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Physiology II Test III > Review > Flashcards

Review Flashcards

1
Q

What functions as an accessory storage depot for energy and as an “ATP Buffer”?

A

phosphocreatine
High energy phosphate bond
3x more abundant than ATP
Cannot participate directly in energy transfer

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2
Q

Essential amino acids

A 
PVT TIM HALL
Phe. 
Val
Thr
Trp
Ile
Met
His
Arg
Leu
Lys
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3
Q

How is a peptide bond formed?

A

aa + ATP -> aa-amp +2Pi
aa-amp + tRNA -> aa-tRNA + AMP
Attachment of tRNA to mRNA codon-anticodon
aa linked to another aa with peptidyl transferase + GTP

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4
Q

How many high energy phosphate bonds are needed to form one peptide linkage?

A

4

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5
Q

Where is urea formed?

A

in the liver

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6
Q

What is the first step of degradation of amino acids?

A

deamination

  • generally involves transamination
  • one end product is ammonia
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7
Q

Diagram the Ornithine (Urea) cycle

A

In the mitocondria:
Ammonia +CO2 -> carbamoyl phosphate
Carbamoyl phosphate + ornithine -> Citrulline

In cytoplasm -> Citrulline + aspartate -> argininosuccinate
Argininosuccinate _> arginine + fumerate
Arginine -> urea + ornithine

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8
Q

Ornithine mnemonic

A 
Word	Molecule
Orange	Ornithine
Colored	Carbamoyl Phosphate
Cats	        Citrulline
Always	Aspartate (enters the cycle)
Ask	       Argininosuccinate
For    	Fumarate (leaves the cycle)
Awesome	Arginine
Umbrellas	Urea (leaves the cycle)
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9
Q

Rate of overall chemical reaction is determined by what?

A

concentration of the enzyme
concentration of the substrate

Michaelis-menten equation

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10
Q

What is the overall rate of a series of chemical reactions determined by?

A

The rate of reaction of the slowest step in the series

Rate-limiting step

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11
Q

What is the major rate-limiting factor for almost all energy metabolism in the body?

A

ADP
*oxidative metabolic pathways or other pathways for the release of energy

ADP concentration increases during cellular activity

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12
Q

Energy equivalent of oxygen =

A
  1. 825 Cal: energy liberated per liter of oxygen with average diet
    * avg of metabolizing 1 liter of oxygen with glucose, fat, protein
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13
Q

Thyroxine increases or decreases rate of chemical reactions in cells and metabolic rate?

A

Increases:
max secretion may increase metabolic 50 to 100% above normal

Loss of thyroid secretion decreases metabolic rate to 40 to 60 % of normal

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14
Q

Testosterone increases or decreases metabolic rate?

A

increases rate 10 to 15%, mainly related to anabolic effect of increase in skeletal muscle mass

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15
Q

What is much of the decline in BMR with increasing age probably related to?

A

loss of muscle mass and replacement with adipose tissue with a lower rate of metabolism

Skeletal muscle accounts for 20 to 30 % of BMR even at rest

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16
Q

Glycogenolysis:

A

is the breakdown of glycogen (n) to glucose-1-phosphate and glycogen (n-1).

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17
Q

Gluconeogenesis:

A

is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as pyruvate, lactate, glycerol, and glucogenic amino acids.

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18
Q

How does the blood flow through the lobule?

A

Portal vein-> sinusoids-> central vein -> hepatic veins

Hepatic artery -> sinusoids -> central vein -> hepatic veins

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19
Q

Describe liver cell plates

A

Two layers of hepatocytes and bile canaliculi lie between the two layers of hepatocytes in each cell plate

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20
Q

What are sinusoids lined with?

A

Endothelial cell

Kupffer cells

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21
Q

What is found between endothelial cells and hepatocytes?

A

Space of Disse

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22
Q

Describe liver blood flow and vascular resistance

A

Liver has high blood flow and low vascular resistance

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23
Q

In the urea cycle, what reaction occurs in the mitochondria?

A

Ammonia + CO2 -> carbamoyl phosphate

+ ornithine

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24
Q

What is the effect of cirrhosis on the liver?

A

Increases liver resistance to blood flow

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25
Q

What is the effect of clot blocking portal vein or major branch?

