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Chapter 12
Circulation
The circulatory system connects with all body tissues
• In many animals, microscopic blood vessels called capillaries
– Form an intricate network among the tissue
Capillary
Nuclei of smooth muscle cells
Red blood cell
LM 7
00×
Figure 23.1A
Capillaries – Are the sites of exchange between blood and
interstitial fluid
Capillary
Interstitial fluid
Tissue cell
Diffusion of molecules
Figure 23.1B
Land vertebrates have double circulation with separate pulmonary and systemic circuits
• Birds and mammals have four-chambered hearts
Pulmonary circuit
Systemic circuit
Right Left
A A
V
Lung capillaries
Systemic capillaries
V
Figure 23.3C
O 2 2 3
4 1
pulmonary capillaries pulmonary
capillaries
systemic capillaries
CO2 O2
CO2
O2
CO2
pulmonary vein
systemic capillaries
O2 CO2
Pulmonary artery External Respiration
At pulmonary capillaries, HCO3– is
converted inside red blood cells to H2O and CO2. CO2 leaves red blood cells
and capillaries.
External Respiration At pulmonary capillaries, O2 enters red
blood cells where it combines with Hb to form HbO2 .
Internal Respiration At systemic capillaries, CO2 enters red
blood cells. Some combine with Hb to form HbCO2. Most is converted to
HCO3–, which is carried in the plasma.
Hb now combines with H+ to form HHb.
Internal Respiration At systemic capillaries, HbO2 inside red blood cells becomes Hb and O2.
O2 leaves red blood cells and capillaries.
The Mammalian Cardiovascular System
• The mammalian heart
– Has two thin-walled atria that pump blood into the ventricles
– Has thick-walled ventricles that pump blood to all other body organs
Right atrium Left
atrium
Semilunar valve
Semilunar valve
Atrioventricular (AV) valve
Atrioventricular (AV) valve
Right ventricle Left
ventricle
Figure 23.4A
Figure 23.4B
1
2 7
8
9
2
3
4
5
6
4 10
3
9
8
Superior vena cava
Capillaries of head, chest, and arms
Pulmonary artery
Capillaries of left lung
Pulmonary vein
Aorta
Left atrium Left ventricle
Aorta
Capillaries of abdominal region and legs
Inferior vena cava
Right ventricle
Right atrium
Pulmonary vein
Capillaries of right lung
Pulmonary artery
Blood Flow through the Human Cardiovascular System The structure of blood vessels fits their functions
• A single layer of epithelial cells
– Forms the walls capillaries
• Arteries and veins
– Have smooth muscle and connective tissue
Capillary Epithelium
Basement membrane Valve
Epithelium
Smooth muscle
Connective tissue
Vein
Venule Arteriole
Artery
Connective tissue
Smooth muscle
Epithelium
The heart contracts and relaxes rhythmically • During diastole
– Blood flows from the veins into the heart chambers
• During systole
– Contractions of the atria push blood into the ventricles
– Stronger contractions of the ventricles propel blood into the large arteries
A cardiac cycle
Heart is relaxed. AV valves are open.
1 2 Atria
contract.
Systole
Diastole
0.4 sec
0.1sec
0.3 sec 3 Ventricles contract. Semilunar valves are open.
1 2
3
• Cardiac output
– Is the amount of blood/minute pumped into the systemic circuit
• Heart valves
– Prevent the backflow of blood
The pacemaker sets the tempo of the heartbeat • The pacemaker (SA node) generates electrical
signals that trigger contraction of the atria
• The AV node relays these signals to the ventricles
1 2 3 4
Pacemaker (SA node) AV node
Specialized muscle fibers
Apex
Right ventricle
Right atrium
ECG
• An electrocardiogram (ECG)
– Records the electrical changes in the heart
• Heart rate
– Adjusts to body needs
1 2 3 4
ECG
What is a heart attack? • A heart attack is damage to cardiac muscle
– Usually resulting from a blocked coronary artery
Aorta Superior Vena cava
Pulmonary artery
Left coronary artery
Right coronary artery
Blockage
Dead muscle tissue
Figure 23.8A
• In atherosclerosis
– Plaques develop in the inner walls of arteries and can block blood flow
Connective tissue
Smooth muscle
Epithelium
LM 1
60 ×
LM 6
0 ×
Plaque
Figure 23.8B
Blood exerts pressure on vessel walls • Blood pressure
– Is the force blood exerts on vessel walls
– Depends on cardiac output and the resistance of vessels
• Pressure is highest in the arteries
– And lowest in the veins
• Pressure is highest in the arteries
– And lowest in the veins
