20.4: Udhibiti wa Homeostatic wa Mfumo wa Vascular

Malengo ya kujifunza

• Jadili taratibu zinazohusika katika udhibiti wa neural wa homeostasis ya mishipa
• Eleza mchango wa homoni mbalimbali kwa udhibiti wa figo wa shinikizo la damu
• Tambua madhara ya zoezi kwenye homeostasis ya mishipa
• Jadili jinsi shinikizo la damu, damu, na mshtuko wa mzunguko huathiri afya ya mishipa

Ili kudumisha homeostasis katika mfumo wa moyo na mishipa na kutoa damu ya kutosha kwa tishu, mtiririko wa damu lazima uelekezwe daima kwa tishu kama zinavyofanya kazi zaidi. Kwa maana halisi, mfumo wa moyo na mishipa hushiriki katika ugawaji wa rasilimali, kwa sababu hakuna mtiririko wa kutosha wa damu ili kusambaza damu sawa na tishu zote wakati huo huo. Kwa mfano, wakati mtu anapofanya kazi, damu zaidi itaelekezwa kwenye misuli ya mifupa, moyo, na mapafu. Kufuatia chakula, damu zaidi inaelekezwa kwenye mfumo wa utumbo. Ubongo tu hupokea utoaji wa damu zaidi au chini ya mara kwa mara ikiwa unafanya kazi, kupumzika, kufikiri, au kushiriki katika shughuli nyingine yoyote.

Jedwali\(\PageIndex{1}\) hutoa usambazaji wa damu ya utaratibu wakati wa kupumzika na wakati wa zoezi. Ingawa data nyingi zinaonekana mantiki, maadili ya usambazaji wa damu kwa integument yanaweza kuonekana kushangaza. Wakati wa zoezi, mwili husambaza damu zaidi kwenye uso wa mwili ambapo inaweza kuondokana na joto la ziada linalozalishwa na shughuli zilizoongezeka katika mazingira.

Jedwali\(\PageIndex{1}\): Mzunguko wa damu wa Mfumo Wakati wa Kupumzika, Zoezi la Kali, na Zoezi la Maximal katika Mtu M

Organ	Kupumzika (ml/min)	Zoezi kali (ml/min)	Zoezi la juu (ml/min)
Misuli ya mifupa	1200	4500	12,500
Moyo	250	350	750
Ubongo	750	750	750
Integument	500	1500	1900
Figo	1100	900	600
Utumbo	1400	1100	600
Wengine   (yaani, ini, wengu)	600	400	400
Jumla	5800	9500	17,500

Njia tatu za homeostatic zinahakikisha mtiririko wa kutosha wa damu, shinikizo la damu, usambazaji, na hatimaye perfusion: neural, endocrine, na taratibu za udhibiti. Wao ni muhtasari katika Kielelezo\(\PageIndex{1}\).

Kielelezo\(\PageIndex{1}\): Muhtasari wa Mambo ya Kudumisha Homeostasis Mtiririko wa kutosha wa damu, shinikizo la damu, usambazaji, na perfusion huhusisha autoregulatory, neural, na endocrine taratibu.

Udhibiti wa Neural

Mfumo wa neva una jukumu muhimu katika udhibiti wa homeostasis ya mishipa. Maeneo ya msingi ya udhibiti ni pamoja na vituo vya moyo na mishipa katika ubongo vinavyodhibiti kazi zote za moyo na mishipa. Aidha, majibu ya neural ya jumla kutoka kwa mfumo wa limbic na mfumo wa neva wa uhuru ni sababu.

Vituo vya Mishipa ya Mishipa katika ubongo

Udhibiti wa neva wa shinikizo la damu na mtiririko hutegemea vituo vya moyo na mishipa vilivyo katika medulla oblongata. Kundi hili la neuroni huitikia mabadiliko katika shinikizo la damu pamoja na viwango vya damu vya oksijeni, dioksidi kaboni, na ioni za hidrojeni. Kituo cha moyo na mishipa kina vipengele vitatu vilivyounganishwa:

• Vituo vya cardioaccelerator huchochea kazi ya moyo kwa kusimamia kiwango cha moyo na kiasi cha kiharusi kupitia kuchochea huruma kutoka kwa ujasiri wa kasi ya moyo.
• Vituo vya cardioinhibitor hupunguza kazi ya moyo kwa kupungua kwa kiwango cha moyo na kiasi cha kiharusi kupitia kuchochea parasympathetic kutoka kwa ujasiri wa vagus.
• Vituo vya vasomotor vinasimamia tone la chombo au contraction ya misuli laini katika vyombo vya habari vya tunica. Mabadiliko ya kipenyo huathiri upinzani wa pembeni, shinikizo, na mtiririko, unaoathiri pato la moyo. Wengi wa neuroni hizi hufanya kupitia kutolewa kwa neurotransmita norepinephrine kutoka neurons huruma.

Ingawa kila kituo kinafanya kazi kwa kujitegemea, sio tofauti ya anatomically.