A

Blockage of return blood from spleen and intestines

Increase in capillary pressure in intestinal wall -> loss of fluid -> death

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26
Q

How much blood does the liver normally store?

A

10% of body’s volume = 450 ml
High blood pressure in right atrium can put backpressure on liver and cause the liver to increase blood volume up to 1.5 liters
-may occur during cardiac failure with peripheral congestion

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27
Q

What part of the liver is highly permeable to plasma?

A

sinusoids

-efferent lymph has a protein concentration similar to plasma

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28
Q

What causes ascites

A

Higher than normal back pressure in hepatic veins causes fluid to transude into lymph. Fluid leaks through liver capsule into abdominal cavity
Fluid is almost pure plasma
Large amount of fluid in abdominal cavity = asites

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29
Q

Functions of liver in carbohydrate metabolism

A

stores glycogen
converts galactose and fructose into glucose
gluconeogenesis
Forms many intermediate products of carbohydrate metabolism

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30
Q

Functions of liver in fat metabolism

A

Oxidation of fatty acids for energy
Synthesis of cholesterol, phospholipids, lipoproteins
Synthesis of fats from proteins and carbohydrates

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31
Q

Functions of liver in protein metabolism

A

deamination of amino acids
formation of urea
formation of plasma proteins
interconversion of aa

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32
Q

What vitamins does the liver store?

A

A, D, B12

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33
Q

Functions of liver in formation of coagulation factors

A

fibrinogen
prothrombin
accelerator globulin
Factors VII, IX, X

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34
Q

What produces and secretes bile?

A

liver

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35
Q

What are the components of bile?

A

Bile acids (cholic and chenodeoxycholic acids-hepatocytes; deoxycholic acid and lithocholic acid - bacteria)
Water and electrolytes
Cholesterol and phospholipids
Pigments and organic molecules

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36
Q

How is bilirubin formed?

A
  1. old damaged RBCs in reticuloendothelial tissue rupture
  2. heme released
  3. hemoglobin phagocytized
  4. split into heme & globin
  5. heme ring opened to free iron
  6. Fe transported in blood by transferrin; heme becomes straight chain of pyrrole nuclei
  7. heme oxygenase forms biliverdin
  8. free (unconjugated) bilirubin leaves Mo
  9. attached to plasma albumin to enter liver
  10. becomes conjugated
  11. secreted by active transport into intestines
  12. converted by bacteria into urobilinogen
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37
Q

what is bilirubin conjugated with?

A

Glucuronic acid - majority
sulfate
other

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38
Q

What happens to urobilinogen?

A

Oxidized into excreted products OR:
Reabsorbed into the blood and carried back to the liver TO BE:
re-excreted by the liver OR:
excreted in the urine

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39
Q

What is jaundice?

A

yellowish tint to the body tissues; caused by quantities of bilirubin in the extracellular fluids
Common causes:
increased hemolysis
Obstruction of bile ducts or damage to liver

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40
Q

What are the major types of pancreatic islet cells?

A

Alpha: secrete glucagon, 25%
Beta: secrete insulin and amylin, 60%
Delta: secrete somatostatin

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41
Q

What does somatostatin and amylin do?

A

Somatostatin inhibits insulin and glucagon secretion

Amylin inhibits insulin secretion

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42
Q

What happens if there is a lack of insulin in the process of fat storage?

A

Large amounts of acetoacetic acids are formed in the liver
Carnitine transport mechanism in the liver is activated
B-oxydation results in excess of acetyl-CoA
Excess acetoacetic acids causes acidosis
Increase of ketone bodies in the blood

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43
Q

How does glucagon lead to break down of liver glycogen and increased gluconeogenesis?

A 
Adenyl cyclase
cAMP
Protein kinase
phosphorylase b kinase
phosphorylase b to a
degradation of glycogen
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44
Q

Metabolic syndrome:

A 
Obesity
insulin resistance
fasting hyperglycemia
increased lipid triglycerides
decreased HDL levels
hypertension
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45
Q

Describe Ion-channel-linked receptors

A

used primarily by neurotransmitters

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46
Q

Describe G protein-linked hormone receptors

A

7 transmembrane segments

Some are inhibitory some are stimulatory

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47
Q

Describe Enzyme-linked hormone receptor

A

Single pass
Intracellular enzyme may be part of the receptor or separate
Example: leptin receptor (JAK-STAT)

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48
Q

Describe intracellular hormone receptor and gene activation

A

Receptor inside the cell for lipid soluble hormones

Activated hormone-receptor complex binds to promoter sequence of DNA

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49
Q

What are examples of lipid soluble hormones?

