Ch. 17 - Endocrine System Flashcards
Secretion
• controlled release of chemicals from a cell
4 classes of chemical messengers
1) Autocrine
2) Paracrine
3) Neurotransmitter
4) Endocrine
Paracrine
- produced by a wide variety of tissues and secreted into extracellular fluid; has a localized effect on other tissues
- secreted by one cell type into extracellular fluid and effect surrounding cells
Examples of Paracrine
- somatostatin
- histamine
- eicosanoids
Autocrine
• secreted by cells in a local area; influences the activity of the same cell from which it was secreted
Examples of Autocrine
- eicosanoids (prostaglandins, thromboxanes, prostacyclins, leukotrienes)
- good examples are those secreted by white blood cells during an infection
Neurotransmitter
- produced by neurons
- secreted into a synaptic cleft by presynaptic nerve terminals;
- travels short distances;
- influences postsynaptic cells
Examples of neurotransmitters
- acetylcholine
* epinephrine
Endocrine
• secreted into the blood by specialized cells; travels some distance to target tissues; results in coordinated regulation of cell function
Examples of endocrine
- thyroid hormones
- growth hormone
- insulin
- epinephrine
- estrogen
- progesterone
- testosterone
- prostaglandins
4 principle mechanisms of communication
1) gap junctions
2) neurotransmitter
3) Paracrine (local) hormone
4) hormones
Endocrine system
• glands, tissues, and cells that secrete hormones
Endocrinology
• The study of this system and the diagnosis and treatment of its disorders
Endocrine glands
• organs that are traditional sources of hormones
Hormones
• Chemical messengers that are transported by the bloodstream and stimulate physiological responses in cells or another tissue or organ, often a considerable distance away
_______ hormones bind to nuclear receptors, usually found in nucleus; _______ hormones bind to membrane-bound receptors
lipid-soluble; water-soluble
Chemical messengers
• allows cells to communicate with each other to regulate body activities
Secretions travel through ducts
• exocrine system
Secretions travel in bloodstream
• endocrine system
The tendency for one hormone to bind to only one type of receptor is called
•specificity
An increase in follicle-stimulating hormone causing an increase in luteinizing hormone receptors in ovary cells is an example of
• up-regulation
The process of one hormone activating multiple proteins, each which activates many enzymes, which produce an enormous amount of the final product
Amplification
Does the endocrine or nervous system have longer lasting effects?
• endocrine
Water-soluble hormones
- polar molecules
* include: protein hormones, peptide hormones, and most amino acid derivative hormones
Lipid-soluble hormones
- non polar
* include: steroid hormones, thyroid hormones, and fatty acid derivative hormones, such as certain eicosanoids
Transport of lipid-soluble hormones
• because of their small size and low solubility in aqueous fluids, lipid soluble hormones travel in the bloodstream bound to binding proteins
Transport of water-soluble hormones
• because water soluble hormones can dissolve in blood, many circulate as free hormones, meaning that most of them dissolve directly into the blood and are delivered to their target tissue without binding to a binding protein
Acute hormone secretion
- occurs when the hormones concentration changes dramatically and irregularly and it’s circulating levels differ with each stimulus
- levels can rapidly fluctuate in the blood
- example ➡️ epinephrine
Chronic hormone secretion
- relatively stable levels are maintained over a long period of time
- example ➡️ thyroid hormone
Episodic hormone secretion
- fluctuates on a regular cycle
* example ➡️ reproductive hormones regulating menstruation
Blood-borne molecules directly stimulate the release of hormones
Humoral stimuli
Neurons release a neurotransmitter into a synapse that influences the hormone producing cells
Neural stimuli
A hormone stimulates the secretion of another hormone
Hormonal stimuli
ANP is released by the atria to lower blood pressure
humoral stimuli
Hormones from the hypothalamus can prevent the release of hormones from the pituitary gland
neural stimuli
thyroid hormones control their own blood levels by inhibiting their pituitary tropic hormone
hormonal stimuli
Negative feedback
- most hormones secretions are regulated by this
- whereby a hormones secretions are regulated by the hormone itself
- example ➡️ thyroid hormones inhibit the secretion of TRH from the hypothalamus and TSH from the anterior pituitary
- self limiting system
Positive feedback
- occurs when a hormone is stimulated by a tropic hormone to secrete more of their own hormone as well as the tropic hormone
- example ➡️ prolonged estrogen stimulation promotes a release of luteinizing hormone
- self propagating system
Which ovarian hormone is involved in a positive feedback loop with the hypothalamus and the anterior pituitary?
• estrogen
Which hormone is released by the anterior pituitary as a part of that positive feedback loop between it and the ovary?
• Luteinizing hormone
Which hormone is released by the corpus luteum after ovulation and causes a negative feedback loop with the hypothalamus in the anterior pituitary?
• progesterone
Which hormone is released by the hypothalamus as a part of that positive feedback loop between it and the ovary?
• gonadotropin-releasing hormone (GnRH)
A process in which the body senses a change, and activates mechanisms to reverse that change
Negative feedback
Causes a self amplifying cycle where is a physiological change leads to an even greater change in the same direction
Positive feedback
Steroid hormones bind to
• protein receptors in the cytoplasm or nucleus of the target cell
What is the mode of action of steroid hormones?
- stimulation of mRNA transcription at that site
* which then codes for the synthesis of specific proteins
Are steroid hormones water soluble?
