A & P Chapter 19 - Blood Vessels

Arteries

Carry blood away from heart

Arterioles

Carry blood to capillaries

Capillary

Site of exchange between substances between blood and tissue

Venules

Small Vein

Veins

Carry blood into heart

Tunica Intima

Made of endothelium

• Subendothelial Layer - Elastic Membrane , Interenal

Tunica Media

Smooth Muscle (Contraction), Vasoconstriction & Vasodilation

Arteries Walls

Thicker, smaller lumen

Veins Walls

Thinner, larger lumen

Arterioles and Venules

Same walled but just smaller

Capillary

Made up of basement membrane and endothelium

Lumen of Artery

Round

Lumen of vein

Collapsed, ovular

Elastic Artery

Largest in body, highest number of elastic fibers

Aorta

Muscular Artery

Medium Sized, lots of smooth muscle,

Carry blood into specific organs

Help with vasoconstriction & vasodilation

Arterioles

Smaller, thinner walls, carry blood to capillaries, VD & VC

Capillary facts

• Arteriole → Capillary → Venule

• 10-100 BV connected in a capillary

• Site of gas exchange, the bed of the capillary

Microcirculation

Flow from arteriole to a venule via a capillary bed

Capillaries are

Semi-permeable across the endothelium

Continuous Capillary

Most common, least permeable

• Skin, muscles, lungs & CNS

• Tight Junctions between squamous cells

  • Intercellular cleft - gap within cells

Fenestrated Capillary

• Increased permeability

• Found in the kidneys and small intestine

• Fenestration = Opening or pore in capillary

Sinusoid Capillary

Most permeable

• Large fenestrations

  • Macrophages live in the liver for detoxification

Mesenteric Capillary Bed

• Metarteriole

• Thoroughfare Channel

Both are a part of Vascular Shunt - Which allows to bypass gas exchange

• When precapillary sphincters are closed, they contract

Veins - Carry blood towards the heart

Venule - no elastic fibers

• empty into veins

• Veins - Blood resevoir

Blood Volume 

60% Veins and Venules

Venous Valves

Aid in preventing backflow since pressure is low in veins

Varicose Veins

Blood is distended and sinks to the lower body

Muscular Pump of veins

Compresses vein and pushes blood upwards

Respiratory pump

Aids in breathing

Sympathetic Venoconstriction

Smooth muscle constriction in veins

Sinuses 

Flattened/widened veins with thin walls

Anasamoses

Connection of Blood Vessels

Arterial Anastamoses

Alternative pathways, coronary

Atriovenous Anastamoses

Shunts in capillaries

Venous Anastamoses

Seen in the skin, very abundant

Total Blood flow is equivalent to

Cardiac Output

Blood Flow and Pressure have a 

Direct relationship

Blood flow and resistance have an

Inverse relationship

Resistance

Opposition to bloodflow

• BV Diameter is the #1 determining factor

Blood Viscosity - Thickness

• Increased viscosity, increased thickness

• Higher hematocrit, higher viscosity

• More BV, more resistance

• Turbulence - irregular flow

Blood pressure

Most likely found in brachial arteries,

Highest pressure in arteries

As we move away from the heart BP goes down

Systolic BP

Ventricular Systole

Diastolic

Ventricular Diastole

MAP

Mean Arterial Pressure

Pressure Decreases

As we move along the CS frmo the heartP

Pressure is lowest

in the veins, veins need assistance

Pulse pressure

Difference between systolic and diastolic pressure (120/80) = 40 mmHg

MAP =

Diastolic + Pulse Pressure /3

= (120/80)

80 + (40/3) = 93.33 mmHg

Ventricles spend more time in

Diastole

Central Venous Pressure

Pressure in the Vena Cava near the Right Atrium 

(2-4 mmHg)

CVP determines pressure of RV

Determines EDV of RV and SV of Ventricles (Frank-Straling Mechanism)

