Cardiovascular System: Blood Vessels

Endothelium

• Endothelium is the name for simple squamous epithelium.
• Simple squamous describes the structure: one cell thick, one layer thick.
• Has a basement membrane (the floor of the cells).
• The basement membrane is selectively permeable: it allows some things to pass through, but not others.

Tunica Interna (Tunica Intima)

• Innermost layer of a blood vessel.
• Secretes chemicals that stimulate:
  • Vasodilation (widening of blood vessels)
  • Vasoconstriction (narrowing of blood vessels).
• Secretes chemicals that repel blood cells and platelets (e.g., prostacyclin).
  • Prostacyclin: a platelet repellent, preventing blood clot formation.

Tunica Media

• Middle layer of a blood vessel.
• Provides for vasomotion:
  • Vasoconstriction: Smooth muscle contracts, decreasing blood flow.
  • Vasodilation: Smooth muscle relaxes, increasing blood flow.

Tunica Externa (Tunica Adventitia)

• Outermost layer of a blood vessel.
• Contains vasa vasorum
  • Vessel on a vessel: small blood vessels that feed the outer layers of larger blood vessels.

Blood Vessel Structure

• Lumen: The cavity or passageway inside the blood vessel, containing blood.
• Blood in the lumen is in direct contact with the tunica interna (intima).
• Tunica Intima: Called "intima" because it is in intimate contact with the blood.
• Diffusion: Movement of molecules from high concentration (blood) to low concentration (tissues).
  • Effective for short distances, but is a slow process.
• Oxygen and nutrients diffuse from the blood through the tunica intima to nourish the vessel walls.
• Inner half of tunica media receives oxygen and sugar via diffusion.
• Outer half of tunica media and tunica externa are too far from the lumen to receive adequate nourishment via diffusion, so they are supplied by the vasa vasorum.

Artery vs. Vein

• Similarities: Both have three layers (tunica interna, tunica media, tunica externa), vasa vasorum, basement membrane and endothelium.
• Differences:
  • Valves: Veins have valves; arteries do not.
  • Elastic Layer: Arteries have an elastic layer; veins do not.
  • Wall Thickness: Arteries have thicker walls than veins.
  • Smooth Muscle: Tunica media is thicker in arteries because they have more smooth muscle.
  • Lumen Diameter: Veins generally have a larger lumen diameter than arteries.
• Capillary: A very small blood vessel; "like a straw with a tight wrapper around it."

Identifying Arteries and Veins on Microscope Slides

• Artery:
  • Thicker walls due to more smooth muscle to provide support.
  • Lumen tends to stay open.
  • Tunica intima/interna has a rippled appearance (more bumpy).
  • Intima is super rippled.
• Vein:
  • Thinner walls.
  • Lumen tends to collapse on itself.
  • Tunica intima is smoother.
  • Larger lumen diameter(evenwhencollapsed).
  • Intima is mildly rippled or smooth vs the bumpy artery.

Artery Characteristics

• Thicker walls due to more smooth muscle, collagen fibers, and elastic tissue.
• More muscular.
• Can withstand more blood pressure.
• Arteries provide more vasomotion (vasodilation and vasoconstriction).
• Retain their shape.

Classifying Arteries

• Conducting (Elastic) Arteries:
  • Large arteries (e.g., aorta, aortic branches, brachiocephalic, common carotids, subclavian, pulmonary trunk).
  • Expand during systole (ventricular contraction and emptying) as blood enters.
  • Recoil during diastole (ventricular relaxation).
• Distributing (Muscular) Arteries:
  • Distribute blood to specific limbs and organs.
  • Examples: Brachial, femoral, renal, splenic, left gastric arteries.

Arterial Sense Organs\Carotid Sinus and Aortic Arch

• Carotid Sinus and Aortic Arch:
  • Baroreceptors (pressure sensors).
  • Detect changes in blood pressure by the degree of stretching.
    • Increased stretch indicates high blood pressure.
    • Decreased stretch indicates low blood pressure.
• Carotid Sinus Reflex and Aortic Arch Reflex:
  • If baroreceptors detect a rise in blood pressure:
    • Increase parasympathetic stimulation (apply the brakes, take foot off the gas).
    • Decrease sympathetic stimulation.
    • This lowers heart rate and causes vasodilation, lowering blood pressure.
  • If baroreceptors detect a drop in blood pressure:
    • Increase sympathetic stimulation (press the gas).
    • Decrease parasympathetic stimulation.
    • This increases heart rate and causes vasoconstriction, raising blood pressure.

Control of Blood Pressure

• Blood pressure can be quickly raised or lowered by vasoconstricting or vasodilating blood vessels.

Arterial Sense Organs\Chemoreceptors

• Carotid Bodies and Aortic Bodies:
  • Chemoreceptors (taste the blood figuratively):
    • Taste the blood: monitor blood composition
    • Monitor blood composition.
    • Inform the respiratory center to adjust breathing to stabilize pH ($7.35-7.45$).
    • Work with buffers to maintain blood pH.
      Note:: Carotid sinus and aortic sinuses detect blood pressure via baroreceptors. They are not detecting sinus pressure.

