Circulation and Gas Exchange
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程洪强，博士，副教授， 浙江大学医学院病理与病理生理学系
研究兴趣：心血管生物学与分子病理
电话：13735827063 电邮：hqcheng11@zju.edu.cn
主页：http://mypage.zju.edu.cn/hqcheng
地址：医学院科研楼A324
Concepts
• Overviews
• Double Circulation
• Blood Vessels
• Gas Exchange
Overview: Trading Places
• Every organism must exchange materials with its
environment
• Exchanges ultimately occur at the cellular level by
crossing the plasma membrane
• In unicellular organisms, these exchanges occur directly
with the environment
• For most cells making up multicellular organisms, direct
exchange with the environment is not possible
• Gills (腮) are an example of a specialized exchange system
in animals
•
•
O2 diffuses from the water into blood vessels
CO2 diffuses from blood into the water
•
Internal transport and gas
exchange are functionally
related in most animals
蝾螈的一种
Circulation Systems
• Diffusion （扩散）time is
proportional to the square of the
distance
• Diffusion is only efficient over
small distances
• In small and/or thin animals, cells
can exchange materials directly with
the surrounding medium
• In most animals, cells exchange
materials with the environment via a
fluid-filled circulatory system
Gastrovascular Cavities
• Some animals lack a circulatory system
• Some cnidarians (刺丝胞动物), such as jellies, have
elaborate gastrovascular cavities
• A gastrovascular cavity functions in both digestion and
distribution of substances throughout the body
• The body wall that encloses the gastrovascular cavity is
only two cells thick
• Flatworms have a gastrovascular cavity and a large
surface area to volume ratio
Gastrovascular Cavities
Circular
canal
Mouth
Gastrovascular cavity
Mouth
Pharynx
Radial canals
5 cm
2 mm
(a) The moon jelly Aurelia, a cnidarian
(b) The planarian Dugesia, a flatworm
Evolutionary Variation in
Circulatory Systems
• A circulatory system
minimizes the diffusion
distance in animals with
many cell layers
Evolutionary Variation in
Circulatory Systems
General Properties of Circulatory
Systems
• A circulatory system has
– A circulatory fluid
– A set of interconnecting vessels
– A muscular pump, the heart
• The circulatory system connects the fluid that surrounds
cells with the organs that exchange gases, absorb
nutrients, and dispose of wastes
• Circulatory systems can be open or closed, and vary in
the number of circuits in the body
Respiratory
system
250 mm
External environment
CO2 O
Food
2
Mouth
Lung tissue (SEM)
70 m2
Interstitial
fluid
Circulatory
system
100 mm
Lining of small
intestine (SEM)
Excretory
system
Anus
Unabsorbed
matter (feces)
Metabolic waste products
(nitrogenous waste)
50 mm
200 m2
Cells
Digestive
system
Blood vessels in
kidney (SEM)
1000 m2
Open Circulatory Systems
• In insects, other arthropods（节肢动物）, and most
molluscs（软体动物）, blood bathes the organs
directly in an open circulatory system
• In an open circulatory system, there is no distinction
between blood and interstitial fluid, and this general
body fluid is called hemolymph（血淋巴液）
(a) An open circulatory system
Heart
Hemolymph in sinuses
surrounding organs
Pores
Tubular heart
Closed Circulatory Systems
• In a closed circulatory system, blood is confined to
vessels and is distinct from the interstitial fluid
• Closed systems are more efficient at transporting
circulatory fluids to tissues and cells
• Annelids, cephalopods, and vertebrates have closed
circulatory systems
(b) A closed circulatory system
Heart
Interstitial fluid
Blood
Small branch
vessels in
each organ
Dorsal
Auxiliary
vessel
hearts
(main heart)
Ventral vessels
Organization of Vertebrate
Circulatory Systems
• Humans and other vertebrates have a closed circulatory
system called the cardiovascular system
• The three main types of blood vessels are arteries, veins,
and capillaries
• Blood flow is one way in these vessels
• Arteries branch into arterioles and carry blood away
from the heart to capillaries
• Networks of capillaries called capillary beds are the
