Body Fluids and Circulation: Class 11 Biology Chapter 15 Hinglish mein

Tumhara body lagbhag 30 trillion cells se bana hai, aur inmein se shayad hi koi bahar ki duniya ko chhoota hai. Liver ke andar gehrai mein baitha ek cell hawa ya paani tak khud nahi pahunch sakta. Oxygen, glucose aur amino acids use pahunchane padte hain, aur uska carbon dioxide aur urea jama hone se pehle wahan se hatana padta hai. Akela diffusion yeh kaam sirf bahut chhoti doori par kar paata hai: yeh oxygen ko kuch cells ke paar second ke ek hisse mein le jaata hai, lekin ek centimetre tay karne mein ghante laga deta hai. Isliye jo bhi animal kuch millimetre se zyada mota hai, use ek transport system chahiye.

Evolution ne do bade jawab diye hain. Ek hai aas-paas ke maahaul se hi dhulaai karwana: sponges aur Hydra jaise coelenterates bahar ka paani body ke canals aur cavities mein behte rehne dete hain, aur har cell us behti dhaara se materials ki adla-badli karta hai. Doosra tareeka, jo bade animals apnate hain, ek internal fluid hai jise har cell ke paas se dhakela jaata hai. Hamare liye woh fluid blood hai, aur uska saath deta hai ek doosra fluid, lymph. Is chapter mein hum dono fluids ko khol kar dekhenge, phir blood ko chalate rehne wale heart aur vessels, unhe adjust karne wale controls aur unhe bigaadne wale disorders ko follow karenge.

15.1 Blood

Blood ki ek boond microscope ke neeche rakho aur woh ek-jaisa laal rang gaayab ho jaata hai. Tumhe ek halke liquid mein tairte cells aur cell ke tukde dikhte hain, jaise paani mein sabudana ke daane. Biologists blood ko ek connective tissue maante hain, haalaanki thoda anokha. Iske cells aapas mein sate hue nahi hote, balki ek liquid matrix mein latke rehte hain, jise plasma kehte hain, aur in latke hue hisson ko formed elements kehte hain. Doosre connective tissues ki tarah yeh bhi mesoderm se banta hai, aur organs ke beech materials le jaakar har organ ko har doosre organ se jodta hai.

15.1.1 Plasma

Plasma (प्लाज़्मा) ek gaadha, thoda viscous liquid hai, straw jaisa halka peela, jo blood ka aadhe se thoda zyada hissa, lagbhag 55 per cent, banata hai. Iska 90–92 per cent paani hai, isiliye yeh itna kuch ghol kar le ja paata hai. Proteins aur 6–8 per cent hote hain, aur inmein teen sabse khaas hain (Table 15.1).

Bacha hua ek-do per cent ek mila-jula saamaan hai. $\mathrm{N}\mathrm{a}{\phantom{X}}^{+}$, $\mathrm{C}\mathrm{a}{\phantom{X}}^{2+}$, $\mathrm{M}\mathrm{g}{\phantom{X}}^{2+}$, $\mathrm{H}\mathrm{C}\mathrm{O}{\phantom{X}}_3{\phantom{X}}^{-}$ aur $\mathrm{C}\mathrm{l}{\phantom{X}}^{-}$ jaise mineral ions salt balance aur pH ko steady rakhte hain. Plasma body ki delivery van bhi hai: gut se absorb hue ya stores se nikle glucose, amino acids aur lipids isi mein baith kar un tissues tak jaate hain jo inhe use karte hain, isliye kisi bhi pal har ek ka thoda hissa isme maujood hota hai. Plasma clotting factors ka ek set bhi le jaata hai, jo tab tak band rehte hain jab tak koi injury unhe activate na kare. In factors ko hata do, jaise tube mein blood clot hone par hota hai, to jo saaf fluid bachta hai woh serum hai.

15.1.2 Formed Elements

Formed elements (संगठित पदार्थ) blood ka baaki lagbhag 45 per cent hissa banate hain. Ye teen tarah ke hote hain: red blood cells yaani erythrocytes, white blood cells yaani leucocytes, aur platelets, jinhe thrombocytes bhi kehte hain. Fig. 15.2 inhe ek line mein saath-saath dikhata hai.

Erythrocyte ka kaam respiratory gases ko le jaana hai, aur iska poora design isi kaam ke liye bana hai. Yeh haemoglobin (हीमोग्लोबिन) se bhara hota hai, ek laal, iron wala protein jo cells ko, aur blood ko, unka rang deta hai; ek healthy insaan ke blood mein har 100 mL mein iska 12–16 g hota hai. Jagah banane ke liye zyaadatar mammals ka RBC mature hote samay apna nucleus bahar nikaal deta hai, aur ek aisi disc ban jaata hai jo dono taraf se andar dabi ho, yaani biconcave shape. Adults mein ye cells red bone marrow mein bante hain, aur blood mein baaki har cell se zyada hote hain: ek healthy adult aadmi ke har cubic millimetre mein lagbhag 5 se 5.5 million hote hain.