Pia kuna idadi ndogo ya neurons ambayo hudhibiti vasodilation katika vyombo vya ubongo na misuli ya mifupa kwa kufurahi nyuzi za misuli laini katika nguo za chombo. Wengi wa hizi ni neurons ya cholinergic, yaani, hutoa asetilikolini, ambayo kwa upande huchochea seli za endothelial za vyombo ili kutolewa oksidi ya nitriki (NO), ambayo husababisha vasodilation. Wengine hutoa norepinefrini inayofunga kwa receptors β ₂. Neurons chache hutoa NO moja kwa moja kama neurotransmitter.

Kumbuka kwamba kuchochea kali ya misuli ya mifupa inao tone ya misuli. Sifa kama hiyo hutokea kwa sauti ya mishipa katika vyombo. Kama ilivyoelezwa hapo awali, arterioles kawaida ni sehemu ndogo: Kwa kuchochea maximal, radius yao inaweza kupunguzwa hadi nusu ya hali ya kupumzika. Kupanua kamili ya arterioles nyingi inahitaji kwamba kusisimua hii ya huruma kufutwa. Wakati ni, arteriole inaweza kupanua kwa kiasi cha asilimia 150. Ongezeko kubwa kama hilo linaweza kuathiri sana upinzani, shinikizo, na mtiririko.

Baroreceptor Reflexes

Baroreceptors ni vipokezi maalumu vya kunyoosha vilivyo ndani ya maeneo nyembamba ya mishipa ya damu na vyumba vya moyo vinavyoitikia kiwango cha kunyoosha kinachosababishwa na kuwepo kwa damu. Wanatuma msukumo kwenye kituo cha moyo na mishipa ili kudhibiti shinikizo la damu. Baroreceptors ya mishipa hupatikana hasa katika sinuses (cavities ndogo) ndani ya aota na mishipa ya carotid: sinuses aortic hupatikana katika kuta za aota inayopanda tu kuliko valve ya aortic, ambapo sinuses carotid ziko chini ya mishipa ya ndani ya carotid . Pia kuna baroreceptors ya chini ya shinikizo iko katika kuta za pango la venae na atrium sahihi.

Wakati shinikizo la damu linapoongezeka, baroreceptors hutambulishwa kwa ukali zaidi na kuanzisha uwezekano wa hatua kwa kiwango cha juu. Kwa shinikizo la chini la damu, kiwango cha kunyoosha ni cha chini na kiwango cha kurusha ni polepole. Wakati kituo cha moyo na mishipa katika medulla oblongata kinapokea pembejeo hii, husababisha reflex ambayo inao homeostasis (Kielelezo\(\PageIndex{2}\)):

• Wakati shinikizo la damu linapoongezeka sana, baroreceptors moto kwa kiwango cha juu na husababisha kuchochea parasympathetic ya moyo. Matokeo yake, pato la moyo huanguka. Kusisimua kwa huruma ya arterioles ya pembeni pia itapungua, na kusababisha vasodilation. Pamoja, shughuli hizi husababisha shinikizo la damu kuanguka.
• Wakati shinikizo la damu linapungua chini sana, kiwango cha kurusha baroreceptor hupungua. Hii itasababisha ongezeko la kuchochea huruma kwa moyo, na kusababisha pato la moyo kuongezeka. Pia itasababisha kuchochea huruma ya vyombo vya pembeni, na kusababisha vasoconstriction. Pamoja, shughuli hizi husababisha shinikizo la damu kuongezeka.

Kielelezo\(\PageIndex{2}\): Reflexes ya Baroreceptor kwa kudumisha Homeostasis ya Vas Kuongezeka kwa shinikizo la damu husababisha kuongezeka kwa viwango vya kurusha baroreceptor, ilhali kupungua kwa shinikizo la damu husababisha viwango vya polepole vya moto, vyote viwili vinavyoanzisha utaratibu wa homeostatic wa kurejesha shinikizo la damu.

Baroreceptors katika pango la venae na atrium ya kulia hufuatilia shinikizo la damu kama damu inarudi moyoni kutokana na mzunguko wa utaratibu. Kwa kawaida, damu inapita ndani ya aorta ni sawa na mtiririko wa damu tena kwenye atrium sahihi. Ikiwa damu inarudi kwenye atrium sahihi kwa kasi zaidi kuliko kutolewa kutoka ventricle ya kushoto, receptors ya atrial itachochea vituo vya moyo na mishipa ili kuongeza kurusha ushirikano na kuongeza pato la moyo hadi kufikia homeostasis. Kinyume chake pia ni kweli. Utaratibu huu unajulikana kama reflex ya atrial.

Reflexes ya Chemoreceptor

Mbali na baroreceptors ni chemoreceptors kwamba kufuatilia viwango vya oksijeni, dioksidi kaboni, na ions hidrojeni (pH), na hivyo kuchangia homeostasis mishipa. Chemoreceptors ufuatiliaji wa damu iko karibu na baroreceptors katika dhambi za aortic na carotid. Wao huashiria kituo cha moyo na mishipa pamoja na vituo vya kupumua katika medulla oblongata.

