6.2 Transport system

6.2.1- heart: chambers, blood vessels, valves, rout of blood

   
   
   
   

 

  
     
     
 

6.2.2 Coronary arteries

 
Like all organs, your heart is made of tissue and requires a supply of oxygen and nutrients. Although its chambers are full of blood, the heart receives no nourishment from this blood. The heart receives its own supply of blood from a network of arteries, called the coronary arteries.

Two major coronary arteries branch off from the aorta near the point where the aorta and the left ventricle meet:

  • the right coronary artery (RCA) which supplies the right atrium and right ventricle. It branches into the posterior descending artery which supplies the bottom portion of the left ventricle and back of the septum.
  • the left main coronary artery, which branches into:
    • the circumflex artery, which supplies blood to the left atrium, side and back of the left ventricle
    • the left anterior descending artery (LAD), which supplies the front and bottom of the left ventricle and the front of the septum

 
     

6.2.3

Systole

Diastole

 

6.2.4 Heart beat

  File:Reizleitungssystem 1.png

 
 

The sinoatrial node (abbreviated SA node or SAN, also called the sinus node) is the impulse generating (pacemaker) tissue located in the right atrium of the heart, and thus the generator of sinus rhythm. It is a group of cells positioned on the wall of the right atrium, near the entrance of the superior vena cava. These cells are modified cardiac myocytes. Though they possess some contractile filaments, they do not contract.

Although all of the heart's cells possess the ability to generate the electrical impulses (or action potentials) that trigger cardiac contraction, the sinoatrial node is what normally initiates it, simply because it generates impulses slightly faster than the other areas with pacemaker potential. Because cardiac myocytes, like all muscle cells, have refractory periods following contraction during which additional contractions cannot be triggered, their pacemaker potential is overridden by the sinoatrial node.

In the absence of extrinsic neural and hormonal control, cells in the SA node, situated in the upper right corner of the heart, will naturally discharge (create action potentials) at about 70-80 beats/minute.[2] Because the sinoatrial node is responsible for the rest of the heart's electrical activity, it is sometimes called the primary pacemaker.

If the SA node does not function, or the impulse generated in the SA node is blocked before it travels down the electrical conduction system, a group of cells further down the heart will become the heart's pacemaker. These cells form the atrioventricular node (AV node), which is an area between the atria and ventricles, within the atrial septum.

The atrioventricular node (abbreviated AV node) is a part of electrical control system of the heart that co-ordinates heart rate. It electrically connects atrial and ventricular chambers. [1] The AV node is an area of specialized tissue between the atria and the ventricles of the heart, specifically in the posteroinferior region of the interatrial septum near the opening of the coronary sinus, which conducts the normal electrical impulse from the atria to the ventricles. The AV node is quite compact (~1 x 3 x 5 mm).[2] It is located at the center of Koch's Triangle--a triangle enclosed by the septal leaflet of the tricuspid valve, the coronary sinus, and the membraneous part of the interatrial septum.[3]

 
     
  File:Cardiac Cycle Left Ventricle.PNG  
  Cardiac cycle is the term referring to all or any of the events related to the flow or pressure of blood that occurs from the beginning of one heartbeat to the beginning of the next.[1] The frequency of the cardiac cycle is the heart rate. Every single 'beat' of the heart involves three major stages: atrial systole, ventricular systole and complete cardiac diastole. The term diastole is synonymous with relaxation of a muscle. Throughout the cardiac cycle, the blood pressure increases and decreases. The cardiac cycle is coordinated by a series of electrical impulses that are produced by specialized heart cells found within the sino-atrial node and the atrioventricular node. The cardiac muscle is composed of myocytes which initiate their own contraction without help of external nerves (with the exception of modifying the heart rate due to metabolic demand).

6.2.5 Arteries, capillaries and veins

   
   
   
 
     

6.2.6 Blood composition

 

In vertebrates, it is composed of blood cells suspended in a liquid called blood plasma. Plasma, which comprises 55% of blood fluid, is mostly water (90% by volume [1] ), and contains dissolved proteins, glucose, mineral ions, hormones, carbon dioxide (plasma being the main medium for excretory product transportation), platelets and blood cells themselves. The blood cells present in blood are mainly red blood cells (also called RBCs or erythrocytes) and white blood cells, including leukocytes and platelets (also called thrombocytes).

