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Blood and Immunity

Blood as a Connective Tissue

• Blood is a fluid connective tissue. It transports oxygen, carbon dioxide, and glucose.
• It helps in thermoregulation due to its contact with cells that generate heat through cellular respiration.
• Cellular respiration: Glucose + O2 \rightarrow CO2 + H_2O + Heat
• Shivering is an involuntary muscle contraction that increases cellular respiration to produce heat, raising blood temperature.
• Men typically have 5-6 liters of blood, while women have 4-5 liters due to stature and menstruation.
• Iron supplementation is more critical for women due to periodic blood loss during menstruation.
  • Excess iron in men can lead to hemochromatosis, a condition where iron deposits damage organs.
  • Treatment for hemochromatosis includes therapeutic bloodletting (donating blood).
• Red blood cells circulate for approximately four months.
  • They lack a nucleus, preventing mitosis and protein synthesis for repair.
  • The bioconcave disc shape of red blood cells allows flexibility for navigating capillaries and maximizes hemoglobin content for transporting respiratory gases.
• Capillaries are the smallest blood vessels, requiring cells to pass through in single file.
• Red blood cells lack a nucleus and ribosomes; thus they cannot transcribe mRNA to synthesize new proteins.

Red Blood Cell Production

• All blood cells originate from a stem cell called a hemocytoblast.
  • When more red blood cells are needed, hemocytoblasts differentiate into cells with a nucleus.
  • These cells create hemoglobin and eventually dissolve their nucleus to become mature red blood cells (erythrocytes).

Functions of the Circulatory System

• Transports respiratory gases.
• Transports digestive system byproducts (nutrients).
• Circulates endocrine system hormones (chemical messages).
• Provides protection via white blood cells.
• Facilitates blood clotting through platelets.
• Regulates fluid balance.

Bone Marrow and Hematopoiesis

• Red bone marrow, found in spongy bone of vertebrae, ilium, and sternum, is responsible for blood cell production.
  • Compact bone is dense and doesn't allow for bone growth.
  • Spongy bone contains open spaces to allow hematocytoblasts production
• Hematopoiesis is the process of making more blood cells.
• Bone marrow biopsies can be performed to examine blood cells, often taken from the ilium due to accessibility and reduced risk to organs.
• Hematologists are blood doctors while nephrologists are Kidney doctors (related to the Nephron).

Blood Cell Production Regulation

• Low oxygen levels or decreased red blood cell numbers signal the body to produce more red blood cells.
• Rapid blood volume decrease may indicate internal bleeding, prompting platelet production to fix leaks.

White Blood Cells (Leukocytes)

• White blood cells protect against infections and have nuclei, enabling complex functions.
• Mnemonic to remember the abundance of white blood cells: "Never Let Monkeys Eat Bananas" (Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils).
  • Neutrophils: Most abundant, respond to acute infections.
  • Lymphocytes: Involved in acquired immunity, produce antibodies.
  • Monocytes: Clean-up crew, elevated during chronic infections.
  • Eosinophils: Elevated during parasitic infections and allergic reactions.
  • Basophils: Least abundant, release chemicals (like histamine) to aid other blood cells.
• Antihistamines counteract histamine's leakiness effect, reducing symptoms like runny nose and swelling.

Platelets and Blood Clotting

• Platelets are cytoplasmic fragments pinched off from megakaryocytes.
  • They are essential for blood clotting due to their stickiness.
  • Platelets have a lifespan of about ten days.
• Aspirin thins blood by making platelets less sticky, reducing the risk of coronary artery blockage.
  • It must be taken regularly to maintain the effect.
  • Platelet comes from cell fragments.

Respiratory Gas Exchange and Lymphatic System

• The heart sends blood to the lungs, where oxygen is taken in and carbon dioxide is released (pulmonary ventilation and external respiration).
• Boyle's Law.
• Oxygen goes into the capillaries, while carbon dioxide goes into the lungs. Gas exchange occurs through simple squamous cells (Type I cells in the lungs).
  • Type II are cuboidal producing surfactant to allow external respiration to work
• Internal respiration occurs at the tissues.
• The lymphatic system is a parallel system to the circulatory system, collecting excess fluids and immune cells.
  • Lymph nodes filter lymph, trapping pathogens; doctors palpate lymph nodes to check for swelling, indicating infection.
• Lymph nodes are strategically located (e.g., in joints) to act as checkpoints against infection spread.
• Lymph node biopsies are used to check for disease spread, such as cancer metastasis.
  • Cancer spreads via blood vessels or lymphatic vessels.
• Lymphatic disruption can lead to lymphedema (swelling) due to fluid buildup.

Immune System: Non-Specific vs. Acquired

• Non-specific (innate) defenses provide broad protection.
  • Skin with stratified squamous epithelium protects against external threats.
  • Inflammation, characterized by redness, heat, swelling, and pain, is a non-specific response.
  • Phagocytosis: Eating cells (endocytosis)
  • Exocytosis: pooping it out
• Acquired (adaptive) immunity develops after exposure to a specific pathogen, creating memory cells for targeted responses.
  • Involves B cells and T cells (lymphocytes).
  • Long