Nucleus na hone ki ek keemat hai: RBC apni marammat ke liye naye proteins nahi bana sakta. Lagbhag 120 din tak patli capillaries mein se nikalte-nikalte yeh ghis jaata hai aur tod diya jaata hai, zyaadatar spleen mein, jise isiliye 'graveyard of RBCs' ka nickname mila hai. Count ko steady rakhne ke liye bone marrow ko purane cells utni hi tezi se badalne padte hain jitni tezi se woh khatam hote hain, aur Example 15.1 dikhata hai ki yeh kitni tezi hai.

White blood cells, yaani leucocytes, kaafi kam hote hain: average 6000–8000 per cubic millimetre, lagbhag har 700 red cells par ek. Har ek mein nucleus hota hai lekin haemoglobin nahi, isiliye ye rangheen dikhte hain, aur zyaadatar thode hi samay jeete hain. Microscope ke neeche stain karne par ye do groups mein bant jaate hain: granulocytes (neutrophils, eosinophils aur basophils), jinka cytoplasm saaf dikhne wale granules se bhara hota hai, aur agranulocytes (lymphocytes aur monocytes), jinmein saaf granules nahi hote. Table 15.2 paanchon ko compare karta hai.

Paanchon ko alag-alag duty wali ek defence force samjho. Lymphocytes, jo do main roop mein hote hain, B aur T lymphocytes, body ke immune responses chalate hain, jo tum Class 12 mein padhoge. Neutrophils aur monocytes safaai wali team hain: ye phagocytes hain jo andar ghuse bacteria aur doosre foreign organisms ko nigal kar khatam kar dete hain. Eosinophils infections se ladne mein madad karte hain, khaas kar parasitic worms se, aur allergic reactions mein bhi shaamil hote hain. Basophils histamine, serotonin aur heparin chhodte hain, ye chemicals inflammation chalate hain, yaani infected cut ke aas-paas laali aur sujan.

Platelets poore cells nahi balki chhote tukde hain jo bone marrow ke giant cells, megakaryocytes, se toot kar nikalte hain. Ek cubic millimetre blood mein normally inke 1.5–3.5 lakh (150 000–350 000) hote hain. Inki main duty clotting shuru karna hai: damaged vessel par ye jama hote hain aur aise chemicals chhodte hain jo clotting process ko chalu kar dete hain (Section 15.1.4). Isliye jab count gir jaata hai, jaise dengue mein ho sakta hai, to insaan ko aasaani se neel pad jaate hain aur bleeding rokna mushkil hota hai.

15.1.3 Blood Groups

Healthy blood ke do samples test tube mein bilkul ek jaise dikhte hain, phir bhi unhe milana khatarnak ho sakta hai. Farq red cells ki surface par baithe molecules mein hai. Antigen (प्रतिजन) ek aisa chemical hai jo immune response shuru kar sakta hai; antibody body ka banaya ek protein hai jo kisi khaas antigen se judta hai. Jab antibodies apne matching antigen wale red cells se milti hain, to ye kai cells ko aapas mein jod kar gucche bana deti hain (agglutination), aur gucchon mein fanse cells khatam ho jaate hain. Chaalees se zyada blood-group systems pata hain, lekin har jagah transfusion services sabse pehle do check karti hain: ABO aur Rh.

15.1.3.1 ABO grouping

ABO system do antigens, A aur B, par tika hai, jo kisi insaan ke red cells par ho bhi sakte hain aur nahi bhi. Sirf A wale cells group A dete hain, sirf B wale group B, dono wale group AB, aur dono na hon to group O. Plasma mein un dono antigens mein se us antigen ke khilaaf natural antibodies hoti hain jo insaan ke apne cells par nahi hota. Isliye group A plasma mein anti-B hota hai, group B plasma mein anti-A, group O plasma mein dono aur group AB plasma mein koi nahi (Table 15.3, Fig. 15.3).

Table ke aakhri do columns ke peeche ka rule ek hi sawaal hai: kya recipient ki antibodies ko donor ke red cells par koi matching antigen milega? Group O cells par na A hota hai na B, isliye kisi bhi recipient ki antibodies unse chipak nahi sakti, aur group O walon ko universal donors kehte hain. Group AB plasma mein koi bhi antibody nahi hoti, isliye group AB wale log kisi bhi ABO group ke cells le sakte hain aur unhe universal recipients kehte hain. 11Donor ki apni antibodies ko aam taur par ignore kiya jaata hai kyunki woh recipient ke kahin zyada blood volume mein ghul kar patli ho jaati hain. Practice mein hospitals jab bhi ho sake matching group ke red cells hi dete hain.

