Anatomy Ch 21
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What's the vaso vasorium?
- vessels to the vessels
- tiny blood vessels in the tunica externa that supply blood to the tissues of the vessel
Name the vessel types as they leave the LV, go through the body and reenter the RA.
- 1. Arteries - large, then med, then small - elastic & muscular
- 2. Arterioles - BP control - vasodilation/ constriction
- 3. Capillaries - exchange of substances
- 4. Venules
- 5. Veins - blood reservoir via venodilation / constriction
Name the 3 layers of an artery. Name the tissue types. Which layers have elastic fibers?
- 1. Tunica Interna - innermost layer - direct contact with blood as it flows thorugh lumen - 3 layers
- - endothelium (simple squamous epithelium) that is continuous with the endocardium
- - basement membrane
- - internal elastic lamina (thin plate) - elastic fibers
- 2. Tunica media - middle - thickest- 3 layers
- - smooth muscle - circular arrangement
- - Elastic fibers
- - external elastic lamina
- 3. Tunica externa - external layer -
- - 2 layers of CT that contain elastic fibers and collagen fibers
- - provides structural support
What layer is the endothelium?
What's the purpose of the externa?
How are smooth muscles arranged in the media layer?
The endothelium is part of the tunica interna - it is made of simple squamous epithelial tissue - it is continuous with the endocardium.
The tunica external provides structural support and helps anchor the vessels to surrounding tissues. - the vaso vasorium is in this layer.
The smooth muscle fibers are arranged in concentric layers.
What is a lumen?
What is compliance?
The lumen is the interior opening of the vessel around which the tunicas are arranged.
Compliance is accomplished by the elastic fibers in the tunicas that allows vessels to expant to prevent rising pressure (that can cause rupture)
What's the difference between an elastic & muscular artery?
What is the purpose of recoil?
- Elastic artery - largest arteries - aorta & pulmonary trunk
- thinner walls with lots of elastic fibers
- conducting arteries - conduct blood to medium size muscular arteries
- *able to pump blood forward - expand as blood is pumped into them and recoil as the heart relaxes
- Muscular artery - medium size arteries - more smooth muscle and less elastic fibers in tuncia media
- - vadodialtion & vasoconstriction - controls rate of blood flow
- - distributing arteries - muscular arteries branch and distribute blood to all organs
What does sympathetic imput to an arteriole cause?
increased lactic acid levels?
direct trauma to arterioles?
Which has a thinner media layer: elastic or muscular artery?
The large elastic artery has a thinner turnica media that has lots of elastic fibers. The medium muscular artery has a thick layer of smooth muscle
How do arterioles regulate BP?
Does vasoconstriction increase or decrease SVR?
Does venoconstriction raise or lower SVR?
- Arterioles regulate BP by changing diameter (regualtes resistance)
- Vasoconstriciton increases SVR (systemic vascular resistance) and thus increases blood pressure
Venoconstriction would also increase SVR and increase blood pressure
What is your microcirculation?
What is a capillary bed? How is velocity of flow lowered through it? Why is lower velocity advantageous?
What is its function?
Microcirculation is the flow of blood from a metarteriole (the end of the arteriole that tapers into the capillaries) through the capillary bed and into a postcapillary venule.
A capillary bed is a network of 10- 100 capillaries that arise from a single metarteriole.
How many layers does a capillary have?
A capillary only has the tunica interna - a single layer of endothelial cells and a basement membrane
- capillaries are exchange vessels - they excange substances between the blood and interstitial fluid
- substances cross 1 layer of cells to enter intersticial space.
What's a precapillary sphincter?
What's their purpose?
Precapillary sphincter - rings of smooth muscle fibers that control the flow of blood through the capillary - located at the metarteriole-capillary junction.
Metarteriole - terminal end of an arteriole that tapers into the thoroughfare channel - capillaries branch of the metarteriole and thoroughfare channel.
Throughfare channel - a direct route thorough the capillary bed - runs from the arteriole to the venule and bypasses the capillaries - precapillary sphincter but no muscle on the venule end
What is tissue perfusion?
What is it related to? is it constant?
What is the normal blood flow through the capillary bed?
When does it increase? How do precapillary sphincters work? metarterioles work?
- At any given time blood flow through about 25% of the capillaries.
- This amount increases when a tissue is active such as when a muscle is contracting.
Precapillary sphincters - vasocontraction/ vasodilation -control the blood flow in the capillary - they alternate contraction and relaxation which is called vasomation
. The metarterioles participate in the contraction and relaxation of vasomotion.
Describe the 3 types of capillaries & their functions.
