Chapter 42

Circulatory System

Learning Objectives

Compare and contrast a closed and open circulatory system

List the 4 major components of blood Describe plasma components and function Compare and contrast erythrocytes and leukocytes Explain the function of lymphocytes Describe the function and structure of antibodies Diagram the pulmonary and systemic circulatory

systems Identify the major structures of the mammalian heart

Animal Circulatory Systems

Muscular heart pumps specialized fluid (such as blood) through tubular vessels

Blood Carries O2 and nutrients to body tissues

Carries away CO2 and wastes

Open and Closed Circulatory Systems Open circulatory system

In most invertebratesHeart pumps hemolymph into vessels that empty

into body spaces (sinuses) before returning to the heart

Closed circulatory system In some invertebrates and all vertebrates Blood is confined in blood vessels throughout the

body (does not mix with interstitial fluid)

Vertebrate Circulatory Systems

Evolved from a heart with a single series of chambers (single circuit) to a double heart that pumps blood through separate pulmonary and systemic circuits

42.2 Blood and Its Components

Plasma is an aqueous solution of proteins, ions, nutrient molecules, and gases

Erythrocytes are the oxygen carriers of the blood

Leukocytes provide the body’s front line of defense against disease

Platelets induce blood clots that seal breaks in the circulatory system

Mammalian Blood

A fluid connective tissueBlood cells (erythrocytes, leukocytes,

platelets)Suspended in a fluid matrix (plasma)

Plasma and Plasma Proteins

Contains water, ions, dissolved gases (O2 and CO2), glucose, amino acids, lipids, vitamins, hormones, and plasma proteins

Plasma proteinsAlbumins (transport, osmotic balance, pH)Globulins (transport, immunoglobins)Fibrinogen (blood clotting)

Blood Cells

Erythrocytes Contain hemoglobin (transports O2 from lungs to

body) Leukocytes

Defend body against infecting pathogens Platelets

Functional cell fragments that trigger clotting

Fig. 42.6a, p. 954

Erythrocyte (red blood cell)

Leukocyte (white blood cell)

Platelets

Fig. 42.6b, p. 954

Plasma

Leukocytes and platelets

Packed cell volume, or hematocrit

Erythrocytes

Fig. 42.7, p. 955

Leukocytes

Monocyte/macrophage EosinophilB lymphocyte

Basophil

Platelets NeutrophilT lymphocyte

Natural killer (NK) cell

Erythrocyte

Lymphoid stem cell

Myeloid stem cell

Pluripotent stem cell

megakaryocyte

(marrow) (lymph)

Types of Defense

Non-specific Specific (antibody-mediated)

Fig. 43.1, p. 974

Bacteria at injury site

Macrophages Mast cells

CytokinesCapillary

ChemokinesNeutrophils

Histamine

Neutrophils sticking to wallEndothelial cell

of capillary

1. A break in the skin introduces bacteria.

2. Activated mast cells release histamine.

3. Histamine and cytokines dilate local blood vessels.

4. Chemokines attract neutrophils, which pass between cells of the blood vessel wall.

5 Neutrophils engulf the pathogens and destroy them.

1

2

3

5

4

Adaptive (Acquired) Immunity

Triggered by antigensExogenous or endogenous macromolecules

(proteins or polysaccharides) Recognized by B cells and T cells via

antibodies Targets particular pathogens or toxin

molecules

Light and Heavy Polypeptide Chains in an Antibody Molecule

Fig. 43.11b, p. 985

b. Agglutination

Antigen Antibody

Bacterium

Immunological Memory

First encounter with an antigen elicits a primary immune response

Later exposure to the same antigen elicits a rapid secondary immune response with a greater production of antibodies

The Mammalian Heart

A four-chambered pumpTwo atria at top of heartTwo ventricles at bottom of heartAtrioventricular (AV) valves between atria and

ventriclesSemilunar (SL) valves between ventricles and aorta /

pulmonary arteries Blood is pumped into two separate circuits

Pulmonary circuit (right heart)- to the lungsSystemic circuit (left heart)- to the body