Kwa kuwa tishu hutumia oksijeni na kuzalisha dioksidi kaboni na asidi kama bidhaa za taka, wakati mwili unapofanya kazi zaidi, viwango vya oksijeni huanguka na viwango vya dioksidi kaboni hupanda huku seli zinapitia kupumua kwa seli ili kukidhi mahitaji ya nishati ya shughuli. Hii inasababisha ioni nyingi za hidrojeni kuzalishwa, na kusababisha pH ya damu kushuka. Wakati mwili unapumzika, viwango vya oksijeni ni vya juu, viwango vya dioksidi kaboni ni vya chini, hidrojeni zaidi inafungwa, na pH huongezeka. (Tafuta maudhui ya ziada kwa undani zaidi kuhusu pH.)

Chemoreceptors kukabiliana na kuongeza dioksidi kaboni na viwango vya ioni hidrojeni (kuanguka pH) kwa kuchochea cardioaccelerator na vituo vasomotor, kuongeza pato la moyo na constricting vyombo vya pembeni. Vituo vya cardioinhibitor vinasimamishwa. Kwa kuanguka dioksidi kaboni na viwango vya ioni hidrojeni (kuongezeka kwa pH), vituo vya cardioinhibitor vinasukumwa, na vituo vya cardioaccelerator na vasomotor vasomotor vasomotor vasomotor vasomotor hupungua Ili kudumisha vifaa vya kutosha vya oksijeni kwenye seli na kuondoa bidhaa za taka kama vile dioksidi kaboni, ni muhimu kwamba mfumo wa kupumua uitikie mabadiliko ya mahitaji ya kimetaboliki. Kwa upande mwingine, mfumo wa moyo na mishipa utasafirisha gesi hizi kwa mapafu kwa kubadilishana, tena kwa mujibu wa mahitaji ya kimetaboliki. Uhusiano huu wa udhibiti wa moyo na mishipa na kupumua hauwezi kusisitizwa.

Njia nyingine za neural pia zinaweza kuwa na athari kubwa juu ya kazi ya moyo. Hizi ni pamoja na mfumo wa limbic unaounganisha majibu ya kisaikolojia kwa uchochezi wa kisaikolojia, pamoja na kusisimua kwa ujumla na parasympathetic.

Endocrine kanuni

Udhibiti wa Endocrine juu ya mfumo wa moyo unahusisha catecholamines, epinephrine na norepinephrine, pamoja na homoni kadhaa zinazoingiliana na figo katika udhibiti wa kiasi cha damu.

Epinephrine na Norepinephrine

Catecholamines epinephrine na norepinephrine hutolewa na medula ya adrenal, na kuongeza na kupanua majibu ya mwili wa huruma au “kupigana-au-ndege” (angalia Kielelezo\(\PageIndex{1}\)). Wao kuongeza kiwango cha moyo na nguvu ya contraction, wakati muda constricting mishipa ya damu kwa viungo si muhimu kwa ajili ya ndege au-mapambano majibu na kuelekeza mtiririko wa damu kwa ini, misuli, na moyo.

Antidiuretic homoni

Antidiuretic homoni (ADH), pia inajulikana kama vasopressin, ni secreted na seli katika hypothalamus na kusafirishwa kupitia njia hipothalamic-hypophyseal kwa posterior tezi ambapo ni kuhifadhiwa mpaka kutolewa juu ya kusisimua neva. Trigger ya msingi inayosababisha hypothalamus kutolewa ADH inaongeza osmolarity ya maji ya tishu, kwa kawaida katika kukabiliana na hasara kubwa ya kiasi cha damu. ADH inaashiria seli zake zilizolengwa kwenye figo ili kurejesha maji zaidi, hivyo kuzuia upotevu wa maji ya ziada katika mkojo. Hii itaongeza viwango vya jumla vya maji na kusaidia kurejesha kiasi cha damu na shinikizo. Aidha, ADH inakabiliana na vyombo vya pembeni.

Mfumo wa Renini-Angiotensin-Aldosterone

Utaratibu wa renin-angiotensin-aldosterone una athari kubwa juu ya mfumo wa moyo (Kielelezo\(\PageIndex{3}\)). Renini ni enzyme, ingawa kwa sababu ya umuhimu wake katika njia ya renini-angiotensin-aldosterone, vyanzo vingine vinatambua kama homoni. Seli maalumu katika figo zinazopatikana katika vifaa vya juxtaglomerular hujibu mtiririko wa damu uliopungua kwa kuficha renini ndani ya damu. Renin waongofu plasma protini angiotensinogen, ambayo ni zinazozalishwa na ini, katika hali yake kazi-angiotensin I angiotensin huzunguka katika damu na kisha kuongoka katika angiotensin II katika mapafu. Mmenyuko huu huchochewa na enzyme ya angiotensin-kuwabadili enzyme (ACE).

