The Vascular System Flashcards
Arteries & Arterioles
- Thick walls, smooth muscle w/ elastic tissue to withstand pressure
- Carry blood away from heart
- thickest
“rubber band”
Capillaries
- Tiniest vessels, single-cell thick for easy diffusion
- Exchange of materials b/t blood and body cells
Venules & veins
- One-way valves in thin-walled vessels surrounded by thin layer of smooth muscle giving low resistance to blood flow
- Returns blood to heart
“Reserve” (more or less blood to the heart)
Tunic adventitia
Outermost layer
Tunica media
Intermediate layer
Tunics intima
Interior lining
Compliance
The ability of a vessel to stretch
- not the same as recoil
- high compliance = high stretch
Veins are more compliant, but less…
Elastic than arteries
High compliance allows?
Blood to pool (sit) in the veins
- ab 3.2 liters
High elasticity allows?
Arteries to keep blood flowing
- even when the heart isn’t active atm
Hardening arteries
Increase in bp
- why bp increases with age
Flow is proportional to
Change in pressure
- Fluid flows only if there is a positive pressure gradient (delta P1- delta P2)
- No pressure gradient, so NO flow
- Flow depends on change in pressure, NOT ABSOLUTE PRESSURE
—-systemic vs pulmonary = diff pressures, but same flow
Flow is irreversibly proportional to
Resistance (aka 1/R)
- Resistance is caused by friction
- Resistance is proportional to 1/radius^4, so doubling the radius increases the flow 16x
—constricting = decrease in blood flow
- pressure falls over distance as energy is lost bc of friction
Hydrostatic pressure
Pressure exerted on the walls of the container
Distribution of blood flow
- Regulated by muscular walls of the arterioles (due to highest level of resistance)
—-spend more time closer to 80 (120/80) due to longer diastole (passive filling) - Regulation of calcium levels of arteriolar smooth muscle
—-smooth muscle does not have troponin & tropomyosin
—-amnt of calcium still is an affect
Distribution of blood flow: Extrinsic control
- Autonomic nervous system (primarily sympathetic NS)
— increase input = increase contraction
— decrease input = increase dilation - Hormones (Epi)
— increase levels = constriction
— decrease levels = dilation
ex: Angiotensin, vasopressin, ANF
Distribution of blood flow: Intrinsic (local) control
Happening in a particular tissue
- Active hyperemia = vasodilation leads to increased blood flow after increased metabolic activity
ex: O2, CO2, pH, lactate, adenosine K+ (all local metabolic factors
- Reactive hyperemia = vasodilation leads to increased blood flow due to flow blockage
ex: increase resistance, decreases flow
- Flow autoregulation = changes in response to changing blood pressure to maintain constant flow
— low pressure = dilation (decreases pressure, but then changes delta P so regulates flow)
— high pressure = contraction (Drives flow, but also increases resistance)
* takes place in kidney
- Injury = increased blood flow stimulated by chemical release from injured cells leading to inflammation
ex: histamine
As blood flows through capillary beds, the flow should be slow enough to allow?
Transfer of nutrients & wastes (via diffusion)
Some factors affecting flow
- pressure gradient (CO)
- vessel radius
- blood viscosity
- vessel length
- total blood volume
- temperature
How is blood returned to the heart with such a low venous blood pressure?
gravity
Venous pressure
Is very low
- 10-15 mmHg
Venous pressure
- Decrease compliance: by stimulating muscles (nerves, hormones, etc.)
- One-way valves: critical in veins
- Skeletal muscle pump
- Respiratory pump: inhalation + exhalation
- Cardiac suction: heart itself can aid in blood return, atria
The key role of circulatory system is?
