Ch. 42

Trading Places• Occurs across a moist cell membrane• Must be dissolved in water to enter

the cell membrane (osmosis)• May need internal transport if cells

are isolated• Animals gain oxygen and nutrients

while shedding carbon dioxide and wastes

Trading PlacesDiffusion too slow• time of diffusion is proportional to the square

distance the chemical must travelTwo Solutions 1.Body size and shape keep many or all cells in direct

contact with the environment2.Circulation

•reduces the distance a substance must diffuse to enter or leave a cell

•Fluid is moved between each cell’s immediate surroundings andthe tissues where exchange with the environment occurs

Gastrovascular Cavities• Cnidarians and Platyhelminthes• No specific internal transport

(circulatory) system• Functions in digestion and

distribution of nutrients• Gastrodermal cells have direct

access to nutrients– nutrients only have short distance

to diffuse

General Properties of Circulatory Systems

3 basic components1.Heart

– A muscular pump

2.Circulatory fluid3.Set of

interconnecting vessels

Open Circulatory System• Hemolymph bathes

the internal organs directly while moving through sinuses

• Circulation results from contraction of the dorsal vessel (heart) and body movements

• Relaxation of the “heart” draws the blood back into the ostia (pores)

• Not energy expensive

• Arthropods and most mollusks

Closed Circulatory System• Blood is confined to

vessels and is distinct from the interstitial fluid

• Heart pumps blood into larger vessels– Major vessels branch

• In organs, nutrients are exchanged through capillaries b/w blood and interstitial fluid

• Effective delivery of O2

• Annelids, squids, octopus, vertebrates

Organization of Vertebrate Circulatory Systems

Cardiovascular system

Arteries Arterioles Capillaries Venules Veins

Capillary beds •Networks of

capillaries that infiltrate every tissue

Heart has at least 2 chambers

• Atria– Receives the

blood

• Ventricle– Pumping out

blood

Organization of Vertebrate Circulatory Systems

Single Circulation• Blood only passes

through the heart once per circuit

Double Circulation• Blood passes through

two circuits• Pulmonary circuit• Systemic circuit• Pulmocutaneous circuit

– Capillaries in both skin & lungs

Organization of Vertebrate

Circulatory Systems

Double Circulation in Vertebrates

Mammalian Circulation1. RV contracts blood to lungs via

pulmonary arteries2. Blood exchanges O2 and CO2 in the capillary

beds of the lungs3. Pulmonary veins LA bicuspid LV

pumps blood into the systemic circuit via the aorta

4. First 2 branches of the aorta are coronary arteries to supply heart muscle

5. Diffusion between capillaries from blood to tissues and tissues to blood

6. Capillaries join venules veins superior/inferior vena cava RA tricuspid valve RV

Mammalian Heart and Circulation

Cardiac cycle1.Complete

sequence of contraction and relaxation

Systole• heart contracts

and pumps the blood

Diastole• heart relaxes and

heart fills with blood

Mammalian Heart…a closer look

Mammalian Heart…a closer look

Cardiac output• Volume of blood each ventricle

pumps per minute• Average is 5 L/min• Determined by two factors

– Heart rate•The number of heartbeats per minute

– Stroke volume•Amount of blood pumped by a ventricle in a

single contraction•Average in a human is 70 mL

Mammalian Heart…a closer lookValves

• prevent backflow of blood

Atrioventricular valves (between atria and ventricles)

• Bicuspid and tricuspidSemilunar valves

(between ventricles and arteries)

• Aortic and pulmonaryHeart Murmur• defect in one or more of

the valves that allows backflow to occur

Maintaining the Heart’s Rhythmic BeatMyogenic (autorhythmic)

cells• self-excitableSinoatrial node (SA node)• pacemaker• Cluster of cells that

controls the rhythm• contracts and stimulates

the AV node• can be influenced by

outside forcesAtrioventricular node• Delay of 0.1 second before

stimulating specialized muscle fibers called bundle branches and Purkinje fibers

Blood Vessel Structure and Function

Lumen lined with endothelium• Smooth to minimize friction

Blood Flow Velocity

Blood slows as it moves from arteries to arterioles to capillaries

• Total cross sectional area is much greater in capillary beds

Blood Pressure

Blood PressureHydrostatic force that blood exerts

against a vessel wallPressure greater in arteries and

during systole Systolic• top #• Arterial blood pressure is highest

when the heart contracts during ventricular systole

Diastolic• bottom #

A sphygmomanometer, an inflatable cuff attached to a pressure gauge, measures blood pressure fluctuations in the brachial artery of the arm over the cardiac cycle.

• The arterial blood pressure of a healthy human oscillates between about 120 mm Hg at systole and 70 mm Hg at diastole.

Blood Pressure RegulationPhysical/emotional stress triggers

nervous and hormonal responsesNitric Oxide• Major inducer of vasodilationEndothelin• Major inducer of vasoconstriction

Blood Pressure and Gravity

Gravity is a major influence

Return of venous blood to heart –

1.Rhythmic contractions of smooth muscle

2.Contraction of skeletal muscles

3.Change in pressure in thoracic cavity

Capillary Function

Only 5-10% of capillaries have blood in them at any one given time

• Each tissue has so many capillaries that tissues have a blood supply all of the time

Capillary FunctionFluid exchange b/w capillaries and

interstitial fluid• Endocytosis and exocytosis• Simple diffusion• Blood pressure drives fluids out of

capillaries• Presence of blood proteins pulls fluid back

in

Fluid Return by Lymphatic System

Lose 4-8 L of fluid from capillaries to tissues daily

• Return to the blood via the lymphatic system

• Fluid lost by capillaries lymph

• Lymph nodes surround lymph vessels– Filter the lymph and

house cells that attack viruses and bacteria

Blood

Cellular ElementsErythrocytes (red

blood cells)• Oxygen transport• Biconcave disks• Lack nuclei• Contain hemoglobin

– Iron containing protein that transports the O2

• Sickle cell anemia

Cellular ElementsLeukocytes (white blood

cells)• 5 major types• Fight infection

– Phagocytic– Develop specialized B

cells and T cells to mount immune responses against foreign substances

Thrombocytes (platelets)• cellular fragments• Structural and molecular

functions in blood clotting

Blood Clotting

Stem Cells and Replacement of Cellular

ElementsStem Cells• Multipotent;

dedicated to replenishing body’s blood cell population

Erythropoietin (EPO)

• Hormone from kidney

• Stimulates RBC production

• Negative feedback

Cardiovascular DiseaseCholesterol metabolismLow Density Lipoprotein (LDL)• Delivers cholesterol to cells for

membrane productionHigh Density Lipoprotein (HDL)• Scavenges extra cholesterol for return to

the liverInflammation

Cardiovascular DiseasesAtherosclerosis• chronic cardiovascular

disease characterized by plaques that develop on the inner walls of arteries and narrow the width of the vessel

Thrombus• a blood clot that blocks

a major vessel• embolus – moving clot

Cardiovascular DiseasesAteriosclerosis•degenerative condition of the arteries where plaque hardens

Hypertension•high blood pressure•may promote atherosclerosis

Cardiovascular DiseasesHeart attack• death of

cardiac muscle resulting from prolonged blockage of one or more coronary arteries

Cardiovascular DiseasesStroke•death of

nervous tissue in the brain often resulting from blockage of arteries in the brain