Angiotensin II ni vasoconstrictor yenye nguvu, na kuongeza shinikizo la damu. Pia huchochea kutolewa kwa ADH na aldosterone, homoni inayozalishwa na kamba ya adrenal. Aldosterone huongeza reabsorption ya sodiamu ndani ya damu na figo. Kwa kuwa maji hufuata sodiamu, hii huongeza reabsorption ya maji. Hii kwa upande huongeza kiasi cha damu, na kuongeza shinikizo la damu. Angiotensin II pia huchochea kituo cha kiu katika hypothalamus, hivyo mtu anaweza kutumia maji mengi, tena kuongeza kiasi cha damu na shinikizo.

Kielelezo\(\PageIndex{3}\): Homoni zinazohusika katika Udhibiti wa kidole cha Shinikizo la damu Katika utaratibu wa renin-angiotensin-aldosterone, kuongeza angiotensin II itachochea uzalishaji wa homoni ya antidiuretic na aldosterone. Mbali na renin, figo huzalisha erythropoietin, ambayo huchochea uzalishaji wa seli nyekundu za damu, na kuongeza kiasi cha damu.

Erythropoietin

Erythropoietin (EPO) hutolewa na figo wakati mtiririko wa damu na/au viwango vya oksijeni hupungua. EPO huchochea uzalishaji wa erythrocytes ndani ya mchanga wa mfupa. Erythrocytes ni kipengele kikubwa cha sumu ya damu na inaweza kuchangia asilimia 40 au zaidi kwa kiasi cha damu, jambo muhimu la mnato, upinzani, shinikizo, na mtiririko. Aidha, EPO ni vasoconstrictor. Overproduction ya EPO au ulaji wa kupindukia wa EPO synthetic, mara nyingi ili kuongeza utendaji wa riadha, itaongeza mnato, upinzani, na shinikizo, na kupungua kwa mtiririko pamoja na mchango wake kama vasoconstrictor.

Atrial Natriuretic homoni

Siri na seli katika atiria ya moyo, atrial natriuretic homoni (ANH) (pia inajulikana kama atiria natriuretic peptide) ni secreted wakati kiasi cha damu ni juu ya kutosha kusababisha uliokithiri kunyoosha ya seli za moyo. Viini katika ventricle huzalisha homoni yenye athari sawa, inayoitwa B-aina ya homoni ya natriuretic. Homoni za Natriuretic ni wapinzani wa angiotensin II. Wao kukuza hasara ya sodiamu na maji kutoka figo, na kukandamiza renini, aldosterone, na uzalishaji ADH na kutolewa. Vitendo hivi vyote vinasaidia kupoteza maji kutoka kwa mwili, hivyo kiasi cha damu na kushuka kwa shinikizo la damu.

Autoregulation ya Perfusion

Kama jina lingeweza kupendekeza, taratibu za udhibiti hazihitaji kusisimua kwa neva maalum wala udhibiti wa endocrine. Badala yake, haya ni ya ndani, mifumo ya udhibiti ambayo inaruhusu kila mkoa wa tishu kurekebisha mtiririko wake wa damu - na hivyo perfusion yake. Njia hizi za mitaa ni pamoja na ishara za kemikali na udhibiti wa myogenic.

Ishara za Kemikali zinazohusika katika udhibiti wa udhibiti

Ishara za kemikali zinafanya kazi kwa kiwango cha sphincters ya precapillary ili kuchochea kikwazo au kufurahi. Kama unavyojua, kufungua sphincter ya precapillary inaruhusu damu kuingilia ndani ya kapilari fulani, wakati kuzuia sphincter ya precapillary kwa muda hufunga mtiririko wa damu kwenye eneo hilo. Sababu zinazohusika katika kusimamia sphincters ya precapillary ni pamoja na yafuatayo:

• Ufunguzi wa sphincter unasababishwa katika kukabiliana na viwango vya oksijeni vilivyopungua; kuongezeka kwa viwango vya dioksidi kaboni; kuongezeka kwa viwango vya asidi lactic au bidhaa nyingine za kimetaboliki ya seli; kuongeza viwango vya ions potasiamu au ions hidrojeni (kuanguka pH); kemikali za uchochezi kama vile histamines; na kuongezeka kwa joto la mwili. Hali hizi pia huchochea kutolewa kwa NO, vasodilator yenye nguvu, kutoka seli za endothelial (angalia Mchoro\(\PageIndex{1}\)).
• Kupunguza sphincter ya precapillary husababishwa na viwango tofauti vya wasimamizi, ambayo husababisha kutolewa kwa endothelins, peptidi yenye nguvu ya vasoconstricting iliyofichwa na seli za endothelial. Siri za sahani na prostaglandini fulani zinaweza pia kusababisha msimamo.

