Circulatory System: Blood, Lymph & Tissue Fluid

• The circulatory system consists of all body parts that help in the transportation of materials.
• The circulatory system in animals comprises: a fluid transport medium (blood and lymph), a control center (heart), and a path for the transport medium to circulate (blood vessels and lymph).

Fluids in the Body

• An adult human body contains 40 liters of fluid.
• 25 liters of this fluid is intracellular, found within the cells.
• The remaining 15 liters include extracellular fluid within the body.
• The extracellular fluid that forms the transport medium is of three types: blood, tissue fluid and lymph.

Blood

• Blood is a red fluid circulating through the heart and blood vessels.

Tissue Fluid

• Tissue fluid is a colorless fluid found between cells in various organs.
• Blood plasma and WBCs move out of capillaries into surrounding spaces to form tissue fluid.
• Tissue fluid bathes the cells, allowing them to absorb oxygen and nutrients while giving off carbon dioxide and wastes.

Lymph

• Lymph is a faint yellow fluid in lymph vessels.
• Most tissue fluid enters minute lymph vessels and is called lymph.
• Lymph consists of WBCs but lacks RBCs and platelets.
• Lymph vessels empty lymph back into the bloodstream through the subclavian vein.

Types of Blood Circulatory Systems

• Open circulatory system
• Closed circulatory system

Open Circulatory System

• Materials exchange directly between cells and blood.
• Blood enters interstitial spaces and circulates there.
• Few blood vessels are present and they are not extensive.
• Vessels are open-ended, opening into common cavities called the haemocoel.

Closed Circulatory System

• Blood circulates within closed vessels so blood is distinct from the interstitial fluid.
• The heart pumps blood into vessels that reach tissues and organs.
• Gas exchange occurs in the bloodstream in smaller vessels (capillaries) and tissues.

Components of the Circulatory System

• Blood is the fluid that carries material
• The heart serves as the pumping organ
• Blood vessels are the tubes through which fluid flows.
• Lymph is the fluid that helps with the immune system and fluid balance.

Blood as a Connective Tissue

• Blood is a fluid connective tissue.
• Blood comprises 55% plasma and 45% formed elements (WBCs, RBCs, and platelets).
• Blood delivers oxygen and nutrients to cells and tissues throughout the body.
• Blood makes up 8% of body weight.
• An average adult possesses 5-6 liters of blood.

Composition of Blood

• Blood contains plasma, which carries most materials in dissolved form.
• Plasma, mainly water, carries minerals, amino acids, glucose, urea (waste), hormones, and dissolved proteins.

Formed Elements in Blood

• Red blood cells (RBCs)
• White blood cells (WBCs)
• Platelets

Plasma

• Plasma makes up 50% of blood volume
• It is pale yellow in color and consists of salts, nutrients, water, and enzymes.
• It contains vital proteins needed for overall health.
• Plasma transfusions are given to patients with liver failure and life-threatening injuries.

Red Blood Cells (Erythrocytes)

• Red blood cells contain hemoglobin, which carries oxygen for respiration.
• Human RBCs are small, biconcave, thin, and lack mitochondria and a nucleus when mature.
• The biconcave shape increases the surface area-to-volume ratio which improves gas exchange.
• Lack of a nucleus provides additional space for hemoglobin, which is used in oxygen transport.
• Oxygen binds to hemoglobin and reaches every cell.
• Lack of mitochondria helps in maximizing the amount of oxygen delivered to tissues.
• Red blood cells have an average life span of 120 days.
• Old or damaged RBCs break down in the liver and spleen, and new RBCs are produced in bone marrow.

Erythropoietin

• Red blood cell production is controlled by erythropoietin, a hormone released by the kidneys when oxygen levels are low.

Hemoglobin

• Hemoglobin is an iron-containing pigment in red blood cells.
• Hemoglobin mainly transports oxygen and carbon dioxide.
• Deficiency of iron or vitamin B12 in food leads to a deficiency of hemoglobin, known as anemia.

Anemia Symptoms

• Low red blood cell count
• Pale skin and a tired appearance
• Loss of stamina
• Dizziness
• Low oxygen supply to tissues
• Low metabolic rate and respiration
• Rapid heartbeat

WBCs (Leukocytes)

• White blood cells (leukocytes) are less common than red blood cells (less than 1% of blood cells).
• WBCs are involved in immune responses, recognizing and neutralizing invaders (bacteria and viruses).
• White blood cells are larger than red blood cells
• WBCs have a normal nucleus and mitochondria.
• White blood cells come in five major types split in two groups, named for their appearance under a microscope.

Granulocytes

• Granulocytes(neutrophils, eosinophils, and basophils) have granules in their cytoplasm when viewed under a microscope.

