Transport

Transport and Cardiac System

Capillaries and Chemical Exchange

  • Definition: Capillaries are the narrowest blood vessels, with a diameter of about 10 µm.

  • Structure: Capillaries branch and rejoin to form a capillary network.

  • Function: They transport blood through almost every tissue in the body, with two exceptions: the lens and the cornea of the eye.

    • These tissues must remain transparent; therefore, they lack blood vessels.

  • Function of Blood Transport: Blood itself should not enter the tissues; only the materials it carries should pass.

Tissue Fluid

  • Fluid Composition: The fluid that leaks out of capillaries is known as tissue fluid, which is similar but not identical to blood plasma.

    • Tissue fluid contains:

    • Oxygen (O2)

    • Glucose

    • Other substances found in blood plasma (with the exception of large proteins like hemoglobin)

  • Function: Tissue fluid circulates between cells in tissue, enabling them to absorb useful substances and excrete waste products.

  • Re-Entry to Capillaries: The tissue fluid eventually re-enters the capillary network.

  • Fenestrated Capillaries: Some tissues may have a higher number of small pores in capillary walls, known as fenestrated capillaries.

    • These allow greater volumes of tissue fluid to produce, speeding up exchange between the tissue and blood.

Structure of Arteries and Veins

Comparison

  • Arteries:

    • Thicker wall

    • Narrower lumen

    • Circular in section

    • Inner surface is corrugated

    • Contains more visible fibers in the wall

  • Veins:

    • Thinner wall

    • Wider lumen

    • Circular or flattened in section

    • No inner surface corrugation

    • Few or no fibers visible in the wall

Adaptations of Arteries

  • Tissue Plan: Arteries have thicker tunicas and narrower lumens compared to veins, which increases blood pressure.

  • Composition: Elastic fibers can constitute up to 50% of the dry mass of artery walls.

  • Systolic Pressure: The peak pressure in an artery caused by heart contractions pushes the arterial wall outwards, highlighting the importance of elasticity in elastic fibers.

    • When stretched, these fibers store potential energy.

  • Diastolic Pressure: At the end of each heart beat, the arterial pressure falls, and the stretched fibers return to their original state.

  • Smooth Muscle Cells: Arteries contain circular smooth muscle cells.

    • Vasoconstriction: When these muscles contract, the lumen's diameter narrows.

    • Vasodilation: When relaxed, the lumen widens.

Valves in Blood Vessels

  • Purpose: To prevent backflow of blood, valves are present in blood vessels.

  • Varicose Veins: Occur when pocket valves weaken or become damaged, causing blood to flow backwards in the vein, resulting in swelling and enlargement.

  • Location: Varicose veins typically develop in the legs due to the challenge of venous return against gravity.

Causes of Occlusion of Coronary Arteries

  • Atherosclerosis: Refers to the hardening and narrowing of arteries due to cholesterol deposition.

    • Atheromas: Fatty deposits that develop in arteries and narrow the vessel lumen.

  • Consequences: Restricted blood flow increases pressure in arteries, leading to damage from sheer stress, eventually leading to fibrous tissue repair which reduces vessel elasticity.

  • Formed Plaques: As the arterial lining degrades, atherosclerotic plaques form.

  • Thrombus Formation: If a plaque ruptures, it triggers clotting, creating a thrombus that can restrict blood flow. If dislodged, it becomes an embolus, potentially blocking smaller arterioles.

Consequences of Coronary Artery Occlusion

  • Health Risks: Atherosclerosis can induce blood clots that lead to coronary heart disease, which is critical as myocardial tissue requires oxygen and nutrients from the coronary arteries to function.

    • If blood flow is impaired, heart tissue supplied by the affected artery begins to die.

    • A completely blocked coronary artery can result in an acute myocardial infarction (heart attack).

Treatments for Blockages

  • Surgical Interventions: Underlying blockages in coronary arteries may be addressed through:

    • By-pass surgery

    • Balloon angioplasty for stenting

Water Transport in Plants and Heart Physiology

Water Transport in Xylem

  • Transpiration: Loss of water by transpiration creates tension through capillary action in nearby xylem tissue, promoting water pull.

  • Cohesion-Tension Theory: This mechanism explains how water and dissolved minerals move up the xylem.

Takotsubo Syndrome

  • Definition: Also known as “broken heart syndrome,” it results from extreme grief and causes an enlarged left ventricle, potentially leading to heart collapse and death.

Circulatory Systems

Single and Double Circulation

  • Single Circulation: Common in fish; characterized by a two-chambered heart that pumps blood to gills for oxygen and carbon dioxide exchange.

  • Double Circulation: Present in mammals; involves a four-chambered heart functioning in two systems:

    • Pulmonary circulation: Involves lungs.

    • Systemic circulation: Oxygen delivery throughout the body.

