Topic 9: Chpt 16 and chpt 24 Flashcards
What is blood, and what is its primary function?
Blood is a connective tissue composed of cellular elements suspended in plasma. It is the circulating portion of the extracellular compartment, responsible for carrying material from one part of the body to another.
What is plasma, and what percentage of blood does it make up?
Plasma is the fluid matrix of blood, making up about 60% of the blood volume. It is composed of water (92%), proteins (7%), and dissolved organic molecules, ions, trace elements, and gases (1%).
How is total blood volume calculated for a 70-kg man and a 58-kg woman?
A 70-kg man has about 5 liters of blood (7% of body weight), with 2 liters of blood cells and 3 liters of plasma. A 58-kg woman has about 4 liters of total blood volume.
What is the composition of plasma, and how does it compare to interstitial fluid?
Plasma is composed of water (92%), proteins (7%), and dissolved organic molecules, ions, trace elements, and gases (1%). It is identical to interstitial fluid except for the presence of plasma proteins.
What are the main proteins found in plasma, and what percentage do they constitute?
The main proteins in plasma are albumins (60%), globulins, clotting protein fibrinogen, and iron-transporting protein transferrin, making up more than 90% of all plasma proteins.
Where are most plasma proteins produced, and what are immunoglobulins?
Most plasma proteins are made by the liver and secreted into the blood. Immunoglobulins (antibodies) are a type of globulin synthesized and secreted by specialized blood cells.
How do plasma proteins affect osmotic pressure and fluid balance in the body?
The presence of proteins in the plasma increases the osmotic pressure of the blood, pulling water from the interstitial fluid into the capillaries and offsetting filtration out of the capillaries created by blood pressure.
What are the functions of plasma proteins?
Plasma proteins participate in blood clotting, defense against foreign invaders, and act as carriers for steroid hormones, cholesterol, drugs, and certain ions. Some plasma proteins also act as hormones or extracellular enzymes.
What makes up the remaining 1% of plasma’s composition?
The remaining 1% of plasma is composed of dissolved organic molecules (amino acids, glucose, lipids, nitrogenous wastes), ions (Na+, K+, Cl-, H+, Ca2+, HCO3-), trace elements, vitamins, dissolved oxygen (O2), and carbon dioxide (CO2).
What is the role of albumins in the plasma?
Albumins are the most prevalent plasma proteins, making up about 60% of the total. They help maintain osmotic pressure and act as carriers for various substances in the blood.
How do plasma proteins contribute to the body’s defense mechanisms?
Plasma proteins, including immunoglobulins (antibodies), play a crucial role in the body’s defense against foreign invaders by participating in the immune response.
What role do plasma proteins play in blood clotting?
Plasma proteins such as fibrinogen are essential for blood clotting, helping to prevent excessive bleeding and promote wound healing.
How do plasma proteins function as carriers?
Plasma proteins carry steroid hormones, cholesterol, drugs, and certain ions (such as iron) through the blood, aiding in their transport and distribution throughout the body.
In what ways can plasma proteins act beyond transport and defense?
Some plasma proteins act as hormones, regulating various physiological processes, and as extracellular enzymes, catalyzing biochemical reactions outside cells.
What are the three main cellular elements found in blood?
The three main cellular elements in blood are red blood cells (RBCs or erythrocytes), white blood cells (WBCs or leukocytes), and platelets (thrombocytes).
What are red blood cells and their primary function?
Red blood cells (RBCs or erythrocytes) transport oxygen from the lungs to tissues and carbon dioxide from tissues to the lungs. They lose their nuclei by the time they enter the bloodstream.
What are platelets, and what is their role in the body?
Platelets (thrombocytes) are cell fragments that split off from megakaryocytes. They lack a nucleus and play a key role in coagulation, which is the process of blood clot formation to prevent blood loss in damaged vessels.
What are white blood cells, and what is their primary function?
White blood cells (WBCs or leukocytes) are fully functional cells that play a key role in the body’s immune responses, defending against foreign invaders such as parasites, bacteria, and viruses. Their work is usually carried out in the tissues rather than in the circulatory system.
