Blood Vessels

Pulmonary vs. Systemic Circulation

• Pulmonary circulation carries deoxygenated blood from the right ventricle to the lungs and returns oxygenated blood to the left atrium.

• Systemic circulation carries oxygenated blood from the left ventricle to the body and returns deoxygenated blood to the right atrium.

• Example: The pulmonary artery carries blood to the lungs, while the aorta distributes blood to systemic tissues.

Arteries vs. Veins

• Arteries have thicker walls, more smooth muscle, and elastic tissue; they maintain a round shape and do not have valves (except in the pulmonary trunk and aorta).

• Veins have thinner walls, larger lumens, often appear collapsed, and contain valves to prevent backflow.

• Tunic layers: Both have three layers: tunica intima, tunica media, and tunica externa, but the tunica media is much thicker in arteries.

• Veins as blood reservoirs: Most blood in the body is found in veins due to their high capacitance.

Types of Arteries

• Conducting (Elastic) arteries: Large arteries (e.g., aorta) with abundant elastic fibers to accommodate pressure changes.

• Distributing (Muscular) arteries: Medium-sized arteries that distribute blood to specific organs; more smooth muscle, less elastic tissue.

Types of Capillaries

• Continuous capillaries: Most common; found in muscle, skin, and brain; have uninterrupted endothelial lining.

• Fenestrated capillaries: Have pores; found in kidneys, intestines, and endocrine glands; allow greater permeability.

• Sinusoidal capillaries: Large gaps; found in liver, spleen, and bone marrow; allow passage of large molecules and cells.

Blood Pressure (BP) Measurement

• Systolic pressure: Measured during ventricular contraction; corresponds to turbulent flow (Korotkoff sounds).

• Diastolic pressure: Measured during ventricular relaxation; corresponds to laminar flow (no sound).

• Hypotension: Abnormally low BP; Hypertension: Abnormally high BP (clinical vs. borderline values depend on guidelines).

Factors Limiting Blood Flow

• High blood viscosity, small vessel radius, long vessel length, and low blood pressure all decrease blood flow.

• The most significant determinant is vessel radius (Poiseuille's Law):

• Where = flow, = pressure difference, = radius, = viscosity, = length.

Regulation of Blood Flow and Pressure

• Vasodilation (increased flow) occurs with low O2, high CO2, low pH, decreased sympathetic stimulation, and decreased production of epinephrine, norepinephrine, renin, and ADH.

• Sympathetic nervous system (SNS) maintains vasomotor tone (baseline constriction).

• BP increases with SNS activation (vasoconstriction), no stretch of baroreceptors, high CO2, low O2, low pH, CNS ischemic response, and hormone release (epi/norepi, renin, aldosterone, ADH).

• BP decreases with baroreceptor stretch, low CO2, high O2, high pH, inhibited hormone release, and ANP release from the right atrium.

• The kidney is the most important organ for long-term BP regulation.

Baroreceptors

• Peripheral baroreceptors: Located in the aorta and carotid arteries; detect stretch (BP changes).

• Cardiac baroreceptors: Located in the right atrium; detect increased venous return (increased BP).

Lymphatic System

Functions of the Lymphatic System

• Returns interstitial fluid and leaked plasma proteins to the blood.

• Absorbs and transports dietary fats from the intestine (via lacteals).

• Provides immune defense by filtering lymph and housing lymphocytes.

Composition and Flow of Lymph

• Lymph contains proteins, microbes, cancer cells, and fluid from tissues.

• Lymph flows from lymphatic capillaries → lymphatic vessels → lymph nodes → lymphatic trunks → lymphatic ducts → venous circulation.

Structure of Lymphatic Capillaries

• Composed of endothelial cells with minivalves that open with increased interstitial pressure.

• Anchored by collagen fibers; highly permeable to fluids and particles.

Lymphatic Disorders

• Elephantiasis: Caused by parasitic infection (e.g., filarial worms) blocking lymphatic vessels, leading to severe swelling (lymphedema).

