Review of A&P I and II -- Let's Help Each Other Out

Alicia18 · May 22, 2006

For whoever mentioned it on the summer break thread, I that find hemostasis, intrinsic and extrinsic, has slipped my mind. Will research on my own, but might cool to have discussion or something.

Alicia18 · May 22, 2006

Hemostasis is involved in creating a blood clot. A good link with a mini-video is http://www.mhhe.com/biosci/esp/2002_general/Esp/folder_structure/tr/m1/s7/trm1s7_3.htm

I believe that the difference between extrinsic and intrinsic mechanisims is that the clotting process is started by COLLAGEN seeping into the blood vessel from the OUTSIDE for EXTRINSIC, and CHEMICAL FACTORS from INSIDE the blood vessel triggering the clotting process for INTRINSIC.

I'm not completely certain on this part, though, and would appreciate if someone could perhaps make more clear exactly what happens during these two hemostatic processes.

Okay, I've started the ball rolling. Someone else's turn.

Please?

atrice, BSN, RN · May 22, 2006

Sounds cool....but first I have to get started. I took A&P I in the spring of 04' and A&P II during fall of 04'.....and micro. in the spring of 05'. The last year (fall 05' & sping 06') has been basically a blow off year of just waiting to apply. I had 2 gen. courses to take so i had to put off applying a whole year. My school figures in gpa, hesi score.....along w/ all gen./prereq classes complete toward the degree. If you don't have everything complete you might as well forget about getting in.....so I really need to review!!!!!

atrice, BSN, RN · May 22, 2006

The extrinsic pathway begins outside the bldstrm., in the vessel wall.

The intrinsic pathway begins inside the bldstrm., w/ the activation of a circulating proenzyme.

These two pathways converge at the common pathway.

The Extrinsic Pathway:

-begins w/ the release of Factor III by damaged peripheral tissues or endothelial cells.

-the greater the damage, the more tissue factor is released & the faster clotting occurs.

-Factor III (aka- tissue factor [TF]) then combines w/ Ca 2+ and another clotting factor (Factor VII) to form an enzyme complex capable of activating Factor X.

The Intrinsic Pathway:

-begins w/ the activation of proenzymes (usually Factor XII) exposed to collagen fibers @ the injury site.

-the pathway continues w/ assistance of PF-3, a platelet factor released by aggregating platelets.

-platelets also release a variety of other factors that accelerate the reactions of the intrinsic pathway.

-after a series of linked reactions, activated Factors VIII & IX combine to form an enzyme complex capable of activating Factor X.

The Common Pathway (clot formation):

-Begins when enzymes from either the extrinsic or intrinsic pathway activate Factor X, forming the enzyme prothrombinase.

-Prothrombinase converts the proenzyme prothrombin into the enzyme thrombin.

-Thrombin then completes the clotting process by converting fibrinogens, a plasma protein, to insoluble strands of fibrin.

So, you have:

Factor X-->prothrominase-->thrombin-->fibrinogen-->fibrin-->forms clot.

Alicia18 · May 22, 2006

I truly must not have understood this concept when I studied it. I kick myself now for selling my book. Would you say that, following the definitions given below, that extrinsic hemostasis is the same as primary hemostasis and that intrinsic hemostasis is the same as secondary hemostasis. This question can be for anyone who wishes to answer. i'm having very little luck finding good websites to answer my questions...

Primary hemostasis is characterized by vascular contraction, platelet adhesion and formation of a soft aggregate plug. It begins immediately after endothelial disruption. Injury causes temporary local contraction of vascular smooth muscle. Vasoconstriction slows blood flow, enhancing platelet adhesion and activation.

Adhesion occurs when circulating von Willebrand factor(vWf) attaches to the subendothelium. Next, glycoproteins on the platelet surface adhere to the "sticky" von Willebrand factor(vWf). Platelets collect across the injured surface. These platelets are then "activated" by contact with collagen. Collagen-activated platelets form pseudopods which stretch out to cover the injured surface and bridge exposed fibers. The collagen-activated platelet membranes expose receptors which bind circulating fibrinogen to their surfaces. Fibrinogen has many platelet binding sites. An aggregation of platelets and fibrinogen build up to form a soft plug. Platelet aggregation occurs about 20 seconds after injury.

Primary hemostasis is short lived. The immediate post injury vascular constriction abates quickly. If flow is allowed to increase, the soft plug could be sheared from the injured surface, possibly creating emboli.

Secondary hemostasis is responsible for stabilizing the soft clot and maintaining vasoconstriction. Vasoconstriction is maintained by platelet secretion of serotonin, prostaglandin and thromboxane. The soft plug is solidified through a complex interaction between platelet membrane, enzymes, and coagulation factors.

Coagulation factors are produced by the liver and circulate in an inactive form until the coagulation cascade is initiated. The cascade occurs in steps. The completion of each step activates another coagulation factor in a chain reaction which leads to the conversion of fibrinogen to fibrin.

wildmountainchild · May 24, 2006

I've been a teacher's aide and a professional tutor for anatomy and physiology for two semesters now. My number one reference for my students isn't the textbook or the atlas........it's the coloring book.

Both the anatomy and the physiology coloring books break things down into suprisingly simple (yet technically correct) explanations with very relevant illustrations. BUT....make sure you get the correct books. The author for the text varies between the two books but the illustrator is the same, his name is Wynn Kapit. The Princeton Review coloring books are too abstract and the explanations blow.

If you want to review I recommend coloring! The physio book is arranged into plates explaing different physiological functions with illustrations facing the text. One page of the coloring book text explains what a whole chapter of the physio textbook was trying to get across.

I even use them both as reference books when I want to look something up. If I need to go intomore detail, then I go to the textbooks.

Seriously, pick these great books up! All my students who used them showed increased understanding, increased retention, and were less stressed out during class b/c they understood the info thouroughly.

Good luck. :idea: