Hiso Lecture 3
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What are the main functions of the vascular system?
- Transport nutrients, waste, and hormones between circulation and tissues/organs
- Maintains environemtn of bodily tissues/organs through nutrient, waste, and interstital fluid exchange
- Control rate of blood flow to organs/tissues
What are the three layers of the arterial system?
- Tunica intima
- Tunica media
- Tunica adventitia
What is the job of pre-capillary sphincters?
- Muscular sphincters that control blood flow to capillary beds
- Respond to increased blood flow, local metabolites, and sympathetic input to control flow through beds.
What provides the greatest amount of vasculature in the body?
What is the functional purpose of decreased pressure in capillaries?
Allows for gas and nutrient exchange in the capillary bed to the surrounding tissues
What is laminar flow?
- Stream-lines of flow within a vessel
- Stream-lines flow at different rates and do not mix
- Faster flow in the center of the vessel compared to flow along the edges
What is turbulent flow?
- Flow within vessels occurs in many directions
- Resistance to flow is greater in comparison to laminar flow
- Turbulent flow is enhanced with high velocity, large vessel diameter, and decreased blood viscosity
What causes turbulent flow?
Athersclerosis. Increases blood pressure and puts added pressure on the heart.
What is distensibility?
- Ability of a vessel to stretch (elastic)
- Is an increase in volume due to an increase in pressure
What is Compliance?
- Ability of vessel to stretcha nd hold increased volume
- Total volume of blood "stored" in any portion of hte circulation at a given vascular pressure.
- Indicates the volume increase in a particular vessel (veins) due to increase in pressure.
What is the minimum pressure necessary to maintain perfusino to organs?
MAP of 60mmHg
Valve dysfunction in veins causes what condition?
What does increased volume cause?
- Venous distention that makes the valves unable to prevent fluid back-up
- Creates high hydrostatic pressure allowing fluid to leak into the interstitium = edema
Name the 3 ways capillary transport works
- Intercellular clefts (pores) between adjacent cells that allow fluid and small molecules to "leak out"
- Vesicles within endothelial cells transport materials through cellular cytoplasm
- Fenestrations in endothelial cells
What are three types of capillaries?
Describe Continuous (Somatic) capillaries
- No fenestrations, substances move thru cell MB or between endothelial cells
- Skeletal m, CTs, nervous tissue, lungs, gonads
Describe Fenestrated (visceral) capillaries
- True fenestrations, vary in size and number in tissues
- Kidney, endocrine glands, intestines
Describe sinusoidal capillaries
- Wide spaces between cells permits movement of large molecules
- Liver, spleen, bone marrow, lymph nodes, adrenal cortex
What controls the rate/amount of fluid movement between capillaries and tissues?
Fluid forces within capillaries and interstitium
What two pressures play a factor in hydrostatic pressure?
- capillary hydrostatic pressure
- interstitial fluid pressure
What is lipid soluble that can pass through the plasmalemma?
What are the hydrophilic molecules that the capillaries carry?
- Most proteins
What is colloid osmotic pressure?
Solute pressure of plasma proteins
What 2 things affect colloid osmotic pressure?
- Plasma colloid osmotic pressure (oncotic pressure)
- Interstitial fluid colloid osmotic pressure
Define colloid osmotice pressure
Proteins in solution create osmotic force on fluid
What is capillary osmotic pressure maily due to?
Albumin within the plasma (into capillary)
What is interstitial osmotic pressure due to?
Interstitial fluid solutes (out of capillary)
What is the job of the lymphatic system?
- Remove excess fluid from the interstitium and return them to general circulation
- Absob and transport dietary fats to circulation
- Production of immune cells; monocytes and lymphocytes
What 2 pressures mainly pull into the capillaries?
What 2 pressures mainly push out of the capillaries?
Lymphatics have similar anatomy as the typical ______
How if lymph pumped?
- skeletal muscles
- pulsing arteries
- interstinal peristalsis
- increase in interstitial fluid filtrate
2/3 of all lymph is from the:
Liver & intestines
Any factor that increases vascular filtration and/or decrease reabsorption will ______ lymph formation
What are some factors associated with increased lymph formation?
