B.3 - Cardiovascular system - Simone Damiano · Open vs closed circulatory system 4 Some animals have an open circulatory system (as in arthropods: insects, arachnids, and crustaceans),

Cardiovascular system

1

Circulatory systems

2

Unicellular organisms are in constant contact with their environments, obtaining nutrients and oxygen directly across the cell surface. The same holds true for simple plants and animals, such as algae, sponges, cnidarians (jellyfish), and flatworms.

Larger and more complex plants and animals require methods for transporting materials to and from cells of the body. These organisms have evolved efficient transport systems.

The circulatory system

3

Function of the circulatory system is to transport O2 and nutrients to the cells of the body and to carry away CO2 and other wastes. To do this, the system must keep blood constantly circulating.

Open vs closed circulatory system

4

Some animals have an open circulatory system (as in arthropods: insects, arachnids, and crustaceans), where the transport fluid is hemolymph and is not enclosed in vessels. Hemolymph is analogous to the blood and interstitial fluid (water, proteins, sugars, hormones, etc.) of vertebrates.

Hemolymph =Interstitial fluid

+ blood

Open vs closed circulatory system

5

All vertebrates have a closed circulatory system where blood is transported in vessels, separate from the interstitial fluid. Interstitial fluid is a solution that surrounds the cells of multicellular animals

Single-loop circulation

6

Fish have a single-loop circulatory pathway.

The heart has a single atrium and a single ventricle

Two-circuits circulation

7

Amphibians and most reptiles have a two-circuits circulatory pathway.

The heart is divided into two atria and one ventricle.

8

Birds and mammals have a two-circuits circulatory pathway.

The heart divided into two atria and two ventricles

Two-circuits circulation

9

Evolution of the heart in vertebrates

2-chamberheart

3-chamberheart

4-chamberheart

4-chamberheart

Lancelets Fish Mammals TurtlesAmphibians CrocodiliansSquamates BirdsFigure 50.8 Evolution of the heart in vertebrates. Despite their similarity, the four-chambered hearts of mammals and birds evolved convergently.

50.4 The Four-Chambered Heart and the Blood Vessels

Learning OutcomesExplain the cardiac cycle.1. Describe the role of autorhythmic cells of the SA node.2. Define blood pressure and how it is measured3.

As mentioned earlier, the heart of mammals, birds, and croco-dilians goes through two contraction cycles, one of atrial con-traction to send blood to the ventricles, and one of ventricular contraction to send blood to the pulmonary and systemic cir-cuits. These two contractions plus the resting period between these make up the complete cardiac cycle encompassed by the heartbeat.

The cardiac cycle drives the cardiovascular systemThe heart has two pairs of valves. One pair, the atrioventricular (AV) valves, maintains unidirectional blood flow between the atria and ventricles. The AV valve on the right side is the tricuspid valve, and the AV valve on the left is the bicuspid, or mitral, valve. Another pair of valves, together called the semilunar valves, ensure one-way flow out of the ventricles to the arterial systems. The pulmonary valve is located at the exit of the right ventricle, and the aortic valve is located at the exit of the left ventricle. These valves open and close as the heart goes through its cycle. The closing of these valves produces the “lub-dub” sounds heard with a stethoscope.

The cardiac cycle is portrayed in figure 50.9 . It begins as blood returns to the resting heart through veins that empty into the right and left atria. As the atria fill and the pressure in them rises, the AV valves open and blood flows into the ven-tricles. The ventricles become about 80% filled during this time. Contraction of the atria tops up the final 20% of the 80 mL of blood the ventricles receive, on average, in a resting person. These events occur while the ventricles are relaxing, a period called ventricular diastole. After a slight delay, the ventricles contract, a period called ventricular systole. Contraction of each ventricle increases the pressure within each chamber, causing the AV valves to force-fully close (the “lub” sound), preventing blood from backing up into the atria. Immediately after the AV valves close, the pres-sure in the ventricles forces the semilunar valves open and blood flows into the arterial systems. As the ventricles relax, closing of the semilunar valves prevents backflow (the “dub” sound).

Contraction of heart muscle is initiated by autorhythmic cellsAs in other types of muscle, contraction of heart muscle is stimu-lated by membrane depolarization (see chapters 44 and 47). In skel-etal muscles, only nerve impulses from motor neurons can normally initiate depolarization. The heart, by contrast, contains specialized “self-excitable” muscle cells called autorhythmic fibers, which can initiate periodic action potentials without neural activation. The most important group of autorhythmic cells is the sinoatrial (SA) node, described earlier (figure 50.10) . Located in the wall of the right atrium, the SA node acts as a pacemaker for the rest of the heart by producing spontaneous action po-tentials at a faster rate than other autorhythmic cells. These spontaneous action potentials are due to a constant leakage of Na+ ions into the cell that depolarize the membrane. When the

1026 part VII Animal Form and Function

rav32223_ch50_1018-1037.indd 1026rav32223_ch50_1018-1037.indd 1026 11/19/09 11:44:44 AM11/19/09 11:44:44 AM

Despite their similarity, the four-chambered hearts of mammals and birds evolved convergently.

10

A circulatory system consists of a pump (the heart), a fluid (the blood) and a series of blood vessels (the vascular system).

All together those elements form the cardiovascular system.

The cardiovascular system

11

The heart has four chambers: two atria and two ventricles. A cardiac septum separates the heart into right and left halves

The heart

right ventricle

right atriumleft ventricle

left atrium

septum

12

An artery carries blood away from the heart while a vein takes the blood to the heart. Cardiac valves keep blood moving in the correct direction.

The heart

superior vena cava

semilunar valve

atrioventricular valve

inferior vena cava

pulmonary veins

pulmonary artery

aorta

13

The heart

14

The four valves in the heart are: •The two atrioventricular (AV) valves between the atria and the

ventricles, are the mitral valve (or bicuspid) and the tricuspid valve.

•The two semilunar (SL) valves, which are in the arteries leaving the heart, are the aortic valve and the pulmonary valve.

The heart

15

Electric rhythmic impulse move the heart. The contraction is called systole, the relaxation of the chambers is diastole.

The heartbeat

systole diastole

16

The heartbeat starts from the sinoatrial node (SA), the impulse-generating (pacemaker) tissue. The atrioventricular node (AV) causes the ventricle contraction.

The cardiac conduction system

17

Arteries Blood pressure in arteries and arterioles carries blood away from the heart

Blood vessels

18

Veins Skeletal muscle contractions returns blood in veins and venules to the heart

Blood vessels

19

Capillaries Thin-walled capillaries permit exchange of materials and gas with the tissues.

Blood vessels

20

Cardiovascular systems includes two circuits:

• Pulmonary circuit: pulmonary arteries take O2-poor blood to lungs while pulmonary veins return O2-rich blood to the heart

• Systemic circuit: left ventricles send O2-rich blood to aorta; vena cava takes O2-poor blood back to the right atrium

Pulmonary and systemic circuits

21

Pulmonary and systemic circuits

22

Pulmonary and systemic circuitsA typical human RBC cycle in the circulatory system occurs every 20 seconds. The red blood cell deforms as it enters capillaries, as well as changing color as it alternates in states of oxygenation along the circulatory system.

23

Blood velocity blood depends on pressure and on capillaries area.

Systolic pressure: is the pressure in arteries during ventricular systole. Diastolic pressure: is the pressure in arteries during ventricular diastole.

Blood pressure

24

A stroke (or cerebral ictus) occurs when a small cranial arteriole bursts or is blocked by an embolus.

A heart attack occurs when an coronary artery (the artery that bring O2-rich blood to capillaries of the heart) is completely blocked.

Vascular diseases

25

Healthy life style can help to prevent vascular diseases:

• refraining from smoking • no drugs • controlling weight • healthy diet • monitoring cholesterol • exercising

Vascular diseases

26

Cholesterol is an essential component of cell membranes and is carried by plasmic proteins (LDL and HDL). Anomalies in quantities of LDL or HDL can lead to the formation of cholesterol plaque in blood vessels.

Vascular diseases

27

Blood functions

• Transports substances to and from capillaries where exchanges occur.

• Helps the organism defend against pathogens.

• Helps regulate body temperature.

• Forms clots to prevent hemorrhages.

Blood compositionBlood is composed of a liquid portion called plasma and some formed elements: red blood cells, white blood cells and platelets.

Plasma (92% water, 55% of whole blood)

Formed elements

Platelets and leukocytes (<1%)

Red blood cells (erythrocytes) (45% of whole blood)

NutrientsElectrolytes

GasesRegulatory substancesWaste products

Other solutes (1.5%) Water (91.5%)

Plasma proteins (7%)

Blood Plasma Red Blood Cells

Albumin (54%) Globulins (38%) Fibrinogen (7%) All others (1%)

Plasma Red blood

cells

White blood cells Platelets

Platelets

150,000–300,000/ mm3 blood

4 million–6 million/ mm3 blood

Neutrophils Eosinophils

2–4% 60–70%

Basophils Lymphocytes

20–25%

Monocytes

3–8% 0.5–1%

Figure 50.1 Composition of blood.

participates in temperature regulation. Contraction and dilation of blood vessels near the surface of the body, beneath the epidermis, helps to conserve or to dissipate heat as needed.Protection.3. The circulatory system protects against injury and foreign microbes or toxins introduced into the body. Blood clotting helps to prevent blood loss when vessels are damaged. White blood cells, or leukocytes, help to disarm or disable invaders such as viruses and bacteria (see chapter 52).

