Circulatory and Respiratory Systems Notes

Types of Transports in Animals

• Jellyfish and Flatworms:
  • Possess a gastrovascular cavity with branches running from and toward a central canal.
  • Digested nutrients easily diffuse to all body cells due to the short distance between cells and the cavity.
  • Flatworms are thin enough that diffusion through the gastrovascular cavity is sufficient for all cells.
• Animals with Multiple Cell Layers:
  • Require a true circulatory system with blood as a transport medium.
• Invertebrates (Most Molluscs and All Arthropods):
  • Have an open circulatory system where blood is pumped out of open-ended vessels to bathe organs.
  • Example: Crayfish heart pumps blood out to bathe cells, and nutrients diffuse from blood to cells. Pores draw blood back into the heart when relaxed.
• Animals (Including Humans):
  • Have a closed circulatory system where the heart pumps blood through a closed system of blood vessels.
• Mammalian Hearts:
  • Four chambers: two atria and two ventricles.
  • Two circuits: systemic and pulmonary.
    • Pulmonary: Carries blood between the heart and the lungs.
    • Systemic: Carries blood between the heart and the rest of the organs and tissues.
  • The heart is a double pump with each pump having its own circuit within one organ
  • Necessary to create the pressure needed to get oxygen and nutrients to the body cells in a timely manner, and take up wastes for elimination from the body.

Human Circulatory System

• Major Parts:
  • Heart and Blood Vessels: Arteries and Veins.
• Direction of Blood Flow:
  • Arteries: Pump blood away from the heart.
  • Veins: Pump blood towards the heart.
• Blood Oxygenation:
  • Left side of the heart: Carries oxygenated blood (rich in oxygen, poor in carbon dioxide).
  • Right side of the heart: Carries deoxygenated blood.
• Blood Flow in/out of the Heart:
  • Blood leaves the heart from the ventricles.
  • Blood returns to the heart via the atria.
• Color Coding:
  • Oxygenated blood: Red color in figures and diagrams.
  • Deoxygenated blood: Blue color in figures and diagrams.
• Pulmonary Vessels:
  • Pulmonary Arteries: The only arteries that transport deoxygenated blood from the heart to the lungs.
  • Pulmonary Veins: The only veins that transport oxygenated blood from the lungs to the heart.
• Heart Location and Size:
  • About the size of a fist, located just under the breastbone (sternum).
• Valves in the Heart:
  • Keep blood flowing in one direction.
  • Right Atrioventricular Valve: Tricuspid valve (between the right atrium and right ventricle).
  • Left Atrioventricular Valve: Bicuspid or Mitral valve.
  • Chordae Tendineae: Cords of tissue that hold the valves in place.
  • Valve Function: Blood pressure forces valves to open into ventricles when atria fill. As ventricles contract, blood pressure forces the valves to close.
• Pulmonary Circuit:
  • Right ventricle pumps blood via pulmonary arteries to lung capillaries for gas exchange (picks up oxygen, unloads carbon dioxide).
  • Gas exchange: Unloading carbon dioxide and picking up oxygen.
  • Oxygenated blood returns to the left atrium via pulmonary veins.
• Systemic Circuit:
  • Left atrium pumps blood into the left ventricle, which pumps with great force.
  • Oxygenated blood reaches all organs and tissues.
  • Blood leaves the left ventricle through the aorta (largest blood vessel).
  • Arteries branch off the aorta leading to various organs.
  • Arteries become capillaries, which are the sites of gas and nutrient exchange.
• Deoxygenated Blood Return:
  • Deoxygenated blood returns to the right side of the heart (right atrium) via veins.
  • Superior (anterior) vena cava: Carries blood from the upper body.
  • Inferior (posterior) vena cava: Carries blood from the lower body.
  • Both drain into the right atrium, which pumps blood into the right ventricle, repeating the circuits.