sites of chemical exchange between the blood and
interstitial fluid
• Venules converge into veins and return blood from
capillaries to the heart
• Arteries and veins are distinguished by the direction of
blood flow, not by O2 content
• Vertebrate hearts contain two or more chambers
• Blood enters through an atrium and is pumped out
through a ventricle
Single Circulation
• Bony fishes, rays, and sharks have single circulation
with a two-chambered heart
• In single circulation, blood leaving the heart passes
through two capillary beds before returning
Single Circulation
Movie Time
(a) Single circulation
Gill
capillaries
Artery
Heart:
Atrium (A)
Ventricle (V)
Vein
Body
capillaries
Key
Oxygen-rich blood
Oxygen-poor blood
Zebrafish Heart Beat
Double Circulation
• Amphibian, reptiles, and mammals have double
circulation
• Oxygen-poor and oxygen-rich blood are pumped
separately from the right and left sides of the heart
(b) Double circulation
Pulmonary circuit
Lung
capillaries
A
V
Right
A
V
Left
Systemic
capillaries
Key
Systemic circuit
Oxygen-rich blood
Oxygen-poor blood
Double Circulation
• In reptiles and mammals, oxygen-poor blood flows
through the pulmonary circuit to pick up oxygen
through the lungs
• In amphibians, oxygen-poor blood flows through a
pulmocutaneous circuit to pick up oxygen through the
lungs and skin
• Oxygen-rich blood delivers oxygen through the
systemic circuit
• Double circulation maintains higher blood pressure in
the organs than does single circulation
Heart Evolution
Amphibians
• Frogs and other amphibians have a three-chambered
heart: two atria and one ventricle
• The ventricle pumps blood into a forked artery that
splits the ventricle’s output into the pulmocutaneous
circuit and the systemic circuit
• When underwater, blood flow to the lungs is nearly
shut off
Mammals and Birds
• Mammals and birds have a four-chambered heart with
two atria and two ventricles
• The left side of the heart pumps and receives only
oxygen-rich blood, while the right side receives and
pumps only oxygen-poor blood
• Mammals and birds are endotherms and require more
O2 than ectotherms
Capillaries of
head and forelimbs
Superior vena cava
Pulmonary
artery
Capillaries
of right lung
Pulmonary
vein
Right atrium
Right ventricle
Pulmonary
artery
Aorta
Capillaries
of left lung
Pulmonary vein
Left atrium
Left ventricle
Aorta
Inferior
vena cava
Capillaries of
abdominal organs
and hind limbs
Aorta
Pulmonary artery
Pulmonary
artery
Right
atrium
Left
atrium
Semilunar
valve
Semilunar
valve
Atrioventricular
valve
Atrioventricular
valve
Right
ventricle
Left
ventricle
Heart Contraction
• 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
Heart Index---Normal Heart
Heart rate
Heart rhythm
Camels and bats represent the two extremes
of the scale, with most other mammals
falling somewhere in between.
Heart rate vs. body size?
75 vs 600 (b = -1/4)
Mouse adult cardiomyocytes
Sarcomeres
Heart Contraction
1 Atrial and
ventricular diastole
0.4
sec
2 Atrial systole and ventricular
Heart
Contraction
diastole
1 Atrial and
ventricular diastole
0.1
sec
0.4
sec
2 Atrial systole and ventricular
Heart
Contraction
diastole
1 Atrial and
ventricular diastole
0.1
sec
0.4
sec
0.3 sec
3 Ventricular systole and atrial
diastole
Heart Index
• The heart rate, also called the pulse, is the number of
beats per minute
• The stroke volume is the amount of blood pumped in a
single contraction
• The cardiac output is the volume of blood pumped
into the systemic circulation per minute and depends on
both the heart rate and stroke volume
Measurable
Heart Function
Heart Development
Akiko Hata. Annu Rev Physiol, 2013
Heart Valves
• Four valves prevent backflow of blood in the heart
• The atrioventricular (AV) valves separate each atrium
and ventricle
• The semilunar valves control blood flow to the aorta
and the pulmonary artery
Cardiac Conduction System
1
SA node
(pacemaker)
ECG
Cardiac Conduction System
1
SA node
(pacemaker)
ECG
2
AV
node
Cardiac Conduction System
1