How many types of mature white blood cells are there, and what are they?
There are five types of mature white blood cells: lymphocytes, monocytes, neutrophils, eosinophils, and basophils.
What do monocytes become when they enter tissues, and what are tissue basophils called?
Monocytes develop into macrophages when they enter tissues. Tissue basophils are called mast cells.
How are white blood cells grouped based on their characteristics?
White blood cells can be grouped as follows:
- Phagocytes (neutrophils, monocytes, macrophages) which can engulf and ingest foreign particles.
- Immunocytes (lymphocytes) responsible for specific immune responses.
- Granulocytes (basophils, eosinophils, neutrophils) which contain cytoplasmic inclusions giving them a granular appearance.
What are phagocytes, and which cells are included in this group?
Phagocytes are cells that can engulf and ingest foreign particles such as bacteria. This group includes neutrophils, monocytes, and macrophages.
What are immunocytes, and which cells are included in this group?
Immunocytes are responsible for specific immune responses directed against invaders. This group includes lymphocytes.
What are granulocytes, and which cells are included in this group?
Granulocytes contain cytoplasmic inclusions that give them a granular appearance. This group includes basophils, eosinophils, and neutrophils.
Where do all blood cells originate from?
All blood cells are descendants of a single precursor cell type known as the pluripotent hematopoietic stem cell, primarily found in bone marrow.
What is the role of pluripotent hematopoietic stem cells?
Pluripotent hematopoietic stem cells can develop into many different cell types. They first become uncommitted stem cells, then progenitor cells, which are committed to developing into specific cell types.
Into what types of cells do progenitor cells differentiate?
Progenitor cells differentiate into red blood cells, lymphocytes, other white blood cells, and megakaryocytes, the parent cells of platelets.
How common are uncommitted stem cells in the bone marrow?
Uncommitted stem cells are rare, making up about one out of every 100,000 cells in the bone marrow.
What is umbilical cord blood, and why is it significant?
Umbilical cord blood, collected at birth, is a rich source of hematopoietic stem cells used for transplants in patients with hematological diseases like leukemia.
How are uncommitted hematopoietic stem cells used in medical treatments?
These stem cells are isolated and grown to replace those killed by cancer chemotherapy. They can be obtained from bone marrow, peripheral blood, or umbilical cord blood.
What is hematopoiesis?
Hematopoiesis is the synthesis of blood cells, beginning early in embryonic development and continuing throughout life.
When and where does hematopoiesis begin in fetal development?
In the third week of fetal development, specialized cells in the yolk sac form clusters that become the endothelial lining of blood vessels and blood cells.
How does the site of blood cell production change during development?
Blood cell production spreads from the yolk sac to the liver, spleen, and bone marrow. By birth, the liver and spleen no longer produce blood cells.
Where does hematopoiesis occur in adults?
In adults, hematopoiesis occurs in the pelvis, spine, ribs, cranium, and proximal ends of long bones.
What is the difference between red and yellow marrow?
Active bone marrow is red due to hemoglobin, while inactive marrow is yellow because of adipocytes (fat cells).
Can inactive marrow resume blood cell production?
Yes, the liver, spleen, and inactive (yellow) marrow can resume blood cell production in times of need.
What percentage of developing cells in active marrow are red blood cells vs. white blood cells?
About 25% of the developing cells are red blood cells, while 75% are destined to become white blood cells.
Why must white blood cells be replaced more frequently than red blood cells?
White blood cells have a shorter lifespan than red blood cells. For example, neutrophils have a 6-hour half-life, and the body must produce over 100 million neutrophils daily. Red blood cells live for nearly four months in circulation.
What controls the production and development of blood cells?
The production and development of blood cells are controlled by cytokines, which are peptides or proteins released from one cell that affect the growth or activity of another cell.
How are newly discovered cytokines often named?
Newly discovered cytokines are often called factors, with modifiers that describe their actions, such as growth factor, differentiating factor, and trophic factor.
What are colony-stimulating factors (CSFs), and what is their role in hematopoiesis?