The most abundant cells in vertebrate blood are red blood cells. These contain hemoglobin, an iron-containing protein, which facilitates transportation of oxygen by reversibly binding to this respiratory gas and greatly increasing its solubility in blood. In contrast, carbon dioxide is almost entirely transported extracellularly dissolved in plasma as bicarbonate ion

 
 
Red blood cells are the most common type of blood cell and the vertebrate body's principal means of delivering oxygen to the body tissues via the blood. The cells are filled with hemoglobin, a biomolecule that can bind to oxygen. They take up oxygen in the lungs or gills and release it while squeezing through the body's capillaries. The blood's red color is due to the color of hemoglobin. In humans, red blood cells develop in the bone marrow, take the form of flexible biconcave disks, lack a cell nucleus, subcellular organelles and the ability to synthesize protein, and live for about 120 days.[1]

Red blood cells are also known as RBCs, red blood corpuscles (an archaic term), haematids or erythrocytes (from Greek erythros for "red" and kytos for "hollow", with cyte translated as "cell" in modern usage). The capitalized term Red Blood Cells is the proper name in the US for erythrocytes in storage solution used in transfusion medicine.[2]

 
 
Type Microscopic Appearance Diagram Approx. %
in adults[6]
See also:
Blood values		 Diameter (μm)[6] Main targets[3] Nucleus[3] Granules[3] Lifetime[6]
Neutrophil 54-62%[5] 10-12 multilobed fine, faintly pink 6 hours-few days
(days in spleen and other tissue)
  Neutrophils defend against bacterial or fungal infection and other very small inflammatory processes that are usually first responders to microbial infection; their activity and death in large numbers forms pus. They are commonly referred to as polymorphonuclear (PMN) leukocytes, although technically PMN refers to all granulocytes. They have a multilobed nucleus which may appear like multiple nuclei, hence the name polymorphonuclear leukocyte. The cytoplasm may look transparent because of fine granules that are faintly pink. Neutrophils are very active in phagocytosing bacteria and are present in large amount in the pus of wounds. These cells are not able to renew their lysosomes used in digesting microbes and die after having phagocytosed a few pathogens
Eosinophil 1-6% 10-12 bi-lobed full of pink-orange (when stained) 8-12 days (circulate for 4-5 hours)
  Eosinophils primarily deal with parasitic infections and an increase in them may indicate such. Eosinophils are also the predominant inflammatory cells in allergic reactions. The most important causes of eosinophilia include allergies such as asthma, hay fever, and hives; and also parasitic infections
Basophil <1% 12-15 bi- or tri-lobed large blue  ?
  Basophils are chiefly responsible for allergic and antigen response by releasing the chemical histamine causing inflammation.
Lymphocyte 25-33% 7-8

-B cells: various pathogens

-T cells:

  1. CD4+ (helper): extracellular bacteria broken down into peptides presented by MHC class 2 molecule.

  2. CD8+ cytotoxic T cells: virus-infected and tumor cells.

  3. γδ T cells:

-Natural killer cells: virus-infected and tumor cells.

deeply staining, eccentric NK-cells and Cytotoxic (CD8+) T-cells [7] weeks to years
 
