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Blood Biochemistry: Hemoglobin, Blood Clotting and Oxygen Transport

February 22, 2025

Blood Biochemistry: The Role of Hemoglobin, Blood Clotting, and Oxygen Transport in Human Physiology

Introduction

Blood biochemistry is a crucial field of study in medical science, focusing on the molecular and cellular mechanisms that enable blood to perform its life-sustaining functions. Among the most critical aspects are hemoglobin, blood clotting, and oxygen transport, each playing an essential role in maintaining homeostasis. Understanding these processes provides insights into various medical conditions such as anemia, hemophilia, and thrombosis.

Role of hemoglobin in oxygen transport,
Steps of blood clotting process,
How blood carries oxygen,
Factors affecting hemoglobin function,
Blood coagulation disorders explained.

1. Hemoglobin: Structure, Function, and Importance

1.1 Structure of Hemoglobin

Hemoglobin (Hb) is a complex protein found in red blood cells (RBCs) that carries oxygen from the lungs to tissues and facilitates the return of carbon dioxide to the lungs for exhalation. It consists of:

Globin protein chains – Two alpha (α) and two beta (β) chains.
Heme group – Each globin chain contains a heme group with an iron (Fe²⁺) ion that binds to oxygen.

1.2 Functions of Hemoglobin

Oxygen Transport: Binds with oxygen in the lungs and releases it in tissues.
Carbon Dioxide Transport: Helps in removing CO₂ from the body.
Buffering pH: Maintains blood pH through the Bohr effect, where hemoglobin binds to protons (H⁺) and carbon dioxide, reducing oxygen affinity.

1.3 Hemoglobin Variants and Disorders

Fetal Hemoglobin (HbF): Found in newborns and has a higher oxygen affinity than adult hemoglobin.
Sickle Cell Hemoglobin (HbS): A mutation in the beta-globin gene results in deformed RBCs, causing sickle cell anemia.
Thalassemia: A genetic disorder causing inadequate or abnormal hemoglobin production.

2. Blood Clotting (Coagulation): Mechanism and Disorders

2.1 The Blood Clotting Cascade

Blood clotting, or coagulation, is a multi-step process that prevents excessive bleeding following vascular injury. The process involves three primary stages:

Vascular Spasm: Constriction of blood vessels to reduce blood loss.
Platelet Plug Formation: Platelets adhere to the exposed collagen fibers and release clotting factors.
Coagulation Cascade: Activation of clotting factors that convert prothrombin to thrombin, which then converts fibrinogen to fibrin, forming a stable clot.

2.2 Major Clotting Factors

Factor I (Fibrinogen)
Factor II (Prothrombin)
Factor VII (Proconvertin)
Factor VIII (Anti-hemophilic factor A)
Factor X (Stuart-Prower factor)

2.3 Disorders of Blood Clotting

Hemophilia: A genetic disorder causing deficiency in clotting factors VIII (Hemophilia A) or IX (Hemophilia B), leading to excessive bleeding.
Thrombosis: Formation of an abnormal blood clot in a blood vessel, potentially causing stroke or deep vein thrombosis (DVT).
Von Willebrand Disease: A bleeding disorder due to defective von Willebrand factor, which stabilizes clot formation.

3. Oxygen Transport and Regulation in Blood

3.1 Oxygen Binding and Release Mechanism

In the lungs, hemoglobin binds with oxygen to form oxyhemoglobin.
In tissues, oxygen is released due to:
- Lower oxygen concentration
- Increased carbon dioxide levels (Bohr effect)
- Lower pH and increased temperature (metabolically active tissues)

3.2 Role of Myoglobin in Oxygen Transport

Myoglobin is a muscle-specific oxygen-binding protein that acts as a reservoir for oxygen in muscle tissues.
It has a higher affinity for oxygen than hemoglobin, ensuring oxygen availability during intense physical activity.

3.3 Factors Affecting Oxygen Transport

Partial pressure of oxygen (pO₂): Determines hemoglobin saturation.
2,3-Bisphosphoglycerate (2,3-BPG): Reduces hemoglobin’s oxygen affinity, promoting oxygen release in tissues.
Carbon monoxide (CO) poisoning: CO binds with hemoglobin more tightly than oxygen, reducing oxygen delivery to tissues.