Figure 23.9A
Pre
ssur
e (m
m H
g)
120 100
80 60 40 20 0
Systolic pressure
Diastolic pressure
Relative sizes and numbers of blood vessels
Velo
city
(cm
/sec
) 50 40 30 20 10 0
Aor
ta
Arte
ries
Arte
riole
s
Cap
illar
ies
Venu
les
Vena
e ca
vae
Vein
s
• Muscle contractions and one-way valves
– Keep blood moving through the veins to the heart
Skeletal muscle
Direction of blood flow in vein
Valve (open)
Valve (closed)
Figure 23.9B
Measuring blood pressure can reveal cardiovascular problems • Blood pressure
– Is measured as systolic and diastolic pressures
Blood pressure 110 systolic 70 diastolic (to be measured)
Rubber cuff inflated with air
Artery
1 2 3 4
Artery closed
Pressure in cuff above 110
110
Pressure in cuff at 110
110
Pressure in cuff at 70
70
Sounds stop
Sounds audible in stethoscope
Figure 23.10
• Hypertension (blood pressure consistently above 140/90 mmHg
– Is a serious cardiovascular problem
• Diet and exercise
– Keep your blood pressure at normal levels
Smooth muscle controls the distribution of blood • Constriction of arterioles and precapillary sphincters
– Controls blood flow through capillary beds
Figure 23.11
1
2
Sphincters relaxed
Sphincters contracted Venule Arteriole
Venule Arteriole
Precapillary sphincters Thoroughfare channel
Capillaries
Thoroughfare channel
Capillaries allow the transfer of substances through their walls
TEM
5,0
00× Muscle
cell
Cleft between two epithelial cells of the capillary wall
Nucleus of epithelial
cell
Capillary wall
Iumen
Interstitial fluid
Figure 23.12A
• The transfer of materials between the blood and interstitial fluid occurs
– By diffusion
– By pressure flow through clefts between epithelial cells
Tissue cells
Osmotic pressure
Arterial end of
capillary
Interstitial fluid
Net fluid Movement out
Net fluid Movement in
Blood pressure
Blood pressure
Osmotic pressure
Venous end of
capillary
• Blood pressure forces fluid out of the capillary at the arterial end
– And osmotic pressure draws fluid at the venous end
STRUCTURE AND FUNCTION OF BLOOD Blood consists of 45% cells (red and white blood cells, platelets) and 55% plasma
• Plasma is about 90% water and contains various inorganic ions, proteins, nutrients, wastes, gases, and hormones
Plasma (55%)
Constituent Major functions
Water Solvent for carrying other substances
Salts (ions) Sodium Potassium Calcium Magnesium Chloride Bicarbonate
Osmotic balance, pH buffering, and nerve and muscle function
Plasma proteins
Fibrinogen Immunoglobulins (antibodies)
Osmotic balance and pH buffering
Immunity
Clotting
Substances transported by blood
Nutrients (e.g., glucose, fatty acids,vitamins) Waste products of metabolism Respiratory gases (O2 and CO2) Hormones
Centrifuged blood
sample
• Red blood cells (erythrocytes) transport O2 bound to hemoglobin
• White blood cells (leukocytes) function both inside and outside the circulatory system to fight infections and cancer
Centrifuged blood
sample
Cellular elements (45%)
Cell type Number per µL (mm3) of blood
Functions
Erythrocytes (red blood cells)
5–6 million Transport of oxygen (and carbon dioxide)
Leukocytes (white blood cells)
5,000–10,000 Defense and immunity
Basophil
Eosinophil
Lymphocyte
Monocyte
Blood clotting 250,000– 400,000
Platelets
Neutrophil
Too few or too many red blood cells can be unhealthy
• Anemia
– Is an abnormally low amount of hemoglobin or red blood cells
Col
oriz
ed S
EM
3,4
00×
• The hormone erythropoietin
– Regulates red blood cell production
• Some athletes
– Artificially increase their red blood cell production, a dangerous practice
Blood clots plug leaks when blood vessels are injured • When a blood vessel is damaged
– Platelets help trigger the conversion of fibrinogen to fibrin, forming a clot that plugs the leak
Col
oriz
ed S
EM
3,4
00×
• The blood-clotting process
Epithelium
1 Platelets adhere to exposed connective tissue
Connective tissue
Platelet Platelet plug
2 Platelet plug forms 3 Fibrin clot traps blood cells
Figure 23.15A
Stem cells offer a potential cure for blood cell diseases • Stem cells divide in bone marrow
– To produce all blood cells
– And may be used to treat some blood disorders Stem cells Stem cells
Erythrocytes Basophils
Eosinophils
Neutrophils Monocytes Lymphocytes
Platelets