15.1.3.2 Rh grouping

Red cells par ek aur antigen ho sakta hai jo transfusion ke liye maayne rakhta hai. Ise Rh antigen (Rh factor) kehte hain kyunki aisa hi ek molecule rhesus monkeys ke red cells par mila tha. Agar tumhare red cells par yeh hai to tum Rh positive (Rh+) ho; agar nahi, to Rh negative (Rh−). NCERT ke hisaab se lagbhag 80 per cent insaan Rh+ hain; yeh alag-alag populations mein badalta hai, aur India mein sirf lagbhag 5–7 per cent blood donors Rh− nikalte hain.

Anti-Rh antibodies anti-A aur anti-B se alag tarah se behave karti hain: ye janm se maujood nahi hoti. Ek Rh− insaan inhe tabhi banana shuru karta hai jab Rh+ red cells body mein aate hain, jaise kisi mismatched transfusion se. Yeh pehla exposure us insaan ko sensitise kar deta hai, aur phir doosra exposure ek gambhir reaction la sakta hai. Isliye har transfusion se pehle ABO group ke saath Rh type bhi match kiya jaata hai.

Pregnancy bhi bina kisi transfusion ke yahi exposure la sakti hai, jab ek Rh− maa ke garbh mein Rh+ baby ho (father Rh+ ho). Fig. 15.4 mein yeh kahani teen sawaalon ke saath follow karo.

• Aisa pehla baby aam taur par safe kyun hota hai? Janm tak placenta dono bloodstreams ko alag rakhta hai, isliye maa ka immune system foetus ke Rh antigen se kabhi milta hi nahi aur abhi tak koi anti-Rh antibodies nahi hoti. Lekin delivery ke samay baby ka thoda blood maa ke circulation mein ris sakta hai, aur uska body anti-Rh antibodies banana shuru kar deta hai.
• Baad wala Rh+ baby khatre mein kyun hota hai? Red cells ke ulat, ye antibodies placenta ke paar ja sakti hain. Agli Rh+ pregnancy mein ye foetus mein ghus kar uske red cells khatam kar deti hain, jisse severe anaemia aur jaundice hota hai, kabhi-kabhi maut bhi. Yahi erythroblastosis foetalis (गर्भ रक्ताणु कोरकता) hai, jiska naam un immature red cells (erythroblasts) par pada hai jo baby ke blood mein bhar jaate hain jab uska marrow kami poori karne ki koshish karta hai.
• Ise kaise roka jaata hai? Pehli delivery ke turant baad (practice mein lagbhag 72 hours ke andar) maa ko anti-Rh antibodies ka injection diya jaata hai. Ye uske blood se baby ke Rh+ cells ko uske apne immune system ke react karne se pehle hi saaf kar deti hain, isliye woh kabhi sensitise nahi hoti aur agla baby surakshit rehta hai.

15.1.4 Blood ka Coagulation

Paper se kata hua cut ek-do minute tak bleed karta hai aur phir ruk jaata hai, jabki uski chhoti vessels ab bhi phati hui hain. Kisi cheez ne leaks ko band kar diya hai. Woh plug ek clot (coagulum) hai, aur use banane wala process, coagulation (रुधिर स्कंदन), chot lagne par body ko bahut zyada blood khone se bachata hai.

Microscope ke neeche clot ek baarik protein threads, fibrin, ka uljha jaal nikalta hai, jismein red cells, platelets aur doosre formed elements, jinmein se kai damaged hote hain, jaal mein machhli ki tarah fanse hote hain. Fibrin pehle se bana hua idhar-udhar nahi tairta. Yeh wahin par soluble plasma protein fibrinogen se banta hai, reactions ki ek chain ke aakhir mein jismein har activate hua substance agle ko chalu karta hai. Aisi chain ko cascade kehte hain (Fig. 15.6).

1. Damaged tissue aur wound par jama hote platelets aise factors chhodte hain jo cascade shuru karte hain. Inmein se koi ek source akele bhi ise shuru kar sakta hai.
2. Phir plasma mein inactive roop mein maujood clotting factors baari-baari ek doosre ko activate karte hain aur ek enzyme complex, thrombokinase, banate hain.
3. Thrombokinase inactive plasma protein prothrombin ko active enzyme thrombin mein badalta hai.
4. Thrombin soluble fibrinogen ko insoluble fibrin threads mein badalta hai, aur unka jaal blood cells ko fansa kar clot banata hai.