Conclusion

The biochemistry of blood is fundamental to life, ensuring oxygen transport, clotting, and cellular respiration. Understanding hemoglobin, coagulation, and oxygen dynamics is vital in diagnosing and treating various hematological disorders. Ongoing research in blood biochemistry provides better therapeutic approaches for conditions like anemia, clotting disorders, and hypoxia.

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MCQs on “Blood Biochemistry: Hemoglobin, Blood Clotting and Oxygen Transport”

1. Hemoglobin is primarily found in:

A) White blood cells
B) Plasma
C) Red blood cells ✅
D) Platelets

Explanation: Hemoglobin is a protein present in red blood cells (RBCs) that carries oxygen from the lungs to body tissues and transports carbon dioxide back to the lungs.

2. The iron-containing component of hemoglobin is called:

A) Globin
B) Heme ✅
C) Myoglobin
D) Ferritin

Explanation: Hemoglobin consists of four globin chains, each attached to a heme group, which contains an iron atom that binds oxygen.

3. Which form of hemoglobin has the highest oxygen affinity?

A) Adult hemoglobin (HbA)
B) Fetal hemoglobin (HbF) ✅
C) Hemoglobin S
D) Hemoglobin C

Explanation: Fetal hemoglobin (HbF) has a higher affinity for oxygen than adult hemoglobin (HbA), allowing the fetus to extract oxygen from the mother’s blood.

4. The Bohr effect describes:

A) Increased oxygen affinity of hemoglobin at high pH ✅
B) Decreased oxygen affinity at low CO₂ levels
C) The role of iron in hemoglobin
D) Oxygen dissociation in myoglobin

Explanation: The Bohr effect states that hemoglobin releases more oxygen in acidic conditions (low pH, high CO₂) and binds more oxygen in alkaline conditions (high pH, low CO₂).

5. The primary function of hemoglobin is:

A) Transporting lipids
B) Oxygen and carbon dioxide transport ✅
C) Blood clotting
D) Immune response

Explanation: Hemoglobin binds oxygen in the lungs and transports it to tissues, while also carrying carbon dioxide back to the lungs for exhalation.

6. What is the normal adult hemoglobin (Hb) level in males?

A) 10-12 g/dL
B) 13-18 g/dL ✅
C) 19-22 g/dL
D) 5-9 g/dL

Explanation: Normal hemoglobin levels in adult males range from 13-18 g/dL, while in females, it is 12-16 g/dL.

7. Oxygen is mainly transported in the blood by:

A) Plasma proteins
B) Hemoglobin ✅
C) White blood cells
D) Platelets

Explanation: About 98% of oxygen is transported by hemoglobin, while a small fraction dissolves in plasma.

8. Which molecule competes with oxygen for binding to hemoglobin?

A) Carbon dioxide
B) Carbon monoxide ✅
C) Nitrogen
D) Water

Explanation: Carbon monoxide (CO) binds to hemoglobin with 200 times more affinity than oxygen, forming carboxyhemoglobin, which impairs oxygen transport.

9. The clotting factor primarily responsible for forming a fibrin clot is:

A) Thrombin
B) Prothrombin
C) Fibrinogen ✅
D) Plasmin

Explanation: Fibrinogen (Factor I) is converted into fibrin by thrombin, forming a mesh-like structure that stabilizes the clot.

10. Which vitamin is essential for blood clotting?

A) Vitamin C
B) Vitamin D
C) Vitamin K ✅
D) Vitamin B12

Explanation: Vitamin K is necessary for synthesizing clotting factors like prothrombin, Factor VII, IX, and X in the liver.

11. The enzyme that converts fibrinogen to fibrin is:

A) Thrombin ✅
B) Plasmin
C) Trypsin
D) Lipase

Explanation: Thrombin (Factor IIa) catalyzes the conversion of fibrinogen into fibrin, which forms the structural framework of blood clots.

12. The anticoagulant heparin acts by inhibiting:

A) Platelets
B) Fibrin formation
C) Thrombin ✅
D) Plasmin

Explanation: Heparin enhances the activity of antithrombin III, which inhibits thrombin, preventing clot formation.

