18. list the structural characteristics of a thrombocyte. describe how each characteristic relates to its function.
19. define hemostasis. list and describe the three steps that occur during hemostasis.
20. list and describe the 3 phases of coagulation.
21. differentiate between the intrinsic and extrinsic pathways.
22. briefly discuss the role each of the following play during the process of coagulation:
a. blood clotting factors
b. calcium
c. vitamin k
d. heparin
23. describe the abo and rh blood typing systems, blood transfusions, pregnancy, and blood typing. include the role antigens and antibodies play.
chapter 18: the cardiovascular system: the heart
24. list the functions of the cardiovascular system, including the blood, heart, and blood vessels.
25. diagram the blood flow the systemic, pulmonary, and coronary circuit.
26. briefly describe the size, location, and orientation of the heart.
27. diagram the layers covers of the pericardium.
28. diagram and structurally describe the layers of the heart wall.
29. describe the anatomy of the heart. include:
right and left atria
interventricular septum
papillary muscles
av valves
right and left ventricles
chordae tendineae
trabeculae carnae
semilunar valves
30. list and describe the great vessels entering and leaving the heart.
31. list the major coronary vessels.
32. identify and briefly describe the role of these two structures that are remnants of fetal circulation: fossa ovalis and ligamentum arteriosum.
33. diagram the flow of blood through the heart. be sure to include all major blood vessels, specify the direction of flow, and differentiate between oxygenated and deoxygenated blood.
34. list and discuss the function of the heart valves. describe the major heart sounds produced by closure

Question

Accepted Answer

# Brief Explanations:
### Question 18
Thrombocytes (platelets) are small, anucleate cell fragments. Their structural features support blood clotting:
1.  **Small, disc shape**: Lets them easily move through narrow blood vessels and accumulate at injury sites.
2.  **Glycoprotein surface receptors**: Bind to damaged vessel walls and other platelets to form clots.
3.  **Cytoplasmic granules (alpha, dense)**: Store clotting factors, calcium, and signaling molecules (like ADP) that trigger platelet activation and aggregation.
4.  **Contractile proteins (actin, myosin)**: Allow platelets to change shape (spreading) when activated, and shrink clots to stop bleeding.

### Question 19
**Hemostasis**: The body's process to stop bleeding from damaged blood vessels.
1.  **Vascular spasm**: Damaged vessels constrict, reducing blood flow to the injury. Triggered by vessel injury and platelet signaling.
2.  **Platelet plug formation**: Platelets stick to damaged vessel collagen, activate (change shape, release granules), and clump together to form a temporary plug.
3.  **Coagulation (blood clotting)**: Fibrin proteins form a mesh that traps blood cells and platelets, creating a stable clot to seal the injury.

### Question 20
The three phases of coagulation:
1.  **Activation of prothrombinase**: A cascade of reactions (intrinsic or extrinsic pathway) activates the enzyme prothrombinase.
2.  **Prothrombin conversion**: Prothrombinase converts prothrombin (a plasma protein) into thrombin (an active enzyme).
3.  **Fibrin formation**: Thrombin converts soluble fibrinogen into insoluble fibrin threads, which cross-link to form a clot mesh.

### Question 21
| Feature | Intrinsic Pathway | Extrinsic Pathway |
|---------|-------------------|-------------------|
| Trigger | Damage to blood vessel lining or contact with foreign surfaces | Tissue damage (release of tissue factor) |
| Reaction Speed | Slow (several minutes) | Fast (seconds) |
| Factors Involved | Factors XII, XI, IX, VIII | Tissue factor (Factor III), Factor VII |
| Location | Starts inside the bloodstream | Starts outside the bloodstream (tissue) |

### Question 22
a.  **Blood clotting factors**: Plasma proteins (numbered I-XIII) that act in a cascade; each activated factor triggers the next, leading to fibrin clot formation.
b.  **Calcium**: Required as a cofactor for multiple steps in both intrinsic and extrinsic coagulation pathways to activate clotting factors.
c.  **Vitamin K**: Necessary for the liver to produce functional clotting factors II, VII, IX, and X (deficiency leads to bleeding disorders).
d.  **Heparin**: An anticoagulant that inhibits thrombin activity, preventing fibrin formation and stopping unwanted clotting.

