circulatory system

Types Of Blood Vessels

  • Multicellular organisms rely on a circulatory system to bring nutrients into the cells and remove waste away from the cells.

Components Of The Circulatory System

  • Definition: Blood vessels carry blood in a loop from the heart to the tissues and then back to the heart.
  • Pathway: artery → arterioles → capillaries → venules → veins

Five Types Of Blood Vessels

  1. Arteries
  2. Arterioles
  3. Veins
  4. Venules
  5. Capillaries

Arteries And Arterioles

  • Arteries:
    • Function: Carry blood away from the heart.
    • Structure:
    • Thick elastic walls that can stretch to handle high blood pressure.
    • Have the highest blood pressure among all blood vessels.
    • Carry blood high in oxygen (except for the pulmonary artery).
    • Produce a detectable pulse.
  • Arterioles:
    • Smaller versions of arteries.
    • Function to funnel blood into capillaries.

Veins And Venules

  • Veins:
    • Function: Carry blood from capillaries back to the heart.
    • Structure:
    • No elastic walls; thinner walls compared to arteries.
    • Larger lumens (space inside the veins) than arteries.
    • Carry oxygen-poor blood (except for the pulmonary vein).
    • Have the lowest blood pressure.
    • No pulse detectable.
    • Blood movement relies on skeletal muscle contractions.
    • Contain valves to prevent backflow (blood moves in the direction of the valve).
  • Venules:
    • Smaller forms of veins.
    • Drain blood from capillary beds and connect to veins.
    • Blood vessels controlled by nerves.

Regulatory Mechanisms of Blood Flow

Vasoconstriction

  • Function: Helps prevent heat loss by reducing blood flow to certain areas.
  • Application: Increases blood flow to skeletal muscles during exercise.

Vasodilation

  • Function: Opens up blood vessels to increase blood flow.
  • Example: Increases blood flow to the skin to help regulate body temperature; may cause redness in the face during exercise.

Capillaries

  • Definition: Tiny blood vessels that connect arterioles to venules; primary site for gas, nutrient, and waste exchange.

Characteristics Of Capillaries

  • Thin-walled to permit rapid diffusion of substances.
  • Greatest total cross-sectional area among blood vessels, leading to the slowest blood velocity to facilitate gas exchange.
  • Small diameter increases friction to slow blood flow, which decreases blood pressure (BP) in capillaries, allowing easier passage of materials between tissues and blood.

Blood Pressure and Velocity in Capillaries

  • BP and blood velocity are lowest in capillaries due to their largest cross-sectional area.

Major Blood Vessels

  • Subclavian Artery: Carries blood to the arms.
  • Subclavian Vein: Carries blood from the arms.
  • Jugular Vein: Carries blood from the head.
  • Carotid Artery: Takes blood to the head via the neck.
  • Mesenteric Artery: Supplies blood to the intestines.
  • Superior Vena Cava: Collects blood from the head, chest, and arms into the right atrium.
  • Inferior Vena Cava: Collects blood from lower body regions and organs to the right atrium.
  • Pulmonary Vein: Carries oxygenated blood to the left atrium from the lungs.
  • Pulmonary Artery: Takes deoxygenated blood from the right ventricle to the lungs.
  • Hepatic Vein: Carries blood from the liver to the inferior vena cava.
  • Hepatic Portal Vein: Carries blood from the small intestine to the liver.
  • Renal Artery: Supplies blood to the kidneys.
  • Renal Vein: Returns blood from the kidneys.
  • Femoral Artery: Supplies blood to the legs.
  • Femoral Vein: Returns blood from the legs.
  • Coronary Artery: Supplies blood to the heart muscle.
  • Coronary Vein: Carries blood from the heart.
  • Aorta: Largest artery, branches lead to all organs; pumps oxygenated blood from the left ventricle.

Flow of Blood to Kidneys

  • Pathway: Left ventricle → aorta → renal artery → renal arterioles → capillaries → venules → renal vein → vena cava → right atrium.

The Heart

Overview

  • Definition: The heart is a muscular organ that acts as a double pump, composed mainly of cardiac muscle.
  • Function: Pumps blood to parts of the body.

