Lecture #18 Date _____

• Chapter 42 ~ Circulation and Gas Exchange

Circulatory system evolution • Gastrovascular cavity: cnidarians and flatworms• Open circulatory: arthropods and most mollusks, organs are bathed in

hemolymph (blood & interstitial fluid) in a central cavity, one or more hearts pump blood into sinuses (spaces surrounding organs) where chemical exchange occurs

• Closed circulatory: blood confined to vessels• Cardiovascular system: in vertebrates contains heart (atria/ventricles), blood

vessels (arteries, arterioles, capillary beds, venules, veins), and blood (circulatory fluid)

Circulatory system evolution (cont.)• Fish: 2-chambered heart; single circuit of blood flow• Amphibians: 3-chambered heart; 2 circuits of blood flow- pulmocutaneous (lungs and skin);

systemic (everything else)• Reptiles: 3-chambered heart, but septum partially divides the single ventricle• Mammals: 4-chambered heart; double circulation with 2 circuits – pulmonary (lungs) and

systemic; complete separation between oxygen-rich and oxygen poor blood

Mammals: double circulation• The right ventricle (1) pumps blood to the lungs

via the pulmonary arteries (2)• Blood flows through the capillary beds (3) in the

lungs, loading O2 and unloading CO2

• Oxygen rich blood returns to the heart via the pulmonary veins to the left atrium (4); then to the left ventricle (5) which pumps blood to the body via the aorta (6)

• Oxygen rich blood reaches the capillary beds in the head and forelimbs (7), then the abdominal organs and hind limbs (8) where gas exchange occurs

• Blood from the head and forelimbs returns to the heart via the superior vena cava (9) while blood from the abdomen and hind limbs returns via the inferior vena cava (10)

• The 2 vena cava dump their blood into the right atrium (11)

Double Circulation

Mammalian Heart – a closer look

• 2 atria, 2 ventricles• 4 different valves –

prevent the backflow of blood and keep it moving in the right direction

• 2 semilunar valves between ventricles and aorta/pulmonary arteries

• 2 atrioventricular valves between atria and ventricles

The Cardiac Cycle

• Cardiac cycle: sequence of filling and pumping (in average human at rest takes 0.8 seconds)

• Systole- contraction• Diastole- relaxation• Cardiac output: volume of blood

per minute• Heart rate- number of beats per

minute• Stroke volume- amount of blood

pumped with each contraction• Pulse: rhythmic stretching of

arteries by heart contraction

The Heartbeat• Sinoatrial (SA) node (“pacemaker”): sets rate and timing of cardiac

contraction by generating electrical signals, located in the wall of the right atrium

• Atrioventricular (AV) node: relay point (0.1 second delay) spreading impulse to walls of ventricles, located in the wall between the right atrium and ventricle

• Electrocardiogram (ECG or EKG)

Blood vessel structural differences

• Capillaries•endothelium; basement membrane

• Arteries•thick connective tissue;

thick smooth muscle; endothelium; basement membrane

• Veins •thin connective tissue; thin smooth muscle; endothelium; basement membrane

The lymphatic system• Lymphatic system: system of

vessels and lymph nodes, separate from the circulatory system, that returns fluid and protein to blood

• Lymph: colorless fluid, derived from interstitial fluid

• Lymph nodes: filter lymph and help attack viruses and bacteria

• Helps body defend against infection, regulates protein volume/concentration in blood, and transports fats from digestive tract to circulatory system

Blood• Plasma: liquid matrix of blood in which cells are suspended (90% water)• Erythrocytes (RBCs): transport O2 via hemoglobin• Leukocytes (WBCs): defense and immunity• Platelets: clotting

Differentiation of blood cells

• Stem cells: pluripotent cells in the red marrow of bones (particularly in the ribs, vertebrae, sternum, and pelvis)

• Pluripotent means these cells have the ability to differentiate into any type of blood cell

• Erythropoietin – hormone produced in kidneys when tissues not getting enough O2, stimulates production of more erythrocytes

Blood Clotting• Blood clotting: fibrinogen (inactive)/ fibrin (active) aggregates into

threads to form a clot• Hemophilia – disease characterized by excessive bleeding• Thrombus (clot) – clotting occurs within a blood vessel restricting

blood flow, associated with cardiovascular disease

Cardiovascular disease• Cardiovascular disease (>50% of all deaths in US), diseases of the heart and

blood vessels• Heart attack- death of cardiac tissue due to coronary blockage• Stroke- death of nervous tissue in brain due to arterial blockage • Atherosclerosis: arterial plaque deposits, narrows arteries• Plaque: consist mostly of fibrous connective tissue and muscle cells infiltrated

with lipids (cholesterol)• Hypertension: high blood pressure, can promote atherosclerosis• Low-density lipoproteins or LDLs: “bad cholesterol”• High-density lipoproteins or HDLs: “good cholesterol”

Gas exchange• The uptake of O2 and the discharge of CO2

• Aquatic: gills, ventilation (increasing the flow of respiratory medium over the respiratory surface), countercurrent exchange

• Terrestrial: tracheal systems (air tubes) and lungs

Mammalian respiratory systems• Larynx (upper part of

respiratory tract)• Vocal cords (sound production)• Trachea (windpipe)

• Bronchi (two tubes to lungs)• Bronchioles • Alveoli (air sacs)• Diaphragm (breathing muscle)

Breathing• Positive pressure breathing: pushes air into lungs (frog)• Negative pressure breathing: pulls air into lungs (mammals)• Inhalation: diaphragm contraction; Exhalation: diaphragm relaxation• Tidal volume: amount of air inhaled and exhaled with each breath (500ml)• Vital capacity: maximum tidal volume during forced breathing (4L)• Regulation: CO2 concentration in blood (medulla oblongata)

Respiratory pigments: gas transport

• Oxygen transport-• Hemocyanin: found in hemolymph

of arthropods and mollusks (Cu)• Hemoglobin: vertebrates (Fe)

• Carbon dioxide transport-• Blood plasma (7%)• Hemoglobin (23%)• Bicarbonate ions (70%)• Deep-diving air-breathers-• Myoglobin: oxygen storing protein