Interactive Physiology

Anat omyRevi ew:Respi r at or ySt r uct ur es Graphics are used with permission of: adam.com (http://www.adam.com/ ) Benjamin Cummings Publishing Co ( http://www.aw.com/bc )

Over vi ew:Respi r at or ySyst em Or gans • Air enters the nose by passing through two openings called the external nares , or nostrils. • Within the nose, the air passes through the nasal cavity , and then travels through the pharynx , a muscular tube which carries both food and air throughout most of its length. • Air then enters the larynx. • After passing through the larynx, air enters the trachea , which is held open by incomplete rings of cartilage. • The trachea divides into a right and a left primary bronchus , which carry the air into the lungs. • Although not part of the respiratory system, the diaphragm and the intercostal muscles play important roles in breathing.

Demo monst r at i onofPl eur aeandt heLungs • Each lung is surrounded by two layers of  serous membrane known as the pleurae. • The relationship between the pleurae and the lungs can be demonstrated by pushing a fist into a waterfilled balloon. The balloon represents the pleurae, and the fist represents the lung. • As the fist pushes into the balloon, notice how the balloon wraps around it, and the opposite surfaces of the balloon almost touch. • The inner part of the balloon which wraps around the fist represents the visceral pleura. The visceral pleura is the part of the pleura which covers the surface of the lungs. • The outer part of the balloon represents the parietal pleura, which lines the mediastinum, the diaphragm, and the thoracic wall. • Notice that the visceral and parietal pleurae are actually a continuation of the same membrane. • The water-filled space between the two layers represents the pleural cavity, which contains pleural fluid.

Vi scer alandPar i e t alPl eur a • The visceral pleura and parietal pleura enclose each lung in a separate sac. The frosty layer you see here covering the lung is the portion of the parietal pleura that lines the anterior thoracic wall. • The visceral pleura covers the surface of the lungs and the cut edges of the parietal pleura. • The pleural cavity is an extremely thin, slit-like space between the pleurae, separating them by a thin layer of pleural fluid. The pleural fluid assists in breathing movements by acting as a lubricant. • The parietal pleura lines the mediastinum, the superior surface of the diaphragm, and the inner thoracic wall.

Br onc hi a lT r e e • The lungs contain many branching airways which collectively are known as the bronchial tree. • Air enters the lungs through the primary bronchi, which branch into secondary bronchi, which in turn branch into tertiary bronchi. • The trachea and all the bronchi have supporting cartilage which keeps the airways open. • Air flows deeper into the lungs as the tertiary bronchi branch repeatedly into smaller bronchi, which eventually branch into bronchioles. • Bronchi Bronchioles oles lack cartila cartilage ge and contain contain more smooth smooth muscle muscle in their their walls walls than the bronchi. bronchi. These features allow airflow regulation by altering the diameter of the bronchioles. • Bronchioles branch further into terminal bronchioles. I nt e r ac t i v ePhy s i o l o gy

• The airways from the nasal cavity through the terminal bronchioles are called the conducting zone. The air is moistened, warmed, and filtered as it flows through these passageways. • Beyond the terminal bronchioles, the air enters the respiratory zone, the region of the lung where gas exchange occurs.

Respi r at or yZone • Beyond the terminal bronchioles lie the structures of the respiratory zone, where we begin to find alveoli, tiny thin-walled sacs where gas exchange occurs. • Respiratory bronchioles have scattered alveoli in their walls. They lead into alveolar ducts, which are completely lined by alveoli. These ducts end in clusters of alveoli called alveolar sacs.

Al v eol ia ndPul mona r yCa pi l l a r i e s • The pulmonary arteries carry blood which is low in oxygen from the heart to the lungs. • These blood vessels branch repeatedly, eventually forming dense networks of capillaries that completely surround each alveolus. • This rich blood supply allows for the efficient exchange of oxygen and carbon dioxide between the air in the alveoli and the blood in the pulmonary capillaries. • Blood leaves the capillaries via the pulmonary veins, which transports the freshly oxygenated blood out of the lungs and back to the heart.

St r uc t ur eofa nAl v eol us • Structure of the inside of an individual alveolus shows three types of cells: 1. simple squamous epithelium 2. alveolar macrophages 3. surfactant-secreting cells • The wall of an alveolus is primarily composed of simple squamous epithelium, or Type I cells. Gas exchange occurs easily across this very thin epithelium. • The alveolar macrophages, or dust cells, creep along the inner surface of the alveoli, removing debris and microbes. • The alveolus also contains scattered surfactant-secreting, or Type II, cells.

Rol eofSur f a ct a nt • The inside surface of the alveolus is lined with alveolar fluid. • The water in the fluid creates a surface tension. Surface tension is due to the strong attraction between water molecules at the surface of a liquid, which draws the water molecules closer together. • As seen here, this force pulls the alveolus inward and reduces its size. If an alveolus were lined with pure water, it would collapse. • Surfactant, which is a mixture of phospholipids and lipoproteins, lowers the surface tension of the fluid by interfering with the attraction between the water molecules, preventing alveolar collapse. • Without surfactant, alveoli would have to be completely reinflated between breaths, which would take an enormous amount of energy.