Agranulocytes

• Agranulocytes (monocytes and lymphocytes), do not have granules in the cytoplasm.
• Some white blood cells engulf and break down pathogens, while others recognize microorganisms and launch immune responses.
• Lifetimes of WBCs range from hours to years.
• New white blood cells are produced in the bone marrow, thymus, lymph nodes, and spleen.

Blood Platelets (Thrombocytes)

• Blood Platelets (Thrombocytes) help clot blood during injury to prevent blood loss.
• Platelets (thrombocytes) are cell fragments involved in blood clotting
• Megakaryocytes break into 2000–3000 platelets
• Platelets are disc-shaped and small.

Blood Clotting Mechanism

• Injury to blood vessels triggers the blood clotting mechanism.
• Platelets clump at the wound site.
• Thrombokinase is released.
• Prothrombin converts to thrombin with the help of calcium ions.
• Fibrinogen turns into fibrin, forming a clot that stops further blood loss.

The Functions of Blood

• Transports materials like glucose, proteins, amino acids, salts, water, and hormones.
• Regulates water (fluid) balance.
• Carries extra water to the kidneys for removal in urine and retains water when there is water scarcity.
• White blood cells and antibodies protect from microorganisms.
• Nutrients from digested food are supplied from the small intestine to body organs.
• Transports waste (CO2) to the lungs and urea to the kidneys for removal.
• Helps maintain body temperature through heat distribution by the high heat carrying capacity of plasma.

Blood Clotting at Injury Sites

• Platelets help with blood clotting by forming a clump at the site of injury, then fibrin completes the clot.

Arteries

• Carry blood away from the heart.
• Have walls with three layers that are thick to bear the pressure of blood that is pumped by the heart.

Veins

• Carry blood towards the heart.
• The three layered walls are thinner than arteries because they bear low blood pressure.
• Valves prevent backflow of blood.

Blood Capillaries

• The thinnest blood vessels.
• There is a wide network of blood capillaries in every organ of the body.
• They facilitate the exchange of oxygen, glucose, amino acids, and waste products.

Arteries vs. Veins

• Arteries carry pure, oxygenated and nutrient-rich blood, while veins carry impure, deoxygenated blood.
• Arteries have rigid, thick, and muscular walls, while veins have thin, collapsible walls.
• Arteries are situated deeply within the body, while veins are superficial and closer to the skin.
• Arteries carry blood away from the heart, while veins carry blood toward the heart.
• Blood pressure is high in arteries and low in veins.
• A pulse is felt in arteries but not veins.
• Oxygen level is high in arterial blood and low in venous blood.
• Carbon dioxide level is low in arterial blood and high in venous blood.
• The lumen is narrow in arteries and wide in veins.
• Valves are absent in arteries and present in veins.

Lymph

• Lymph is extra tissue fluid that enters lymph capillaries from the tissues.
• Lymph capillaries (lacteals) join to form lymph vessels.
• It is similar to blood plasma and has less protein.
• Lymph vessels join with veins, supplying lymph back into the blood.
• Lymph serves as a source of nutrients for cells and helps remove extra tissue fluid and proteins.
• Lymph contains specialized WBCs that kill microorganisms.
• Lymph plays a role in absorbing fats and fat-soluble vitamins (A, D, E, K) in the small intestine.

Heart

• The heart is a hollow muscular organ made of cardiac muscles that pump rhythmically to circulate blood.
• Located in the chest cavity is between the lungs
• Is protected by a two-layered sac called the pericardium
• Pericardial fluid protects the heart from shocks.

Structure of Human Heart

• Human heart is fist-sized and has four chambers (two ventricles and two atria).
• The ventricles act as the lower chambers that pump blood.
• The atria are the upper chambers that receive blood.
• A wall of muscle called the septum separates the right and left regions of the heart.

External Structure of the Heart

• The pericardium is the first structure observed externally.
• The heart is enclosed in a fluid-filled cavity (pericardial cavity) lined by the pericardium.
• It is situated to the left of the chest.
• The pericardium protects the heart, provides lubrication, maintains its position, and allows expansion.

Internal Structure of Heart

• The internal structure includes chambers and valves that control the flow of blood.

Chambers of the Heart

• Vertebrate hearts have different chamber numbers.
• Most fish have two chambers.
• Reptiles and amphibians have three chambers.
• Avian and mammalian hearts (including humans) have four chambers: Left atrium, a right atrium, a left ventricle and a right ventricle.

Atria

• Thin, less muscular walls and smaller than ventricles.
• They are blood-receiving chambers.
• They receive blood through veins at low pressure.
• They have thin walls because they do not bear much blood pressure.