- 1. Continuous capillaries - most common - continuous uninterrupted lining with intercellular clefts between endothelial cells
- - permeable to water, small solutes, gases
- 2. Fenestrated capillaries - windows - oval pores in the endothelial cells
- - greater permeability of fluids and small solutes
- - located where absorbtion and filtration occur: kidney, choroid plexue (CSF)
- 3. Sinusoids - large opening - absent or incomplete BM (basement membrane)
- - allows large substances to pass
- - red bone marrow, liver
What is portal circulation?
Portal system - when blood flows from one capillary network through a vein (called portal vein) and into another capillary network.
- hypophyseal portal system - pituitry gland
- hepatic portal system - liven
What's the structre of a venule? its purpose?
- Venules are very small as they leave the capillary bed and very pourous - oart of microcirculatory exchange - WBCs can exit
- -they have all three layers but the tunica media is very thin
as they continue they get larger and acquire more smooth mucle fibers - these are called muscular venules and exchanged with interstitial fluid doen't occur here.
Do veins have all 3 layers?
Can they withstand high pressure? Why not?
Does a vein have elastic lamina?
- Veins have all three layers but all are thinner than in arteries
- - Tunica external is the thickest
Veins can only withstand low pressure because they have less smooth muscle to give support and they have no internal or external elastic lamina.
Veins have a larger lumen than arteries
Venous sinus - a vein with no smooth muscle - cannot alter is diameter
What's a venous valve? What's it made of?
Where are they? Why? What do they do?
How do vericose veins occur? Why are they associated with edema? What connection does contraction of leg muscles have with venous valves?
- Venous valve - cusp or flap of endothelium that points toward the heart
- - they are found mostly in the limbs and function to prevent back flow of blood (that might be caused by gravity) - they also help prevent low blood pressure and low venous return to the heart.
Vericose veins - caused by leaky venous valves - allows blood to backflow and pool which increses pressure and causes fluid to leak into the interstitial space - causes edema (extra fluid) in the interstitial space
What's an anastomosis?
Anastomosis - connecitons of blood vessels that are flowing to the same area - allow for collateral circualtion
Collateral circulation - alternate routes for blood to flow if one way becomes temporarily blocked
end artery - no anastomones - no collateral circuation - obstruction interrrupts the blood supply (causes death to that segment)
What is your blood resevoir? Its purpose?
When does its volume change?
What is your blood distribution?
The blood resevoir is composed of systemic veins and venules - the larges percentage of blood is in these structure but blood can be moved quickly if necessary.
If blood is needed somewhere quickly (sympathetic input), the veins can venoconsrict which reduces blood in the veins and allows it to flow elsewhere.
- Blood distribution:
- 64% - veins and venules
- 13% - arteries
- 7% - capillaries
- 9% - pulmonary blood vessels
- 7% - heart
Name the 3 types of capillary exchange
Colloid osmotic pressure
What is edema?
Where does extra fluid go?
- 1. Diffusion - most commonly used - passive transport becuase substances move down the gradient
- - substances move through intercellular clefts or directly through endothelial cell (if lipid soluble)
- - large substances use fenestrated or sinusoid capillaries
- - Diffusion is NOT used in most of the brain - the BBB contins tight cell junctions that dont permit movement.
- 2. Transcytosis - active transport - only used by small quantity of material
- - substances are enclosed in vesicles and enter endothelial cells through endocytosis - travel across the cell and exit via exocytosis
- - used by large polar (hydrophillic) substances such as insulin and some antibodies
- 3. Bulk Flow - filtration and reabsorption- involves large amounts of substances that move down a pressure gradient (faster than diffusion)
- - balance the equlibrium between the blood and interstitial fluid (pressure determines wheather fluid enters or leaves the bloodstream)
- A. Filtration - driven by blood hydrostatic pressure
- - it is the flow of fluids out of the capillaries and into the interstitial fluid
B. Reabsorption - driven by blood colloid osmotic pressure - it is the flow of liquids out of interstitial fluid and back into capillaries
- Hydrostatic pressure (BHP) - generated by LV pumping
- - interstitial fluid hydrostatic pressure = 0 mm Hg
- - changes as blood flows from arterial end to the venous end of the capillary - 35 mmHg (arterial) to 16 mmHg (venous)
- Colloid osmotic pressure - controlled by substances that cant cross the capillary membrane (large proteins)-osmotic pressure does not change
- BCOP = 26 mmHg
- Interstital fluid osmotic pressure IFOP = 1 mmHg
- Filtration - reabsorption = net filtration pressure
- (BHP+IFOP) - (BCOP+IFHP) = Net filtration
Arterial end: 36 - 26 = 10 mm (filtration happens)
Venous end: 17 - 26 = -9 mm (reabsorption happens)
Edema is an increase in interstitial fluid (filtration > reabsoprtion)
Daily 20 liters of fluid are filtered and 17 are reabsorbed - the extra 3 liters ends up in the lymphatic capillaries and makes it way back to the blood stream
what does flow of blood depend on?
