Vessels

Question 1

What are the different layers of a blood vessel?

Answer 1

Tunica intima - comprised of a 1 cell layer, and a subendothelial layer

Tunica media - smooth muscle tissue

Tunica externa = feeds smooth muscle of the media

Question 2

What are the 3 main types of arteries?

Answer 2

• Elastic artery –> conducting: allow “baloon effect”
  
  • small tunica intima,
  • have elastic fibers throughout the tunica media
  • then have a tunica extera
  • examples - ascending aorta, subclavian artery, common illiac
• muscular artery –> distributing –> supply specific organs
  
  • normal tunica intima,
  • Tunica media is now made up of different layers
    
    • Internal elastic lamina
    • and external elastic lamina
  • Also has a tunica externa
  • examples - femoral artery, splenic artery
• arteriole
  
  • these have the biggest impact on peripheral resistance
  • tunica media with a few layers of smooht muscle

Question 3

How do veins differ from arteries in terms of layers?

Answer 3

• Veins can contain higher volume than in an artery and are more floppy/less rigid
• Higher compliance - can change volume with less change in pressure
• Have all three layers, but a much more significant tunica externa.

Question 4

Comparison of companion vessels

Answer 4

• Larger, and smaller to medium sized veins have valves and a less pronounced tunica media
• Muscular arteries would be similiar size to small to medium sized veins.
  
  • Muscular arteries are fenestrated, mostly because they deliver blood to organs.
• Venule and arteriole are comparible, both have no valves, however the venule contains a much higher volume because there is much less tunica media.

Question 5

What are the three types of capillaries?

Answer 5

• Continuous capillary (majority of capillaries)
• Fenestrated capillary - designed for absorption and secretion
  
  • large amounts of moleulces moving in and out of the blood stream
  • still have a continous basement membrane but have fenestrations.
  • kidney
• sinusoidal capillary
  
  • “dead end”
  • These capillaries are picking up or dumping out.
  • Have discontinued basement membrane with large openings
  • these are in the liver, spleen, red bone marrow.

Question 6

Describe autoregulation and how it pertains to the capillary bed structure.

Answer 6

1. In continuous capillary bed structures, ie no fenestrations and a continous basement membrane
2. We have smooth muscle cells on the arteriole side and then they branch down in to the metaarteriole before turning into capillaries. These metaarterioles still have smooth muscle.
   
   1. these create “precapillary sphincters”
   2. When the sphincters are relaxed, the capillary bed is well perfused
3. When the sphincters contract, blood bypasses the capillary bed
   
   1. this is termed autoregulation
4. Spincters contract when they need to perfuse muscle, and if needed can relax
5. Sympathetic nervous system will activate perfusion to muscle and decrease perfusion to the GI tract.

Question 7

What is blood distribution at rest?

Answer 7

• Pulmonary circulation - 18%
• Heart 12%
• Systemic circulation 70%
  
  • Systemic arteries 10%
  • systemic capillaries 5%
  • systemic veins 55%
• Veins have the most volume in the systemic circulation and this concept is termed as “venous reserve”

Question 8

What are the different types of circulatory pathways?

Answer 8

1. simple pathway
   
   1. Artery –> capillary bed –> vein
2. Alternative pathways
   
   1. Anastomoses
      
      1. Arterial anastomoses –> many different pathways to one target
      2. alternative supplies, ensures blood supply for brain or heart
   2. Anastomoses
      
      1. Venous anastomoss –> many different pathways to drain
         
         1. Ensures blood has a place to drain
   3. Shunts
      
      1. These are arteriovenous anastomoses,
      2. Straight from artery –> vein
      3. faster connection, and used to decrease heat loss
   4. Portal system
      
      1. Two capillary beds before it goes into the venous system
      2. loses a lot of O2
      3. The liver uses this system.

Question 9

Pulmonary circulation

Answer 9

Deoxygenated blood at very low pressure 15-20mmhg comes from the heart and goes to the lung

Comes back to the heart from the lungs at almost no pressure, close to 0mmhg

Question 10

What are the three major veins that enters the hepatic portal vein?