SA node
(pacemaker)
ECG
2
AV
node
3
Bundle
branches
Heart
apex
Cardiac Conduction System
1
SA node
(pacemaker)
ECG
2
AV
node
3
Bundle
branches
4
Heart
apex
Purkinje
fibers
Cardiac Conduction System
• Some cardiac muscle cells are self-excitable, meaning
they contract without any signal from the nervous
system
• The sinoatrial (SA) node, or pacemaker, sets the rate
and timing at which cardiac muscle cells contract
• Impulses that travel during the cardiac cycle can be
recorded as an electrocardiogram (ECG or EKG)
Cardiac Conduction System
• Impulses from the SA node travel to the
atrioventricular (AV) node
• At the AV node, the impulses are delayed and then
travel to the Purkinje fibers that make the ventricles
contract
Cardiac Conduction System
• The pacemaker is regulated by two portions of the
nervous system: the sympathetic（交感神经） and
parasympathetic divisions （副交感神经）
• The sympathetic division speeds up the pacemaker
• The parasympathetic division slows down the
pacemaker
• The pacemaker is also regulated by hormones and
temperature
Artery
LM
Vascular System
Vein
Red blood cells
100 mm
Valve
Basal lamina
Endothelium
Endothelium
Smooth
muscle
Connective
tissue
Capillary
Smooth
muscle
Connective
tissue
Artery
Vein
Capillary
15 mm
Red blood cell
Venule
LM
Arteriole
Velocity
(cm/sec)
5,000
4,000
3,000
2,000
1,000
0
50
40
30
20
10
0
Pressure
(mm Hg)
Area (cm2)
Blood Pressure
120
100
80
60
40
20
0
In the thinner-walled veins, blood flows back to
the heart mainly as a result of muscle action
Systolic
pressure
Diastolic
pressure
Blood Pressure
Blood pressure reading: 120/70
1
3
2
120
120
70
Artery
closed
Sounds
audible in
stethoscope
Sounds
stop
Capillary Function
• 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
• Blood flow is regulated by nerve impulses, hormones,
and other chemicals
• Most blood proteins and all blood cells are too large to
pass through the endothelium
Precapillary sphincters control
flow of blood between arterioles
and venules
Precapillary
sphincters
Arteriole
(a) Sphincters relaxed
Arteriole
(b) Sphincters contracted
Thoroughfare
channel
Capillaries
Venule
Venule
Capillary Function
INTERSTITIAL
FLUID
Net fluid movement out
Body cell
Blood
pressure
Osmotic
pressure
Arterial end
of capillary
Direction of blood flow
Venous end
of capillary
Cardiovascular Disease
• Cardiovascular diseases are disorders of the heart and
the blood vessels
• Cardiovascular diseases account for more than half the
deaths in the United States
• Cholesterol, a steroid, helps maintain membrane fluidity
Atherosclerosis, Heart Attacks,
and Stroke
• One type of cardiovascular disease, atherosclerosis, is
caused by the buildup of plaque deposits within arteries
• Angina pectoris is caused by partial blockage of the
coronary arteries and results in chest pains
• A heart attack, or myocardial infarction, is the death of
cardiac muscle tissue resulting from blockage of one or
more coronary arteries
• A stroke is the death of nervous tissue in the brain,
usually resulting from rupture or blockage of arteries in
the head
Lumen of artery
Endothelium
Smooth
muscle
1
LDL
Foam cell
Macrophage
Plaque
2
Extracellular
matrix
Plaque rupture
4
3
Fibrous cap
Cholesterol
Smooth
muscle
cell
T lymphocyte
Risk Factors and Treatment of
Cardiovascular Disease
• A high LDL to HDL ratio increases the risk of
cardiovascular disease
• The proportion of LDL relative to HDL can be
decreased by exercise, not smoking, and avoiding foods
with trans fats
• Drugs called statins reduce LDL levels and risk of heart
attacks
Risk Factors and Treatment of
Cardiovascular Disease
• Inflammation plays a role in atherosclerosis and
thrombus formation
• Aspirin inhibits inflammation and reduces the risk of
heart attacks and stroke
• Hypertension, or high blood pressure, promotes
atherosclerosis and increases the risk of heart attack and
stroke
• Hypertension can be reduced by dietary changes,
exercise, and/or medication
Homework
• Read Campell book chapter 41:P897-926