Pumps

  1. Right Side: Pumps blood to the lungs.
  2. Left Side: Pumps blood to the rest of the body.

Septum

  • Definition: Wall that divides the left and right sides of the heart, preventing the mixing of oxygenated and deoxygenated blood.

Chambers

  • Each side of the heart has two chambers:
    • Atrium: Small chamber at the top.
    • Ventricle: Larger chamber at the bottom.

Specific Chambers

  • Right Atrium: Receives deoxygenated blood from the body via the vena cavas.
  • Left Atrium: Receives oxygenated blood from the lungs via the pulmonary vein.
  • Right Ventricle: Pumps deoxygenated blood through the pulmonary trunk to the lungs.
  • Left Ventricle: Pumps oxygenated blood out through the aorta to the rest of the body; the largest and most muscular chamber of the heart.

Atrioventricular Valves

  • Definition: Valves between atria and ventricles preventing backflow into the atria.
    • Tricuspid Valve: Separates the right atrium and right ventricle; consists of three flaps (cusps).
    • Bicuspid Valve: Separates the left atrium and left ventricle; consists of two flaps (cusps).

Chordae Tendineae

  • Description: Strong fibers (heart strings) running from the AV valves to the bottom walls of the ventricles.
  • Function: Support valves and prevent them from flipping when they shut.

Semilunar Valves

  • Definition: Valves between the ventricles and the major blood vessels leaving the heart.
  • Characteristics: Do not have chordae tendineae; prevent backflow into ventricles.
    • Right Ventricle: Contains pulmonary semilunar valve.
    • Left Ventricle: Contains aortic semilunar valve.

Coronary Arteries And Veins

  • Definition: Supply oxygenated blood to the heart muscle itself.
  • Implication: If a coronary artery becomes blocked, it can result in a heart attack.

The Route Of Blood

Cardiovascular System Divided into Two Circuits

1. Pulmonary Circuit

  • Definition: Circulation of blood between the lungs and the heart.
  • Pathway:
    • Deoxygenated blood enters the right atrium via superior vena cava and inferior vena cava.
    • Right atrium contracts and forces blood through the tricuspid valve into the right ventricle.
    • Right ventricle contracts and sends blood through the pulmonary semilunar valve into the pulmonary trunk.
    • Pulmonary trunk divides into pulmonary arteries, taking blood to the arterioles of the lungs.
    • Gas exchange occurs in pulmonary capillaries (carbon dioxide diffuses out, oxygen diffuses in).
    • Oxygenated blood enters pulmonary venules, then pulmonary veins, returning to the left atrium.
    • Left atrium contracts, forcing blood through the bicuspid valve into the aorta.

2. Systemic Circuit

  • Definition: Circulation of blood through the body, excluding pulmonary circulation.
  • Pathway:
    • Left ventricle → aorta → tissues and organs → right atrium through vena cavas.

Heartbeat

  • Phases of Heartbeat:
    1. Atria contract while ventricles relax.
    2. Ventricles contract while atria relax.
  • Sounds Produced: Result from valve closures:
    • Lub: Closing of atrioventricular valves.
    • Dub: Closing of semilunar valves.

Heart Nodes

1. Sinoatrial (SA) Node

  • Function: Acts as a pacemaker for the heart, causing regular beating. If it fails, heart beats irregularly.
  • Location: Upper back wall of the right atrium where vena cava enters; triggers atria contraction.

2. Atrioventricular (AV) Node

  • Function: Delays ventricle contraction until atrial contraction is complete. Purkinje fibers facilitate contraction from bottom upwards.

Pulse

  • Definition: Alternate expanding and recoiling of an arterial wall.
  • Locations to Check Pulse: Radial (wrist), carotid (neck).
  • Pulse Rate: Indicates heartbeat rate.
  • Electrocardiogram (ECG): Electrical representation of heart's beating.

Autonomic Control Of The Heartbeat

  • Location: Medulla oblongata of the brain regulates heart rate via sympathetic and parasympathetic nerves.
  • Systems:
    • Sympathetic Nervous System: Increases heart rate and blood pressure (fight or flight response).
    • Parasympathetic Nervous System: Decreases heart rate and blood pressure (maintenance system).

Blood Pressure

Measurement

  • Sphygmomanometer: Instrument that measures blood pressure.