St r uct ur eoft heRespi r at or yMembr ane • The wall of an alveolus and the wall of a capillary form the respiratory membrane, where gas exchange occurs. • The respiratory membrane is made up of two layers of simple squamous epithelium and their basement membranes. This membrane is extremely thin, averaging 0.5 micrometers in width.

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• Notice also that in many regions of the membrane there is no interstitial fluid. This is because pulmonary blood pressure is so low that little fluid filters out of the capillaries into the interstitial space. Oxygen and carbon dioxide can diffuse easily across this thin respiratory membrane.

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OxygenTr anspor t •T r a ns po r to fo x y g e n dur i nge x t e r na lr e s pi r a t i o n:  Wi hi t sl ow sol ubi l i t y ,onl yappr oxi mat el y1. 5% oft heoxy gen i st r a ns po r t e ddi s s o l v e di npl a s ma . • t  T emai ni ng98. 5% di ffusesi nt or edbl oodcel l sandc hemi cal l ycombi neswi t hhemo gl obi n. • her

Hemogl obi n •Wi t hi neachr edbl oodcel l ,t her ear eappr oxi mat el y250mi l l i onhemogl obi nmol ecul es. •Eachhemogl obi nmol ecul econsi st sof : 1.Agl obi nport i oncomposedof4pol ypept i dechai ns. 2.Fouri r oncont ai ni ngpi gment scal l edhemegr oups. •Eachhemogl obi nmol ecul ecant r ansportupt o4oxyg enmol ecul esbecauseeachi r onat om canbi nd oneoxygenmol ecul e. •When4oxygenmol ecul esar eboundt ohemogl obi n,i ti s100% sat ur at ed;whent her ear ef ewer ,i ti s par t i al l ys at ur a t e d. •Oxygenbi ndi ngoccur si nr esponset ot hehi ghpart i alpr essur eofoxygeni nt hel ungs. •Whenhemogl obi nbi ndswi t hoxygen,i ti scal l edoxyhemogl obi n. •Whenoneoxygenbi ndst ohemogl obi n,t heot heroxygenmol ecul esbi ndmorer eadi l y . Thi si scal l ed c o ope r a t i v eb i ndi ng .He mo g l o bi n' sa ffini t yf o ro x y g e ni nc r e a s e sasi t ss a t ur a t i o ni nc r e a s e s.

Oxyhemogl obi nandDeoxyhemogl obi n •T hef o r ma t i o no fo xy he mo g l o bi no c c ur sa sar e v e r s i bl er e a ct i o n,a ndi swr i t t e na si nt hi sc he mi c a l equat i on:

•I nr e v e r s i bl er e a c t i o ns ,t hedi r e c t i o nde pe ndsont hequa nt i t yofpr o duc t sandr e a c t a nt spr e s e nt . •I nt hel ung s ,whe r et hepar t i a lpr e s s ur eo fo xy g e ni shi g h,t her e a c t i o n pr o c e e dst ot her i g ht ,f o r mi ng oxyhemogl obi n.

•I no r g a nst hr o ug ho utt hebo dywhe r et hepa r t i a lpr e s s ur eo fo x y g eni sl o w,t her e a ct i o nr e v e r s e s pr oceedi ngt ot hel ef t .Oxyhemogl obi nr el easesoxygen,f ormi ngdeoxyhemogl obi n,whi chi sal so cal l edr educedhemogl obi n. ,

•No t i c et ha tt hea ffini t yo fhe mo g l o bi nf o ro x y g e nde c r e as e sa si t ss a t ur a t i o nde c r e a se s .

CO2T r a n s p o r t I nt er act i v ePhysi ol ogy

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•Carbondi oxi det r ansport : •Carbondi oxi dei spr oducedbycel l st hr oughoutt hebody . •I tdi ffus e souto ft hec e l l sandi nt ot hes y s t e mi cc api l l a r i e s ,whe r eappr o x i ma t e l y7% i s t r ansport eddi ssol vedi npl asma.  T emai ni ngcar bondi oxi dedi ffusesi nt ot her edbl oodcel l s.Wi t hi nt her edbl oodcel l s, • her approxi mat el y23% chemi cal l ycombi neswi t hhemogl obi n,and70% i sc onver t edt obi car bonat e i ons,whi charet hent r ansport edi nt hepl asma.

CO2  Tr anspor t :Car bami nohemogl obi n( Ti ssues) •Oft het ot alcarbon di oxi dei nt hebl ood,23% bi ndst ot hegl obi nport i on oft hehemogl obi nmol ecul e t of or m car bami nohemogl obi n,aswr i t t e ni nt hi se qua t i o n:

•Carbami nohemogl obi nf ormsi nr egi onsofhi ghPCO ,a sbl o odflo wst hr o ug ht hes y s t e mi cc api l l a r i e s 2 i nt het i s s ue s .

CO2  Tr anspor t :Car bami nohemogl obi n( Lungs) •Thef ormat i onofcarbami nohemogl obi ni srev er si bl e.

•I nt he l ungs ,whi ch hav ea l owerPCO ,carbon di oxi de di ssoci at es f r om car bami nohemogl obi n, 2 di ffus e si nt ot heal v e ol i ,andi sexhal ed.

