D3.2 - Blood and Circulation

Blood and Circulation

• Blood is a connective tissue, linking all cells and organs in the body
• Blood's composition includes a fluid portion (plasma) and a solid portion (cells)

Blood Composition

• Plasma: Makes up 55% of blood volume, primarily water, dissolved gases, proteins, sugars, vitamins, minerals, hormones, and waste products
• Red Blood Cells (Erythrocytes): Specialized for oxygen transport. Lack a nucleus, allowing space for hemoglobin. Their folded disk shape maximizes surface area, facilitating oxygen transport.
• White Blood Cells (Leukocytes): Part of the immune system, defending against infection. Larger than red blood cells and make up 1% of blood volume. Different types like monocytes, neutrophils, and lymphocytes.
• Platelets: Formed from larger cells in bone marrow, play a key role in blood clotting. They lack a nucleus.
• Percentages are approximate: Plasma (55%), red blood cells (45%), and white blood cells/platelets (<1%) of total volume

Red Blood Cells (Erythrocytes)

• Specialized for oxygen transport
• Lack of a nucleus allows for efficient hemoglobin transport
• Hemoglobin is an iron-containing respiratory pigment essential for binding oxygen
• "Folded disk" shape maximizes surface area for oxygen transport

Sickle Cell Anemia

• Genetic condition causing abnormally shaped red blood cells
• Red blood cells are unable to bind hemoglobin and transport oxygen effectively

White Blood Cells (Leukocytes)

• Crucial part of the immune system.
• Make up approximately 1% of blood volume
• Much bigger than red blood cells
• Numbers increase when fighting off infections
• Include monocytes, neutrophils, lymphocytes, etc.

Leukemia

• Cancer of the bone marrow, where white blood cells are produced
• Characterized by an abnormal increase in immature white blood cells, weakening the immune system.
• Impairs normal blood clotting, leading to frequent nosebleeds, and bruising
• Treatments include blood transfusions, chemotherapy, and bone marrow transplants

Platelets

• Formed when larger bone marrow cells break apart, lacking a nucleus.
• Play a critical role in blood clotting, preventing excessive blood loss

Stages of Blood Clotting

• Injured blood vessels release chemical messengers, attracting platelets to the site
• Platelets rupture, releasing substances that combine to create the enzyme thromboplastin
• Thromboplastin combines with calcium ions and prothrombin (a liver-secreted protein), to produce thrombin
• Thrombin reacts with fibrinogen, producing fibrin
• Fibrin strands create a mesh that prevents blood cells from escaping, forming a clot

Functions of Blood

• Transport: Carries cells and various substances (nutrients, waste, hormones, etc.) throughout the body

• Homeostatic Regulation: Maintaining a constant internal body temperature via different mechanisms (like vasodilation and vasoconstriction)

  • Vasodilation: Blood vessels expand, increasing blood flow to the skin's surface. The increased blood flow dissipates heat to the environment.
  • Vasoconstriction: Blood vessels constrict, reducing blood flow to the skin. This prevents heat loss to the environment.
  • Perspiration: Sweat cools the skin by evaporating, further regulating body temperature.
  • Shivering: Involuntary muscle contractions increase metabolism and generate extra body heat, keeping the body warm.

Vasodilation and Vasoconstriction

• Can be influenced by factors like blood pressure, exercise, and substances like nicotine and alcohol.

Hemophilia

• Hereditary blood disorder resulting in insufficient clotting proteins
• Increased risk of uncontrolled bleeding, especially from injuries
• Treated with factor VIII injections, a crucial clotting protein