Tena, mambo haya hubadilisha perfusion ya tishu kupitia athari zao kwenye utaratibu wa sphincter ya precapillary, ambayo inasimamia mtiririko wa damu kwa capillaries. Kwa kuwa kiasi cha damu ni mdogo, sio capillaries zote zinaweza kujaza mara moja, hivyo mtiririko wa damu unatengwa kulingana na mahitaji na hali ya kimetaboliki ya tishu kama inavyoonekana katika vigezo hivi. Kumbuka, hata hivyo, kwamba kupanua na kikwazo cha arterioles kulisha vitanda vya capillary ni utaratibu wa msingi wa kudhibiti.

Jibu la Myogenic

Jibu la myogenic ni mmenyuko wa kuenea kwa misuli ya laini katika kuta za arterioles kama mabadiliko katika mtiririko wa damu hutokea kupitia chombo. Hii inaweza kutazamwa kama kazi kubwa ya kinga dhidi ya kushuka kwa kiasi kikubwa katika shinikizo la damu na mtiririko wa damu ili kudumisha homeostasis. Ikiwa perfusion ya chombo ni ndogo sana (ischemia), tishu zitapata viwango vya chini vya oksijeni (hypoxia). Kwa upande mwingine, perfusion nyingi inaweza kuharibu vyombo vidogo na vidogo zaidi vya chombo. Mitikio ya myogenic ni mchakato wa ndani ambao hutumikia kuimarisha mtiririko wa damu katika mtandao wa capillary unaofuata arteriole hiyo.

Wakati mtiririko wa damu ni mdogo, misuli ya laini ya chombo itakuwa ndogo tu iliyotambulishwa. Kwa kujibu, hupunguza tena, kuruhusu chombo kupanua na hivyo kuongeza harakati za damu ndani ya tishu. Wakati mtiririko wa damu ni wa juu sana, misuli ya laini itapatana kwa kukabiliana na kunyoosha kuongezeka, na kusababisha vasoconstriction ambayo inapunguza mtiririko wa damu.

Kielelezo\(\PageIndex{4}\) muhtasari madhara ya neva, endocrine, na udhibiti wa ndani juu ya arterioles.

Kielelezo\(\PageIndex{4}\): Muhtasari wa Utaratibu wa Kusimamia Arteriole Smooth Misuli na

Athari ya Zoezi kwenye Homeostasis ya Vasuli

Moyo ni misuli na, kama misuli yoyote, hujibu kwa kasi kwa zoezi. Kwa vijana wenye afya, pato la moyo (kiwango cha moyo × kiasi cha kiharusi) huongezeka kwa nonathlete kutoka takriban lita 5.0 (5.25 quarts) kwa dakika hadi kiwango cha juu cha lita 20 (21 quarts) kwa dakika. Kufuatana na hili itakuwa ongezeko la shinikizo la damu kutoka karibu 120/80 hadi 185/75. Hata hivyo, wanariadha wa aerobic wenye mafunzo vizuri wanaweza kuongeza maadili haya kwa kiasi kikubwa. Kwa watu hawa, pato la moyo linaongezeka kutoka takriban lita 5.3 (5.57 quarts) kwa dakika kupumzika hadi zaidi ya lita 30 (robo 31.5) kwa dakika wakati wa zoezi la juu. Pamoja na ongezeko hili la pato la moyo, shinikizo la damu huongezeka kutoka 120/80 wakati wa kupumzika hadi 200/90 kwa maadili ya juu.

Mbali na kazi bora ya moyo, zoezi huongeza ukubwa na wingi wa moyo. Uzito wa wastani wa moyo kwa wasio na nguvu ni kuhusu 300 g, ambapo mwanamichezo itaongeza hadi 500 g. ongezeko hili la ukubwa kwa ujumla hufanya moyo kuwa na nguvu na ufanisi zaidi katika kusukumia damu, kuongeza kiasi cha kiharusi na pato la moyo.

Tissue perfusion pia kuongezeka kama mabadiliko ya mwili kutoka hali ya kupumzika kwa zoezi mwanga na hatimaye kwa zoezi nzito (angalia Kielelezo\(\PageIndex{4}\)). Mabadiliko haya husababisha vasodilation ya kuchagua katika misuli ya mifupa, moyo, mapafu, ini, na integument. Wakati huo huo, vasoconstriction hutokea katika vyombo vinavyoongoza kwenye figo na viungo vingi vya utumbo na uzazi. Mzunguko wa damu kwenye ubongo bado haubadilika kwa kiasi kikubwa ikiwa unapumzika au utumiaji, kwani vyombo vya ubongo havijibu kwa uchochezi wa udhibiti, mara nyingi, kwa sababu hawana receptors zinazofaa.