A 
VARTS
Vitamin D
Adrenal 
Retenoid
Thyroid
Steroidal hormones
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50
Q

Describe polypeptide and protein hormones

A

Stored in secretory vesicles until needed
Synthesized as preprohormones
Released exocytosis mediated via Ca
Some release may involve cAMP

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51
Q

Describe steroids

A

Usually from cholesterol
Three cyclohexyl rings and one cyclopentyl ring
Large quantities of cholesterol esters stored

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52
Q

Describe Amine hormones

A

Derived from tyrosine
Include thyroid and adrenal medullary hormones
Formed by actions of enzymes in cytoplasmic compartments of glandular cells
Thyroid - macromolecules of thryoglobulin and stored in thyroid gland follicle
Catecholamines - formed in adrenal medulla and stored

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53
Q

Describe adenyl cyclase-cAMP signal transduction mechanims

A 
G protein activated
Adenyl cyclase
cAMP
cAMP-dependent protein kinase
Phosphorylates - cascade of enzymes
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54
Q

Describe cell memebrane phospholipid second messenger system

A 
Hormone activates transmembrane receptor
Activates phospholipase C
PIP2 break down into IP3 and DAG
IP3-mobilizes Ca from mit and ER
DAG- activates protein kinase C
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55
Q

Describe calcium-calmodulin phospholipid second messenger system

A

Change in membrane potential can open Ca channels
A hormone interacting with membrane receptors can open Ca channels

Or
Calcium can bind with calmodulin (3-4) and which then activate protein kinases or inhibits

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56
Q

Describe hormones acting directly on DNA

A

Steroid hormones diffuse across cell membrane and bind with receptor in cytoplasm. and then complex binds to DNA (this takes longer than membrane-receptor mediated singaling)

Thyroid homones: bind directly with receptors in nuclues. Remain bound for days to weeks and continue to function

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57
Q

What are the five cell types of Anterior Pituitary?

A 
Somatotropes: HGF
Corticotropes: ACTH
Thyrotropes: TSH
Gonadotropes: LH and FSH
Lactotropes: Prolactin
(FLAT PEG)
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58
Q

Describe magnocellular neurons

A

Posterior pituitary

located in supraoptic(ADH) and paraventricular(Oxytocin) nuclei

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59
Q

How does the hypothalamus control the anterior pituitary?

A

Via hormones called hypothalmic releasing and inhibitory hormones (factors), via hpyothalamic-hypophyseal portal system->median eminence->portal system

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60
Q

What are the functions of the Growth Hormone?

A

Growth(chondrocytes and osteogenic cells)
Protein synthesis
Fatty acid mobilization
Decreases glucose utilization (mimics diabetes)
Causes liver to form somatomedins (Insulin-like GFs)

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61
Q

What factors stimulate GH secretion?

A 
Starvation
Hypoglycemia
Exercise
Excitement
Trauma
Ghrelin
First two hours of deep sleep
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62
Q

How much iodine is required each year?

A

50 mn, our bodies do a pretty good job of recycling iodine

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63
Q

How is iodine absorbed from gut tract?

A

Same manner as chlorides
Sodium-iodide symporter (2:1) in basal membrane of thyroid cell
Energy for this pump comes from Na-K ATPase pump
Iodide can be concentrated inside cell 30-250x times plasma concentration
Iodide is transported across apical membrane of cell into follicle via Cl-I counter-transporter=pendrin

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64
Q

Thyroid cells secrete thryoglobulin(30 molecules of thyroxine) into follicle. Each thyroglobulin molecule has about 70 tyrosine amino acids which bind iodine to form what?

A

thyroid hormones

65
Q

How do iodide ions bind directly to tyrosine?

A

Iodide ions are converted to an oxidized form of iodine (either nascent iodine or I3-) and these can bind directly to tyrosine

66
Q

What is the major hormonal product of iodine metabolism?

A

Thyroxine T4

67
Q

How is thyroxine formed?

A

Formed when two molecules of diiodotyrosine are joined together

68
Q

How is T3 formed?

A

One monoiodotyrosine combines with one diiodotyrosine to form triiodothyronine

69
Q

How are thyroxine and triiodothyronine molecules secreted?

