Endocrine System Concepts Flashcards
Contrast endocrine vs. exocrine function, considering the products released, the location of release, and the fate of released substances.
Endocrine (release into the body): release hormones at the thyroid, parathyroid, adrenal, pineal, pituitary
Exocrine (release out away from the body): release sweat on the skin
Review the difference between paracrine, autocrine, and endocrine function, focusing on the location of target cells of each, and trying to come up with at least one simple example of each. (Autocrine = Interleukin 2 of T cells?, Paracrine = nitric oxide release, interferon release…)
Autocrine
- Feeding itself
Paracrine
- Releasing hormones traveling short distances within a tissue to get to near target cell
Endocrine
-circulates within the bloodstream to get to distant target cell
Explain how and why the down-regulation and up-regulation of hormone receptors work.
If circulating hormone levels are high, the # of receptors is “down-regulated” (drop # of receptors available because you don’t need them)
If they’re low, the # of receptors is “up-regulated” (increase # of receptors available)
Link down-regulation to Type 2 diabetes
Due to too much insulin circulating in the blood caused by a sugar-high diet, insulin receptors on a target cell membrane may be down regulated, or decreased, to desensitize the effects of insulin
Contrast travel of water-soluble and lipid-soluble hormones in the blood. Focusing on how lipid-soluble hormones are carried in the blood, and which type is more prone to being filtered at the glomeruli of the kidney
- Water-soluble hormones dissolve freely in the blood plasma
- Lipid-soluble hormones need to bind to transport proteins in order to temporarily become water-soluble and not get easily filtered at the kidney
Describe the mechanism of action of a lipid-soluble hormone on a target cell, being very detailed.
- Transport protein carrying lipid-soluble hormone through the blood plasma
- Lip-soluble hormones diffuse through the target cell membrane and bind to receptors in the nucleus
Transcription and translation are stimulated to make new proteins
Which of the 4 macromolecules is usually most affected by hormones?
protein
Describe the mechanism of action of a water-soluble hormone on a target cell, being very detailed.
- Water soluble hormones cannot enter the cell directly so they bind to a receptor on the OUTSIDE of the target cell membrane and trigger a whole cascade of events INSIDE the cell
- The binding of hormone (first messenger) to its receptor activates G protein, which activates adenylyl cyclase
- Activated adenylyl cyclase converts ATP to cAMP
- cAMP serves as a second messenger to activate protein kinases
- Activated protein kinases phosphorylate cellular proteins
- Millions of phosphorylated proteins cause reactions that produce physiological responses
- Phosphodiesterase eventually inactivates cAMP to end the cascade
Connect endocrine function (negative feedback loops driven by endocrine organs and key hormones) with blood panel parameters. Consider the contrasting effects, on these blood panel parameters, of stress and the endocrine system.
- Parathyroid gland cells detect lowered Ca concentrations in the blood, so the PTH gene is “turned on” to increase the release of PTH onto the kidneys to retain Ca in the blood. Osteoclasts also increase bone reabsorption to increase blood Ca.
- After fight or flight (stress), insulin is secreted in the kidneys to lower blood sugar levels through the parasympathetic system (rest and recovery)
Give 5 effects of hormones on cellular function, concentrating on the role of proteins in each.
- Stimulate the synthesis of something new within a cell
- Change the permeability of a cell’s membrane
- Change the transport rates of certain substances across a cell’s membrane
- Change the rate of metabolic reaction
- Contract smooth or cardiac muscle
Describe the amplification of a water-soluble hormone at the cellular level
One water-soluble hormone molecule binding to a receptor on the outside of the cell can result in the production of millions of molecules inside the cell
Contrast synergistic and antagonistic effects of hormones, giving an example of each (e.g. epinephrine & norepinephrine for synergistic?)
Synergistic (epinephrine & norepinephrine)
- Sometimes two hormones work together on a cell in a kind of 1-2 punch
- The first hormone “loosens up” the cell and the second has a greater effect on the cell if the first one has already been at work amplifying
Antagonistic (insulin and glucagon)
- Insulin and glucagon have opposite effects on a cell
Name, and give a very brief description of the 3 ways that hormone release is controlled in the body.
ANS innervation,
- craniosacral output (parasympathetic)
- Secrete insulin to lower blood sugar levels after fight or flight
Blood chemistry
- Parathyroid gland cells detect lowered calcium levels in blood which kicks a negative feedback loop to correct calcium levels by bringing them back up
Other hormones ( The HP axis)
- Anterior pituitary hormones
What is the “master endocrine” organ
the hypothalamus is the “master endocrine” organ and it drives the posterior and anterior pituitary, creating the incredibly important HP axis
Specifically, describe how the hypothalamus drives secretion of neurohypophyseal hormones, focusing on hypothalamic nuclei, releasing hormones, the hypothalami-hypophyseal tract, and the specific mechanisms whereby hypothalamic hormones are sent to the neurohypophysis
- The supraoptic and paraventricular nuclei of the hypothalamus produce two neurohypophyseal hormones ADH and oxytocin
- These 2 hormones are packaged into vesicles and shipped down the axons of neurons to the axon terminals in the posterior pituitary
- The axons of those neurons are grouped together to make the “hypothalamohypophyseal tract”
Contrast the two pituitaries (anterior and posterior), focusing on alternate names, sizes, types of tissue, and means of receiving hypothalamic hormones.