Answer 10

1. Splenic vein
2. Superior mesenteric vein
3. Inferior mesenteric vein.
   
   1. These all deliver deoxygenated blood to the liver, but it is very rich in nutrients and different molecules
   2. Could also be recieiving RBC particles from the splenic vein.
4. The hepatic portal system does not recieve blood from the kidneys or the gonads.
5. The liver recieves its blood supply from the hepatic artery

Question 11

Describe the relationship between the cross sectional area of vessels and the blood velocity.

Answer 11

Velocity steeply reduces when cross sectional area increases

Highest velocity is going to be in the ascending aorta

As we reach arterioles, capillaries, venules the cross sectional area reaches its peak and the velocity reaches its lowest value.

Blood velocity doesn’t seem to pick up again until we reach the vena cavas.

Question 12

How do you determine pulse pressure and how do you determine mean arterial pressure?

Answer 12

1. Pulse pressure = systolic Blood pressure - diastolic blood pressure
2. Mean arterial pressure, calculated in a few different ways
   
   1. MAP = CO x TPR
   2. MAP = P(d) + 1/3(Ps-Pd)

Question 13

Describe capillary exchange, filtration and reabsoption

Answer 13

• Filtration - arterial end
  
  • Blood hydrostatic pressure > osmotic pressure
  • Net result - pressure out, fluid out of the blood vessel
• Reabsorption - venous end
  
  • osmotic pressure > hydrostatic pressure
  • net result - pressure in, fluid moves back into the blood vessel.
• The correct blood flow is crucial for adequate exchange of nutrients.

Question 14

What is edema caused by? What is fluid recall caused by?

Answer 14

1. Edema - collection of fluid in the interstitial space.
   
   1. caused by
      
      1. increased filtration
      2. decreased reabsorption
      3. lymphatic obstructution (lymph picks up the extra fluid difference)
   2. Consequences
      
      1. cell death –> necrosis; cerebral edema –> can cause seizures/coma
2. Fluid recall (interstitial fluid) - goes out of the capillary and never comes back
   
   1. hemorrhage
   2. dehydration

Question 15

Compare the different pressures of different vessels from aorta –> vena cava.

Answer 15

MAP pressures

Aorta - 93mmhg

Arteries - 93–>70ish

Arterioles 70ish –> 35

Arterial end of capillary - ~35-40

Venous end of capillary ~20 mmHg

Venules, Veins, <20

Vena cava - approaching 0

Question 16

What is flow in a blood vessel based on?

Answer 16

1. Pressure difference and resistance through a given vessel
2. P1-P2/R = Change in pressure/resistance
3. F ~ ΔP/R
4. This concept is very important for tissue perfusion
   
   1. cardiac ouput
   2. TPR
   3. Vascularity, influenced by angiogenesis/repression

Question 17

Describe the continuation of intermittent blood flow to continuous blood flow.

Answer 17

1) When the ventricle contracts, the semilunar valve opens and a bunch of blood is ejected into the aorta.
2) When the ventricle relaxes, the semilunar valve closes, but now the stretched arterial walls elastic recoil sends blood forward into the rest of the ciruclatory system.

These two concepts allow for blood flow during systole and diastole.

Question 18

Compare capillary pressures from arterial end to the venous end. What do these pressures ensure?

Answer 18

• Starting on the arterial end, at around 40mmHG and ends up at the venule end at around 20mmHG - this assures adequate perfusion “filtration”

Question 19

What are factors of venous return?

Answer 19

1. Pressure gradient (from the heart), cardiac output matters. How much blood the heart pumps out affects how much blood the heart gets in return. Also influences the pressures
2. Gravity - 55% of blood in venous system
3. skeletal muscle pump
   
   1. calf contracts, and when it contracts it squeezes blood in the veins back towwards the heart in a pump like manner. Also pushes it away from the heart, but this is prevented due to one way valves in the veins.
4. Also have the thoracic pump.
   