Colony-stimulating factors (CSFs) are cytokines made by endothelial cells, marrow fibroblasts, and leukocytes. They stimulate the growth of leukocyte colonies in culture and regulate leukocyte production and development (leukopoiesis).
What do CSFs induce in stem cells?
CSFs induce both cell division (mitosis) and cell maturation in stem cells. Mature leukocytes lose their ability to undergo mitosis.
How do existing white blood cells influence leukopoiesis?
Existing white blood cells help regulate the production of new leukocytes, allowing development to be specific and tailored to the body’s needs.
What are some examples of how differential white cell counts are used in diagnosis?
A high total number of leukocytes with increased neutrophils typically indicates a bacterial infection. A high, normal, or low white cell count with an increased percentage of lymphocytes often indicates a viral infection.
How do cytokines affect the production of leukocytes during infections?
During infections, cytokines released by active leukocytes stimulate the production of additional leukocytes. For bacterial infections, this increases neutrophils and monocytes. For viral infections, it often increases lymphocytes.
What is the significance of understanding leukopoiesis for treating diseases?
Understanding leukopoiesis helps develop treatments for diseases characterized by abnormal leukocyte levels, such as leukemias (excess leukocytes) and neutropenias (deficient leukocytes).
What was the historical significance of thrombopoietin (TPO)?
TPO was first described in 1958, and its gene was cloned in 1994. Genetically engineered TPO was used to stimulate platelet production in patients with thrombocytopenia, though the first TPO drugs had to be recalled due to adverse side effects. Newer TPO agonists are now in clinical use.
What is thrombopoietin (TPO), and what is its function?
Thrombopoietin (TPO) is a glycoprotein that regulates the growth and maturation of megakaryocytes, the parent cells of platelets. It is primarily produced in the liver.
What is erythropoietin (EPO), and how does it function in erythropoiesis?
Erythropoietin (EPO) is a glycoprotein that controls red blood cell production (erythropoiesis). It is produced mainly in the kidneys in response to hypoxia (low oxygen levels in tissues).
How does hypoxia influence erythropoietin (EPO) production?
Hypoxia stimulates the production of hypoxia-inducible factor 1 (HIF-1), which activates the EPO gene to increase EPO synthesis, promoting red blood cell production.
What was the progression of scientific discovery and clinical use of erythropoietin (EPO)?
The existence of EPO was suggested in the 1950s, purified two decades later, and its gene identified nine years after that. EPO was then produced by recombinant DNA technology for clinical use, benefiting patients undergoing chemotherapy.
What concerns have been raised about erythropoiesis-stimulating agents?
In 2007, the FDA issued new dosing instructions and warnings about the increased risk of blood clots in patients taking higher doses of erythropoiesis-stimulating agents.
What roles do interleukins play in hematopoiesis and the immune system?
Interleukins, such as IL-3, are cytokines released by white blood cells to act on other white blood cells, playing crucial roles in hematopoiesis and the immune system.
How are interleukins named, and what is an example of their function?
Interleukins are numbered once their amino acid sequences are identified, such as interleukin-3 (IL-3). They are important in immune responses and hematopoiesis.
What is the most abundant cell type in blood and how many are there per microliter?
Erythrocytes, or red blood cells, are the most abundant cell type in blood, with about 5 million per microliter. This is compared to 4,000-11,000 leukocytes and 150,000-450,000 platelets per microliter.
What are the primary functions of red blood cells?
The primary functions of red blood cells are to facilitate oxygen transport from the lungs to cells and carbon dioxide transport from cells to the lungs.
How is the ratio of red blood cells to plasma clinically indicated?
The ratio is indicated by the hematocrit, which is expressed as a percentage of total blood volume.
How is hematocrit determined?
Hematocrit is determined by drawing a blood sample into a capillary tube, centrifuging it, and measuring the column of packed red cells as a percentage of the total sample volume.
What is the normal range of hematocrit for men and women?
The normal range of hematocrit is 40-54% for men and 37-47% for women.
Why is the hematocrit test valuable?