A

Apical surface of thyroid cells pinch off small portions of the follicular colloid to form pinocytic vesicles
Lysosomes fuse with vesicles and digest thryoglobulin molecules to release the hormones and then they diffused into the blood and bound to plasma proteins synthesized in the liver

70
Q

What happens to most of the iodinated tyrosine in the thyroglobulin?

A

Does not become thryoid hormones but is recycled usuing a deiodinase enzyme

71
Q

Why are thyroid hormones slowly released to tissue cells?

A

Plasma proteins have a high affinity for thyroid hormones, so the hormones are released slowly to tissue cells

72
Q

What effect do large doses of injected thryoxine have on metabolic rate?

A

Has no discernible effect for several days

73
Q

Thyroid effects on specific bodily mechanisms

A 
Stimulation of carbohydrate metabilism
Stimulation of fat metabolism
Effect on plasma and liver fats
Increased requirement for vitamins
increased BMR
Decreased body weight
74
Q

Thyroid effects on cardiovascular system

A 
Increased blood flow and cardiac output
Increased heart rate
Normal arterial pressure
Increased respiration
Increased GI motility
Excitatory effects on CNS
Effects on muscle function
Muscle tremor
Effect on sleep, other endocrine glands and sexual function
75
Q

What are the causes of hyperthyroidism?

A

Grave’s disease and Adenoma

76
Q

What are the symptoms of hyperthyroidism?

A 
High state of excitability 
Intolerance to heat
Increased sweating
Mild to extreme weight loss
Varying degrees of diarrhea
Muscle weakness
Nervousness or other psychic disorders
Extreme fatigue 
Inability to sleep
Tremor in hands
Exophthalmos
77
Q

What are the treatments to hyperthyroidism?

A

Surgical removal of most of thryoid gland

Treatment with radioactive iodine

78
Q

What causes hypothyroidism?

A

Hasimoto disease (autoimmunity)
Endemic goiter
Cretinism

79
Q

What are the symptoms of hypothyroidism?

A

Generally opposite of those hyperthyroidism
Myxedema
Atherosclerosis

80
Q

What are the treatments to hypothyroidism?

A

Oral medication

81
Q

What are some antithryoid drugs?

A

Thiocyanate ions
Propylthiouracil
Iodides

82
Q

One of the best known stimuli for increasing the rate of thyroid releasing hormone secretion is what?

A

Cold

83
Q 
Which of the following is a common cause of hyperthyroidism?
Hashimoto
Graves
Endemic goiter
Cretinism
A

Graves disease

84
Q

The basal membranes of thyroid cells contain symporters for iodide. What ion is co-transported with iodine by these symporters?

A

Sodium

85
Q

Down regulation of receptors may occur as a result of which of the following?
Inactivation of some of the intracellular protein signalling molecules
Activation of some of the receptor molecules
Increased production of receptors
Increase int he target cell’s responsiveness to the hormone

A

Inactivation of some of the intracellular protein signaling molecules

86
Q

Describe the medulla of the adrenal gland

A

Secretes epinephrine and norepinephrine

Functionally related to sympathetic nervous system

87
Q

Describe the cortex of the adrenal gland

A

Secretes corticosteroids

  • mineralocorticoids
  • glucocorticoids
  • androgenic hormones
88
Q

Describe corticosteroids

A

Synthesized from cholesterol
Provided mostly by LDLs in the plasma
Cholesterol converted to pregnenolone in mitochondria by cholesterol demolase (rate limit-step)

89
Q

What increases the number of LDL receptors?

A

ACTH

90
Q

What increases the conversion of cholesterol to pregnenolone?

A

Both ACTH and angiotensin II

91
Q

What is the major mineralocorticoid?

A

Aldosterone and half life is about 20 min

92
Q

What do zona glomerulosa secrete?

A

Mineralocorticodes
Controlled mainly by angiotension II and K
*especially affects the electrolytes (Na and K)

93
Q

What secretes glucocoticoids?

A

Zona fasiculata
Major is cortisol
Contolled mainly by ACTH
*affects increased blood glu concentration

94
Q

What secretes androgenic hormones?

A

Zona reticularis

DHEA, Estrogen

95
Q

What happens if there is a lack of aldosterone?

