Download L14: Circulation, Part 2

The Cardiac Cycle
1
Cardiac cycle
• Systole:
contraction
phase
• Diastole:
relaxation phase
• ~0.8 seconds
Animal Circulation, Part 2
Lecture 14
Winter 2014
– (72 beats/min)
• What are the
heart sounds?
Fig. 42.8
The Cardiac Cycle
2
How Does the Heart Maintain its Beat?
3
• Autorhythmic
• Cardiac output
– Contract/relax w/o input from nervous system
• Volume of blood each ventricle pumps/min
– Heart rate: number of beats/min
– Stroke volume: amount of blood pumped by a
ventricle in a single contraction
• Sinoatrial (SA) node
–
–
–
–
Pacemaker
Generates electrical impulse
Spreads through walls of atria
Both atria contract
Fig. 42.9
How Does the Heart Maintain its Beat?
4
How Does the Heart Maintain its Beat?
5
• Atrioventricular (AV) Node
– Impulse from SA node reaches AV node
– Signal delayed 0.1 sec
• Atrium finishes contracting
• Impulse passed to
Bundle branches
& Purkinje fibers
• Ventricle
contraction begins
at apex
Fig. 42.9
Fig. 42.9
1
How Does the Heart Maintain its Beat?
6
7
Blood Vessel Structure & Function
• Other regulatory cues for SA node
• Nervous
• What differences
did you see
between arteries
and veins in the
sheep heart
dissection?
• How do these
different structures
inform on their
function?
– Sympathetic & parasympathetic nerves
• Hormones
– Epinephrine
• Body Temperature
– 1C increase raises heart rate by ~10
beats/min
Fig. 42.10
Blood Flow Velocity & Pressure
8
Blood Flow Velocity & Pressure
• Why does blood slow
down when it reaches
capillaries?
9
• Blood flows from
area of high
pressure to area of
low pressure
• Capillaries narrow,
increase
resistance,
pressure greatly
reduced
Fig. 42.11
Fig. 42.11
Blood Flow Velocity & Pressure
• Arterial blood
pressure highest
during ventricular
systole
– Systolic pressure
– Stretches arteries
• Pulse
• During ventricular
diastole, elastic walls
of arteries recoil
– Reduced pressure
– Diastolic pressure
10
11
Regulation of Blood Pressure
• Nervous and hormonal control
– Smooth muscles of arterioles
• Vasoconstriction
– Contraction of arteriole walls
– Blood pressure increases in arteries
• Vasodilation
– Relaxation of arteriole walls
– Blood pressure decreases in arteries
• Can direct blood flow to specific parts of body
– Need to increase cardiac output to maintain blood
pressure/flow throughout body
Fig. 42.11
2
How Does the Blood in Veins Return to the
Heart?
12
13
Capillary Function
• Rhythmic contractions of smooth muscle in
venules & veins
• Contraction of skeletal muscles during exercise
• Capillaries lack smooth
muscles
• How to control flow?
– Contraction/relaxation of
arterioles
– Precapillary sphincters
• Change in pressure of
thoracic (chest) cavity
during inhalation
– Vena cava & other large
veins near heart expand
& fill with blood
• Rings of smooth muscle
located at entrances to
capillary beds
• Valves prevent
backward flow of blood
Fig. 42.14
Fig. 42.13
14
Capillary Function
• Capillaries are where exchange between blood and
interstitial fluid occurs
• What controls direction of fluid flow?
15
Lymphatic System
• Problem: More fluid leaves capillaries due to
pressure than returns to capillaries due to
osmotic pressure
• Solution: Return via lymphatic system
– System of vessels and nodes, separate from
circulatory system, that returns fluid, proteins
and cells to the blood
– Lymph
– Blood pressure
– Osmotic pressure
• Blood proteins
(albumin) &
blood cells
• Colorless fluid, derived from interstitial fluid, that is
part of the lymphatic system
Fig. 42.15
16
Lymphatic System
Fig. 43.7
Blood Composition & Function
17
Fig. 42.17
3
Blood Composition & Function
18
Blood Clotting
19
Fig. 42.18
Fig. 42.17
4