binds to DNA region
- > send a message via mRNA directing protein synthesis
Target cell specificity
- > target cells must have specific receptors to which the hormone binds
- ACTH (adrenocorticotropic hormone) receptors are only found on certain cells of the adrenal cortex
- thyroxin receptors are found on nearly all cells of the body
target cell activation
- > target cell activation depends on 3 factors:
1. blood levels of the hormone
2. relative number of receptors on or in the target cell
3. affinity of binding between receptor and hormone
target cell activation
- > hormones influence the number of their receptors.
- > receptors are dynamic
- > Up-regulation: target cells form more receptors in response to low levels of the hormone
- > Down-regulation: target cells lose receptors in response to high levels of the hormone
Hormones in the blood
- > Hormones are removed from the blood by:
- degrading enzymes
- kidneys
- liver
- half-life- the time required for a hormones blood level to decrease by half
*insulin vs. cortisol
Interaction of hormones at target cells
Multiple hormones may interact in several ways
- permissiveness
- synergism
- antagonism
permissiveness
one hormone cannot exert its effects without another hormone being present
ex: reproductive hormones and thyroid hormone)
synergism
more than one hormone produces the same effects on a target cell (glucagon & epinephrine cause liver to release glucose to blood)
anatgonism
one or more hormones opposes the action of another hormone (insulin and glucagon)
control of hormone release
Blood levels of hormones:
- are controlled by negative feedback systems
- vary only within a narrow desirable range
Hormones are synthesized and released in response to:
- humoral stimuli (fluid)
- neural stimuli
- hormonal stimuli (cascade effect)
control of hormone release
Blood levels of hormones:
- are controlled by negative feedback systems
- vary only within a narrow desirable range
Hormones are synthesized and released in response to:
- humoral stimuli (fluid)
- neural stimuli
- hormonal stimuli (cascade effect)
humoral stimuli
- changing blood levels of ions and nutrients directly stimulates secretion of hormones
- example: calcium (Ca 2+) in the blood
- declining blood calcium concentration stimulates the parathyroid glands to secrete PTH (parathyroid hormone)
*PTH causes calcium concentrations to rise and the stimulus is removed
neural stimuli
Nerve fibers stimulate hormone release
-> in response to stress sympathetic nervous system fibers stimulate the adrenal medulla to secrete catecholamines (NE& E)
hormonal stimuli
Hormones stimulate other endocrine organs to release their hormones
- hypothalamic hormones stimulate the release of most anterior pituitary hormones
- anterior pituitary hormones stimulate targets to secrete still more hormones
- **hypothalamic-pituitary-target endocrine organ feedback loop: hormones from the final target organs inhibit the release of the anterior pituitary hormones
- tropic hormones: hormones that stimulate other hormones
nervous system modulation
- The nervous system modifies the stimulation of endocrine glands and their negative feedback mechanisms
ex: under severe stress, the hypothalamus and the sympathetic nervous system are activated…. as a result, blood glucose levels will rise - without the NS the endocrine system is strictly mechanical (i.e home thermostat)
The pituitary gland and hypothalamus
-> the pituitary gland (hypohysis) has 2 major lobes:
- Posterior pituitary (lobe) (neurohypophysis):
* neural tissue, hormone storage, does not manufacture - Anterior pituitary (lobe) (adenohypophysis):
* glandular tissue
*Hypothalamus has direct control over posterior lobe and indirect control over anterior lobe
where is the hormone calcitonin produced
thyroid gland
pituitary-hypothalamic relationships
Posterior lobe:
- neural connection to the hypothalamus
- nuclei of the hypothalamus (cell bodies) synthesize the neurohormones oxytocin and antidiuretic hormone (ADH)
- when cell bodies in hypothalamus are stimulated, axons in posterior pituitary release hormones into bloodstream
- posterior pituitary is an extension of hypothalamus
pituitary hypothalamic relationships
Anterior lobe
- NO direct neural connection but a vascular connection
- via the hypophyseal portal system (hormones travel via capillaries and veins)
- hormones secreted by neurons in hypothalamus circulate to anterior pituitary
-ant pituitary- “master endocrine gland”- recently dethroned by hypothalamus
anterior pituitary hormones
