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106 Cards in this Set
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- Back
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4 functions of the kidney |
1. Removal of useless or harmful material 2. Maintain the osmotic balance of body 3.Maintain the acid-base balance of the body 4.Daily Excretion of Urine |
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What are the 3 processes operating in the nephron? |
1. Glomerular Filtration -> a non-selective process that moves materials from inside the glomerular capillary into Bowman’s capsule 2. Tubular Reabsorption -> a selective process that moves material from the lumen of nephron back into the blood. 3. Tubular Secretion -> a selective process that moves material from the blood into the lumen of nephron tubule. |
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Filtration is enhanced by what 4 mechanisms? |
1.) Large surface area of the glomerulus. 2.) Afferent arteriole always has a larger diameter than the efferent arteriole. 3.) Smaller diameter offers great resistance to the blood flowing out of the glomerulus which causes higher pressure in glomerular capillaries 4.) The glomerular capillaries have a large number of pores. |
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Inner wall of Bowman's Capsule is called? |
Podocytes |
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What is Glomerular Blood Hydrostatic Pressure |
Blood pressure within the glomerulus that is forcing material into Bowman’s Capsule; Averages 60 mmHg |
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What is Capsular Hydrostatic Pressure? |
Force from inside the Bowman’s capsule that resists movement of material into capsule. |
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What is Blood Colloidal Osmotic Pressure |
Due to the osmotic gradient created by imbalance of protein; Water moves back into the capillary at an average force = 30mmHg |
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Glomerular Filtration Pressure Formula: |
Glomerular Filtration Pressure (GFP) = Blood Glomerular Hydrostatic Pressure – (capsular hydrostatic pressure + blood colloidal osmotic pressure) |
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What can possibly cause renal shutdown? |
1. Could occur if systemic blood pressure drops 2. Could occur if proteins pass through membrane -> alters osmotic pressure 3. Could occur if diameters of afferent and/or efferent arteriole change. |
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Substance used for concentration must meet certain criteria: |
1. Filterable 2. Not secreted or reabsorbed by nephron 3. Something not stored 4. Something not metabolized 5. Should not be toxic |
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What is a good substance for concentration? |
inulin |
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What is tubular reabsorption? |
Selective process that moves material from the lumen of nephron back into the blood; reabsorbs 99+% of filtrate |
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Tubular reabsorption occurs by ? |
Active transport and passive processes (diffusion/osmosis). |
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How are amino acids reabsorbed? |
By active transport |
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How is glucose reabsorbed? |
by active transport involving a carrier molecule |
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What is “glycosuria”? |
Glucose in urine |
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What causes glycosuria? |
blood glucose is higher than 170 mg glucose/100ml blood |
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How is sodium reabsorbed? |
Sodium is reabsorbed by active transport |
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Most reabsorption of Na+ occurs in? |
THE PCT |
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Na+ reabsorption occurs at _______ rate at all times. |
Maximum rate |
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The remainder of Na+ is reabsorbed in? |
The DCT |
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What does aldosterone do? |
It stimulates the reabsorption of Na+ and the secretion of K+ in the distal convoluted tubule and collecting duct. |
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How are anions reabsorbed? |
When Na+ is reabsorbed by active transport, it makes the blood more electropositive so anions follow Na+ into blood due to electrostatic attraction. |
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What does the juxtaglomerular cell release when blood pressure is low? |
Renin |
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What is renin? |
an enzyme that changes the plasma protein angiotensinogen into angiotensin I |
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How is angiotensin I converted to angiotensin II? |
Angiotensin I must circulate to the lungs where a second enzyme called “converting” enzyme converts Angiotensin I into Angiotensin II. |
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What are the functions of angiotensin II? |
a. Constricts arterioles -> increase resistance which increases blood pressure. b. Creates a sensation of thirst -> a person drinks water making it available to increase blood volume ( which also increases blood pressure). c. Stimulates the release of aldosterone -> causes Na+ reabsorption and K+ secretion in the distal convoluted tubule and collecting duct d. Stimulates the release of ADH -> makes epithelial cells of distal convoluted tubule and collecting duct permeable to water. e. Reabsorb NA+ and water -> increases blood volume and decreases urine volume. |
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___ of the kidney blood supply goes to the cortex and only ___ to the medulla. |
95%, 5% |
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What are the actions of ADH? |
1. Makes the epithelial cells of DCT and collecting duct permeable to water. 2. In large quantities ADH causes vasoconstriction (vasopressin).
