Blood Vessels Flashcards
What are the layers of a blood vessel?
- Tunica Adventitia
- Tunica Media (only in arteries)
- Tunica Intima
What are the characteristics of the tunica Intima?
Contains the:
- Endothelium - simple squamous cells w/ basement membrane
- Internal Elastic Lamin - connective tissue to Tunica Media
What are the characteristics of the Tunica Media?
Contains:
- smooth muscle - circular muscle that contracts and squeezes lumen (vasoconstriction or vasodilation for relaxation)
- Elastin fibers - for stretch & recoil
What are the characteristics of the Tunica Adventitia?
Outer most layer of the blood vessel
Contains:
- Elastin
- Smooth muscle
What are the general properites of arteries?
- Contractility
- Extensability / Elasticity
What is the general property of arteries, contractility?
- Vasoconstriction/Vasodilation controlled by smooth muscle
- Controlled by Autonomic nervous system (sympathetic only)
- Increase frequency of stimulation = increase in norepinephrine = vasoconstriction
- Decrease frequency of stimulation = decrease in norepinephrine = vasodilation
What is the general property of arteries, Extensibility/Elasticity?
- The ability to stretch and recoil
- allows for pressure changes
- Vasoconstriction = pressure increase
- Vasodilation = pressure decrease
- allows for pressure changes
How does the Elasticity/Extensibility of Arteries create a pressure reservoir?
Stretch and recoil of arteries allows them to store potential energy (Stretch) and convert it to Kinetic energy (recoil)
- During Systole
- Blood surges into the aorta and causes stretch
- During Diastole
- Drop in blood pressure causes elastin fibers to recoil and push blood forward
What are the types of arteries?
- Elastic (large) - conducting artery
- Muscular (medium) - distributing artery
- Resistance (small)
What are the characteristics of Elastic Arteries?
The LARGE arteries
- the blood pressure reservoirs
- conducting arteries because they conduct blood away from heart
- Lots of smooth muscle to generate force
- Less contractility then medium arteries because the circumference of the large arteries is much larger
What are the characteristics of Muscular arteries?
Distributing arteries b/c they distribute to body
- Lots of smooth muscle
- Greater contractility
- Control where blood is distributed
- Can cut off blood flow to get it where it’s needed (Blood shunting)
- Greater contractility
- Collateral Circulation
- A preferred route for blood but there are alternative routes to get to the same tissue (anastomoses)
What are the characteristics of the small arteries?
More smooth muscle than elastic arteries
- like Medium arteries so they can completely shut off blood flow
What are the characteristics of arterioles?
Branching off from small arteries leads to Arterioles which eventually lead to Capillary Bed
- Do not have ELASTIN
- 1 to 5 layers of smooth muscle
- The most contractility for vasoconstriction/vasodilation
- blood shunting to regulate blood flow to tissue
- The most contractility for vasoconstriction/vasodilation
What are the characteristics of capillaries?
- Microscopic in size
- Distribution in some areas higher than others (skeltal muscle)
- Only contains Tunica Intima layer for Exchange
- Simple squamous cells allow for diffusion w/ interstitial fluid
What are pre-capillary sphincters?
Localized/tissue level control of blood shunting
- Just before a arteriole reaches a capillary bed
- vasoconstriction/dilation to control blood flow to the capillary bed
What is vasomotion?
blood flow through capillary bed
- stop and go motion
- sphincter open/closing
- at rest occurs 5x/min, during exercise will occur faster ~15x/min
What are the types of capillaries?
- Continuous
- Fenestrated
- Sinusoids
What are the characteristics of continuous capillaries?
- Simple squamous cells that overlap
- skeletal muscle, lungs, connective tissue
- normal capillary
What are the characteristics of Fenestrated capillaries?
arrangement just like continuous capillary but the cells are perforated
- the perforations are holes through the cell that connect one side of cell to the other side
- For filtration (think kidneys)
What are the characteristics of Sinusoid capillaries?
Large gaps between the cells
- most permeable
- where you need to screen blood for (spleen -screen for pathogens and damaged RBCs and liver - screens for damaged RBCs)
What are the characteristics of Venules/Veins?
