BIOL 2114 – Chapter 20 Study Notes: Blood Vessels & Circulation

BIOL 2114 – Chapter 20 Explained Study Notes: Blood Vessels & Circulation

Vessel Basics

  • Arteries
    • Carry blood away from the heart (usually oxygenated).
  • Arterioles
    • Regulate blood pressure and resistance.
  • Capillaries
    • Site of gas, nutrient, and waste exchange.
  • Venules
    • Collect blood from capillaries.
  • Veins
    • Carry blood toward the heart and contain valves to prevent backflow.

Arteries vs Veins

  • Arteries
    • Thick walls, small lumens, no valves, high pressure.
  • Veins
    • Thin walls, large lumens, presence of valves, low pressure.
    • Rely on skeletal muscle and breathing to assist in moving blood.

Vessel Wall Layers (Tunics)

  • Tunica intima
    • Inner endothelial layer that lines the lumen of blood vessels.
  • Tunica media
    • Composed of smooth muscle controlling the diameter and blood pressure of the blood vessel.
  • Tunica externa
    • Outer layer made of connective tissue that provides protection and structural support.

Capillary Beds

  • Metarterioles
    • Connect arterioles to capillaries, facilitating blood flow regulation.
  • Precapillary sphincters
    • Muscular rings that regulate blood flow into capillary beds, opening and closing based on tissue needs.

Blood Pressure

  • Systolic pressure
    • Pressure in arteries during ventricular contraction, reflecting the highest pressure in the arteries.
  • Diastolic pressure
    • Pressure in arteries during ventricular relaxation, indicating the lowest pressure in the arteries.
  • Pulse pressure
    • Difference between systolic and diastolic pressures, calculated as:
      extPulsePressure=extSystolic−extDiastolicext{Pulse Pressure} = ext{Systolic} - ext{Diastolic}
  • Korotkoff sounds
    • Sounds heard while measuring blood pressure with a sphygmomanometer, indicative of changes in blood flow.
  • Factors affecting blood pressure
    • Dependent on
    • Cardiac output
    • Blood volume
    • Resistance of blood vessels
    • Elasticity of blood vessel walls
    • Viscosity of blood.

Venous Return

  • Mechanisms aiding in venous return to the heart include:
    • Skeletal muscle pump
    • Respiratory pump
    • Venous valves
    • Pressure gradients that facilitate movement towards the heart.

Capillary Exchange

  • Mechanisms
    • Occurs via diffusion, filtration, and osmosis.
  • Pressures involved
    • Hydrostatic pressure
    • Pushes fluid out of capillaries.
    • Osmotic pressure
    • Pulls fluid into capillaries.
  • Fluid imbalance
    • Excess filtration can result in edema, a condition characterized by excess fluid in tissues.

Hormonal Blood Pressure Control

  • Baroreceptors
    • Sensory receptors that detect stretch and changes in blood pressure.
  • Key hormones affecting blood pressure
    • Epinephrine and norepinephrine
    • Increase heart rate and cause vasoconstriction.
    • Antidiuretic hormone (ADH)
    • Increases water retention and blood volume.
    • Renin-Angiotensin-Aldosterone System (RAAS)
    • Significantly raises blood pressure.
    • Erythropoietin
    • Stimulates increased production of red blood cells.
    • Atrial natriuretic hormone (ANH)
    • Lowers blood pressure by promoting vasodilation and increasing sodium and water excretion.

Shock Types

  • Hypovolemic shock
    • Results from low blood volume, commonly due to hemorrhage or dehydration.
  • Cardiogenic shock
    • Caused by heart pump failure, leading to inadequate perfusion of tissues.
  • Septic shock
    • Induced by an infection causing widespread vasodilation and a drop in blood pressure.
  • Neurogenic shock
    • Results from loss of sympathetic tone, often due to spinal cord injury.
  • Anaphylactic shock
    • A severe allergic reaction causing systemic vasodilation and fluid leakage.
  • Obstructive shock
    • Caused by physical blockages in circulation, such as pulmonary embolism.

Heart Failure

  • Left-sided heart failure
    • Causes pulmonary congestion due to blood backing up into the lungs.
  • Right-sided heart failure
    • Leads to systemic edema from blood accumulating in the body's tissues.

Circulation Pathways

  • Pulmonary circulation
    • Moves blood between the heart and lungs for gas exchange.
  • Systemic circulation
    • Moves blood between the heart and the rest of the body, delivering oxygen and nutrients.

Major Arteries

  • Aorta branches
    • Include
    • Brachiocephalic artery
    • Left common carotid artery
    • Left subclavian artery.
  • Abdominal branches of the aorta
    • Celiac trunk, mesenteric arteries, renal arteries, and gonadal arteries.

Upper Limb Blood Flow

  • Vascular pathway:
    • Subclavian artery → Axillary artery → Brachial artery → Radial & Ulnar arteries → Palmar arches → Digital arteries.

Lower Limb Blood Flow

  • Vascular pathway:
    • External iliac artery → Femoral artery → Popliteal artery → Tibial arteries → Dorsalis pedis artery.

Venous Return to Right Atrium

  • Major veins include:
    • Superior vena cava, Inferior vena cava, and Coronary sinus.

Hepatic Portal Circulation

  • Blood from digestive organs flows to the liver via the hepatic portal vein, which then exits the liver via the hepatic veins to the inferior vena cava.

Fetal Circulation

  • Foramen ovale
    • A shunt that directs blood from the right atrium to the left atrium, bypassing the lungs.
  • Ductus arteriosus
    • Connects the pulmonary trunk to the aorta, allowing blood to bypass pulmonary circulation.
  • Ductus venosus
    • Shunts a portion of umbilical vein blood flow to the inferior vena cava, bypassing the liver.

Common Diseases

  • Varicose veins
    • Result from valve failure leading to blood pooling in the veins.
  • Arteriosclerosis
    • Characterized by hardening of the artery walls.
  • Atherosclerosis
    • Involves plaque buildup within the arteries, narrowing them and impeding blood flow.