Capillaries

Describe The anatomy of a Typical Blood Vessel

• Lumen

• tunica interna

• tunica media

• tunica externa with vasa vasorum

Lumen

• where blood actually is

• central opening space

• stomach has a lumen

• small intestine has a lumen

Tunica Interna

• innermost layer of bloody vessel

• endothelium

• simple squamous epithelium

• elastic and collagen tissue

Tunica Media

• smooth muscle (more in arteries)

• spindle shaped

Tunica Externa

• as vessels

• vasa vasorum

• connective tissue

Vasa Vasorum

provide blood to arteries

Elastic (Conducting) Arteries

• moving blood through the body

• aorta

• larger blood vessels

Muscular (Distributing) Arteries

• what blood goes where

• vasoconstriction

• vasodilation

Vasoconstriction

• sympathetic input

• vessels get smaller

• less blood is distributed

• norepinephrine as neurotransmitter

Vasodilation

• lack of sympathetic input

• vessels get bigger

• more blood is distributed

Arterioles (Resistance Vessels)

• diameter is smaller

• increases resistance

• can have smooth muscle around it

Anatomy of Capillary

• simple squamous epithelium

• stay the same size

• permeable

• fenestrated

• sinusoidal

• gas exchange

• precapillary sphincter

• med arterial (shunt)

Permeable (capillary)

• things can move between cells

• tight junctions not here

• likely desmosomes

• leaky (things can get through)

• size determines what gets through (filtration)

Fenestrated (Window) (Capillary)

• additional openings

• found in kidneys

• extra opening

• more leaky (can’t fit cells through though)

Sinusoidal (Capillary)

• found in liver

• large in the lumbar

• more leaky (can fit cells through)

Precapillary Sphincter (Capillary)

• circular muscle

• before blood goes into capillary

• constrict = send blood away

• never fully close (will kill it)

How Substances are Exchanged Between Capillaries and Tissue Fluids

• diffusion

• filtration and hydrostatic pressure

• osmosis and osmotic pressure

• lipid solubility and particle size

• lymphatic vessels

• artery end

• vein end

• can cause swelling (edema)

• histamines

Diffusion (Substance Exchange in Capillaries)

• most important process

• O2, CO2, fatty acids, glucose, ions

Filtration and Hydrostatic Pressure (Substance Exchange in Capillaries)

• smaller molecules pass through pores

• based on size (small things can be pushed out)

Osmosis/Osmotic Pressure (Substance Exchange in Capillaries)

• colloid pressure

• water goes back into artery

Lipid Solubility & Particle Size (Substance Exchange in Capillaries)

• proteins and cells too large to pass

Lymphatic Vessels (Substance Exchange in Capillaries)

• return extracellular fluid to blood stream

Artery End (Substance Exchange in Capillaries)

• more leaves than comes in

Vein End (Substance Exchange in Capillaries)

• more comes in than leaves

Can Cause Swelling (Substance Exchange in Capillaries)

• due to lymphatic vessels

• accumulation of edema

Histamines (Substance Exchange in Capillaries)

• make capillaries more leaky

• more openings to push stuff through

• more liquid into extracellular space (more edema)

Role of Lymphatic Capillaries in Maintaining Tissue Fluid Volume

• returning lymph to bloodstream

• help maintain normal blood pressure and volume

• prevent fluid form building up around tissue (edema)

Blood Reservoirs (Veins)

• storage (hold large volume of blood)

• most of our blood is in our veins

Capacitance Vessels (Veins)

• capacity to hold a high volume of blood

• no longer distributing

• can lose 25% of blood and still hold blood pressure

Venous Valves (Veins)

• keeps blood moving in one direction

• similar to semilunar valve

• prevent backflow

Vein Facts

• no internal or external elastic band

• contracted skeletal muscles push blood through vein (get back to heart)

• breathing can promote blood flow for veins

Central Venous Pressure

pressure of blood in large veins of chest near the right atrium, reflecting the amount of blood returning to the heart and the heart’s ability to pump blood into the arterial system

Systolic Blood Pressure (SBP)

• feel pulse here

• when vessels contract

• tied to QRS complex

Diastolic Blood Pressure (DBP)

• when vessels are relaxed

Pulse and Pulse Pressure (PP)

• PP = SBP - DBP

• difference between systolic and diastolic blood pressure

Mean Arterial Pressure (MAP)

• DBP + 1/3 (PP)

Cardiac Output

• amount of blood pumped by the heart (ventricles) per minute

• heart rate x stoke volume

End-Diastolic Volume (Preload) (Frank-Starling Law of the Heart)

• end diastolic volume of blood in ventricle

• before contraction

• before systole

• what you start with

• preload goes down when you don’t have as much blood

• increase preload = stoke volume increase

Contractility (Frank-Starling Law of the Heart)

• contracting with more force

• with sympathetic nervous system

• cardiac muscle is striated

• cardiac muscle fibers at overly shortened

• likes to work on left side of Frank-Starling graph

• cannot go all the way to right (force will go down)

• eject less than delivered

• increase contractility = increase (to a point) stroke volume

Afterload (Frank-Starling Law of the Heart)

• systole and blood being pushed to aorta (needed to open valve)

• working against to eject blood

• move to move blood

• against aortic pressure

• increase afterload = decrease stroke volume

Baroreceptor

• types of mechanoreceptor

• stimulated by physical movement

• pressure pushes on baroreceptor (in aorta and carotid artery)

• effector = heart (first)

• effector = blood vessels

Blood Pressure Too High

decrease heart rate (and mean arterial pressure)

Blood Pressure Too Low

increase heart rate (and mean arterial pressure)

Increase Heart Rate

decrease stroke volume (move further towards the left side of the Frank-Starling graph)

Mean Arterial Pressure Prediction Equation

• MAP = cardiac output x total peripheral resistance

• MAP = heart rate x stroke volume x total peripheral resistance