Week_5-2_Cardiac_Cycle_and_Blood_Pressure__1_

Course Overview

• Course Title: Anatomy & Physiology (BIOL 103)

• Credits: 5

• Week 5 Content Overview: 5 major sections to study.

Course Outline

1. Describe parts of the human body using anatomical terms (~2%)

2. Analyze structure-function relationships (~60%)

   • Cardiac cycle

   • Blood pressure

3. Explain homeostatic mechanisms in the human body (~10%)

4. Discuss microbiology and body defenses against infections (~15%)

5. Conduct laboratory activities (~15%)

Cardiovascular System Recap

• Key Topics:

  • Structural parts of the cardiovascular system

  • Blood flow through the heart, lungs, and tissues

  • Atrial Septal Defect (hole in the heart)

  • Permanent Pacemaker Implant Surgery - PreOp® Patient Education

Heart Actions

• Function: Constant pumping action by heart chambers.

  • Systole: Contraction of heart chambers.

  • Diastole: Relaxation of heart chambers.

• Cardiac Cycle Events:

  1. Atria contract (atrial systole) while ventricles relax (ventricular diastole).

  2. Ventricles contract (ventricular systole) while atria relax (atrial diastole).

  3. Brief relaxation of the entire heart.

Cardiac Muscle Cells

• Characteristics:

  • Similar to skeletal muscle cells but arranged in branching networks.

  • Connected by intercalated discs which transmit cardiac impulses.

Cardiac Conduction System

• Function: Initiates and transmits electrical impulses for heartbeats.

• Components:

  1. Sinoatrial (SA) Node

  2. Atrioventricular (AV) Node

  3. AV Bundle (Bundle of His)

  4. Bundle Branches

  5. Purkinje fibers

• SA Node: Self-exciting; pacemaker of the heart in the posterior right atrium.

Atrioventricular (AV) Node

• Function: Delays electrical impulses to ensure atria complete contraction before ventricular contraction.

• AV Bundle: Transmits impulses through the interventricular septum; divides into bundle branches.

Purkinje Fibers

• Spread impulses to the ventricular wall and papillary muscles for coordinated contraction.

Electrocardiogram (ECG)

• Definition: Recording of electrical changes during a cardiac cycle.

• Components:

  • P Wave: Atrial contraction

  • QRS Complex: Ventricular contraction; atrial relaxation occurs but is masked.

  • T Wave: Ventricular relaxation.

Heart Sounds

• Description: Created by vibrations as heart valves close.

• Types:

  • Lubb: First heart sound during ventricular systole (AV valves closing).

  • Dupp: Second heart sound during ventricular diastole (aortic and pulmonary valves closing).

• Murmurs: Abnormal sounds due to valve damage.

Heart Rate Regulation

• Average resting heart rate: 70 to 75 beats/minute (normal range: 60 to 100 bpm).

• Regulated by:

  1. Blood pressure changes

  2. Emotions

  3. Body temperature

  4. Ion concentrations (e.g., Hyperkalemia decreases heart rate; Hypercalcemia increases heart action).

Central Nervous System Control

• Medulla oblongata: Links cardiovascular and respiratory systems; controls heart rate, breathing, and blood pressure through neurotransmitter signaling.

Blood Vessels

• Components:

  • Arteries

  • Arterioles

  • Capillaries

  • Venules

  • Veins

• Function: Closed circuit carrying blood away from the heart and back.

Arteries and Arterioles: Structure and Function

• Artery Structure:

  • Tunica interna: Innermost layer; smooth surface to prevent clots.

  • Tunica media: Thick middle layer of smooth muscle.

  • Tunica externa: Outermost layer of connective tissue.

• Function: Transport blood under high pressure.

Capillaries

• Definition: Smallest blood vessels connecting arterioles to venules.

• Structure: Single layer of endothelium allowing substance exchange.

• Permeability: Varies by tissue based on cell junction openings.

Exchanges in Capillaries

• Processes: Exchange of gases, nutrients, and wastes via diffusion, filtration, and osmosis.

• Mechanisms: Hydrostatic pressure and colloid osmotic pressure drive filtration and reabsorption.

• Overall Flow: More fluid leaves capillaries by filtration than returns by osmosis; lymphatic vessels manage excess fluid.

Venules and Veins

• Function of veins: Return blood to heart; regulate flow with flap-like valves to prevent backflow.

Blood Pressure (BP)

• Definition: Force exerted by blood against blood vessel walls; systemic arterial pressure typically referenced.

Arterial Blood Pressure

• Measurement in context of the cardiac cycle:

  • Systolic Pressure: Max pressure during ventricular contraction.

  • Diastolic Pressure: Min pressure during ventricular relaxation.

  • Normal Range: 120/80 mmHg at rest.

Factors Affecting Blood Pressure

1. Cardiac Output (CO): Affects BP directly.

   • Formula: CO = Stroke Volume × Heart Rate.

2. Blood Volume: Average adult volume ≈ 5 L.

   • BP is directly proportional to blood volume; dehydration lowers BP.

3. Peripheral Resistance (PR): Friction between blood and vessel walls affects flow and pressure.

4. Blood Viscosity: Higher viscosity increases BP!

Control of Blood Pressure

• BP Regulation Mechanisms:

  1. Baroreceptor reflexes

  2. Cardiac center adjustments

  3. Emotional state reactions

  4. Ion concentrations affecting resistance.

Conclusion

• Understanding the cardiovascular system's anatomy and physiology is crucial for comprehending how the heart functions and how blood pressure is regulated.