The hematocrit test provides a rapid and inexpensive way to estimate a person’s red cell count and can be collected by simply sticking a finger.
How do red blood cells mature in the bone marrow?
In the bone marrow, committed progenitor cells differentiate into large, nucleated erythroblasts. As erythroblasts mature, the nucleus condenses, the cell shrinks, and the nucleus is pinched off and phagocytized by bone marrow macrophages. Other organelles break down, and the final immature cell, called a reticulocyte, enters circulation and matures into an erythrocyte in about 24 hours.
Describe the structure of mature red blood cells.
Mature red blood cells are biconcave disks, shaped like jelly doughnuts with the filling squeezed out. They are membranous bags filled with enzymes and hemoglobin, lacking a nucleus and mitochondria.
How do red blood cells generate ATP?
Without mitochondria, red blood cells rely on glycolysis as their primary source of ATP.
Why do red blood cells become more fragile as they age?
Red blood cells cannot make new enzymes or renew membrane components due to the lack of a nucleus and endoplasmic reticulum, leading to a loss of membrane flexibility and increased fragility.
What allows red blood cells to change shape as they pass through capillaries?
The flexibility of red blood cells is due to a complex cytoskeleton composed of filaments linked to transmembrane attachment proteins.
What are the morphological changes in red blood cells indicative of disease?
Red blood cells can become spherical in spherocytosis, crescent-shaped in sickle cell anemia, abnormally small (microcytic) in iron-deficiency anemia, and pale (hypochromic) due to lack of hemoglobin
What is hemoglobin, and what is its role?
Hemoglobin is the main component of red blood cells, responsible for oxygen transport. It is a large, complex protein with four globular protein chains, each wrapped around an iron-containing heme group.
What are the different isoforms of globin proteins in hemoglobin?
The most common isoforms are alpha, beta, gamma, and delta. Adult hemoglobin (HbA) typically has two alpha chains and two beta chains, while a small portion has two alpha chains and two delta chains (HbA2).
What is the composition of each heme group in hemoglobin?
Each heme group consists of a carbon-hydrogen-nitrogen porphyrin ring with an iron atom in the center. About 70% of the body’s iron is found in these heme groups.
Why is dietary iron important for hemoglobin synthesis?
Hemoglobin synthesis requires an adequate supply of iron, which is primarily obtained from red meat, beans, spinach, and iron-fortified bread.
How is iron absorbed and transported in the body?
Iron is absorbed in the small intestine by active transport, binds to the carrier protein transferrin, and is transported in the blood. The bone marrow uses iron to make the heme group of hemoglobin for developing red blood cells.
Where is excess iron stored in the body?
Excess iron is stored mostly in the liver inside a protein molecule called ferritin, which can release soluble iron when needed for hemoglobin synthesis.
What are the symptoms and consequences of iron toxicity?
Initial symptoms of iron toxicity include gastrointestinal pain, cramping, and internal bleeding. Severe consequences can include liver failure, which can be fatal.
How long do red blood cells live in circulation, and what happens to them as they age?
Red blood cells live for about 120 ± 20 days. As they age, they become increasingly fragile and may rupture in narrow capillaries or be engulfed by macrophages in the spleen.
What happens to the components of destroyed red blood cells?
Amino acids from hemoglobin’s globin chains are recycled into new proteins, and some iron from heme groups is reused for new heme groups. The spleen and liver convert heme remnants into bilirubin, which is processed by the liver.
How is bilirubin processed and excreted?
Bilirubin is carried by plasma albumin to the liver, metabolized, and incorporated into bile. Bile is secreted into the digestive tract, and bilirubin metabolites are excreted in feces. Some metabolites are filtered by the kidneys and contribute to the yellow color of urine.
What is jaundice, and what causes it?
Jaundice is a condition where elevated bilirubin levels cause yellowing of the skin and eyes. It can result from rapid breakdown of fetal hemoglobin in newborns or liver disease preventing bilirubin processing.
Why are newborns particularly susceptible to bilirubin toxicity?
Newborns are susceptible because their fetal hemoglobin is being broken down and replaced with adult hemoglobin, leading to elevated bilirubin levels.
What is anemia, and what are common symptoms?
Anemia is a condition where hemoglobin content is too low, leading to insufficient oxygen transport. Symptoms include tiredness and weakness, especially during exercise.
What are hemolytic anemias, and what causes them?
Hemolytic anemias occur when red blood cell destruction exceeds production. They are often hereditary, with fragile cells due to defective or deficient cytoskeletal proteins. They can also be acquired diseases.
What is hereditary spherocytosis?
Hereditary spherocytosis is a defect where the erythrocyte cytoskeleton does not link properly, making cells spherical instead of biconcave. These cells rupture easily and cannot withstand osmotic changes.
What is sickle cell disease, and what causes the sickle shape of red blood cells?
Sickle cell disease is a genetic defect where valine replaces glutamate in hemoglobin’s beta chain. This abnormal hemoglobin (HbS) crystallizes upon oxygen release, causing cells to sickle and block blood flow, leading to tissue damage and pain from hypoxia.
How is sickle cell disease treated?
One treatment involves hydroxyurea, which inhibits DNA synthesis and induces production of fetal hemoglobin (HbF), preventing HbS crystallization and sickling. Research is also exploring bone marrow transplants and gene therapy as potential cures.
What causes iron-deficiency anemia, and what are its characteristics?
Iron-deficiency anemia occurs when iron loss exceeds intake, slowing hemoglobin synthesis. It results in low red blood cell count or low hemoglobin content, causing smaller (microcytic) and paler (hypochromic) red blood cells.
Why are women who menstruate more likely to suffer from iron-deficiency anemia?
Menstruating women are more likely to suffer from iron-deficiency anemia due to iron loss in menstrual blood.
What is polycythemia vera, and what are its effects?
Polycythemia vera is a stem cell dysfunction producing too many blood cells, causing high hematocrit levels (60-70%). This increases blood viscosity, making it more resistant to flow through the circulatory system.
What happens to hematocrit levels when an athlete overhydrates?
Overhydration temporarily decreases hematocrit due to increased plasma volume. Correcting the volume overload restores normal hematocrit levels.
What is relative polycythemia, and what causes it?
Relative polycythemia occurs when red blood cell count is normal, but hematocrit is elevated due to low plasma volume, such as in dehydration.
What are common causes of jaundice in newborns and adults?
In newborns, jaundice is caused by the breakdown of fetal hemoglobin and replacement with adult hemoglobin. In adults, it is commonly caused by liver disease preventing bilirubin processing and excretion.
What is the role of the spleen in red blood cell turnover?
The spleen filters and engulfs old and fragile red blood cells, breaking them down and recycling components like amino acids and iron.
How is bile related to bilirubin, and what is its function in the body?
Bile, produced in the liver, contains metabolized bilirubin. It is secreted into the digestive tract to aid in digestion and excretion of bilirubin metabolites through feces.
How can sickle cell disease impact blood flow and oxygen delivery?
Sickle-shaped cells can block blood flow in small vessels, causing hypoxia, tissue damage, and pain. This obstruction prevents adequate oxygen delivery to tissues.
What are the potential consequences of untreated iron-deficiency anemia?
Untreated iron-deficiency anemia can lead to severe fatigue, weakness, and compromised immune function due to inadequate oxygen transport to tissues.
What are the symptoms and treatment options for polycythemia vera?
Symptoms include increased blood viscosity and resistance to flow. Treatment may involve phlebotomy, medications to reduce blood cell production, and managing symptoms to prevent complications.
What diagnostic tests are used to identify anemia and other red blood cell disorders?
Diagnostic tests include complete blood counts (CBC), hematocrit measurements, and examining red blood cell morphology and hemoglobin content.
What happens to red blood cells in hypertonic and hypotonic media?
In hypertonic media, red blood cells shrink and develop a spiky surface. In hypotonic media, they swell and form a sphere without membrane disruption.
What does the morphology of red blood cells indicate?
The morphology of red blood cells can provide clues to the presence of diseases, such as spherocytosis (spherical shape), sickle cell anemia (sickle shape), and iron-deficiency anemia (microcytic and hypochromic cells).
How is hemoglobin structured, and what are its components?
Hemoglobin is a large, complex protein with four globular protein chains, each wrapped around an iron-containing heme group. It has several isoforms, including alpha, beta, gamma, and delta chains.
What are the dietary sources of iron, and how is iron absorbed?
Dietary sources of iron include red meat, beans, spinach, and iron-fortified bread. Iron is absorbed in the small intestine by active transport.
How is iron transported and stored in the body?
Iron is transported in the blood by the carrier protein transferrin. Excess iron is stored in the liver within a protein molecule called ferritin.
How does hydroxyurea treat sickle cell disease?
Hydroxyurea inhibits DNA synthesis and induces the production of fetal hemoglobin (HbF), which prevents HbS crystallization and red blood cell sickling.
What are some acquired causes of hemolytic anemia?
Acquired causes of hemolytic anemia include immune reactions, infections, drugs, and exposure to toxic chemicals. These factors can lead to increased destruction of red blood cells.
What is the role of albumin in bilirubin transport?
Albumin binds to bilirubin in the plasma and transports it to the liver for processing and excretion in bile.
What is mean corpuscular volume (MCV), and what does it indicate?
Mean corpuscular volume (MCV) is the size of red blood cells. It can be abnormally large or small in certain diseases, indicating the presence of conditions such as iron-deficiency anemia (microcytic cells).
How do macrophages in the spleen contribute to red blood cell turnover?
Macrophages in the spleen engulf old and fragile red blood cells, breaking them down and recycling their components such as amino acids and iron.
What is hyperbilirubinemia, and how does it manifest?
Hyperbilirubinemia is elevated bilirubin levels in the blood, causing jaundice, which results in yellowing of the skin and eyes.
How does bilirubin contribute to the color of urine and feces?
Bilirubin metabolites are filtered from the blood by the kidneys, contributing to the yellow color of urine. It is also incorporated into bile and excreted in feces, contributing to their color.
What is the role of scavenging macrophages in red blood cell turnover?
Scavenging macrophages in the spleen engulf and digest old red blood cells, recycling their components like amino acids and iron.
How are platelets produced, and what is their origin?
Platelets are cell fragments produced in the bone marrow from huge cells called megakaryocytes. Megakaryocytes develop their large size by undergoing DNA replication up to seven times without nuclear or cytoplasmic division, resulting in a polyploid cell with a lobed nucleus.
How do megakaryocytes contribute to platelet formation?
The outer edges of megakaryocytes extend through the endothelium into the lumen of marrow blood sinuses, where the cytoplasmic extensions fragment into disk-like platelets.
What are the characteristics and components of platelets?
Platelets are smaller than red blood cells, colorless, and lack a nucleus. Their cytoplasm contains mitochondria, smooth endoplasmic reticulum, and numerous membrane-bound vesicles called granules, which are filled with a variety of cytokines and growth factors.
How many types of granules are found in platelets, and what do they contain?
There are at least three different types of granules in platelets. One type of granule contains more than 280 different proteins, including VEGF (promotes angiogenesis) and matrix metalloproteinases (MMPs).
What is the lifespan of platelets, and what are their primary roles?
Platelets have a typical lifespan of about 10 days. They are best known for their role in helping stop blood loss but also act as immune cells and mediators of the inflammatory response.
How do platelets contribute to the immune system and inflammation?
Platelets help the immune system fight infectious diseases such as malaria and may contribute to the inflammatory process of atherosclerosis.
What is Platelet-Rich Plasma (PRP) therapy, and what is its intended benefit?
PRP therapy involves using the growth factors and cytokines inside platelet granules to promote healing of tendons and ligaments, which have minimal blood supply and heal slowly. The therapy gained popularity after Tiger Woods used it for knee surgery recovery.
Describe the size and color of platelets and their life span.
Platelets are smaller than red blood cells, colorless, and have a typical lifespan of about 10 days.
