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Val 307 > Red Blood Cells > Flashcards

Red Blood Cells Flashcards

1
Q

What is the shape of RBCs? What is the function of their shape?

A
  • Biconcave and disk-like
  • Allows them to squeeze through small capillaries
  • Low volume and high-surface area, which renders them more efficient in gas exchange
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2
Q

What percentage of blood volume is composed of erythrocytes?

A

40%

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3
Q

What percentage of RBCs by weight is hemoglobin?

A

35%

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4
Q

What percentage of the RBCs dry-matter is composed of hemoglobin?

A

96%

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5
Q

What is hemoglobin composed of?

A
  • Four polypeptide chains
  • Two alpha chains
  • Two beta chains
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6
Q

What is each globin chain composed of?

A
  • Each globin chain possesses a heme molecule

- At the center of the four nitrogens within a heme molecule fits an iron atom

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7
Q

Why is histidine a key amino acid in hemoglobin?

A

Histidine binds iron and stabilizes the molecule within the heme ring

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8
Q

What is oxyhemoglobin?

A
  • Contains iron and binds oxygen

- Red tint, which makes oxygen-rich arterial blood red

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9
Q

What is deoxyhemoglobin?

A
  • Oxygen is not bound in deoxyhemoglobin

- Venous blood is a darker shade of purple

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10
Q

What is a pulse oxymeter? What does it measure in healthy individuals?

A
  • Measures the percentage of oxyhemoblogin and deoxyhemoglobin based on their differences in colour
  • The regular reading is 97%, which means that 97% of hemoglobin within capillaries is oxidized
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11
Q

What occurs to the pulse oxidation value if there are issues transporting oxygen?

A

Decreases to below 90%, which indicates respiratory distress

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12
Q

How is it possible for an individual to have a 97% reading from the pulse oxymeter, and still not be able to get enough oxygen to their tissues?

A
  • If they are anemic, or histidine deficient, they are able to bind oxygen, but there is not enough hemoglobin to transport oxygen to peripheral tissues
  • The existing hemoglobin molecules may all be filled with oxygen, giving a high oximeter reading
  • But there are not enough hemoglobin molecules to carry the needed oxygen to the tissues
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13
Q

What is carboxyhemoglobin?

A

Binds carbon monoxide

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14
Q

How does carbon monoxide poisoning occur?

A

CO binds to hemoglobin 250 times stronger than oxygen binds, which means that CO does not let go to allow oxygen to replace it

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15
Q

Which form of hemoglobin may not be differentiated from oxyhemoglobin through a blood sample?

A

Carboxyhemoglobin, as it is extremely red

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16
Q

What is carbaminohemoglobin?

A

Binds CO2

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17
Q

What percentage of CO2 is transported via hemoglobin? Where is the rest contained?

A
  • 10% is transported via hemoglobin

- The rest is contained within bicarbonate

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18
Q

Which vasodilator may be carried bound to hemoglobin? What is its function?

A
  • Nitric oxide
  • Efficient strategy that allows the release of NO within capillaries if oxygen levels are low, providing an increased efficiency in oxygen transport
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19
Q

What is met-hemoglobin?

A

Contains iron oxidized to the ferric (Fe3+) state, and is a brown colour

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20
Q

What is fetal hemoglobin?

A
  • Contains two alpha-chains and two gamma-chains

- More efficient at picking up oxygen, which is necessary as it is getting oxygen from the maternal blood

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21
Q

What occurs in the months following birth?

A

Fetal hemoglobin is broken down, and new RBCs with regular adult hemoglobin are made

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22
Q

How is glucose transported into erythrocytes?

A

GLUT1

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23
Q

What is hemoglobin A1c a marker for?

A

Monitoring tool of long-term glucose control since red blood cells have a life-span of 120 days

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24
Q

What activates glucose within an erythrocyte?

A

Hexokinase converts glucose to glucose-6-phosphate

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25
Q

What occurs from the reduction of met-hemoglobin? By what?

A
  • Forms hemoglobin

- By NADH

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26
Q

The levels of which glycolytic intermediate controls how easy it is to release oxygen to tissues?

A

1,3-diphosphoglycerate

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27
Q

What is the most common genetic disease? What kind of genetic disease is it?

