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 O 2 and unloading CO 2 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 O 2 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 O 2, 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 O 2 and the discharge of CO 2 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: CO 2 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