Structure of the Heart

Flow of Blood

  1. Deoxygenated blood enters the right atrium via the superior and inferior vena cava.

  2. Blood flows into the right ventricle, passing through the semilunar valve into the pulmonary artery (the only artery carrying deoxygenated blood).

  3. Blood is sent to the lungs for oxygenation.

  4. Oxygenated blood returns through the pulmonary vein (the only veins carrying oxygenated blood) to the left atrium.

  5. Blood moves to the left ventricle and is pumped into the aorta for distribution to the body.

Systolic and Diastolic Pressure

  • Systolic Phase: Heart contraction increases blood pressure; normal systolic pressure is approximately 110 +/- mmHg.

  • Diastolic Phase: Heart relaxation decreases blood pressure; normal diastolic pressure is approximately 70 +/- 10 mmHg.

Heartbeat Control

  • Mechanism: Heartbeat originates from myogenic muscle contractions, where myocytes (muscle cells) initiate contractions autonomously.

  • Sinoatrial Node: Clusters of myocytes that serve as the pacemaker, regulating heartbeat rates.

  • Signal Pathway: Signals from the sinoatrial node prompt the atria to contract, which then relay signals to the AV node to trigger ventricular contraction.

  • Delay Time: There is a 0.1-second delay from the sinoatrial node reaction to AV node reaction.

Graphical Representation of Heartbeat

  • Autonomic Control of Heart Rate: The autonomic nervous system regulates how quickly the heart beats based on bodily conditions.

    • Exercise Effect: Increased CO2 levels detected by chemoreceptors trigger heart rate acceleration via signals to the sinoatrial node.

    • Resting Heart Rate: Decreases in CO2 prompt the vagus nerve to lower heart rate.

    • Hormonal Influence: Adrenaline leads to rapid heartbeat during fight or flight responses.

The Cardiac Cycle

  • Definition: Sequence of mechanical and electrical events repeating each heartbeat, encompassing diastole (relaxation) and systole (contraction).

  • Cycle Breakdown:

    • 0.0 to 0.1 seconds: Atria contract, increasing blood pressure, pumping blood into ventricles. Semilunar valves remain closed.

    • 0.1 to 0.15 seconds: Ventricles contract, atrioventricular valves close to prevent backflow.

    • 0.15 to 0.4 seconds: Ventricular pressure exceeds atrial pressure, causing semilunar valves to open, allowing blood flow to pulmonary artery.

    • 0.4 to 0.45 seconds: Ventricular contraction decreases, leading semilunar valves to close as ventricular pressure drops.

    • 0.45 to 0.8 seconds: Atrioventricular valves open again as atrial pressure rises, allowing blood flow from veins into atria and ventricles.

Risk Factors in Coronary Heart Disease

Atherosclerosis

  • Definition: Development of atheroma, a fatty tissue, in the arterial wall.

  • LDL Involvement: Low-density lipoproteins (LDL) accumulate in arteries.

  • Phagocyte Role: Phagocytes attracted to sites engulf cholesterol and fats, expanding in size.

  • Plaque Development: Smooth muscle cells create a cap over the atheroma which narrows the artery lumen and impedes blood flow.

  • Risk of Rupture: An excessively pressurized cap can explode, resulting in blood clots and potential heart attacks.

Contributing Factors

  • Genetics: Predisposition to high cholesterol levels.

  • Age: Increased risk in older individuals due to decreased artery elasticity.

  • Sex: Males have higher risk than females.

  • Smoking: Constricts blood vessels, increases blood pressure, and decreases oxygenation.

  • Diet: High fat/saturated cholesterol diet increases plaque deposits.

  • Exercise: Physical inactivity raises risk through weakened circulation.

  • Obesity: Leads to increased blood pressure and plaque formation.

  • Stress: Increased cortisol levels linked to higher atherosclerosis risk.

Xylem and Phloem Transport

Xylem Structure

  • Cell Type: Composed of dead cells fortified with lignin for strength.

  • Functionality: Capable of conducting water and minerals from the roots.

Phloem Structure

  • Cell Type: Composed of living cells with a nucleus and organelles.

    • Sieve Tubes: Contain fewer organelles, while companion cells are equipped with a nucleus, ribosomes, and mitochondria.

    • Sieve Plate: Contains pores to facilitate sap flow.

Translocation of Sugars

  1. Photosynthesis produces glucose in leaves, converted to sucrose.

  2. Companion cells assist in transporting sucrose into the phloem, which raises the solute concentration.

  3. Increased solute concentration causes water to enter from xylem, increasing hydrostatic pressure.

  4. This pressure gradient facilitates the movement of sucrose to sink cells (e.g., roots) with the assistance of companion cells.

  5. Water exits the phloem back into the xylem.

Lymphatic System

  • Function: The lymphatic system collects lymphatic fluids through small vessels, routing through lymph nodes before returning to the veins.

  • Purpose of Lymph Nodes: They filter bacteria, viruses, and even cancer cells from lymph fluid, linking lymphatic functions to the immune system.