Download Chapter 13: Circulation

Chapter 13 Lecture Notes
page 1
perfusion refers to blood flow through tissues or organs
adequate perfusion is required for homeostasis
blood pressure is the force that drives perfusion
blood pressure is due to:
 the force produced by the ventricles during ventricular systole
 peripheral resistance caused by constriction of blood vessels
(arterioles)
A. blood vessel structure and function
general structure:
 tunica interna = endothelium (simple squamous e.) overlying a thin
layer of c.t.
 tunica media = elastic fibers and smooth muscle in varying
proportions
o elastic recoils to maintain blood pressure during diastole
o muscle relaxes to dilate vessel (vasodilation) or contracts to
constrict vessel (vasoconstriction); controlled mostly by
sympathetic division
BIOL 2404
Strong/Fall 2006
Chapter 13 Lecture Notes
page 2
 tunica externa = c.t. that anchors blood vessels to surrounding
structures
1. arteries carry blood away from the heart and channel the blood to the
areas of the body that need perfusion
thick walls, especially tunica media
a. elastic arteries - tunica media mostly elastic fibers
(loss of elasticity will increase systolic pressure)
b. muscular arteries - tunica media mostly smooth muscle
c. arterioles - tunica media all smooth muscle
2. capillaries allow exchange between blood and tissue fluid
a. capillary structure
 walls consist of endothelium only
 thin cells allow materials to diffuse through cells
 gaps between endothelial cells facilitate exchange
o in some capillaries these gaps are not present (brain)
o in some capillaries the endothelial cells have small
openings that increase permeability (kidneys)
 blood flow is slow
b. capillary beds
 arterioles give rise to a network of capillaries
BIOL 2404
Strong/Fall 2006
Chapter 13 Lecture Notes
page 3
 the opening of each capillary is controlled by smooth muscle
cells (precapillary sphincter)
 not all sphincters are open at the same time
 the capillaries drain into a small vein
3. veins return blood to the heart and store “extra” blood
 thin wall (lower pressure)
 valves prevent backflow
 hold about 60% of total blood volume at rest
B. blood pressure and flow
1. blood flow = pressure gradient  peripheral resistance
a. pressure gradient
 blood goes from where pressure is higher to where it is lower
 the gradient is caused by the force of the heart’s contraction
b. peripheral resistance reduces blood flow
 most resistance is from friction between the blood and vessel
wall
 the smaller the vessel diameter, the higher the resistance
 high blood viscosity also increases resistance
2. arterial blood pressure
a. systolic - peak blood pressure in arteries during ventricular systole
BIOL 2404
Strong/Fall 2006
Chapter 13 Lecture Notes
page 4
b. diastolic - lowest blood pressure in arteries during ventricular
diastole
c. pulse pressure = systolic P - diastolic P
3. measuring blood pressure
 a pressure cuff is inflated around the upper arm until the pressure in
the cuff is higher than systolic pressure
 a stethoscope is placed over the brachial artery distal to the cuff to
listen for turbulent blood flow
 air is slowly released from the cuff
 when turbulent blood flow is first heard, the pressure on the dial is
systolic pressure
 when the sounds of turbulent blood flow end, the pressure on the dial
is diastolic pressure
4. autoregulation of blood flow
 the distribution of blood to different parts of the body depends on
their relative need for oxygen and nutrients
 blood flow is adjusted by a combination of local and systemic
controls
 autoregulation occurs as a result of changes in the level of oxygen
and carbon dioxide in a tissue:
 high oxygen, low carbon dioxide and high pH cause smooth
muscle cells in arterioles and precapillary sphincters to
contract, decreasing local blood flow
 low oxygen, high carbon dioxide and low pH cause smooth
muscle cells in arterioles and precapillary sphincters to relax,
increasing local blood flow
BIOL 2404
Strong/Fall 2006
Chapter 13 Lecture Notes
page 5
5. systemic reflex control of arterial blood pressure
 receptors located in arteries monitor blood pressure, oxygen, carbon
dioxide and pH
 they send afferent signals to the cardiovascular centers in the
medulla oblongata, which in turn control ANS signals to the heart and
blood vessels
a. baroreceptors ( stretch receptors) monitor blood pressure
low blood pressure
reduced stretch on baroreceptors
decreased afferent signals
cardiovascular centers interpret this as the need to
increase blood pressure
 sympathetic signals to SA node increase HR
 sympathetic signals to ventricular myocardium
increase contractility and SV
 sympathetic signals to vessels causes
vasoconstriction, increasing PR
blood pressure is increased
b. chemoreceptors monitor the level of carbon dioxide, pH and
oxygen in the blood
high blood carbon dioxide (low blood pH)
cardiovascular centers interpret this as the need to
increase perfusion by increasing blood pressure
 sympathetic signals to SA node increase HR
 sympathetic signals to ventricular myocardium
increase contractility and SV
 sympathetic signals to vessels causes
vasoconstriction, increasing PR
blood pressure is increased
BIOL 2404
Strong/Fall 2006
Chapter 13 Lecture Notes
page 6
6. hormonal control of blood pressure
a. epinephrine and norepinephrine
b. ADH - major effect is indirect (conserves water, maintains blood
volume)
c. angiotensin II - causes vasoconstriction in response to low blood
pressure or volume
d. atrial natriuretic peptide - causes kidneys to excrete more sodium
in response to high blood pressure
C. circulatory pathways
1. pulmonary circuit
 pressure supplied by right ventricle
 low pressure system
 takes low-oxygen blood to lungs and brings high-oxygen blood back
to heart
right ventricle
pulmonary trunk
left and right pulmonary arteries
pulmonary capillaries
pulmonary veins (superior and inferior, L and R)
left atrium
2. systemic circuit




pressure supplied by left ventricle
high pressure system
takes oxygen to tissues and removes CO2
distributes nutrients and transports wastes to kidneys
left ventricle
aorta
arteries
BIOL 2404
Strong/Fall 2006
Chapter 13 Lecture Notes
page 7
capillaries
veins
superior and inferior vena cava
right atrium
3. coronary circulation
left and right coronary arteries leave aorta just above aortic SL valve
a. left coronary artery
anterior interventricular a.
in anterior interventricular sulcus
supplies interventricular septum and anterior
walls of both ventricles
circumflex a.
in atrioventricular sulcus
supplies left atrium and post. left ventricle
b. right coronary artery
marginal a.
along right margin of heart
supplies right ventricle
posterior interventricular a.
in posterior interventricular sulcus
supplies interventricular septum and posterior
walls of both ventricles
BIOL 2404
Strong/Fall 2006
Chapter 13 Lecture Notes
page 8
4. cranial circulation
L and R internal carotid arteries
L and R vertebral arteries
basilar artery
cerebral arterial circle (circle of Willis)
cerebral capillaries
dural sinuses
L and R internal jugular veins
5. hepatic portal circulation
portal system = two capillary beds joined by a portal vessel
capillaries of small intestine, part of large intestine and stomach
superior mesenteric vein
capillaries of spleen, stomach and pancreas
splenic vein
capillaries of distal large intestine and rectum
inferior mesenteric vein
liver
liver sinusoids
hepatic veins
inferior vena cava
BIOL 2404
Strong/Fall 2006