What does increased SVR (systemic vascular resistance) do to flow?
CO = amount of blood flow thought tissues in one min (when CO increases perfusion (blood flow) increases)
Blood flow to tissues depends on:
1. Pressure difference - blood flows from hight to low pressure - the greater the difference, the greater the flow
2. Resistance - SVR - greater resistance = less flow
Increased SVR slows down flow and increases blood pressure
What is BP? (Equation)
- BP = CO x SVR (assuming a normal blood volume)
- CO (cardiac output) x systemic vascular resistance
CO = HR x SV
Pressure drops as you get further from the LV.
What is the pressure change as blood moves through the system?
Blood pressure is about 35 mmHg in the arteries, arterioles and into capillaries
at the venous end of capillaries it is 16 mmHg
0 mmHg as blood flows into RV
since blood moves from high pressure to low pressure this pressure gradient help blood return to the heart.
What is your systolic BP?
Systolic blood pressure is the highest pressure attained in arteries during systole
Diastolic blood pressure is the lowest pressure in arteries during diastole
- Mean BP is the average blood pressure in arteries - it is about 1/3 of the way between the diastolic and systolic pressures
- MAP = diastolic BP + 1/3 (systolic BP- diastolic BP)
The pulse pressure is the difference between the systolic and diastolic pressures. (normally about 40 mmGh)
Name the 3 factors involved in SVR.
What is polycythemia? does it increase or decrease SVR? why?
What does vessel diameter decrese do to SVR? Increased length?
SVR = systemic vascular resistance - the opposition to blood flow (must be overcome for blood to flow)
- 1. lumen size - smaller the lumen - greater the resistance
- 2. Blood viscosity - higher viscosity - greater resistance
- 3. Blood vessel length - longer blood vessel - greater resistance
Polycythemia is when the % or RBC in blood is high - blood will be thicker (more viscous) and the SVR will increase.
Decreased vessel diameter will increase SVR and so will increased vessel length.
What vessels contribute most to SVR? What vessel primarily control it?
Aterioles, capillaries, and venules contribute to SVR (small vessels) but one of the functions of the arteriels is to control SVR by vasoconstriction/ vasodilation.
Name the 3 mechanisms involved in venous return.
How does the skeletal muscle pump increase venous return?
The respiratory pump?
Does inspiration increase or decrese venous return? How?
Venous return = volume of blood flowing back to the heart - caused by pressure difference between venuels (18 mmHg) and RA (0 mmHg)
- 1. Heart pump - contration of LV
- 2. Skeletal muscel pump (leg) - contration of leg muscles pushes blood through the proximal valve (while distal valve is closed to prevent back flow)
- 3. Respiratory pump - the diaphram moves down during inhilation which causes more pressure in the abdominal cavity and less pressure in the thoracic cavity - abdominal veins are constricted and blood moves to the lower pressure in the thoracic cavity
Is the velocity (length covered/ min) of blood flow the same throughout the circulation? Explain why/ why not?
- Velocity of blood flow decreases as it is deverted into more branches
- velocity is greatest in the arteries and decreases as it moves to arterioles and then capillaries - slowest in capillaries which allows for exchange of materials - increases agian as branches unite - moving to venules and them to veins
Name the 4 mechanisms of BP control
- 1. Cardiocascular center - located in the medulla oblongata
- - Uses sympathetic and parasympathetic to control heart
- -- Increase in sympathetic stimulation
- **cardiac accelerator nerves - increase HR/ SV - beta adrenergic (EPI, NOR) receptors in heart
- **Vasomotor nerves - constriction/ dilation of atrioles/ venules - alpha adrenergic receptors (NOR, EPI) on blood vessles
- -- Increase in parasympathetic stimulation-
- **vagus nerve - decreases HR - muscarinic cholinergic (ACh) receptors on blood vessels
- -Receives input from:
- a. Higher brain centers - cerebral cortex, limbic system, hypothalamous
- 2. Neural Control - hypoththalamus (brain of ANS)
- b. Proprioceptors - joints - info on movement changes
- c. Baroreceptors - monitor pressure in blood vessels (sence degree of stretch) - located in the carotid artery and the aortic arch (↑ BP = more stretch - causes ↓CO - causes ↓ vessel diameter - ↓ BP).
