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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