Transport in Animals - Exam Notes

Transport in Animals

Introduction

• Vein: A blood vessel that carries blood towards the heart.
• Artery: A blood vessel that carries blood away from the heart.
• Heart: The central organ responsible for pumping blood throughout the body.

Vital Substances and the Need for Transport

• Simple Animals: Substances diffuse directly from cell to cell.
• Larger Multicellular Animals: Require a circulatory system.
  • Blood: Transports dissolved gases, nutrients, and wastes.
  • Blood Vessels: Channels through which blood flows.
  • Heart: Pumps blood around the body.
  • Valves: Ensure unidirectional blood flow, preventing backflow.

Types of Circulatory Systems

Open Circulatory System

• Blood is pumped from the heart at low pressure into the haemocoel (body cavity).
• Blood bathes internal organs directly and moves slowly through tissues.
• Blood returns to the heart via collecting vessels.
• Inefficient; found only in small organisms.
• Examples: Crustaceans, snails, insects.

Closed Circulatory System

• Blood remains within blood vessels.
• Tissue fluid is found between vessels and cells.
• Very effective; allows for rapid and high-pressure blood flow.

Human Circulatory System (Cardiovascular System)

• William Harvey: Demonstrated blood circulation (accepted in 1628).
• Double Circulatory System:
  • Two "pumps" (sides of the heart).
    • Right Side: Heart $\rightarrow$ Lungs $\rightarrow$ Left side of the heart (Pulmonary Circuit).
    • Left Side: Heart $\rightarrow$ Rest of the body $\rightarrow$ Right side of heart (Systemic Circuit).

Pulmonary and Systemic Circuits

• Pulmonary Circuit: Involves the right side of the heart pumping deoxygenated blood to the lungs for gaseous exchange (CO2 for O2), and the return of oxygenated blood to the left atrium.
• Systemic Circuit: Involves the left side of the heart pumping oxygenated blood to the body for gaseous exchange (O2 for CO2), and the return of deoxygenated blood to the right atrium.

Advantages of a Double Circulatory System

• Pulmonary System: Allows for efficient gaseous exchange (O2 uptake).
• Systemic System: Allows blood to be pumped under high pressure for quick transport of oxygen to the cells.
• Tissue fluid can form when blood plasma is pushed out of the capillaries, providing a medium for substance exchange.

The Heart

• The pump of the body.
• Beats approximately 2.5 billion times in an average lifetime, pumping over 300 million liters of blood.
• Located in the middle of the thorax, between the lungs (mediastinum).
• Protected by the sternum.

External Appearance of the Heart

• Surrounded by the pericardium: Two membranes (parietal and visceral) that move over each other when the heart beats.
• Coronary Arteries: Supply the heart with O2 and nutrients; blockages lead to heart attacks (myocardial infarction or coronary thrombosis).
• Can have fat deposits.

Internal Appearance of the Heart

• Four chambers:
  • 2 Atria (upper chambers): Small, thin-walled receiving chambers.
  • 2 Ventricles (lower chambers): Thick-walled pumping chambers (especially the left ventricle).

Chambers of the Heart

• Right Atrium: Receives deoxygenated blood from the body via the Superior Vena Cava, Inferior Vena Cava, and coronary sinus.
• Left Atrium: Receives oxygenated blood from the lungs via the Pulmonary Veins.
• Right Ventricle: Receives deoxygenated blood from the right atrium and sends it to the lungs via the Pulmonary Artery.
• Left Ventricle: Receives oxygenated blood from the left atrium and sends it to the body via the Aorta.

Internal Structures of the Heart

• Myocardium: Layer of the heart wall composed of cardiac muscle.
• Septum: Divides the left and right sides of the heart.
• Endocardium: Smooth membrane lining the heart.
• Papillary Muscles: "Bumps" in the ventricles, to which tendinous cords (chordae tendineae) extend to the AV valves.

Valves of the Heart

• Two sets of valves ensure unidirectional blood flow.

Atrioventricular Valves (AV Valves)

• Tricuspid Valve: Between the right atrium and ventricle (3 flaps).
• Mitral/Bicuspid Valve: Between the left atrium and ventricle (2 flaps).
• Prevent backflow of blood into the atria.
• When ventricles contract, the valves are pushed closed.
• Tendinous cords anchor the flaps.

Semilunar Valves

• Located at the base of the blood vessels leaving the heart.
• Pulmonary Semilunar Valve
• Aortic Semilunar Valve
• Contain 3 half-moon-shaped flaps/cusps.

Blood Flow Through the Heart

Right Side

• Low pressure.
• Deoxygenated blood from the body $\rightarrow$ Superior and Inferior Vena Cava $\rightarrow$ Right Atrium $\rightarrow$ Tricuspid Valve $\rightarrow$ Right Ventricle $\rightarrow$ Pulmonary Semilunar Valve $\rightarrow$ Pulmonary Artery $\rightarrow$ Lungs.

