The Endocrine System Flashcards
What are hormones, and what secretes them?
Hormones are signaling molecules secreted directly into the bloodstream by glands.
What are the three types of hormones?
Peptides, steroids, amino acid derivatives
How are peptide hormones made?
- cleaved from larger post-translational proteins
- Golgi modifies, activates, and directs them
How do peptide hormones work? Does the receptor type matter? What is this process called?
- A signaling cascade
- They are charged, so must bind to extracellular receptor
- Acts as a first messenger, binds to a receptor and triggers a second signal, the second messenger
- Receptor type determines what happens in the cell
What is amplification?
- One hormone molecule binding to multiple receptors before being degraded
- Or each receptor activates multiple enzymes, each creating lots of second messengers
- Results in increased signal intensity
What are 3 common second messengers?
cAMP, IP3, calcium
Describe the activation of a G protein by a peptide hormone.
- Peptide hormone binds to G protein-coupled receptor
- Receptor is triggered to either activate or inhibit an adenylate cyclase
- This enzyme will either raise or lower levels of cAMP
- cAMP can then bind to intracellular targets (for example, protein kinase A, which phosphorylates transcription factors)
What are 2 differences between peptide and steroid hormones?
- Peptide effects are rapid but short-lived, while steroids are slower but longer-lived
- Peptides are water-soluble so can travel freely in bloodstream, steroids are lipid-soluble and must be carried by proteins in the blood
How are steroid hormones made? Which organs produce them?
- Derived from cholesterol
- Produced by gonads and adrenal cortex
How do steroid hormones work?
- Pass through the membrane, so receptors are intracellular or intranuclear
- Bind to receptor and the whole complex undergoes conformational change
- Receptor binds directly to DNA, either increasing or decreasing transcription
What is dimerization?
-A form of conformational change for steroid hormones, where two receptor-hormone complexes are paired
Are the proteins that carry steroid hormones through the bloodstream specific? Why do their concentrations matter?
- Some are and some aren’t
- Hormones aren’t active while attached to them, so levels of carrier proteins can change the levels of active hormones (like more carrier protein released, less hormone perceived by the body - a lot of it is bound to the proteins)
What are amino acid-derivative hormones made of?
1 or 2 AAs with additional modifications
Examples of amino acid-derivative hormones and how fast they act?
- Epinephrine, norepinephrine - fast onset but short-lived
- Triiodothyronine, thyroxine - slower but longer duration on metabolic rate
- end in “in” or “ine” a lot
Examples of peptide hormones?
ADH, insulin
-end in “in” or “ine” a lot
Examples of steroid hormones?
Sex hormones
-end in “one” or “ol” or “oid” a lot
What are direct hormones?
Act directly on a target tissue
What are tropic hormones? Where are they usually secreted from?
- Require an intermediary to act
- Brain and anterior pituitary gland
What does the hypothalamus do?
- Regulates pituitary through tropic hormones
- Portal system connects the organs
- Receives input from lots of places
- Regulates satiety, sleep-wake cycles, blood osmolarity
How is hypothalamus activity controlled?
Negative feedback
What is the system that connects the hypothalamus and the pituitary?
The hypophyseal portal system: blood vessels that connect the hypothalamus with the anterior pituitary gland
(hypophysis is an alternative name for pituitary)
What hormone does the anterior pituitary release in response to each of the following tropic hormones from the hypothalamus?
- GnRH
- GHRH
- TRH
- CRH
- PIF (dopamine)
- FSH and LH
- GH (growth)
- TSH (thyroid-stimulating)
- ACTH (adrenocorticotropic)
- Causes a decrease in prolactin
What are the axes? What is their function:?
- HPX, hypothalamus-pituitary-target organ level
- Negative feedback system, where final secretion binds to receptors for it in hypo/pituitary to inhibit more secretion
What is the relationship between the hypothalamus and posterior pituitary? What does the posterior pituitary do?
- Hypothalamus neurons send their axons into posterior pit
- Post pit can then release oxytocin and ADH
Which 4 tropic hormones does the ant pit make?
- FSH
- LH
- ACTH
- TSH
FLAT
Which 3 direct hormones does the ant pit make?
- Prolactin
- Endorphins
- GH (growth hormone)
PEG
When does lactation begin? What is the process of lactation hormonally?
- After expulsion of the placenta, when estrogen, progesterone, and dopamine levels drop, allowing for prolactin secretion
- Newborn latches, causing activation of hypothalamus
- Oxytocin released from post pit, causing contraction of smooth muscle in breast
- Hypothalamus stops releasing dopamine into ant pit, allowing prolactin release, causing milk production
How does GH work?
- Prevents glucose uptake in tissues that aren’t growing
- Stimulates breakdown of fatty acids
- Increases availability of glucose overall for growth
What problems can result from abnormal GH amounts?
- Gigantism: too much GH before epiphyseal plates seal
- Dwarfism: too little GH
- Acromegaly: too much GH in adulthood, leading to only smaller bones growing too much (like hands, feet)
When is ADH secreted?
- in response to low blood volume or increased blood osmolarity
- acts in kidney, where it increases the permeability of its collecting duct to water, so more water retention
What causes oxytocin secretion? What type of feedback loop does it have?
- Childbirth, suckling, bonding behavior
- Positive feedback loop that ends with birth
What are T3 and T4 made of, what do they do, and where are they secreted from?
- Produced by the iodination of tyrosine
- Secreted from follicular cells in thyroid gland
- Reset basal metabolic rate by controlling energy production efficiency and altering glucose/fatty acids
- More T3/4 = more cellular respiration
What problems can result from an abnormal thyroid?
- Hypothyroidism: too little/none of thyroid hormone secreted; causes lethargy, slowed heart rate, weight gain, decreased body temp
- Cretinism: deficiency in hormones can cause intellectual/development problems in kids
- Hyperthyroidism: excess of thyroid hormone can cause tumor; weight loss, heat intolerance, fast breath and heart rate
Where is calcitonin secreted from? What does it do?
- C-cells (parafollicular cells) of thyroid produce calcitonin
- Decreases plasma calcium by
1. increasing Ca excretion from kidneys
2. decreasing Ca absorption from gut
3. Increasing storage of Ca in bone - Stimulated by lots of Ca in blood
What are the parathyroid glands? What do they do?
- 4 structures that sit on posterior surface of thyroid
- Produce PTH
What does PTH do?
- Antagonist to calcitonin, raising blood Ca levels (decreases Ca excretion by kidneys, increasing Ca absorption in gut, increases bone resorption)
- Promotes phosphorus homeostasis (increases resorption of phosphate from bone, reduces reabsorption of phosphate in kidney - these cancel each other)
- Activates Vitamin D for absorption
- So overall effect is increase in blood Ca levels and little effect on phosphate
Where are the adrenal glands located? What do they consist of?
- On top of the kidneys
- Each gland has a cortex and a medulla with different functions
What does the adrenal cortex secrete? What are the three classes these hormones fall into?
Secretes corticosteroids, which are steroid hormones that can be divided into three classes:
- Glucocorticoids
- Mineralocorticoids
- Cortical sex hormones
What are glucocorticoids? What do they do? What are 2 examples? What hormone regulates them?
- Steroid hormones (corticosteroids) from adrenal cortex
- Regulate glucose levels
- Ex: cortisol and cortisone
- Raise blood glucose by increasing gluconeogenesis and decreasing protein synthesis
- Can also decrease inflammation response
- Cortisol is a stress hormone, released during times of stress
- CRF from hypothalamus –> ACTH from pituitary –> glucorticoids
What are mineralocorticoids? What do they do? What are examples?
- Used in salt-water homeostasis in kidneys
- Ex: aldosterone, which increases sodium reabsorption in kidney to increase water/blood volume and pressure (water follows salt, so plasma osmolarity stays constant)
- Also decreases K and H ion reabsorption in kidneys so they are excreted in urine
What system regulates aldosterone concentration?
Renin-angiotensin-aldosterone system:
- Decreased BP causes juxtaglomerular cells of kidney to secrete renin
- Renin cleaves an inactive angiotensinogen (plasma protein) to its active form, angiotensin I
- Angiotensin I is converted to angiotensin II by angiotensin-converting enzyme (ACE)
- Angiotensin II stimulates adrenal cortex to secrete aldosterone
- When BP is restored, there is a decreased drive to stimulate renin release.
What are cortical sex hormones? What happens if there are disorders related to cortical sex hormones production?
