3.4 – The Circulatory System

Importance of Circulation (Internal Transport)• carries oxygen and nutrients to the cells for cellular respiration• carries wastes away from cells (with lymph and excretory

system)• carries chemical messages from endocrine organs to target

tissues• carries immune cells to infection sites• distributes heat• maintains levels of body fluids (with kidneys), pH

• the human heart beats about 70 times/minute non-stop from when you first draw breath until you die, pumping enough blood to fill 2 large ships

• 96 000 km of blood vessels are never more than 2 cells away from the human body’s 10 000 000 000 000

Parts of the Circulatory System

Blood● more than ½ of blood

is plasma consisting of water, protein, nutrients, urea, mineral salts, vitamins, gases, and heat

plasma proteins help maintain homeostasis

• globulins produce antibodies to defend against pathogens

• fibrinogens are important in blood clotting

rest of blood is composed of formed elements consisting of red blood cells, white blood cells, and platelets

Red Blood Cells (Erythrocytes)• primary function is transport of O2 and CO2

anucleate, biconcave disk provides greater surface area for gas exchange● live for about 120 days at least 5 000 000 are produced

each day in bone marrow, produced by nucleated stem cells

each RBC contains 280 000 000 haemoglobin molecules (haeme = iron-containing pigment, globin = protein structure)

4 Fe molecules attach to protein structure and bind to oxygen oxyhaemoglobin complex gives blood it’s red colour once oxygen is given up, the protein changes shape and appears bluish

White Blood Cells (Leucocytes)● much less numerous than RBC (1 in 700)nucleated, classified by shape of nucleus

and appearance of granules in the cytoplasm

granulocytes and agranulocytes are both produced in the bone marrow, but agranulocytes are modified in the lymph tissue

Platelets● also anucleate and

produced in nucleated stem cells in the bone marrow

(small fragments of cytoplasm break off from a megakaryocyte)irregularly-shaped

platelets move through the smooth blood vessels until they strike a sharp edge (i.e. a tear), where they initiate blood-clotting reactions

The Heart made up of cardiac muscle,

nerve, and connective tissue a fluid-filled membrane called the

pericardium surrounds the heart fluid bathes the heart, preventing friction between its outer wall and the covering membrane

the heart consists of two separate pumps separated by the septum

pumping action is synchronized the right side collects deoxygenated blood from the body tissues and pumps it to the lungs for gas exchange (pulmonary circuit) the left side receives oxygenated blood from the lungs and pumps it to the body cells (systemic circuit)

Blood Vessels

Arteries arteries carry blood away from

the heart they have thick walls with

distinct layers outer and inner connective

tissue middle muscle and elastic

connective tissue thick and elastic to withstand

pressure generated by pulses of blood as they are pumped out of the heart

arteries branch into arterioles which have a middle layer of smooth muscle

Capillaries composed of a single

layer of cells, capillaries are the site of fluid and gas exchange between blood and body cells

most are 0.4-1.0 mm long and less than 0.005 mm in diameter (RBC must pass through in single file)(Fig. 3, P. 252)

capillary beds are easily damaged by high BP or impact (bruising occurs as blood enters space between tissue)

O2 and CO2 diffuse across capillary walls

proteins cross by active transport (exocytosis and endocytosis)

water-soluble ions and vitamins pass through spaces between endothelial cells

Veins deoxygenated blood collects in small veins (venules) as capillaries

merge

BP in venules is reduced to 15-20 mm Hg thinner walls of veins contain smooth muscle that rhythmically massage

blood back to the heart

Disorders and Diseases of the Circulatory System cardiovascular disease includes hypertension (sustained high blood

pressure), arteriosclerosis, atherosclerosis, heart attack (destruction of the heart muscle), and stroke (interrupted blood flow to the brain)

factors affecting health of the heart:high blood cholesterolsmokingdiabetes mellitushypertensionsedentary lifestylerapid weight gain or losscongenital factors

Hypertension increased resistance to blood flow

results in weakening and rupture of blood vessels

increased connective tissue to support weak vessels makes them less elastic which further increases blood pressure

sometimes hereditary , but usually diet-related (i.e. salt )

Artherosclerosis lipid droplets join together

and form blockages in arteries

calcium and other minerals form on top of the fat to form a fibrous net of plaque (artherosclerosis, the most common type of arteriosclerosis = “artery disease”)

narrowing the artery diameter increases blood pressure

blood clots form around deposits

inadequate blood supply to the heart results in diseases that kills more Canadians than any other

Coronary Artery Disease