- d. Chemoreceptors - monitor chamicals in blood vessels (CO2, O2, pH) - located in carotid bodies and aortic bodies
- -reflex responds to hypercpnia (↑ CO2), hypoxia (↓ O2) , and acidosis (↓ pH) which leads to ↑ in cardiac output, vasoconstriciton, and increased BP
- 3. Hormonal Control
- - a. RAA system - renin-angiotensin-aldosterone -
- renin - releasead by kidneys when BP is low
- angiotensin cenvering enzyme ACE - (lung when renin)
- angiotensin II - vasoconstrictor - stimulates release of aldosterone - increases blood volume (+BP) by resporbing water and sodium in kidneys
- -b. Adrenal gland - EPI, NOR secreted from adrenal medulla as response to sympathetic stimulation - increases HR, SV
- ** EPI, NOR stimulates vasoconstriciton in skin and abdominal organs
- **EPI, NOR stimulates vasodilation in cardiac and skeletal muscle
- c. ADH - pituitary gland (made in hypothal) in response to low blood volume
- **vasopressin = vasoconstriction
- ** causes H20 resorption in kidney
- d. Atrial Natriuretic Peptide ANP - made by atrail myocardial cells - increase in BP stretches RA and causes it to realese ANP
- **ANP stimulates vasodiation and sodium and water elimination in kidneys
- 4. Autoregulation - ability of tissue to adjust blood flow to meet metabolic demands
- - responds to local physical (warming=vasodilaiton, cooling=vasoconstriction)
What is vasomotor tone?
Is it always present? Why?
Vasomotor tone - product of CV center in medulla oblongata - it is a constant state of partial vasoconstriction that sets the resting level of the SVR
Explain how low BP pr volume is involved in the RAA system.
- . Hormonal Control-
- a. RAA system - renin-angiotensin-aldosterone -
- 1. renin - releasead by kidneys when BP or volume is low
- 2. angiotensin cenvering enzyme ACE - (released from lung when renin is present)
- 3. angiotensin II - vasoconstrictor - stimulates release of aldosterone -
- 4. aldosterone - increases blood volume (+BP) by resporbing water and sodium in kidneys
- Adrenal gland - EPI, NOR secreted from adrenal medulla as response to sympathetic stimulation - increases HR, SV
- ** EPI, NOR stimulates vasoconstriciton in skin and abdominal organs
- **EPI, NOR stimulates vasodilation in cardiac and skeletal musclec.
ADH - pituitary gland (made in hypothal) in response to low blood volume**vasopressin = vasoconstriction** causes H20 resorption in kidneys.
- Atrial Natriuretic Peptide ANP - made by atrail myocardial cells - increase in BP stretches RA and causes it to realese ANP
- **ANP stimulates vasodiation and sodium and water elimination in kidneys
What is the role of autoregulation in BP control?
- Autoregulation - ability of local tissue to adjust blood flow to meet metabolic demands
- responds to local:
- 1. physical changes
- (warming=vasodilaiton, cooling=vasoconstriction)
- *myogenic response - smooth muscle in arteriole walls contracts more when stretched and relaxes when less stretch (↑ stretch = vasoconstriciton = less flow)
- 2. Local chemical changes -
- vasodilatin chemicals - lactic acid, H+, K+, adensine, NO
- vasoconstricting chemicals - thromboxane, serotonin
- hypoxia - in systemic circulation causes dilation to catch more O2
- in pulmonary circulation - vessels constrict in low O2 area so blood moves to better oxygenated areas of the lung
What is shock?
What are the 4 types?
- Shock is the result of inadequate perfusion (not enough oxygen & nutrients, build-up of waste)
- 1. Hemodynamic = loss of blood
- 2. Cardiogenic = pump failure
- 3. Obstructive = no venous return to heart
- 4. Vasogenic = low SVR
- The body responds to increase perfusion pressure
- 1. ANS – sympathetic response –increases HR, SV, SVR to increase BP
- 2. Hormonal – RAA, ADH – to increase volume & SVR
- 3. Local – vasodilation of capillaries to increase perfusion
The local response is to vasodilate the smallest vessels to increase tissue perfusion
What are the signs of shock?
- 1. Low BP
- 2. High HR but weak pulse
- 3. Cold skin – less perfusion (skin is not a priority)
- 4. Low pH – increased lactic acid from anaerobic production of ATP
- 5. Delirium/ confusion – low perfusion to brain
- 6. Low urine output – will cause renal failure if shock is prolonged
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