Blood Vessels Arteries carry blood away from the heart Arterioles (small branches of arteries)

deliver blood to capillaries Capillaries exchange material with

interstitial fluid Venules collect blood from capillaries Veins return blood to the heart

Blood Vessels

Blood leaves the heart in large arteries Branch into smaller arterioles

Arterioles deliver blood to capillary networksCapillaries exchange substances between blood

and interstitial fluid Small venules collect blood from capillaries

Join into larger veins that return blood to heart

Fig. 42-9, p. 957

To systemic circuit

Superior vena cava (returns blood from head, upper limbs)

Left pulmonary veins (return blood from lungs)From pulmonary circuit

Pulmonary arteries (to lungs)

Aorta

Right pulmonary veins (return blood from lungs)

AV (TV) Valve (shown open)

Left atrium

AV (MV) valve (shown open)

Right ventricle

Left ventricle

Inferior vena cava (returns blood flow from trunk, legs)

Septum

To systemic circuit

Right atrium

Semilunar (SL) valvesAtrioventricular (AV) valves

KEY

VC-from body

To body

PV

AV

Fig. 42.10, p. 958

systemic circuit

Capillary networks of head and forelimbs

pulmonary circuit

pulmonary circuit

Superior vena cava

Aorta

Pulmonary artery

Pulmonary artery

LA

Pulmonary vein

Pulmonary vein

RA

RV LV

Capillary network of right lung

Capillary network of left lung

Inferior vena cava

To lower body parts

Capillary networks of abdominal organs and lower limbs

systemic circuit

The Cardiac Cycle

Systolic pressure Contraction of ventricles pushes blood into arteries

at peak pressure or maximum pressure exerted when the heart contracts

Diastolic pressure Between contractions, blood pressure in arteries

falls to a minimum pressure or the minimum pressure in the arteries when the heart is at rest.

Systole–diastole sequence is the cardiac cycle

Fig. 42-11b, p. 959

SL valves

Left atrium

Right atrium

AV valves

Right ventricle

Left ventricle

1. Heart is fully relaxed; atria begin to fill with blood; AV and SL valves are closed.

2. Blood fills atria and pushes AV valves open; ventricles begin to fill.

3. Atria contract, filling ventricles completely.

4. Ventricles begin to contract, forcing AV valves closed; SL valves remain closed.

5. Ventricles contract fully, forcing SL valves open and ejecting blood into arteries.

Fig. 42.11a, p. 959

Systolic blood pressure

Diastolic blood pressure

Pre

ssu

re (

mm

Hg

)

Normal: 120/80 or less Prehypertension: 120/80 to 139/89 Hypertension: 140/90 or above

Arteries

Artery walls Inner endothelial layerMiddle layer of smooth muscleOuter layer of elastic fibers

Arterioles (smallest arteries) constrict and dilateRegulate flow and pressure of blood into

capillaries

Exchange Across Capillary Walls

Rate of blood flowSlower in capillaries than in arteries and veinsMaximizes time for exchange of substances between

blood and tissues Two major mechanisms drive exchange of

substances Diffusion along concentration gradientsBulk flow

Veins

Veins have thinner walls than arteriesAllows vessels to expand and contract Veins act as blood reservoirs as well as conduits

Pressure from movements of skeletal muscles and respiration help return blood to heart One-way valves prevent blood from flowing

backward

Disorders of the Circulatory System Atherosclerosis

Atherosclerosis

Cholesterol should be well below 200 mg/dL If above 240 mg/dL, statins are usually

prescribed White women between the ages of 45 and 64

years have the highest cholesterol levels High LDL and triglyceride levels are more

dangerous than high HDL levels

Magnitude of Coronary Disorders

Leading cause of death 2007: 615,651 One third of all adults has high blood pressure

and of the remaining, most have prehypertension

One is very six adults has high blood cholesterol

One third of adults are overweight, one third are obese, and 6% are extremely obese

17% of children 2-17 years old are obese

Metabolic Syndrome

Abdominal obesity

Atherogenic dyslipidemia

Raised blood pressure

Insulin resistance ± glucose intolerance

Proinflammatory state (CRP) Prothrombotic state

http://circ.ahajournals.org/cgi/content/full/109/3/433 2004