A
  • Glucose-6-phosphate dehydrogenase deficiency

- X-linked recessive (more common in men)

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28
Q

What is the function of glucose-6-phosphate dehydrogenase?

A
  • Key enzyme that brings glucose to the pentose phosphate pathway to maintain the reducing equivalence of NADPH
  • NADPH allows glutathione to be reduced to its active form to destroy free radicals and maintain the integrity of the cell
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29
Q

What is the primary issue with G6PD deficiency?

A

Glutathione cannot be regenerated, and the redox status of the cell may no longer be controlled

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30
Q

What are consequences of G6PD deficiency?

A
  • Stresses causing oxidative stress affect the stability of the RBC (no glutathione to control oxidative stress), which causes hemolytic anemia
  • The increase in breakdown of RBCs causes an increased production of bilirubin
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31
Q

What issues with the liver may arise with G6PD deficiency?

A

Jaundice due to the increased production of bilirubin

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32
Q

What dietary substance worsens oxidative stress caused by G6PD deficiency?

A

Fava beans

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33
Q

What explains the commonality of G6PD deficiency?

A

RBCs are not hospitable to the malaria parasite, reducing their likelihood to acquire malaria

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34
Q

Differentiate sickle cell anemia and G6PD deficiency.

A
  • Sickle cell anemia occurs due to an SNP in a hemoglobin molecule
  • G6PD deficiency occurs due to multiple SNPs in the gene encoding the enzyme within an RBC
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35
Q

What is the reduced form of iron? What is the oxidized form of iron?

A
  • Ferrous is reduced (Fe2+)

- Ferric is oxidized (Fe3+)

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36
Q

Under what form is iron absorbed in the small intestine? How is it stored within the enterocyte?

A
  • Absorbed through a transporter as Fe2+

- Stored within enterocytes bound to ferritin, under the Fe3+ form

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37
Q

Why is iron always bound to proteins?

A
  • Free minerals are toxic

- Free iron is a very potent pro-oxidant

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38
Q

How does iron escape the enterocyte to enter circulation? What occurs afterwards?

A
  • Fe2+ crosses the basolateral membrane through ferroportin

- Fe2+ is then converted to Fe3+, which binds to transferrin in plasma

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39
Q

How many transferrin iron-binding sites are there? How many iron molecules are normally bound? Under what form?

A
  • Transferrin possesses 6 binding sites

- Two Fe3+ molecules are normally bound

40
Q

Where does transferrin transport iron?

A

To the bone marrow where RBCs are made

41
Q

Where are RBCs catabolized? What happens to each component?

A
  • In the liver
  • Amino acids are recycled
  • Heme is metabolized to bilirubin, which may be excreted in bile or urine
  • Iron is recycled to transferrin, or stored in the liver bound to ferritin
42
Q

How is anemia diagnosed? What is the quantity for men and women?

A
  • Based on low-hemoglobin levels
  • Men: fewer than 140 grams/L
  • Women: fewer than 120 grams/L
43
Q

How should anemia be diagnosed prior to compromised function?

A
  • Measuring plasma ferritin (biomarker for liver ferritin, which decreases during depletion of iron stores)
  • Measuring transferrin (decreased saturation)
44
Q

What are the four sequential changes with development of iron deficiency?

A

1) Depletion of iron stores
2) Changes in iron transport
3) Defective erythropoiesis
4) Iron deficiency anemia

45
Q

What is an indicator of the depletion of iron stores?

A

Decreased plasma ferritin

46
Q

What occurs during changes in iron transport?

A
  • Increased absorption efficiency
  • Increased transferrin iron binding
  • Decreased transferrin saturation percentage
  • Increased transferrin receptors on the bone marrow
47
Q

What occurs during defective erythropoiesis?

A

Heme is not produced from protoporphyrin, causing free erythrocyte protoporphryin

48
Q

What are the characteristics of iron-deficient erythrocytes?

A
  • Microcytic (smaller)

- Hypochromic (paler)

49
Q

What are the four causes of iron deficiency?

A

1) Decreased dietary iron
2) Inhibition of absorption
3) Increased red blood cell mass
4) Increased losses

50
Q

What might inhibit iron absorption?

A
  • Mineral interactions (calcium and zinc supplements)

- Absorption inhibitors

51
Q

When would increased red blood cell mass cause iron deficiency?