   1. When you take a breath, your diaphragm goes from a dome and flattens out. It decreases pressure in the thoracic cavity.
   2. this decrease in pressure causes blood to get “sucked” up into the thoracic cavity, increasing venous return. Inspiration increases blood flow into the thoracic veins.
   3. Upon expiration there is release of compression in the abdominal vessels, and an increased pressure in the thoracic cavity. The release of compression allows blood to flow into the heart and abdominal veins.

Question 20

What are the different factors affecting blood pressure? (directly proportional) What organs influence these factors?

Answer 20

1. Cardiac output
2. blood volume
3. peripheral resistance
4. The heart and the kidneys influence these factors.
5. Viscosity of the blood, length of blood vessel, as well as diameter.

Question 21

What are factors that regulate peripheral resistance?

Answer 21

1. Peripheral resistance is defined as the opposition to flow of blood in vessels, and is a funciton of the vessel radius, vessel length, and blood viscosity
2. Vessel radius
   
   1. vasoconstrition narrows the vessel and forces blood through a narrower lumen, increasing peripheral resistance and increasing blood pressure
   2. Vasodilation widens the vessel and decreases peripheral resistance and blood pressure
3. Vessel length
   
   1. longer vessels increase peripheral resistance, which raises blood pressure
   2. shorter vessels decrease peripheral resistnace and this lowers blood pressure
4. blood viscosity
   
   1. increased viscosity creates an opposition to blood flow, increasing peripheral resistance and blood pressure
   2. decreased viscosity allows blood to flow more freely through vessels, decreasing peripheral resistance and blood pressure.

Question 22

What are the different ways we regulate blood flow and pressure? What is the objective?

Answer 22

1. Objective - to maintain adequate perfusion
2. A auto-regulation of local blood flow
   
   1. –> uses precapillary sphincters
3. Systemic
   
   1. Hormonal regulation involves
      
      1. nor epi and epi
      2. aldosterone
      3. ADH
      4. Ang II
      5. ANP
   2. Neural regulation
      
      1. autonomic NS

Question 23

Describe the renin-angiotensin-aldosterone system.

Answer 23

1) Kidney detects low blood pressure or are stimulated by the sympathetic nervous system; renin enzyme is then released

Angiotensinogne is actively produced by the liver, (inactive)

Renin converts angiotensinogen to angiotensin I (also inactive)

Ang I then gets converted to Ang II by angiotensin-converting enzyme. This is anchored to the internal walls in capillaries, especially capillaries in the lungs.

Angiotensin II is the active hormone, it increases blood pressure by causing vasoconstriction, and then causes the release of aldosterone. So it stimulates the thirst center and also increses blood pressure.

Aldosterone acts on the kidneys to increase reabsorption of Na+ and blood volume increasing blood volume and blood pressure and excretes K+ and H+

Question 24

What does HCTZ, ACEi, ARB, do?

Answer 24

1. HCTZ - affects blood volume but not TPR
2. ACEi - prevents convertion to angiotensin II
3. ARB - binds to Angiotensin II receptors. Doesn’t allow to bind.

Question 25

Neural regulation –> integration of 3 autonomic reflexes.

Answer 25

1. Baroreflex
   
   1. Stretch reflects pressure
   2. In carotid and aortic sinus
2. Chemoreflex
   
   1. influences blood flow and respiratory cycle
   2. O2 CO2 and pH
   3. Uses carotid and aortic bodies
3. Medulally ischmeic reflex
   
   1. reflects cerebral blood flow –> leads to Systemic vasoconstriction –> very high BP

Question 26

What are the effects of neural regulation?

Answer 26

• The cardiovascular center (within the medulla oblongata)
  
  • Contains the vasomotor center
    
    • affects blood vessels
  • The cardiac center (affects rate)
    
    • cardioacceleratory center
    • cardioinhibitory center
  • Baroreceptors and chemoreceptors feed information into the cardiovascular center

Question 27

Summary of factors that effect MAP

Answer 27

Question 28

Compare and contrast systemic circulation blood flow during rest and during strenuous exercise

Answer 28

• At rest cardiac output = 5250
• During exercise Cardiac output = 17,500
• Overall
  
  • decrease
    
    • kidney, abdominal organs, other
  • increase
    
    • brain, heart, skin, skeletal muscles,