Biochemistry Exam 3: Hemostasis & Clotting

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Questions and Answers

What is a common symptom associated with Addison's disease?

Excessive sweating

Muscle weakness (correct)

High blood pressure

Increased appetite

How do glucocorticoids influence phospholipase A2 (PLA2) activity?

They have no effect on PLA2 activity

They decrease PLA2 activity (correct)

They completely inhibit PLA2 activity

They increase PLA2 activity

Which eicosanoid is synthesized by platelets and increases platelet aggregation?

Prostacyclin

Leukotrienes

Thromboxane (correct)

Arachidonic acid

What effect does aspirin have on cyclo-oxygenase (COX)?

It irreversibly inhibits COX Signup and view all the answers

What is a key feature of collagen's molecular structure?

Triple-helical structure Signup and view all the answers

What vitamin is essential for post-translational modifications of prolines and lysines in collagen synthesis?

Vitamin C Signup and view all the answers

What condition results from vitamin C deficiency related to collagen synthesis?

Scurvy Signup and view all the answers

How does glycine contribute to the structure of collagen?

Forms tightly packed turns Signup and view all the answers

What is the primary action of heparin as an anticoagulant?

Binds to antithrombin to enhance its action Signup and view all the answers

Which coagulation factor is involved in the PT test?

Factor VII Signup and view all the answers

What characterizes Glanzman's thrombasthenia?

Defective fibrinogen receptors Signup and view all the answers

What is the primary function of platelets during hemostasis?

Form a platelet plug Signup and view all the answers

What does a prolonged prothrombin time indicate?

Vitamin K deficiency or warfarin use Signup and view all the answers

What triggers the activation of platelets?

Contact with subendothelial collagen Signup and view all the answers

What is the primary purpose of the bleeding time test?

To measure platelet plug formation and blood vessel constriction Signup and view all the answers

Which substance is added to the blood during the PT test to initiate clotting?

Tissue factor (thromboplastin) Signup and view all the answers

Which of the following substances inhibit platelet aggregation?

Prostaglandin I2 (PGI2) Signup and view all the answers

What common condition is indicated by petechiae?

Platelet deficiency Signup and view all the answers

What is the consequence of irreversible activation of a platelet?

Platelet shape changes and new receptors appear Signup and view all the answers

What does the PTT test primarily evaluate?

Intrinsic pathway of coagulation Signup and view all the answers

What occurs during the vasoconstriction phase of hemostasis?

Instantaneous reduction of blood loss Signup and view all the answers

What role does fibrinogen play in platelet aggregation?

Acts as a non-covalent bond between platelets Signup and view all the answers

What happens to a platelet during activation?

Its cytoskeleton rearranges, changing its shape Signup and view all the answers

Which of the following is not involved in hemostasis?

Activation of megakaryocytes Signup and view all the answers

What effect does lead have on ferrochelatase during heme synthesis?

Replaces Fe2+ in ferrochelatase Signup and view all the answers

What is the consequence of heme synthesis deficiency?

Microcytic anemia Signup and view all the answers

How does hepcidin regulate iron uptake in the body?

Downregulates ferroportin Signup and view all the answers

What is the fate of free iron in the body?

It is kept at low levels due to its toxicity. Signup and view all the answers

What does the degradation of heme produce?

Biliverdin and bilirubin Signup and view all the answers

Why is bilirubin accumulation problematic?

It leads to jaundice when accumulated. Signup and view all the answers

What is the primary role of transferrin in iron metabolism?

To transport iron from blood into cells Signup and view all the answers

How is d-ala synthesized affected by lead poisoning?

It becomes a neurotoxin particularly in developing brains. Signup and view all the answers

Which enzyme is primarily responsible for breaking down starch in the saliva?

Amylase Signup and view all the answers

What is the main role of lactoferrin in saliva?

Sequestering iron from microorganisms Signup and view all the answers

What happens to dental enamel when the pH drops below 5.5?

Net demineralization begins Signup and view all the answers

Which immunoglobulin class is the most important defense mechanism in saliva?

IgA Signup and view all the answers

What structural feature distinguishes the organization of enamel rods?

Perpendicular orientation to the enamel surface Signup and view all the answers

What is the main consequence of an acidic environment for dental enamel?

Acidic environment leads to demineralization Signup and view all the answers

Which gland is responsible for producing watery, amylase-rich saliva?

Parotid gland Signup and view all the answers

How does salivary lysozyme protect against bacterial infection?

By hydrolyzing B-1,4-glycosidic bonds Signup and view all the answers

What effect does estrogen have on bone density?