- Same Basic tunics as arteries (tunica adventitia, tunica media, tunica intima) BUT:
- Tunica media is much thinner (don’t need as much muscle
- Larger Lumen
- Doesn’t hold shape due to thinner wall
- Very distensible
- For blood pooling
- Valves
- to prevent back flow
How does Blood pressure influence blood flow? What are the blood pressures of the arteries vs capillaries vs veins?
Blood flows from area of high pressure to area of low pressure
Arterial Pressure > Capillary Pressure > Veinous Pressure
Explain the concept of blood reservoirs and what role veins play in it?
Majority of blood in body (~60%) is in the veinous system at any given time because of the larger lumen
- Skin, liver, spleen
This blood can be shuttled to needed areas during exercise
- Vasoconstriction cuts off blood flow to the veins in these areas and forces more blood straight back to heart
- Gets more blood oxygenated and pumped to skeletal muscle
What are the main mechanisms of capillary exchange?
- Diffusion
- Vesicular Transport
- Bulk Flow
What is the method of capillary exchange, diffusion?
- occurs directly though the simple squamous cells
- follows concentration gradients
What is the method of capillary exchange, vesicular transport?
AKA Transcytosis
- Molecule will fuse with cell membrane (invaginates)
- forms vessicle which carries molecule to other side
- vessicle fuses w/ cell membrane on other side
- releases contents on other side of cell
What is bulk flow?
Method of capillary exchange for filtration/reabsorption
STARLINGs Law of the Capillaries (BULK FLOW)
- Blood hydrostatic pressure
- Pressure of fluid pushing against blood vessel walls
- BHP drops as blood flows from arteriole through capillary to veinous end
- Arteriole BHP = 30 mmHg
- Capillary bed BHP = 20 mmHg
- Veinous end BHP = 10 mmHg
- Blood contains solutes that contribute to osmotic pressure
- the solutes attract water into capillary
- Interstitial fluid has osmotic pressure pulling water out of capillary
- IF Osmotic pressure = 8 mmHg
What is the Net filtration Pressure of capillary exchange (Starling’s Law of Capillaries)?
Net Filtration Pressure
- Blood Hydrostatic Pressure (in arterial end) + Interstitial Fluid Osmotic Pressure (Outward force) = 30 mmHg + 8 mmHg = 38 mmHg
- Blood Coloid Osmotic Pressure + Interstitial Fluid Hydro Pressure (inward Force) = 28 mmHg + 0 mmHg) = 28
- Net Forces = 38- 28 = 10 mmHg pushing out in the arterial end
The only thing that changes as blood flows through blood vessel (artery, capillary, vein) is the Blood hydrostatic pressure
- The net forces are going to change as blood flows through because of this change
At arterial end = fluid moving out (FILTRATION)
At Capillary = Net Pressure is 0 mmHgAt Veinous end = fluid moving in (REABSORPTION)
What occurs to the fluid that is pushed through the capillary into the interstial fluid during bulk flow?
85% of fluid that got pushed out in arterieal end gets reabsorbed in the veinous end
the other 15% gets pushed into lymphatic system
What determines bulk flow filtration or reabsorption?
Outward Forces
- Blood Hydrostatic Pressure (BHP)
- Arterial End = 30 mmHg
- Venous End = 10 mmHg
- Interstitial Osmotic Pressure (IOP)
- 8 mmHg
Inward Forces
- Interstitial Fluid Hydrostatic Pressure (IFHP)
- 0 mmHg
- Blood Colloid Osmotic Pressure (BCOP)
- 28 mmHg
Calculate the Net Filtration Pressure for the arterial end of a capillary.
NFP = outward forces – inward forces
= (BHP + IFOP) – (BCOP + IFHP)
= (30 + 8) – (28 + 0)
= (38) – (28) = + 10 mm Hg = positive filtration pressure
net flow of fluid is out of the capillary and into the interstitial space. This is filtration.
Calculate the Net Filtration Pressure for the venous end of a capillary.
NFP = outward forces – inward forces
= (BHP + IFOP) – (BCOP + IFHP)
= (10 + 8) – (28 + 0)
= (18) – (28) = - 10 mm Hg = negative filtration pressure
net flow of fluid is into the capillary and into the ninterstitial space. This is reabsorption.
