Blood Functions and Composition

Functions of Blood

• Transports oxygen, nutrients, and hormones to cells
• Transports carbon dioxide and wastes from cells
• Provides defense against external threats and cancerous/virus-infected cells
• Maintains homeostasis, including temperature, pH, and fluid levels

Blood Composition

• Plasma consists of water, protein, nutrients, and hormones
• The buffy coat contains white blood cells (leukocytes) and platelets
• Hematocrit mainly comprises red blood cells (erythrocytes)
• Typical hematocrit ranges are 37-47% for women and 42-52% for men

Hematocrit

• Defined as the percentage of red blood cells in total blood volume
• Anemia can affect hematocrit

Plasma Components

• Water makes up 92% of plasma
• Albumin is the most abundant protein in blood, functions as a carrier for fatty acids and contributes to osmotic pressure
• Fibrinogen, produced in the liver, is the least abundant plasma protein and contributes to clotting
• Alpha/beta globulins transport iron, lipids, and fat-soluble vitamins
• Gamma globulins (immunoglobulins) are antibodies that neutralize foreign substances

Hemopoiesis

• Classic name for "blood cell production"

Blood Cell Production

• Myeloid stem cells give rise to platelets, erythrocytes, basophils, neutrophils, eosinophils, and monocytes
• Lymphoid stem cells produce white blood cells, including natural killer cells, T cells, and B lymphocytes

Erythrocytes

• Immature: called a reticulocyte
• Mature red blood cells lack organelles for more hemoglobin space and increased oxygen-carrying capacity
• Biconcave shape increases surface area for gas exchange
• Must deform to move through capillaries

Hemoglobin Forms

• Oxyhemoglobin is hemoglobin bound to oxygen, is bright red, and is 100% saturated in the lungs and 40% at rest
• Deoxyhemoglobin has released oxygen and is dark red; myoglobin picks up oxygen in tissues
• Carbaminohemoglobin is bound to carbon dioxide; CO2 binds to amino acids within Hb

Erythrocyte Formation & Breakdown

• Iron, copper, zinc, folate, and B12 are key for erythrocyte formation
• A red blood cell typically functions for 120 days
• Biliverdin (green) and bilirubin (yellow) are pigments from the breakdown of the non-iron portion of heme
• Globin breaks down into amino acids and returns to the bone to form new RBCs
• Iron from heme stores in the liver or spleen as ferritin or hemosiderin

Iron Regulation

• Low iron levels reduce hepcidin, increasing iron export from storage via ferroportin

Anemia vs Hypoxia vs Ischemia

• Anemia is low iron, which reduces functional RBCs and decreases oxygen-carrying capacity
• Hypoxia is a general condition of low oxygen
• Ischemia is low blood flow, which can cause hypoxia

Hemoglobin Concentration

• Typical hemoglobin concentrations are 14-18 g/dL for men and 12-16 g/dL for women

Leukocyte Differentiation

• Neutrophils comprise 50-70% of leukocytes and stain neutral pink
• Eosinophils make up 2-4% of leukocytes and stain dark pink
• Basophils are the least common leukocytes and stain dark blue or purple

Neutrophils

• Polymorphonuclear, rapid responders that target bacteria and fungi
• High counts indicate infection; low counts increase infection risk
• Efficiently perform phagocytosis

Eosinophils

• Acidic stain, possess 2-3 nuclear lobes
• High counts result from allergies, parasitic infections, autoimmune diseases
• Low counts result from drug toxicity and stress
• Target parasitic worms and counteract histamines/inflammation

Basophils

• Least common leukocyte
• Stained with alkaline stains
• Release histamines and heparin
• High counts are associated with allergies, parasitic infections, and hypothyroidism
• Low counts can be due to pregnancy, stress, and hyperthyroidism

Phagocytosis & Histamines

• Neutrophils efficiently perform phagocytosis
• Both Neutrophils and Eosinophils perform phagocytosis and counteracts histamine, respectively
• Basophils release histamine and heparin (opposes clotting)

Lymphocytes

• Natural killer cells recognize cells lacking "self" proteins, and are non-specific
• B cells generate antibodies as part of the acquired/adaptive (humoral) immune system and create memory cells
• T cells generate antibodies as part of the acquired/adaptive (humoral) immune system and create memory cells
• Monocytes become macrophages after leaving circulation, acting as antigen-presenting cells (APCs), releasing antimicrobial defensins, and engulfing pathogens

Positive Chemotaxis

• Leukocytes follow chemical signals to areas of high concentration by squeezing between capillary cells
• At damaged tissues, monocytes become macrophages that phagocytize pathogens, and eosinophils and neutrophils release chemicals

Lymphoma

• A cancer characterized by overproduction of B and/or T cells in the spleen and lymph nodes
• Hodgkin's lymphoma is often curable
• Non-Hodgkin's lymphoma has a 74% survival rate

Hemostasis

• Technical term for stopping blood flow
• Normal platelet count is 150,000-450,000 platelets per mL of blood
• Platelets clump together to prevent blood loss

Blood Transfusions

• Type A blood cannot receive type B blood due to anti-B antibodies in type A blood
• Type O blood is the universal donor
• Rh+ blood can receive Rh+ and Rh- blood

The Heart - Anatomy

• Atria are the upper chambers that receive blood from the body and lungs
• Ventricles are the lower chambers that pump blood out to the body and lungs
• Atrioventricular valves (tricuspid and bicuspid/mitral) are between the atria and ventricles, preventing backflow
• The tricuspid valve is on the right, and the bicuspid (mitral) valve is on the left
• Semilunar valves (aortic and pulmonary) are between the ventricles and large arteries, preventing backflow
• Chordae tendineae are fibrous cords attached to papillary muscles and AV valves, preventing valve flapping
• Papillary muscles contract to pull AV valves closed

Heart Wall Layers

• Epicardium: serous membrane for lubricative outer covering [simple squamous]
• Myocardium: cardiac muscle tissue for muscular contractions
• Endocardium: protective inner lining of chambers and valves [simple squamous]

Coronary Circulation

• Heart's blood supply, ensures the heart muscle receives oxygen and nutrients

Heart Rhythms

• Normal sinus rhythm: 60-100 bpm
• Tachycardia: >100 bpm
• Bradycardia: <60 bpm

Heart Rate Increase

• First, the parasympathetic influence of the vagus nerve, then sympathetic stimulation are withdrawn

Stroke Volume

• Stroke volume (SV): Blood volume in mL ejected from the ventricles per contraction
• Normal SV is 55-100 mL
• SV = EDV (end diastolic volume) - ESV (end systolic volume)

Ejection Fraction

• Percentage of EDV represented by SV
• EF = SV/EDV * 100%
• Typical EF is 55-70%

Preload

• Preload: The "pre-stretch" on the myocardium as the ventricles fill
• Stretch increases sarcomere length, improving cross-bridge formation, increasing contractility
• Factors affecting preload: skeletal muscle pump, respiratory pump, and sympathetic stimulation

Frank-Starling Mechanism

• Change in contractility
• The force would diminish if the myocardial sarcomeres continued to lengthen
• This is limited by heart anatomy (endocardium)
• EDV decreases and HR increases since filling time is reduced

Afterload

• Pressure required to eject blood during ventricular contraction
• Pressure is proportional to resistance in the vascular system, recorded as systolic pressure
• This will affect the stroke volume, end-systolic volume, end-diastolic volume, and left ventricular end-diastolic pressure

Cardiac Output

• Amount of blood pumped by each ventricle per minute
• CO = HR x SV

Inotropic vs Chronotropic

• Refer to preload, contractility, and afterload

Blood Flow Regulation

• Cardioaccelerator centers increase HR, vasodilation in skeletal muscle
• Cardioinhibitor centers reduce HR and stroke volume
• Vasomotor centers control smooth muscle tone in tunica media
• Short-term blood pressure decrease – neurally driven
• Long-term blood pressure decrease – kidney driven

Cardiac Cycle

• Electrical activity of the Heart
• Atrial Diastole - Passive process filling, passive filling
• Atrial Systole - Depolarization moves blood into ventricles
• Ventricular Diastole - Isovolumic relaxation
• Ventricular Systole - Blood ejection from ventricles

Isovolumic Phases

• building pressure no change in volume. contraction is the phase where the ventricles contract with all valves closed
• no change in volume. relaxation is the phase where the ventricles relax with all valves closed

AV Node Delay

• To let the atria fully contract and pass blood into the ventricles before ventricular stimulation/contraction
• The delay lasts ~100ms

The Heart

• The 6 limb leads use 4 electrodes, and the 6 chest leads create 12 views
• ECG picks up outside the cell
• Traveling toward exploring lead- positive deflection
• Traveling away from exploring lead – negative deflection

Wilson's central terminal

• The central reference point (electrically) for the 6 chest leads

Electrical Mechanical Relationship

• P-wave: atrial depolarization, contraction
• QRS: atrial repolarization is covered up by ventricular depolarization
• T-wave: ventricular repolarization, relaxation
• PR- interval :tells about AV delay
• ECG looking at QRS comple
• ST Segment – beginning of ventricle repolarization, should be flat;
• isoelectric line- where charge is 0