Human Physio Blood and Blood Flow

Overview: Cardiovascular system

  • Arteries take blood away from the heart.
  • Veins return blood to the heart
  • Series flow: blood travels through ==systemic== and ==pulmonary== circuits in series

Functional model of the cardiovascular system

  • Arteries connect to arterioles, that connect to capillaries, that connect to venules, that connect to veins.
  • Systemic arteries maintain pressure during ventricular relacation by changing vessel diameter.

Summary

<<Deoxygenated blood enters the right atrium through superior and inferior vena cava.<<

<<Blood enters right ventricle through triscuspid valve.<<

<<Blood exits right ventricle through pulmonary valve and enters pulmonary artery.<<

<<Left and right pulmonary arteries send blood to lungs, where gas exchange occurs.<<

[[Oxygenated blood returns to heart via pulmonary veins and enters left atrium.[[

[[Blood enters left ventricle through mitral valve.[[

[[Blood exits left ventricle through aortic semilunar valve to enter aorta.[[

[[Aorta distributes blood to the rest of body.[[

Characteristics of blood vessel types

  • Endothelium - thin layer, inner lining of all blood vessels
  • Surrounded by layers of smooth muscle, elastic and fibrous connective tissue
  • Blood vessel types vary in diameter and composition
  • Veins have larger diameter and thinner walls as compared to arteries

Pressure gradients in driving blood flow

  • Pressure = force exerted by blood through vessel

  • Heart creates pressure gradient for bulk flow of blood

  • Pressure gradient (△P)

    = P at one end of a blood vessel - P at the other end of a blood vessel

  • △P in systemic circuit > △P in pulmonary circuit

Pressure gradients in blood flow

  • Pressure gradient cause a fluid to flow
  • Flow α △P

Resistance in blood flow

  • Blood Flow = driving force = pressure gradient
  • △P drives the blood flow in circulatory system
  • Flow direction - high pressure to low pressure
  • Factors that affect the blood flow in the cardiovascular system
    • Resistance (R) and △P

Flow rate = △P/R

Resistance opposes blood flow

  • Resistance to flow - tendency of cardiovascular system to oppose blood flow
  • Flow α 1/R
  • Factors affecting resistance in blood vessels: equation derived from Poiseuille’s Law
    • {{^^Radius (r) of vessel^^{{
    • {{In arterioles (and small arteries) - can regulate radius{{
    • {{Length of vessel (L){{
    • {{Blood viscosity{{
    • {{dependent on amount of RBCs and proteins in plasma{{
  • Change in ==diameter== → change in resistance and flow
    • blood vessels dramatically alter blood flow during ==vasoconstriction== or ^^vasodilation^^

Total peripheral resistance (TPR)

  • TPR = combined resistance of all blood vessels within the systemic circuit
  • Flow through network varies with resistance
    • Vasoconstriction in network → increase resistance → decrease flow
    • Vasodilation in network → decrease resistance → increase flow

Pressure throughout systemic circulation

  • Blood pressure - highest in arteries and decreases continuously as it flows through circulatory system
  • Systolic pressure - exerted on vessel walls when heart contracts
  • Diastolic pressure - pressure during relaxation
  • Pulse pressure (strength of pressure wave) - systolic pressure - diastolic pressure
  • Mean arterial pressure (mean arterial pressure, MAP) is the average arterial pressure throughout one cardiac cycle, systole and diastole
    • diastole pressure + 1/3 pulse pressure

Arteries serve as a pressure reservoir

}}Pressure transferred to blood vessels when heart contracts}}

  1. Ventricular contraction

    1. Ventricular contracts.
    2. Semilunar valve opens.
    3. Aorta and arteries expand and store pressure in elastic walls.

]]Pressure maintained in blood vessels while heart relaxes]]

  1. Ventricular relaxation

    1. Isovolumic ventricular relaxation occurs
    2. Semilunar valve shuts, preventing flow back into ventricle.
    3. Elastic recoil of arteries sends blood forward into rest of circulatory system.

Arterial Blood Pressure

  • Pressure in the aorta
  • Varies with cardiac cycle
  • Systolic blood pressure = maximum pressure - due to ejection of blood into aorta
  • Diastolic blood pressure = minimum pressure - not zero due to elastic recoil

Elastic recoil: the inherent resistance of a tissue (arteries) to changes in shape, and the @@tendency of the tissue to revert to its original shape once deformed.@@

Mean arterial pressure (MAP)

  • Mean arterial pressure (MAP) represents the “average” pressure of blood in the arteries, that is, the average force driving blood into vessels that serve the tissues.

Lymphatic system

  • Systems of vessels, lymph nodes and organs
  • Fluid in the lymphatic system (lymph), carried through the ducts and returned to cardiovascular system
  • Allow one-way movement of interstitial fluid from tissues into the circulation

Functions of lymphatic system

  • return fluid and proteins filtered out capillaries to circulatory system
  • ==pick up fat absorbed== at small intestine and transfer back to circulatory system
  • serve as filter to ==help capture and destroy pathogens==

Lymph flow

  • valves on lymph vessels
  • depend of smooth muscle contractions in larger lymph vessels

Composition of blood

Blood

  • Circulation portion of extracellular fluid
  • Carry material from one part of body to another

Blood composition

  • Plasma
  • Erythrocytes (RBC)
    • Transport O2 from lung to tissues and CO2 from tissues to lungs
  • Leukocytes (WBC)
    • Lymphocytes - found in lymphatic system, B- & T-cells
    • Monocytes - exit bloodstream and become macrophages
    • Neutrophils - phagocyte for bacteria & secretes cytokines
    • Eosinophils - phagocyte for parasites & cytokines related to allergies
    • Basophils - mediate inflammation & allergies via cytokine release (histamine)
  • Platelets
    • Coagulation - process by which blood clots prevent blood loss

Hematocrit test

  • Measure fraction of RBC to the total blood volume

Hematopoiesis

  • controlled by ^^cytokines^^
  • Erythropoiesis (RBC production)
    • cytokine erythropoietin (EPO)
    • EPO made in kidney cells, released in response to low O2 levels in tissues
  • White blood cell production
    • cytokine colony-stimulating factors (CSFs)
    • CSFs made by endothelial cells and white blood cells
  • Platelet production
    • thrombopoietin (TPO) regulate growth and maturation of megakaryocytes
    • TPO produced in liver primarily and kidney

Red blood cells (RBCs)

  • Lack nucleus or organelles

  • Packed with hemoglobin

  • Important characteristics of RBCs:

    • concave shape allows for 30% more surface area for carrying O2
    • 97% of their content is haemoglobin - binding both O2 and CO2

  • Morphology of red blood cells can provide clues to presence of disease

    • e.g. sickle cell disease: cells shaped like sickle or crescent moon

    genetic defect with abnormal haemoglobin molecules that cause RBCs to change shape

White blood cells (WBCs)

Platelets

  • Cytoplasmic fragments derived from megakaryocytes

  • Colourless

  • Cell fragments

    • No nucleus
    • Has organelles and granules

  • Granules containing secretory products

  • Platelets are important in blood clotting

  • Hemostasis = stop bleeding

  • Three steps to stop bleeding

    Vasoconstriction → Platelet plug formation → Coagulation (formation of a blood clot)

Platelet plug formation

  1. Exposed collagen binds and activates platelets
  2. Platelet factors are released.
  3. Factors attract more plateleets.
  4. Platelets aggregate into platelet plug.

Summary

  • [ ] Describe the properties of different blood vessels types
  • [ ] Explain the concepts of pressure gradients and resistance in blood flow through blood vessels
  • [ ] Describe the major components of blood and their functions