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Ch. 34- Animal Circulation (What is a circulatory system? (Made up of 3…

- - - - In this system, the circulatory fluid is hemolymph. The heart contractions pump the hemolymph through the circulatory vessels and into the sinuses, which allows for nutrient exchange to occur. Then, the heart relaxes and draws the hemolymph back in. Body movements can also help to squeeze sinuses and circulate hemolymph.
        
        Present in arthropods and some molluscs
        
        The advantage to this system is that lower hydrostatic pressures make them less energetically costly
    - - In this system, the circulatory fluid is blood. It is confined to vessels and is distinct from interstitial fluid. The heart(s) pumps blood into large vessels that branch out and infiltrate the organs and tissues of the organism. This allows for chemical exchange to occur between the blood and interstitial fluid, and then between the interstitial fluid and the body cells.
        
        Present in annelids, most cephalopod molluscs, and all vertebrates
        
        The advantages to this system are that a relatively high blood pressure enables effective delivery of oxygen and nutrients in large, active animals. And that it's well suited for regulating blood distribution to different organs.
- - - - The heart contains two or more chambers:
        
        Atria: chambers that receive blood entering heart
        
        Ventricle --- chambers that pump blood out of the heart
      - The 3 types of blood vessels are as follows:
        
        Arteries: carry the blood away from the heart and to the organs found throughout the body
        
        Capillaries: microscopic vessels that form networks called capillary beds, which infiltrate tissues and permit the diffusion of chemicals between the blood and interstitial fluid
        
        Veins: carry blood towards the heart
- - - - The coronary arteries supply blood to the heart muscle, and capillary beds branch out in the head, arms, abdomen, and legs to supply blood throughout the rest of the body. Within the capillaries, oxygen diffuses into the body tissues and carbon dioxide diffuses into the blood. The capillaries join together to form venules, which convey blood to the veins. The now oxygen-poor blood returns to the heart through the vena cava, which empties it back into the right atrium. The oxygen-poor blood then flows into the right ventricle and the cycle repeats itself.
        
        Step-by-step Image of Blood Flow:
- - - - Systole: the contraction phase of the cardiac cycle that pumps blood out
      - Diastole: the relaxation phase of cardiac cycle that fills the heart with blood
    - - Atrial systole and ventricular diastole: During this phase, atrial contraction forces all the remaining blood in the atria into the ventricles
      - Ventricular systole and atrial diastole: During this phase, ventricular contraction pumps the blood into large arteries through the semilunar valves
      - Atrial and ventricular diastole: During this relaxation phase, the blood returning from large veins flows back into the atria and then into the ventricles through the atrioventricular valves
      - How these steps relate to blood pressure:
        
        Blood flow slows as it goes from bigger vessels to smaller vessels. As a result, blood pressure is high when blood is pumped away from the heart and into the arteries. The pressure is low however when blood has finished traveling through the capillaries and reenters the veins (moving towards the heart).
- - - - These pacemaker cells in the sinoatrial node of the heart are autorhythmic, meaning they repeatedly contract and relax without signals from the nervous system. They set the rate and timing for all other cardiac cells, and produce electrical impulses that spready rapidly within the heart tissue.
        
        These electrical impulses spread to the walls of the atria causing them to contract in unison. During the contraction, the impulses reach the atrioventricular node delaying the impulse for about 0.1 seconds. This allows the atria to empty completely before the ventricles contract. After the delay happens, the electrical impulses spread to the heart apex, move to the ventricles, and cause them to contract in unison.
        
        To detect the electrical impulses in the heart, you can use an electrocardiogram (ECG or EKG), which is displayed as a graph of current against time showing the stages in the cardiac cycle.
- - - - Microscopic vessels that forms networks called capillary beds
        
        Structure: Endothelium (1 layer of endothelial cells) + basal lamina
    - - Carry blood towards the heart
        
        Structure: Endothelium + thin layer of smooth muscle + thin layer of connective tissue
    - - These carry blood away from the heart to the organs
        
        Structure: Endothelium + thick layer of smooth muscle + thick layer of connective tissue
        How they Work: Hormones and nervous system signals act on arteries to dilate or constrict arteries, which control blood flow to different body parts
        
        The connective tissues contain elastic fibers that allow the vessel to stretch and recoil
        
        The endothelium is a single layer of flattened epithelial cells that have a smooth surface that minimizes resistance to blood flow
    - - Blood pressure is high when it flows into arteries and travels throughout the body. The layer of connective tissues is strong and allows for the arteries to stretch as blood flows into it and recoil pushing it further into the body.
      - The veins however have to tolerate a much lower blood pressure, which is why they muscles and connective tissues are thin.
    - - Vasoconstriction is the narrowing of the blood vessels causing the force of blood against the arteries and walls to increase, therefore increasing blood pressure.
      - Vasodilation is the widening of the blood vessels causing the force of blood against the vessels to lessen, therefore decreasing blood pressure.
- - - - Blood pressure, or hydrostatic pressure, drives the fluid out of capillaries and into the tissues
      - Blood proteins, or osmotic pressure, pull fluid back into capillaries from the tissues.
        
        There ends up being a net loss of fluid out of the capillaries due to blood pressure being the greater of the two forces.
        
        This creates a gradient allowing for the diffusion of nutrients to occur. The nutrients are transported from the interstitial fluid into cells using a variety of mechanisms. Any blood plasma that is lost is regained at the venule end of the capillary bed. The lymphatic system takes care of any fluid that exits the body. This network of tiny vessels is intermingled with the capillaries of the cardiovascular system. The fluid inside is lymph, and the vessels have valves to prevent backflow, as well as rhythmic contractions to move the fluid into smaller vessels. Along the vessels are lymph nodes, which filter the lymph and house immune system cells that protect against bacteria and viruses.
        
        This exchange is needed to remain living and to conduct physiological processes, and occurs only in one direction as diffusion goes from high to low concentrations but not vice versa.