hematology and wound healing

what is the pathophysiology of hematopoeisis?

• formation of blood

• sickle cell disease

• anemias: iron, vitamin B12, folic acid, deficiencies; chronic disease/inflammation

what is the pathophysiology of hemostasis?

• maintenance of blood

• platelet disorders

• coagulation disorders: e.g. hemophilia, von Willebrand disease, clotting factor deficiencies

• stroke

• wound healing

what is hematopoiesis?

• formation of blood cellular components

• plasma: water (92%), proteins (7%), salts, organic molecules, gases (1%)

• cellular elements: RBCs, platelets (split off from megakaryocytes), WBCs

what is hematocrit?

• ratio of RBCs to plasma, expressed as a % after centrifugation

• percentage of total blood volume occupied by packed (centrifuged RBCs)

what is erythropoiesis?

production of RBCs

what is leukopoiesis?

production of WBCs

what is the complete blood count?

• hematocrit: the % of total blood volume occupied by packed (centrifuged) RBCs
• hemoglobin: reflects the O-carrying capacity of RBCs
• red cell count
• total white count: includes all types of leukocytes, but does not distinguish between them
• differential white cell count: presents estimates of the relative proportions of the 5 types of leukocytes
• platelets: suggestive of the blood's ability to clot
• mean corpuscular volume, hemoglobin, hemoglobin concentration

what are red blood cells?

• crucial for their O-carrying capacity
• responsibility falls within the RBC Hb
• each human RBC contains ~270 million of Hb molecules
• each Fe atom with Hb bind 1 O molecule

what is hemoglobin?

• composed of 4 globin chains (2 ⍺, 2 β), each centered around a heme group
• each heme group consists of a porphyrin ring with and iron atom at the center

what is the development of RBC in the bone marrow?

• mature blood cells squeeze through the endothelium to reach the circulation
• fragments of megakaryocyte break off to become platelets
• the stroma is composed of fibroblast-like reticular cells, collagenous fibers, and extracellular matrix

what is the stimulation of erythropoiesis?

• regulated by a feedback loop
• a decrease in tissue O concentration signals the kidneys to increase the production and release of erythropoietin into the plasma, which increases production and maturation of RBCs
• under normal circumstances, the RBC mass is kept at an almost constant level by EPO, matching new erythrocyte production to the natural rate of loss of RBCs

what is the process of the Hb and red cell lifecycle?

→ iron ingested from the diet
→ iron absorbed by active transport
→ transferring protein transports Fe in plasma
→ bone marrow uses Fe to make Hb as a part of RBC synthesis
→ RBCs live ~120 days in the blood
→ spleen destroys old RBCs and converts Hb to bilirubin
→ bilirubin and metabolites are excreted in urine and feces
→ liver metabolizes bilirubin and excretes it in bile
→ liver stores excess Fe as ferritin

what is sickle cell anemia?

• the most common familial hemolytic anemia
• caused by a mutation in β-globin that creates sickle Hb (HbS): its presence is protective against falciparum malaria
• selective pressure in the HbS allele is prevalent in areas where malaria is/was endemic
• in the US, ~8% of people of African descent are heterozygous HbS carriers, and ~1 in 600 have sickle cell anemia

what is the pathogenesis of sickle cell anemia?

• the sickling of red cells is initially reversible on reoxygenation
• membrane distortion produced by each sickling episode leads to damage to the membrane skeleton
• with time, the cumulative damage creates irreversibly sickled cells that are prone to hemolysis

what are the major pathologic consequences of the sickling of red cells?

• chronic moderately severe hemolytic anemia, due to red cell membrane damage
• vascular obstruction: result in ischemic tissue damage and pain crisis

what is the process of sickle cell anemia leading to microvascular occlusion?

→ RBC containing HbS
→ deoxygenation
→ reversibly sickled cell
→ inflammation, increased transit time, expression of adhesive molecules by sickle cells
→ microvascular occlusion

what are anemias?

• affects a large part of the world's population (~25%)
• group of diseases characterized by a decrease in either Hb or circulating RBCs, resulting in reduced O-carrying capacity of the blood
• can result from inadequate RBC production, increased RBC destruction, or blood loss

what is hemorrhage?

directly associated with blood loss

what are production anemias?

• folate/vitamin B12 deficiency: limits RBC production
• iron deficiency: limits Hb production

what are destruction anemias?

• inflammation
• autoimmune: marked for premature destruction
• drug-induced immune/hemolytic: marked for premature destruction

what is hemostasis?

• precisely orchestrated process involving platelets, clotting factors, and endothelium

• occurs at the site of vascular injury

• leads to the formation of a blood clot, which serves to prevent/limit the extent of bleeding

• primary/secondary

what is primary hemostasis?

