Chapter 26

Chapter 26: Circulatory System

Chapter Objectives

  • Upon completion of this chapter, the reader should be able to:

    • 26.1: State the structures that make up the circulatory system

    • 26.2: Describe the functions of the circulatory system

    • 26.3: Describe the functions of the various types of blood cells

    • 26.4: Describe blood flow through the heart

    • 26.5: Describe common disorders of the circulatory system

Introduction

  • The circulatory system is essential for life.

  • It includes the following components:

    • Heart

    • Blood

    • Arteries

    • Veins

    • Capillaries

  • Functions of the circulatory system include:

    • Oxygen flow throughout the body

    • Blood circulation

    • Transport of nutrients to body tissues

    • Removal of waste products from the body

    • Movement of hormones throughout the body

Blood (1 of 3)

  • Blood is composed of:

    • 40 percent cells

    • 60 percent plasma

  • Plasma is formed of various proteins:

    • Albumin: Draws water into the bloodstream.

    • Globulins: Provide antibodies for immune response.

    • Fibrinogen: Aids in the clotting process.

  • Hematology: The study of blood, which includes:

    • Setting up for blood collection

    • Running blood analysis samples

    • Restraining patients for blood collection

    • Completing blood testing kit samples

Blood (2 of 3)

  • Blood tube samples should be labeled with:

    • Patient’s name

    • Owner’s name

    • Date

    • Test procedure

  • Centrifuge: A machine that spins blood at high speeds, separating cells from serum.

  • Serum constitutes 30–45 percent of total blood contents.

  • Red blood cells (RBCs) or erythrocytes:

    • Most abundant blood cell type.

    • Function: Transport oxygen throughout the body.

    • Produced in the bone marrow within the medullary cavity (process known as erythropoiesis).

    • Constantly being produced and replaced.

    • Contain hemoglobin, which binds oxygen.

Blood (3 of 3)

  • White blood cells (WBCs) or leukocytes:

    • Function: Main defense against infection.

    • Types of white blood cells include:

    • Neutrophils: Attack any microorganisms in tissues.

    • Lymphocytes: Produce antibodies in response to pathogens.

    • Eosinophils: Fight allergic reactions and assist in controlling inflammation; also help prevent parasitic infections.

    • Monocytes: Remove organisms, dead cells, and foreign particles.

    • Basophils: Involved in allergic reactions.

  • Platelets or thrombocytes:

    • Function: Aid in clotting time and make blood vessels constrict to prevent excessive bleeding.

Blood Components

  • Overview of the primary components that make up blood.

Knowledge Check

  • Q: Which type of blood cell carries oxygen?

    • Options:

    • Erythrocyte

    • Lymphocyte

    • Thrombocyte

    • Neutrophil

  • A: Erythrocytes contain hemoglobin, enabling oxygen transport.

The Heart

  • The heart is an organ with four chambers and is located between the lungs.

  • Myocardium: The wall of the heart made of thick cardiac muscle.

  • Endocardium: Thin inner layer of muscle that lines the chambers of the heart.

  • Epicardium: The outer thin covering of the myocardium.

  • Pericardium: The fibrous sac that surrounds the heart, providing protection and maintaining its beating action.

Blood Flow (1 of 2)

  • The circulatory system includes:

    • Systemic circulation: Delivers oxygenated blood to the entire body.

    • Oxygen is delivered to the lungs, where it is exchanged for carbon dioxide.

  • Veins: Carry blood back to the heart.

  • Arteries: Carry blood away from the heart.

  • Arterioles: Smaller branches of arteries that further branch into capillaries.

  • Capillaries: The smallest blood vessels that allow for the exchange of materials between blood and tissues.

  • Valves: Prevent backflow of blood, keeping it flowing in one direction.

  • Arteries: Characterized by thick, muscular walls; this property is used to determine pulse or heart rate.

Blood Flow (2 of 2)

  • Blood flow through the heart occurs as follows:

    1. Oxygen-poor blood flows into the heart from the body via the vena cava.

    2. It enters the right atrium, passes into the right ventricle.

    3. Blood is then pumped out to the lungs via pulmonary arteries.

    4. Oxygen-rich blood returns to the heart from the lungs through pulmonary veins.

    5. It flows into the left atrium, then into the left ventricle.

    6. Blood exits the heart through the aorta.

Internal Structure and Blood Flow Through the Heart

  • Detailed overview of how blood circulates through the heart and the internal structure's role in this process.

Blood Pressure

  • Blood pressure is generated as blood flows through the heart.

  • Vasoconstriction: Occurs during contraction, resulting in decreased vessel diameter, which increases blood pressure.

  • Vasodilation: Happens during relaxation, resulting in increased vessel diameter, which decreases blood pressure.

  • Blood pressure is a measure of one complete contraction of the heart in the cardiac cycle and consists of two phases:

    • Systole: Contraction phase, corresponds to the top number of blood pressure reading; this is normally the higher value.

    • Diastole: Relaxation phase, corresponds to the bottom number of the blood pressure reading; this is typically the lower value.

  • Blood pressure is measured in millimeters of mercury (mm Hg).

Veins

  • The primary role of the veterinary assistant in venipuncture is the restraint of the animal.

  • Common veins for blood collection in dogs and cats include:

    • Cephalic veins: Located on the anterior surface of the front limb.