Kama vasodilation hutokea katika vyombo vya kuchaguliwa, matone ya upinzani na damu zaidi huingia ndani ya viungo vinavyotoa. Hatimaye damu hii inarudi kwenye mfumo wa vimelea. Kurudi kwa uharibifu kunaimarishwa zaidi na misuli ya mifupa na pampu za kupumua. Kama damu inarudi moyoni kwa haraka zaidi, kuongezeka kwa preload na kanuni ya Frank-Starling inatuambia kuwa contraction ya misuli ya moyo katika atria na ventricles itakuwa nguvu zaidi. Hatimaye, hata wanariadha bora mafunzo itakuwa uchovu na lazima kupitia kipindi cha mapumziko kufuatia zoezi. Pato la moyo na usambazaji wa damu kisha kurudi kwa kawaida.

Zoezi la kawaida linalenga afya ya moyo na mishipa kwa njia mbalimbali. Kwa sababu moyo wa mwanariadha ni mkubwa kuliko wa nonathletic, kiasi cha kiharusi kinaongezeka, hivyo moyo wa riadha unaweza kutoa kiasi sawa cha damu kama moyo usio na athletic lakini kwa kiwango cha chini cha moyo. Ufanisi huu umeongezeka unaruhusu mwanariadha kufanya mazoezi kwa muda mrefu kabla ya uchovu wa misuli na huweka dhiki kidogo juu ya moyo. Zoezi pia lowers ngazi ya jumla cholesterol kwa kuondoa kutoka mzunguko aina tata ya cholesterol, triglycerides, na protini inayojulikana kama chini wiani lipoproteins (LDL), ambayo ni sana kuhusishwa na hatari ya kuongezeka kwa ugonjwa wa moyo na mishipa. Ingawa hakuna njia ya kuondoa amana za plaque kutoka kuta za mishipa isipokuwa upasuaji maalumu, mazoezi haina kukuza afya ya vyombo kwa kupunguza kiwango cha malezi ya plaque na kupunguza shinikizo la damu, hivyo moyo hauna kuzalisha nguvu nyingi kushinda upinzani.

Kwa ujumla kidogo kama dakika 30 ya zoezi noncontinuous juu ya kozi ya kila siku ina athari ya manufaa na imekuwa umeonyesha kupunguza kiwango cha mashambulizi ya moyo kwa karibu asilimia 50. Wakati daima ni vyema kufuata chakula na afya, kuacha sigara, na kupoteza uzito, tafiti zimeonyesha wazi kwamba fit, watu overweight inaweza kweli kuwa na afya kwa ujumla kuliko watu sedentary mwembamba. Hivyo, faida za zoezi la wastani hazikubaliki.

Mazingira ya kliniki katika Homeostasis ya

Ugonjwa wowote unaoathiri kiasi cha damu, tone la mishipa, au kipengele kingine chochote cha utendaji wa mishipa ni uwezekano wa kuathiri homeostasis ya mishipa pia. Hiyo ni pamoja na shinikizo la damu, damu, na mshtuko.

Shinikizo la shinikizo la damu na

Shinikizo la damu lililoinua linajulikana kliniki kama shinikizo la damu. Inafafanuliwa kama vipimo vya shinikizo la damu sugu na vinavyoendelea vya 140/90 mm Hg au hapo juu. Shinikizo kati ya 120/80 na 140/90 mm Hg hufafanuliwa kama prehypertensive. Kuhusu Wamarekani milioni 68 sasa wanakabiliwa na shinikizo la damu. Kwa bahati mbaya, shinikizo la damu ni kawaida ugonjwa wa kimya; kwa hiyo, wagonjwa wa shinikizo la damu wanaweza kushindwa kutambua uzito wa hali yao na kushindwa kufuata mpango wao wa matibabu. Matokeo yake ni mara nyingi mashambulizi ya moyo au kiharusi. Shinikizo la damu pia inaweza kusababisha aneurism (ballooning ya mishipa ya damu unasababishwa na kudhoofika kwa ukuta), ugonjwa wa mishipa ya pembeni (kizuizi cha vyombo katika mikoa ya pembeni ya mwili), ugonjwa wa figo sugu, au kushindwa kwa moyo.

Kuharibika damu

Upungufu mdogo wa damu unasimamiwa na hemostasis na ukarabati. Hemorrhage ni upotevu wa damu ambao hauwezi kudhibitiwa na taratibu za hemostatic. Awali, mwili hujibu kwa damu kwa kuanzisha mifumo yenye lengo la kuongeza shinikizo la damu na kudumisha mtiririko wa damu. Hatimaye, hata hivyo, kiasi cha damu kitahitaji kurejeshwa, ama kupitia michakato ya kisaikolojia au kupitia uingiliaji wa matibabu.

Kwa kukabiliana na kupoteza damu, uchochezi kutoka kwa baroreceptors husababisha vituo vya moyo na mishipa ili kuchochea majibu ya huruma ili kuongeza pato la moyo na vasoconstriction. Hii kwa kawaida hushawishi kiwango cha moyo kuongezeka hadi juu ya vipande 180-200 kwa dakika, kurejesha pato la moyo kwa viwango vya kawaida. Vasoconstriction ya arterioles huongeza upinzani wa mishipa, wakati msongamano wa mishipa huongeza kurudi kwa moyo. Hatua hizi mbili zitasaidia kuongeza shinikizo la damu. Kusisimua kwa huruma pia husababisha kutolewa kwa epinephrine na norepinephrine, ambayo huongeza pato la moyo na vasoconstriction. Ikiwa upotevu wa damu ulikuwa chini ya asilimia 20 ya jumla ya kiasi cha damu, majibu haya pamoja yangerejea shinikizo la damu kwa kawaida na kuelekeza damu iliyobaki kwenye tishu.

