If sperm are able to reach and penetrate the ovum, the ovum becomes a fertilized zygote containing a full complement of DNA. The human body is the entire structure of a human organism, and consists of a head, neck, torso, two arms and two legs. The alimentary canal is made up of the oral cavity, pharynx, esophagus, stomach, small intestines, and large intestines. The vagina is an elastic, muscular tube that connects the cervix of the uterus to the exterior of the body. These tubes are called lymph vessels or lymphatic vessels. Human Anatomy Gray's Anatomy.
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The human body is the most complicated machine in the world and the entire structure of a human organism, and consists of a head, neck, torso, two arms and two legs The human body is the most complicated machine in the world.
We see with it, hear with it, breathe with it, walk and run with it, and sense pleasure with it. Its bones, muscles, arteries, veins and internal organs are organized with marvellous design, and when we examine this design in detail we find even more amazing facts.
The human body is the entire structure of a human organism, and consists of a head, neck, torso, two arms and two legs. By the time the human reaches adulthood, the body consists of close to 10 trillion cells, the basic unit of life. This section needs expansion. You can help by adding to it. Human Anatomy Gray's Anatomy. Journal of Lipid Research. Webster's New World Medical Dictionary. Lymph capillary Lymphatic vessel. Lymph trunk Lymph Lymphangion. Nutrient artery Arteriole Metarteriole Elastic artery.
Diagram showing the formation of lymph from interstitial fluid labeled here as "Tissue fluid". Formed from interstitial fluid. Anatomical terminology [ edit on Wikidata ]. A phagocyte is a cell that attracts by chemotaxis , adheres to, engulfs, and ingests foreign bodies. Promonocytes are made in the bone marrow, after which they are released into the blood and called circulating monocytes , which eventually mature into macrophages meaning "big eaters", see below.
Some macrophages are concentrated in the lungs, liver Kupffer cells , lining of the lymph nodes and spleen, brain microglia, kidney mesoangial cells, synovial A cells, and osteoclasts. They are long-lived, depend on mitochondria for energy, and are best at attacking dead cells and pathogens capable of living within cells.
Once a macrophage phagocytizes a cell, it places some of its proteins, called epitopes, on its surface—much like a fighter plane displaying its hits. These surface markers serve as an alarm to other immune cells that then infer the form of the invader.
All cells that do this are called antigen presenting cells APCs. The non-fixed or wandering macrophages roam the blood vessels and can even leave them to go to an infection site where they destroy dead tissue and pathogens. Emigration by squeezing through the capillary walls to the tissue is called diapedesis or extravasation. The presence of histamines at the infection site attract the cells to their source.
Natural killer cells move in the blood and lymph to lyse cause to burst cancer cells and virus-infected body cells. They are large granular lymphocytes that attach to the glycoproteins on the surfaces of infected cells and kill them. Polymorphonuclear neutrophils , also called polys for short, are phagocytes that have no mitochondria and get their energy from stored glycogen. They are nondividing, short-lived half-life of 6—8 hours, 1—4 day lifespan , and have a segmented nucleus.
The neutrophils provide the major defense against pyogenic pus-forming bacteria and are the first on the scene to fight infection. They are followed by the wandering macrophages about three to four hours later. The complement system is a major triggered enzyme plasma system. It coats microbes with molecules that make them more susceptible to engulfment by phagocytes.
Vascular permeability mediators increase the permeability of the capillaries to allow more plasma and complement fluid to flow to the site of infection. They also encourage polys to adhere to the walls of capillaries margination from which they can squeeze through in a matter of minutes to arrive at a damaged area.
Once phagocytes do their job, they die and their "corpses," pockets of damaged tissue, and fluid form pus. Eosinophils are attracted to cells coated with complement C3B, where they release major basic protein MBP , cationic protein, perforins, and oxygen metabolites, all of which work together to burn holes in cells and helminths worms. Their lifespan is about 8—12 days. Neutrophils, eosinophils, and macrophages are all phagocytes.
Dendritic cells are covered with a maze of membranous processes that look like nerve cell dendrites. Most of them are highly efficient antigen presenting cells. There are four basic types: Langerhans cells, interstitial dendritic cells, interdigitating dendritic cells, and circulating dendritic cells.
Our major concern will be Langerhans cells , which are found in the epidermis and mucous membranes, especially in the anal, vaginal, and oral cavities. These cells make a point of attracting antigen and efficiently presenting it to T helper cells for their activation.
Each of the cells in the innate immune system bind to antigen using pattern-recognition receptors. These receptors are encoded in the germ line of each person. This immunity is passed from generation to generation. Over the course of human development these receptors for pathogen-associated molecular patterns have evolved via natural selection to be specific to certain characteristics of broad classes of infectious organisms.
There are several hundred of these receptors and they recognize patterns of bacterial lipopolysaccharide, peptidoglycan, bacterial DNA, dsRNA, and other substances. Clearly, they are set to target both Gram-negative and Gram-positive bacteria. Lymphocytes come in two major types: B cells and T cells. Their total mass is about the same as that of the brain or liver.
B cells are produced in the stem cells of the bone marrow; they produce antibody and oversee humoral immunity. T cells are nonantibody-producing lymphocytes which are also produced in the bone marrow but sensitized in the thymus and constitute the basis of cell-mediated immunity.
The production of these cells is diagrammed below. Parts of the immune system are changeable and can adapt to better attack the invading antigen. There are two fundamental adaptive mechanisms: Macrophages engulf antigens, process them internally, then display parts of them on their surface together with some of their own proteins.
This sensitizes the T cells to recognize these antigens. All cells are coated with various substances. CD stands for cluster of differentiation and there are more than one hundred and sixty clusters, each of which is a different chemical molecule that coats the surface. The large number of molecules on the surfaces of lymphocytes allows huge variability in the forms of the receptors. They are produced with random configurations on their surfaces.
There are some 10 18 different structurally different receptors. Essentially, an antigen may find a near-perfect fit with a very small number of lymphocytes, perhaps as few as one.