Lecture 21- Vascular Foundations I: the circulatory system Flashcards
CV system transports substances entering the body:
oxygen, nutrients, water
CV system substances leaving the body:
metabolic waste, heat, CO2
CV system substances moved around the body:
wastes, hormones, immune cells and antibodies
The arteries are described as a “…”
pressure reservoir
(maintains the pressure); elastic
–> stretches to accomodate
–> snaps back to maintain pressure
Arterioles are described as “…”
adjustable screws that can tighten or loosen
–> main site of blood pressure regulation (through vasoconstriction or vasodilation
exchange between O2 and CO2 takes place at
exchange epithelium in the capillaries
Veins are describes as a “…”
volume reservoir; compliant
stretches but does not snap back
blood flow= flow rate=
volume/time= cardiac output (L/min)
there is a — times increase in cardiac output with sympathetic stimulation
5
ex. at rest CO= 5.8 L/min,
during exercise CO= 25.6 L/min
why is variable distribution of blood flow to tissues possible?
due to parallel arrangement of arterioles
pressure — with distance due to —
decreases with distance due to friction
heart contracts –> creates a driving pressure –> blood flows out
resistance to blood flow increases as radius of a blood vessel —
decreases
resistance in a blood vessel: vasodilation vs. vasoconstriction
vasodilation= decreased resistance
vasoconstriction= increased resistance
arterioles ONLY receive — input
sympathetic input
“white water rafting”
in the aorta, blood flow is very turbulent and high velocity
“lazy floating down the river”
in arteries, it is more calm.
wide, lazy, floating down the river, slow velocity
pressure — as we move away from the heart
decreases
velocity of blood flow (cm/min)
= distance traveled by a fixed volume of blood per unit time (cm/min)
when does velocity of blood increase or decrease?
increases as flow rate (L/min) increases
decreases as CSA of blood vessels increase (larger tubes= slower flow)
explain why pressure drops with distance from the heart?
as blood flows through circulation it loses pressure, which creates a pressure gradient
pressure is lost due to FRICTION:
- friction within the blood
- friction between blood and vessel walls
blood and laws of fluid flow (3)
flow is prop to pressure gradient
F ∝ ΔP
flow is inversely prop to resistance
F ∝ 1/R
together…
F ∝ ΔP/R
very low pressure in the veins…
- need help to be pumped back up
- skeletal muscle pump
- valves prevent backflow
what would happen if valves aren’t working properly?
varicose veins, edema, blood pooling
venous return (VR)=
the flow of blood into the right atrium from the peripheral vessels
- skeletal muscle pump helps maintain VR
blood flow is slowest through the…
capillaries
- capillaries have greatest CSA
- exchange is happening at the capillaries so we want it to be slow to ensure O2 and CO2 is properly exchnaged
what determines the velocity of blood flow through that vessel type?
the TOTAL cross sectional area of the vessels
capillaries have the smallest individual diameter but they have the…
largest total cross sectional diameter
…therefore slowest velocity!!!
precapillary sphincter
ring of smooth muscle that can tighten or relax to close off capillaries in response to local signals
–> or maximize response when needed
metarterioles
= bypass
divert blood flow if sphincters are closed
they also allow larger materials (ex. WBCs) to bypass narrow capillaries and reach venous circulation
capillary density is related to….
your bodies’ needs
single layer of flattened epithelial cells: movement of…
-diffusion of gases
- osmosis (water)
- movement of materials through larger pores
do proteins leak out of capillaries?
no
about —-L per day of fluid is filtered out of capillaries
3L/day
-excess tissue fluid is picked up by lymphatic vessels and returned to venous system
lymph is dumped back in at the…
subclavian vein
-but also checked by lymph nodes, spleen etc. first