Calcium ions ($\mathrm{C}\mathrm{a}{\phantom{X}}^{2+}$) kai steps par zaroori hain, isliye jis blood mein free calcium kam ho woh clot nahi kar sakta. Ek reaction ki jagah lamba cascade kyun? Har activate hua enzyme molecule agle substance ke kai molecules ko activate karta hai, isliye wound par ek chhota trigger jaldi se itna fibrin bana deta hai ki wound seal ho jaaye, jabki baaki jagah blood liquid hi rehta hai.

15.2 Lymph (Tissue Fluid)

Capillary un soaker hoses jaisi behave karti hai jinse kitchen gardens mein paani diya jaata hai. Iski deewar cells ki sirf ek layer hai, aur andar ke blood ka pressure liquid ko iske paar bahar dhakelta hai. Jo bahar risata hai woh plasma ka filtrate hai: paani, ions, glucose aur doosre chhote molecules aasaani se nikal jaate hain, jabki plasma proteins aur blood cells bahut bade hain aur andar hi reh jaate hain. Har tissue ke cells ko bhigone wala yeh filtrate tissue fluid (interstitial fluid) hai: ismein plasma jaise hi mineral ions hote hain lekin protein bahut kam.

Koi bhi cell blood ko seedha nahi chhoota; oxygen, nutrients aur wastes andar aate ya bahar jaate hue hamesha is fluid ko paar karte hain. Agar saara filtrate wahin pada rahe to tissues sooj jaayenge, isliye ise nikaalna padta hai. Iska zyaadatar hissa wapas capillaries mein samaa jaata hai. Baaki ko band sire wali lymph capillaries utha leti hain aur vessels ke ek shaakhaon wale network, lymphatic system, se le jaati hain, jo gardan ke neeche ki taraf badi veins mein khaali hota hai. In vessels ke andar isi fluid ko lymph (लसीका) kehte hain (Fig. 15.7).

Lymph mein red cells nahi hote, isliye yeh rangheen hota hai. Iske main cells lymphocytes hain, jo vessels ke saath piroye lymph nodes mein badhte hain, isliye lymphatic system body ki immune defence ka bhi ek khaas hissa hai. Lymph ek transport route bhi hai: hormones aur nutrients ismein safar karte hain, aur digest hua fat isi raaste gut se nikalta hai. Small intestine ke har villus mein ek lymph vessel, lacteal, hota hai jo fat absorb karta hai, aur yeh fat lymph se guzarne ke baad hi blood tak pahunchta hai.

15.3 Circulatory Pathways

Animals do mein se ek tareeke se blood pump karte hain, aur farq is baat ka hai ki heart se nikalne ke baad blood ke saath kya hota hai (Fig. 15.8). Insects, prawns, spiders, snails aur mussels (arthropods aur molluscs) mein heart blood ko kuch badi vessels mein dhakelta hai jo bas khatam ho jaati hain. Blood organs ke beech khuli jagahon, sinuses, mein beh jaata hai, tissues ko seedha bhigota hai aur dheere-dheere heart tak wapas aata hai: yeh open circulatory system hai. 22Octopus aur squid jaise cephalopod molluscs iska apvaad hain: unka circulation zyaadatar closed hota hai. Earthworms aur doosre annelids, aur hum samet saare chordates, apna blood vessels ke ek bina toote loop ke andar rakhte hain, aur materials cells tak sirf patli capillary walls ke paar pahunchte hain: yeh closed circulatory system hai.

Blood ko vessels ke andar rakhne ka bada fayda hai: body use mod sakti hai. Kuch vessels ko chauda aur kuch ko patla karke yeh daud ke samay leg muscles ko, lunch ke baad gut ko ya garam dopahar mein skin ko zyada blood bhejti hai. Pressure bhi zyada rakha ja sakta hai, jisse blood tezi se chalta hai. Isiliye closed system ko dono mein zyada faydemand maana jaata hai.

Har vertebrate mein chambers wale muscular heart se chalne wala closed system hota hai. Vertebrate evolution ke dauraan jo badla woh hai chambers ki sankhya, aur uske saath yeh ki oxygen se bharpoor blood ko oxygen de chuke blood se kitni achchhi tarah alag rakha jaata hai (Fig. 15.9, Table 15.4).

