Circulatory System

Purpose

• Transport gases, nutrient molecules, hormones and waste

• Regulate Internal Temperature

  • Protect against blood loss, diseases / toxins (immunity)

Components of Circ. System

• Heart : Muscular organ that pumps blood through the body

• Blood vessels : System of hollow tubes through which blood moves

• Blood : Fluid that transports nutrients, oxygen and carbon dioxide

Types of Circ. System

1. Open Circulatory System : Blood flows freely within the body cavity and makes direct contact with organs and tissues (EX : Insects, Crustaceans)

2. Closed Circulatory System : Blood is kept contained within vessels, Materials must pass through vessel wall to get to organs (EX : Earthworms, Birds, Humans)

Requirements for Circ. System

• Oxygen : Required to release the energy of food

• Food nutrients : For energy and to build up cellular structures

• Water : Cells are mostly water, cells must also get ride of wastes (CO₂ + Urea)

Blood components

Plasma, Platelets, Red Blood Cells, White Blood Cells

Plasma

• Mostly water

• Dissolved molecules and ions (Glucose, Amino Acids, Hormones)

• pH balance

• Plasma Proteins - including antibodies and blood clotting proteins

Platelets

• Fragments of cells and function in blood clotting

Red Blood Cells

• Hemoglobin in R.B.C carries O₂

• Made in the bone marrow

• Dead R.B.C’s are broken down by the liver

• Biconclave disc shaped cells - Lack a nucleus at maturity

White Blood Cells

• Protect against infection

• Destroy bacteria

• Produce antibodies

• Found in both Circ. and Lymphatic Systems

Arteries

• Carry blood away from the heart at high pressure

• Carry oxygen rich blood

• Exception : Pulmonary Artery, which carries deoxygenated blood to the lungs

• Thick and highly elastic walls → withstand high pressure as ventricles contract

• Buried deep in the body for protection

• Arteries branch into smaller vessels called arterioles

Capillaries

• Very thin (1 cell thick) → exchange of materials between the blood and body tissues

• Oxygen and Carbon Dioxide diffuse across the walls of the capillaries

• Capillaries collect into venules (smaller than veins)

Veins

• Carry blood back to the heart at low pressure (most overcome force of gravity)

• Thin-walled vessels that are larger in diameter than arteries

• Not as elastic as arteries, so they rely on muscle contractions to move blood towards the heart

Movement of Blood in the Veins

• Valves : Every few centimeters along a vein allows blood to flow in one direction, toward the heart

• Muscle Action : Skeletal muscle activity in the surrounding muscle helps squeeze the veins

• Breathing Action : Creates a negative pressure in the chest which sucks the blood to the heart

The Heart

• Amphibians, reptiles, mammals have double circulation

• O₂-poor and O₂-rich blood are pumped separately from the left and right side of the heart

• Lungs (Pulmonary Circuit) / Body Cells (Systemic Circuit)

• 2 Atria collect blood from veins

• 2 Ventricles pump blood away from the heart through the arteries

Heart Valves

• 2 Atrioventricular Valves

  • Separate the Atriums from the Ventricles

  • Tricuspid Valve on right side (deoxygenated blood)

  • Bicuspid (Mitral) valve on left side (oxygenated blood)

• 2 Semilunar valves

  • Seperates the Ventricles from the Atriums

  • Aortic Valve seperates the left ventricle from the Aorta

  • Pulmonary Valve Seperates the right ventricle from the pulmonary artery

The Heart Beat

• “Lub-Dub” sound of heart beat is caused by the recoil of blood against the AV valves (Lub) then against the semilunar valve (Dub)

• Backflow of blood through a defective valve causes a heart murmur

Cardiac Cycle

• The heart contracts and relaxes in a Rhythmic cycle called the cardiac cycle

• The contraction, or pumping phase is called ‘systole’

• The relaxation, or filling phase is called ‘diastole’

• Blood pressure measured from the arm at heart height

• Blood pressure for a healthy 20 year is 120 mm Hg at systole and 70 mm Hg at diastole

Cardiac Cycle Step 1

• Atrial / Ventricular diastole

• AV valves open, SL valves close

• Atria and Ventricles fill with blood

Cardiac Cycle Step 2

• Atrial systole, Ventricular diastole

• AV valves open, SL valves close

• Ventricles fill with blood

Cardiac Cycle Step 3

• Atrial diastole, Ventricular Systole

• AV valves close, SL valves open

• Blood pumps into the arteries

Cardiac Cycle Control

• Pacemaker cells : Specialized cells in the right Atrium generates signals to contract

• The brain can act to increase or decrease heart rate

• An ECG measures electrical impulses controlling heart muscles

Heart Attack

Block coronary artery (artery that supplies the heart muscle)

Stroke

Rupture or blockage of arteries in the head

Arrhythmia

• Problem with rhythm or speed of heartbeat, can lead to insufficient blood flow to the brain or other organs

• Can be treated with medications / surgery to implant an artificial pacemaker