The exchange of gases, fluids, and nutrients at the tissues
- this takes place in the microcirculation
Arteriolar end: Outward forces
Hydro. pressure = 37mmHg
Osmotic potential = 0mmHg
Total outward force = 37mmHg
Arteriolar end: Inward forces
Hydro. pressure = 1mmHg
Osmotic potential = 25mmHg
Total outward force = 26mmHg
Venule End: Outward forces
Hydro. pressure = 17mmHg
Osmotic potential = 0mmHg
Total outward force = 17mmHg
Venule End: Inward forces
Hydro. pressure = 1mmHg
Osmotic potential = 25mmHg
Total outward force = 26mmHg
Net outward pressure: Arteriolar
11 mmHg
- results in ultrafiltration (more pressure out than in, fluid and gases pushed out)
Net inward pressure: Venules
-9 mmHg
- results in reabsorption (more pressure in than out, brings fluids and gases in)
How much blood flows through all capillary beds in one day?
24 x 60 x 5 = 7,200 L/day
- total filtered = 20 L/day
- total reabsorbed = 17 L/day
- unabsorbed = 3 L/day
What happens to this additional 3 liters?
It is picked up by the lymphatic system
The lymphatic system
- Has an ending, unlike blood vessels
- Fluid flows one way
Lymphatic system: Structure
- Complex network of thin-walled vessels in proximity to the capillary network
—-thin-walled = not a lot of pressure - Composed of cells with openings b/t the, that act as one-way valves
Lymphatic system: Functions
- Removal of excess fluid
- Transport of fats from intestine
- Assist immune response
How we move lymph fluid?
- skeletal muscle pump
- respiratory pump
How the lymph gets collected?
- lymph nodes = swellings
—where wbc reside
Edema
Accumulation of excess fluid in the interstitial space
Causes of edema
- Filtration far greater than absorption
- Inadequate drainage of lymph
Filtration far greater than absorption…
- increase arterial blood pressure (hydrostatic pressure)
- increase venous pressure
- increase interstitial proteins (osmotic pressure)
— not supposed to have a lot of proteins here
— proteins came from breaking cells apart - increase permeability
— damage to other cells increases permeability; release histamine, loosen tight junctions - decrease plasma proteins
— malnutrition, edema in GI tract (abdominal)
Inadequate drainage of lymph…
- Blocked lymph
Blood pressure regulation
Blood pressure control involves both the cardiovascular system and the renal system
Some factors affecting flow
*1. Pressure gradient (CO)
*2. Vessel radius
3. Blood viscosity
4. Vessel length
5. Total blood volume
6. Temperature
* = what our body uses min by min, sec by sec; controlled by ANS
Blood pressure regulation
- Short-term regulation = baroreceptor reflex
- Long-term regulation = Urinary system
Blood pressure regulation: Short-term regulation
Baroreceptor reflex
- baroreceptors = cells loaded with mechanosensitive receptors located predominantly at the aortic arch and carotid sinus
- Mean arterial pressure (MAP) = diastolic + 1/3 pulse pressure
- pulse pressure = difference b/t systolic & diastolic
Increased arterial blood pressure
- Increase firing of baroreceptors
- Increased activation of parasympathetic nervous system NS
— Increase release of Ach from vagus nerve
— Decrease HR, increase CO - Decreased activity of sympathetic NS
— Decrease vasoconstriction, decrease total peripheral resistance (TPR)
— Decrease HR (decrease CO)
— Decrease contraction force (decrease CO)
Decreased arterial blood pressure
- Decreased firing of baroreceptors
- Decreased activation of parasympathetic NS
— Increase release of Ach from vagus nerve - Increased activity of sympathetic NS
— vasoconstriction
— Increase TPR
— Increase venous return - Increase HR (increase CO)
- Increase contraction force (increase CO)
Why does your HR increase when you exercise?
- ATP breakdown
- Increase metabolism, decreases Oxygen levels, CO2 increases
- pH drops drastically
- Local factors initiate muscles to vaso-dilate
- Hyperemia
Renin-Angiotensin-Aldosterone
- Renin is secreted by the kidneys in response to chronic low arterial blood pressure
- Angiotensinogen is always present (secreted by liver) and is converted to angiotensin I by renin
- Angiotensin I is converted to angiotensin II by angiotensin converting enzyme (ACE)
—-ACE = where covid binds
Zymogen
inactive protein that needs to be activated by a protease
Angiotensin II
vaso-constrictor
Angiotensin II acts on what?
The adrenal cortex to release aldosterone
- Aldosterone acts on kidney to conserve sodium