13. Which blood component initiates clot formation?

A) Platelets ✅
B) Red blood cells
C) Plasma
D) Neutrophils

Explanation: Platelets adhere to damaged blood vessels and release clotting factors that initiate the coagulation cascade.

14. The extrinsic pathway of blood clotting is triggered by:

A) Platelets
B) Tissue factor (Factor III) ✅
C) Collagen
D) Factor VIII

Explanation: Tissue factor (Factor III) is released from damaged tissues and initiates the extrinsic clotting pathway.

15. Hemophilia is caused by the deficiency of:

A) Factor IX
B) Factor VIII ✅
C) Factor X
D) Fibrinogen

Explanation: Hemophilia A is caused by Factor VIII deficiency, while Hemophilia B is due to Factor IX deficiency.

16. The major buffer system that maintains blood pH is:

A) Phosphate buffer
B) Protein buffer
C) Bicarbonate buffer ✅
D) Calcium buffer

Explanation: The bicarbonate (HCO₃⁻) buffer system maintains blood pH at 7.35-7.45 by balancing carbonic acid and bicarbonate levels.

17. The oxygen dissociation curve is shifted to the right by:

A) High pH
B) High CO₂ levels ✅
C) Low temperature
D) Low 2,3-BPG

Explanation: High CO₂, acidity, temperature, and 2,3-BPG shift the curve right, promoting oxygen release to tissues.

18. Which gas is carried primarily as bicarbonate ions in the blood?

A) Oxygen
B) Carbon dioxide ✅
C) Nitrogen
D) Helium

Explanation: 70% of CO₂ is transported as bicarbonate (HCO₃⁻) via the enzyme carbonic anhydrase.

19. The lifespan of red blood cells is approximately:

A) 60 days
B) 90 days
C) 120 days ✅
D) 150 days

Explanation: RBCs live for 120 days before being destroyed in the spleen and liver.

20. The most common type of hemoglobin in adults is:

A) HbA ✅
B) HbS
C) HbC
D) HbF

Explanation: HbA (Hemoglobin A) makes up 96-98% of adult hemoglobin, while HbA₂ and HbF are found in small amounts.

21. Which enzyme catalyzes the formation of carbonic acid (H₂CO₃) in red blood cells?

A) Catalase
B) Carbonic anhydrase ✅
C) Lipase
D) Peroxidase

Explanation: Carbonic anhydrase catalyzes the reversible reaction of CO₂ + H₂O → H₂CO₃, which helps in carbon dioxide transport.

22. The heme group in hemoglobin contains which metal ion?

A) Calcium
B) Magnesium
C) Iron ✅
D) Zinc

Explanation: Iron (Fe²⁺) in the heme group binds oxygen, allowing hemoglobin to transport oxygen in the blood.

23. Sickle cell anemia is caused by a mutation in which gene?

A) Albumin
B) Beta-globin ✅
C) Alpha-globin
D) Myoglobin

Explanation: Sickle cell disease results from a mutation in the HBB gene, leading to abnormal hemoglobin (HbS) formation.

24. Which form of hemoglobin is present in sickle cell disease?

A) HbA
B) HbS ✅
C) HbF
D) HbC

Explanation: In sickle cell anemia, hemoglobin HbS causes RBCs to assume a sickle shape, leading to blockage and reduced oxygen transport.

25. A lack of intrinsic factor leads to which type of anemia?

A) Iron-deficiency anemia
B) Aplastic anemia
C) Pernicious anemia ✅
D) Sickle cell anemia

Explanation: Intrinsic factor, secreted by the stomach, is required for vitamin B12 absorption. Its deficiency leads to pernicious anemia.

26. The primary site of erythropoiesis in adults is:

A) Liver
B) Kidney
C) Bone marrow ✅
D) Spleen

Explanation: Erythropoiesis (RBC production) occurs in the red bone marrow of long bones in adults.

27. Which of the following increases oxygen release from hemoglobin?

A) Decreased CO₂
B) Increased pH
C) Increased 2,3-BPG ✅
D) Low temperature

Explanation: 2,3-BPG (2,3-bisphosphoglycerate) binds to hemoglobin, reducing oxygen affinity and enhancing oxygen release to tissues.