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What is the cause of ADH release? |
a. In response to low blood volume/high solute concentration ; the osmoreceptors allow release of ADH. b. ADH release is stimulated by “Atrial baroreceptors” ; receptors in the atria that in response to low blood volume in atria stimulate ADH release. |
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What are the actions of aldosterone? |
stimulates NA+ reabsorption and K+ secretion in the DCT and collecting duct. |
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What is the cause of release of aldosterone? |
1. Angiotensin II of the renin-angiotensin pathway stimulates aldosterone release. 2. NA+ -> high blood levels of NA+ inhibit aldosterone release, low blood levels of Na+ stimulate aldosterone release. 3. K+ -> high extracellular concentration of K+ stimulates aldosterone, low extracellular concentration of K+ inhibits aldosterone release. |
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_________ results from a lack of hormones being produced by the adrenal cortex, including aldosterone. |
Addison's Disease |
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Aldosterone insufficiency results in: |
a. Excessive loss of NA+ b. Retention of K+ c. Loss of bicarbonate ions; lead to acidosis |
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What is Atrialnaturitic Hormone (peptide)? |
a. Released by cells in the right atrium due to excessive blood volume stretching the atria b. Actions i. Inhibits reabsorption of Na+ ii. Inhibits the release of ADH iii. Causes general dilation of arteries and veins. |
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What are Diuretics? |
any substance or mechanism that causes diuresis -> produces an increased urine volume ->abnormal amounts of urine being passed. |
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In what 2 ways do diuretics function? |
1. Increase glomerular filtration 2. Decrease tubular reabsorption |
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Discuss the process of diuretics that increase glomerular filtration: |
1. Increase cardiac output -> ex. Digitalis -> that slows but strengthens cardiac contraction 2. Dilate the afferent arteriole -> ex. Caffeine, theophylline (intea) or alcohol 3. Exposing the body to cold temperatures a. Constrict superficial blood vessels to conserve body heat. b. Blood is shunted to core of the body raising core blood pressure -> increases filtration. |
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Discuss the process of diuretics that decrease tubular reapsorbtion: |
1. Inhibit the release of ADH a. Alcohol b. Some anesthetics (some inhibit and stimulate release of ADH c. Diabetes insipidus disease that results from a lack of ADH production 2. Increase the osmotic load of filtrate a. Increase the osmotic load of filtrate with a substance that can not be reabsorbed we alter the osmotic gradient and therefore water reabsorption.
b. “diabetes mellitus” -> excess glucose in the filtrate can not be reabsorbed -> results in less tubular reabsorption.
c. Can administer urea as a diuretic but if it accumulates it becomes toxic as uremia.
d. Good diuretics -> mannitol -> can be given as a tablet or by IV.
3. Temporarily stop some tubular reabsorption mechanism.
a. Use of drugs containing mercury compounds temporarily posion the NA+/K+ pump -> stops NA+ reabsorption -> leads to diuresis. |
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Discuss the first mechanism of hormonal action: |
First mechanism is used by hydrophilic hormones and involves 2 messengers
1. The hydrophilic hormone is the first messenger and circulates in the blood until it reaches a target cell.
2. The hydrophilic hormone then attaches to a specific receptor on the outside of plasma membrane of the target cell.
3. When the hormone binds to the receptor on the outside of the cell, it causes the activation of an attached g-protein on the inside of cell.
4. Activated g-proteins will have different effects in different types of target cells. For instance: a. Open or close specific ion channels. b. Changes the activity of certain intracellular enzymes.
5. An activated G-protein might increase the activity of the enzyme “adenyl cyclase” which converts ATP into cyclic AMP molecule (second messenger).
6. Cyclic AMP then causes changes to the cells physiology -> what changes depends on the hormone that initiated the process. a. Hormones functioning in this may include ADH, FSH, GH, insulin, etc.
The first mechanism is fast and short lived. |
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Discuss the second mechanism that involves gene activation |
1. Hydrophobic hormones (lipid soluble) -> freely pass through the plasma membrane of cells.
2. Pass through the cytoplasm and the nuclear envelope to enter the nucleus.
3. In target cells, there is a receptor within the nucleus that the hydrophobic hormone attaches to.
4. Combination of receptor and hormone then attach to a promoter region and activate gene transcription.
5. Cause transcription producing a new molecule of messenger RNA.
6. Newly formed mRNA goes through the cytoplasm where it is translated into a new protein.
7. Then newly formed protein changes the physiology of the target cell. All of steroid hormones function in this manner estrogen, progesterone, testosterone, etc.
