Transport+and+Circulation

by Simmy & Jerico Transport/Circulation Page

Intro

A lesson about blood flow and circulation
A teacher was giving a lesson on the circulation of the blood. Trying to make the matter clearer, he said: "Now, students, if I stood on my head the blood, as you know, would run into it, and I should turn red in the face."

"Yes, sir," the boys said.

"Then why is it that while I am standing upright in the ordinary position the blood doesn't run into my feet?"

A little fellow shouted, "'It's because yer feet ain't empty."

The circulatory system is an organ system that passes nutrients (such as Amino acids,electrolytes and lymph), gases, hormones, blood cells, etc. to and from cells in the body to help fight diseases, stabilize body temperature and pH, and to maintain homeostasis. This system may be seen strictly as a blood distribution network, but some consider the circulatory system as composed of the cardiovascular system, which distributes blood, and the lymphatic system, which distributes lymph. While humans, as well as other vertebrates, have a closed cardiovascular system (meaning that the blood never leaves the network of arteries, veins and capillaries), some invertebrate groups have an open cardiovascular system. The most primitive animal phyla lack circulatory systems. The lymphatic system, on the other hand, is an open system. Two types of fluids move through the circulatory system: blood and lymph. The blood, heart, and blood vessels form the cardiovascular system. The lymph, lymph nodes, and lymph vessels form the lymphatic system. The cardiovascular system and the lymphatic system collectively make up the circulatory system.

Circulatory System Outline (Taken from Chapters 42.1 and 42.2 of the AP Bio Book)
 * Bodily Transfer of Nutrients
 * Diffusion (smaller organisms)
 * Circulatory Systems (blood/interstitial fluid)


 * Invertebrate Circulation
 * Gastrovascular Cavities: hydras and cnidarians
 * Thin body wall (roughly 2 cells thick)
 * Interstitial fluid is continuous with water
 * Digestion and distribution occurs in the cavity
 * Short-distance diffusion
 * “Simple” Circulation
 * Open Systems (insects, mollusks)
 * No distinction between blood and interstitial fluid
 * This mixed liquid is called hemolymph
 * Heart pumps through sinuses (spaces around the organs)
 * Heart is tubular and dorsal
 * Body movement creates pressure to allow the system to operate
 * Closed Systems
 * Distinction between blood and interstitial fluid
 * Heart provides pressure for fluid movement
 * Advantages
 * Open systems are much less complex and require less energy to work
 * Closed systems are much more efficient and allow for bulk transport


 * Vertebrate Circulation (closed system) (“cardiovascular system”)
 * Heart containing atria and ventricles
 * Atria – storage for blood
 * Ventricles – pumping mechanism
 * Blood Vessels
 * Arteries – deliver blood to capillaries/organs
 * Veins – return blood from capillaries to the heart
 * Capillaries – microscopic, porous vessels found in tissue; allows for diffusion of gases and chemicals into and out of blood; found in capillary beds
 * Arterioles – small vessels that arteries branch into to carry blood to capillaries
 * Venules – smaller subunits of veins
 * Metabolic rate is directly proportional to the complexity of the organism’s circulatory system
 * Different forms of vertebrate circulatory systems:
 * Fish
 * One atrium, one ventricle
 * Blood from ventricle goes to the gills (gill circulation); it “picks up” O2 and “drops off” CO2
 * Oxygen-rich blood continues to the rest of the body (systemic circulation)
 * Two circuit-system
 * Slower (less blood pressure)
 * Constrained maximum metabolic rate


 * Amphibians
 * Two atria, one ventricle
 * Pulmocutaneous circuit (blood first moves to skin and gas exchange organs from the right atria)
 * Blood moves to the gas exchange area then back to the heart with O2
 * In the heart, blood re-mixes and blood leaves the left atria to enter the systemic circuit
 * Double Circulation – much higher potential metabolic rate than fish
 * Reptiles
 * Similar Double Circulation system as is found in amphibians
 * Pulmonary Circuit (lungs) and Systemic Circuit
 * Three-chambered heart
 * A septum divides the ventricle, which allows for less mixing of O2-rich and O2-poor blood
 * Snakes, turtles, and lizards have an “incomplete” septum
 * Crocodiles have a complete septum
 * Mammals and Birds
 * Completely separated ventricles
 * Left side pumps only O2-rich blood
 * Right side pumps and receives O2-poor blood
 * The four-chamber heart is essential to endotherms; high metabolic demands
 * Most effective O2 transport


 * The Heart
 * Double Pump (right side to lungs, left side to system)
 * Cardiac muscles, myogenesis (no nerve impulse required to contract)
 * Capillaries in cardiac wall
 * Coronary arteries supply blood, oxygen, and nutrients to the heart
 * Branches off aortae
 * Pacemaker: in charge of contraction, affected by hormones and some nerve impulses


 * Blood Vessels
 * Arteries: Thick walled tubes; helps avoid bulges and leaking, helps in pumping blood, and may withstand high pressure. The narrow passage (lumen) helps maintain high pressure
 * Veins: Thin walled tubes; less pumping, allows vein to be adjacent to muscle, little danger of bursting. The wide lumen helps with the slow flow of blood
 * Capillaries: thin layer of cells (porous layer); small particle diffusion, plasma leakage for tissue fluid formation. Narrow lumen for fitting in small spaces.