Lymphatic Organs and Tissues

• Lymph nodules: Aggregates of lymphoid tissue (e.g., tonsils in pharynx, Peyer's patches in small intestine).

• Lymph nodes: Filter lymph; contain cortex (B cells) and medulla (T cells, macrophages); found in clusters (cervical, axillary, inguinal regions).

• Spleen: White pulp (lymphocyte-rich, immune function) vs. red pulp (RBC destruction, blood storage).

• Thymus: Site of T cell maturation; essential for adaptive immunity in early life.

Blood

Functions of Blood

• Transportation of gases, nutrients, hormones, and waste products.

• Regulation of pH, temperature, and fluid volume.

• Protection against blood loss (clotting) and infection (immune cells).

Components of Whole Blood

• Plasma: Liquid matrix (about 55%); contains water, proteins, nutrients, hormones, and waste.

• Formed elements: Red blood cells (RBCs), white blood cells (WBCs), and platelets.

Plasma Proteins

• Albumin: Maintains osmotic pressure.

• Globulins: Transport proteins and antibodies.

• Fibrinogen: Involved in blood clotting.

Hemoglobin (Hb)

• Protein in RBCs that binds O2 and CO2.

• Normal range: Males 13-18 g/dL; Females 12-16 g/dL.

• Types: Oxyhemoglobin (O2-bound), Carbaminohemoglobin (CO2-bound), Deoxyhemoglobin (no O2).

• Hb is recycled: Iron is reused, heme is converted to bilirubin and excreted.

Hematopoiesis

• All blood cells derive from hematopoietic stem cells in bone marrow.

• Erythropoiesis (RBC production) requires iron, protein, vitamin B12, and folic acid.

Blood Typing

• Based on presence of antigens (A, B, Rh) on RBCs and antibodies in plasma.

• Transfusion compatibility depends on matching antigens and avoiding antibody reactions.

• Blood testing in pregnancy is important to prevent hemolytic disease of the newborn (Rh incompatibility).

Leukocytes (WBCs)

Platelets

• Fragments of megakaryocytes; essential for blood clotting (hemostasis).

Normal Hematocrit and Hemoglobin Values

Blood Disorders

• Anemia: Low RBCs or Hb; causes include iron deficiency, vitamin B12 deficiency, blood loss.

• Leukemia: Cancer of WBCs; abnormal proliferation of immature leukocytes.

• Thrombocytopenia: Low platelet count; increased bleeding risk.

• Polycythemia: Excess RBCs; increases blood viscosity.

Immunity

Non-Specific vs. Specific Immunity

• Non-specific (innate) immunity: General defenses (e.g., barriers, phagocytes, inflammation).

• Specific (adaptive) immunity: Targeted response involving lymphocytes (B and T cells).

Surface Barriers

• Skin, acidic mucosa, lysozyme (in tears/saliva), mucus (traps microbes).

Three Lines of Defense

• First line: Physical and chemical barriers (skin, mucous membranes).

• Second line: Chemicals and cells (phagocytes, inflammation, fever, complement).

• Third line: Specific immunity (B and T lymphocytes).

Antibody-Mediated vs. Cell-Mediated Immunity

• Antibody-mediated (humoral) immunity: B cells produce antibodies that target extracellular pathogens.

• Cell-mediated (cellular) immunity: T cells destroy infected or abnormal cells directly.

B and T Lymphocytes

• B lymphocytes: Mature in bone marrow; produce antibodies.

• T lymphocytes: Mature in thymus; include helper T cells (coordinate response) and cytotoxic T cells (kill infected cells).

Acquisition of Humoral Immunity

HIV/AIDS

• Human Immunodeficiency Virus (HIV) attacks helper T cells, weakening the immune system and leading to Acquired Immunodeficiency Syndrome (AIDS).

• Increases susceptibility to opportunistic infections and certain cancers.

Additional info: Some details (e.g., specific blood disorders, exact BP values) were inferred based on standard Anatomy & Physiology curricula.