Circulation and Blood Flow

Blood Flow Dynamics

  • Overview of Last Session

    • Covered mathematics and physics of blood circulation.
    • Focused on how pressure drives blood through vessels.
    • Discussed factors affecting blood pressure and flow.

  • Key Variables Affecting Blood Flow

    • Five main factors affecting resistance:
      1. Cardiac Output
      2. Compliance
      3. Blood Viscosity
      4. Blood Volume
      5. Vessel Length and Diameter
    • Understanding how each factor can change is crucial for exams.

Atherosclerosis and Blood Flow Restrictions

  • Atherosclerotic Plaque Formation

    • Discussed arteriosclerosis and atherosclerosis causes.
    • Aging increases likelihood of plaque development.
    • Plaques form due to inflammation from artery injuries (high blood sugar, high blood pressure, etc.).
    • Composition of Atherosclerotic Plaque:
    • Made of lipids and congealed blood (from dead blood cells).
    • Plaques cause narrowing and stiffening of arteries, leading to significantly reduced blood flow.

  • Consequences of Blood Flow Restriction

    • Plaques can lead to heart attacks, strokes, and other disorders.
    • Importance of monitoring and understanding plaques in cardiovascular health.

Mechanisms for Blood Movement Through Veins

  • Two Main Pump Systems

    • Respiratory Pump

    • Inhalation decreases thoracic cavity pressure, pulling blood into the chest.

    • Exhalation raises thoracic pressure, pushing blood into the heart.

    • Blood moves from high pressure to low pressure; fundamental physics principle of pressure.

    • Skeletal Muscle Pump

    • Contraction of skeletal muscles compresses veins, increasing pressure and pushing blood upward against gravity.

    • Essential for maintaining blood flow, especially in the legs.

Bulk Flow in Capillaries

  • Definition of Bulk Flow

    • Movement of fluids between capillaries and surrounding tissue; critical for gas exchange.

  • Types of Pressure in Bulk Flow

    • Hydrostatic Pressure
    • Equivalent to blood pressure; pushes fluid out of capillaries into tissue.
    • Osmotic Pressure
    • Pressure exerted by water movement from higher osmolarity (concentration) to lower osmolarity; encourages fluid to flow back into capillaries.

  • Net Filtration Pressure

    • The balance of hydrostatic and osmotic pressures dictates fluid movement direction.
    • Hydrostatic pressure usually higher at the start of capillaries; osmotic pressure encourages reabsorption towards the end of capillaries.

Blood Homeostasis

  • Definition of Blood Homeostasis

    • Mechanisms that maintain steady blood flow despite fluctuations in factors like viscosity or volume.

  • Factors Easily Changed

    • Vessel diameter, cardiac output, blood volume.

  • Nervous Regulation of Circulation

    • Controlled primarily by the cardiac centers in the medulla oblongata.
    • Cardioaccelerator Center: Increases heart rate.
    • Cardioinhibitor Center: Decreases heart rate.
    • Vasomotor Control Centers: Adjust smooth muscle contraction around blood vessels for dilation or constriction.
    • Sensory Receptors: Baroreceptors monitor blood pressure changes; chemoreceptors detect chemical signals (e.g., low oxygen).

  • Example Reflexes

    • Atrial Reflex: Responds to excess blood in the atrium, increasing heart rate to prevent stretching damage.

Hormonal and Autoregulatory Mechanisms

  • Hormones Affecting Blood Pressure

    • Epinephrine and Norepinephrine: Increase heart rate and direct blood flow during fight or flight responses.
    • Antidiuretic Hormone (ADH): Encourages water reabsorption in kidneys; raises blood volume and pressure.
    • RAAS Pathway: Increases blood pressure through vasoconstriction and water reabsorption.
    • Erythropoietin: Stimulates red blood cell production, increasing blood viscosity and pressure.
    • Atrial Natriuretic Hormone: Lowers blood volume and pressure when atrial cells are stretched with too much blood.

  • Autoregulatory Mechanisms

    • Local responses within blood vessels (e.g., vasodilation in reaction to low oxygen levels during exercise).
    • Myogenic Response: Smooth muscle in arteries constricts in response to excessive stretch, regulating blood flow.

Disorders of Blood Circulation

  • Hypertension

    • Defined as consistently high blood pressure (systolic > 130 mmHg).
    • Risks: Aneurysms, kidney disease, heart attacks, strokes.

  • Hemorrhage

    • Loss of significant blood volume; treated through compensatory heart rate increase and vasoconstriction.

  • Circulatory Shock

    • Inadequate blood supply to tissues, resulting from:
    • Hypovolemic Shock: Low blood volume (e.g., hemorrhaging, dehydration).
    • Cardiogenic Shock: Heart failure (e.g., heart attack, arrhythmia).
    • Vascular Shock: Due to diminished vascular resistance or lost muscular control.
    • Obstructive Shock: Blockage in a blood vessel (e.g., embolism).

Blood Circulation Pathways

  • Pulmonary Circuit

    • Simplified structure from right ventricle through pulmonary arteries to lungs for gas exchange, returning oxygenated blood to the left atrium.

  • Aortic Branches

    • Asymmetrical branching (e.g., brachiocephalic artery on the right).
    • Recognition of important arteries in labs.

  • Major Thorax and Abdominal Pathways

    • Key vessels: Celiac trunk supplies blood to the liver, stomach, and spleen.
    • Recognition of iliac and femoral arteries/veins in limbs.

  • Venous System

    • Veins follow arteries closely; key exceptions noted.
    • Hepatic Portal System: Drains blood from abdominal organs, discussed in lab.

  • Conclusion

    • Reminder to prepare for next topic on the lymphatic system in upcoming lectures.