28. Which condition results in excessive blood clotting?

A) Hemophilia
B) Thrombosis ✅
C) Anemia
D) Leukemia

Explanation: Thrombosis is the formation of abnormal blood clots that can block blood vessels, leading to conditions like stroke or heart attack.

29. Which clotting factor is also called Christmas Factor?

A) Factor V
B) Factor IX ✅
C) Factor X
D) Factor XIII

Explanation: Factor IX, also known as the Christmas Factor, is deficient in Hemophilia B.

30. Which anticoagulant prevents vitamin K-dependent clotting factor formation?

A) Heparin
B) Warfarin ✅
C) Aspirin
D) Streptokinase

Explanation: Warfarin inhibits the recycling of vitamin K, reducing the synthesis of clotting factors II, VII, IX, and X.

31. Myoglobin differs from hemoglobin in that:

A) It binds oxygen more strongly ✅
B) It is present in red blood cells
C) It transports carbon dioxide
D) It has four heme groups

Explanation: Myoglobin, found in muscles, has a higher oxygen affinity than hemoglobin and functions as an oxygen reserve.

32. What is the function of plasmin?

A) Clot formation
B) Fibrin degradation ✅
C) Platelet aggregation
D) Red blood cell formation

Explanation: Plasmin breaks down fibrin, dissolving clots in a process called fibrinolysis.

33. The enzyme responsible for converting prothrombin to thrombin is:

A) Plasmin
B) Factor X ✅
C) Factor VIII
D) Carbonic anhydrase

Explanation: Activated Factor X (Xa), along with calcium and phospholipids, converts prothrombin to thrombin, triggering clot formation.

34. What is the oxygen-binding capacity of one hemoglobin molecule?

A) 1 oxygen molecule
B) 2 oxygen molecules
C) 4 oxygen molecules ✅
D) 8 oxygen molecules

Explanation: Each hemoglobin molecule has four heme groups, allowing it to bind four oxygen (O₂) molecules.

35. The function of von Willebrand factor (vWF) is to:

A) Activate thrombin
B) Bind platelets to damaged vessels ✅
C) Break down fibrin
D) Convert fibrinogen to fibrin

Explanation: vWF helps platelets adhere to the endothelium, stabilizing Factor VIII and initiating clot formation.

36. The primary site of hemoglobin breakdown is:

A) Kidney
B) Bone marrow
C) Liver and spleen ✅
D) Lungs

Explanation: Aged RBCs are broken down in the liver and spleen, where hemoglobin is converted into bilirubin.

37. Hemoglobin’s ability to bind oxygen is influenced by:

A) CO₂ levels
B) pH
C) Temperature
D) All of the above ✅

Explanation: Oxygen binding to hemoglobin is regulated by CO₂ concentration, pH (Bohr effect), temperature, and 2,3-BPG levels.

38. Which protein stores iron in the body?

A) Myoglobin
B) Transferrin
C) Ferritin ✅
D) Hemoglobin

Explanation: Ferritin is the major iron-storage protein, while transferrin transports iron in the blood.

39. Hemoglobin is made up of:

A) 1 alpha and 1 beta chain
B) 2 alpha and 2 beta chains ✅
C) 4 gamma chains
D) 3 alpha and 1 beta chain

Explanation: Hemoglobin A (HbA) consists of 2 alpha and 2 beta globin chains.

40. Which form of hemoglobin is predominant in a newborn?

A) HbA
B) HbF ✅
C) HbC
D) HbS

Explanation: Fetal hemoglobin (HbF) predominates in newborns, gradually replaced by HbA after birth.

41. The oxygen dissociation curve for hemoglobin is:

A) Linear
B) Hyperbolic
C) Sigmoidal ✅
D) Parabolic

Explanation: Hemoglobin shows a sigmoidal (S-shaped) curve due to cooperative oxygen binding.

42. Which disorder is caused by excess bilirubin in the blood?

A) Thrombosis
B) Jaundice ✅
C) Hemophilia
D) Leukemia

Explanation: Jaundice occurs when excess bilirubin accumulates, leading to yellowing of skin and eyes.

43. Which of the following enhances oxygen delivery to tissues?

A) High pH
B) Low temperature
C) Increased 2,3-BPG ✅
D) Low CO₂

Explanation: 2,3-BPG reduces hemoglobin’s oxygen affinity, helping release oxygen in tissues.