Lecture, Heart and Circulation

Heart and Circulation Overview

  • Introduction by Rabea Basri

Cardiovascular System

  • The heart is part of the vascular system, enabling blood pump throughout the body.

  • Closed system transporting oxygen and nutrients, removing CO2 and metabolic wastes.

Functions of Blood

Transportation

  • Delivers oxygen and nutrients to cells.

  • Removes carbon dioxide and waste products from cells.

  • Transports hormones to target tissues.

Regulation

  • Maintains body temperature.

  • Regulates pH, water, and electrolyte levels.

Protection

  • Clotting mechanisms prevent fluid loss.

  • White blood cells fight against disease.

Components of the Cardiovascular System (CVS)

Heart

  • Composed of 4 chambers: 2 atria & 2 ventricles.

  • Acts as the pump providing necessary force for blood circulation.

Blood Vessels

Arteries and Arterioles

  • Carry blood from the heart to the body.

  • Arteries act as distribution channels to organs.

Venules and Veins

  • Collect and return blood from tissues to the heart.

  • Veins serve as reservoirs for blood return.

Capillaries

  • Fine vessels connecting arterioles and venules.

  • Sites for gas (O2, CO2) exchange and nutrient/waste exchange between blood and tissues.

Construction of the Cardiovascular System

Two Major Circulatory Systems

  • Right Side: Pumps blood to lungs via pulmonary artery, returns to left atrium.

  • Left Side: Pumps blood to body via aorta, returns to right atrium.

Circulation Process

  • Blood circulates through systemic (high-pressure) and pulmonary (low-pressure) systems.

  • Systemic circulation starts at left ventricle and ends at right atrium.

  • Pulmonary circulation starts at right ventricle and ends at left atrium.

Series Arrangement of Circulations

  • Blood moves sequentially through systemic and pulmonary circulations.

  • Both ventricles must pump equal blood volume.

Systemic and Pulmonary Circulations Flow

  • Blood flow schematic including major arteries, veins, and valves in the heart and lung system.

Engineering Perspective on Systemic Circulation

  • High resistance circuit showing pressure differences between arteries and veins.

  • The left ventricle generates more pressure than the right ventricle, necessary for systemic circulation.

Basic Functions of the Cardiovascular System

Heart

  • Left side: High-pressure side pumping blood into systemic arteries.

  • Right side: Low-pressure side pumping blood into pulmonary arteries.

Blood Vessels

Arteries

  • Elastic arteries (aorta and pulmonary artery) distend during systole; recoil during diastole aids blood flow continuation.

Arterioles

  • Act as resistance vessels, regulating blood flow to capillaries.

Veins

  • High compliance vessels that store blood and adjust volume based on condition.

General Function

  • Maintains homeostasis by ensuring adequate blood flow despite continuous metabolic activities.

Heart Anatomy

Heart Structure

  • Located in the thoracic cavity, covered by the pericardium.

  • Composed primarily of cardiac muscle (myocardium).

Chamber Structure

  • The human heart has four chambers: two atria and two ventricles, separated by septums.

Cardiac Valves and Functions

Types of Valves

  • Two AV valves: Tricuspid (right) and Mitral (left).

  • Two semi-lunar valves: Aortic and Pulmonary.

Valve Functionality

  • Ensures unidirectional blood flow through the heart during contractions and relaxations.

Right Ventricle Function

  • Pumps low-pressure blood through the pulmonary circulation.

  • Performs efficiently under normal conditions but can thicken in high resistance scenarios.

Left Ventricle Function

  • Pumps high-pressure blood throughout systemic circulation.

  • Thicker walls due to higher pressure requirements.

Blood Flow Mechanism

  • Blood pumped during systole and filled during diastole, resulting in pulsatile flow.

Types of Blood Vessels

Arteries and Arterioles

  • Strong vessels carrying blood from the heart.

  • Aorta as the primary artery under high pressure.

Capillaries

  • Extensive branching allows for maximal surface area for nutrient and gas exchange.

Veins and Venules

  • High capacity for blood volume.

  • Muscle contractions assist blood return to the heart.

Peripheral Resistance

  • The resistance met by blood flow due to vessel diameter and blood viscosity.

  • Key factor for maintaining arterial blood pressure.

Cardiac Cycle Overview

  • Defined as phases of contraction (systole) and relaxation (diastole).

  • Each heartbeat corresponds to one complete cycle involving atrial/ventricular actions.

Phases of Cardiac Cycle

  • Systole: Atria contract, filling ventricles.

  • Diastole: Ventricles contract, pumping blood into circulation.

Heartbeat Duration

  • Average cycle duration corresponds to a heart rate of 75 bpm, with systole lasting approximately 0.3 sec and diastole lasting approximately 0.5 sec.

Heart Sounds

Types

  1. First Sound (LUB) - indicates ventricular contraction.

  2. Second Sound (DUB) - indicates end of systole.

  3. Third Sound - benign in youth but indicates ventricular filling.

  4. Fourth Sound - indicates end of filling and occurs before first sound.

Conducting System of the Heart

  • Electrical impulses generated by specialized muscle tissues initiate heart contractions.

Components of Conducting System

  1. SA Node (pacemaker): Generates impulses (70/min).

  2. AV Node: Delays impulses for ventricle filling.

  3. Bundle of His: Conducts impulses to ventricles.

Functionality of SA and AV Nodes

  • Impulses spread through heart, promoting atrial contraction and allowing for ventricular filling before contraction.