The second process takes longer to finish but is but also lasts much longer. |
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Discuss nerve stimulation |
In some mechanisms nerve impulses cause release of the hormone. i. Ex. ADH and oxytocin can be released due to nerve impulses, as well as hormones from the adrenal medulla. |
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Discuss Direct Negative Feedback |
a. The substance being controlled by the hormone feeds back and controls release of the hormone.
b. Aldosterone i. High blood Na+ levels inhibit release of aldosterone -> decrease Na+ ii. Low blood Na+ levels stimulate release of aldosterone -> increases iii. K+ also. reabsorption and therefore lower blood NA+ levels. NA+ reabsorption and therefore increases blood NA+ levels. |
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What is a neurohumor? |
a chemical produced by the nervous system that controls release of hormones by the endocrine system. Most neurohumors are produced by the hypothalamus and referred to as regulating factors or regulating hormones. |
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What are the two types of regulating factors? |
Releasing factors and Inhibiting factors |
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Define Positive Feedback Mechanisms |
The release of the hormone causes additional release of the hormone |
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What is the function of lutenizing hormone |
surges to cause ovulation |
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What are the functions of Oxytocin |
a. Actions in females: i. Stimulates contraction of uterine smooth muscle cells during pregnancy but especially during labor and delivery.
ii. Stimulates contraction of “myoepithelial cells” in the mammary glands that result in milk letdown.
b. Actions in males:
i. Primarily stimulates contraction of smooth muscle in the prostate gland during the male orgasm.
c. Control of oxytocin release:
i. Stretch of the uterus and the suckling reflex stimulate release of oxytocin ii. Progesterone inhibits release of oxytocin. |
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What are the actions of Growth Hormone? |
1. Primary effect on the skeleton and skeletal muscle: promotes mitosis.
2. Promotes the transport of amino acids into the cells which makes them available for protein anabolism.
3. Stimulates the liver to release “somatomedins” which stimulate growth at the epiphyseal plate -> increases length of bone.
4. Maintains size of body parts after maturity.
5. Promotes lipid catabolism -> lipolysis -> mobilizes lipids making them available for cellular respiration
6. Stimulates glycogenesis -> stores glucose as glycogen -> which conserves glucose so it is available when needed by nervous system. |
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What are the functions of Growth Hormone Releasing Hormone (GHRH) or somatocrinin? |
GHRH stimulates release of GH ii. GHRH is released by the hypothalamus in response to: 1. Low blood glucose levels 2. Increased amino acids 3. Stress 4. Strenuous exercise |
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What are the functions of Growth Hormone Inhibiting Hormone? or somatostatin |
i. GHIH inhibits release of GH ii. GHIH is released from the hypothalamus in response to: 1. High blood glucose levels 2. Low amino acids 3. Increased fatty acids |
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What is the effect of abnormal secretions of Growth Hormone in children? |
1. Hyposecretion of GH (underproduction) -> results in early closing of epiphyseal plates -> pituitary dwarfism.
2. Hypersecretion of GH (overproduction) -> leads to extra growth at epiphyseal plate -> gigantism |
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What is the effect of abnormal secretions of Growth Hormone in adults? |
1. Hyposecretion usually occurs due to atrophy of the pituitary -> pituitary cachexia or Simmond’s Disease
a. Lack of protein anabolism and this leads to premature aging and senility.
2. Hypersecretion -> condition called “acromegaly”
a. There is a thickening of the cancellous bone throughout the body. This leads to enlarged hands and feet, thickening of the skull, and protrusion of the orbital ridge.
b. About ¼ develop diabetes mellitus c. Sometimes have muscle weakness d. May have progressive vision failure. |
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What is the action of Adrenocorticotrophic Hormone (ACTH)? |
Adrenocorticotrophic Hormone (ACTH) a. Stimulates the adrenal cortex to produce “glucorticoids” b. Release of ACTH is controlled by the neurohumor Corticotropin Releasing Hormone c. What controls the release of CRH? (CRH) from the hypothalamus. i. Released in response to low glucorticoids and/or stress. ii. Release is inhibited by high glucocorticoids. |
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What is the function of Thyroid Stimulating Hormone (TSH) |
a. Action : stimulates the follicle cells of the thyroid gland to produce thyroid hormone (thyroxine) b. Release of TSH is stimulated by the neurohumor thyrotropin releasing hormone (TRH) c. What controls the release of TRH: i. Stimulated by low thyroxine levels and low metabolic rate ii. Inhibited by high thyroxine levels and high metabolic rate. |
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What is the function of Prolacting (PRL) or lactogenic Hormone? |
i. In females -> initiates and maintains lactation of hormone primed mammary glands.
