Laboratory Practical Study Guide: Blood, Heart, and Circulation

Blood Typing and Histology

Blood Cell Identification

Understanding the cellular components of blood is essential for recognizing normal and abnormal blood samples under the microscope.

• Red Blood Cells (Erythrocytes): Biconcave, anucleate cells responsible for oxygen transport.

• White Blood Cells (Leukocytes): Five main types, each with distinct morphology and function:

  • Neutrophils: Multi-lobed nucleus, pale granules; 50-70% of leukocytes.

  • Lymphocytes: Large, round nucleus, scant cytoplasm; 20-40%.

  • Monocytes: Kidney-shaped nucleus, abundant cytoplasm; 2-8%.

  • Eosinophils: Bilobed nucleus, red-orange granules; 1-4%.

  • Basophils: Bilobed or S-shaped nucleus, dark blue granules; 0.5-1%.

• Platelets (Thrombocytes): Small, anucleate cell fragments involved in clotting.

Example: In a typical blood smear, neutrophils are the most abundant white blood cells observed.

Blood Typing (ABO and Rh Systems)

Blood type is determined by the presence or absence of specific antigens on the surface of red blood cells and corresponding antibodies in the plasma.

• ABO System: Four main blood types: A, B, AB, O.

• Rh Factor: Presence (+) or absence (−) of the D antigen.

• Antigens: Proteins on RBCs (A, B, Rh).

• Antibodies: Found in plasma; react against absent antigens.

Blood Type	Antigens on RBCs	Antibodies in Serum
A	A	Anti-B
B	B	Anti-A
AB	A, B	None
O	None	Anti-A, Anti-B

• Transfusion Reactions: Occur if incompatible blood types are mixed, leading to agglutination and hemolysis.

Example: A person with type A blood has A antigens and anti-B antibodies; receiving type B blood would cause a transfusion reaction.

Heart Histology and Anatomy

Cardiac Muscle Histology

Cardiac muscle tissue is specialized for continuous, rhythmic contraction.

• Striated fibers with centrally located nuclei.

• Intercalated discs connect cells, allowing synchronized contraction.

Example: Under the microscope, intercalated discs appear as dark lines between cardiac muscle cells.

Heart Anatomy

The heart consists of four chambers and associated valves, with distinct structures for fetal and adult circulation.

• External Structures: Apex, aorta, right/left atria, right/left ventricles, pulmonary trunk, brachiocephalic trunk, superior vena cava.

• Internal Structures: Right/left atria, right/left ventricles, bicuspid (mitral) valve, tricuspid valve, chordae tendineae, papillary muscles, interventricular septum, pulmonary and aortic semilunar valves, pectinate muscles.

• Fetal Circulation: Structures such as the foramen ovale and ductus arteriosus aid in fetal blood flow; these become the fossa ovalis and ligamentum arteriosum in adults.

Example: The bicuspid (mitral) valve is located between the left atrium and left ventricle.

Blood Flow Pathway

Blood flows through the heart in a specific sequence to ensure oxygenation and systemic delivery.

• Right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary trunk → lungs → left atrium → bicuspid (mitral) valve → left ventricle → aortic valve → aorta → systemic circulation.

Blood Vessels: Histology and Anatomy

Arteries and Veins: Histology

Arteries and veins have distinct structural layers (tunics) visible under the microscope.

• Tunica intima: Endothelial lining.

• Tunica media: Smooth muscle (thicker in arteries).

• Tunica externa (adventitia): Connective tissue.

• Arteries: Thicker walls, rounder lumen, more elastic tissue.

• Veins: Thinner walls, larger, irregular lumen, valves present.

Example: The tunica media is much thicker in arteries than in veins, allowing them to withstand higher pressure.

Major Arteries and Veins

Knowledge of the major arteries and veins is essential for understanding systemic and pulmonary circulation.

• Arteries above the diaphragm: Ascending aorta, aortic arch, thoracic aorta, pulmonary trunk, brachiocephalic trunk, right/left common carotid, subclavian, axillary, brachial arteries.

• Arteries below the diaphragm: Abdominal aorta, right/left renal, internal/external iliac, umbilical, femoral arteries.

• Veins above the diaphragm: Superior vena cava, right/left brachiocephalic, subclavian, external/internal jugular, axillary, brachial veins.

• Veins below the diaphragm: Inferior vena cava, right/left renal, internal/external/common iliac, femoral, umbilical veins.

Example: The right subclavian artery supplies blood to the right upper limb.

Lymphatic System Structure

The thymus is a primary lymphoid organ involved in T cell maturation, located in the mediastinum above the heart.

Electrocardiography (EKG), Pulse, and Blood Pressure

Electrocardiography (EKG)

An EKG records the electrical activity of the heart, displaying characteristic waves and intervals.

• P wave: Atrial depolarization.

• QRS complex: Ventricular depolarization (and atrial repolarization).

• T wave: Ventricular repolarization.

• P-R interval: Time from atrial to ventricular depolarization (normal: 0.12–0.20 s).

• Q-T interval: Time for ventricular depolarization and repolarization (normal: 0.32–0.40 s).

• QRS interval: Duration of ventricular depolarization (normal: 0.08–0.12 s).

• Isoelectric point: The baseline of the EKG, where there is no net electrical activity.

• Heart rate calculation: $\text{Heart Rate (bpm)} = \frac{60}{\text{R-R interval (s)}}$

Example: If the R-R interval is 0.8 seconds, the heart rate is $\frac{60}{0.8} = 75$ bpm.

Pulse and Blood Pressure

Pulse and blood pressure are vital signs reflecting cardiovascular health.

• Equipment: Sphygmomanometer (blood pressure cuff), stethoscope.

• Pulse: Palpated at arteries (e.g., radial, carotid).

• Blood Pressure (BP): Systolic/diastolic pressure measured in mmHg.

• Pulse Pressure: $\text{Pulse Pressure} = \text{Systolic BP} - \text{Diastolic BP}$

• Mean Arterial Pressure (MAP): $\text{MAP} = \text{Diastolic BP} + \frac{1}{3}(\text{Systolic BP} - \text{Diastolic BP})$

• Physiological Effects: Body position and exercise can increase heart rate and blood pressure due to increased sympathetic activity.

Example: If BP is 120/80 mmHg, pulse pressure is 40 mmHg, and MAP is $80 + \frac{1}{3}(40) = 93$ mmHg.

Dissection Terms and Structures

Heart and Vessel Identification

Be able to identify the following structures in dissection specimens (steer/sheep heart, fetal pig):

• Heart External: Apex, aorta, right/left atria, right/left ventricles, pulmonary trunk, brachiocephalic trunk, superior vena cava.

• Heart Internal: Right/left atria, bicuspid (mitral) valve, tricuspid valve, chordae tendineae, papillary muscles, interventricular septum, pulmonary and aortic semilunar valves, pectinate muscles.

• Major Arteries and Veins: As listed above, including those specific to fetal pig anatomy.

• Lymphatic System: Thymus.

Example: The chordae tendineae anchor the atrioventricular valves to papillary muscles in the ventricles.

Additional info:

• Review the lab manual's introduction, syllabus, and strategies for further support and exam preparation.

• Practice identifying structures on both models and actual dissection specimens.