CO2T r a ns por t :Bi c ar bona t eI ons( Ti s sue s) •Oft het o t a lc a r bo n di o x i dei nt hebl o od,70% i sco nv e r t e di nt obi c a r bo na t ei o nswi t hi nt here dbl o od c e l l s ,i nas e q ue nc eofr e v e r s i bl er e a c t i o ns .Thebi c a r bo na t ei o nst he ne nt e rt hepl a s ma . •I nr e g i o nswi t hhi g hPCO ,carbon di oxi deent er st heredbl oodcel landcombi neswi t hwat ert of orm 2 car boni caci d. Thi sre act i on i scat al yze d by t heenzymecarboni canhydrase.Thesamere act i on occur si nt hepl asma,butwi t houtt heenzymei ti sver ysl ow. •Carboni caci d di ssoci at esi nt ohydrogen i onsand bi car bonat ei ons.Thehydrogeni onspr oducedi n t hi sr eact i onarebuffer edbybi ndi ngt ohemogl obi n.Thi si swri t t enasHHb. •I n ordert o mai nt ai n el ect ri calneut r al i t y,bi carbonat ei ons di ffuse outoft he r ed bl ood cel land c hl o r i dei onsdi ffus ei n.Thi si sc al l e dt hec hl or i deshi f t . •Wi t hi nt hepl asma,bi carbonat ei onsactasabufferandpl ayan i mport antr ol ei nbl oodpH cont r ol .

CO2T r a ns por t :Bi c ar bona t eI ons( Lungs ) •I nt hel ung s ,c a r bo n di o x i dedi ffus e so uto ft hepl a s maandi nt ot heal v e o l i .Thi sl o we r st hePCO i n 2 t hebl o od,c a us i ngt hec he mi c a lr e a ct i o nst or e v e r s eandpr o ce edt ot hel e f t . •I nt hel ungs,t hebi carbonat ei onsdi ffusebacki nt ot heredbl ood cel l ,andt hechl ori dei onsdi ffuse outoft her e dbl oodc el l .Re cal lt hatt hi si sc al l e dt hec hl or i des hi f t . •Thehydr ogen i onsar er el ease df r om hemogl obi n,and combi newi t ht hebi car bonat ei on t of or m c ar b oni ca ci d. •Carboni caci dbr eaksdown i nt ocarbon di oxi deandwat er .Thi sre ver sereact i on i sal socat al yzedby t heenzy mecar boni canhydr ase.

Summar y:Lungs •Summaryofext er nalr espi r at i oni nt hel ungs. •Al t ho ug hwewi l ll o oka tt hepr o c e s s e ss t e pb ys t e p,t he yac t ua l l yo cc urs i mul t a ne o us l y . •Re me mbe r ,g a s e sal wa y sf o l l o wt he i rpa r t i a lpr e s s ur eg r a di e nt s . I nt er act i v ePhysi ol ogy

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•Asyougot hr ought hest eps,pl acet henumber st hatcor r espondwi t ht hest epsi nt hebl anksont hi s di agr am: •Dur i ng ext er nalr espi r at i on,a smal lamountofoxygen ( 1)r emai ns di ssol ved i nt he pl asma. However ,t hemaj ori t yoft heoxygen ( 2)cont i nuesi nt ot her ed bl ood cel l s,wher ei tc ombi nes  wi t hdeoxyhemo gl obi n( 3)t of or m oxyhemo gl obi n( 4) ,r el easi ngahydr ogeni on( 5) . •Whenhemogl obi ni ssat ur at edwi t hoxygen,i t saffini t yf orcar bon di oxi dedecr eases.Anycarbon di oxi decombi ned wi t h hemogl obi n( 6)di ssoci at esand di ffusesoutoft hered bl ood cel l( 7) , t hr ough t he pl asma and i nt ot he al veol i .I n ot herwords,oxygen l oadi ng f aci l i t at es carbon di o x i deunl o adi ngf r o m he mo g l o bi n.Thi si nt e r a c t i o ni sc a l l e dt heHa l da nee ffe c t . •Thehydr ogeni on r el easedf r om hemogl obi n combi neswi t h abi car bonat ei on ( 8) ,whi chdi ffuses i nt ot he r ed bl ood cel lf r om t he pl asma i n exchange f ora chl ori de i on ( 9) .Recal lt hatt hi s exc hange i st he chl ori de shi f t .The r eact i on bet ween hydr ogen and bi car bonat ei ons f orms c ar boni cac i d( 10) . •Car boni caci dt hen bre aksdown i nt o wat erand car bon di oxi de ( 11) ,cat al yz ed by t heenzy me car boni canhydr ase.Thewat erproduced by t hi sr eact i on may l eavet he r ed bl ood cel l ,or r emai n aspartoft hecyt opl asm.Thecar bon di oxi dedi ffusesoutoft heredbl ood cel l( 12)i nt o t hepl asmaand t hen i nt ot heal veol i .Thesmal lamountofcar bon di oxi det r ansport ed i nt he pl asmadi ffusesi nt ot heal veol i