- Secrete androgens and estrogens
- Adrenal testosterone has a small role in men because testes already secrete a lot of androgens
- But because the ovaries don’t secrete many androgens, females are very sensitive to disorders of cortical sex hormone production
- Like an excess of androgen production in adrenal cortex would result in ambiguous/male genitalia in females
- Same thing in men with excessive estrogen
In summary, what are the 3 functions of the corticosteroids? (Hint: 3 S’s)
- Salt (mineralocorticoids)
- Sugar (glucocorticoids)
- Sex (cortical sex hormones)
What does the adrenal medulla do? How does it secrete hormones?
- Produces epinephrine and norepinephrine
- Specialized nerve cells secrete them directly into bloodstream
What type of hormone is epinephrine/norepinephrine? What do they do to the body? What is their relationship to cortisol?
- Amino acid derivative called catecholamines
- Fight or flight response: increase basal metabolic rate, increase glucose breakdown, dilate bronchi, increase heart rate
- Cortisol mediates long-term (slow) stress responses, while catecholamines control short-term (fast) stress responses
- Cortisol also increases catecholamine synthesis
Do the pancreas have exocrine or endocrine functions?
Both - exocrine means it secretes substances into ducts; endocrine means it secretes substances directly into bloodstream
How is the endocrine component of the pancreas organized?
- Hormone-producing cells grouped into clusters called islets of Langerhans throughout pancreas
- Islets have three types of cells: alpha, beta, delta cells
- Each cell secretes a different hormone: alpha-glucagon, beta-insulin, delta-somatostatin
What is glucagon and what does it do?
- Secreted by alpha cells in islets of Langerhans
- Increases glucose production by triggering gluconeogenesis, glycogenolysis, degradation of protein and fat
- Secreted because of low glucose levels but also certain GI hormones
What is insulin and what does it do?
- Secreted by beta cells in islets of Langerhans
- Antagonistic to glucagon so secreted when blood glucose levels are high
- Induces muscle and liver cells to take up glucose and store it as glycogen
- Stimulates fat and protein synthesis
What does an excess of insulin cause?
-Hypoglycemia: low blood glucose concentration
What does an underproduction of insulin cause?
-Diabetes mellitus: hyperglycemia (too much blood glucose)
Why do diabetics often report polyuria (increased urination) and polydipsia (increased thirst)?
- Excessive glucose in kidneys will overwhelm their ability to reabsorb glucose, resulting in its presence in urine
- As glucose can’t readily cross the cell membrane, its presence in the filtrate leads to excess of water and increase in urination/thirst
What are the two types of diabetes?
- Type I (insulin-dependent): autoimmune destruction of beta-cells of pancreas, resulting in low/absent insulin production; needs insulin injections for glucose uptake to avoid hyperglycemia
- Type II (non-insulin-dependent): receptor-level resistance to the effects of insulin; partially inherited/partially environmental (high carb diets); take certain drugs
What is somatostatin and what does it do?
- Inhibits insulin and glucagon secretion
- stimulated by high blood glucose and amino acid concentrations
- Produced by pancreas
- Also decreases growth hormone secretion
What do gonadotropins cause their target organs to do?
- Gonadotropins (LH and FSH) cause testes to secrete testosterone - sexual differentiation, secondary sex traits
- Cause ovaries to secrete estrogen and progesterone
What does the pineal gland do?
- Secretes melatonin
- Involved in circadian rhythms, sleepiness
Are there endocrine regions in the GI tract? If so, where?
Stomach and intestine; release hormones because of certain nutrients
Summarize the 3 endocrine functions of the kidneys.
- ADH increases water permeability in collecting duct
- R-A-Aldo system increases Na/water reabsorption
- Also produce erthyropoietin, which stimulates bone marrow to increase RBC production in response to low blood O2 levels
What endocrine function does the heart have?
- Releases ANP peptide to help salt and water balance
- When cells in atria are stretched from excess blood volume, they release ANP
- This promotes Na excretion and therefore increases urine volume
- Antagonistic to aldosterone
What endocrine function does the thymus have?
- Behind sternum
- Releases thymosin for proper T-cell development and differentiation
- Thymus atrophies by adulthood
Which 3 hormones are involved in water homeostasis? Where does each come from, and what effect does each have on blood volume and osmolarity?
- ADH: (posterior pituitary) increases BV and decreases BO
- Aldosterone (adrenal cortex): increases BV and has no effect on BO
- ANP (heart): decreases BV and has no effect on BO
Which two hormones are involved in calcium synthesis? Where does each come from, and what effect do they have on blood Ca concentrations?
- Calcitonin: (C-cells of thyroid) decrease Ca levels
2. PTH: (parathyroid glands) increase Ca levels