Capillaries

• Diameter: Approximately 5 micrometers, while a red blood cell is about 7.5 micrometers in diameter.
• Single capillary: A single layer of endothelium and a basement membrane.
• No tunica media or tunica externa.
  Characteristics of a Capillary
• Red blood cell is more flexible than previous lectures
• One cell thick- very permeable

Red Blood Cell Flexibility

• Red blood cells must fold, bend, twist, and contort (rouleau) to pass through capillaries.
• To facilitate this, red blood cells are flexible and durable.
• The spleen is where old red blood cells go to die because of its narrow capillaries.
• Old red blood cells are not as flexible or durable because they lack a nucleus and organelles.
• This lack of organelles is beneficial because it prevents the red blood cell from consuming the oxygen it is transporting.
• Graveyard for old blood cells and a point for new blood cells to be produced

Blood and Bodily Fluids such as: urine, saliva , tears, sweat

• Plate of material exchange

Capillary Types

• Continuous Capillaries:

  • Most common type; found throughout the body.
  • Contain tight junctions and appear as an intact tube.
  • Have intercellular clefts (gaps between cells) that allow small molecules like water and sugar to pass through.
  • Cells connected with grount
    *Fenestrations capillaries
    *Think of a sheet of paper with holes punched in it.
    *Each hole is called a fenestration(s).
    *Still cannot hold some platelets
    Location for Fenestration Capillaries:
    *Brain
    *Small intensities
  • Kidneys
    All liquids in our body come from blood
    Urine and Spinal Fluid: Are only small enough to pass and are not bloody
    Sweat is salty (water and salt is small enough to pass through blood, but red blood cells are too big. Hence our sweat comes from blood

• Fenestrated Capillaries:

  • Have fenestrations (small pores) through the endothelial cells.
  • More leaky than continuous capillaries.
  • Found in: choroid plexus, ciliary bodies, kidneys, small intestine.

• Sinusoids:

  • Have large fenestrations and an incomplete basement membrane.
  • Allow proteins and blood cells to pass through.
  • Found in: liver, red bone marrow, spleen.
    Incomplete Basement Membrane- allow Proteins and blood cells can pass through them

Capillary Beds

• A network of capillaries, resembling a spider web or volleyball net.
• In the skin, a capillary bed can change its diameter to regulate blood flow based on temperature.
  • On a cold day, blood flow to the skin is reduced.
  • On a warm day, blood flow to the skin is increased.

Veins

• Thin-walled and flaccid (easily collapse).
• Blood pressure is lower the further away from the heart.
• Do not retain their shape because of thin walls.
• Veins have valves to help maintain blood flow against gravity. Arteries do not have valves, because they have higher pressure so they don't need valves.

Venules

• Venules- medium veins filled with vaneous valves

Function of Venous Valves

*Pressure in veins is not high enough to push blood against the gravity
*Maintain blood flow against gravity
*Valves keep blood from flowing into venous system

Skeletal Muscle Pump

• The massaging action of skeletal muscles helps propel blood through the veins - Gokurt example
• Muscles Contract Bulge veins and squeeze
  Blood is already inside- Then looks like squeezed there
  Valves prevent the muscles from moving in the opposite direction
  If a person has a desk job kick foot up and keep blood pump going
  Large Veins: Internal jugular veins, pulmonary veins, the renal veins, and the vena cava.
  Varicose veins is the bulgy form and the valves not working as well
  Compression sock can help, compression provide support with bulgy veins or sagging feeling

Blood Flow

• Blood normally flows from the heart to arteries, then to capillaries, then to veins, and back to the heart.
  *Capillaries connects with arteries and veins.
• Portal System: A blood vessel connecting two capillary networks.
• Found in:
  • Kidneys
  • Hypothalamus and pituitary gland
  • Intestines and liver
    Simple way: simplest pathway is what we wrote up here, heart to arteries, arteries, capillaries, capillaries to veins, and then back to the heart.

Portal- Classic two classic capillary beds connected to a single blood vessel.

Flow and Perfusion

• Flow: The amount of blood (mL) flowing through a blood vessel, organ, or tissue in a given time (minutes).
• Perfusion: Flow per given volume or mass of tissue (mL/min/g).
• Example: If an eyeball and a leg both receive 1 gallon of blood per minute (flow), the eyeball receives more blood for its size (perfusion) because it is smaller.

Blood Pressure

• The force that blood exerts against a vessel wall.
• Systolic Blood Pressure: The highest arterial blood pressure attained during ventricular contraction (systole).
• Diastolic Blood Pressure: The lowest arterial blood pressure during ventricular relaxation (diastole).
  *Post pressure to absorb.
  Normal Blood Pressure: -120/80
  Reminder: Just because the perfect average and be a slight change
• Mean Arterial Pressure (MAP): The average arterial pressure during a single cardiac cycle.

Blood Pressure Conditions

• Hypertension: Chronic resting blood pressure higher than 140/90.
  • Can lead to:
    • Increased workload on the heart
    • Damage to blood vessels
    • Heart attack
    • Stroke
    • Renal failure
    • Retinal damage (vision impairment, blindness) due to damage to capillaries in the retina.
• Hypotension: Chronic low resting blood pressure.
  Blood slows if going to the brain going to gravity.