What types of proteins are found in the granules of platelets?
The granules in platelets contain more than 280 different proteins, including VEGF (which promotes angiogenesis) and matrix metalloproteinases (MMPs).
How do megakaryocytes become polyploid?
Megakaryocytes become polyploid by undergoing DNA replication up to seven times without nuclear or cytoplasmic division.
What role do platelets play in the inflammatory response?
Platelets act as immune cells and mediators of the inflammatory response, helping the immune system fight infections like malaria and contributing to the inflammatory process of atherosclerosis.
What is the role of megakaryocytes’ lobed nuclei?
The lobed nuclei result from megakaryocytes undergoing DNA replication up to seven times without nuclear or cytoplasmic division, creating a polyploid cell with multiple copies of its DNA.
Describe the cytoplasmic extensions of megakaryocytes.
The cytoplasmic extensions of megakaryocytes extend through the endothelium into marrow blood sinuses and fragment into disk-like platelets.
What is the theory behind PRP therapy for tendons and ligaments?
The theory behind PRP therapy is that growth factors and cytokines inside platelet granules will promote healing in tendons and ligaments, which have minimal blood supply and are notoriously slow to heal.
How do platelets contribute to the body’s response to infectious diseases?
Platelets help the immune system fight infectious diseases such as malaria, acting as immune cells and mediators of the inflammatory response.
Why is it challenging for the body to repair a damaged blood vessel while maintaining blood flow?
The body must plug holes in damaged blood vessels without blocking the vessel entirely, as cells downstream need oxygen and nutrients. The repair “patch” must also withstand blood pressure to avoid being blown out.
What are the first steps taken by the body to stop blood loss from a damaged vessel?
The body first decreases pressure in the vessel to create a secure mechanical seal in the form of a blood clot. Once the clot is in place and blood loss has stopped, the body’s repair mechanisms take over, dissolving the clot and clearing debris.
Define hemostasis and its importance.
Hemostasis (from haima, blood + stasis, stoppage) is the process of keeping blood within a damaged blood vessel. It is crucial to prevent excessive blood loss and maintain circulatory system integrity.
What is the opposite of hemostasis?
The opposite of hemostasis is hemorrhage (from -rrhagia, abnormal flow), which is the uncontrolled flow of blood from a damaged vessel.
What are the three major steps of hemostasis?
The three major steps of hemostasis are: 1) vasoconstriction, 2) temporary blockage of a break by a platelet plug, and 3) coagulation, the formation of a clot that seals the hole until tissues are repaired.
Describe the first step of hemostasis.
The first step is immediate constriction of damaged vessels (vasoconstriction) to decrease blood flow and pressure within the vessel temporarily. This can be aided by applying pressure to a bleeding wound.
What causes vasoconstriction during hemostasis?
Vasoconstriction is caused by paracrine molecules released from the endothelium of the damaged vessel.
What happens during the second step of hemostasis?
The second step involves the mechanical blockage of the hole by a loose platelet plug. Platelet adhesion occurs, where platelets stick to exposed collagen, become activated, release cytokines, and aggregate to form a plug.
How do platelets become activated, and what role do they play in hemostasis?
Platelets become activated by adhering to exposed collagen in the damaged area. Activated platelets release cytokines that reinforce vasoconstriction and activate more platelets, forming a loose platelet plug.78
What is an example of a positive feedback loop in hemostasis?
Platelets activating more platelets is an example of a positive feedback loop.
Describe the third step of hemostasis.
The third step is the formation of a fibrin protein mesh that stabilizes the platelet plug to form a clot. This involves a series of enzymatic reactions known as the coagulation cascade.
What is the coagulation cascade, and what is its end product?
The coagulation cascade is a series of enzymatic reactions that result in the formation of fibrin, a protein that stabilizes the platelet plug to form a clot.
How do exposed collagen and tissue factor contribute to hemostasis?
Exposed collagen and tissue factor initiate the formation of a fibrin protein mesh by triggering the coagulation cascade.
What role does fibrin play in hemostasis?
