O‗zbekiston respublikasi oliy va o‗rta maxsus ta‘lim vazirligi toshkent viloyati chirchiq davlat pedagogika instituti

Bloodvessels first make their appearance in several scattered vascular areaswhich are developed simultaneously between the entoderm and the mesoderm of the yolk-sac, i. e.,outside the body of the embryo. Here a new type of cell, the angioblastor vasoformative cell,is differentiated from the mesoderm. These cells as they divide form small, dense syncytial masses which soon join with similar masses by means of fine processes to form plexuses.These plexuses increase both by division and growth of its cells and by the addition of new angioblasts which differentiate from the mesoderm. Within these solid plexuses and also within the isolated masses of angioblasts vacuoles appear through liquefaction of the central part of the syncytium into plasma. The lumen of the bloodvessels thus formed is probably intracellular. The flattened cells at the periphery form the endothelium. The nucleated red blood corpuscles develop either from small masses of the original angioblast left attached to the inner wall of the lumen or directly from the flat endothelial cells. In either case the syncytial mass thus formed projects from and is attached to the wall of the vessel. Such a mass is known as a blood island and hemoglobin gradually accumulates within it. Later the cells on the surface round up, giving the mass a mulberry-like appearance. Then the red blood cells break loose and are carried away in the plasma. Such free blood cells continue to divide. The term blood islandwas originally used for the syncytial masses of angioblasts found in the area vasculosa, but it is probably best to limit the term to the masses within the lumen from which the red blood cells arise as Sabin 88has done. Blood islands have been seen in the area vasculosa in the omphalomesenteric vein and arteries, and in the dorsal aorta.
Qonning o‘pka qon tomirlar orqali o‘ng yurakdan chap yurakka xarakati o‘pkada qon aylanishini (kichik qon aylanish doirasini) tashkil qiladi. Qolgan


kichik son aylanish doirasi
apmepua toSts / kapi/g/tyarlar


apmepisofo Vo kapi/i/jppsiap
katta kon aylstish Eoirosi 33- ⁴²
oshqa a‘zolarning qon bilan taminlanishi (va ulardan qonning qaytib kelishi) tizim qon aylanishi, deb ataladi (katta qon aylanish doirasi). Bu ikkala bo‘lim yagona qon aylanish xizimini tashkil qiladi, uning ikkita nuqtasida (chap va o‘ng yurakda) qo‘ng a kinetik energiya beriladi.
Yurak darajasi. Kamida yurak bir minutda taxminan 70 marotaba uradi.Yurak urushi tezlashishi taxicardia, sekinlashishi esa brodikardia deb ataladi,ritim buzilish sabablari bo‘shliq tugunidagi(excitation)qo;zg;alish,kuchaytirishning noto‘g‘ri rivojlanishning, A-V tugundagi o;tkazish ularni uzatishning sekinlashishi yoki meokardiadagi o‘z o‘zidan payda bo‘gan qo‘g‘alishlar quvvatini o‘z ichiga oladi. Bo‘lmacha fibrillartion minutiga ortiqcha 350 yurak urushidan bo‘lmacha .
Yurakning qon qaydash faoliyati birin-ketin bo‘shashiщi (diastola) va qisqarishta sistolaga bog‘liq. Diastola vaqtida bo‘lmalar va qorinchalar qo‘ng a to‘ladi, sistola vaqtida esa qon qorinchalardan yirik arteriyalarga (aorta va o‘pka arteriyasiga) otilib chiqadi. Bu arteriyalar yurakdan chiqadigan joyda yarim oy qopqoqlar bor, ular qonning yurakka qaytarishga yo‘l qo‘ymaydi.Bolmalar va qorinchalar o‘rtasida ham ikki (chap tomonda) va uch (o‘ng tomonda) tavaqali qopqoqlar bor. Ana shu qopqoqlar, qorinchalar sistolasida qonni qorinchalardan bo‘lmalarga qaytishiga to‘sqinlik qiladi. Qon qorinchalarga tushishdan oldin yirik venalar orqali (kavak venalar va o‘pka venasi) bo‘lmalarga quyiladi. Bo‘lmalar sistolasi tufayli qon qorinchalarga o‘tadi.
Qonni yurakka yetkazib beradigan qon tomirlar venalar, deb ataladi, qonni yurakdan chetga tarqatuvchi qon tomirlar arteriyalar deyiladi.
Muskul tolasi yurakning funksional unsuri hisoblanadi. U bir-biriga uchma- uch ulangan miokard hujayralari miotsitlardan iborat bo‘lib, umumiy sarkoplazmatik parda bilan qoplangan.
Morfologik va funksional xossalariga ko‘ra , yurakning muskul tolalari ikki turga bo‘linadi: 1) bo‘lmalar va qorinchalarning ishchi tolalari, ular yurak muskulining asosiy massasini tashkil qilib, yurakning qon xaydash faoliyatini amalga oshiradi; 2) ritm yetakchisi vazifasini va o‘tkazish tizimini tashkil qiluvchi atipik tolalar. Bu tolalar qo‘zg‘alishni ro‘yobga chiqaradi va uni miokardning ishchi tola qariga o‘tkazadi. Yurak muskuli (miokard) qo‘zg‘aluvchanlik, o‘tkazuvchanlik, qisxaruvchanlik, avtomatiya xossalariga ega. Yurak muskuli nerv to‘qimasi va skelet muskullari bilan bir qatorda qo‘zg‘aluvchan to‘qimalarga kiradi. Demak, u tinchlik potensialiga ega, bo‘sag‘adan yuqori tasirotlarga xarakat potensiali bilan javob qaytaradi, bu potensialni o‘tkaza oladi.
Miokardning skelet muskulidan farqi shuki, u funksional birlik (sinsitiy) dan iborat. Qo‘zg‘alish miokardning qaysi bir nuqtasida vujudga kelmasin, butun miokardga tarqalib, tolalarni hammasini qo‘zg‘atadi. Buning sababi shundaki, miokardning ishchi tolalari oraliq neksuslar yordamida o‘z aro bog‘langan. Neksuslarning elektr oqimiga ko‘rsatadigan qarshilig‘i juda kam. Ular orqali qo‘zg‘alish qarshilikka uchramay, tez tarqaladi. Shuning uchun ham yurak yakka tola singari «bor yoki yo‘q» qonuniga bo‘ysinadi.