General Biology/Tissues and Systems/Lymphatic System
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General Biology | Getting Started | Cells | Genetics | Classification | Evolution | Tissues & Systems | Additional Material
Lymphatic system: one-way, or open, system. Takes up interstitialfluid not taken up by venules.
Lymphatic structures:
1. lymphatic capillaries
2. lymphatic vesicles
3. lymph nodes
4. lymphatic organs (spleen and thymus)
Lymph: movement in mammals thru one-way valves, similar to bloodmovement in veins. (Some non-mammals have lymphatic hearts of unknown embryonicorigin. Frogs and salamanders have several.) Lymph rejoins cardiovascularsystem into a large vein near the heart via single large thoracic duct.
As lymph passes thru system, passes lymphocytes, second partof immune system.
Heart: pumps blood, design varies between animals. In adult mammal,four chambers form two separate circulations
1. pulmonary circulation to and from lungs and
2. systemic circulation to and from tissues of body.
Everything in the heart comes in pairs: 2 atria, 2 ventricles (leftand right).
Diagrams usually drawn as animal were on its back.
Pattern of blood flow thru heart: blood returning from majorveins (vena cava) enters right atrium, contraction there deliversblood to right ventricle thru a tricuspid valve, one of atrialventricular valves (AV valve). Contraction of right ventricle drives bloodthru semi lunar valve into pulmonary circuit and to lungs.Blood return to heart in pulmonary veins, is oxygenated. Goes toleft atrium, which contracts and delivers blood to left ventricleby way of aortic semi-lunar valve, then goes to systemic circulation.
Both atria and ventricles contract in unison, left morepowerful than right (to all system vs. just lungs).
Systole: heart contraction, diastole: heart relaxed
Timing of heart contraction: ventricles rebound to relaxedshape (diastole), and semi-lunar valves close. Both atria(singular: atrium) fill with blood coming from pulmonary and systemic circulations.Pressure rises in the atria and blood begins to move into the ventricles.The atria then contract, forcing more blood into the ventricles. Thereis a pause, then ventricles contract. This raises ventricle pressure, atrio-ventricular(AV) valves shut and semi-lunar valves open, forcing blood from theleft ventricle into the major arteries and from the right ventricle intothe aorta.
Control for this action doesn’t rely on nervous stimulation, has intrinsicrhythmicity, called myogenic. This is the case in mammal as wellas in mollusk hearts. Other animals have neurogenic hearts thatrely on nervous stimulation for heart action, originating in the cardiacganglion.
The rythmicity of mammalian heart relies on the sino-atrial (SA)node, or pacemaker. This is a phylogenic (based on evolutionaryhistory) remnant of an early vertebrate heart that had one morechamber than modern hearts.
How the heart contracts: waves of depolarization startin SA node and spread thru atria. Connectile tissue pausesthe spread of depolarization at the atrial ventricular node. Signal continuedby bundle branches to lower ventricle, begins to stimulateheart to contract. Contraction starts at bottom of heart at heart apex,then signals spread thru heart.
Medulla (in the brain) controls autonomic nervous system. (Themedulla is part of the brain, is continuous with the spinal cord, and controlsinvoluntary actions of the body). Sympathetic cardiac acceleratorconnects to spinal cord, uses norepinephrine to signal. Parasympatheticcardio-inhibitory center reaches heart thru Vagus nerve, usesacetylcholine to signal. Hyperpolarizes membrane to inhibit heartcontraction. (Autonomic nervous system: two parts working in contra tocontrol from both sides.) Dominant effect here is inhibitory. Ifwe cut Vagus nerve, heart rate promptly rises about 25 bpm.
General Biology | Getting Started | Cells | Genetics | Classification | Evolution | Tissues & Systems | Additional Material
