Blood & Lymphatics Overview

Functions of Blood

• Transport Gases
  Delivers dissolved gases, such as oxygen and carbon dioxide, from the lungs to tissues and facilitates their exchange. Oxygen binds to hemoglobin in red blood cells (RBCs) for effective delivery, while carbon dioxide is transported back to the lungs for exhalation.

• Distribute Nutrients
  Blood carries essential nutrients absorbed from the digestive tract, including amino acids, simple sugars, fatty acids, and vitamins, to all cellular tissues to support metabolic processes.

• Transport Waste
  It carries metabolic waste products, including urea and creatinine, from cells to the kidneys for filtration and eventual excretion, playing a critical role in maintaining homeostasis.

• Distribute Hormones
  The circulatory system transports hormones secreted by endocrine glands, such as insulin and adrenaline, to target organs and tissues to initiate physiological responses and regulate various bodily functions.

• Immune Defense
  Blood plays a vital role in the immune system by transporting white blood cells (WBCs) and platelets to sites of infection or injury, where they help defend against pathogens, allergies, and foreign invaders.

Components of Blood

• Blood consists of two primary components:

  • Plasma (~60%): The liquid portion that contains water, electrolytes, proteins, nutrients, hormones, and waste products.

  • Formed Elements (~40%): The cellular components that include red blood cells, white blood cells, and platelets.

Formed Elements

• Red Blood Cells (RBCs)
  Also known as erythrocytes, they are responsible for oxygen transport. Their biconcave shape increases surface area for gas exchange and facilitates flexibility for navigating through capillaries. They lack a nucleus and organelles, accounting for approximately 99.9% of formed elements.

  • Clinical Note: Sickle Cell Anemia is a genetic disorder characterized by abnormal hemoglobin, leading to crescent-shaped RBCs that obstruct blood flow and result in painful crises.

• White Blood Cells (WBCs)
  Also known as leukocytes, they are essential for the immune response. They comprise various types including:

  • Neutrophils: Most abundant, they rapidly respond to bacterial infections by engulfing pathogens.

  • Eosinophils: Large cells involved in combating allergic reactions and parasitic infections, characterized by three distinct lobes.

  • Basophils: Release histamine and heparin during allergic responses, contributing to the inflammatory process.

  • Monocytes: Large, kidney-shaped cells that differentiate into macrophages to engulf and digest pathogens.

  • Lymphocytes: Include T-cells, B-cells, and Natural Killer (NK) cells; critical for specific immunity, developing an adaptive response to pathogens.

• Platelets
  Small cell fragments that play an essential role in hemostasis, they aggregate at injury sites to form blood clots, minimizing blood loss.

Plasma

Composed of approximately 92% water, plasma serves as the medium for transporting cells and various substances. It contains proteins such as:

• Albumin: The most abundant protein that maintains oncotic pressure, preventing fluid leakage from blood vessels.

• Globulins: Comprised of antibodies (immunoglobulins) and transport proteins that bind and carry molecules like hormones and lipids.

• Fibrinogen: Precursor to fibrin, it is crucial for blood coagulation and wound healing.

Blood Typing

• Type A: Contains surface antigen A and anti-B antibodies in plasma.

• Type B: Contains surface antigen B and anti-A antibodies in plasma.

• Type AB: Both A and B antigens, with no antibodies in plasma, is the universal recipient.

• Type O: Lacks antigens and has both anti-A and anti-B antibodies, making it the universal donor.

• Rh Factor: Indicates the presence (+) or absence (-) of the Rhesus factor; vital in blood transfusions and pregnancy considerations.

Tissue/Capillary Fluid Exchange

• Hydrostatic Pressure: The force exerted by fluid within blood vessels, pushing fluid out into surrounding tissues.

• Colloid Osmotic Pressure: Generated by proteins in blood plasma that attract water back into capillaries, important for maintaining fluid balance (oncotic pressure ~25 mmHg).

Clinical Note: Edema

An abnormal accumulation of interstitial fluid, often resulting from high blood pressure or decreased plasma protein concentration (hypoalbuminemia), leading to swelling and potential tissue damage.

Lymphatic System

• Functions:

  • Transports interstitial fluid (lymph) back to the bloodstream, maintaining fluid balance.

  • Provides immune defense by producing lymphocytes and filtering pathogens.

  • Absorbs fats and fat-soluble vitamins from the small intestine, transporting them to the bloodstream.

• Lymphatic Structure:
  Comprised of closed-end lymphatic capillaries that absorb excess interstitial fluid, proteins, and pathogens, draining into larger lymphatic ducts and nodes.

  • Lymph Nodes: Act as filters for lymph, producing lymphocytes, and containing phagocytic cells that engulf and remove pathogens and cellular debris.

Body Water Distribution

• Intracellular Fluid: ~27-30 L, the majority of body water, found within cells, crucial for cell function and metabolism.

• Extracellular Fluid: ~14-16.5 L, including interstitial fluid and blood plasma, important for transporting nutrients and oxygen to cells.

• Water Intake/Excretion: Daily intake ranges from 1.5-2.5 L, with excretion through kidneys, lungs, skin, and gastrointestinal tract, playing a critical role in hydration and homeostasis.

This overview encapsulates the major functions, components, interactions, and clinical significance of the blood and lymphatic systems essential for understanding human health.