• keeps blood inside the damaged blood vessel
• vasoconstriction, platelet plug, coagulation

what is secondary hemostasis?

• involves the coagulation cascade for the deposition of fibrin and clot stabilization

• maturity of the platelet plug

• production of fibrin

what are the key mechanisms that facilitate hemostasis?

• vascular constriction

• primary platelet plug formation: primary hemostasis

• clot propagation through fibrin formation: secondary hemostasis

• clot breakdown through fibrinolysis

what is the process of platelet plug formation?

→ intact endothelium releases prostacyclin and NO, preventing platelet adhesion
→ exposed collagen in damaged blood vessel wall binds and activates platelets
→ release of platelet factors
→ factors attract more platelets
→ platelets aggregate into platelet plug

what is platelet adhesion?

mediated largely by interactions with vWF: acts as a bridge between the platelet surface receptor glycoprotein Ib (GpIb) and exposed collagen

what is platelet activity?

• platelet adhesion
• platelets rapidly change shape following adhesion, converting from smooth discs to spiky "sea urchins" with greatly increased surface area
• secretion of granule contents
• platelet aggregation

what is platelet aggregation?

• follows their activation
• the conformational change that occurs with platelet activation allows binding of fibrinogen, which forms bridges between activated platelets, leading to their aggregation

what is the secretion of granule contents?

• release reaction; degranulation
• occurs along with changes in shape
• the 2 events are often referred to together as platelet activation

what is the coagulation summary?

• prothrombinase complex, activated by protein C, converts prothrombin to thrombin
• thrombin causes the accumulation of fibrinogen and platelets
• plasminogen activator converts plasminogen to plasmin
• plasmin dissolves fibrin clots

what is the importance of the endothelium in coagulation?

• the balance between the anticoagulant and procoagulant activities of endothelium often determines whether clot formation, propagation, or dissolution occurs
• the antithrombotic properties of endothelium can be divided into activities directed at platelets, coagulation factors, and fibrinolysis

what are the factors that inhibit thrombosis?

• heparin-like molecule: inactivates thrombin and other coagulation factors

• tissue factor pathway inhibitor: inactivates tissue factor-VIIa complexes

• endothelial protein C receptor and thrombomodulin: activates protein C (requires protein S), which then inactivates factors Va and VIIIa

endothelial effects:

• PGI2, NO, adenosin diphosphatase: inhibits platelet aggregation

• t-PA: activates fibrinolysis

what are bleeding/coagulation disorders?

• may stem from abnormalities of vessels (including their supportive connective tissue), platelets, or coagulation factors, alone, or in combination
• bleeding may result from systemic conditions that inflame/damage endothelial cells
• deficiencies of platelets (thrombocytopenia): an important cause of bleeding
• in disorders stemming from defects in one or more coagulation factors

what are the disorders of primary hemostasis involved with platelets due to?

• increased destruction of platelets, which can be immune-mediated or non-immune-mediated

• decreased production of platelets

• platelet dysfunction

• contraction of the vessel wall

• plug and fibrin formation

what is platelet destruction?

• heparin-induced thrombocytopenia (HIT syndrome)
• immune reaction to the use of heparin, leading to paradoxical hypercoagulation and reduced platelet count

what are the platelet deficiencies caused by?

• glanzmann thrombasthenia: conformational change of GpIIb-IIa complex
• von Willebrand disease: binding of GpIb to von Willebrand factor
• bernard-soulier syndrome: GpIb

what is hemophilia?

• inherited defects involving coagulation factors
• types: A, B, C

what is von willebrand disease?

inherited defects involving coagulation factors

what is hemophilia A?

• most common type: 8 out of 10 people
• do not have enough cloting factor VIII

what is hemophilia B?

• aka Christmas disease
• less common type
• caused by a deficiency in clotting factor IX

what is hemophilia C?

• aka deficiency of factor XI
• mild form
• inherited differently from hemophilia A/B
• can be passed to both male and female children

what is hypercoagulability?

• refers to an abnormally high tendency of the blood to clot
• usually caused by alterations in coagulation factors
• important risk factor for thrombosis
• alterations that lead to hypercoagulability can be divided into primary (genetic) and secondary (acquired) disorders

what is thrombosis?

• thrombus: a solid mass within a chamber of the heart or within a blood vessel
• thrombi can develop anywhere in the cardiovascular system

what are the factors predisposing to thrombus formation?

• e.g. virchow triad
• stasis of blood (e.g. due to congestive heart failure, obesity, immobilization): particularly common predisposing condition in patients who develop venous thrombi
• hypercoagulability: hypercoagulable states may contribute to the development of thrombi in any location, and include hereditary conditions and various acquired states
• endothelial damage: plays a major role in many arterial thrombi

what are the hereditary conditions predisposing to thrombosis?