Summar y:Ti ssues Summa r yo fi nt e r na lr e s pi r a t i o ni nt het i s s ue s . •Asyougot hr ought hest eps,pl acet henumber st hatcor r espondwi t ht hest epsi nt hebl anksont hi s di agr am: • Dur i ng i nt e r na lr e s p i r a t i o n,a smal lamountofcar bon di oxi de ( 1)r emai ns di ss ol ve di nt he pl asma,butmostoft hecarbondi oxi de( 2)cont i nuesi nt ot here dbl ood cel l swher emuchofi t co mbi nes wi t h wat er t of or m car boni c aci d( 3) or co mbi nes wi t h hemogl obi n t of or m car bami nohemogl obi n( 11) . Thi sre act i on i scat al yze d by car boni canhydr ase.  Thecar boni c a c i dt he ndi s s o c i a t e si nt ohy dr o g e na ndbi c a r bo na t ei o ns( 4) . •Dur i ngt hec hl o r i des hi f t ,bi c a r bo na t ei o ns( 5)di ffus eouto ft her e d bl o od c e l li ne x c ha ng ef o r c hl or i dei ons( 6) .Bi carbonat ei onsactasbuffer swi t hi nt hepl asma,cont r ol l i ngbl oodpH. •Wi t hi nt here d bl ood cel l ,hydrogen i ons( 7)ar ebuffer ed by hemogl obi n( 8) .When hemogl obi n  bi ndshydr ogen i ons,i thasal oweraffini t yf oroxy gen.Asar esul t ,oxygen ( 9)di ssoci at esf r om hemogl obi n,di ffusesoutoft hered bl ood cel land i nt ot het i ssues.Thei nt er act i on bet ween hemogl obi n' saffini t yf oroxygenandi t saffini t yf orhydr ogen i onsi scal l edt heBohreffect .By f o r mi nghy dr o g e ni o ns ,c a r bo ndi o x i del o adi ngf a c i l i t a t e sox y g e n unl o adi ng . •The smal lamountofoxygen t r anspor t ed i nt he di ssol ved st at e( 10)al so di ffusesoutoft he pl a s maandi nt ot het i s s uec e l l s .

Pul monar yVent i l at i on Graphics are used with permission of: adam.com (http://www.adam.com/ ) Benjamin Cummings Publishing Co ( http://www.aw.com/bc )

Boyl e' sLaw:Rel at i onshi pBet weenPr essur eandVol ume • In order to understand ventilation, we must first look at the relationship between pressure and volume. • Pressure is caused by gas molecules striking the walls of a container. • The pressure exerted by the gas molecules is related to the volume of the container. • This large sphere contains the same number of gas molecules as the original sphere. Notice that in this larger volume, the gas molecules strike the wall less frequently, thus exerting less pressure.

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• In this small sphere, the gas molecules strike the wall more frequently, thus exerting more pressure. Notice that the number of gas molecules has not changed. • These demonstrations illustrate Boyle's Law, which states that the pressure of a gas is inversely proportional to the volume of its container. Thus, if you increase the volume of a container, the pressure will decrease, and if you decrease the volume of a container, the pressure will increase.

Qui e tI ns pi r a t i on:Mus cl eCont r a ct i on • The volume of the thoracic cavity is changed by muscle contraction and relaxation. • During quiet inspiration, the diaphragm and the external intercostal muscles contract, slightly enlarging the thoracic cavity. • As we learned from Boyle's Law, increasing the volume decreases the pressure within the thoracic cavity and the lungs. • Notice how the diaphragm flattens and moves inferiorly while the external intercostal muscles elevate the rib cage and move the sternum anteriorly. These actions enlarge the thoracic cavity in all dimensions. • As we learned from Boyle's Law, increasing the volume decreases the pressure within the thoracic cavity and the lungs.

Qui e tEx pi r a t i on:Mus cl eRe l a xa t i on • Quiet expiration is a passive process, in which the diaphragm and the external intercostal muscles relax, and the elastic lungs and thoracic wall recoil inward. • This decreases the volume and therefore increases the pressure in the thoracic cavity. • As the diaphragm relaxes, it moves superiorly. As the external intercostal muscles relax, the rib cage and sternum return to their resting positions. These actions decrease the size of the thoracic cavity in all dimensions, and therefore increase the pressure in the thoracic cavity.

Mus cl e sofDe epI ns pi r a t i ona ndEx pi r a t i on • Deep breathing uses forceful contractions of the inspiratory muscles and additional accessory muscles to produce larger changes in the volume of the thoracic cavity during both inspiration and expiration. During deep inspiration, the diaphragm and the external intercostal muscles contract more forcefully than during quiet breathing. Additionally, the sternocleidomastoid and scalenes contract, lifting the rib cage higher. These actions further increase the volume. As we learned from Boyle's Law, this decreases the pressure within the thoracic cavity. • Deep or forceful expiration is an active process. The internal intercostal muscles depress the rib cage, and the external oblique, internal oblique, transversus abdominis and rectus abdominis muscles compress the abdominal organs, forcing them superiorly against the diaphragm. These actions can dramatically decrease the volume, and further increase the pressure within the thoracic cavity, producing forceful expiration.