Left Side

• Very high pressure.
• Oxygenated blood from lungs $\rightarrow$ Left Atrium (via FOUR Pulmonary Veins) $\rightarrow$ Mitral Valve $\rightarrow$ Left Ventricle $\rightarrow$ Aortic SL Valve $\rightarrow$ Aorta $\rightarrow$ Body.

The Heartbeat

• "Lub-dup" sound.
  • LUB: Closing of the AV valves (louder & longer).
  • DUP: Closing of the SL valves (short & sharp).
• Heard using a stethoscope.

Cardiac Cycle

• All events taking place as blood flows through the heart during one complete heartbeat.
• Approximately 70 beats/min (humans).
• Each heartbeat lasts approximately 0.8 seconds.
• Systole: Cardiac muscle contracts (blood forced out).
• Diastole: Cardiac muscle relaxes (blood flows in).

Stages of the Cardiac Cycle

• Cardiac Diastole (0.4 seconds): All chambers relaxed, blood flows into the heart via open AV valves; SL valves are closed.
• Atrial Systole (0.1 seconds): Atria contract, pushing blood into the ventricles.
• Ventricular Systole (0.3 seconds): Ventricles contract, pumping blood into the aorta and pulmonary artery simultaneously. The atria relax.

Stroke Volume

• Each ventricle pumps out the same volume of blood per beat.
• Stroke Volume: Approximately 70mL/beat.

Heart Beat Control

• Heart muscle is myogenic; contractions arise within the tissue itself.

Sino-Atrial (SA) Node

• Located in the right atrium.
• Generates the heartbeat by sending electrical impulses into both atria to contract.

Atrioventricular (AV) Node

• Triggered by the SA node.
• Sends impulses to the ventricles via the bundle of His (fibres).
• Bundle divides into two bundles, running down the septum.
• Fibres fan out through the ventricular wall via Purkinje fibres.
• Stimulation initiates a wave of contraction, causing contraction of the ventricles.

ECG - Electrocardiogram

• P Wave: Depolarization of atria in response to SA node triggering.
• QRS Complex: Depolarization of ventricles, triggers main pumping contractions.
• T Wave: Ventricular repolarization.
• PR Interval: Delay of AV node to allow filling of ventricles.
• ST Segment: Beginning of ventricle repolarization, should be flat.

Heart Rate Control: Nervous and Chemical Stimulation

Nervous

• For HR to change, the SA node needs to be stimulated by the autonomic nervous system.
• Medulla oblongata sends impulses along the sympathetic nerve fibres to increase HR (exercise, stress).
• SA nodes send out more waves of impulse, increasing heart rate.
• Impulses along the parasympathetic fibres decrease HR, reducing the number of impulses the SA node sends out.

Chemical

• Hormones travel in blood (slower effect).
• Attach to receptors on heart muscle and change their contraction.
  • Epinephrine (adrenaline): Increases HR (stress).
  • Thyroxine: Increases HR.

How Exercise Affects Heart Rate

• Increased venous return to the heart.
  • Vessels dilate, carrying more blood.
  • SA node stimulated by sympathetic fibre.
  • HR increases, and a larger volume of blood is pumped out more quickly.
• Increased levels of CO2 in blood.
  • Lowers the pH, stimulating the SA node by sympathetic fibres.
  • Increases HR to take deoxygenated blood more quickly to the lungs for excretion.

Pulse

• Regular expansion and contraction of an artery, caused by the heart pumping blood.
• Felt where an artery is close to the surface.
• Each throb = heartbeat.
• Pulse Rate: Number of heartbeats per minute (bpm).

Blood Vessels

• The body contains between 5 and 6 liters of blood.
• Blood travels in blood vessels: Arteries, Veins, and Capillaries.
• Arteries: Away from the heart.
• Veins: Toward the heart.
• Capillaries: Connect arterial and venous systems; sites of gaseous exchange.

Blood Flow Sequence

Arteries $\rightarrow$ Arterioles $\rightarrow$ Capillaries $\rightarrow$ Venules $\rightarrow$ Veins

Structure of Arteries and Veins

Three layers surrounding a lumen:

• Inner Layer: Squamous endothelial cells (smooth surface).
• Middle Layer: Circularly arranged smooth muscle cells and elastic fibres.
• Outer Layer: Inelastic collagen fibres (strength).

