Topic 23- Circulation

Outcomes:

Organizer 1: Sequence Types of Circulatory Systems

(Evolutionary progression of circulation types)

1. No circulatory system (small/simple animals → diffusion only).

2. Open circulatory system:

   • Hemolymph bathes tissues directly.

3. Closed circulatory system:

   • Blood confined to vessels.

   • More efficient delivery of oxygen/nutrients.

Organizer 2: Compare and Contrast Circulatory Systems

Organizer 3: Sequence Human Heart Function

(Pathway of electrical and mechanical heart activity)

1. SA Node generates impulse (pacemaker).

2. Atria contract simultaneously.

3. Signal delayed at AV Node.

4. Impulse moves through Bundle branches.

5. Signal spreads via Purkinje fibers.

6. Ventricles contract (blood pumped to lungs and body).

7. Valves (AV and Semilunar) open/close to prevent backflow.

Organizer 4: Hypothesize and Diagnose the Impact of Variability on Human Heart Function

Organizer 5: Compare and Contrast Types of Blood Vessels

Organizer 6: Sequence Human Blood Flow

(Path of blood through the body)

1. Right atrium (receives deoxygenated blood).

2. Right ventricle (pumps to lungs via pulmonary artery).

3. Lungs (oxygenates blood).

4. Left atrium (receives oxygenated blood).

5. Left ventricle (pumps to body via aorta).

6. Arteries → arterioles → capillaries (gas/nutrient exchange).

7. Venules → veins → vena cava → right atrium (cycle repeats).

Organizer 7: Sequence the Function of the Lymphatic System

(How lymph moves and functions)

1. Blood plasma leaks into tissues → forms interstitial fluid.

2. Lymphatic capillaries absorb interstitial fluid → now called lymph.

3. Lymph moves through lymphatic vessels.

4. Lymph passes through lymph nodes (filtered for pathogens).

5. Lymph re-enters bloodstream via lymph ducts into major veins.

Organizer 8: Hypothesize and Diagnose the Impact of Variability on the Lymphatic System

Organizer 9: Compare and Contrast Lymphatic and Blood Systems

I. Basics of the Circulatory System

A. Overview

• Purpose: A circulatory system transports nutrients, gases (O₂, CO₂), and wastes throughout the body.

• Necessity:

  • Small, simple organisms (like flatworms) rely on simple diffusion.

  • Larger or more complex organisms need a transport system because diffusion alone is too slow.

• Key Components:

  1. Fluid: Carries nutrients, gases, and waste.

  2. Interconnecting Vessels: Network through which the fluid moves.

  3. Pump: (Usually a heart) generates pressure to move the fluid.

B. Types of Circulatory Systems

• Open Circulatory System:

  • Fluid = Hemolymph.

  • Hemolymph bathes body tissues directly.

  • Found in many invertebrates (e.g., insects, mollusks).

• Closed Circulatory System:

  • Fluid = Blood.

  • Blood stays confined within vessels, delivering materials directly to cells via capillaries.

  • Found in vertebrates and some invertebrates (e.g., annelids).

II. Vertebrate Circulation

A. General Features

• Closed system called the cardiovascular system:

  • Blood circulates through vessels in a loop.

  • Three types of vessels:

    • Arteries: Carry blood away from the heart.

    • Capillaries: Thin-walled sites of exchange with tissues.

    • Veins: Carry blood toward the heart.

  • Note: Arteries and veins are classified by direction of flow, not oxygen content.

• Flow Pattern:

  • Arteries → Arterioles → Capillaries → Tissues → Venules → Veins.

• Heart:

  • Muscular organ, generally composed of 2 or more chambers:

    • Atria (singular: atrium): Receive blood.

    • Ventricles: Pump blood into arteries.

  • Pericardium: A connective tissue sac that surrounds and protects the heart.

B. Comparison Across Vertebrates

III. The Human Heart

A. Structure and Function

• Cardiac Output: Volume of blood pumped per minute by the left ventricle.

  • Formula: Cardiac Output = Heart Rate × Stroke Volume.

• Heart Rate: Beats per minute (bpm). Normal range: ~60–100 bpm.

• Stroke Volume: Amount of blood pumped in a single contraction.

• Heart Valves: Prevent backflow of blood.

  • Atrioventricular (AV) valves: Between atrium and ventricle.

    • Right AV valve: Tricuspid valve.

    • Left AV valve: Mitral (bicuspid) valve.

  • Semilunar valves: Between ventricles and arteries.

    • Pulmonary valve and Aortic valve.

• Heartbeat Sounds:

  • "Lub": Closing of AV valves.

  • "Dub": Closing of semilunar valves.

  • Heart Murmurs: Abnormal sounds due to backflow.

B. Initiation of Heartbeat

• Sinoatrial (SA) Node: Natural pacemaker; initiates each heartbeat.

  • Autorhythmic cells generate action potentials via Ca²⁺ channels.

  • Atria contract simultaneously upon SA node stimulation.

• Atrioventricular (AV) Node:

  • Located between the right atrium and ventricle.

  • Delays impulse (~0.1 sec) allowing atria to empty before ventricles contract.

• Bundle Branches & Purkinje Fibers:

  • Carry signal quickly to the apex and walls of ventricles, causing them to contract.

• Artificial Pacemakers: Devices that replace or regulate the SA node if faulty.

C. Regulation of the Heartbeat

• Nervous System:

  • Baroreceptors: Monitor blood pressure and send signals to the brain (medulla).

  • Autonomic Nervous System:

    • Sympathetic division: Speeds up heart rate.

    • Parasympathetic division: Slows down heart rate.

• Endocrine System:

  • Hormones like epinephrine (adrenaline) can increase heart rate during stress.

• Temperature Effects:

  • Fever or elevated body temperature can increase heart rate.

IV. Blood Vessels

A. Structure of Blood Vessels

• Arteries and Veins (three layers from inside out):

  1. Endothelium: Smooth inner lining for reduced friction.

  2. Smooth Muscle:

     • Thicker and more elastic in arteries to withstand pressure.

  3. Connective Tissue: Provides strength with collagen fibers.

• Capillaries:

  • Composed only of endothelium and a basal lamina.

  • Site of gas, nutrient, and waste exchange with tissues.

B. Mechanisms of Exchange

• Exchange Sites: Blood ↔ Tissue via capillaries.

• Plasma: The liquid component of blood; some plasma filters out to form interstitial fluid.

• Forces at Capillaries:

  • Blood Pressure: Pushes fluid out of capillaries.

  • Osmotic Pressure: Pulls fluid back into capillaries.

  • Net Result:

    • Arterial end → fluid moves out.

    • Venous end → fluid moves in (but not all fluid returns).

    • ~15% of fluid remains outside vessels and must be returned.

V. The Lymphatic System

A. Functions

• Returns fluid that leaks from capillaries back to the blood.

• Absorbs lipids from the digestive tract.

• Defends against infections via lymphocytes (WBCs).

B. Anatomy

• Lymph Vessels: Spread throughout the body, parallel to veins.

• Lymph Nodes:

  • Filter lymph.

  • Contain immune cells that fight pathogens.

• Lymph:

  • Fluid containing white blood cells, bacteria, and other waste.

• Edema:

  • Swelling due to accumulation of interstitial fluid.

  • Often caused by blocked lymph nodes or poor lymphatic drainage.