ii. In males -> it may make the interstitial cells in the testes more sensitive
b. Prolactin Inhibiting Hormone (PIH) -> neurohumor from the hypothalamus that inhibits release of prolactin.
i. Hormones estrogen and progesterone stimulate the release of Prolactin Inhibiting Hormone (PIH)
c. Suckling reflex -> stimulates release of prolactin from the pituitary. i. May cause the release of a Prolactin Releasing Hormone from the hypothalamus.
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What is the function of Follicle Stimulating Hormone? |
In females: 1. Stimulates development of follicles within the ovary -> normally resulting in one mature follicle per cycle.
2. Stimulates the follicle cells to produce the hormone estrogen.
ii. In males: 1. It initiates the process of sperm production.
b. FSH release is stimulated by the neurohumor Ganatotropin Releasing Hormone (GnRH).
i. High levels of estrogen in females and high levels of testosterone in males inhibit the release of GnRH.
ii. Low levels of estrogen in females and low levels of testosterone in males stimulate the release of GnRH from the hypothalamus. |
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What is the function of lutenizing hormone? |
In females: 1. Stimulates ovulation -> release of a secondary oocyte from the ovary.
2. Stimulate follicle cells left in the ovary after the ovulation to transform into a “corpus luteum”
a. Temporary endocrine structure that produces estrogens and progesterone
ii. In males:
1. Stimulates development of Interstitial cells in the testes.
2. Initiates secretion of testosterone b. Release of LH is stimulated by Ganatotropin Releasing Hormone (GnRH) from the hypothalamus:
i. Low levels of estrogen or testosterone stimulate release of GnRH
ii. High levels of estrogen or testosterone inhibit release of GnRH. |
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What is the function of Melanocyte Stimulating Hormone? |
a. Actually a fragment of ACTH -> that is broken off b. Action: increases skin pigmentation by increasing the amount of melanin produced and the dispersion of melanin c. MSH may not normally be produced in adults except during pregnancy some diseases. d. The release of MSH is stimulated by Corticotropin Releasing Hormone (CRH) i. It is inhibited by the neurotransmitter Dopamine. |
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What is a Follicle Cell? |
involved in the formation of thyroid hormone-> make 2 forms: Cells extract “iodine” and the amino acid “tyrosine” from the blood |
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Thyroid Gland produces mostly what? |
T4 |
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Why is 1/3 of the T4 converted by peripheral tissues? especially in the lungs and liver into T3? |
Because T3 is more potent. |
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If thyroid hormone is not immediately needed it is what? |
It is attached to a protein called thyroglobulin (TGB) for storage; makes it more stable |
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When the thyroid hormone is needed, what happens? |
under the influence of TSH -> the thyroid hormone separates from thyroglobulin and is released into blood.
Once in the blood, thyroid hormone binds with a protein called “Thyroxine Binding Globulin” (TBG). 1. In the form the thyroxine is referred to as “protein bound iodine” (PBI) |
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Actions of the thyroid hormone both T3 and T4: |
i. Involved in at least 20 different enzyme systems ii. Stimulate metabolism --> both anabolic reactions and catabolic reactions iii. Works with GH to promote growth iv. Increases permeability of mitochondria increase energy availability. v. Increase reactivity of nervous system especially the ANS vi. Critical during development to the growth of neurons.