• Fishes ka heart do chambers wala hota hai, ek atrium aur ek ventricle. Yeh body se sirf deoxygenated blood leta hai aur use gills tak pump karta hai; wahan blood oxygen leta hai aur seedha body mein jaata hai, phir heart mein lautta hai. Har chakkar mein blood heart se ek baar guzarta hai: single circulation.
• Amphibians aur zyaadatar reptiles mein teen chambers hote hain: do atria aur ek single ventricle. Lungs, skin ya gills se lautne wala oxygenated blood left atrium mein aata hai, jabki body se deoxygenated blood right atrium mein aata hai. Dono atria ek hi ventricle mein khaali hote hain, jahan dono dhaarayein kuch had tak mil jaati hain, isliye ventricle se jo nikalta hai woh dono ka mishran hota hai. Blood heart mein do baar lautta to hai, lekin dono circuits alag nahi hain: incomplete double circulation.
• Crocodiles, birds aur mammals mein chaar chambers hote hain: do atria aur do ventricles. Heart ka right side sirf oxygen-poor blood sambhalta hai aur left side sirf oxygen-rich blood, beech mein ek poori deewar hoti hai, isliye dono dhaarayein alag rehti hain. In animals mein do alag circuits hote hain aur isliye poora double circulation (Section 15.4).

15.3.1 Human Circulatory System

Hamara blood vascular system teen cheezon se banta hai: khud blood, use le jaane wali vessels (ek closed, shaakhaon wala network) aur use chalane wala muscular, chambers wala heart.

Mutthi bandh karo: tumhara heart lagbhag itna hi bada hai. Yeh thoracic cavity mein dono lungs ke beech, thoda left ki taraf jhuka hua, ek do-layer wale thaile, pericardium, ke andar baitha hai; layers ke beech ka pericardial fluid ise bina ragad ke dhadakne deta hai. Blood aur muscle ki tarah heart bhi mesoderm se banta hai.

Heart chaar chambers wala ek double pump hai (Fig. 15.10): upar do chhote atria (singular atrium) jo blood lete hain, aur neeche do bade ventricles jo use bahar pump karte hain. Teen deewarein, yaani septa, inhe baant-ti hain, jaisa Table 15.5 dikhata hai; har atrium aur uske neeche wale ventricle ke beech ke septum mein ek opening hoti hai jo us side ke dono chambers ko jodti hai.

Chaar valves flow ko ek-taraf banate hain. Har valve blood ke aage badhne par dhakel kar khul jaata hai aur blood ke peeche jaane ki koshish par jhatke se band ho jaata hai:

• right atrium → right ventricle: tricuspid valve, teen flaps (cusps) wala;
• left atrium → left ventricle: bicuspid ya mitral valve, do flaps wala;
• right ventricle → pulmonary artery aur left ventricle → aorta: semilunar valves, jinka naam unke aadhe-chaand jaise cusps par pada hai.

Mazboot dor, chordae tendineae, tricuspid aur bicuspid valves ke cusps ko ventricle walls se baandhe rakhti hain taaki woh palat kar atria mein na chale jaayein. Isliye blood sirf ek taraf ja sakta hai: atrium se ventricle, phir ventricle se artery, kabhi wapas nahi.

Poora heart cardiac muscle se bana hai. Ventricles ki deewarein atria ki deewaron se kahin moti hain: atria ko sirf apne theek neeche wale ventricles ko bharna hota hai, jabki ventricles ko blood heart se bahar dhakelna padta hai, aur left ventricle, jo poore body ko supply karta hai, ki deewar sabse moti hoti hai.

Is muscle ke beech se ek khaas tarah ki cardiac muscle guzarti hai, nodal tissue, jo woh electrical signals banati aur aage bhejti hai jinse heart dhadakta hai (Fig. 15.11). Iske hisse ek raasta banate hain:

1. sino-atrial node (SAN, शिरा-अलिंद पर्व), right atrium ke upar right kone mein ek patch;
2. atrio-ventricular node (AVN), right atrium ke neeche uski left side par, atrioventricular septum ke theek upar;
3. atrio-ventricular bundle (AV bundle, ya bundle of His), nodal fibres ka ek bundle jo AVN se atrioventricular septum ke raaste interventricular septum ke upar tak jaata hai, jahan yeh right aur left bundle branch mein bant jaata hai;
4. Purkinje fibres, baarik shaakhaayein jo har bundle branch se uske ventricle ki muscle mein phail jaati hain.

Heart ko dhadakne ke liye brain ke order ki zaroorat kyun nahi? Nodal tissue autoexcitable hai: iske cells bina kisi bahari stimulus ke apne aap action potentials fire karte hain. Alag hisse alag natural rates par fire karte hain, aur SAN sabse tez hai, lagbhag 70–75 per minute. Band ke sabse tez drummer ki tarah yeh taal set karta hai: har SAN impulse heart mein phail jaata hai aur dheeme hisson ke apne firing point tak pahunchne se pehle hi beat shuru kar deta hai. Isliye SAN heart ka pacemaker hai, aur normal resting heart rate, 70–75 beats per minute (average 72), bas iska firing rate hai. AVN signal ko thoda der se aage bhejta hai, jisse ventricles ke contract hone se pehle atria ko poori tarah khaali hone ka samay mil jaata hai.

