A&p Ii - Blood Vessels

Front 1

3 Main Types of Blood Vessels

Back 1

3 major types:

Arteries & arterioles…..carry blood away from heart, toward capillaries.

Capillaries….microscopic ‘exchange’ vessels.

Venules & veins…..carry blood from capillaries back toward heart.

Front 2

vessel walls
(3 possible layers)

Back 2

1. Tunica intima: simple squamous lining, common to all vessels
2. Tunica media: combination of smooth muscle and elastic connective tissue.
3. Tunica adventitia (= T. externa) Loose/areolar connective tissues

Front 3

Arteries

Back 3

Have all three tunics. When blood comes out of the left ventricle, it enters the largest Arteries.

Front 4

elastic arteries

Back 4

Have much elastic CT in tunica media. These branch into smaller muscular ones, with little elastic CT. Are not very subject to constriction/dilation, and generally maintain relatively constant diameters.

Front 5

muscular arteries

Back 5

Smaller muscular branch, with little elastic CT. Do constrict and dilate. Ultimately, the smallest ones give rise to arterioles (with diameters of <0.5mm)

Front 6

arterioles

Back 6

The smallest muscular arteries give rise to these (with diameters of <0.5mm).

Front 7

capillaries

Back 7

Arterioles deliver blood to them, and undergo structural changes as they travel from the artery to them. Proximal arterioles (near artery) have all 3 tunics, w/ a well-developed t. media. As we approach them, arterioles lose the T. adventitia entirely, and T. media is greatly reduced. Blood then goes from the them, to venules, then to the veins to the two venae cavae (SVC, IVC.)

Front 8

What happens to blood pressure as the blood goes through this cycle?

Back 8

There is a continual drop. There is a fluctuation between systolic and diastolic in the arteries, but as get into the arterioles, there is a dramatic decrease and by the capillaries, there is no fluctuation at all.

Front 9

thoroughfare channel

Back 9

Most capillaries exist as parts of a capillary bed, consisting of 10-100 true capillaries and a “shunt.” Between the arterioles on the way to the venules through the capillary bed.

Front 10

pre-capillary sphincters

Back 10

at the entrance of each true capillary that can open and shut. When open, blood will flow through the capillary bed.

Front 11

3 things affecting capillary exchange include:

Back 11

1. Hydrostatic pressure
2. mechanical or fluid pressure
3. Osmotic factors
Concentration gradients and effect on diffusion

Front 12

capillary exchange at the proximal end

Back 12

there is a greater hydrostatic pressure inside the capillary as compared to outside. There is more pressing out than outside pressing in. Osmotic factors—interstitial fluid outside proximal end is slightly hypertonic compared to the inside.
Concentration gradients—O2 is > in blood. CO2 is decreased in blood, and glucose is > in blood as compared to interstitial fluid

Front 13

capillary filtration

Back 13

Capillaries are thin walled (only T. intima) and so movement of fluid out of the capillary into the interstitial space is favored on the proximal end. Capillaries do a filtration process. So technically, it is not blood moving out of the capillary because all the RBCs and most plasma proteins stay inside. So what goes out becomes interstitial fluid

Front 14

capillary exchange at the distal end

Back 14

As the blood gets to the distal end, there is an increase in the concentration of RBCs and plasma proteins. So as get to the end of the capillary, things are reversed; with more hydrostatic pressure outside than inside and fluid is slightly hypotonic on the outside. So movement of fluid into the distal end of the capillary is favored (with CO2, NH3). Most of the fluid returns to the distal end. Most, but not all. Any plasma protein that did leak out cannot return to the capillary. So there will be some excess protein containing fluid in the interstitial fluid. Something has to be done with it and what it does, is to enter the lymphatic capillaries (e.g. lacteals). Once fluid is in the lymphatic capillaries, it joins lymph circulation and eventually returns to the blood.

Front 15

post-capillary venules

Back 15

So, now we go past the capillary into the venules and into the veins. Venules undergo structural changes, and begin as these, composed of the T. intima and a thin adventitia. They are almost as permeable as capillaries, and are the main sites of WBC pavementing and extravasation. Distal ends of venules have 3 tunics, but T. media is very thin.