    • Jugular veins: Found in the neck on either side of the trachea.

    • Saphenous veins: Located on the lateral and medial surfaces of the distal tibia.

    • Femoral veins: Situated on the medial aspect of the thigh near the groin.

Polling Activity

  • Discussion prompts for the audience:

    • Should it be standard practice to take the patient’s blood pressure and pulse at every visit? (Options: Yes / No)

    • Should veterinary assistants be allowed to perform venipunctures? (Options: Yes / No)

Heart Sounds

  • Heart sounds are created by the closing of heart valves and can be heard using a stethoscope.

  • Controlled by the sinoatrial node (SA node), known as the pacemaker of the heart, which regulates the heart's rhythm.

  • The first heart sound (“lub”) is produced by the closure of the AV valves.

  • The second heart sound (“dub”) is caused by the closure of the aorta and pulmonary valve.

  • Cardiac cycle: Includes one complete contraction (systole) and relaxation (diastole).

  • Normal heart rates vary according to species, as well as the health and fitness levels of the animal.

Heart Rates

  • Measured in beats per minute (bpm).

  • Heart rates should be compared to known normal ranges for various species.

  • Factors influencing heart rate include:

    • Stress

    • Fear

    • Anxiety

    • Nervousness

    • Diseases affecting the animal

Electrocardiography (1 of 2)

  • Electrocardiography is the evaluation of the electrical currents of the heart through the use of machines.

  • Electrocardiogram (ECG): A recording of the electrical activity of the heart.

  • Electrocardiograph: The machine that records the heart's electrical currents, displaying its rhythm as waves or lines that form peaks.

  • Each peak and drop is identified by a letter that relates to the heart’s activity and functions.

Electrocardiography (2 of 2)

  • P wave: Formed at the SA node; reflects the flow of electricity and blood through the atrium, indicating a contraction has taken place.

  • QRS wave or QRS complex: A series of peaks and drops that show the electrical current and blood flow through the AV node, causing contraction in the ventricles.

  • T wave: Represents the last peak, indicating that the electrical impulse has traveled through the entire heart and that contraction and repolarization are complete.

Common Diseases and Conditions of the Circulatory System

  • Diagnoses for circulatory conditions typically involve:

    • Physical examination

    • Radiology

    • Electrocardiography

    • Ultrasound

  • Heart murmur: Result of an abnormal valve leading to abnormal blood flow, creating a “swishing” noise upon auscultation.

Arrhythmias

  • Defined as changes in the heartbeat's rhythm, rate, or conduction.

  • Types of arrhythmias include:

    • Tachycardia: Heart rate exceeding normal limits (faster than normal).

    • Bradycardia: Heart rate below normal (slower than normal).

    • Sinus arrhythmia: Heart rate increases with inhalation and decreases with exhalation; appears normal but shows a change in breathing pattern.

    • Cardiac arrest: Condition where the heart is not contracting appropriately, similar to a heart attack in humans, which can be caused by conditions like atrial fibrillation (A-fib) or ventricular fibrillation (V-fib).

    • V-fib: Can lead to asystole, resulting in the heart ceasing to contract.

Shock

  • Shock is a critical state occurring when blood loss leads to reduced oxygen delivery to tissues, often resulting from trauma or heart conditions; it represents a medical emergency requiring immediate care.

  • Signs of shock include:

    • Weakness and depression

    • Rapid heart rate with a weak pulse

    • Increased respiration rates and drop in body temperature

    • Mucous membranes appear white to gray

    • Decreased capillary refill time (CRT)

  • Treatment generally involves addressing the underlying cause and often administering fluids.

Hypovolemic Shock and Septic Shock

  • Hypovolemic shock: Caused by insufficient blood volume due to either internal or external blood loss, which may result from hemorrhaging, vomiting, or diarrhea.

  • Septic shock: A condition that arises when a severe infection invades the body, causing numerous blood vessels to dilate, which results in decreased blood output.

Summary

  • The cardiovascular system consists of:

    • Heart

    • Blood

    • Blood vessels

  • Main functions include the transportation of oxygen and nutrients to all body structures.

  • Arteries: Carry blood away from the heart.

  • Veins: Return blood to the heart.

  • Diseases and disorders include:

    • Alterations in the heart's rate and rhythms.

    • Severe blood loss from trauma necessitates urgent medical attention.

Clinical Situation

  • Scenario Overview: Dr. Jansen and Dale, a veterinary assistant, visit a farm to examine a Thoroughbred named Roscoe, who is lethargic and has had a decreased appetite.

  • Examination findings include:

    • Pale mucous membranes

    • Decreased heart rate (HR) and respiratory rate (RR)

    • 5–10 percent dehydration

    • Conclusion: Potential suspicion of parasites or autoimmune disease due to symptoms indicating anemia.

  • Anemia leads to low red blood cell counts, resulting in reduced oxygen transport.

  • Blood samples and a fecal sample were collected for further diagnostic work.

Clinical Situation Questions

  • What are some possible causes for the anemia?

  • What factors could prevent the horse from having anemia?

  • What treatment options might Dr. Jansen discuss with the owner?

Self-Assessment

  • Reflect on:

    • What concepts in this chapter presented the biggest challenges?

    • Thoughts on the topic of arrhythmias?

    • Essential skills highlighted in this chapter and personal improvement strategies.