15.3.2 Cardiac Cycle

Har heartbeat sikudne aur dheela hone ka ek hi sequence hai, jo minute mein lagbhag 72 baar dohraya jaata hai. Kisi chamber ke contract hone ko systole aur relax hone ko diastole kehte hain. Ek hi rule sequence ki har valve movement samjha deta hai: valve ki apni koi muscle nahi hoti, isliye woh bas tab khulta hai jab uske peeche ka pressure saamne ke pressure se zyada ho, aur tab band hota hai jab blood ulti taraf behne ki koshish kare. Is rule ko yaad rakh kar Fig. 15.12 mein ek round follow karo, us pal se shuru karke jab chaaron chambers relaxed hain.

1. Joint diastole. Har chamber relaxed hone par tricuspid aur bicuspid valves khule latakte hain aur semilunar valves band rehte hain. Venae cavae aur pulmonary veins se aane wala blood atria se hokar ventricles mein jaata hai, jo passively bharte hain.
2. Atrial systole. SAN ka ek action potential dono atria ko ek saath contract karata hai. Ye bharne wale blood ka aakhri hissa andar dhakelte hain, jisse ventricles ka bharna lagbhag 30 per cent badh jaata hai.
3. Ventricular systole. Signal AVN aur AV bundle ke raaste ventricles tak jaata hai, aur bundle of His aur uske fibres ise ventricular muscle mein phailate hain. Ventricles contract hote hain jabki atria relax hote hain. Jaise-jaise ventricular pressure badhta hai, blood atria ki taraf wapas dhakela jaata hai aur tricuspid aur bicuspid valves zor se band ho jaate hain.
4. Ejection. Pressure tab tak badhta rehta hai jab tak woh pulmonary artery aur aorta ke pressure se zyada na ho jaaye. Semilunar valves dhakel kar khul jaate hain aur blood heart se nikal jaata hai.
5. Ventricular diastole. Ventricles relax hote hain aur unka pressure arteries ke pressure se neeche gir jaata hai. Wapas fisalne laga blood semilunar valves ko band kar deta hai.
6. Refilling. Ventricular pressure tab tak girta rehta hai jab tak woh atria ke pressure se neeche na ho jaaye, jo poore samay veins se bharte rahe hain. Ab atrial pressure jeet jaata hai, tricuspid aur bicuspid valves khul jaate hain, blood phir ventricles mein behta hai, aur heart SAN ke agle fire tak wapas joint diastole mein aa jaata hai.

In events ka ek poora round, ek atrial systole se agle tak, ek cardiac cycle (हृद् चक्र) banata hai: ismein atria aur ventricles dono ek-ek baar contract (systole) aur relax (diastole) hote hain. Ek heartbeat ek cycle hai, isliye iska duration heart rate se nikalta hai:

72 beats per minute par $60\mathrm{/}72\approx 0.83$, isliye har cycle lagbhag 0.8 s chalti hai. 3372 beats per minute par atria lagbhag 0.1 s aur ventricles lagbhag 0.3 s ke liye systole mein rehte hain; lagbhag 0.4 s tak chaaron chambers ek saath aaram karte hain. Ye approximate timings extra detail hain, NCERT text ka hissa nahi. Har cycle mein ek ventricle lagbhag 70 mL blood bahar pump karta hai; yeh uska stroke volume hai. Har ventricle ek minute mein jitna blood pump karta hai woh cardiac output (हृद् निकास) hai.

Ek resting adult ke liye 70 mL × 72 per minute ≈ 5000 mL, yaani har ventricle se minute mein lagbhag 5 L blood. Body demand ke hisaab se dono factors adjust karta hai. Exercise ke dauraan nerves aur hormones heart rate badhaate hain aur har contraction ko zyada zordaar banate hain, isliye cardiac output resting value ka kai guna ho sakta hai. Regular training heart ko bada aur mazboot banati hai, isliye athlete ka stroke volume bada hota hai, resting heart rate aksar kam hota hai, aur maximum cardiac output bina training wale insaan se kahin zyada hota hai (Example 15.2).

Heartbeat ki jaani-pehchaani 'lub–dub' muscle ke sikudne ki awaaz nahi hai; yeh valves ke jhatke se band hone ki awaaz hai. Pehli, lambi aur bhaari lub tab banti hai jab ventricular systole shuru hote hi tricuspid aur bicuspid valves band hote hain. Doosri, chhoti aur tez dub tab banti hai jab ventricles ke relax hone par semilunar valves band hote hain. Jo valve theek se band nahi hota woh blood ko ek extra 'whoosh' jaisi awaaz ke saath wapas risne deta hai, jise murmur kehte hain; isiliye doctors heart problems pakadne ke liye stethoscope se ye awaazein sunte hain.