I nt r apul monar yPr essur eChanges • Now let's look at the specific pressure changes that occur in the lungs during breathing. For reasons described later, the lungs closely follow the movements of the thoracic wall. • The pressure within the lungs is called the intrapulmonary, or intra-alveolar, pressure. • Between breaths, it equals atmospheric pressure, which has a value of 760 millimeters of mercury at sea level. When discussing respiratory pressures, this is generally referred to as zero. I nt er act i v ePhysi ol ogy

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• During inspiration, the volume of the thoracic cavity increases, causing intrapulmonary pressure to fall below atmospheric pressure. This is also known as a negative pressure. Since air moves from areas of high to low air pressure, air flows into the lungs. Notice that at the end of inspiration, when the intrapulmonary pressure again equals atmospheric pressure, airflow stops. • During expiration, the volume of the thoracic cavity decreases, causing the intrapulmonary pressure to rise above atmospheric pressure. Following its pressure gradient, air flows out of the lungs, until, at the end of expiration, the intrapulmonary pressure again equals atmospheric pressure.

I nt r apl eur alPr essur e • Intrapleural pressure is the pressure within the pleural cavity. Intrapleural pressure is always negative, which acts like a suction to keep the lungs inflated. • The negative intrapleural pressure is due to three main factors: 1. The surface tension of the alveolar fluid. • The surface tension of the alveolar fluid tends to pull each of the alveoli inward and therefore pulls the entire lung inward. Surfactant reduces this force. 2. The elasticity of the lungs. • The abundant elastic tissue in the lungs tends to recoil and pull the lung inward. As the lung moves away from the thoracic wall, the cavity becomes slightly larger. The negative pressure this creates acts like a suction to keep the lungs inflated. 3. The elasticity of the thoracic wall. • The elastic thoracic wall tends to pull away from the lung, further enlarging the pleural cavity and creating this negative pressure. The surface tension of pleural fluid resists the actual separation of the lung and thoracic wall.

I nt r a pl e ur a lPr e ss ur eCha nge s • Intrapleural pressure changes during breathing: • As the thoracic wall moves outward during inspiration, the volume of the pleural cavity increases slightly, decreasing intrapleural pressure. • As the thoracic wall recoils during expiration, the volume of the pleural cavity decreases, returning the pressure to minus 4, or 756 millimeters of mercury.

EffectofPneumot hor ax • If you cut through the thoracic wall into its pleural cavity, air enters the pleural cavity as it moves from high pressure to low pressure. This is called a pneumothorax. • Normally, there is a difference between the intrapleural and intrapulmonary pressures, which is called transpulmonary pressure. The transpulmonary pressure creates the suction to keep the lungs inflated. In this case, when there is no pressure difference there is no suction and the lung collapses.

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• The lungs are completely separate from one another, each surrounded by its own pleural cavity and pleural membranes. Therefore, changes in the intrapleural pressure of one lung do not affect the other lung.

Anat omyRevi ew:Ur i nar ySyst em Gr aphi csar eusedwi t hpermi ssi onof : ada m. c om ( http://www.adam.com/ ) Benj ami nCummi ngsPubl i shi ngCo( http://www.aw.com/bc )

TheUr i nar ySyst em  Theur i nar ysys t em i scomposedofpai r edki dneysandur e t er s,t heur i nar ybl adder ,andt heur e t hr a. •Ur i nei spr oducedi nt heki dneys,andt hendr ai nst hr ought heur et er st ot heuri narybl adder ,wher e t heur i nei ss t o r e d .Ur i nei se l i mi na t e df r o mt hebo dyt hr o ug ht heur e t hr a . •

Ex t e r na lSt r uc t ur eoft heKi dne y s Eachbeanshapedki dneyi sembeddedi naf at t yadi posecapsul e. •Theki dne y sa r er e t r o pe r i t o ne a l ,l y i nga ga i ns tt hedo r s a lbo dywa l li nt heuppe ra bdo me n. •Ana dr e na lg l a nd,whi c hi spa r to ft hee ndo c r i nes y s t e m,l i e so nt o po fe a c h ki dne y . •Se v e r a ls t r uc t ur e se nt e ro re x i tt hec onc a v es ur f ac eoft heki dne yatt her e nalhi l us ,i nc l udi ngt he ur e t e ra ndt her e na lv e i n,whi c hdr a i nsi nt ot hei nf e r i o rv e nac a v a. •

Bl oodSuppl yoft heKi dneys  Whent her enalv ei ni sr emo v edandt heki dneyi sshowni nf r ont alsect i on,y oucanseet hedeeper r e na la r t e r ya ndi t sc o nne c t i o nt ot hea bdo mi na la or t a . •Br anchi ngf r om t herenalart eryaret hesegment alandl obarart er i es. •T o g e t he r ,t he s ev e s s e l spr o v i det heki dne y swi t har i c hbl o ods uppl yunde rhi g hpr e s s ur et ha ta l l o ws t hem t ocont i nuousl yfil t erandcl eanset hebl ood. •