What occurs if BHP > net osmotic pressure? What occurs if BHP < net osmotic pressure?
If BHP > net osmotic pressure, then filtration occurs
If BHP < net osmotic pressure, then reabsorption occurs
Starling’s law of the capillaries = 85% of the fluid filtered by the capillaries is reabsorbed. What happens to the other 15%?
The other 15% goes into the lymphatic system
How is blood flow measured?
ml/min
What is the relationship between blood flow velocity and total cross sectional area of the vascular tree?
Total Cross Sectional Area Increase = Decrease in velocity b/c total cross sectional area increases in the arteriole/capillary level
- Increased surface area = Increase friction = Decrease in velocity
Total Cross Sectional Area Decrease = Increase in velocity b/c total cross sectional area decreases in the larger arteries/veins
- Decrease surface area = decrease friction = Increase in velocity
What are the principal determinants of Blood Pressure?
- Cardiac Output
- Blood Volume
- Peripheral Resistance
How is cardiac output a determinant of Blood Pressure?
Increasing Heart Rate or Stroke Volume Increases Blood Pressure
CO = SV x HR
CO = (EDV – ESV) x HR
How is blood volume a determinant of blood pressure?
Blood volume = lose blood = decrease BP
Hypertension
- Dr. recommends decreasing salt intake
- NaCl => Na+ and Cl- in solution
- these ions attract water and increase blood volume
What determines peripheral resistance?
- How thick blood is = viscosity
- More solutes you add to blood = more viscous
- Solute example: Erythrocytes
-
Blood vessel length
- the more tissue you have the more blood vessels you need to support that tissue (increase of blood vessel length)
- increase length = increase friction/resistance
-
Vessel Radius
- Larger diameter = less resistance
- Smaller diameter = more resistance
What is sytemic vascular resistance?
Total peripheral resistance
- the major function of arterioles is vasoconstriction and vasodilation
- Increase Norepinephrine = Vasoconstriction = Decrease Diameter = Increase Resistance = Increase BP
- Decrease Norepinephrine = Vasodilation = Increase Diameter = Decrease Resistance = Decrease BP
What is the difference between localized vasoconstriction and systemic vasoconstriction?
- Systemic vasoconstriction will increase blood pressure everywhere
- Localized will vasoconstrict in one place and vasodilate in another = causing blood to flow away from vasoconstricted area and to the vasodilated area
What happens to blood flow routing when there is increase in activity in skeletal muscle?
Increased activity in skeletal muscle → increased oxygen demand =
Vasodilation in skeletal muscle → decreased resistance in vessels
What happens to blood flow routing when there is decrease in activity in the gut?
Decreased activity in gut→ decreased oxygen demand = Vasoconstriction in gut → increased resistance in vessels
What are the mechanisms of venous return?
- Decreasing Total cross-sectional area
- Venous valves
- Skeletal muscle pumps
- Respiratory pump
How does decreasing cross sectional area work in venous return?
Total cross sectional area decreases from capillaries to veins
- increase in velocity and pressure
- decreased friction/resistance
How do venous valves work in venous return?
Like semilunar valves and especially useful for lower limbs
- prevent backflow
How do skeletal muscle pumps work in venous return?
Muscle contracts and expands in the middle (gaster) and the contractions squeezes the nearby veins to force the blood forward
- Like “milking” the veins pushing forward
How does the respiratory pump work in venous return?
Inhale = pressure in thoracic cavity decreases (volume of cavity increases)
Lowering pressure in thoracic cavity assists in blood flow return from periphery to thoracic cavity
- Pressure Gradient increases
- Periphery pressure is higher than thoracic cavity pressure
How is blood pressure and flow regulated?
The cardiovascular center of the medulla controls blood pressure and flow through nervous input and nervous output
What does the cardiovascular center of the medulla consist of?
- cardioacceleratory center - increase heart rate (Sympathetic NS)
- cardioinhibitory center - decrease heart rate (Parasympathetic NS)
- vasomotor center - vasoconstriction and vasodilation (Only Sympathetic)
What are the nervous inputs to the cardiovascular venter of the medulla?