Blood plasma is a fl uid matrixBlood plasma is the matrix in which blood cells and platelets are suspended. Interstitial (extracellular) fluids originate from the fluid present in plasma. Although plasma is 92% water, it also contains the follow-ing solutes:

Nutrients, wastes, and hormones.1. Dissolved within the plasma are all of the nutrients resulting from digestive breakdown that can be used by cells, including

glucose, amino acids, and vitamins. Also dissolved in the plasma are wastes such as nitrogen compounds and CO2 produced by metabolizing cells. Endocrine hormones released from glands are also carried through the blood to their target cells.Ions.2. Blood plasma is a dilute salt solution. The predominant plasma ions are Na+, Cl–, and bicarbonate ions (HCO3

–). In addition, plasma contains trace amounts of other ions such as Ca2+, Mg2+, Cu2+, K+, and Zn2+.Proteins.3. As mentioned earlier, the liver produces most of the plasma proteins, including albumin, which constitutes most of the plasma protein; the alpha (α) and beta (β) globulins, which serve as carriers of lipids and steroid hormones; and fi brinogen, which is required for blood clotting. Blood plasma with the fi brinogen removed is called serum.

Formed elements include circulating cells and plateletsThe formed elements of blood cells and cell fragments include red blood cells, white blood cells, and platelets. Each element has a specific function in maintaining the body’s health and homeostasis.

ErythrocytesEach microliter of blood contains about 5 million red blood cells, or erythrocytes. The fraction of the total blood volume that is occupied by erythrocytes is called the blood’s hematocrit; in humans, the hematocrit is typically around 45%. Each erythrocyte resembles a doughnut-shaped disk with a central depression that does not go all the way through. Ma-ture mammalian erythrocytes lack nuclei. The erythrocytes of vertebrates contain hemoglobin, a pigment that binds and transports oxygen. (Hemoglobin was described more fully in the previous chapter when we discussed respiration. ) In verte-brates, hemoglobin is found only in erythrocytes. In inverte-brates, the oxygen-binding pigment (not always hemoglobin) is also present in plasma.

LeukocytesLess than 1% of the cells in human blood are white blood cells, or leukocytes; there are only 1 or 2 leukocytes for every 1000 erythrocytes. Leukocytes are larger than erythrocytes and have nuclei. Furthermore, leukocytes are not confined to the blood as erythrocytes are, but can migrate out of capillaries through the intercellular spaces into the surrounding intersti-tial (tissue) fluid. Leukocytes come in several varieties, each of which plays a specific role in defending against invading microorganisms and other foreign substances, as described in chapter 52. Granular leukocytes include neutrophils, eosinophils, and ba-sophils, which are named according to the staining properties of granules in their cytoplasm. Nongranular leukocytes in-clude monocytes and lymphocytes. In humans, neutrophils are the most numerous of the leukocytes, followed in order by lym-phocytes, monocytes, eosinophils, and basophils.

chapter 50 The Circulatory System 1019www.ravenbiology.com


Blood plasmaBlood plasma is the matrix in which blood cells and platelets are suspended. Interstitial (extracellular) fluids originate from the fluid present in plasma. Although plasma is 92% water, it also contains solutes:

Nutrients, wastes, and hormones Dissolved within the plasma are all of the nutrients resulting from digestive breakdown that can be used by cells, including glucose, amino acids, and vitamins. Also dissolved in the plasma are wastes and CO2 produced by cells. Hormones released from glands are also carried through the blood. Ions Blood plasma is a salt solution. The predominant plasma ions are Na+, Cl–, and bicarbonate ions (HCO3–). In addition, plasma contains trace amounts of other ions such as Ca2+, Mg2+, Cu2+, K+, and Zn2+.

