Main Difference – Hemostasis vs Homeostasis
Animals are multicellular organisms and their bodies are made up of trillions of cells. In order to work as a single unit, the functions of the cells must be regulated. Hemostasis and homeostasis are two processes involved in the regulation of the functions of the body. The main difference between hemostasis and homeostasis is that hemostasis is the mechanism that helps the circulatory system to perfuse the right organs whereas homeostasis is the mechanism by which the biological system maintains an equilibrium state. Hemostasis prevents bleeding through wound healing and blood clotting. The endocrine system of the body is involved in homeostasis.
Key Areas Covered
1. What is Hemostasis
– Definition, Steps, Function
2. What is Homeostasis
– Definition, Types, Function
3. What are the Similarities Between Hemostasis and Homeostasis
– Outline of Common Features
4. What is the Difference Between Hemostasis and Homeostasis
– Comparison of Key Differences
Key Terms: Blood Clotting, Hemostasis, Negative Feedback Loops, Platelet Plug, Positive feedback Loops, Primary Homeostasis, Secondary Hemostasis, Vascular Spasm, Vasoconstriction
What is Hemostasis
Hemostasis refers to the arrest of the escape of blood from the circulation system in animals. The blood can escape from the circulation system either naturally by clot formation or vessel spasm or artificially by compression or ligation. During hemostasis, the blood flow is slowed down and a clot is formed to prevent the blood loss. The hemostasis changes blood from a liquid to a gelatinous state.
Steps Involved in Hemostasis
Three steps are involved in the hemostasis that occurs in a rapid sequence;
- vascular spasm
- formation of a platelet plug
- blood clotting.
The ceasing of the blood flow initiates the tissue repair.
Figure 1: Hemostasis Steps
The main steps involved in hemostasis are shown in figure 1.
Vascular spasm (Vasoconstriction)
Vascular spasm refers to the narrowing of blood vessels to reduce the blood flow during injury while clot formation. It is mediated by the contraction of the smooth muscles lining a blood vessel. An injury to a vascular smooth muscle triggers the vasoconstriction response. The injured endothelial cells secrete signaling molecules to activate platelets such as thromboxane A2. The intense contraction of the blood vessels increases the blood pressure of the affected, large blood vessels. In small blood vessels, it brings the internal walls of the vessels together, stopping the blood flow completely.
Formation of a Platelet Plug
The formation of a platelet plug is the beginning of the blood clot formation. Platelet adherence, activation, and aggregation are the three steps of the formation of the platelet plug.
Platelet Adherence
The exposed subendothelial collagen releases von Willebrand Factor (VWF) during the injury, allowing the platelets to form adhesive filaments. These filaments facilitate the adherence of the platelets with the subendothelial collagen.
Platelet Activation
The binding of the subendothelial collagen to the receptors of the adhered platelets activates them. The activated platelets release various chemicals including ADP and VWF, allowing more platelets to bind to the adhered platelets.
Platelet Aggregation
During platelet aggregation, new platelets aggregate with the barrier to form the plug. The VWF serves as the glue between platelets themselves and platelets and the subendothelial collagen. The aggregation of platelets is shown in figure 2.
Figure 2: Platelet Aggregation
The small wounds will be completely covered with the platelet plug. But if the wound is large enough to flow the blood out from the vessel, a fibrin mesh is produced by the coagulation cascade, preventing the bleeding. Thus, the formation of the platelet plug is referred to as the primary hemostasis while the coagulation cascade is referred to as the secondary hemostasis.
Blood Clotting
Blood clotting is the process by which a blood clot is formed by coagulation in order to prevent further bleeding during the injury. It occurs through a series of reactions known as the coagulation cascade. The three pathways involved in the blood clotting are the intrinsic (contact) pathway, extrinsic (tissue factor) pathway, and the common pathway. Both intrinsic and extrinsic pathway feed into the common pathway.
Intrinsic Pathway
The intrinsic pathway is induced by the contact of the negatively-charged molecules such as lipids or molecules from bacteria. It finally activates the factor X in the common pathway.
Extrinsic Pathway
The extrinsic pathway releases thrombin that cleaves fibrinogen into fibrin. The fibrin is a component of the coagulation cascade, which aids the blood vessel repair. This pathway is initiated by the release of tissue factor III by the damages tissues, activating factor X to convert prothrombin into thrombin.
Common Pathway
The prothrombin is converted into thrombin by the activated factor X by either of the above two pathways. The ultimate formation of fibrin forms the mesh, strengthening the platelet plug.
What is Homeostasis
Homeostasis refers to the tendency to maintain a relatively stable internal condition by a system of feedback controls. The endocrine system of the body plays a vital role in homeostasis, regulating the activity of the body via the action of hormones. The hormones are released into the circulation by the stimulation of the endocrine organs by a stimulus. The amount of hormone released is determined depending on the stimulus. Homeostasis is maintained by the feedback mechanisms. The negative feedback loops are involved in the majority of the homeostasis, maintaining the system at the set point. The positive feedback loops move the system away from its initial state.
Negative Feedback Loops
The negative feedback loops draw the change to its reverse direction, maintaining a constant, internal environment. The stimulus is recognized by the sense organs of the body. The nerve impulses are transmitted to the corresponding control centers of the brain. The information from the brain is transmitted to the effector organs. The regulation of the body temperature in warm-blooded animals is an example of a negative feedback loop. The mechanism of action of a negative feedback loop and the regulation of the body temperature is shown in figure 3.
Figure 3: Body Temperature Regulation
The maintenance of the oxygen/carbon dioxide balance, blood sugar levels, blood pressure, acid/base balance, water balance (osmoregulation), calcium levels, blood pH, and energy balance are the examples of other negative feedback loops.
Positive Feedback Loops
Positive feedback loops are involved in the amplification of the stimulus. During childbirth, the uterine contractions are stimulated by oxytocin. The release of more oxytocin produces stronger contractions.
Similarities Between Hemostasis and Homeostasis
- Hemostasis and homeostasis are two mechanisms involved in the maintenance of the functions of the body.
Difference Between Hemostasis and Homeostasis
Definition
Hemostasis: Hemostasis is the stopping of a flow of blood from the circulation system in animals.
Homeostasis: Homeostasis is the tendency to maintain a relatively stable internal condition by a system of feedback controls.
Significance
Hemostasis: Hemostasis helps the circulatory system to perfuse the right organs.
Homeostasis: Homeostasis is the mechanism by which the biological system maintains an equilibrium state.
Function
Hemostasis: Hemostasis prevents blood loss from the circulation when a blood vessel is ruptured.
Homeostasis: Homeostasis maintains stable internal conditions.
Examples
Hemostasis: Wound healing and blood clotting occur in hemostasis.
Homeostasis: Regulation of the body temperature, acidity, and alkalinity occurs in homeostasis.
Conclusion
Hemostasis and homeostasis are two processes that maintain the proper functioning of the body. Hemostasis prevents the blood loss from the circulation system while homeostasis maintains a constant internal environment. The main difference between hemostasis and homeostasis is the role of each process.
Reference:
1. “Hemostasis.” Hemostasis | Boundless Anatomy and Physiology, Available here.
2. “Homeostasis (Article).” Khan Academy, Available here.
Image Courtesy:
1. “1909 Blood Clotting” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia
2. “Thrombocyte aggregation” By Dietzel65, Steffen Dietzel – Own work (CC BY-SA 3.0) via Commons Wikimedia
3. “105 Negative Feedback Loops” By OpenStax (CC BY 4.0) via Commons Wikimedia
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