Abdominal Pelvic Organs and Cardiovascular System Review

Course Logistics and Midterm Preparation

• Quiz Information:

  • The quiz is due by $10:00$ tonight.

  • Students who want to review their performance should email the instructor. The instructor will provide the specific question missed, the answer provided by the student, and the correct answer.

  • Feedback is handled on an individual basis to avoid wasting class time, as errors vary among students.

• Midterm Lab Exam (Cat Anatomy):

  • The exam will involve identifying structures on a cat specimen.

  • A significant portion of the test (nearly half) is dedicated to cat anatomy: $10$ questions on abdominal/pelvic structures and $12$ questions on cardiovascular (artery) structures, totaling $22$ questions ($44$ points).

  • Instructional videos are provided and heavily emphasized as the primary tool for success because specimens vary in appearance.

Cat Abdominal and Pelvic Anatomy

• Mesentery Proper:

  • This is a structure that anchors and holds down the small intestines.

  • It is identified by its appearance as a fan-like membrane attached to the jejunum and ileum.

• Small Intestines:

  • Duodenum: Approximately $2$ inches long in a cat (significantly shorter than the $8$-$12$ inches in humans). It is identified by its immediate connection to the stomach.

  • Jejunum and Ileum: In a cat dissection, the difference between the jejunum (middle segment) and ileum (final segment) is visually indiscernible unless the surrounding landmarks are visible.

  • Identification Strategy: If a pin is placed in the small intestine, the question may ask for the first (duodenum), middle (jejunum), or final (ileum) segment. Landmarks include the stomach for the duodenum and the colon/cecum for the ileum.

• Mesenteries of Other Regions:

  • Mesoduodenum: The mesentery associated specifically with the duodenum.

  • Mesocolon: The mesentery attached to the large intestine (colon).

• Large Intestine (Colon):

  • Identified by its diameter, which is approximately twice the diameter of the small intestine.

  • Cecum: A small pouch where the ileum enters the large intestine at a $90^{\circ}$ angle.

• Liver and Gallbladder:

  • Liver: The cat liver typically has five lobes (though the instructor summarizes them as two right and two left for simplicity).

  • Gallbladder: Described as a "deflated balloon" located between the two right lobes of the liver.

• Stomach and Greater Omentum:

  • Greater Omentum: A fatty apron-like structure. It is highly variable between cats; in some, it appears thick and fatty, while in others, it withers and dries quickly after the cat is opened.

• Pancreas:

  • Located underneath the stomach. The stomach must be lifted to view it.

  • In preserved cats, the pancreas is fragile, often appearing dried and crumbly. It may have the same color and texture as the spleen.

• Spleen:

  • Located in the "left lateral gutter" of the abdominal cavity.

• Kidneys and Diaphragm:

  • Diaphragm: A muscular partition between the thoracic and abdominal cavities; a high-priority structure for the midterm.

  • Kidneys: The right kidney is usually visible; the left kidney is deeper and often obscured. Orientation is always based on the patient (the cat), not the observer (e.g., "cat’s right").

• Urinary and Reproductive Structures:

  • Urinary Bladder: Located in the pelvic region.

  • Uterus: In female cats, the uterine body is located above the bladder.

General Cardiovascular Principles

• The Circulatory System:

  • Composed of the pump (heart), the vessels (arteries and veins), and the fluid (blood).

  • Artery (Definition): Any vessel carrying blood away from the heart.

  • Vein (Definition): Any vessel carrying blood back toward the heart.

• Blood Composition and Nutrients:

  • Red blood cells primarily transport oxygen ($O_2$) and carbon dioxide ($CO_2$).

  • Nutrients (amino acids, free fatty acids, triglycerides, carbohydrates) are dissolved in and carried by the plasma (serum).

• Oxygenation and Hemoglobin Color:

  • Hemoglobin is red when fully oxygenated and blue when approximately $50\%$ oxygenated.

  • Blood turns red instantly upon contact with air ($O_2$).

  • Hemoglobin typically holds up to four oxygen molecules. It gives up the first and second easily, the third only under stress (e.g., emphysema), and never the fourth while the patient is alive.

Heart Anatomy and Circuits

• Shape and Location:

  • The heart is shaped like a cone.

  • The Base is the superior, medial face of the cone.

  • The Apex is the inferior, lateral point, comprised mostly of the Left Ventricle.

  • The traditional "Valentine" shape originated from early studies of three-chambered amphibian hearts (frogs).

• Heart Layers:

  • Parietal Pericardium: The tough, outer sac. It is non-stretching (described as tougher than leather).

  • Visceral Pericardium (Epicardium): The thin, delicate inner layer on the heart surface.

  • Myocardium: The thick muscular middle layer.

  • Endocardium: The smooth inner lining of the chambers and valves.

• Chambers and Septa:

  • Atria: Two upper chambers, thin-walled, responsible for filling the ventricles (about $70\%$ of filling is passive).

  • Ventrcles: Two lower chambers. The left ventricle has a significantly thicker wall than the right because it pumps blood through the systemic circuit.