15.3.3 Electrocardiogram (ECG)

Section 15.3.2 mein tumne jo bhi contraction follow kiya, woh ek electrical signal se shuru hota hai. Us electricity ka ek bahut chhota hissa body mein phail kar skin tak pahunchta hai, jahan electrodes use pakad sakte hain. Ise record karne wali machine electrocardiograph hai, aur uska record ek electrocardiogram yaani ECG (विद्युत हृद्लेख) hai: har cardiac cycle mein heart ki electrical activity ka ek graph.

Standard ECG ke liye teen electrodes kaafi hain: ek-ek dono kalaaiyon par aur ek left takhne par, aur jab tak ye lage rehte hain machine record karti rehti hai. Jo cardiologist zyada detail chahta hai woh chhaati par extra electrodes ki ek row lagata hai; yeh chapter teen-lead wale version tak hi rehta hai. Trace ke peaks aur dips ko P se T tak ke letters se naam diya gaya hai (Fig. 15.14):

• P wave: depolarisation (electrical excitation) ki ek wave dono atria par phailti hai, aur uske baad unka contraction hota hai.
• QRS complex: ventricles depolarise hote hain. Ye Q ke ek pal baad contract hona shuru karte hain, isliye QRS complex ventricular systole ki shuruaat ka sanket hai.
• T wave: ventricles repolarise hote hain, yaani excitation se ubhar kar apni resting state mein laut-te hain. T wave khatam hone par systole khatam ho jaata hai.

Har QRS complex ek ventricular beat hai, isliye kisi pata samay mein QRS complexes ginne se heart rate milta hai, aur do pados ke R peaks ke beech ka samay ek cycle ki length hai (Example 15.3). 44Atria bhi repolarise hote hain, lekin unka chhota signal kahin bade QRS complex ke dauraan aata hai aur usmein chhup jaata hai. Doctors ECG waise hi padhte hain jaise tum kisi jaane-pehchaane word mein typo pakadte ho: same electrode positions se record kiye healthy hearts ki traces ka shape bahut milta-julta hota hai, isliye jo wave bahut lambi, bahut chaudi, gaayab ya galat jagah ho woh kisi sambhavit problem ka sanket ban kar ubhar aati hai, jaise damaged heart muscle ya conducting pathway mein koi kharaabi.

15.4 Double Circulation

Arteries blood ko heart se door le jaati hain aur veins use wapas laati hain. Kisi ko bhi aar-paar kaato to teen parton wali deewar dikhti hai (Fig. 15.15):

• tunica intima: andar ki lining, flat (squamous) endothelial cells ki ek single sheet;
• tunica media: beech ki parat, smooth muscle aur elastic fibres se bani;
• tunica externa: bahar ki parat, collagen fibres se bharpoor fibrous connective tissue.

Dono ko compare karo to beech ki parat hi farq banati hai: yeh vein mein artery se kahin patli hoti hai. Yeh unke kaam se mel khata hai. Artery har ventricular dhakke ka poora zor jhelti hai aur use khinch kar wapas apni jagah aana padta hai, jabki vein mein blood kam pressure par lautta hai. Capillaries, jo sabse chhoti arteries ko sabse chhoti veins se jodti hain, ki deewarein sirf endothelium ki hoti hain, isiliye tissues ke saath exchange wahin hota hai.

Ab ek single red cell ko ek poore safar par follow karo (Fig. 15.16). Yeh oxygen ki kami ke saath right ventricle se nikalta hai aur pulmonary artery se hokar lungs tak jaata hai. Lung capillary mein yeh ek second se bhi kam mein carbon dioxide utaarta hai aur oxygen leta hai, phir pulmonary veins se left atrium tak lautta hai. Yeh pehla chakkar, right ventricle se left atrium tak, pulmonary circulation hai.

Phir left ventricle ise aorta mein dhakel deta hai. Aorta arteries mein bant-ti hai, arteries arterioles mein aur arterioles capillaries mein, jahan hamara red cell aakhirkaar ek tissue tak pahunchta hai: oxygen, nutrients aur doosri supplies bahar jaati hain, carbon dioxide aur wastes andar aate hain. Venules, phir veins, phir do venae cavae mein se ek dwara ikattha hokar yeh right atrium se phir heart mein ghusta hai. Yeh doosra chakkar, left ventricle se right atrium tak, systemic circulation hai. Do chakkar matlab har safar mein heart se do baar guzarna, isliye is vyavastha ko double circulation (दोहरा परिसंचरण) kehte hain.