Blood Pressure Defined

  • Definition: Pressure of the blood against the walls of arteries and arterioles, created by heart's pumping action.
  • Note: Blood pressure decreases with distance from left ventricle.
  • Typical Reading: Ratio of systole over diastole (e.g., 120/80 mmHg).

Types of Blood Pressure

1. Systolic Blood Pressure

  • Definition: Highest arterial pressure during ventricular contraction.
  • Normal Value: Highest normal BP is 120 mmHg.

2. Diastolic Blood Pressure

  • Definition: Lowest arterial pressure during ventricular relaxation.
  • Normal Value: Lowest normal BP is 80 mmHg.

Factors Regulating Blood Pressure

  1. Arteries vs. Veins: Blood pressure is higher in arteries compared to veins.
  2. Antidiuretic Hormone (ADH): Released from posterior pituitary gland; promotes water reabsorption, increasing blood volume and pressure.
  3. Aldosterone: Released from adrenal cortex; causes sodium reabsorption, leading to increased water retention, blood volume, and pressure.
  4. Carotid Arteries and Stretch Receptors: Increased BP sends signals to medulla oblongata to adjust heart rate and lower BP if needed.
  5. Nervous System Types:
    • Sympathetic Nervous System: Increases heart rate and BP, constricting arterial lumen.
    • Parasympathetic Nervous System: Decreases heart rate and BP, expanding arterial lumen.
  6. Conditions:
    • Hypertension: Elevated blood pressure (e.g., 150/100 mmHg) caused by factors like high salt diets, stress.
    • Hypotension: Low blood pressure (e.g., 100/60 mmHg).
    • Blood Velocity:
      • Decreases at capillaries due to increased cross-sectional area.

Capillary Fluid Exchange

Capillary Bed

  • Definition: Network of numerous capillaries.

Precapillary Sphincters

  • Definition: Muscle rings around arterioles controlling blood flow into capillary beds.
  • Function: Contract to shut off blood flow in response to shock or cold temperatures.

Capillary Fluid Exchange

  • Materials Exchanged: Oxygen, nutrients (glucose, amino acids), carbon dioxide, water.
  • Two Sides of Capillary Bed:
    • Arterial Side: Higher blood pressure; pushes fluids (containing oxygen and nutrients) into tissues.
    • Venous Side: Lower blood pressure allows waste materials (e.g., carbon dioxide, urea) to diffuse back into capillaries.

Fetal And Adult Circulation

Overview

  • Fetus: Develops inside the mother's uterus.
  • Key Difference: Fetus receives oxygenated blood via the placenta, not using lungs.
  • Placenta: Responsible for waste removal and nourishment of fetus before birth.

Unique Features in Fetus:

  1. Oval Opening: Opening between right and left atria; allows blood mixing, potentially causing "blue babies" if it doesn't close after birth.
  2. Arterial Duct: Connects pulmonary artery to the aorta, bypassing non-functioning fetal lungs.
  3. Umbilical Arteries and Veins: Carry wastes and oxygen; veins return oxygenated blood to fetus.
  4. Venous Duct: Connects umbilical veins with posterior vena cava, allowing oxygenated blood to bypass the liver.

Path Of Blood Through Fetus

  • Flow:
    • Blood starts in the right atrium → left atrium via oval opening → right ventricle → pulmonary artery; most goes through ductus arteriosus into aorta → to tissues → umbilical arteries lead to placenta for gas/nutrient exchange → umbilical vein carries oxygenated blood into venous duct → passes through liver, then joins inferior vena cava; mixed blood returns to the heart.

Components Of Blood

Overview

  • Water Content: Approximately 70% of body mass; most within cells, some in tissues, lymph, and blood vessels.
  • Function of Blood: Maintain homeostasis; transport gases, wastes, nutrients; clotting; fight infections.

Components Of Blood

  1. Plasma: Liquid portion of blood.
  2. Formed Elements: Red blood cells, white blood cells, and platelets.

Plasma Components

  • Water: Maintains blood volume; absorbed from large intestine.
  • Plasma Proteins:
    • Fibrinogen: Clotting proteins made in liver.
    • Globulins: Involved in fighting infection (antibodies), made in liver.
  • Gases: Oxygen and carbon dioxide transported from lungs and tissues.
  • Nutrients: Include glucose, fats, amino acids absorbed from small intestine.
  • Salts: Essential Ions (Na+, K+, Cl) and vitamins from intestines.
  • Hormones and Waste Materials: Produced in metabolism (e.g., urea, ammonia).