Fibrin stabilizes the platelet plug to form a stable clot that seals the hole in the damaged vessel.
What happens as the damaged vessel repairs itself?
As the damaged vessel repairs itself, the clot retracts, and fibrin is slowly dissolved by the enzyme plasmin. Scavenger leukocytes ingest and destroy the debris.
What is the role of plasmin in hemostasis?
Plasmin slowly dissolves the fibrin in the clot, aiding in clot retraction and removal as the wound heals.
Why is it important to maintain the proper balance during hemostasis?
Proper balance is crucial because too little hemostasis can lead to excessive bleeding, while too much can create a thrombus, a blood clot that can block the vessel and stop blood flow.
What is a thrombus, and why is it dangerous?
A thrombus is a blood clot that adheres to the undamaged wall of a blood vessel. A large thrombus can block the vessel’s lumen, stopping blood flow, which can be dangerous.
What happens when a blood vessel wall is first damaged?
When a blood vessel wall is damaged, exposed collagen and chemicals from endothelial cells activate platelets. Normally, the endothelium separates collagenous matrix fibers from circulating blood, but damage exposes the collagen, causing platelets to adhere.
How do platelets adhere to collagen, and what helps them?
Platelets adhere to collagen with the help of integrins, which are membrane receptor proteins linked to the cytoskeleton. Binding activates platelets, causing them to release contents of their intracellular granules.
What substances do activated platelets release?
Activated platelets release serotonin (5-hydroxytryptamine), ADP, and platelet-activating factor (PAF). PAF sets up a positive feedback loop by activating more platelets and initiating pathways that convert platelet membrane phospholipids into thromboxane A2.
What are the roles of serotonin and thromboxane A2 in hemostasis?
Serotonin and thromboxane A2 are vasoconstrictors. They also contribute to platelet aggregation, along with ADP and PAF, leading to the formation of a growing platelet plug that seals the damaged vessel wall.
What prevents the platelet plug from spreading beyond the injury site?
Platelets do not adhere to normal endothelium. Intact vascular endothelial cells convert their membrane lipids into prostacyclin, an eicosanoid that blocks platelet adhesion and aggregation. Nitric oxide released by normal endothelium also inhibits platelet adhesion.
How does the combination of platelet attraction and repulsion create a localized response?
Platelet attraction to the injury site and repulsion from the normal vessel wall create a localized response that limits the platelet plug to the area of damage.
What is coagulation, and how does it convert a platelet plug into a clot?
Coagulation is the process by which fluid blood forms a gelatinous clot. It involves two pathways (intrinsic and extrinsic) that merge into one, leading to the creation of thrombin, which converts fibrinogen into insoluble fibrin polymers that stabilize the platelet plug.
Describe the intrinsic pathway of coagulation.
The intrinsic pathway, also known as the contact activation pathway, begins when damage to tissue exposes collagen. Collagen activates factor XII, starting the cascade. This pathway uses proteins already present in the plasma.
Describe the extrinsic pathway of coagulation.
The extrinsic pathway, also called the cell injury pathway or tissue factor pathway, starts when damaged tissues expose tissue factor (factor III). Tissue factor activates factor VII, initiating the extrinsic pathway.
What happens when the intrinsic and extrinsic pathways of coagulation converge?
The two pathways converge at the common pathway to create thrombin, the enzyme that converts fibrinogen into insoluble fibrin polymers. These fibrin fibers become part of the clot.
How was coagulation initially regarded, and what is the current understanding?
Coagulation was initially regarded as a simple cascade, with each enzyme converting an inactive precursor into an active enzyme. Current understanding shows that it is a complex network with interactions between intrinsic and extrinsic pathways, sustained by positive feedback loops
What is the final step of coagulation?
The final step of coagulation is the conversion of fibrinogen into fibrin, catalyzed by thrombin. Fibrin fibers weave through the platelet plug and trap red blood cells within their mesh, stabilizing the clot.
How is the clot stabilized?
Active factor XIII converts fibrin into a cross-linked polymer, stabilizing the clot.