A

During pregnancy or growth

52
Q

When would increased losses cause iron deficiency?

A
  • GI bleeding: early sign of undiagnosed colon cancer or an ulcer
  • Heavy menstrual losses (RDA of iron for women is twice the amount of men)
53
Q

What percentage of iron intake is absorbed overall?

A

10-15%

54
Q

How is the efficiency of iron absorption increased in the deficient state?

A
  • Increasing synthesis of intestinal ferric reductase
  • Increasing synthesis of divalent (Fe2+) metal transporter on the brush border of enterocytes
  • Increasing synthesis of ferroportin on the basolateral surface of enterocytes
55
Q

If there is a problem with iron deficiency, why don’t we add more iron to wheat flour and pasta fortifications?

A

Because of the frequency of the genetic disease hemochromatosis

56
Q

What percentage of heme iron is absorbed? What percentage of non-heme iron is absorbed?

A
  • Heme iron: 25% absorbed

- Non-heme iron: 1 to 50% (10% average)

57
Q

What substances aid in the absorption of non-heme iron? Why?

A
  • Substances that reduce iron to Fe2+ (orange juice, vitamin C)
  • Because iron is absorbed as reduced ferrous iron (Fe2+) and NOT as Fe3+ (oxidized ferric iron)
58
Q

Which compounds in the diet inhibit the absorption of non-heme iron?

A
  • Polyphenols
  • Tannins
  • Phytates
  • Oxalates
59
Q

What is the RDA for iron of men and women?

A
  • Men: 8 mg/d

- Women: 18 mg

60
Q

What indicates that iron deficiency is not an issue for men? What indicates that it is for women?

A
  • Men: for all stages of life, intake is greater then the RDA
  • Women: prior to menopause (and after menarche), the RDA is substantially higher than the actual intake
61
Q

What is ferroportin?

A

Iron transporter on the basolateral membrane of enterocytes and reticuloendothelial cells

62
Q

What is hepcidin?

A
  • Peptide hormone produced in the liver

- Decreases ferroportin, which makes it harder for iron to get out of stores for absorption

63
Q

What occurs to hepcidin during iron deficiency?

A
  • Lower capability to transport oxygen, which signals the liver to decrease hepcidin synthesis
  • A lower hepcidin level increases ferroportin, iron absorption, and iron release from stores
  • More iron is available to synthesize red blood cells
64
Q

What other factors increase hepcidin synthesis?

A
  • Infections and chronic inflammatory diseases

- Cytokines, particularly IL-6, increase hepcidin and transferrin

65
Q

What is the rationale behind increasing hepcidin synthesis during an infection or an inflammatory disease?

A
  • Iron causes oxidative stress and it may be a limiting nutrient in bacterial infections
  • The strategy is to limit iron supply or to keep it tied-up in stores to prevent bacteria from accessing iron (achieved through hepcidin and transferrin)
66
Q

Is iron overload and toxicity more common than iron deficiency in men?

A

Yes

67
Q

What is hemochromatosis? How many types are there?

A
  • Genetic autosomal recessive disease characterized by a chronic overload of iron accompanied by tissue damage and oxidative stress, along with high iron stores in the liver and spleen
  • There are 5 types
68
Q

What causes very efficient iron transport in hemochromatosis?

A

Decreased hepcidin synthesis increases ferroportin synthesis

69
Q

What causes cirrhosis in hemochromatosis?

A

Iron deposition as hemosiderin in the liver

70
Q

What is the treatment for hemochromatosis?

A
  • Drugs that bind iron, preventing its high absorption

- Consuming low-iron products

71
Q

What part of iron metabolism is regulated? What isn’t regulated?

A
  • Iron excretion is NOT regulated

- Iron absorption is regulated

72
Q

What hormone is synthesized in response to decreased oxygen supply? What organ synthesizes the hormone? What is its function?

A
  • Erythropoietin is synthesized by the kidney

- Protein hormone that acts in the bone marrow to increase erythropoiesis (maturation of RBCs from stem cells)

73
Q

Describe two methods of illegal blood doping.

A
  • Injecting EPO

- Extracting blood to freeze and then re-infusing back into their body

74
Q

What occurs to erythropoietin if an individual donates blood?