Decreases the production of interleukin-6, reducing bone resorption. Signup and view all the answers

Which function of calcium is involved in cell signaling?

Activation of blood platelets. Signup and view all the answers

How does parathyroid hormone (PTH) regulate calcium levels in the body?

Promotes calcium absorption in the intestines. Signup and view all the answers

What is the role of osteoclasts in bone remodeling?

They are involved in bone resorption through matrix erosion. Signup and view all the answers

Which hormone is released in response to low blood calcium levels?

Parathyroid hormone (PTH). Signup and view all the answers

What is the role of vitamin D in calcium homeostasis?

It enhances calcium absorption in the intestine. Signup and view all the answers

What is the consequence of high calcium levels in the blood?

It inhibits PTH release. Signup and view all the answers

Which of the following conditions promotes osteoclast activity?

Immobilization and continuous PTH. Signup and view all the answers

Study Notes

Biochemistry Exam 3 Study Notes

Hemostasis and Blood Clotting:
Clotting begins with physical aggregation of platelets at the site of injury.
Platelets are small, non-nucleated cells formed from megakaryocytes.
Inactive platelets have surface receptors for molecules like collagen, thromboxane A2 (TXA2), and ADP.
Activation of these receptors triggers a cascade of events leading to clot formation, including vasoconstriction, platelet aggregation, and the coagulation cascade.
Platelet activation is an irreversible process.
Inactive platelets are inhibited by PGI2 and cyclic AMP.
Active platelets are stimulated by TXA12 and ADP which promote coagulation.
Blood clotting can be triggered by external trauma or internal injury to the endothelial layer.
Key steps in clot formation include vasoconstriction, platelet plug formation, and the coagulation cascade.
Role of Calcium and Vitamin K in Blood Clotting:
Calcium is essential for clotting.
Clotting factors that bind calcium all have modified amino acids.
Vitamin K is a cofactor for gamma-carboxylation of clotting factors.
Clotting factors not gamma carboxylated cannot bind calcium and are therefore not active in the clotting process.
Anticoagulants:
Antithrombin III is a natural inhibitor of coagulation.
Heparin catalyzes the irreversible inactivation of thrombin and factor Xa
Aspirin and warfarin are two drugs that inhibit coagulation.
Warfarin is a vitamin K antagonist, slowing clotting factor synthesis in the liver.
Fibrinolysis is the breakdown of vascular clots.
Blood Clotting Tests:
PT (Prothrombin Time) tests the extrinsic pathway.
PTT (Partial Thromboplastin Time) tests the intrinsic pathway.
These tests are used to evaluate coagulation factors.
Heme Biosynthesis:
Heme is a prosthetic group for proteins involved in oxygen transport and electron transfer.
The porphyrin ring is made up of 4 pyrrole rings with an iron center.
Heme synthesis is carried out in mitochondria and cytoplasm
Specific steps of heme synthesis require specific enzymes.
Key enzymes include δ-aminolevulinate synthase, porphobilinogen deaminase, and ferrochelatase
Heme synthesis is regulated differently in liver and bone marrow.
Free heme inhibits d-aminolevulinate synthase.
Lead poisoning inhibits δ-aminolevulinate dehydratase and ferrochelatase.
Iron Uptake, Transport, and Storage:
Iron is essential for heme synthesis.
Iron absorption in the intestine is highly inefficient with control of transfer into blood via transferrin.
The concentration of transferrin controls iron levels, via iron-binding or storage in the liver (ferritin) and cells.
Hemoglobin Breakdown:
Hemoglobin is broken down in macrophages in the liver and spleen.
The porphyrin ring is partially degraded.
The components (iron, globin) are recycled.
Bilirubin Metabolism:
Bilirubin is a byproduct of heme degradation.
Bilirubin is initially unconjugated (insoluble in water)
Unconjugated bilirubin is transformed into conjugated bilirubin (soluble in water) primarily in the liver.
Conjugated bilirubin is excreted in the bile.
The insoluble bilirubin is metabolized further in the gut into stercobilin, which gives feces its color.
Neonatal Jaundice:
Bilirubin is a toxic substance.
High bilirubin levels can cause damage to the central nervous system in neonates who lack a blood-brain barrier.
Phototherapy is typically used to treat jaundice by converting bilirubin to more water-soluble forms in infants

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Prepare for your Biochemistry Exam 3 with a focus on hemostasis and blood clotting. This quiz covers essential topics such as platelet function, the coagulation cascade, and the crucial roles of calcium and vitamin K in the clotting process. Test your knowledge and ensure you're ready for the exam!