### Question 23
- **ABO System**: Based on antigens (A, B) on red blood cells (RBCs):
  - Type A: A antigens on RBCs, anti-B antibodies in plasma
  - Type B: B antigens on RBCs, anti-A antibodies in plasma
  - Type AB: A + B antigens, no anti-A/B antibodies (universal recipient)
  - Type O: No A/B antigens, anti-A + anti-B antibodies (universal donor)
  - Transfusion risk: Antibodies in recipient plasma attack mismatched antigens on donor RBCs, causing RBC rupture.
- **Rh System**: Based on the Rh(D) antigen on RBCs:
  - Rh-positive: Rh antigen present; Rh-negative: no Rh antigen, no natural anti-Rh antibodies.
  - **Pregnancy risk**: If Rh-negative mother carries Rh-positive fetus, mother may develop anti-Rh antibodies. In subsequent Rh-positive pregnancies, these antibodies can attack fetal RBCs (hemolytic disease of the newborn).
- **Blood typing**: Tests for presence of A/B/Rh antigens on RBCs, and corresponding antibodies in plasma, to determine safe transfusion matches.

### Question 24
- **Blood**: Transports oxygen, nutrients, waste, hormones; regulates pH/temperature; defends against infection; aids in clotting.
- **Heart**: Acts as a muscular pump to generate pressure and circulate blood through the body.
- **Blood vessels**:
  - Arteries: Carry oxygenated blood away from the heart to tissues.
  - Capillaries: Site of nutrient, gas, and waste exchange between blood and cells.
  - Veins: Carry deoxygenated blood back to the heart from tissues.

### Question 25
- **Systemic circuit**: Oxygenated blood leaves left ventricle → aorta → body arteries → capillaries (gas exchange) → body veins → venae cavae → right atrium.
- **Pulmonary circuit**: Deoxygenated blood leaves right ventricle → pulmonary trunk → pulmonary arteries → lung capillaries (oxygen pickup) → pulmonary veins → left atrium.
- **Coronary circuit**: Oxygenated blood from aorta → coronary arteries → heart muscle capillaries → cardiac veins → coronary sinus → right atrium (feeds the heart itself).

### Question 26
- **Size**: Roughly the size of a closed fist, ~250-350 grams in adults.
- **Location**: In the mediastinum (thoracic cavity), between the lungs, tilted left (2/3 of heart lies left of the midline).
- **Orientation**: Apex (bottom, pointed end) faces left/inferiorly; base (top, broad end) faces right/superiorly, where major blood vessels attach.

### Question 27
Pericardium layers (outer to inner):
1.  **Fibrous pericardium**: Tough, connective tissue outer layer; anchors the heart and prevents overfilling.
2.  **Serous pericardium**: Thin, double-layered membrane:
    - **Parietal layer**: Lines the inner surface of the fibrous pericardium.
    - **Visceral layer (epicardium)**: Covers the outer surface of the heart muscle.
    - **Pericardial cavity**: Space between parietal and visceral layers, filled with pericardial fluid to reduce friction.

### Question 28
Heart wall layers (outer to inner):
1.  **Epicardium**: Thin, outer layer (visceral pericardium); contains blood vessels and fat for heart muscle support.
2.  **Myocardium**: Thick, middle layer of cardiac muscle; contracts to pump blood; the thickest layer (thickest in left ventricle).
3.  **Endocardium**: Thin, inner layer of endothelial cells; lines heart chambers and valves, continuous with blood vessel endothelium.

