Circulatory and Lymphatic - Part 2

Heart as a Pacemaker

• Sinoatrial (SA) node initiates heartbeats at a rate of 70-80 bpm.
• Atrioventricular (AV) node serves as a secondary pacemaker at 40-60 bpm.
• Atrioventricular bundle, bundle branches, and Purkinje fibers can generate impulses at 20-40 bpm.

Regulation of Heart Rate

• Starling’s law states that increased heart stretch results in more forceful contractions.
• Adjusting heart rate is the primary method to influence cardiac output.

Electrocardiogram (ECG)

• An ECG measures electrical activity of the myocardium:
  • P wave indicates atrial depolarization.
  • QRS wave indicates ventricular depolarization.
  • T wave indicates ventricular repolarization.

Heart Rate Control

• The SA node’s rhythm is modified by physiological factors.
• Nerve sets influence heart rate: one enhances, the other diminishes it.
• Hormones like epinephrine increase heart rate.
• Heart rate rises with body temperature and physical exertion.

Cardiac Cycle and Output

• Atria contract simultaneously, followed by ventricular contraction.
• Systole refers to contraction; diastole refers to relaxation.
• Cardiac output (CO) formula: CO = heart rate (HR) x stroke volume (SV).
• Average cardiac output ranges from 5.25 L/min to 35 L/min.

Blood Vessels

• Blood vessels facilitate blood transport and nutrient exchange.
• Types of blood vessels:
  • Arteries: carry oxygenated blood away from the heart.
  • Arterioles: smaller branches of arteries.
  • Capillaries: smallest vessels for nutrient and waste exchange.
  • Venules: small veins that transport blood from capillaries.
  • Veins: carry deoxygenated blood back to the heart.

Fetal Circulation

• Unique structures enable material exchange between fetus and mother.
• Lung, kidney, and digestive systems are inactive before birth.
• After delivery, the infant’s lungs initiate oxygen intake, ending placental blood flow.

Immune System: Key Concepts

• Immunity is the body's ability to resist damage or disease.
• Susceptibility refers to vulnerability to infections.

Types of Immunity

• Innate (nonspecific) immunity:

  • Present at birth; reacts to all microbes similarly.
  • First line includes physical barriers, second line involves immune cells and inflammation.

• Adaptive (specific) immunity:

  • Involves tailored responses to specific microbes.
  • Relies on lymphocytes (B cells and T cells).

Lymphatic System

• Aims to maintain homeostasis through fluid drainage and disease defense.
• Lymph plasma is a fluid transported by lymphatic vessels, differing from interstitial fluid by its location.
• Lymphoid tissue contains many lymphocytes.

Lymphatic Trunks and Ducts

• Right lymphatic trunks empty into venous junctions; may form the right lymphatic duct.
• The thoracic duct on the left side is the main route for lymph return to blood circulation.

Thymus

• Bilobed organ located mediastinally, crucial for immune function.
• Lined with lymphoid tissue and has a rich vascular supply, appearing red.
• Age-related changes include fatty infiltration replacing lymphoid tissue.

Spleen

• Largest mass of lymphatic tissue in the body, located in the left hypochondriac region.
• White pulp supports immune functions (phagocytosis).
• Red pulp involved in blood cell management:
  • Removal of damaged red blood cells and platelets.
  • Storage of platelets.

Lymph Nodes

• Approximately 600 bean-shaped nodes scattered along lymphatic vessels.
• Act as filters in the lymphatic system, supporting immune responses.

This quiz covers key concepts in cardiovascular physiology, focusing on the heart's pacemaker functions, heart rate regulation, and the interpretation of electrocardiograms (ECG). It highlights the roles of different nodes, hormones, and physiological factors in controlling heart rhythm and cardiac output. Test your knowledge of these essential topics in cardiac health and function.