Red Blood Cells

Overview

  • Function: Transport oxygen throughout the body.
  • Structure: Biconcave discs produced by stem cells in red bone marrow.
  • Lifespan: 120 days; destroyed by macrophages in liver and spleen.
    • Recycling:
    • Iron from hemoglobin is recovered for reuse.
    • Heme degrades to bile pigments.
    • Globin reused for proteins.
  • Oxygen Transport by Hemoglobin:
    • Oxyhemoglobin (HbO2): Hemoglobin carrying oxygen; bright red.
    • Reduced Hemoglobin (HHb): Hemoglobin carrying protons and acting as a buffer; dark purple.
    • Carbaminohemoglobin: Hemoglobin carrying carbon dioxide; 70% of CO2 is transported as bicarbonate (HCO3−).
  • Carbonic Anhydrase: Enzyme that speeds up reactions involving CO2 in RBCs; releases H+ for pH balance.
  • Carbon Monoxide (CO): A poisonous compound that binds to hemoglobin more effectively than oxygen.

White Blood Cells

Overview

  • Function: Defend against infections by engulfing pathogens (phagocytosis) or producing antibodies.
  • Structure: Larger than RBCs, have nuclei.
  • Types:
    • Granulocytes: Have granules in cytoplasm, multi-lobed nucleus, phagocytic activity.
    • Neutrophils: Primarily attack bacteria.
    • Basophils: Release histamine causing inflammation.
    • Eosinophils: Manage allergic responses.
    • Agranulocytes: Lack granules, single nucleus.
    • Lymphocytes: T cells and B cells, involved in immune response.
    • Monocytes: Differentiate into macrophages post-blood circulation.

Platelets

Overview

  • Function: Key role in blood clotting to prevent excessive blood loss.
  • Structure: Colorless, smaller than RBCs, appear like plates; produced in bone marrow.

Blood Clotting Mechanism

Requirements

  • Components: Platelets and plasma proteins; calcium ions and vitamin K.

Steps in Clot Formation

  1. Platelets clump at the puncture site to seal the leak.
  2. Calcium ions are essential for the clotting reaction.
  3. Threads entangle red blood cells and platelets forming the clot (scab).

Lymphatic System

Overview

  • Definition: A vascular transport system that is a one-way system starting in tissues and emptying into the bloodstream of the circulatory system.

Similarities and Differences with Circulatory System

  • Similarities: Both have vessels (veins with valves and capillaries) serving as transport systems.
  • Differences: Lymphatic system operates as an open system, while the circulatory system is a closed system.

Functions Of The Lymphatic System

  1. Recovery of Lymph: Collects tissue fluid from surrounding area for return.
  2. Digestion: Absorbs fats and soluble vitamins from the small intestine (via lacteals) and transfers to blood.
  3. Immunity: Cleanses lymph, removes pathogens, produces lymphocytes (white blood cells).
    • Lymph: Tissue fluid originating from blood plasma, transporting nutrients and immune cells; lacks platelets and RBCs.

Lymphatic Vessels

  • Structure: Thin-walled lymph capillaries, analogous to veins with valves; no "lymph arteries" since there is no pump, movement driven by osmotic pressure and skeletal muscle contractions.
  • Lymph Ducts: Contain one-way valves to prevent backflow.
    • Right Lymphatic Duct: Drains the right side of the body (head, neck, chest); empties into right subclavian vein.
    • Thoracic Duct: Drains lymph from the rest of the body; empties into left subclavian vein.

Other Components of the Lymphatic System

  1. Thymus Gland: Above the heart; produces and matures T cells.
  2. Lacteals: Lymph vessels at intestinal villi; absorb fats.
  3. Bone Marrow: Site for RBC and WBC production.
  4. Lymph Nodes: Found in regions like neck and groin; swollen during infections, produce/store B lymphocytes, have macrophages for pathogen removal.
  5. Spleen: Behind the stomach; site where lymphocytes meet antigens, filters blood by removing old RBCs, recycles iron to bone marrow.