Blood Vessel Structure and Function

• General Structure (Except Capillaries):
  1. Innermost Layer: Endothelium
     • Surrounds the lumen (central space of vessel).
     • Made of a single layer of flattened epithelial cells.
     • Provides a smooth lining for easy blood flow.
  2. Middle Layer:
     • Smooth muscle cells and elastic fibers.
     • Muscle cells control lumen size (vasoconstriction and vasodilation).
     • Elastin allows stretching and recoil.
  3. Outer Layer:
     • Connective tissue with fibers.
     • Protects the vessel, attaches it to surrounding structures, and allows stretching and recoil.
• Capillaries Structure:
  • Made of only one layer of tissue: a thin wall of endothelial cells.
• Arteries
  • Carry blood away from the heart.
  • Highest blood pressure, therefore thickest middle layers and relatively thick outer layer.
  • Types:
    • Elastic Arteries: Include the aorta and its branches.
      • Closest to the heart, experience greatest pressure.
      • Greatest amount of elastin in the middle layer.
      • Expand when the heart contracts and recoil when the heart relaxes, propelling blood forward.
      • Expansion and relaxation felt as the 'pulse.'
    • Muscular Arteries:
      • Mostly smooth muscle in the middle layer.
      • Deliver blood to organs of the body.
• Arterioles
  • Smaller vessels that branch from arteries.
  • Connect to capillaries.
  • Blood pressure drops rapidly in the arterioles.
• Capillaries
  • Smallest and thinnest vessels, arranged as capillary beds in organs and tissues.
  • Link arterioles and venules.
  • Made of a thin layer of endothelium to facilitate the exchange of materials between blood and cells.
  • Oxygen and nutrients diffuse out of the blood into the cells.
  • Carbon dioxide and other cellular wastes flow from the cells into the bloodstream.
  • Blood pressure must be low in capillaries.
• Venules
  • Carry blood to veins.
• Veins
  • Return blood to the heart.
  • Formed when venules join together.
  • Experience the lowest blood pressure; therefore, the middle layer is much thinner than in arteries.
  • The outermost layer is the thickest layer, although still thinner than in an artery.
  • Large lumen to hold a large volume of blood.
  • Special adaptations to help blood return to the heart:
    • Valves: Prevent backflow, mainly in limbs.
    • Skeletal Muscle Action: Muscles contract, press against veins, and force blood through one-way valves toward the heart.
  • Damaged valves can result in blood pooling in stretched veins (varicose veins).
• Gravity and the Circulatory System
  • Gravity constantly pulls blood downward.
  • Mammals have mechanisms, including a strong heart muscle, to pump blood against gravity.
  • Giraffes - tall with extremely long necks - must have powerful hearts to pump blood to the brain when standing.
  • When a giraffe bends over, blood flows toward the head, nearly doubling blood pressure.
  • Giraffes have special valves and sinuses to protect the brain.
• Connections: What is a Heart Attack?
  • Heart cells need oxygen and nutrients to function.
  • Coronary arteries supply the heart muscle with oxygenated blood.
  • Coronary arteries branch off the aorta as it exits the heart.
  • A heart attack occurs when a coronary artery becomes blocked.
  • Cardiac muscle cells are starved of oxygen, causing heart tissue to malfunction and die.
  • Scar tissue forms over the damaged tissue, decreasing the heart's ability to contract for two-thirds of victims that survive.
  • Coronary arteries are blocked by lipids (e.g., cholesterol) that accumulate and form plaque.
  • Plaque narrows vessels and makes a rough surface that can stimulate blood clot formation.
  • Blood clots can become trapped in narrowed vessels, completely blocking them off.

Blood Pressure

• Definition:
  • Measure of the force of blood against the arterial walls, measured in millimeters of mercury (mmHg).
• How it Works:
  • Blood pressure occurs when the left ventricle contracts, causing arteries to stretch.
  • Arteries recoil and push the blood onward when the heart relaxes; this stretching and recoiling can be felt as the pulse.
• Blood Pressure Reading:
  • Systolic Blood Pressure: Force on the artery walls when the heart is contracting (systole).
  • Diastolic Blood Pressure: Force when the heart is relaxing (diastole).
  • Typical Reading: Around 120/80 mmHg.
• Hypertension
  • High blood pressure is diagnosed when blood pressure readings are persistently elevated: Systolic blood pressure exceeds 140 and/or diastolic pressure exceeds 90 mmHg.
• Impacts: Hypertension forces the heart to work harder, may enlarge and weaken it, and can also damage the walls of arteries. It increases the risk of heart attack and stroke.

Blood Functions and Components

• Functions of Blood in the Human Body:

  • Transportation:
    • Nutrients and oxygen are distributed to all body cells.
    • Metabolic wastes and carbon dioxide are transported for elimination.
    • Hormones are transported from glands to target organs or tissues.
  • Regulation:
    • Maintains homeostasis in the body by helping to maintain water balance, body temperature, and pH balance.
  • Protection:
    • An important part of the immune system, protects against bacteria and viruses.

