Blood Composition and Physiology

Albumin is a protein synthesized by the liver and plays a crucial role in maintaining the blood's colloid osmotic pressure. It also transports various substances, including fatty acids, cholesterol, hormones, and drugs.

The correct affirmation about blood is that its average pH is around 7.4, slightly alkaline.

The statement that the hematocrit represents the number of red blood cells in blood is incorrect. Hematocrit is the percentage of red blood cells in the total blood volume.

Erythropoietin, a hormone that stimulates red blood cell production, is primarily produced by the kidneys (90%).

Pernicious anemia is caused by a lack of intrinsic factor (IF) in the stomach, leading to a deficiency in vitamin B12 absorption.

The statement that hemoglobin can effectively function outside red blood cells is incorrect. Hemoglobin is contained within red blood cells and its primary function is to transport oxygen.

Leukocytes are the mobile units of the body's defense system, actively fighting infections. They are distinct from red blood cells and monocytes.

Monocytes, a type of white blood cell, transform into tissue macrophages, which are specialized cells that engulf and destroy foreign invaders.

Chemotaxis is the process by which cells, particularly leukocytes, are attracted to a chemical signal released by injured tissue or invading pathogens. This signal guides them to the site of inflammation.

The Monocyte-Macrophage System in the lungs involves tissue macrophages residing in the alveolar walls. These macrophages phagocytize inhaled particles, either digesting them or forming a capsule if they are undigestible.

The initial line of defense against infection during inflammation is the tissue macrophage, which rapidly phagocytizes invaders. As the response progresses, neutrophils invade the area, followed by monocytes that differentiate into macrophages.

Vasoconstriction of local blood vessels is not a typical feature of inflammation; instead, it’s characterized by vasodilation, increased capillary permeability, swelling, warmth, and redness.

The thymus is a bilobed organ situated in the anterior mediastinum. It serves as the T cell classroom, where these immune cells differentiate and mature. As we age, the thymus becomes less active and may be difficult to see on a chest X-ray.

Epithelial barriers, the first lines of defense, belong to the innate immune system. The innate immune system lacks immune memory, unlike the adaptive immune system.

Lymph nodes are encapsulated lymphoid organs that filter lymph fluid. They have one afferent lymphatic vessel and many efferent vessels. The flow through a lymph node is afferent vessel --> subcapsular sinus --> medullary sinus --> trabecular sinus --> efferent vessel.

The innate immune system is characterized by its rapid and nonspecific response, meaning it attacks a wide range of pathogens without targeting specific invaders. It also lacks immune memory, so each encounter with a pathogen triggers a similar response.

The statement that memory cells are not created in cellular immunity is incorrect. Both humoral and cellular immunity produce memory cells, which enable a faster and stronger response upon subsequent exposure to the same antigen.

Cytotoxic T cells are responsible for directly killing infected cells or cancerous cells. They recognize antigens presented by MHC class I molecules on the surface of target cells.

The three main types of antigen-presenting cells are macrophages, B lymphocytes, and dendritic cells. These cells engulf antigens, process them, and present them to T lymphocytes, initiating a specific immune response.

MHC class I is present on all nucleated cells and presents peptides from intracellular pathogens, triggering cytotoxic T cell activation.

The complement system is a cascade of proteins activated in response to infection. It plays various roles in immunity, including opsonization, chemotaxis, viral neutralization, lysis, and anaphylactic reactions.

Hemostasis is the process that stops bleeding. It involves three main steps: vascular constriction, platelet plug formation, and blood coagulation.

The spleen is a large lymphoid organ that filters blood. It removes old and damaged red blood cells and platelets. More than half of the platelets in circulation are removed by the spleen.

Platelets, small cell fragments important for blood clotting, are formed in the bone marrow from megakaryocytes.

Fibrin, a protein that forms the meshwork of a blood clot, is stabilized by the fibrin-stabilizing factor (also known as Factor XIII) released from platelets and found in plasma.

The extrinsic pathway is initiated by tissue trauma, whereas the intrinsic pathway is triggered by contact between blood and collagen exposed within the injured blood vessel. The two pathways converge to activate factor X, which leads to the formation of thrombin.

The oxygen-hemoglobin dissociation curve shows the relationship between the partial pressure of oxygen in the blood and the percentage of hemoglobin saturated with oxygen. It demonstrates that as the partial pressure of oxygen increases, the percentage of hemoglobin bound to oxygen also increases.

The inspiratory “ramp” signal, a pattern of nerve impulses from the respiratory center in the brainstem, gradually increases the activity of inspiratory muscles, leading to a smooth and controlled increase in lung volume during inspiration.

The peripheral chemoreceptor system, located in the carotid and aortic bodies, monitors blood oxygen, carbon dioxide, and pH levels. It sends signals to the respiratory center in the brainstem, adjusting breathing rate and depth to maintain blood gas homeostasis.