e. Control of release of thyroid hormone involves TSH f. Abnormalities of thyroid hormone secretion: g. Control of release of thyroid hormone involves TSH |
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What are the abnormalities of thyroid hormone secretion: |
Hyperthyroidism and hypothyroidism |
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What are the effects of hyperthyroidism? |
high metabolic rate 2. excitable and nervous increased bowel activity 3. excessive sweating 4. rapid pulse 5. grave’s disease |
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What is the treatment for hyperthyroidism? |
to remove some or all of thyroid gland antithyroid drugs, surgery, or radioactive iodine. |
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What are the effects of hypothyroidism? |
Low metabolic rate 2. Dry skin 3. Mental and physical sluggishness 4. In children cretinism usually congenital underdeveloped nervous system 5. In adults myxedema puffy hands and feet, menstrual irregularities in women. |
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What is the function of parafollicular cells? |
Produce hormone called “calcitonin” |
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What is the function of calcitonin? |
Inhibits osteoclast activity. This prevents bone breakdown and the movement of minerals out of the bone. Maintains normal blood calcium levels. |
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What is hypercalcemia? |
high blood calcium which stimulates release of calcitonin. It also stimulates release of parathyroid hormone |
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What is hypocalcemia? |
low blood calcium which inhibit release of calcitonin. Also inhibits release of parathyroid hormone |
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What does the parathyroid gland produce? |
Parathyroid hormone/Parathormone |
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What are the actions of the parathyroid hormone in the digestive system? |
i. Increases calcium absorption in the intestines. ii. Also causes a slight increase in magnesium and phosphate absorption. iii. Depends upon adequate amounts of Vitamin D |
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What are the actions of the parathyroid hormone in the bones? |
i. Parathyroid hormone stimulates osteoclast activity to increase bone breakdown. |
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What are the actions of the parathyroid hormone in the kidney? |
i. Inhibits the reabsorption of phosphate
ii. Increases the reabsorption of calcium and magnesium from the filtrate.
net effect is to raise blood calcium levels and lower blood phosphate levels. |
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What are the two of the abnormal secretion levels: |
Hypoparathyroidism and Hyperparathyroidism |
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What is hypoparathyroidism? |
i. High urine calcium and low urine phosphate can lead to kidney stones which may block the ureter.
ii. Low blood calcium and high blood phosphate leads to uncontrolled muscle excitability; twitches and tetanic contractions without nerve stimulation.
iii. Historically this occurred when parathyroid gland was removed with thyroid.
iv. Treatment is oral calcium and vitamin D |
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What is hyperparathyroidism? |
i. Low urine calcium and high blood calcium. ii. Results in high osteoclast activity remove excess minerals from the bones that are replaced with fibrous connective tissue called “osteitis fibrose cystica” 1. Bones are fragile, tender, painful, and may lead to deformity iii. After result of a “tumor” 1. Treatment surgical removal followed by oral calcium and vitamin D. |
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What are the actions of insulin? |
i. Major function insulin attaches to the surface of a cell and allows glucose to enter the cell.
ii. Stimulates glycogenesis in the liver Storing glucose as glycogen.
iii. Inhibits glycogenolysis in the liver prevent glycogen breakdown
iv. Stimulates lipogenesis in the liver forming triglycerides for storage.
v. Inhibits lipolysis in the liver breakdown of lipids
vi. Inhibits gluconeogenesis in the liver Prevents the conversion of fats and/or proteins to glucose.
Net effect is to lower blood glucose levels. |
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What is hyperglycemia? |
high blood glucose levels which stimulates release of insulin. Stimulates the delta cells to secrete Growth Hormone Inhibiting Hormone (somatostatin). |
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What is Hypoglycemia? |
low blood glucose levels inhibits release of insulin. Stimulates release of glucagon |
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What is responsible for diabetes mellitus? |
Hyposecretion
i. Person will have very high blood glucose levels.
ii. But the cells are starving to death since the glucose cannot enter the cells.
1. Neurons are affected most by the lack of insulin can lead to coma and eventual death. |
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What is the treatment for diabetes mellitus? |
i. Biguanides - such as metformin inhibits gluconeogenesis lowers blood glucose levels by preventing the formation of glucose.
ii. Sulforamides glipizide, gluotrol, etc.