- Increased CHP
- Decreased COP
- Increased IFOP
- Increased capillary permeability
What does filling of lymph vessels cause?
Reflexive smooth muscle contraction
Intermittent lymphatic compression also created by
- Skeletal muscle contraction
- Bodily movements
- Pulsation of arteries adjacent to lymphatics
- External compression
How are lymphatic capillaries different than normal capillaries?
- Incomplete or absent basal lamina
- One end of lymph capillary ends blindly
- Have wider lumens than blood capillaries
- Anchoring filaments assist in maintaining open channels of smaller capillaries
Why do tissues need blood?
- Deliver oxygen, nutrients
- Remov CO2, hydrogen ions
- Maintain ionic concentration of tissues
- Transport hormones
Each tissue controls its own ______ ______ to exactly meet metabolic demands
Define acute control
Rapid changes in local dilation and concstriction
Give an example of acute control
- Arterioles, met-arterioles, and pre-capillary sphincters are controlled within seconds of changes in the metaboli needs of a tissue
- Changes create immediate increase or decreases blood flow
Define long-term control
Adaptation over days-to-months
Give an example of long-term control
- Tissues adapt to chronically altered metabolic needs by increasing overall vascularity
- Vascularity increase occurs
- in number and size of capillaries and
What is the Vasodilator Theory (Acute)?
Increased metabolic rate or decreased oxygen (or other nutrient) availability causes icnreased release of vasodilator molecules from "needy" tissue
Name some vasodilator substances
- H+ ions
What can cause Acute Blood Flow changes?
- High altitude
- Carbon Monoxide poisoning
Define the oxygen-Lack Theory (Acute)
- Oxygen (and other nutrients) are required for muscle contraction and metabolic activity of other tissues
- Decreased availability of oxygen (and/or other nutrients) creates vasodilation
Define Active hyperemia
- Increase in blood flow to a tissue due to icnreased metabolic activity
- E.g. Skeletal muscle during intesnse exercise
Define Reactive hyperemia
- Transient increase in blood flow to tissue immediately following an ischemic period
- E.g. - Create blockage to blood flow; once blockage is remove BF increases over normal to compensate for ischemia
Dilation of larger arteries occurs as a result of:
- Shear stress on arterial wall (increased blood flow) stimulates release of EDRF (endotehlium-derived relaxing factor or nitric oxide - NO)
- NO causes larger arteries to dilate to support increased blood flow in the smaller vessels
Increase in tissue vascularity accompanies:
A chronically increased demand for blood flow (e.g. endurance training)
What is VEGF?
- Vascular endothelial growth factor
- A small peptide released from tissues under increased metabolic demand
What else can stimulate new vasculature (not exercise)?
- Can actually cause growth of collateral circulation to create a "bypass"
- Occurs frequently in coronary arterial system
What is Humoral Control of Blood Flow?
Substances that are released by the endocrine system can affect the level of vasoconstriction/vasodilation
How does norepinephrine/epinephrine affect blood flow?
Vasoconstrictors released form the adrenal gland (sympathetic system)
How does Angiotensin II affect blood flow?
- Vasoconstrictor produced in the liver
- Circulates in the blood in an inactive form
- Usually activated in the lung by the kidney hormone renin
- Serves as a strong vaseconstrictive agent
How does Vasopressin (ADH) affect blood flow?
- Vasoconstrictor formed by the hypothalamus and released from the posterior pituitary
- Main function is to increase water resorption from the renal tubules back into the blood
How does Endotelin affect blood flow?
- Vasoconstrictor produced by endothelium of damaged vasculature
- Powerful stimulator of vasoconstriction to reduce blood loss during hemorrhage
How does Bradykinin affect blood flow?
- Activated by kallikrein from cells and the blood, especially from tissue damage or intial stages of the inflammatory process
- Powerful stimulator of vasodilation and increased vascualr permeability
How does Histamine affect blood flow?
- Vasodilator released from nearly all bodily cells (especially mast cells/basophils)
- Also stimulates increased vascular permeability
- Main "cause" of allergic reactions
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