Factors that regulate MAP

CO = HR x SV

• Stroke Volume and Heart Rate increase

Resistance

• Vasoconstriction

• Blood viscosity and BV length

Factors that regulate BP

Short -Term 

• nervous and endocrine

Long term 

• Renal 

Nervous System

• Mechanical (Baroreceptors ) - Change in pressure

• Chemoreceptors - Chemical changes of a fluid

• Cardiovascular Center of Medulla

  • Hypothalamus

  • Cerebral Cortex

    • Accel & Inhibitory center

    • Vasomotor Center - diameter of artieries

      • Vasomotor Tone - Constriction

Baroreceptors

Detect change in arteries

Neural Control of BP

• Afferent Pathway going to Medulla

  • HR decreases

• Effector

  • Decreases HR, SA Node

  • Lowers contractility of Heart

  • Dilation of BV and Arterioles

• When CO decreases, BP decreases

• Negative Feedback

Hormones that increase BP

• NE and Epi - Increase HR & Cardiac Output 

• Angiotensin II - Total Peripheral Resistance

• ADH - Increases Water Reabsorption, Raising Blood Volume

• Aldosterone - Increases Blood Volume (Salt and Water loss)

Hormones that Decrease BP

• Atrial Natruietic Peptide - Released w Hypertension

  • Will get eliminated as Urine 

    • Decreases Blood Volume along with pressure

  • Arterioles will vasodilate

Direct Renal Mechanism

• If there is less pressure, there are less kidney filtration

• Less urine forming, increases blood volume which increases MAP

Indirect Renal Mechanism

• Baroreceptors are released when pressure is high

• Sympathetic Mode - Releases Renin

• Renin Relases Angiotensin

  • Aldosterione - Sodium Reabsorption

    • Increases BV, Increases Pressure

ADH release by PP gland

Increases water reabsorption by kidneys

Thirst center

In hypothalamus Target the Artierioles - Vasoconstriction, Increase Resistance

Orthostatic Hypotension

• Got up too quickly, temporary

Chronic Hypotension

•  Long term condition

Circulatory Shock

BV inadequately fill form heart and cannot circulate blood normally

Primary Hypertension (90%)

•  Caused by genes and environmental factors

Secondary Hypertension (10%)

• Due to identifiable conditions - homeostatic imbalance

Intrinsic

• Within

• Paracrine Signlaing

• Also known as autoregulation or local control

• Extrinsic Controls

• Control is from outside of the tissue or organ 

• Uses nerves or hormones

Vasodilation

• Increase in size of lumen

• Resistance goes down

• Increase in blood flow

• Decrease in Sympathetic Tone - ANP

Vasoconstriction

• Size of lumen down

• Increase resistance

• Decrease of bloodflow

• Endothelins = Released by damaged endothelium cells

• Increase in Sympathetic Tone - Hormonal - 5 Hormones

• When we study cardiac output, at rest, the BV is 5L/min

• 20% of Blood flow in skeletal muscle

• Significant to Digesive, Renal and Cardio

• At exercise, CO increases to 17.5 

• Increased to the muscle

• Intrinsic controls allow blood vessels to dilate and arterioles bring the blood to the muscles

• Extrinsic reduces control to other organs

• MAP is maintained

• Blood flow will vary with fiber type and activity

• O2 goes down for aerobic CR

  • Vasodilation which increases blood flow

Hyperemia

Increase of BF that goes to a specific area

Total area goes up

 speed of blood flow goes down

• Flows fastest in Aorta and arteries

• Goes down as it passes through to the venae cavae

  • Slowest in capillaries which will allow for adequate time for exchange of gases, nutrients and materials between blood and body tissues

Diffusion

• - High to low concentration

  • Lipid-soluble substances

  • Movement between intercellular cleft

  • Movement through the fenestrations

Active transport

• Pinocytosis, large substances

Each day, 20L of fluid filters through capillaries at the arteriole end

• Flow through interstitial space, most will be absorbed at the venous end

• Excess fluid will get picked up by lymphatic system

Hydrostatic pressure

• Fluid pressing against some type of boundary

  • Capillary wall

  • Pressure that is forcing fluid out of the capillary

Osmotic pressure

• nondiffusable solutes

  • Pull fluids towards boundary 

  • Plasma proteins - Albumin, too large to diffuse and helps to maintain osmotic pressure in the blood

Hydrostatic pressure at the arteriole end

41.3 mmHg - pushing into interstitial space

Inward force of osmotic pressure

•  28 mmHg - pushing into interstitial space

Net pressure

• 13.3 mmHg

• Fluids and materials will exit at the arteriole end

At Venule

• Outward force, including hydrostatic pressure, osmotic pressure does not change do to albumins staying in the blood

  • Inward force is now higher, inward movement of materials

There are 2 distinct places that exchange of materials happens,

exits at arteriole, brought in at venule side

Edema

•  = abnormal increase in amount of interstitial fluid

  • Could result from incompetent venous valves & blockage