• i.e. primary hypercoagulable states
• factor V leiden mutation: mutation in the factor V gene (incidence of 2-15% of the Caucasian population)
• prothrombin gene mutation: causes an elevated level of prothrombin (incidence of 1-2% of the general population)

what are acquired states predisposing to thrombosis?

• i.e. secondary hypercoagulable states
• myocardial infarct, tissue damage (e.g. surgery, trauma, burns), cancer, prosthetic cardiac valves, disseminated intravascular coagulation (DIC), heparin-induced thrombocytopenia, and anti-phospholipid antibody syndrome

what are the fates of thrombi?

propagation, organization, recanalization, dissolution, embolization

what is the virchow's triad?

hypercoagulable state, endothelial injury, circulatory stasis

what is the pathophysiology of endothelial injury?

• trauma/surgery
• venopunctures
• chemical irritation
• indwelling catheters
• atherosclerosis

what is the pathophysiology of circulatory stasis?

• immobility/paralysis
• surgery: >30 min general anesthesia
• obesity
• acute medical illness requiring hospitalization

what is the pathophysiology of a hypercoagulable state?

• malignancy (diagnosed/occult)
• pregnancy/postpartum
• inflammatory bowel disease
• nephrotic syndrome
• drugs: estrogen, estrogen contraceptives, tamoxifen, raloxifene
• thrombophilia: antiphospholipid Ab, prothrombin gene mutation, protein S/C deficiency, factor V leiden, antithrombin deficiency, factor VII/XI excess

what is transient ischemic attack (TIA)?

• caused by the systemic activation of coagulation and results in the formation of thrombi throughout the microcirculation

• platelets and coagulation factors are consumed and fibrinolysis is activated

• widespread activation of both the coagulation system and the fibrinolytic system

what is the mechanism of TIA?

release of tissue factor and widespread damage to endothelial cells

what is embolism?

• embolus: detached thrombus (intravascular solid, liquid, or gaseous mass) that is carried by the blood from its point of origin to a distant site, where it often causes tissue dysfunction/infarction

• vast majority of emboli derive from dislodged thrombi (hence the term thromboembolism)

• emboli are composed of fat droplets, bubbles of air/nitrogen, atherosclerotic debris (cholesterol emboli), tumor fragments, bits of bone marrow, or amniotic fluid

• emboli lodge in vessels too small to permit further passage, resulting in partial/complete vascular occlusion

• depending on their origin, emboli may arrest anywhere in the vascular tree

what is the primary consequence of systemic embolization?

ischemic necrosis (infarction) of downstream tissues, except for the pulmonary circulation

what is deep vein thrombosis (DVT)?

• most venous thrombi occur in the superficial or the deep veins of the leg
• superficial venous thrombi usually arise in the aphenous system
• more serious in the larger leg veins at or above the knee joint
• prone to embolize
• may cause local pain and edema, but collateral channels often circumvent the venous obstruction
• entirely asymptomatic in ~50% of patients and are recognized only after they have embolized to the lungs

what are superficial venous thrombi?

• rarely embolize
• cause pain, local congestion, and swelling from impaired venous outflow
• predisposing the underlying skin to the development of infections and varicose ulcers

what is primary thromboembolism?

pulmonary emboli originate from deep venous thrombi and are responsible for the most common form of thromboembolic disease

what are the complications of pulmonary thromboemboli?

• sudden death: if there's obstruction of >60% of the pulmonary vasculature, sudden death of the patient can result
• pulmonary infarct: due to occlusion of the blood vessel and resultant ischemic injury of the lung parenchyma
• pulmonary hypertension: obstructive lesions compromising a significant % (usually >60%) of the pulmonary arterial circulation increase the work of the right ventricle, leading to pulmonary hypertension

what is infarct/stroke?

• localized area of dead (necrotic) cells within an organ
• heart (myocardial), pulmonary (embolism), brain (stroke)
• can be described as: ischemic, hemorrhagic, transient ischemic attack (mini stroke)
• can sometimes cause temporary/permanent disabilities, depending on how long the brain lacks blood flow and which part is affected

what is ischemic vs. hemorrhagic stroke?

• ischemic: blood clot blocks blood flow to part of the brain
• hemorrhagic: artery ruptures, causing bleeding around the brain

what are the risk factors of stroke?

• being overweight/obese
• physical inactivity
• heavy/binge drinking
• use of illegal drugs (e.g. cocaine, meth)

what are the non-modifiable factors of stroke?