a .Growth hormone (GH)
b. Thyroid-stimulating hormone (TSH) or thyrotropin*
c. Adrenocorticotropic hormone (ACTH)*
d. Follicle-stimulating hormone (FSH)*
e. Luteinizing hormone (LH)*
f. Prolactin (PRL)
*tropic hormones
growth hormone (GH) *anterior pituitary hormone
- stimulates most cells, but targets bone and skeletal muscle, anabolic hormone
- promotes protein synthesis and encourages use of fats for fuel
- GH release is regulated by hypothalamic hormones:
- growth hormone-releasing hormone (GHRH)
- growth hormone-inhibiting hormone (GHIH) (somatostatin)
homeostatic imbalances of growth hormone
- Hypersecretion:
- in children results in gigantism
- in adults results in acromegaly (after epiphyseal plates have closed)
Hyposecretion:
*in children results in pituitary dwarfism
thyroid-stimulating hormone (thyrotropin)
*anterior pituitary hormone
- stimulates the normal development and secretory activity of the thyroid
- regulation of TSH release
- inhibited by rising blood levels of thyroid hormones that act on the pituitary and hypothalamus
*negative feedback system
Adrenocorticotropic Hormone (Corticotropin) *anterior pituitary hormone
- stimulates the adrenal cortex to release corticosteroids (glucosteroids)
- regulation of ACTH release:
- triggered by hypothalamic corticotropin-releasing hormone (CRH) in a daily rhythm
- internal and external factors such as fever, hypoglycemia, and stressors can alter the release of CRH
gonadotropins
*anterior pituitary hormone
- Follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
- Secreted by gonadotrophs of the anterior pituitary
- FSH stimulates gamete (egg or sperm) production
- LH promotes production of gonadal hormones (testosterone and progesterone)
- Absent from the blood in prepubertal boys and girls
prolactin (PRL)
*anterior pituitary hormone
- secreted by lactotrophs of the anterior pituitary
- stimulates milk production in females
- blood levels rise toward the end of pregnancy
- suckling stimulates PRL release and promotes continued milk production
posterior pituitary
- contains axons of hypothalamic neurons
- stores antidiuretic hormone (ADH) and oxytocin
- ADH and oxytocin are released in response to nerve impulses
antidiuretic hormone (ADH)
- Hypothalamic osmoreceptors respond to changes in the solute concentration of the blood
- Produced in hypothalamus, stored in posterior pituitary
- If solute concentration is high
- ADH is synthesized and released, ADH targets collecting ducts & inhibits urine formation
oxytocin
- Released in significantly higher amounts during childbirth
- Stimulates uterine contractions (synthetic oxytocic drugs used to induce labor)
- Hormonal trigger for milk ejection
- Also acts as a neurotransmitter in brain. Considered the “cuddling hormone”, promotes bonding and trust
thyroid gland
- produces thyroid hormone (T3/T4) and calcitonin
- Colloid (thyroglobulin + iodine) stored in the lumen of the follicles and is the precursor of T3/T4
- Thyroid hormone:
- Effects all cells of the body
- Increases metabolic rate & heat production
- Maintenance of blood pressure
- Regulation of tissue growth
- Development of skeletal and nervous systems
- Reproductive capabilities
homeostatic imbalance of thyroid hormone
- hyposecretion: lethargy, feeling chilled, dry skin, sluggish (hoshimoto’s disease)
- goiter-follicles produce colloid but no iodine, so colloid accumulates
-hypersecretion: nervousness, rapid HR, sweating, weight loss, bulging eyeballs (graves disease)
calcitonin (thyroid hormone)
- produced by parafollicular cells
- antagonist to parathyroid hormone (PTH)
- inhibits osteoclast activity and release of Ca2+ from bone matrix
- bone sparing effect: given to patients with paget’s disease and osteoporosis
parathyroid glands
- 4 to 8 tiny glands located behind thyroid (not related)
- contain chief cells that secrete parathyroid hormone (PTH)
- PTH- most important hormone in Ca2+ homeostasis
- Ca homeostasis critical for NN transmission, MM contraction and blood clotting
parathyroid hormone
-if low blood calcium:
gets Ca+ from:
*bone (stimulates osteoclasts)
- kidney (reabsorbs calcium)
- intestine (increases absorption of calcium)
adrenal glands
-Paired, pyramid-shaped organs atop the kidneys
-Structurally and functionally, they are two glands in one
*Adrenal cortex—
three layers of glandular tissue that synthesize and secrete corticosteroids
*Adrenal medulla—
nervous tissue; part of the sympathetic nervous system
adrenal cortex
3 layers and the corticosteroids produced:
*zona glomerulosa: mineralocorticoids (aldosterone) superficial
- zona fasciculata: glucocorticoids (cortisol)- middle layer
- zona reticularis: sex hormones, or gonad corticoids- innermost layer
mineralocorticoids (adrenal glands)
- regulate electrolytes (primarily Na+ and K+) in ECF
- importance of Na+: affects ECF volume, blood volume, blood pressure, levels of other ions
- aldosterone: is the most potent mineralocorticoid
- stimulates Na+ reabsorption and water retention by the kidneys
glucocorticoids (cortisol)
adrenal glands
- Cortisol is the most significant glucocorticoid
- Released in response to ACTH, patterns of eating and activity, and stress “fight/flight”
- Prime metabolic effect is gluconeogenesis—formation of glucose from fats and proteins
- Promotes rises in blood glucose, fatty acids, and amino acids
glucocorticoids (cortisol)
adrenal glands
- Keep blood sugar levels relatively constant
- Maintain blood pressure by increasing the action of vasoconstrictors
- Inflammatory response
- Immune system
*ideal amounts of glucocorticoids promote normal function, but too much cortisol exert anti-immune effects
homeostatic imbalance (adrenal glands)
Cushing’s syndrome – increase in glucocorticoid from ACTH-releasing pituitary tumor or from clinical administration of glucocorticoid drugs
Addison’s disease – deficits in glucocorticoids and mineralocorticoids (lose weight, hypotension, dehydration)
synthetic corticosteroids (prednisone)
used in treatment of many diseases with excessive inflammation or overactive immune system
- RA
- MS
- asthma
- lupus
- joint inflammation
gonadocorticoids (sex hormones)
adrenal gland
-Most are androgens (male sex hormones) that are converted to testosterone in tissue cells or estrogens in females
- May contribute to:
- The onset of puberty
- The appearance of secondary sex characteristics
- Sex drive
adrenal medulla (part of ANS)
-Chromaffin cells secrete epinephrine (80%) and norepinephrine (20%)
- These hormones cause
- Blood glucose levels to rise
- Blood vessels to constrict
- The heart to beat faster
- Blood to be diverted to the brain, heart, and skeletal muscle
adrenal medulla
-epinephrine:
stimulates metabolic activities, bronchial dilation, and blood flow to skeletal muscles and the heart
-Norepinephrine:
influences peripheral vasoconstriction and blood pressure
pineal gland
- Small gland hanging from the roof of the third ventricle
- Pinealocytes secrete melatonin, derived from serotonin
- Melatonin may affect:
- Timing of sexual maturation and puberty
- Day/night cycles
- Physiological processes that show rhythmic variations (body temperature, sleep, appetite)
- Hypothalamus (“biological clock”) has many melatonin receptors
- Exposure to bright lights resets clock
pancreas
-Triangular gland behind the stomach
-Has both exocrine and endocrine cells:
*Acinar cells (exocrine)
produce an enzyme-rich juice for digestion
- Pancreatic islets (endocrine) (islets of Langerhans)
- Alpha cells produce glucagon (a hyperglycemic hormone)
- Beta cells produce insulin (a hypoglycemic hormone)
glucagon (pancreas)
- Major target is the liver, where it promotes:
- Glycogenolysis—breakdown of glycogen to glucose
Gluconeogenesis—synthesis of glucose from lactic acid and noncarbohydrates
-Release of glucose to the blood
glycogenolysis
breakdown of glycogen to glucose
gluconeogenesis
synthesis of glucose from lactic acid and noncarbohydrates
insulin (pancreas)
Effects of insulin:
*Lowers blood glucose levels
- Enhances membrane transport of glucose into fat and muscle cells
- Inhibits glycogenolysis and gluconeogenesis
homeostatic imbalances of insulin
Diabetes mellitus (DM) – type 1 or type 2
-Due to hyposecretion or hypoactivity of insulin
- Three cardinal signs of DM
- Polyuria—huge urine output
- Polydipsia—excessive thirst
- Polyphagia—excessive hunger and food consumption – “starving in the land of plenty”
ovaries and placenta
-Gonads produce steroid sex hormones
- Ovaries produce estrogens and progesterone responsible for:
- Maturation of female reproductive organs
- Appearance of female secondary sexual characteristics
- Breast development and cyclic changes in the uterine mucosa
-The placenta secretes estrogens, progesterone, and human chorionic gonadotropin (hCG)
testes
- Testes produce testosterone that:
- Initiates maturation of male reproductive organs
- Causes appearance of male secondary sexual characteristics and sex drive
- Is necessary for normal sperm production
- Maintains reproductive organs in their functional state