A

total loss causes death in a matter of days
-unless extensive salt therapy and mineralocorticoid injections are available
K levels in ECF rise
Na and Cl are lost rapidly from urine
Total ECF and BV greatly reduced

Diminished cardiac output goes to shock-like state
Hyperkalemia and serous cardiac toxicity

96
Q

What happens if there is an excess of aldosterone?

A

Increase ECF and arterial pressure
Small effect on plasma Na concentration bc Na reabsorption in renal tubules is accompanied by equivalent amount of water reabsorption
Hypokalemia and muscle weakness
K goes from ECF into most cells of the body
Alkalosis

97
Q

How does aldosterone lead to sodium reabsorption?

A

Aldosterone diffuses into tubular epithelial cells
Combines with mineralocorticoid receptor proteins
Aldosterone-receptor complex diffuses into nucleus
RNA transcription is induced
Sodium-potassium ATPase pump proteins formed
Epithelial sodium channel is formed
Na pumped to renal interstitial fluid

98
Q

Increased concentrations of _____ and _____ greatly increases aldosterone secretion.

A

K and angiotensin II

99
Q

What is necessary for aldosterone secretion but has little effect in controlling rate of secretion?

A

ACTH

*regulation of aldosterone secretion is almost entirely independent of the regulation of cortisol secretion

100
Q

What are the functions of glucocorticoids?

A

Stimulates gluconeogenesis
Increase enzymes to convert aa to glucose
mobilizes aa from extrahepatic tissues
Decrease glucose utilization by cells
“adrenal diabetes”
Enhances transport of aa into hepatic cells
resists stress
resists inflammation
causes resolution of inflammation
block inflammatory response to allergic rxn
decreases # of eosinophils and lymphocytes in blood

101
Q

Describe hypoadrenalism

A

Addison’s disease - primary: due to injury to adrenal cortex
Secondary: due to impaired function of pituitary gland
Disturbances:
-due to mineralocorticoid deficiency
-due to glucocorticoid deficiency
-melanin pigmentation

102
Q

Describe hypoadrenalism disturbances due to mineralocorticoid defieciency

A 
Decreased extracellular fluid volume
Hyponatremia
Hyperkalemia
Mild acidosis
Rise in RBC concentration 
Decrease in cardiac output 
Decrease in blood pressure
Death from shock
103
Q

Describe hypoadrenalism disturbances due to glucocorticoid deficiency

A

Loss of ability to maintain normal blood glucose coencentrations between meals
Reduction in both proteins and fats leading to depression of other bodily functions
Muscle weakness
Highly susceptible to stress

104
Q

Describe hypoadrenalism disturbances due to melanin pigmentation

A

May be caused by loss of negative feedback to pituitary, allowing increased amounts of MSH
Results in uneven distribution of pigmentation, especially in thin skin areas

105
Q

What are the causes of hyperadrenalism?

A 
Cushing's disease
Adenomas of anterior pituitary
Abnormal function of hypothalamus
Ectopic secretion of ACTH by tumor
Adenomas of adrenal cortex
Excess ACTH secretion is cause of Cushing's
106
Q

What are the characteristics of hyperadrenalism?

A 
Buffalo torso
moon face
acne and hirsutism
Hypertension
increased blood glucose
107
Q

What are the three layers from lateral to medial of the adrenal gland cortex?

A

Zona glomerulosa
Zona fasiculata
Zona reticularis

108
Q

What does an increase in Ca ion above normal do to the nervous system?

A

Causes progressive depression of the nervous system

  • symptoms begin to appear when the blood Ca level rises above 12 mg/dl
  • Reflex activities of the nervous system are sluggish
  • There is constipation and lack of appetite
109
Q

What does a decrease in Ca ion concentration do to the nervous system?

A

Nervous system becomes more excited

110
Q

How much of the total body calcium is in the extracellular fluid?

A

.1 percent - 1300 mg

111
Q

How much of the total body calcium is in the cells and organelles?

A

1 percent = 13,000 mg

112
Q

Where is 98.9% of the total body calcium stored?

A

Bone = 1,000,000 mg

113
Q

Where is most of the total body phosphate stored?

A

in bones = 85%

114
Q

Where is 14 to 15% of the total body phosphate?

A

Cells

115
Q

Where is less than 1% of total body phosphate located?