- higher brain centers – cerebral cortex, limbic system, hypothalamus
- Think conscious thought or emotion affect HR
- baroreceptors – monitor arterial blood pressure
- chemoreceptors – monitor O2, CO2, and H+ in arterial blood
What are the nervous outputs from the cardiovascular center of the medulla?
- cardioaccelerator nerves (sympathetic) – increase HR and contractility
- vagus nerve (X) (parasympathetic) – decrease HR
- vasomotor nerves (sympathetic) – vasoconstriction/vasodilation
Walk through the basics of neural control of blood pressure.
- Baroreceptors in the Carotid or Aortic sinuses detect high or low blood pressure
- The cardiovascular center in the medulla reads the amount of firing from the baroreceptors as high or low BP (Lots of firing = high BP or Low firing = low BP)
- The Medulla will sends signal down Sympathetic (spinal nerve) or Parasympathetic fibers (vagus nerve)
- Signal travels to the SA Node to either increase or decrease Heart Rate
- Sympathetic fibers release norepinephrine on SA Node
- Makes SA node more permeable to Sodium = Increase heart rate
- Parasympathetic fibers release acetylcholine on SA Node
- Makes SA node less permeable to sodium = decrease heart rate
- Sympathetic fibers release norepinephrine on SA Node
- Increase/decrease Heart Rate = Increase/decrease BP
Go through the negative feedback mechanism of Neural control for Low Blood Pressure.
- Homeostasis disrupted by low blood pressure
- Baroreceptors in carotid and aortic sinuses are stretched less, resulting in decreased rate of nerve impulses to the cardiovascular center
- increased sympathetic output via cardioacceleratory center and decreased parasympathetic output from cardioinhibitory center
- Results in:
- Increased contractility = Increased stroke volume
- Increased heart rate = Increased cardiac output
- Increased vasoconstriction = Increased resistance
- Increased Blood Pressure and return to homeostasis
Go through the mechanism of negative feedback for neural control of high blood pressure.
- Homeostasis disrupted by High blood pressure
- Baroreceptors in carotid and aortic sinuses are stretched more, resulting in increased rate of nerve impulses to the cardiovascular center
- Decreased sympathetic output via cardioacceleratory center and Increased parasympathetic output from cardioinhibitory center
- Results in:
- Decreased contractility = Decreased stroke volume
- Decreased heart rate = Decreased cardiac output
- Decreased vasoconstriction = Decreased resistance
- Decreased Blood Pressure and return to homeostasis
What are the types of hormonal control of blood pressure?
- Angiotensin II = increase BP
- Aldosterone = increase BP
- Atrial Natriuretic Peptide (ANP) = Decrease BP
- Antidiuretic Hormone (ADH/vasopressin) = Increase BP
- Epinephrine/Norepinephrine = Increase BP
How does Angiotensin II work to control Blood Pressure?
potent vasoconstrictor → increased resistance → increased BP
How does Aldosterone work to control blood pressure?
promotes sodium retention by kidneys:
increased water retention → increased blood volume → increased BP
How does Atrial Natriuretic Peptide (ANP) work to control blood pressure?
decreases sodium retention by kidneys
decreased water retention → decreased blood volume → decreased BP
How does Antidiuretic Hormone (ADH or Vasopressin) work to control blood pressure?
increase water retention by kidneys → increase blood volume →
increase BP
How does epinephrine and norepinephrine work to control blood pressure?
potent vasoconstrictor → increased resistance → increased BP
increased HR + increased SV = increased CO → increased BP
What is autoregulation (local control)?
Ability of tissues to regulate their own blood supply
What is the metabolic theory of autoregulation?
Inadequate Perfusion:
- Decreased O2 → vasodilation
- Increased wastes (CO2, H+, K+, adenosine) → vasodilation
Once you get adequate Perfusion again = vasoconstriction
How do tissues maintain adequate perfusion?
They use vasoactive chemicals
- Secreted by platelets, endothelial cells, perivascular tissues with trauma
- Histamine, prostaglandins
What is reactive hyperemia?
blood reentering tissue that was starved of oxygen