Lymphocytes are much more common in the lymphatic system. Lymphocytes are distinguished by having a deeply staining nucleus which may be eccentric in location, and a relatively small amount of cytoplasm. The blood has three types of lymphocytes:
  • B cells: B cells make antibodies that bind to pathogens to enable their destruction. (B cells not only make antibodies that bind to pathogens, but after an attack, some B cells will retain the ability to produce an antibody to serve as a 'memory' system.)
  • T cells:
    • CD4+ (helper) T cells co-ordinate the immune response and are important in the defense against intracellular bacteria. In acute HIV infection, these T cells are the main index to identify the individual's immune system activity. Research has shown [10] that CD8+ cells are also another index to identify human's immune activity.
    • CD8+ cytotoxic T cells are able to kill virus-infected and tumor cells.
    • γδ T cells possess an alternative T cell receptor as opposed to CD4+ and CD8+ αβ T cells and share characteristics of helper T cells, cytotoxic T cells and natural killer cells.
  • Natural killer cells: Natural killer cells are able to kill cells of the body which are displaying a signal to kill them, as they have been infected by a virus or have become cancerous
Monocyte   2-8% 14-17 Monocytes migrate from the bloodstream to other tissues and differentiate into tissue resident macrophages or dendritic cells. kidney shaped none hours-days
Macrophage   21 (human)[8] 13 (rat)[9] Phagocytosis (engulfment and digestion) of cellular debris and pathogens, and stimulation of lymphocytes and other immune cells that respond to the pathogen.   activated=days immature=months-years
Dendritic cells     Main function is as an antigen-presenting cell (APC) that activates T lymphocytes.   similar to macrophages
  White blood cells (WBCs), or leukocytes (also spelled "leucocytes"), are cells of the immune system defending the body against both infectious disease and foreign materials. Five[1] different and diverse types of leukocytes exist, but they are all produced and derived from a multipotent cell in the bone marrow known as a hematopoietic stem cell. Leukocytes are found throughout the body, including the blood and lymphatic system.[2]

The number of leukocytes in the blood is often an indicator of disease. There are normally between 4×109 and 11×109 white blood cells in a litre of blood, making up approximately 1% of blood in a healthy adult.[3] In conditions such as leukemia, the number of leukocytes is higher than normal, and in leukopenia, this number is much lower. The physical properties of leukocytes, such as volume, conductivity, and granularity, may change due to activation, the presence of immature cells, or the presence of malignant leukocytes in leukemia.

 
  Platelets, or thrombocytes, are small, irregularly shaped anuclear cells, 2-4µm in diameter, which are derived from fragmentation of precursor megakaryocytes. The average life span of a platelet is between 8 and 12 days. Platelets play a fundamental role in hemostasis and are a natural source of growth factors[1]. They circulate in the blood of mammals and are involved in hemostasis leading to the formation of blood clots. Like red blood cells, platelets have no nucleus
     
 

6.2.7 Solutes in blood

     
  Antibodies (also known as immunoglobulins[1], abbreviated Ig) are gamma globulin proteins that are found in blood or other bodily fluids of vertebrates, and are used by the immune system to identify and neutralize foreign objects, such as bacteria and viruses. They are typically made of basic structural units—each with two large heavy chains and two small light chains—to form, for example, monomers with one unit, dimers with two units or pentamers with five units. Antibodies are produced by a kind of white blood cell called a plasma cell. There are several different types of antibody heavy chains, and several different kinds of antibodies, which are grouped into different isotypes based on which heavy chain they possess. Five different antibody isotypes are known in mammals, which perform different roles, and help direct the appropriate immune response for each different type of foreign object they encounter.[2
 
 

Three kinds of chemical signaling can be distinguished;

  • autocrine - the cell signals itself through a chemical that it synthesizes and then responds to. Autocrine signaling can occur

    • solely within the cytoplasm of the cell or

    • by a secreted chemical interacting with receptors on the surface of the same cell

  • paracrine - chemical signals that diffuse into the area and interact with receptors on nearby cells. Examples are:

  • endocrine - the chemicals are secreted into the blood and carried by blood and tissue fluids to the cells they act upon.

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/H/Hormones.html

 
Hormones (from Greek ὁρμή - "impetus") are chemicals released by cells that affect cells in other parts of the body. Only a small amount of hormone is required to alter cell metabolism. It is essentially a chemical messenger that transports a signal from one cell to another. All multicellular organisms produce hormones; plant hormones are also called phytohormones. Hormones in animals are often transported in the blood. Cells respond to a hormone when they express a specific receptor for that hormone. The hormone binds to the receptor protein, resulting in the activation of a signal transduction mechanism that ultimately leads to cell type-specific responses.

Endocrine hormone molecules are secreted (released) directly into the bloodstream, while exocrine hormones (or ectohormones) are secreted directly into a duct, and from the duct they either flow into the bloodstream or they flow from cell to cell by diffusion in a process known as paracrine signalling

 
 

Chemical classes of hormones

Vertebrate hormones fall into three chemical classes: