Ch19, pt 1

Perfusion: The process of getting blood flow to the tissue.
- If an artery gets blocked, the capillary beds would not be perfused, resulting in a lack of blood distribution to surrounding cells.
- Important to ensure a minimum perfusion of all tissues for proper function.

Don't forget the blood volume percentages:
- Plasma: 45% to 63% of blood volume.
- Formed Elements: 37% to 55%, which includes:
- Erythrocytes (red blood cells)
- Leukocytes (white blood cells)
- Platelets
The hematocrit is the volume percentage of formed elements in the blood.
- Higher hematocrit: Typically observed in males due to:
- Influence of androgens like testosterone: Stimulates red blood cell production more than female hormones like estrogen.

Blood is classified as a fluid connective tissue originating from the mesoderm during embryonic development.
Functions of blood include:
- Transport: Carries gases, nutrients, hormones, etc.
- Maintains homeostasis of interstitial fluid (the fluid between cells).
- Interstitial fluid can be thought of as the "air" surrounding individual cells when likened to an atmosphere.
Organ systems monitor interstitial fluid conditions to maintain homeostasis, regulating variables such as:
- pH: Normal pH of plasma ranges from 7.35 to 7.45.
- Importance: Small pH changes indicate large shifts in acidity.
- Ion concentration, amino acids, and glucose concentration.

Plasma is primarily composed of:
- Water: Approximately 92% of plasma.
- Plasma proteins: ~7% of plasma volume, including:
- Albumins: Major proteins essential for transporting lipids and steroid hormones, helping maintain oncotic pressure in blood vessels.
- Globulins: Include antibodies (immunoglobulins) and transport proteins for ions and lipid-soluble substances.
- Fibrinogen: A precursor to fibrin, necessary for blood clotting.
- Regulatory proteins: Include hormones and enzymes, with inactive forms known as proenzymes.
Electrolytes are ions key for physiological functions (e.g., sodium, potassium, chloride).
Organic Nutrients: Include carbohydrates, lipids, and amino acids, which are crucial for cell metabolism and function.
Organic Wastes: Such as carbon dioxide (CO₂), urea, creatinine, bilirubin, and ammonium ions need to be excreted to maintain health.

Blood also plays a role in defending against pathogens (agents causing disease) including viruses, bacteria, and fungi.
- Immune response: Elimination of pathogens and toxins via various blood cell types.
Aberrant cells: Cells that grow uncontrolled due to mutations can form tumors.
- Distinction between tumors (localized) and cancer (invasive).

Temperature Regulation: Blood maintains body temperature.
Regular review of blood conditions such as:
- pH between 7.35 and 7.45.
- Hormones influencing metabolism and growth, including insulin, glucagon, and cortisol.

Erythrocytes
- The most abundant cells in blood, responsible for oxygen transport; about 99% of blood components.
- Identified as red blood cells; clinically often referred to as RBCs.
Leukocytes: Comprise a variety of white blood cells with distinct functions in immunity. Types include:
- Neutrophils: Contain granules and multi-lobed nuclei.
- Eosinophils: Larger granules, typically stained red/orange, with bilobed nuclei.
- Basophils: Stain dark blue, contain histamine for inflammatory responses.
- Lymphocytes: Small cells with a large nucleus, involved in immune recognition.
- Monocytes: Largest white blood cells with a kidney-shaped nucleus, develop into macrophages in tissues; known for their phagocytic abilities.
- Platelets (Thrombocytes): Derived from megakaryocytes; crucial for clotting via the formation of fibrin.

Hemoglobin:
- A protein made of four globin chains, each containing a heme unit that binds oxygen.
- Each hemoglobin molecule can bind four molecules of oxygen.
- Erythrocytes are essentially sacs filled with hemoglobin (280 million molecules per cell).
Erythropoiesis:
- The process of red blood cell production mainly hormone-regulated by erythropoietin (EPO), secreted by the kidneys upon oxygen deficiency.
- Normal production rate: 3 million red blood cells per second.
- Lifespan of RBCs: Approximately 120 days; old cells are recycled primarily by the spleen and macrophages.
- Breakdown of heme results in bilirubin, which is processed by the liver.
- Jaundice: Result of excess bilirubin accumulation in the body, recognizable through yellowing of skin/sclera.

Blood serves multifaceted roles, including the transport of substances, immune defense, maintenance of homeostasis, and regulation of body temperature.
Proper operation of blood involves monitoring and regulating its components and ensuring cellular health through systemic processes and feedback mechanisms.