Ushiriki wa ziada wa endocrine ni muhimu, hata hivyo, kurejesha kiasi cha damu kilichopotea. Utaratibu wa angiotensin-renin-aldosterone huchochea kituo cha kiu katika hypothalamus, ambayo huongeza matumizi ya maji ili kusaidia kurejesha damu iliyopotea. Muhimu zaidi, huongeza reabsorption ya figo ya sodiamu na maji, kupunguza kupoteza maji katika pato la mkojo. Figo pia huongeza uzalishaji wa EPO, na kuchochea malezi ya erythrocytes ambayo si tu kutoa oksijeni kwa tishu lakini pia kuongeza jumla ya kiasi cha damu. Kielelezo\(\PageIndex{5}\) summarizes the responses to loss of blood volume.

Figure \(\PageIndex{5}\): Homeostatic Responses to Loss of Blood Volume.

Circulatory Shock

The loss of too much blood may lead to circulatory shock, a life-threatening condition in which the circulatory system is unable to maintain blood flow to adequately supply sufficient oxygen and other nutrients to the tissues to maintain cellular metabolism. It should not be confused with emotional or psychological shock. Typically, the patient in circulatory shock will demonstrate an increased heart rate but decreased blood pressure, but there are cases in which blood pressure will remain normal. Urine output will fall dramatically, and the patient may appear confused or lose consciousness. Urine output less than 1 mL/kg body weight/hour is cause for concern. Unfortunately, shock is an example of a positive-feedback loop that, if uncorrected, may lead to the death of the patient.

There are several recognized forms of shock:

• Hypovolemic shock in adults is typically caused by hemorrhage, although in children it may be caused by fluid losses related to severe vomiting or diarrhea. Other causes for hypovolemic shock include extensive burns, exposure to some toxins, and excessive urine loss related to diabetes insipidus or ketoacidosis. Typically, patients present with a rapid, almost tachycardic heart rate; a weak pulse often described as “thread;” cool, clammy skin, particularly in the extremities, due to restricted peripheral blood flow; rapid, shallow breathing; hypothermia; thirst; and dry mouth. Treatments generally involve providing intravenous fluids to restore the patient to normal function and various drugs such as dopamine, epinephrine, and norepinephrine to raise blood pressure.
• Cardiogenic shock results from the inability of the heart to maintain cardiac output. Most often, it results from a myocardial infarction (heart attack), but it may also be caused by arrhythmias, valve disorders, cardiomyopathies, cardiac failure, or simply insufficient flow of blood through the cardiac vessels. Treatment involves repairing the damage to the heart or its vessels to resolve the underlying cause, rather than treating cardiogenic shock directly.
• Vascular shock occurs when arterioles lose their normal muscular tone and dilate dramatically. It may arise from a variety of causes, and treatments almost always involve fluid replacement and medications, called inotropic or pressor agents, which restore tone to the muscles of the vessels. In addition, eliminating or at least alleviating the underlying cause of the condition is required. This might include antibiotics and antihistamines, or select steroids, which may aid in the repair of nerve damage. A common cause is sepsis (or septicemia), also called “blood poisoning,” which is a widespread bacterial infection that results in an organismal-level inflammatory response known as septic shock. Neurogenic shock is a form of vascular shock that occurs with cranial or spinal injuries that damage the cardiovascular centers in the medulla oblongata or the nervous fibers originating from this region. Anaphylactic shock is a severe allergic response that causes the widespread release of histamines, triggering vasodilation throughout the body.
• Obstructive shock, as the name would suggest, occurs when a significant portion of the vascular system is blocked. It is not always recognized as a distinct condition and may be grouped with cardiogenic shock, including pulmonary embolism and cardiac tamponade. Treatments depend upon the underlying cause and, in addition to administering fluids intravenously, often include the administration of anticoagulants, removal of fluid from the pericardial cavity, or air from the thoracic cavity, and surgery as required. The most common cause is a pulmonary embolism, a clot that lodges in the pulmonary vessels and interrupts blood flow. Other causes include stenosis of the aortic valve; cardiac tamponade, in which excess fluid in the pericardial cavity interferes with the ability of the heart to fully relax and fill with blood (resulting in decreased preload); and a pneumothorax, in which an excessive amount of air is present in the thoracic cavity, outside of the lungs, which interferes with venous return, pulmonary function, and delivery of oxygen to the tissues.