• age: >55 yrs
• race/ethnicity: African Americans and Hispanics
• sex: men > women; women are usually older when they have strokes and are more likely to die of strokes
• hormones: use of birth control pills or hormone therapies that include estrogen increases risk

what are the medical risk factors of stroke?

• high BP and cholesterol
• cigarette smoking or secondhand smoke exposure
• diabetes, obstructive sleep apnea, COVID-19 infection
• cardiovascular disease: heart failure, defects, infection; irregular heart rhythm (e.g. atrial fibrillation)
• personal/family history of stroke, heart attack, or transient ischemic attack

what are the complications of stroke?

• paralysis or loss of muscle movement: may become paralyzed on one side of the body, or lose control of certain muscles (e.g. those on one side of the face or one arm)
• difficulty talking or swallowing: affects control of the muscles in the mouth and throat, making it difficult to talk clearly, swallow, or eat; leads to difficulty with language (speaking, reading, writing)
• memory loss or thinking difficulties: many people who have had strokes experience some memory loss, thinking, reasoning, making judgments, and understanding concepts
• emotional problems, changes in behavior, self-care: may have more difficulty controlling their emotions, or they may become withdrawn, or develop depression
• pain: numbness or other unusual sensations may occur in the parts of the body affected by stroke

what is wound/tissue healing?

• following mild injury, which damages the epithelium but not the underlying tissue: resolution occurs by regeneration
• after more severe injury with damage to the connective tissue framework, repair is by scar formation

what are the key phases of wound healing?

• coagulation/hemostasis: form blood clot

• acute inflammation: form scab with fibroblasts and MP

• tissue proliferation: fibroblasts proliferating above subcutaneous fat

• tissue remodeling/maturation: freshly healed epidermis and dermis

what are the phases of the normal wound healing process?

1. hemostasis

2. acute inflammation

3. tissue proliferation

4. tissue remodeling/maturation

what is the acute inflammatory phase?

• neutrophils enter the wound to destroy bacteria and remove debris

• as the neutrophils leave, MP arrive to continue clearing debris

• these cells also secrete growth factors and proteins that attract immune system cells to the wound to facilitate tissue repair

• begins when the wound develops, lasts 4-6 days

• marked by edema, erythema, inflammation, and pain

• healing process triggered

• immune system works to prevent microbial colonization

what is the proliferative phase?

• 3 distinct stages: filling the wound, contraction of the wound margins, covering the wound

• during the first stage, shiny, deep red granulation tissue fills the wound bed with connective tissue, and new blood vessels are formed

• during contraction, the wound margins contract and pull toward the center of the wound

• in the third stage, epithelial cells arise from the wound bed or margins and begin to migrate across the wound bed in a leapfrog fashion until the wound is covered with epithelium

• often lasts anywhere from 4-24 days

• fibroblasts lay collagen in the wound bed, strengthening new granulation tissue

what is the maturation phase?

• features new tissue that slowly gains strength and flexibility

• collagen fibers reorganize, the tissue remodels and matures

• there is an overall increase in tensile strength (though max strength is limited to 80% of the pre-injured strength)

• the maturation phase varies greatly from wound to wound, often lasting anywhere from 21 days to 2 yrs

• length of time depends on patient- and wound-related complicating factors (e.g. duration of wound, patient comorbidities, wound infection status)

• filled-in wound is covered and strengthened

• scar tissue forms

• the healing process is complex and susceptible to interruption due to local and systemic factors: includes moisture, infection, maceration (local), age, nutritional status, body type (systemic)

what are the major components of acute inflammation?

• dilation of small vessels
• increased permeability of the microvasculature
• emigration of the leukocytes (neutrophils and MP) from the microcirculation

what is the process of wound/tissue healing?

stimulus:
→ microbes enter cell OR necrotic tissue
production of mediators:
→ recognition by sentinel cells in tissues
→ mast/dendritic cells and MP release mediators (amines, cytokines)
influx of leukocytes, plasma proteins:
→ vasodilation, increase vascular permeability → edema
→ recruitment of leukocytes
→ elimination of microbes, dead tissue
→ neutrophils and MP release cytokines and growth factors
→ resolution and repair

what is the process of sickle cell anemia leading to extravascular hemolysis?

→ RBC containing HbS
→ deoxygenation
→ reversibly sickled cell
→ additional cycles of deoxygenation
→ end-stage, nondeformable, irreversibly sickle cell
→ rapidly phagocytosed by MP
→ extravascular hemolysis

what are the effects of thrombin?

• converts fibrinogen to fibrin
• converts factor XIII to factor XIIIa
• platelet aggregation and degranulation
• monocyte and lymphocyte activation
• endothelial activation → neutrophil adhesion