Human Immunity and Blood

Breast milk is a complex biological fluid containing macronutrients like protein, immune cells like white blood cells, and protective antibodies (such as IgA) that help build the baby's immune system. Therefore, all of the listed components are passed to the baby.

Type O blood is considered the universal donor because its red blood cells do not have A or B antigens on their surface, meaning it can be transfused into patients of any blood type without causing an immune reaction.

Individuals with blood type O (specifically O negative) are considered universal donors because their red blood cells do not have A, B, or Rh antigens on their surface, preventing an immune response in recipients of any blood type.

Individuals with blood type AB (specifically AB positive) are universal recipients because their blood contains both A and B antigens and lacks anti-A and anti-B antibodies, meaning they can receive red blood cells of any type.

A person with type A blood has anti-B antibodies in their plasma, meaning they cannot receive blood containing B antigens (types B and AB). Therefore, they can only safely receive type A or type O (the universal donor) blood.

Registration involves administrative tasks like showing ID, filling out demographic forms, and reading educational materials. Measuring temperature, blood pressure, and hemoglobin is part of the health history/physical screening phase that occurs after registration.

Red blood cells, or erythrocytes, have an average lifespan of about 120 days in the human body. After this period, they become worn out and are destroyed by macrophages in the spleen and liver. New red blood cells are continuously produced in the bone marrow to replace them.

The cellular portion of human blood consists of three primary types of cells: red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes). Each type has a distinct and vital role, such as oxygen transport, immune defense, and blood clotting. Together, they make up about 45 percent of blood volume.

Platelets (thrombocytes) are cell fragments in the blood that play a crucial role in blood clotting to stop bleeding when blood vessels are damaged. Red blood cells (RBCs) transport oxygen, and white blood cells (WBCs) are involved in the immune response.

Phagocytic white blood cells provide non-specific immunity by engulfing and digesting any foreign pathogens they encounter, regardless of the pathogen's specific identity. In contrast, the production of antibodies by lymphocytes is a highly specific immune response tailored to target specific antigens.

Thrombin is an active enzyme that catalyzes the conversion of the soluble plasma protein fibrinogen into insoluble fibrin strands. These fibrin strands form a mesh that traps blood cells to form a clot.

Platelets (thrombocytes) adhere to damaged blood vessel walls and release clotting factors that initiate the coagulation cascade. While damaged tissues also release clotting factors, among the blood cells listed, platelets are the primary source.

Macrophages are crucial components of the innate immune system. They act as sentinel cells that are among the first to detect and engulf invading pathogens, and they also release cytokines to recruit and activate other immune cells to the site of infection.

Macrophages, Natural Killer (NK) cells, and neutrophils are all cellular components of the innate immune system, providing rapid, non-specific defense against pathogens. Since all of the listed options are indeed part of the innate immune system, the correct choice is that all are part of it.

The skin acts as a physical and chemical barrier that prevents pathogens from entering the body, making it the primary first line of defense. Internal immune cells like macrophages, dendrites, and neutrophils act as the second line of defense once pathogens have breached this barrier.