• Components of Blood

  • Average adult has about 5 liters of blood.
  • Considered a 'fluid tissue' made up of cells suspended in liquid called plasma that work together to fulfill specific functions.
  • Major components: red blood cells (erythrocytes), white blood cells (leukocytes), platelets (thrombocytes), and plasma.
  • After centrifuging, blood cells separate from plasma and settle at the bottom of the test tube.
  • Plasma makes up about 55% of the volume of blood, while cells make up the remaining 45% of the volume.
  • Red blood cells are the most plentiful of the blood cells, making up about 44% of the volume of blood.
  • White blood cells and platelets make up the remaining 1% of blood volume.
  • One milliliter of blood contains about 5 to 6 million red blood cells, 5000 to 10 000 white blood cells, and 250 000 - 400 000 platelets.

• Plasma

  • Fluid part of blood.
  • Thick, sticky, yellowish fluid that is largely water (90%).
  • Carries blood proteins, nutrients (glucose, fatty acids, vitamins), salts, dissolves gases, waste products from cell metabolism, and hormones.
  • Three important groups of plasma proteins are:
    • Albumins: work with salts to create osmotic pressure that draws water back into capillaries, helps maintain body fluid levels (the osmotic balance), and therefore have an important role in keeping homeostasis in the body.
    • Globulins: produce antibodies that are important in the immune response.
    • Fibrinogens: essential to blood clotting.

• Red Blood Cells (Erythrocytes)

  • Small, biconcave cells.
  • Shape provides greater surface area for gas exchange.
  • Primary function: to transport oxygen to the body's organs and tissues.
  • Contain a large, complex protein called haemoglobin that greatly increases the amount of oxygen that blood can carry.
  • About 250 million haemoglobin molecules are found in each red blood cell.
  • Each haemoglobin molecule can carry 4 molecules of oxygen.
  • Haemoglobin contains iron, which gives blood its red colour.
  • Erythrocytes are continually being produced in bone marrow in a process called erythropoiesis (erythro = red blood cell; poiesis = to make).
  • Lack a nucleus and mitochondria, which are a type of cell organelles involved in cellular respiration: live only 3 to 4 months before they are broken down and their iron is returned to the bone marrow where it is recycled into haemoglobin for new erythrocytes.
  • Any condition that lowers blood oxygen levels causes an increase in the rate of erythropoeisis.
  • The term anemia is used to describe a condition where there are low levels of haemoglobin or red blood cells, causing a reduction in the amount of oxygen delivered to tissues.
  • The most common symptom of anemia is low energy levels: Anemia may result from hemorrhage (ie; blood loss), various diseases (such as some types of cancer), or from a dietary deficiency of iron. Depending on the cause, a blood transfusion, iron pills, or a diet rich in iron may be needed.

• Leukocytes (White Blood Cells)

  • The main function of leukocytes is to fight infections caused by foreign invaders such as bacteria, and prevent cancer cells from growing.
  • They spend most of their time in interstitial fluid patrolling for invaders: Their numbers can increase dramatically whenever they engage in battle with an invader.
  • The main criteria used to identify the different types of leukocytes are; the shape and size of the nucleus, and the presence or absence of granules in the cytoplasm.
  • A special dye called Wright's stain gives these structures a characteristic colour in each type of cells. There are 5 main types of white blood cells that fall into two groups:
    • The granulocytes group have small cytoplasmic granules and include neutrophils, eosinophils, and basophils
    • The agranulocytes group lack granules and include monocytes and lymphocytes. All white blood cells are produced from stem cells in bone marrow.
  • Neutrophils and monocytes are two common types of leukocytes that are dispatched from the blood stream to tissues to destroy microbes. They squeeze through clefts between capillary cells and move toward the invading microbe in a process called diapedesis. When they reach the invader they engulf them (in a process called phagocytosis), and then release enzymes that not only digest the invader, but also destroy the white blood cell itself. Pus is made up of the remaining protein fragments of the white blood cells and the microbe. These cells also help tissues heal by removing cellular debris left after an injury or infection.
  • Other important leukocytes are the lymphocytes. Some lymphocytes produce antibodies to help destroy pathogens, others attack the invaders directly, and other act to preserve a memory of the pathogen in case of future invasion.