Dono loops ko alag rakhne ke do fayde hain. Tissues ko hamesha poora oxygenated blood milta hai, jo mammals ki active muscles aur garam body ke liye zaroori hai. Aur har loop apne pressure par chal sakta hai: left ventricle blood ko poore body mein high pressure par dhakelta hai, jabki right ventricle use naazuk lungs mein kahin kam pressure par bhejta hai.

Do khaas routes jaanne laayak hain. Stomach aur intestine se nikalne wala blood seedha heart mein nahi lautta. Hepatic portal vein use pehle liver le jaati hai, taaki absorb hue nutrients aur nuksaandeh substances blood ke systemic circulation mein milne se pehle liver se guzar jaayein; is link ko hepatic portal system kehte hain. (Portal vein ek organ ki capillaries se shuru hokar doosre organ ki capillaries mein khatam hoti hai.) Heart apne chambers mein tezi se behte blood se lagbhag kuch nahi leta: uski muscle ko vessels ka apna coronary system khilaata hai, jismein coronary arteries aorta ke base se nikalti hain aur coronary veins wapas right atrium mein khaali hoti hain.

15.5 Cardiac Activity ka Regulation

Body se nikala gaya frog ka heart sahi salt solution wali dish mein kuch der tak dhadakta rehta hai, jabki uski har nerve kati hoti hai. Transplant kiya gaya human heart recipient ki nerves se dobara nahi joda jaata, phir bhi saalon tak dhadakta hai. Isliye beat heart ke andar se, uske nodal tissue se, shuru honi chahiye. Heart apni normal activity khud regulate karta hai, isliye use myogenic (muscle se shuru hone wali beat) kehte hain.

Brain phir bhi rhythm ko tez ya dheema kar sakta hai. Brain ke sabse neeche wale hisse, medulla oblongata, mein ek control centre autonomic nervous system (ANS) ki do branches ke zariye instructions bhejta hai, aur hormones ek teesra input jodte hain (Fig. 15.17, Table 15.6).

15.6 Circulatory System ke Disorders

Blood pressure arteries ki deewaron par blood ka dhakka hai, jise millimetres of mercury (mm Hg) mein naapa jaata hai. 120/80 jaisi reading, jise '120 over 80' bolte hain, ke do hisse hote hain. Pehla, systolic pressure, woh peak hai jo ventricles ke pump karte samay aata hai; doosra, diastolic pressure, sabse kam value hai, jab ventricles aaram karte hain. 120/80 ki reading normal maani jaati hai.

High blood pressure (hypertension) ka matlab hai pressure ka normal se upar bane rehna: agar kai alag mauqon par li gayi readings 140/90 ya usse upar rehti hain, to us insaan ko hypertension hai. Yeh aksar saalon tak koi symptoms nahi deta, phir bhi heart se zarurat se zyada kaam karwata hai aur arteries ko nuksaan pahunchata hai, jisse heart disease hoti hai, aur samay ke saath yeh brain (strokes) aur kidneys ko bhi nuksaan pahuncha sakta hai.

Coronary artery disease (CAD) mein problem khud coronary arteries mein hoti hai. Kai saalon mein fat aur cholesterol ke jamaav, calcium aur fibrous tissue ke saath, unki deewaron mein plaque ke roop mein jama ho jaate hain. Yeh process, atherosclerosis (ek naam jo NCERT CAD ke liye bhi use karta hai), arteries ko sakht bana deta hai aur unka lumen patla kar deta hai, isliye heart muscle tak kam blood pahunch paata hai (Fig. 15.18).

Patli hui arteries baithe rehne par shayad kaafi blood de dein, lekin jaldi-jaldi seedhiyan chadhte samay nahi. Tab heart muscle mein oxygen ki kami ho jaati hai aur woh achaanak, tez chest pain se iska sanket deti hai, jo aksar left arm ya jaw tak phailta hai: yeh angina (angina pectoris) hai. Koi bhi condition jo heart muscle tak blood flow ghataaye, ise paida kar sakti hai. Angina kisi bhi umar mein aur aadmi-aurat dono mein ho sakta hai, lekin middle age ke baad yeh zyada common ho jaata hai.

Log aksar 'heart failure', 'heart attack' aur 'cardiac arrest' ko aise use karte hain jaise inka matlab ek hi ho; aisa nahi hai (neeche ka comparison). Heart failure mein heart dhadakta rehta hai lekin itna kamzor pump karta hai ki body ki zaroorat poori nahi hoti, isliye blood uske peeche veins mein ruk jaata hai. Lungs mein fluid jama hone (congestion) se insaan ki saans phoolti hai, isiliye iska poora naam congestive heart failure hai. Heart attack heart muscle ke ek hisse ka achaanak damage hai jab uski blood supply kat jaati hai, aam taur par kisi patli coronary artery mein clot se. Cardiac arrest mein heart poori tarah se theek se dhadakna band kar deta hai.