I nt er nalSt r uct ur eoft heKi dne y I nt e r na l l y ,t hehuma n ki dne yi sc o mpo s e do ft hr e edi s t i nc tr e g i o ns :

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1.RenalCort ex •Theout er mostl ayeri scal l ed t her enalcort ex.I tcont ai nsaboutonemi l l i on nephr ons,t he fil t e r i nguni t st hatf o r m ur i ne . •TypesofNephr ons: •Co r t i c alne phr o ns-l i ec o mpl e t e l ywi t hi nt hec o r t e x •Juxt amedul l arynephr ons-l i ei nbot ht hecort exandmedul l a 2.RenalMedul l a •The mi ddl el aye ri s cal l ed t he r enalmedul l a,i n whi ch you can seet he t r i angul arr enal pyr ami ds.Thesepyr ami dsl ookst r i at edbecauseofparal l elbundl esofduct scarr yi ngur i ne f r om t henephr ons. •Thear easbet weenpyrami dsar et her enalcol umns. Theyar eext ensi onsoft hecor t ext hat pr o v i dear o ut ef o rt hepa s s ag eo fbl o odv e s s e l sa ndne r v e st oandf r o mt heo ut e rc o r t e x . 3.RenalPel vi s •Thef unne l s ha pe dr e na lpe l v i si swi t hi nt her e nals i nus .Ther e nalpe l v i sc ol l e c t sur i nef r o m t hepy r a mi dsa ndc o nv e y si ti nt ot heur e t e rf o rp as s a get ot heur i nar ybl a dde r .

Nephr onOver vi ew I nt er act i v ePhysi ol ogy

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•Thenephr on i st hest ruct ur alandf unct i onaluni toft heki dneys.I tc ons i s t sofas pe c i al i z e dt ubul ar s t r uc t ur eandc l o s el yas s oc i at e dbl o odv e s s el s .

Nephr onSt r uct ur e:Associ at edBl oodVessel s •Bl ood ent er i ngt heki dneyt hr ough t here nalart eryflowsfir sti nt ot hesegment alart eri esandt hen i nt ot hel obara r t e r i e s. •Fr o mt he r e ,i te nt e r st hei nt e r l o bara r t e r i e s ,t hear c uat ear t e r i e s ,t hes mal li nt e r l o bul ara r t e r i e s ,and t hes t i l ls ma l l e ra ffe r e nta r t e r i o l e s ,whi c he mpt yi nt oac api l l a r ybe dc al l e dt heg l o me r ul us . •L ea di ngawa yf r o mt heg l o me r ul usi st hee ffe r e nta r t e r i o l e .No t i c et h att heaffe r e nta r t e r i o l ei sl a r g e r i ndi a me t e rt hant hee ffe r e ntar t e r i o l e . •Bl o odpas s e sf r o mt hee ffe r e ntar t e r i o l ei nt ot hepe r i t ubul arc api l l ar i e sandv as ar e c t a. •Fr om t her e,bl ood drai ns i nt ot he i nt er l obul arvei n,flows i nt ot he arc uat e vei n and ent er st he i nt e r l o barv e i n,e v e nt ual l yr e a c hi ngt her e nalv e i n.

Nephr onSt r uct ur e:Tubul arSegment s •Theexpanded ‘ cup-s haped’endoft het ubul esur r oundi ngt hegl omer ul usi scal l edt hegl omer ul ar , orBowman’ s,capsul e. •Wat erandsol ut espassf r om t hebl oodi nt ot hegl omer ul arcapsul e,andt henflow i nt ot hepr oxi mal c o nv o l ut e dtubul e ,o rPCT . •Af t ermanyl oopsandconvol ut i ons,t het ubul est r ai ght ensout ,andflui dflowsdownt hedesce ndi ng, ort hi n,segmentoft hel oopofHenl ei nt ot hemedul l aryregi on,andt henupt heascendi ng,or t hi c k,s e g me ntbac ki nt ot hec or t i c alr e g i o n. •Fr om t he l oop ofHenl e,t he flui dt hen ent er st he t wi st s and t ur ns oft he ear l y and l at e di st al c onv o l ut e dt ubul e ,o rDCT ,e v e nt ual l ye mpt y i ngi nt oac o r t i c alc o l l e c t i ngduc t . •Thi sductext endsi nt ot hemedul l a,f ormi ngt hemedul l arycol l ect i ngduct ,whi ch carr i est heuri ne t hr o ug ht het ubul e so ft her e na lpy r a mi dst ot h er e na lpe l v i s .