A

Erythropoietin synthesis increases

75
Q

What occurs to erythropoietin at a higher altitude?

A
  • Erythropoietin synthesis increases

- Higher hemoglobin and hematocrit

76
Q

Which amino acid and TCA cycle intermediate is heme composed of? What do they combine to form?

A
  • Glycine and succinyl-CoA

- Combine to form aminolevulinate (ALA)

77
Q

Describe the synthesis of heme.

A

1) Glycine and succinyl-CoA form aminolevulinate (ALA)
2) ALA forms porphobilinogen
3) Porphobilinogen forms the linear tetrapyrole
4) Linear tetrapyrole forms a ring (uroporphobilinogen)
5) Ferrochelase places an iron in the center of the ring, producing heme

78
Q

What are porphyria diseases?

A

Accumulation of porphyrin intermediates

79
Q

What is acute intermittent porphyria? What is it characterized by?

A
  • Results from a deficiency in PBG deaminase (porphobilinogen to linear tetrapyrole)
  • Neurological and psychological disturbances
80
Q

What is porphyria cutanea tarda? What is it characterized by?

A
  • Results from a deficiency in UPG decarboxylase (uroporphyrinogen to coproporphyrinogen)
  • Skin issues, such as blistering upon contact with light, dark pigmentation, and increased hair growth upon exposure to light
  • Tend to avoid daylight, causing a pale skin colour
  • Are behind the legends of werewolves
81
Q

What is the molecular cause of sickle cell anemia?

A
  • Single SNP (glutamate substitution for valine) in a globin chain of the hemoglobin molecule
  • Glutamate is a carboxylic acid, possessing a negatively charged carboxylic group, while valine is a hydrocarbon and non-polar
82
Q

What are the consequences of sickle cell anemia in homozygotes?

A
  • Hemoglobin polymerizes when oxygen concentration is low, which prevents the cells from carrying oxygen, causing the cells to sickle
  • Sickled red blood cells may become stuck within capillaries, causing ischemia due to the inability to provide sufficient oxygen to tissues
83
Q

What explains the commonality of sickle cell anemia?

A

Heterozygotes are resistant to malaria, which is a survival advantage

84
Q

Is heme soluble or insoluble?

A

Insoluble

85
Q

What occurs when the heme releases iron? What happens to the iron?

A
  • Heme is converted to biliverdin

- Iron is either stored bound to ferritin, or transported via transferrin to the bone marrow

86
Q

What is biliverdin metabolized to in the liver?

A
  • Bilirubin, which is an insoluble, toxic waste product

- Bilirubin cannot be recycled, and must be excreted

87
Q

How is bilirubin transported in the blood?

A

Bound to albumin

88
Q

What occurs to bilirubin in the liver?

A

Conjugated with glucuronic acid to form bilirubin diglucuronide, which is transported to the intestine for excretion in bile

89
Q

What may occur to bilirubin in the intestine?

A
  • May be acted on by the gut microbiota
  • Reabsorbed and secreted within urine (urobilin)
  • Excreted in feces (stercobilin)
90
Q

What is jaundice? What is it also known as?

A
  • Also known as icterus

- Characterized by a yellowish pigmentation of the skin or whites of the eyes due to high bilirubin levels

91
Q

What is the cause of pre-hepatic jaundice?

A
  • Caused by a large production of biliverdin due to an increased destruction of RBCs
  • Due to malaria or G6PD deficiency
92
Q

What is the cause of hepatic jaundice?

A
  • Caused by liver disease (hepatocellular)
  • Hepatitis, cirrhosis, alcoholic liver disease
  • Reduces the ability of the liver to metabolize or excrete bilirubin
93
Q

What is the cause of post-hepatic jaundice?

A
  • Due to an issue with bile drainage (obstructive)

- Biliary atresia, causing cholestasis, inhibiting bile flow to the duodenum

94
Q

What is cholestasis? How is it diagnosed?

A
  • A condition in which the components of bile are confined to the liver and cannot flow to the duodenum
  • Diagnosed by pale feces (due to a lack of pigment in the intestine) and dark urine
95
Q

Why do neonates frequently possess jaundice? What is the treatment?

A
  • Due to a production of bilirubin greater than their capacity to metabolize
  • The treatment aims to destroy bilirubin via ultraviolet light

Val 307 (15 decks)

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