1. Circulation and Gas Exchange
Chapter 42
Circulation and Gas Exchange

2. The Mammalian Heart: A Closer Look
A closer look at the mammalian heart provides a better understanding of double circulation

3. Pulmonary artery Aorta Anterior vena cava Pulmonary artery Right
LE 42-6
Pulmonary artery
Aorta
Anterior
vena cava
Pulmonary
artery
Right
atrium
Left
atrium
Pulmonary
veins
Pulmonary
veins
Semilunar
valve
Semilunar
valve
Atrioventricular
valve
Atrioventricular
valve
Posterior
vena cava
Right
ventricle
Left
ventricle

4. The heart contracts and relaxes in a rhythmic cycle called the cardiac cycle
The contraction, or pumping, phase is called systole
The relaxation, or filling, phase is called diastole

5. LE 42-7 Atrial systole; ventricular Semilunar diastole valves closed
0.1 sec
Semilunar
valves
open
AV valves
open
0.3 sec
0.4 sec
Atrial and
ventricular
diastole
AV valves
closed
Ventricular systole;
atrial diastole

6. The heart rate, also called the pulse, is the number of beats per minute
The cardiac output is the volume of blood pumped into the systemic circulation per minute

7. Maintaining the Heart’s Rhythmic Beat
Some cardiac muscle cells are self-excitable, meaning they contract without any signal from the nervous system

8. The sinoatrial (SA) node, or pacemaker, sets the rate and timing at which cardiac muscle cells contract
Impulses from the SA node travel to the atrioventricular (AV) node
At the AV node, the impulses are delayed and then travel to the bundle of His then to the Purkinje fibers that make the ventricles contract

11. Impulses that travel during the cardiac cycle can be recorded as an electrocardiogram (ECG or EKG)
Pacemaker
generates wave of
signals to contract.
Signals are delayed
at AV node.
Signals pass
to heart apex.
Signals spread
throughout
ventricles.
SA node
(pacemaker) AV
node
Bundle
branches
Purkinje
fibers
Heart
apex
ECG

12. The pacemaker is influenced by nerves, hormones, body temperature, and exercise

13. Concept 42.3: Physical principles govern blood circulation
The physical principles that govern movement of water in plumbing systems also influence the functioning of animal circulatory systems

14. Blood Vessel Structure and Function
The “infrastructure” of the circulatory system is its network of blood vessels
All blood vessels are built of similar tissues and have three similar layers

15. LE 42-9 Artery Vein 100 µm Endothelium Valve Basement membrane
Smooth
muscle
Smooth
muscle
Capillary
Connective
tissue
Connective
tissue
Artery
Vein
Arteriole
Venule

16. Structural differences in arteries, veins, and capillaries correlate with functions
Arteries have thicker walls that accommodate the high pressure of blood pumped from the heart

17. In the thinner-walled veins, blood flows back to the heart mainly as a result of muscle action

18. LE 42-10 Direction of blood flow in vein (toward heart) Valve (open)
Skeletal muscle
Valve (closed)

19. Blood Flow Velocity
Physical laws governing movement of fluids through pipes affect blood flow and blood pressure
Velocity of blood flow is slowest in the capillary beds, as a result of the high resistance and large total cross-sectional area

20. LE 42-11
5,000
4,000
Area (cm2)
3,000
2,000
1,000 50 40
Velocity (cm/sec) 30 20 10
120
Systolic
pressure
100 80
Pressure (mm Hg) 60
Diastolic
pressure 40 20
Aorta
Arteries
Arterioles
Capillaries
Venules
Veins
Venae cavae

21. Blood Pressure
Blood pressure is the hydrostatic pressure that blood exerts against the wall of a vessel
Systolic pressure is the pressure in the arteries during ventricular systole; it is the highest pressure in the arteries
Diastolic pressure is the pressure in the arteries during diastole; it is lower than systolic pressure
Blood pressure is determined by cardiac output and peripheral resistance due to constriction of arterioles

22. LE 42-12_4 Blood pressure reading: 120/70 Pressure in cuff above 120
below 120
Pressure
in cuff
below 70
Rubber cuff
inflated
with air
120
120 70
Sounds
audible in
stethoscope
Sounds
stop
Artery
Artery
closed

23. Capillary Function
Capillaries in major organs are usually filled to capacity
Blood supply varies in many other sites

24. Two mechanisms regulate distribution of blood in capillary beds:
Contraction of the smooth muscle layer in the wall of an arteriole constricts the vessel
Precapillary sphincters control flow of blood between arterioles and venules

25. LE 42-13ab
Precapillary sphincters
Thoroughfare
channel
Arteriole
Venule
Capillaries
Sphincters relaxed
Arteriole
Venule
Sphincters contracted

26. Capillaries and larger vessels (SEM) 20 µm
LE 42-13c
Capillaries and larger vessels (SEM)
20 µm

27. The critical exchange of substances between the blood and interstitial fluid takes place across the thin endothelial walls of the capillaries
The difference between blood pressure and osmotic pressure drives fluids out of capillaries at the arteriole end and into capillaries at the venule end

28. LE 42-14
Tissue cell
INTERSTITIAL FLUID
Net fluid
movement out
Net fluid
movement in
Capillary
Capillary
Red
blood
cell
15 µm
Direction of
blood flow
Blood pressure
Osmotic pressure
Inward flow
Pressure
Outward flow
Arterial end of capillary
Venous end

29. Fluid Return by the Lymphatic System
The lymphatic system returns fluid to the body from the capillary beds
This system aids in body defense
Fluid reenters the circulation directly at the venous end of the capillary bed and indirectly through the lymphatic system