Arteries

Structure

• Deep in the body.
• Thick middle layer with a large amount of elastic fibres and muscle tissue (withstand high pressure).
• Elastic fibres allow walls to stretch.
• Smooth muscles control lumen diameter:
  • Vasoconstriction: Muscles contract, reducing blood flow to an organ.
  • Vasodilation: Muscles relax, increasing blood flow to an organ.
• Outer connective tissue layer strengthens walls (prevent bursting).
• Lumen has a regular shape.

Functions

• Carry oxygenated blood away from the heart to the tissues under high pressure.
• Pressure reservoirs: Keep blood moving during diastole.
• Control blood distribution to various organs.

Capillaries

Structure

• Smallest blood vessels.
• Very narrow lumen (0.007 mm).
• Walls are extremely thin (single layer of squamous endothelium).
• RBC can get very close to body cells for diffusion.
• Tiny pores (clefts).
• Slow blood flow and low pressure

Functions

• Easy diffusion of substances between blood and cells.
• Phagocytes can move in and out of vessels (pores).

Veins

Structure

• Thin walls with a small amount of muscle tissue.
• "Floppy" due to a large lumen with an irregular shape.
• Large veins have SL valves.

Functions

• Carry blood back to the heart.
• Carry deoxygenated blood.

Varicose Veins

• Enlarged veins where SL valves don’t function properly.
• Blood not kept moving causes a clot, leading to thrombosis.
• If the clot is carried to the lungs, it leads to a pulmonary embolism.

Blood Pressure (BP)

• Force exerted by blood against the walls of the vessels.
• Two factors maintain BP:
  1. Pumping of the heart.
  2. Narrowness of smaller arterioles (peripheral resistance).
• BP in arteries rises and falls due to ventricular systole (rise) and general diastole (drop).

Systolic BP

• Left ventricle contracts, pushing blood into the aorta.
• Maximum pressure reached in the aorta when ventricles contract.
• Average in healthy adult: 120mm Hg.

Diastolic BP

• Walls of the aorta and elastic arteries recoil, maintaining pressure on the reduced blood volume.
• Lower pressure in aorta during ventricular diastole.
• Average in healthy adult: 80mm Hg.

Importance of BP

• Ensures a steady flow of blood through the capillaries to supply all cells.
• BP in capillaries must be much lower than in the arterioles to prevent rupture of thin walls and allow increased diffusion time.

BP Measurements

• Measured using a BAUMANOMETER.
• First number (higher) = systole stage.
• Second number (lower) = diastole stage.
• Recorded as systolic over diastolic (e.g., 120/80 mm Hg).
• Normal BP in adults = 110-139/ 60-89.

Blood

• A vital fluid that transports nutrients to all body organs and tissues and carries away waste materials.
• Adult body: Approximately 5L of blood.
• Made up of blood plasma and blood cells.

Plasma

• Watery, straw-colored liquid.
• Contains dissolved substances (nutrients, waste, ions, hormones, gases), plasma proteins (Fibrinogen and Albumen), and antibodies.

Plasma Transports:

• Blood cells
• Carbon dioxide as bicarbonate ions to the lungs
• Nutrients
• Urea from liver to kidneys
• Hormones from endocrine glands
• Heat from muscles and liver (37◦)
• Blood clotting factors
• Antibodies

Blood Cells

• Red Blood Cells (erythrocytes)
• White Blood Cells (leucocytes)
• Platelets (thrombocytes)

Red Blood Cells (Erythrocytes)

• 95% of blood cells.
• Made in the red (spongy) bone marrow.
• Lifespan: 120 days (broken down in liver and spleen).
• Approximately 7 microns in diameter.
• Biconcave discs (large surface area for oxygen collection and release).
• Haemoglobin (haem = red pigment; requires iron).
• No nucleus and few organelles.
• Flexible (fits through narrow capillaries).
• Carry oxygen = oxyhaemoglobin (bright red blood).
• Can carry a small amount of CO2 (carbaminohaemoglobin).

White Blood Cells (Leucocytes)

• Fewer than RBCs (1 WBC for every 700 RBCs).
• Produced in red bone marrow, spleen, and lymph glands.
• Lifespan: only a few days or hours.
• Irregular in shape; some can change shape.
• Large nucleus and colorless cytoplasm.

Types of White Blood Cells

• Granulocytes: Large and contain granules (e.g., neutrophils - 50-70% of WBCs).
• Agranulocytes: Small, have an unlobed nucleus and no granules (e.g., lymphocytes - 25-40% of WBCs).

Functions of White Blood Cells

• Defense against disease and illness.
• Phagocytes (neutrophils and monocytes) destroy bacteria and foreign particles via phagocytosis.
• Lymphocytes produce antibodies that fight infections.

Platelets (Thrombocytes)

• Smallest constituent of blood.
• Enclosed by a membrane and have no nucleus.
• Seen as spheroid but have hair-like filaments.
• Have tiny granules (substances for forming blood clots).
• Start the process of clot formation when a blood vessel is broken.
• Stick to vessel walls to plug the break and release clotting substances.