Ce l l ul a rF ea t ur e soft heRe na lCor pus cl e  Thegl ome r ul us,wi t hi t sl ar geri ncomi ngaffer entar t er i ol eandsmal l erout goi ngeffer entar t er i ol e,i s nest ed wi t hi nt hegl omerul arcapsul esomet hi ngl i keafistt hrusti nt oabal l oon.Toget her ,t hese s t r uc t ur e sar ec al l e dt her e na lc o r pus c l e . •Thevi s c e r a ll a y e ro ft hegl o me r ul a rc aps ul ei sma deupo fs pe c i a l i z e dc e l l scal l e dpo do c y t e s ,whi c h s ur r o undt hepe r me a bl eca pi l l a r i e s . •Be t we e nt hevi s c e r a la nd pa r i e t a ll a y e r soft hec aps ul el i e st hec a ps ul a rs pa ce ,whi c hc o l l e c t st he flui dandsol ut esbei ngfil t er edf r om t hebl ood. •I nl o ng i t udi nals e c t i o n,t heendo t he l i a ll i ni ngs ho wss mal lo pe ni ng sc al l e df e ne s t r a t i o ns ,whi c hal l o w f ort hepassageofwat erandsol ut essuchasi onsandsmal lmol ecul es. •The r ear ef e ne s t r at i onsbe t we e ne ndo t he l i alc e l l si nt hec api l l ar y . •Theporousbasementmembraneencl osest hecapi l l aryendot hel i um. • Sur r oundi ng t he basement membrane i sal aye r ofpodocyt es.Thes e ce l l s have l ar ge ‘ l egl i ke’ e xt e ns i o ns ,whi c hi nt ur nha v esmal l‘ f r i ng e l i ke ’e xt e ns i o nsc al l e dpe di c e l s . •Pe di c e l sf r o m adj ac e ntar e a si nt e r di g i t at el o os e l yt of o r ms pac e sc al l e dfil t r a t i ons l i t s . •Subst ancesbei ng fil t er ed mustpassfir stt hr ough t he f enest r at i ons,t hen t hr ough t he basement membr ane,andfinal l yt hr ought hefil t r at i onsl i t sandi nt ot hecapsul arspace. •Toge t her ,t he capi l l ary endot hel i um,base mentmembrane,and podocyt esmake up t he fil t r at i on membr ane . •Ex t e ndi ngf r o mt hepo do cy t ec e l lbo dyar el e g l i kee x t e ns i o nsc ont ai ni ngt hef r i ng e l i kepe di c e l s .The e x t e ns i o nsandpe di c e l swr a par o undt hec api l l ar yandi nt e r d i g i t at et of o r mt hefil t r a t i o ns l i t s . •

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 Acr osssect i onoft hefil t r at i onme mbr aner e v eal sal ar gepodocyt ewi t hi t snucl eusandpedi cel s.The  whi t ear easar epor t i onsoft hecapsul arspace.Gapsbe t weent hepedi cel sar et hefil t r at i onsl i t s. •Thebasementmembraneoft hecapi l l aryendot hel i um separat est hepodocyt ef r om t hecapi l l arywi t h i t sf e ne st r at i ons . •Not i cet hatt hefil t r at i on membr anepermi t st heescapeofsmal lmol ecul es,whi l epr event i ngl arge mol ecul esf r om l eavi ngt hebl oodst r eam andpassi ngt hr oughi nt ot hecapsul arspace. •

Cel l soft hePr oxi malConvol ut edTubul e( PCT)  Thesi mpl ecuboi dalcel l soft hepr oxi malconv ol ut edt ubul ear ecal l edbr ush bor dercel l sbecauseof t he i rnume r o usmi c r o v i l l i ,whi c hpr o j e c ti nt ot hel ume no ft het ubul e . •Thesemi cr ovi l l igr eat l yexpand t hesurf aceareaoft hel umi nalmembr ane,adapt i ngi twel lf ort he pr o c e s sofr e a bs o r pt i o n. • Ti ghtj unct i ons bet ween adj acentcel l s per mi tpassage ofwat erbutl i mi tt he escape ofl arg e mo l e c ul e sf r o mt het ubul a rl ume ni nt ot hei nt e r s t i t i a ls pa c e . •Thehi g hl yf o l de dba s ol a t e r a lme mbr a neo ft hec e l l sc o nt a i nsnume r o usi nt e g r a lpr o t e i nsi nv o l v e di n passi ve or act i ve t r ansport of subst ances bet ween t he i nt r acel l ul ar and i nt er st i t i al spaces. Numer ousmi t ochondri apr ovi det heATPnecessaryf ort heseact i vet r ansportpr ocesses. •T hek e yf e a t ur eo ft he s ec e l l si st ha tt he yar ehi g hl ype r me abl et owa t e ra ndma nys o l ut e s . •

Ce l l soft heThi nLoopofHe nl e •T hec e l l so ft het hi ns e g me nto ft hede s c e ndi ngl o opo fHe nl ear es i mpl es q ua mo use pi t he l i a lc e l l s . •T he s ec e l l sl a c kbr us hbo r d e r s ,whi c hr e duc e st he i rs ur f a c ea r e af o rr e a bs o r pt i o n. •Thesecel l s cont i nue t o be per meabl et o wat er ,t hey possessr el at i vel yf ew i nt egr alprot ei ns t hat f unc t i o na sac t i v et r a ns po r tmo l e c ul e sf o rr e abs or b i ngs ol ut e sf r o mt hefil t r a t e . •T heke yf e at ur eo ft he s ec e l l si st hatt he yar ehi g hl ype r me abl et owa t e rbutno tt os ol ut e s .