Chapter Review

Neural, endocrine, and autoregulatory mechanisms affect blood flow, blood pressure, and eventually perfusion of blood to body tissues. Neural mechanisms include the cardiovascular centers in the medulla oblongata, baroreceptors in the aorta and carotid arteries and right atrium, and associated chemoreceptors that monitor blood levels of oxygen, carbon dioxide, and hydrogen ions. Endocrine controls include epinephrine and norepinephrine, as well as ADH, the renin-angiotensin-aldosterone mechanism, ANH, and EPO. Autoregulation is the local control of vasodilation and constriction by chemical signals and the myogenic response. Exercise greatly improves cardiovascular function and reduces the risk of cardiovascular diseases, including hypertension, a leading cause of heart attacks and strokes. Significant hemorrhage can lead to a form of circulatory shock known as hypovolemic shock. Sepsis, obstruction, and widespread inflammation can also cause circulatory shock.

Interactive Link Questions

Listen to this CDC podcast to learn about hypertension, often described as a “silent killer.” What steps can you take to reduce your risk of a heart attack or stroke?

Answer: Take medications as prescribed, eat a healthy diet, exercise, and don’t smoke.

Review Questions

Q. Clusters of neurons in the medulla oblongata that regulate blood pressure are known collectively as ________.

A. baroreceptors

B. angioreceptors

C. the cardiomotor mechanism

D. the cardiovascular center

 

Answer: D

Q. In the renin-angiotensin-aldosterone mechanism, ________.

A. decreased blood pressure prompts the release of renin from the liver

B. aldosterone prompts increased urine output

C. aldosterone prompts the kidneys to reabsorb sodium

D. all of the above

 

Answer: C

Q. In the myogenic response, ________.

A. muscle contraction promotes venous return to the heart

B. ventricular contraction strength is decreased

C. vascular smooth muscle responds to stretch

D. endothelins dilate muscular arteries

 

Answer: C

Q. A form of circulatory shock common in young children with severe diarrhea or vomiting is ________.

A. hypovolemic shock

B. anaphylactic shock

C. obstructive shock

D. hemorrhagic shock

 

Answer: A

Critical Thinking Questions

Q. A patient arrives in the emergency department with a blood pressure of 70/45 confused and complaining of thirst. Why?

A. This blood pressure is insufficient to circulate blood throughout the patient’s body and maintain adequate perfusion of the patient’s tissues. Ischemia would prompt hypoxia, including to the brain, prompting confusion. The low blood pressure would also trigger the renin-angiotensin-aldosterone mechanism, and release of aldosterone would stimulate the thirst mechanism in the hypothalamus.

Q. Nitric oxide is broken down very quickly after its release. Why?

A. Nitric oxide is a very powerful local vasodilator that is important in the autoregulation of tissue perfusion. If it were not broken down very quickly after its release, blood flow to the region could exceed metabolic needs.

References

Centers for Disease Control and Prevention (US). Getting blood pressure under control: high blood pressure is out of control for too many Americans [Internet]. Atlanta (GA); [cited 2013 Apr 26]. Available from: www.cdc.gov/features/vitalsigns/hypertension/

Glossary

anaphylactic shock

type of shock that follows a severe allergic reaction and results from massive vasodilation

aortic sinuses

small pockets in the ascending aorta near the aortic valve that are the locations of the baroreceptors (stretch receptors) and chemoreceptors that trigger a reflex that aids in the regulation of vascular homeostasis

atrial reflex

mechanism for maintaining vascular homeostasis involving atrial baroreceptors: if blood is returning to the right atrium more rapidly than it is being ejected from the left ventricle, the atrial receptors will stimulate the cardiovascular centers to increase sympathetic firing and increase cardiac output until the situation is reversed; the opposite is also true

cardiogenic shock

type of shock that results from the inability of the heart to maintain cardiac output

carotid sinuses

small pockets near the base of the internal carotid arteries that are the locations of the baroreceptors and chemoreceptors that trigger a reflex that aids in the regulation of vascular homeostasis

circulatory shock

also simply called shock; a life-threatening medical condition in which the circulatory system is unable to supply enough blood flow to provide adequate oxygen and other nutrients to the tissues to maintain cellular metabolism

hypertension

chronic and persistent blood pressure measurements of 140/90 mm Hg or above

hypovolemic shock

type of circulatory shock caused by excessive loss of blood volume due to hemorrhage or possibly dehydration

myogenic response

constriction or dilation in the walls of arterioles in response to pressures related to blood flow; reduces high blood flow or increases low blood flow to help maintain consistent flow to the capillary network

neurogenic shock

type of shock that occurs with cranial or high spinal injuries that damage the cardiovascular centers in the medulla oblongata or the nervous fibers originating from this region

obstructive shock

type of shock that occurs when a significant portion of the vascular system is blocked

sepsis

(also, septicemia) organismal-level inflammatory response to a massive infection

septic shock

(also, blood poisoning) type of shock that follows a massive infection resulting in organism-wide inflammation

vascular shock

type of shock that occurs when arterioles lose their normal muscular tone and dilate dramatically