Exam Study Notes: Systemic Circulation

Systemic Circulation - Blood Vessels

Arteries/Arterioles:

  • Carry blood away from the heart to tissues.

  • Have three layers:

    1. Inner Endothelium Layer: Provides a smooth surface to reduce friction.

    2. Thick Walls: Composed of smooth muscle to resist blood pressure and change diameter to control blood pressure. These layers contain elastic fibers for stretching and recoil.

    3. Outer Connective Tissue (Collagen) Layer

  • Arterioles are smaller branches of arteries.

  • Sphincters open/close to allow blood to pass from arterioles to capillary beds.

  • Control of blood flow:

    • Contraction of smooth muscle in arteries (middle layer) causes blood pressure to increase in the rest of the body.

Veins/Venules:

  • Carry blood toward the heart.

  • Venules are small vessels that drain blood from capillaries and join to form a vein.

  • Walls are composed of smooth muscle, but are thinner than arterial walls that consist of

    • Epithelium

    • Collagen

  • Valves close to prevent blood from flowing away from the heart.

Capillaries:

  • Narrow, microscopic vessels branching from arterioles.

  • Walls are one cell layer thick (cell membrane) to assist with cell membrane transport.

  • Exchange across walls:

    • Gases (O2, CO2): Diffusion.

    • Molecules (glucose, amino acids): Facilitated transport.

  • Networks of capillaries exist at organs/muscles.

  • Sphincters leading from arterioles open/close, so more/less blood flows to specific areas as needed.

Capillary Beds:

  • Example: Increased blood flow to muscles when exercising.

Capillary-Tissue Fluid Exchange

  • Arterial End of the Capillary:

    • Blood pressure: 30 \, mmHg

    • Osmotic pressure: 21 \, mmHg

    • Net pressure: Water moves out because blood pressure is greater than osmotic pressure.

  • Venous End of the Capillary:

    • Blood pressure: 15 \, mmHg

    • Osmotic pressure: 21 \, mmHg

    • Net pressure: Water moves in because blood pressure is less than osmotic pressure.

  • Components:

    • Protein, red blood cell, salt, amino acids, glucose, water, oxygen, carbon dioxide.

  • Precapillary sphincters, arteriole, artery, capillaries, venule, arteriovenous shunt, tissue cell, vein.

Systemic Circulation: Blood Velocity, Cross-Sectional Area, Blood Pressure

  • Blood pressure decreases with increasing distance from the heart.

  • Cross-sectional area is highest at the capillaries.

  • Blood velocity decreases with increasing distance from the heart.

  • When blood reaches capillaries, it starts to return to the heart, and velocity increases due to breathing/muscle contraction.

Systemic Circulation - Blood Vessels

  • Carotid arteries: Take blood to/from the head.

  • Subclavian vein: Takes blood from heart chambers to the rest of the body.

  • Renal artery: Take blood to/from the kidneys.

  • Jugular veins

  • Subclavian artery

  • Renal vein

  • Posterior vena cava

  • Anterior vena cava

  • Aorta

  • Mesenteric vein

  • Mesenteric artery: Blood from aorta to to small intestine.

  • Iliac artery: Take blood to/from the legs.

  • Femoral vein

  • Iliac vein

  • Femoral artery

Systemic Circulation - Hepatic Portal System

  • Hepatic artery/vein: Blood from aorta to liver

  • Inferior mesenteric artery/vein: Blood from colon to hepatic portal vein; blood from aorta to colon.

  • Hepatic portal vein: Blood from intestines to liver (for processing).

  • Superior mesenteric artery/vein: Blood from small intestine to hepatic portal vein; blood from aorta to the small intestine.

  • Liver, small intestine, and colon are surrounded by capillary beds.

  • Blood from the liver goes to the posterior vena cava.

Fetal vs. Adult Circulation Problems Facing Fetus:

  1. Cannot access air, so there's no point in sending blood to the lungs.

  2. The mother is responsible for nutrient intake and waste removal.

Solution #1:

  • Arterial Duct (Ductus Arteriosus): Connects pulmonary artery/aorta; much of the blood that would have been pumped from the heart to the lungs is directed to the aorta instead.

  • Oval Opening (Foramen Ovale): Opening between the right and left atrium in the heart, covered by a flap that acts like a valve.

    • Some blood is pumped through the flap from the right to the left side of the heart, bypassing the pulmonary circuit.

    • If the opening does not close after birth, it can cause mixing of blood, leading to “blue babies,” which may require open-heart surgery.

Fetal Circulation Solution #2

  • Placenta:

    • Umbilical arteries/veins:

      • Take deoxygenated blood to/oxygenated blood from the placenta

    • Vascularized membrane shared by mother/fetus:

      • Site of exchange of gases, nutrients, and wastes

  • Venous Duct (Ductus Venosus):

    • Connects the umbilical vein to the vena cava to bring blood back to the fetus's heart.

    • Attaches at the fetus's liver, bypassing most of the liver.

  • Chemicals ingested by the mother (alcohol, drugs) can harm the fetus.

  • Foramen ovale

Path of Blood Through Fetus

  • Mix of oxygenated/deoxygenated blood moves from the right to the left atrium of the heart via the oval opening.

  • Right ventricle of the heart to the pulmonary artery tissue (nutrient/waste exchange).

  • Umbilical arteries (deoxygenated blood) go to the placenta (exchange of gases and nutrients).

  • Umbilical vein (oxygenated blood) to venous duct bypasses liver.

  • Posterior vena cava.

  • Arterial duct + left ventricle of the heart lead to the aorta.