A

in extracellular fluid

  • not nearly as well regulated as that of calcium
  • large changes in the level of phasophate in the extracellular fluid does not cause major immediate effects on the body
116
Q

What are the effects of hypocalcemia?

A

Causes nervous system excitement (due to increase perm to Na)
tetany
Also could cause seizures

117
Q

Describe tetany

A

First sign of tetany usually occurs in the hand, resulting in carpopedal spasm
Ordinarily occurs when the blood concentration of calcium falls from its normal level of 9.5 mg/dl to about 6 mg/dl
Usually lethal at 4 mg/dl

118
Q

What are the normal rates of intake each day for calcium and phosphorus?

A

1000mg/day

119
Q

Normally, divalent ions are poorly absorbed. So what promotes calcium absorption by the intestines, so that about 35% of ingested calcium is absorbed?

A

Vitamin D

120
Q

Describe how 900 mg of the 1000 mg of daily is excreted in the feces

A

About 350 is absorbed but 250 mg/day of the absorbed calcium enters intestines via secreted GI jices and sloughed mucosal cells

121
Q

How much of ingested Ca is excreted in the urine?

A

10% = 100 mg/day

1000 mg/day intake

122
Q

How much of plasma Ca is not filtered by glomerular capillaries and why?

A

41% bc it is bound to plasma proteins and is too large to be filtered

123
Q

How much Ca in the filtrate is reabsorbed by the renal tubules?

Describe phosphate filtration

A

99%
*it was combined with anions or ionized and filtered through the glomeruli

Renal phosphate excretion is controlled by an over-flow mechanisms and PTH can greatly increase phosphate excretion

124
Q

Calcium precipitate is also called what?

A

Hydroxyapatite crystals

125
Q

Where do hydroxyapatite crystals form?

A

Not in normal tissues

They do precipitate in the bone because normal inhibitors that are present in almost all tissues and plasma(including bone) to prevent such precipitation, there is another inhibitor in the bone to inhibit that inhibitor

Inhibitor in the bone is called pyrophosphate

126
Q

How are collagen fibers formed in the initial stage of bone production?

A

Osteoblasts secrete collagen monomers which polymerize rapidly to form collagen fibers
The precipitation of calcium along the collagen fibers eventually forms hydroxyapatite crystals

127
Q

The initial calcium salts to be deposited are in what form?

A

Amorphous (noncrystalline) form

128
Q

When do amorphous calcium salts convert into hydroxyapaptite crystals?

A

A period of weeks or months and a few percent may remain in the amorphous form

129
Q

What calcium form in the bone can be absorbed rapidly when there is need for extra calcium in the extracellular fluid

A

Amorphous salts

130
Q

What happens if salts are injected intravenously?

A

The Ca ion concentration may increase immediately to high levels
However, within 30 to 60 min, the Ca ion concentration returns to normal
*also return to normal this quickly if large quantities of Ca ions are removed from the circulating body fluids

131
Q

What are the three hormones that control calcium balance?

A

Vitamin D
PTH
Cacitonin

132
Q

How does Vitamin D control Ca?

A

Causes intestines, kidneys, and bones to increase absorption of Ca into extracellular fluid
Vitamin D receptors present in most cells in the body located in nuclei of target cells
Vitamin D receptor forms complex with retinoid-x receptor which then binds to DNA
*Sometimes vitamin D suppresses transcription

133
Q

How does the increase of Vitamin D cause intestinal absorption of Ca?

A

Formation of calbindin occurs after 2 days (it is a Ca-binding protein that is in brush border of epithelial cells)
Ca moves through basolateral membrane of cell by facilitated diffusion
Calbidin remains in the cell for weeks after active Vitamine D is removed from body

134
Q

Besides calbindin, how is Ca absorbed due to increased vitamin D

A

A calcium-stimulated ATPase in the brush border of the epithelial cells
An alkaline phosphatase in the epithelial cells
Weak effect on reabsorption in renal tubules

135
Q

What does extreme quantities of Vitamin D cause?

A

Absorption of bone

136
Q

In the absence of Vitamin D, the effect of _____ in causing bone absorption is greatly reduced or even prevented?

A

PTH

137
Q

Vitamin D in smaller quantities promotes what?

A

Bone calcification

138
Q

What does excess activity of the parathyroid gland cause on calcium absorption?

A

Causes rapid absorption of calcium salts from the bones.