• Platelets

  • Platelets prevent us from bleeding to death when we injure a blood vessel by helping to form blood clots to seal the damaged vessel.
  • They form in the bone marrow.
  • Like red blood cells, they have no nucleus (enucleate).

• Blood Clotting

  • maintains homeostasis in the body by preventing blood loss from torn or ruptured blood vessels, and by providing support for weakened blood vessels that are in danger of rupturing.
  • Trillions of platelets move through the normally smooth vessels: They initiate the blood clotting process when they strike and adhere to a rough surface (for example, a ripped blood vessel after a cut).
  • First, they release chemicals that make other platelets in the vicinity sticky: These sticky platelets form a platelet plug that may be sufficient to seal very minor injuries to the blood vessel.
  • In more serious injuries, platelets release a protein called thromboplastin.
  • Thromboplastin, along with calcium ions and other factors, causes prothrombin (a plasma protein) to transform into thrombin.
  • Thrombin acts as an enzyme, converting the fibrinogen molecule into fibrin threads.
  • These fibrin threads form a mesh, trapping red blood cells, and preventing them from leaving the damaged blood vessel; this also prevents microbes from getting into the body.

• Connections: Leukemia

  • Leukemia is a cancer of white blood cells where they begin to divide uncontrollably.

Exchanging Gases: The Respiratory System

• Lungs are the organs that allow gas exchange between the air and the blood: A set of tubes conducts air from outside the body to the lungs.

• The trachea is a single large tube: It is supported by rings of cartilage to prevent its collapse.

• The trachea branches off into bronchi:

  • There are primary, secondary and tertiary bronchi, which deliver air to increasingly smaller bronchioles.

• There are two types of bronchioles: terminal and respiratory:

  • The respiratory ones deliver air to clusters of tiny sacs, called alveoli.

• Alveoli are thin-walled and surrounded by capillaries, and are the site of gas exchange: Each alveolus is covered by only a thin layer of epithelium (simple squamous epithelium to be specific), which makes gas exchange via diffusion possible.

• Oxygen molecules efficiently pass by diffusion from the alveoli into the capillaries: At the same time, carbon dioxide (a by-product of cellular respiration) diffuses from the blood, across the capillaries, and into the alveoli.

• The carbon dioxide leaves the alveoli (and lungs) as exhaled air.

• Connections: Composition of exhaled air: If we are exhaling carbon dioxide, and we need oxygen for cellular processes, why does mouth-to-mouth resuscitation in first aid work?

  • This is because exhaled air contains oxygen as well.
  • The composition of exhaled air is about 5.6\% carbon dioxide, (normal air contains about 0.04\% carbon dioxide), yet is about 14\% oxygen (whereas normal air is about 20.9\% oxygen).

• The Mechanism of Breathing

  • Breathing involves moving air in and out of the lungs: Breathing is accomplished by the movement of the diaphragm, which is the muscle that separates the chest cavity (containing the lungs) from the abdominal cavity.
  • Muscles in between ribs also help to move the chest wall outward and upward.
  • During inhalation, the diaphragm moves downward and the muscles in between the ribs contract: These events cause the volume of the chest cavity to increase (see Figure 15). The result of the increased volume is a decreased pressure (compared to the air pressure outside the body).
  • Therefore, air flows naturally from the outside in through the trachea, bronchi, and bronchioles to the alveoli.
  • Exhalation is accomplished by the chest wall and diaphragm simply returning to the normal (relaxed) position: During relaxed breathing, there is no muscle contraction involved in exhalation.

• Homeostasis and Breathing

  • With exercise, the amount of carbon dioxide in the blood increases because cells are using glucose more rapidly. When carbon dioxide dissolves in water, a weak acid, called carbonic acid, is formed. The presence of even a weak acid lowers the pH of the blood. Some brain cells plus cells in the aortic arch (directly after oxygenated blood has left the heart) and carotid arteries are sensitive to pH changes. If a lower pH is sensed, nerve impulses are sent to the diaphragm and the ribcage muscles. This causes a faster contraction of these, forcing a faster and more forceful breathing. This increases the amount of air that is being let into the lungs, which, in turn, increases the amount of gas exchange. When exercise stops, the carbon dioxide levels go down, and breathing returns to normal.