Rucete ✏ Campbell Biology In a Nutshell
Unit 7 ANIMAL FORM AND FUNCTION — Concept 42.4 Blood Components Function in Exchange, Transport, and Defense
1. Composition of Blood
- Blood is composed of plasma (55%) and cellular elements (45%)
- Plasma contains water, electrolytes, proteins (albumin, antibodies, fibrinogen), nutrients, hormones, and gases
- Proteins help maintain osmotic balance, pH buffering, immunity, and clotting
2. Red Blood Cells (Erythrocytes)
- Most numerous cells; biconcave shape improves gas exchange
- Lack nuclei and mitochondria to maximize hemoglobin content
- Each cell carries ~250 million hemoglobin molecules (~1 billion O₂)
- Sickle-cell disease deforms cells and impairs circulation
3. White Blood Cells (Leukocytes)
- Defend against pathogens through phagocytosis or immune signaling
- Include lymphocytes, which mediate adaptive immunity
- Circulate in blood, lymph, and interstitial fluid; increase during infection
4. Platelets and Blood Clotting
- Platelets trigger clotting when vessels are damaged
- Clotting cascade: platelets release clotting factors → convert prothrombin to thrombin → converts fibrinogen to fibrin
- Hemophilia results from defective clotting proteins
- Thrombus (internal clot) can cause strokes or heart attacks
5. Blood Cell Production
- All blood cells originate from stem cells in red bone marrow
- Stem cells differentiate into lymphoid progenitors (→ B and T cells) and myeloid progenitors (→ RBCs, platelets, other WBCs)
- Erythropoietin (EPO) from kidneys regulates red blood cell production in response to low oxygen
- EPO is sometimes abused by athletes to boost performance
6. Cardiovascular Disease
- Atherosclerosis results from cholesterol-rich plaques narrowing arteries
- LDL delivers cholesterol; HDL removes excess—high LDL/HDL ratio is risky
- Stents reopen arteries; statins lower LDL
- Hypertension (≥140/90 mmHg) damages vessels and promotes plaque buildup
- Aspirin helps reduce clot risk through anti-inflammatory effects
In a Nutshell
Blood carries out essential functions for survival: transporting oxygen and nutrients, defending against pathogens, and maintaining balance. Red blood cells, white blood cells, and platelets each play key roles. Disorders like clotting defects or cardiovascular disease impair circulation but can often be managed through medical or lifestyle interventions.