1. Stimulate the beta cells to produce more insulin.
iii. Insulin synthetic humulin. Injected the amounts vary
iv. Etc. |
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What is the action of glucagon? |
i. Promotes glycogenolysis in the liver liver breaks down glycogen and releases glucose into blood.
ii. Promotes gluconeogenesis in the liver increases conversion of lipids and/or protein into glucose.
iii. Both have a net effect to increase blood glucose levels. |
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What inhibits glucagon? |
1. GHIH inhibits the release of gucagon. |
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What is the function of Zona glomerulosa? |
outer portion of cortex. Produces mineralocorticoids
95% of all mineralocorticoid activity is due to “aldosterone”
b. Actions: stimulates reabsorption of Na+ and secretion of K+ in the distal convoluted tubule and collecting duct
c. Control of aldosterone: direct negative feedback involving blood levels of Na+ and extracellular levels of K+. |
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What is the function of Zona Fasciculata |
Middle portion of cortex. Produces glucorticoids |
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What is the function of Zona reticularis |
Inner portion of cortex. Produces gonadocorticoids. |
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What does the Adrenal Medulla produce? |
amines or ratechelamines. |
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______ is the most abundant glucocorticoid and is responsible for 95% of all glucorticoid activity. |
Cortisol |
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What are the actions of of glucorticoids? |
i. Works with other hormones to: 1. Promote normal metabolism 2. Deal with stress
ii. Increases muscle protein breakdown mobilizes amino acids.
iii. Increases rate of gluconeogenesis uses the newly available amino acids to make glucose.
1. Increase blood glucose levels.
iv. Improves the reactivity to stress both physical and emotional stress increased availability of glucose makes body more alert.
v. Increases CNS excitability.
vi. Inhibits inflammatory rolls and their secretions so they are considered anti-inflammator and/or anti-allergic.
vii. Vasoconstrictors they make blood vessels more sensitive to the vasomotor center. |
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Corticotropin Releasing Hormone controls the release of? |
glucocorticoid |
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Low glucocorticoid levels and/or stress causes _____ |
stimulate release of CRH. |
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_____ stimulates the anterior pituitary to release ACTH. |
CRH |
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_____ stimulates adrenocortex to secrete glucocorticoids. |
ACTH |
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What is the function of gonadocorticoids? |
a. Composed primarily of testosterone and small amounts of estrogen the amounts are the same in both sexes.
i. Testosterone male steroid hormone
ii. Estrogen female steroid hormone
b. Important for protein synthesis and building of muscles in the pre-puberty individual.
c. The amount of these hormones from the adrenal cortex in post-puberty individuals is insignificant. |
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What is the effect of hypersecretion of gonadocorticoids? |
i. Hypersecretion in females masculinizing effect:
1. Development and growth of facial hair beard.
2. Changes in voice
3. Increased muscular strength
4. Growth of the clitoris to resemble a penis.
5. Etc.
ii. Hypersecretion in males rarely causes feminization |
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What is the adrenal medulla? |
sympathomimetic in action = mimics the sympathetic in action = mimic the sympathetic division of the ANS.
a. Composed of chromaffin cells
b. Produces amines or catecholamines
c. Release of the catecholamines is caused by nerve impulses from pre-ganglionic
i. Epinephrine 80% production
ii. Norepinephrine sympathetic neurons:
i. Work in conjunction with the sympathetic nervous system |
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What are the actions of catecholamines? |
i. Increases blood glucose levels by: 1. Mobilizing stored carbohydrates in the liver
2. Breaking down muscle glycogen
ii. Increases heart rate and strengthens contractions
iii. Dilate arterioles to the heart, brain, and skeletal muscle.
iv. Constrict arterioles to digestive, urinary, and reproductive systems.
v. Relaxes visceral smooth muscle decreased peristalsis
vi. Brain more alert. |
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What does the thymus do? |
Produces the hormone Thymosin, etc. Involved in proliferation and programming of T- lymphocytes. |
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What is the pineal gland? |
1. Small gland located superior to the corpora quadrigemina
2. Pineal gland starts to accumulate calcium deposits at puberty referred to as “brain sand”
a. The calcium accumulates due to increased activity. |
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What are the 3 or 4 hormone like substances associated with pineal gland? |
a. Serotonin involved in normal brain physiology.
b. A growth inhibiting factor
c. Adrenoglomerulotropin Believed to stimulate the zona glomerulosa of the adrenal cortex to secrete aldosterone.
d. Melatonin |
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What is the action of melatonin? |
i. Inhibits the release of the neurohumor Gonadotropin Releasing from the hypothalamus.
ii. Release of melatonin involves nerve impulses:
Seasonal Terms Hormone (GnRH) from the hypothalamus. 1. Inhibit reproductive activity
1. Light initiates nerve impulses that inhibit the release of melatonin.
2. Dark no nerve impulses so melatonin is released reproduction is inhibited.
1. Long days
2. Long nights |
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What inhibits oxytocin? |
Progesterone |