Cel l soft heThi ckAscendi ngLoopofHenl eandEar l yDCT •Thee pi t he l i ao ft het hi c ka s c e ndi ngl o opo fHe nl eandt heear l ydi s t a lc o nv o l ut e dt ubul ear esi mi l a r .  The yar ecomposedofcuboi dalcel l s,butt heyhav ese v er als t r uct ur aldi ffer encescompar edt ot he c e l l soft hepr o xi ma lc o nv o l ut e dt ubul e .Fo re x ampl e ,t he s ece l l sha v ef e we ra nds ma l l e rmi c r o v i l l i pr o j e c t i ngi nt ot hel ume n. •I naddi t i o n,t hel umi na lme mbr a nei sc o v er e dbyag l y c opr o t e i nl a y e r ,whi c h,al o ngwi t h‘ t i g ht e r ’t i g ht  j unct i ons,g r e at l yr e s t r i c t st hedi ffus i o no fwat e r . •Thebasol at er almembr anei ssi mi l art ot hatoft he PCT,cont ai ni ng many i nt egr alprot ei ns and cl osel yassoci at edmi t ochondri af orpassi veandact i vemembr anet r ansportpr ocesses. •The key f eat ur e oft hese cel l si st hatt hey arehi ghl y per meabl et o sol ut es,part i cul arl y sodi um c hl o r i de ,butno tt owat e r .

TheJuxt agl omer ul arAppar at us  Ast het hi c k ascendi ngl oopofHenl et r ansi t i onsi nt ot heear l ydi s t alconv ol ut ed t ubul e,t het ubul e r unsa dj a c entt ot hea ffe r e nta nde ffe r e nta r t e r i o l e s . •Wher et hecel l soft heart er i ol esand oft het hi ckascendi ngl oop ofHenl ear ei n cont actwi t h each o t he r ,t he yf o r mt hemo ni t o r i ngs t r uc t ur ec a l l e dt hej ux t a gl o me r ul a ra ppa r a t us . •Themodi fied smoot h muscl ecel l soft heart er i ol es( mai nl yt heaffer entar t er i ol e)i nt hi sareaare c al l e dj ux t a gl o me r ul a ro rJG c e l l s .The s ee nl a r g e dc e l l ss e r v easba r o r e c ep t o r ss ens i t i v et obl o od pr e s s ur ewi t hi nt hear t e r i o l e s . •Cel l soft het hi ck ascendi ngsegmenti n cont actwi t ht hear t er i ol esf orm t hemacul adensa.These c e l l smo ni t o ra ndr e s po ndt oc ha ng e si nt heo smo l a r i t yoft hefil t r a t ei nt het ubul e . •

Ce l l soft heLa t eDCTa ndCor t i c alCol l e ct i ngDuc t

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 Thecuboi dalcel l soft hel at edi s t alconv ol ut ed t ubul eand t hecor t i calcol l ect i ngductf al li nt ot wo di s t i nc ts t r uc t ur a landf unc t i o nalt y pe s :p r i nc i palc e l l sandi nt e r c al at e dc e l l s . 1.Pri  Themo r enume r ouspr i nci palcel l shav ef e w mi cr ovi l l iand basol at er alf ol ds. nci palCel l s  These speci al i z ed cel l sr espond t o cer t ai n hor mo nes t hatr egul at et he cel l ’ s per me abi l i t yt o  wat erandsol ut es,speci fical l ysodi um andpot assi um i ons.Thekeyf eat ur eofpr i nci palcel l si s t ha tt he i rpe r me a bi l i t yt owa t e ra nds o l ut e si sphy s i o l o g i c a l l yr e g ul a t e dbyho r mo ne s . 2.I  When t he aci di t y oft he body i ncr eases,t he i nt er cal at ed cel l s secr e t e nt ercal at ed Cel l s hydr ogen i onsi nt ot heur i net ores t oret heaci d/basebal anceoft hebody. Thekeyf eat ur eof i nt e r c al at e dc e l l si st he i rs e c r e t i o no fhy dr o g eni o nsf o rac i d/bas ebal anc i ng . •

Ce l l soft heMedul l ar yCol l e ct i ngDuc t Pr i nci palce l l s oft he medul l ary col l ect i ng ductar e most l y cuboi dali n shape.The l umi naland  basol at er alme mbr anes ar er el at i v el y smo ot h, and t he cel l s possess f ew mi t oc hondr i a. The per meabi l i t yoft hesecel l st owat erandur eai shormonal l yregul at edast heflui dpassest hr ough t hi sr e gi on. •Theke yf e a t ur eoft he s ec e l l si st he i rho r mo na l l yr e g ul a t e dpe r me a bi l i t yt owa t e ra ndur e a . •

Phot omi cr ogr aphsofCol l ect i ngDuct s I npho t o mi c r o g r a phso fal o ng i t udi na ls e c t i o na ndac r o s ss e c t i o no fc o l l e c t i ngduc t s ,o newi l lno t i c e t hatt heduct sar ecomposed ofcuboi dalcel l s.Thel umen oft hecol l ect i ngduct ,shown i n cr oss sect i on,i smuchl argert han t hel umensoft headj acentt hi ckascendi ngt ubul es.Thi sr eflect st he  v ol umeofflui dt hecol l ect i ngduct scont ai nast he ygat hert heflui df r om manynephr ons.

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