- no
* they are lipid-soluble and need a carrier protein to travel in the blood
What characteristic must a signal molecule have in order to bind with the intracellular receptor?
- it must be able to pass through the cellular membrane
* They are generally Nonpolar and fat-soluble
What do lipid soluble hormones do once inside the cell?
• bind with a specific receptor molecules inside the cytoplasm
What structure is formed after a lipid soluble hormone binds to a receptor molecule in the cytoplasm?
• A hormone-receptor complex is formed
What occurs after the hormone receptor complex is formed in the cytoplasm?
- The hormone-receptor complex moves into the nucleus and binds to DNA
- this stimulates synthesis of mRNA, which codes for a specific proteins
What happens once mRNA is synthesized?
- mRNA moves from nucleus into cytoplasm and binds to ribosomes where it directs the synthesis of specific proteins
- The proteins produce response of cell to the hormone
What is the ultimate result of lipid soluble hormones on cells?
• The production of proteins
3 classes of hormones:
1) amino acid derivatives
2) peptide hormones
3) lipid derivatives or steroid hormones
Hormones that use the cAMP second messenger system (non steroid hormones):
- ACTH
- calcitonin
- epinephrine
- glucagon
- parathyroid hormone
- ADH
The _____ senses high osmolarity in the plasma.
- kidney
* 1st step
________ neurons bring the information of high osmolarity to the hypothalamus.
- sensory
* 2nd step
The supra optic nucleus of the __________ fires impulses in response to the high osmolarity.
- hypothalamus
* 3rd step
The impulses from the hypothalamus travel through the _______ in the hypothalamo-hypophyseal tract.
- infundibulum
* 4th step
Exocytosis of ADH from the synaptic endings in the ______ pituitary.
- posterior
* 5th and final step
Where is dehydration detected?
• by osmoreceptors in the hypothalamus
Antidiuretic hormone (ADH) is released by the
• posterior pituitary
Where is ADH transported to?
• from posterior pituitary through blood stream to kidneys and blood vessels
ADH functions to
- reduce urine volume output, thereby increasing water retention and countering dehydration
- increase vasoconstriction in blood vessels, leading to higher blood pressure and thus countering the blood pressure drop caused by dehydration
After eating a meal, blood sugar levels
• increase
Insulin, released after a meal is eaten by a person who does not have diabetes, will cause blood sugar levels to
• return to about normal
In type I diabetes blood sugar levels remain high after a meal because
• no insulin is released
In type II diabetes blood sugar levels remain high after a meal because
- insulin is release but cells do not receive the signal
* muscle and liver cells do not receive signal
The treatment for Type I diabetes always includes
• insulin
The treatments for Type II diabetes are
- oral thiazolidinedione - increases cell sensitivity to normal insulin
- metformin - effective treatment for obese patients, an oral medication that blocks liver synthesis of glucose
What is the function of insulin?
• allows cells to take up glucose from the blood
The ______ secretes a hormone that increases the body’s metabolic rate, promotes alertness and quickens reflexes, and stimulates the fetal nervous system
• thyroid gland
The _____ secretes ____, which promotes Na + and water retention.
• adrenal cortex; aldosterone
The zona fasciculata in the adrenal gland secretes
• cortisol
Parathyroid hormone is released when blood calcium levels decrease. This is an example of control by _____ stimuli.
• humoral
Produces an increase in the sensitivity of the target cell to the hormone
• up-regulation
Steroid hormones:
a) bind to membrane receptors
b) diffuse easily through the plasma membrane
c) act by activating cAMP
d) are inactived by phosphodiesterase
e) are water soluble
b) diffuse easily through the plasma membrane
Many hours after a meal, alpha cells in the pancreatic islets (islets of Langerhans) secrete
• glucagon, which raised blood glucose
_____ is not a steroid hormone.
a) insulin
b) cortisol
c) progesterone
d) aldosterone
e) estradiol
a) insulin
Absence of iodine in the diet leads to
• hypothyroidism
T4 and T3 are _____ hormones that are mainly transported _____ in the blood.
• monoamine; bound to thyroxine-binding globulin (TBG)
Eicosanoids are derived from
• arachidonic acid
Prostaglandins have all the following roles except:
a) to induce labor contractions
b) to stop fever and pain
c) to constrict or dilate arterioles
d) to act as vasodilators or vasoconstrictors
e) to inhibit gastric secretions
b) to stop fever and pain
Aspirin and ibuprofen block
• the action of cyclooxygenase
All these can cause Cushing syndrome except:
a) ACTH hypersecretion by the pituitary
b) ACTH-secreting tumors
c) hyperactivity of the adrenal cortex
d) hyperactive of the adrenal medulla
e) excess cortisol secretion
d) hyperactivity of the adrenal medulla
Growth hormones (GH) hypersecretion causes gigantism when it begins in childhood, but it is more likely to cause _____ when it begins in adulthood.
• acromegaly
Diabetes mellitus is characterized by:
- NOT hypoglycemia
- polyuria
- polyphagia
- polydipsia
- glycosuria
These statements about diabetes mellitus are correct except:
- the body produces autoantibodies that destroy the pancreatic beta cells in type I DM
- target cells are unresponsive to insulin in type II DM
- both type I and type II DM are characterized by lack of, or low levels of, insulin - false
- diabetic neuropathy is a common long term effect of DM
- type II DM is more common than type I DM