  • Septa: Interatrial septum (between atria) and Interventricular septum (between ventricles). "Inter" means between; "Intra" means inside.

• Valves:

  • Atrioventricular (AV) Valves: Located between atria and ventricles.

    • Tricuspid Valve: Right side.

    • Bicuspid (Mitral) Valve: Left side.

  • Semilunar Valves: Located at the exit of the ventricles.

    • Pulmonic Semilunar Valve: Right side (at the pulmonary trunk).

    • Aortic Semilunar Valve: Left side (at the aorta).

• Anatomical Structures of the Ventricles:

  • Papillary Muscles: Extensions of the ventricular muscle wall.

  • Chordae Tendineae: String-like cords connecting papillary muscles to valve leaflets. Their function is to prevent prolapse (valves flipping backward) during high-pressure contraction, not to pull them open.

Pulmonic and Systemic Circuits

• Pulmonic Circuit (Right Side):

  • Pumps deoxygenated blood to the lungs via the Pulmonary Trunk and Pulmonary Arteries. These are the only blue arteries in the body.

  • Returns oxygenated blood via Pulmonary Veins (usually two from the left and two from the right) to the Left Atrium. These are the only red veins in the body.

• Systemic Circuit (Left Side):

  • Pumps oxygenated blood to the entire body via the Aorta.

  • The venous system (high volume, low pressure) returns blood via the Superior Vena Cava, Inferior Vena Cava, and Coronary Sinus to the Right Atrium.

Coronary Circulation

• Coronary Arteries:

  • They originate at the base of the aorta, just superior to the aortic semilunar valve.

  • Left Coronary Artery Branches:

    1. Anterior Interventricular Branch (also known as the LAD/Left Anterior Descending).

    2. Circumflex Branch (travels in the coronary sulcus).

  • Right Coronary Artery Branches:

    1. Marginal Branch (anterior surface).

    2. Posterior Interventricular Branch (posterior surface).

• Coronary Venous Return:

  • Blood returns through coronary veins into the Coronary Sinus, which empties directly into the Right Atrium.

• Sulci (Grooves):

  • Coronary Sulcus: A "crown"-like circle dividing the atria from the ventricles.

  • Anterior and Posterior Interventricular Sulci: Grooves between the ventricles that house the coronary vessels and protective fat.

The Aortic Arch Branches

• There are three major vessels branching from the human aortic arch:

  1. Brachiocephalic Trunk: Splits into the Right Subclavian Artery (to the arm) and the Right Common Carotid Artery (to the head).

  2. Left Common Carotid Artery.

  3. Left Subclavian Artery: Notable for having a "direct line" to the heart (the basis for the Roman tradition of the wedding ring on the left hand).

Cardiac Conduction and the EKG

• Conduction Pathway:

  1. Sinoatrial (SA) Node: The pacemaker. Located in the right atrium near the coronary sinus. Spontaneously depolarizes ($60$-$70\,bpm$).

  2. Atrioventricular (AV) Node: Located between the right atrium and ventricle ($40\,bpm$ backup rate).

  3. Bundle of His (Atrioventricular Bundle).

  4. Right and Left Bundle Branches.

  5. Purkinje Fibers: Distribute the impulse to the ventricular myocardium.

• Electrocardiogram (EKG) Waves:

  • P Wave: Represents atrial depolarization.

  • QRS Complex: Represents ventricular depolarization. It is a sharp spike because the ventricles are large. This complex masks/hides atrial repolarization.

  • T Wave: Represents ventricular repolarization.

• Clinical EKG Implications:

  • Voltage: Smaller waves may indicate atrophy or cardiomyopathy; larger waves may indicate hypertrophy (e.g., in athletes or patients with obesity/pulmonary disease).

  • Temporal (Timing): Delays between waves can indicate blocks (e.g., bundle branch blocks).

Clinical Pathologies

• Cardiac Tamponade: Bleeding into the tough, non-elastic parietal pericardium sac. This puts pressure on the heart and prevents efficient pumping. It is treated by draining the blood with a needle.

• Heart Murmurs: Sounds caused by leaky or scarred valves (regurgitation). Benign murmurs are common, but severe cases require valve replacement.

• Autoimmune Impact: Diseases like Rheumatoid Arthritis and Systemic Lupus can affect the connective tissue support (endoskeleton) of the heart and valves.

• Aneurysms: Damage to the Tunica Interna (simple squamous epithelium) allows blood to collect between the layers of the artery wall. A dissecting aneurysm is an aneurysm that has grown significantly in length.

• Heparin: Produced naturally by leukocytes to dissolve microscopic clots; used medically during surgery to prevent clotting.

Questions & Discussion

• Question: Is it safe for patients to take heparin in surgery since we produce it naturally?

• Answer: Yes, the body knows how to handle and metabolize heparin. It is preferred in surgery because its effects can be controlled more easily than other anticoagulants.

• Question (during midterm test): Students often ask the instructor if a specific pin is in a valve.

• Answer: The instructor cannot answer this during the test; students are expected to identify valves by their appearance and location.