The Lymphatic System

• Consists of lymphatic vessels, lymph nodes, and lymphoid organs/tissues (tonsils, thymus, spleen, patches in the gastrointestinal tract).
• All parts contain lymph.
• Lymph: Fluid containing WBCs (mainly lymphocytes) drained from tissue spaces.

Constituents of Lymph

• Water, solutes (protein, salts, urea, glucose), and WBCs (lymphocytes and macrophages).
• Lymphocytes:
  • B Lymphocytes: Produce antibodies that enter blood to fight invading germs.
  • T Lymphocytes: Perform many roles in the immune system.
• Macrophages: Trap and digest harmful bacteria & foreign particles through phagocytosis (in lymph nodes); also found in connective tissue.

Functions of the Lymphatic System

1. Helps Maintain Fluid Balance: Collects excess fluid from body tissues and deposits it in the bloodstream (subclavian veins). Build-up of tissue fluid causes swelling (oedema).
2. Helps Defend the Body Against Infection: Has various WBCs.
3. Transports Absorbed Fat: Lymph from intestines called chyle (appear white due to fat content).

Relationship to the Circulatory System

• The lymph system is a subsystem of the circulatory system.
• Lymph forms from plasma that seeps out of blood capillaries, bathes the body cells, and then moves into lymph capillaries.
• It re-enters the blood system near the heart to become part of the blood plasma again.

Blood Transfusion

• Transfer of blood from donor to recipient.
• Highly effective and used to:
  • Restore blood or plasma volume after extensive haemorrhage or burns.
  • Increase the number of RBCs in anaemic people.
• Donors blood must be examined to ensure it doesn’t contain pathogens (e.g., HIV) and for blood group compatibility.

Blood Groups

• Before transfusions, blood must be typed and cross-matched to avoid transfusion reactions (agglutination of RBCs).
• Four major blood groups: A, B, AB, O.

Antigens and Antibodies

• Based on the antigens (agglutinogens) found on the cell membranes of RBCs (A & B).
  • A has A ANTIGEN
  • B has B ANTIGEN
  • AB has BOTH
  • O has NEITHER
• Antibodies and antigens will react, causing RBCs to stick together (agglutination).
• People with the same blood group can exchange blood without ill effects; different blood groups are often incompatible.

Universal Donors and Recipients

• O = UNIVERSAL DONOR (no antigens; no clumping).
• AB = UNIVERSAL RECIPIENT (no antibodies which could affect any blood).

Blood Disorders

Anaemia

• Blood has abnormally low oxygen-carrying capacity (low haemoglobin).
• Symptoms: Tiredness, paleness, shortness of breath, chilly sensation.
• Caused by shortages of substances needed to make RBCs (iron, folic acid, B12), diseases in the bone marrow, excessive breakdown of RBCs (e.g., malaria), or blood loss (e.g., heavy menstrual periods, traumas).

Leukaemia

• Cancer affecting WBCs, which become abnormal and produced in large numbers.
• Fatal without treatment; causes infections, fever, tiredness, paleness, and easy bruising.
• Treated with Chemotherapy, Radio therapy, or Biological therapy (bone marrow transplants).

Hypertension

• Chronic hypertension = persistently 140/90 or higher.
• Silent killer; causes heart to work harder, leading to stroke, heart failure, brain/kidney damage.
• Risk factors include smoking, obesity, type 2 diabetes, stress, sedentary lifestyle, age, heredity, and kidney disease.

Hypotension

• Systolic pressure below 100 mmHg.
• Often associated with long life and old age free of illness.

Circulatory Problems

Coronary Artery Disease (CAD)

• Common cause of death.
• Heart attack when coronary artery is blocked.
• Plaque forms when cholesterol molecules slip below the endothelium of the coronary arteries; if plaques burst, thromboses form and block blood flow.
• Prevention involves healthy blood flow, minimal plaque build-up, and absence of inflammation.
• Risk factors: High bp, smoking, high cholesterol, obesity, type-2 diabetes, stress, sedentary lifestyle, diet (high sugars/fats).
• Treatment: Coronary artery bypass graft or coronary angioplasty.

Stroke (Cerebro-Vascular Accident - CVA)

• Brain attack caused by embolism or haemorrhage.
  1. Thrombosis in the brain artery
  2. Sudden rupture of blood vessel in the brain
  3. Rupture of blood vessels inside the skull but outside the brain
• Symptoms: Paralysis of limbs, speech/swallowing difficulties, visual disturbances, unconsciousness.

Angina

• Chest pain due to certain areas of the cardiac muscle receiving insufficient blood.