 * Heartbeats (negative feedback)
 * The atria collect blood and the atrio-ventricular valve opens at high pressure
 * Atria walls contract, blood flows into ventricles (semilunar valves closed)
 * Ventricle walls contract, atrio-ventricular walls shut, preventing back flow, and semilunar valves open
 * Atria begin to fill back up
 * Ventricles stop contracting when pressure falls; when the ventricular pressure is lower than the atrial pressure, the connective wall reopens and blood from veins enter the atria; repeat.


 * Cardiac Cycle
 * Right ventricle pumps blood to pulmonary arteries
 * Blood goes to left and right lungs
 * O2-rich blood returns to the left atrium
 * Blood flows in the left ventricle
 * Blood enters the aortae (these bring blood to the arteries)
 * The aorta may deliver blood to arteries…
 * Coronary arteries – supplies the heart itself with blood
 * Forelimb arteries – torso and arms
 * Abdominals – legs
 * O2 and CO2 diffusion occurs along the way
 * Capillary beds reform into venules/veins
 * O2-poor blood from the head, neck, and forelimbs channel into a large vein (anterior vena cava)
 * O2-poor blood from the abdominals enter the posterior vena cava
 * Emptying of vena cava into the right ventricle


 * Systole: contraction of the heart
 * Dystole: Relaxation of the heart
 * Volume of blood pumped per minute = cardiac output
 * Cardiac output depends on the heart rate (beats per min.) and the stroke volume (amount of blood pumped by left ventricle)
 * Heart murmurs: defects in heart valves
 * Pulse: the rhythmic stretching of arteries by blood pressure


 * The Heart’s Rhythmic Beat
 * Maintenance of oxygen transport is essential to bodily function (e.g. the brain requires a constant supply of O2
 * Some heart cells are self-excitable
 * Most heart cells are dependent on pacemakers, or the sinoatrial node (SA node)
 * These set the rate and timing of contractions
 * Located in the right atrium wall, near the point where the vena cava enters the heart


 * Hearts with pacemakers are called myogenic hearts
 * Hearts without pacemakers are called neurogenic hearts as they depend on motor neurons, and are often found in arthropods
 * The SA node works by generating electrical impulses and by spreading these impulses to the walls of the atrium, forcing contraction
 * The impulse also passes through the atrioventricular node (AV node)
 * AV nodes delay impulse from hitting the ventricles for 0.1 seconds
 * This delay ensures that the atrium is empty
 * The impulse then hits special muscle fibers which spread it across the ventricle walls

Blood
 * The impulses can be detected by electrocardiograms (ECGs), which can detected the current generated by the impulses at the skin
 * The SA node has a set frequency, but may be altered by various physiological factors
 * Hormones
 * Body temperature
 * Exercise/Movement
 * Stress


 * Plasma, blood cells, and platelets
 * Blood volume is 5.6 liters
 * Transports nutrients, oxygen, and horomones to the tissues. Carbon dioxide, urea, and heat are also carried. (IB 6.2.7)
 * Plasma is the fluid component of blood
 * Red blood cells
 * Transport oxygen around the body
 * White blood cells
 * Defend the body against disease organisms
 * Platelets
 * blood clotting
 * Erythrocytes
 * 25 trillion of them
 * Biconcave shape allows a large surface area to diffuse oxygen quickly.
 * Lack nuclei and mitochondria
 * More space; uses anaerobic respiration
 * Hemoglobin
 * Leukocytes
 * White blood cells
 * Fight infections and pathogens
 * Monocytes and Neutrophils
 * Engulf debris and bacteria
 * Interstitial fluid and lymphatic system
 * Lymphatic System
 * This system consists of lymphatic vessels and lymph tissue
 * Functions in homeostasis of body fluids
 * Balance of proper fluids in the body.
 * As blood flows through capillaries, fluid and blood proteins are lost
 * the lymphatic system functions in returning these back to the blood.
 * Interstitial fluid enters by diffusing into lymph capillaries, which are found among cardiovascular capillaries
 * Absorbs lipids from the gastrointestinal tract
 * Once the fluid enters the lymph capillaries it is called “lymph”
 * lymph nodes
 * Filter the fluid
 * white blood cells remove viruses/bacteria
 * Become swollen when sick because white blood cells are reproducing more rapidly
 * Cardiovascular Disease
 * Disorders of the heart or blood vessels
 * account for more than half of the deaths in the USA.
 * sometimes inherited but mostly the result of lifestyle choices
 * Nongenetic factors: smoking, lack of exercise, a diet rich in animal fat, and high concentrations of cholesterol in the blood.Atherosclerosis
 * examples
 * Atherosclerosis
 * Caused by the buildup of cholesterol within the arteries.
 * This cholesterol forms plaque that blocks bloodflow
 * Alterialsclerosis
 * Calcium deposits; stiffening of arterial walls (loss of elasticity)
 * Cholesterol
 * LDLs – Low density lipoproteins – “bad cholesterol,” associated with the deposition of cholesterol in arterial plaque
 * HDLs – high density lipoproteins – “good cholesterol,” reduces the deposition of cholesterol
 * Hypertension
 * high blood pressure
 * Promotes atherosclerosis and increases the risk of heart attack and stroke
 * A heart attack
 * Is the death of cardiac muscle tissue resulting from blockage of one or more coronary arteries
 * A stroke
 * Is the death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the head