BIOL 3542 Lecture Notes - Lecture 14: Portal Vein, Coronary Circulation, Common Hepatic Artery

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Human Physiology 2
Chapter 14: Cardiovascular Physiology
Overview of the Cardiovascular System
The Cardiovascular System Transports Materials throughout the Body
primary function of cardiovascular system to transport materials
nutrients, water, gases that enter body from external environment
materials that move from cell to cell within body
wastes
because of brain’s sensitivity to hypoxia, homeostatic controls maintain cerebral blood flow
even at the expense of other cells
some wastes transported to liver for processing before elimination
heat moves from body core to dissipate at body surface
The Cardiovascular System Consists of the Heart, Blood Vessels, and Blood
Arteries: blood vessels that carry blood away from heart
Veins: blood vessels that return blood to heart
right side of heart receives blood from tissues, sends it to lungs for oxygenation
left side of heart receives oxygenated blood from lungs and pumps it to tissues
deoxygenated blood not completely devoid of oxygen, just has less than oxygenated blood
in people, oxygenated blood is bright red, deoxygenated blood is darker red
deoxygenated blood can look blue under some conditions (cyanosis)
blood flows from right atrium  right ventricle  pulmonary arteries  lungs  pulmonary
veins  left atrium  left ventricle  aorta  capillariesvena cavae  right atrium
Pulmonary Circulation: blood vessels that go from right ventricle to lungs and back to right
atrium
Superior Vena Cava: joining of veins from upper body
Inferior Vena Cava: joining of veins from lower body
Systemic Circulation: blood vessels that go from left ventricle through tissues and back to right
atrium
Coronary Arteries: nourish heart muscle
coronary arteries  capillaries  coronary veins  right atrium at coronary sinus
ascending branches of aorta go to arms, head, brain
abdominal aorta supplies trunk, legs, internal organs
liver supplied by hepatic artery
kidneys supplied by renal arteries
blood leaving digestive tract goes directly to liver thorough hepatic portal vein
nutrients absorbed by intestine filtered through liver before released into circulation
the two capillary beds of the digestive tract and liver, joined by the hepatic portal vein =
portal system
capillary beds connected in series in kidneys = portal system
hypothalamic-hypophyseal portal system connects hypothalamus and anterior pituitary
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Pressure, Volume, Flow, and Resistance
liquids, gases flow down pressure gradients (P)
heart creates high pressure when it contracts
blood flows out of heart to closed loop of blood vessels
pressure lost continuously as blood moves through blood vessels due to friction between
fluid and vessel walls
area of highest pressure = aorta, systemic arteries
area of lowest pressure = vena cavae
The Pressure of Fluid in Motion Decreases over Distance
Pressure: force exerted by fluid on its container
measured in mmHg in heart/blood vessels
Hydrostatic Pressure: pressure exerted by non-moving fluid; equal force exerted in all directions
proportional to height of water column
pressure falls over distance in flowing system as energy is lost due to friction
pressure exerted by moving system has 2 components:
1. dynamic, flowing component represents kinetic energy of the system
2. lateral component represents hydrostatic pressure (potential energy) exerted on walls of
system
pressure within cardiovascular system called hydrostatic pressure even though it’s a moving
system
Pressure Changes in Liquids without a Change in Volume
pressure created by the contracting heart is transferred to the blood
high pressure blood flows out of ventricle into blood vessels where it displaces the lower-
pressure blood already in the vessels
Driving Pressure: pressure created in ventricles; drives blood through blood vessels
pressure falls when heart relaxes, expands
if blood vessels dilate, pressure falls
if blood vessels contract, pressure increases
Blood Flows from Higher Pressure to Lower Pressure
blood flow through cardiovascular system requires a positive pressure gradient
pressure gradient not the same as absolute pressure in system
flow depends on pressure gradient (P) not absolute pressure (P)
2 identical tubes can have same flow but different absolute pressures
identical pressure difference means identical flow
Resistance Opposes Flow
Resistance: tendency of cardiovascular system to oppose blood flow
blood flow takes path of least resistance
increase in resistance of vessels results in decrease in flow
flow inversely proportional to resistance
if resistance increases, flow decreases
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if resistance decreases, flow increases
fluid flowing through tube influenced by 3 resistance factors:
1. radius of the tube (r)
2. length of the tube (L)
3. viscosity (thickness) of the fluid ()
resistance increases as length of tube increases
resistance increases as fluid viscosity increases
resistance decreases as tube’s radius increases
blood viscosity determined by ratio of red blood cells to plasma and how much protein is in
plasma
normally constant
small changes to viscosity, tube length have little effect on resistance
small changes in tube radius have large effect on fluid flow
Vasoconstriction: decrease in vessel diameter
Vasodilation: increase in vessel diameter
blood flow in cardiovascular system directly proportional to pressure gradient of system and
inversely proportional to resistance of system
if pressure gradient remains constant, flow varies inversely with resistance
Velocity Depends on the Flow Rate and the Cross-Sectional Area
Flow Rate (Q): volume of blood that passes a given point in the system per unit time
liters per minute (L/min) or milliliters per minute (mL/min)
how much blood flows past a point in a given period of time
Velocity of Flow (v): the distance a fixed volume of blood travels in a given period of time
how fast blood flows past a point
v = Q/A
A = cross-sectional area of tube
velocity of flow = flow rate/tube’s cross-sectional area
velocity faster in narrow sections
velocity slower in wider sections
arteries act as pressure reservoir during heart’s relaxation phase
maintain mean arterial pressure (MAP) that is primary driving force for blood flow
MAP influenced by:
1. cardiac output (volume of blood heart pumps per minute)
2. peripheral resistance (resistance of blood vessels to blood flow through them)
Cardiac Muscle and the Heart
The Heart Has Four Chambers
the heart lies in the centre of the thoracic cavity
pointed apex of heart angled down to the left side of the body
broader base lies behind the breastbone (sternum)
heart like inverted cone with apex down, base up
heart lies on ventral side of thoracic cavity between the lungs, with its apex resting on the
diaphragm
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