Front 16

Veins

Back 16

Have 3 tunics, and most also have one-way “pocket” valves.

Front 17

2 factors that help return low pressure venous blood to the heart

Back 17

1. Muscular pump—what makes it work in the veins (esp. lower extremity) is that the veins have one-way valves (similar to semilunar valves). Also most veins are located within or between skeletal muscle. So constriction of a muscle will squeeze the vein. Superficial veins don’t use muscular pump (e.g. greater saphenous) because they are just below the skin.
2. Respiratory pump—increase abdominal pressure, puts increased pressure of the vena cava.

Front 18

Blood Pressure

Back 18

Usually referring to arterial. During systole it increases and during diastole it decreases. So, it is systolic/diastolic with the avg. of 120/80 mmHg. Systolic is never less than diastolic. Pulse pressure is systolic – diastolic (the diff. betw. the two).

Front 19

4 factors affecting blood pressure:

Back 19

1. Cardiac output—the higher the cardiac output, the greater the blood pressure.
2. Peripheral resistance—the drag or friction of blood as it moves down a vessel wall. Greater resistance = increased B.P.
a. blood viscosity—how thick or sticky in the blood. Increased thickness—increase resistance, increased pressure. Determined by hematocrit and # of plasma proteins. (anemics often have low b.p.).
b. vessel diameter—if decrease diameter then will get increased resistance and increased B.P.
c. total length of the blood vessels—the longer the length, the increased the resistance. What determines total length? Weight. If add a one pound of adipose, have to add vessels to supply it. This is why weight loss can decrease blood pressure.
3. blood volume—increase volume, increase pressure.
4. Elasticity of arterial walls also plays a role. Good arteries are elastic. If elasticity in decreased, systolic B.P. is increased.

Front 20

Effects of Medication on Blood Pressure

Back 20

Diuretics will decrease blood volume. Blood thinner decreases viscosity. Beta blockers block sympathetic stimulus, stops vasoconstriction and decrease heart rate.

Front 21

short term regulation of blood pressure:

Back 21

Vessel diameter is controlled by:
1.vasomotor center in the medulla. Part of the sympathetic system. Constantly sends signals out to the vessels causing a moderate state of constriction—vasomotor tone. (if lose vasomotor tone, then faint). Fires faster for constriction. Frequency of firing determines constriction of the fibers. The vasomotor center is influenced by:
a. baroreceptors—specialized pressure receptors in the aortic arch, carotid sinuses. Send signals up to the vasomotor center. Negative feedback reflex. Baroreceptor reflex. E.g.—lying down, B.P. is normal. Then get up fast and gravity drains blood down and there is a rapid drop in B.P. (orthostatic hypotension). So the baroreceptors signals to go slow because of the drop in B.P. the vasomotor center responds by increasing vasoconstriction. They also signal the cardiac center. Cardiac center increased heart rate and cardiac output. Good for short term regulation, but baroreceptors can be reset as to what is normal.
b. Chemoreceptors—sensitive to change in partial pressure of oxygen (PO2, PCO2, and pH). So a decrease in PO2 will increase pCO2and decrease pH and B.P. would increase due to vasomotor constriction and cardiac center increasing heart rate. Respiratory center active in this.
c. Higher brain centers—cortical or limbic. Thoughts or emotions can input to vasomotor. Anger can increase B.P. sudden emotional shock—good or bad can decrease B.P.
3. chemicals and hormones also affect the vessels.
a. epinephrine—a selective vasopressor/constrictor. Constricts dermal and visceral vessels. Epi dilates skeletal, brain, and lung vessels.
b. ADH or vasopressin—vasoconstriction only in very high concentration—hemorrhage.
c. Angiotensin II—powerful constrictor. _____ increase blood pressure selective except for brain and heart. Indirectly affects aldosterone and therefore blood volume.
d. ANF (ANP) indirectly affects the release of (rennin) angiotensin.

Front 22

long term regulation of blood pressure:

Back 22

This is affected by ADH. It is also affected by aldosterone, which increases blood volume and blood pressure (aldosterone does not directly target blood vessels and has no affect on heart rate). ANF counteracts aldosterone with a minor affect).