### Question 29
- **Right/Left Atria**: Upper, thin-walled chambers that receive blood (right: deoxygenated from body; left: oxygenated from lungs).
- **Interventricular septum**: Thick muscle wall separating right and left ventricles, preventing oxygenated/deoxygenated blood mixing.
- **Papillary muscles**: Small, cone-shaped muscles in ventricles; contract during ventricular systole to pull on chordae tendineae.
- **AV valves**: Atrioventricular valves (mitral/bicuspid on left, tricuspid on right) that separate atria and ventricles; prevent backflow into atria when ventricles contract.
- **Right/Left Ventricles**: Lower, thick-walled chambers that pump blood (right: to lungs; left: to body; left ventricle wall is thickest for high pressure).
- **Chordae tendineae**: Cord-like tendons connecting papillary muscles to AV valves; hold valves closed during ventricular contraction.
- **Trabeculae Carnae**: Irregular muscle ridges on inner ventricular walls; help with ventricular contraction and prevent suction.
- **Semilunar valves**: Aortic (left ventricle to aorta) and pulmonary (right ventricle to pulmonary trunk) valves; prevent backflow into ventricles when they relax.

### Question 30
- **Entering the heart**:
  - Superior/inferior venae cavae: Carry deoxygenated blood from body to right atrium.
  - Pulmonary veins: Carry oxygenated blood from lungs to left atrium.
- **Leaving the heart**:
  - Pulmonary trunk: Splits into pulmonary arteries; carries deoxygenated blood from right ventricle to lungs.
  - Aorta: Carries oxygenated blood from left ventricle to the entire body.

### Question 31
Major coronary vessels:
- **Left coronary artery (LCA)**:
  - Anterior interventricular artery (left anterior descending): Feeds anterior left ventricle and interventricular septum.
  - Circumflex artery: Feeds left atrium and posterior left ventricle.
- **Right coronary artery (RCA)**:
  - Posterior interventricular artery: Feeds posterior ventricles and septum.
  - Marginal artery: Feeds right ventricle.
- **Coronary sinus**: Collects deoxygenated blood from cardiac veins and drains into the right atrium.

### Question 32
- **Fossa ovalis**: A thin, oval depression in the interatrial septum. It is the remnant of the foramen ovale, a fetal opening that allowed blood to bypass the non-functional lungs by flowing directly from right to left atrium.
- **Ligamentum arteriosum**: A fibrous cord connecting the pulmonary trunk to the aorta. It is the remnant of the ductus arteriosus, a fetal vessel that shunted blood from the pulmonary trunk to the aorta, bypassing the lungs.

### Question 33
Blood flow through the heart:
1.  Deoxygenated blood → superior/inferior venae cavae → right atrium
2.  Right atrium → tricuspid valve → right ventricle
3.  Right ventricle → pulmonary semilunar valve → pulmonary trunk → pulmonary arteries → lungs (oxygen pickup)
4.  Oxygenated blood → pulmonary veins → left atrium
5.  Left atrium → mitral (bicuspid) valve → left ventricle
6.  Left ventricle → aortic semilunar valve → aorta → body tissues

### Question 34
- **Heart valve function**: All valves prevent backflow of blood:
  - AV valves (mitral, tricuspid): Close during ventricular contraction to stop blood from flowing back into atria.
  - Semilunar valves (aortic, pulmonary): Close during ventricular relaxation to stop blood from flowing back into ventricles.
- **Heart sounds**:
  - **S1 (lub)**: Produced by closure of the AV valves at the start of ventricular contraction (systole).
  - **S2 (dub)**: Produced by closure of the semilunar valves at the start of ventricular relaxation (diastole).

# Answer:
All questions 18-34 are answered above in the corresponding sections.

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QUESTION IMAGE

Question

Explanation:

Question 18

Question 19

Question 20

Question 21

Question 22

Question 23

Answer:

Feature	Intrinsic Pathway	Extrinsic Pathway
Reaction Speed	Slow (several minutes)	Fast (seconds)
Factors Involved	Factors XII, XI, IX, VIII	Tissue factor (Factor III), Factor VII
Location	Starts inside the bloodstream	Starts outside the bloodstream (tissue)