-results in hypercalcemia in the ext. fluid

139
Q

How is PTH formed?

A

Ribosomes - preprohormone with 110 aa
Cleaved - prohormone
ER and golgi-hormone
Packaged in granules - 84 aa

140
Q

Describe the phases of bone absorption due to PTH

A

Rapid phase: begins in minutes - activation of the already existing bone cells (osteocytes) to promote Ca and phosphate absorption
Slow phase: several days or weeks- proliferation of the osteoclasts, followed by greatly increased osteoclastic reabsorption of bone

141
Q

How are osteocytes and osteoblasts activated by PTH?

A

They both have receptor proteins for binding PTH
PTH can activate calcium pump and cause rapid removal of calcium phosphate salts from those amorphous bone crystals that lie near the cells

142
Q

Describe the role of osteoclasts

A

They do not have membrane receptor proteins for PTH
The activated osteoblasts and osteocytes send secondary signals to osteoclasts.
Also receive signal from osteoprotegerin ligand which activates receptors on preosteoclast cells and transforms them into mature osteoclasts that remove bone over a period of weeks or months

143
Q

Describe effects of PTH on renal calcium reabsorption

A

Causes rapid loss of phosphate in the urine due to effect of hormone to diminish proximal tubular reabsorption of phosphate ions

Increases renal tubular reabsorption of calcium: occurs in late distal tubules and beyond
Diminishes phosphate reabsorption
INcreases rate of reabsorption of Mg and H ions
Decreases reabsorption of Na, K and aa ions

144
Q

What happens if PTH does not cause kidneys to increase Ca reabsorption?

A

Urine would eventually deplete both the extracellular fluid and the bones of Ca

145
Q

A large shar of the effect of PTH on its target organs is mediated by ______

A

cAMP

146
Q

What does the slightest decrease in Ca ion concentration in the extracellular fluid cause?

A

The parathyroid glands to increase their rate of secretion

147
Q

What are conditions that decrease Ca ion concentration?

A

Rickets
Pregnancy
Lactation

148
Q

What are conditions that increase the calcium ion concentration above normal( resulting in a reduced size of the parathyroid glands).

A

Excess quantities of Ca in the diet
Increased vitamin D in the diet
Bone absorption caused by other factors such as disease

149
Q

Describe calcitonin

A

Peptide hormone
Secreted by thryoid gland
Tends to decrease plasma Ca concentration
Synthesized in and secreted by parafollicular cells
Weak effect on plasma Ca concentration in the adult human
Any initial reduction of the calcium ion concentration caused by calcitonin leads within hours to a powerful stimulation of PTH secretion
In certain bone diseases, such as Paget disease, osteoclastic activity is greatly accelerated, and calcitonin has a more potent effect of reducing Ca absorption

150
Q

When does hypoparathyroidism occur?

A

When parathyroid glands do not secrete sufficient PTH

  • osteoclasts become almost totally inactive
  • calcium reabsorption from bones is depressed
  • blood ca levels decrease
  • parathyroid glands removed: Ca drops to 6/7 mg/dl within 2 to 3 days.
  • blood phosphate concentration may double
151
Q

What muscles are especially sensitive to tetanic spasms and spasms of these muscles obstruct respiration, which is the usual cause of death

A

laryngeal muscles bc of hypoparathyroidism and drop of Ca blood levels

152
Q

What is primary hyperparathyroidism?

A

An abnormality (usually a tumor) of the parathyroid glands causes inappropriate, excess PTH secretions

This is more prevalent in women because pregnancy and lactation stimulate the parathyroid glands and predispose to the development of such a tumor

153
Q

What is secondary hyperparathyroidism?

A

High levels of PTH occur as a compensation for hypocalcemia

Can be caused by vitamin D deficiency, which can lead to osteomalacia

154
Q

Aldosterone is the major mineralocorticoid and is secreted by what region of the adrenal cortex

A

Zona glomerulosa

155
Q

Cortisol secretion is controlled mainly by which factor?

A

ACTH

156
Q

Is hypernatremia a characteristic of lack of aldosterone?

A

No

157
Q

Adrenal diabetes may occur due to excess of what?

A

glucocorticoids

158
Q

Addison’s disease is due to a deficiency of what corticosteroids?

A

Mineralocorticoids

Glucocorticoids

Physiology II Test III (1 decks)

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