Proteins The liver produces most of the plasma proteins, including albumin, which constitutes most of the plasma protein; globulins, which serve as carriers of lipids and steroid hormones; and fibrinogen, which is required for blood clotting


Formed elements









Plasma Red blood

cells


Platelets

150,000–300,000/ mm3 blood



2–4% 60–70%


20–25%

Monocytes

3–8% 0.5–1%












Formed elementsThe formed elements of blood cells and cell fragments include red blood cells, white blood cells, and platelets

Erythrocytes

Each microliter of blood contains about 5 million red blood cells, or erythrocytes. Each erythrocyte resembles a disk with a central depression. Mature mammalian erythrocytes lack nuclei. The erythrocytes of vertebrates contain hemoglobin, a pigment that binds and transports O2 and found only in erythrocytes.


Formed elements









Plasma Red blood

cells


Platelets

150,000–300,000/ mm3 blood



2–4% 60–70%


20–25%

Monocytes

3–8% 0.5–1%












Formed elementsThe formed elements of blood cells and cell fragments include red blood cells, white blood cells, and platelets

Leukocytes

Less than 1% of the cells in human blood are white blood cells, or leukocytes. Leukocytes are larger than erythrocytes and have nuclei. Furthermore, leukocytes are not confined to the blood as erythrocytes are, but can migrate out of capillaries through the intercellular spaces into the surrounding interstitial (tissue) fluid. Leukocytes play a specific role in defending against invading microorganisms and other foreign substances. Leukocytes include neutrophils, eosinophils, and basophils, which are named according to the staining properties. Nongranular leukocytes include monocytes and lymphocytes.


Formed elements









Plasma Red blood

cells


Platelets

150,000–300,000/ mm3 blood



2–4% 60–70%


20–25%

Monocytes

3–8% 0.5–1%













Formed elements









Plasma Red blood

cells


Platelets

150,000–300,000/ mm3 blood



2–4% 60–70%


20–25%

Monocytes

3–8% 0.5–1%













Formed elements









Plasma Red blood

cells


Platelets

150,000–300,000/ mm3 blood



2–4% 60–70%


20–25%

Monocytes

3–8% 0.5–1%













Formed elements









Plasma Red blood

cells


Platelets

150,000–300,000/ mm3 blood



2–4% 60–70%


20–25%

Monocytes

3–8% 0.5–1%













Formed elements









Plasma Red blood

cells


Platelets

150,000–300,000/ mm3 blood



2–4% 60–70%


20–25%

Monocytes

3–8% 0.5–1%












32

Platelets

Blood clotting involves platelets that release clotting factors at the site of the blood vessel damage. Fibrin threads provide a meshwork for a blood clot.

33

Blood stem cellsHematopoietic stem cells (HSCs), are multipotent stem cells, found in the bone marrow of adults, that can produce all the blood cell types. HSCs can be easily transplanted from pelvic bone.

34

Capillary exchange

Between the arterial end and the venus end, substances diffuse according to the concentration gradient: • CO2 and waste produced by the cells move in • C6H12O6, amino acids and O2 spread out

35

Lymphatic capillaries collect excess tissue fluid (called lymph) and return it to the vascular system

Capillary exchange

36

AB0 classification systemAn antigen is a substance against which the immune system can respond. For example, components of the bacterial cell wall can trigger severe and immediate attacks by WBC. Contrariwise, some antigens are found on the body's own cells and are known as "self-antigens", and the immune system does not attack these.

The membrane of each red blood cell contains millions of self-antigens that are ignored by the immune system.

However, when patients receive blood transfusions, their immune systems will attack any donor red blood cells that contain antigens that differ from their self-antigens.

Blood Type Self Antigen on the RBC

Antibody in the plasma

A A Anti-BB B Anti-A

AB A, B NoneO None Anti-A and Anti-B

37

AB0 classification systemSelf antigens carried on the RBC are classified as A and B and determine the type of blood. Blood group antigens are either sugars (ABO system) or proteins (RH system), and they are attached to various components in the red blood cell membrane

Those molecules behave as antigens when transplanted in incompatible organisms.

OA B ABA antigen

B antigen

38

AB0 classification system

O

AB

AB

39

The effects of nicotine on the cardiovascular system

Nicotine decreases the allowance of the airways and the red blood cells get a higher affinity for CO.

Thus, less oxygen can be passed causing difficulties in breathing. This raises the blood pressure and heart rate which contribute to making the platelets stickier.

Hence, platelets trigger a series of chemical changes that result in the formation of a blood clot. This decreases the amount of blood flowing to the other parts of the body and the blood vessels then constrict.

40

HEART

Documents

B.3 - Cardiovascular system - Simone Damiano · Open vs closed circulatory system 4 Some animals have an open circulatory system (as in arthropods: insects, arachnids, and crustaceans),