Anterior:
- “Adenohypophysis”
- Bigger (75%)
- Endocrine tissue
- Hypophyseal portal system (blood vessels)
Posterior:
- “Neurohypophysis”
- Smaller (25%)
- Nervous tissue
- Hypothalamic-hypophyseal tract (nerves)
Discuss ADH as one of the two neurohypophyseal hormones, focusing on its role in a negative feedback loop offsetting low blood volume at the level of the kidney
- The receptors in the hypothalamus sense low blood volume and high blood osmolarity
- ADH will increase blood volume (at the kidney, Na is pulled out, and where Na goes, water follows)
- Once ADH causes a corrective increase in blood volume and blood osmolarity, osmoreceptors in the hypothalamus will no longer stimulate the release of ADH from the posterior pituitary
Discuss oxytocin as the other, focusing on its role in 2 separate positive feedback loops, facilitating birthing and ejection of breast milk.
- Contraction of smooth muscles in the uterine wall stimulates the release of oxytocin which is sensed by cell bodies in the hypothalamic nuclei (paraventricular). This stimulates the release of more oxytocin, and this increased oxytocin stimulates more contraction of the uterine wall
- Mechanical stimulation of the nipple by suckling infants stimulates the release of oxytocin, which is sensed by cell bodies in the hypothalamic nuclei (paraventricular). This stimulates the release of more oxytocin, and this increased oxytocin stimulates the ejection of breast milk by the mammary glands which can stimulate more sucking from the infant
Understand the role of the infundibulum and the capillary plexus of the posterior pituitary, in the systemic distribution of neurohypophyseal hormones.
- The infundibulum is the thin “stalk” connecting the hypothalamus superiorly with the pituitary inferiorly. It holds the hypothalamohypophyseal tract
- The capillary plexus of the posterior pituitary is a network of capillaries surrounding the posterior pituitary. It’s the point of entrance of neurohypophyseal hormones into the bloodstream
What is the role of each of the 7 hypothalamic hormones?
The hormones either stimulate the release of trophic (hypophyseal) hormones or inhibit their release.
What is the path of the 7 hypothalamic hormones to the anterior pituitary, and the target trophic cells in the anterior pituitary?
- 7 different hypothalamic hormones are released from short neurosecretory cells and diffuse into the primary plexus located around the infundibulum
- From the primary plexus, 7 hypothalamic hormones enter the hypophyseal portal veins for travel to the anterior pituitary and arrive at the 5 types of cells that secrete trophic (hypophyseal) hormones which are: Somatotrophs, Thyrotrophs, Gonadotrophs, Lactotrophs, and Corticotrophs
Explain how negative feedback loops decrease levels of effector hormones in the absence of hypothalamic inhibitory hormones (growth hormone and prolactin). How do you drop effector hormone levels for the other 3 pathways without inhibiting hormones, focusing on which molecules do the inhibition, what organs they target, and what the inhibitory effects are at each organ they target?
Thyropin
- Thyrotropin from the hypothalamus triggers the release of Thyrotrophs from the anterior pituitary, which triggers the release of thyroid-stimulating hormone (TSH) which triggers the release of T3 and T4 from the thyroid gland
- Elevated T3 and T4 in the blood suppress the release of thyrotropin by the hypothalamic neurosecretory cells and thyrotrophs from the anterior pituitary
Gonadotropin
- Gonadotropin from the hypothalamus triggers the release of Gonadotrophs from the anterior pituitary, which triggers the release of follicle-stimulating hormones and luteinizing hormones which triggers the release of sex hormones by the ovaries and testes
- Elevated sex hormones (estrogen and progesterone in females and testosterone in males) in the blood suppress the release of Gonadotropin by hypothalamic neurosecretory cells and Gondadotrophs by the anterior pituitary
Corticotropin
- CRH from the hypothalamus triggers the release of ACTH from the anterior pituitary, which triggers the release of adrenocorticotrophin hormone (ACTH) which triggers the release of cortisol by adrenal glands
- But elevated cortisol levels in the blood suppress the release of CRH by hypothalamic neurosecretory cells & ACTH by the anterior pituitary
Describe the location and general anatomy of the adrenal glands.
- Sit on top of kidneys
- Shaped like a slice of bread
- Heavily vascularized
- Outer cortex (80-90%) of mass surrounds a much smaller inner medulla
Name, locate, and describe the 3 zones of the adrenal cortex (cortical zones) and a key hormone produced in each. Know the general role of the key hormone produced in each zone. Identify which of the 3 regions is most noticeably under hormonal control by the HP axis.
From superficial to deep:
Zona glomerulosa: secretes aldosterone which modifies the amount of Na and water reabsorbed from the urine to help boost blood volume
- Most superficial layer of the adrenal cortex
Zona fasciculata: secretes cortisol which stimulate protein breakdown
- The middle and far largested layer
Zona reticula: secretes weak androgen which have minimal effect on body
- Deepest layer
The zona fascicullata is most noticeably under hormonal control by the HP axis