Ventricles

• Larger and are more muscular chambers which pump blood.
• Connected to larger arteries that deliver blood.
• They have thicker walls compared to atria for forcing blood into arteries.
• The left ventricle has very thick walls to force blood into the aorta.

Valves

• Valves are located in the cardiac chambers.
• Flaps of fibrous tissues ensure one-way blood flow and prevent backflow.
• Atrioventricular valves are between ventricles and atria; and the Tricuspid valve are between the right ventricle and right atrium, and the Mitral valve are between the left ventricle and left atrium.
• Semilunar valves are between the left ventricle and aorta and in the pulmonary artery/right ventricle.

Types of Circulation

• Human hearts separate pure oxygenated and impure blood.

Blood Flow in Right Side of Heart

• The main veins (superior and inferior vena cava) collect impure blood/CO2 from the body and drain it into the right atrium.
• It passes into the right ventricle through the tricuspid valve.
• Blood from the right ventricle is pushed into the the pulmonary arteries, taking it to the lungs for gaseous exchange. Pulmonary circulation is the part of circulation responsible for carrying deoxygenated blood away from the heart
• Pulmonary circulation then brings oxygenated blood back to the heart.

Blood flow in left side of the heart

• Purified blood is supplied from the lungs to the left atrium by the pulmonary veins and into the left ventricle through the mitral valve.
• Blood from the left ventricle is pushed into the aorta, which supplies blood to different parts of the body.

Systemic circulation

• The oxygenated blood is pumped from the heart to every organ and tissue and then back again to the heart through a series of blood vessels.

Coronary circulation

• Coronary circulation supplies oxygenated blood to the heart

Double Circulation

• Humans circulate blood twice through the heart in the cardiopulmonary system.
• The left side of the heart receives oxygenated blood from the lungs and pumps it to body organs.
• The right side receives impure blood, moving oxygen to the blood, then pumping impure blood to the lungs.
• The right side of the heart pumps the impure blood, carrying carbon dioxide to the lungs for gas exchange.
• Blood releases CO2 and takes up fresh oxygen.
• Pure oxygenated blood returns back to the left side of the heart and the cycle is repeated again.

Significance of Double Circulation

• This is present in the heart of mammals and birds separating the flow of oxygenated and deoxygenated blood.
• It supplies sufficient oxygen .to body organs and tissues in mammals and birds because they are warm-blooded and have a high respiration rate.
• Oxygenated blood should move separately to body tissues and cells and should not mix with the deoxygenated blood.
• Cold-blooded animals (fishes, amphibians, and reptiles) have a low rate of respiration and demand less oxygen.
• Cold-blooded animals have partial mixing of oxygenated and deoxygenated blood and the blood carries less oxygen to the body tissues.

Types of Blood flow

• Amphibians’ hearts have two atria receiving blood from different circuits, and one ventricle which results in the mixing of blood reducing the efficiency of oxygenation.
• Arteries supply fresh oxygenated blood to body organs and they divide into smaller branches called arterioles, which divide into blood capillaries.

Blood Capillaries

• Form a network inside organs.
• Blood plasma with dissolved materials exits blood through the thin blood capillary walls and collects into the tissue.

Tissue Fluid

• An intermediate medium between blood and tissue cells.
• Contains oxygen, amino acids, glucose, mineral ions, and proteins for body cells

Body cells take up required materials and release wastes (CO2):

• CO2 dissolves into the blood plasma in the red blood cells.

Cardiac Cycle

• A sequential event in the heart which is cyclically repeated and consists of systole and diastole of the atria and ventricles.
• the duration of a cardiac cycle is 0.8 seconds

Stroke Volume

• During a cardiac cycle, each ventricle pumps approximately 70 ml of blood called stoke volume.

Cardiac Output

• Stroke volume x heart rate
• Defined as the volume of blood pumped out by each ventricle per minute (averages 5000 ml.)

Joint Diastole

• Blood is received by the atria from the pulmonary veins and vena cava.
• As tricuspid and bicuspid valves are open.
• Blood flows into the left and the right ventricles
• Semilunar valves are closed.

Atrial Systole

• The SAN (Sinoatrial Node) generates an action potential, stimulating both atria simultaneously resulting in contraction

SAN - Sinoatrial Node

• Located in the right atrium, initiates electrical impulses causing the heart to beat (the heart’s natural pacemaker)

Ventricular Systole

• The action potential conducts to the ventricular side by the AVN (Atrio-Ventricular Node) and AV bundle (Atrioventricular Bundle) that transmits it through the ventricle.
• Ventricular muscles contract (ventricular systole) and the atria relax (diastole).

Tricuspid and Bicuspid Valves

• During ventricular systole, pressure increases closing the tricuspid and bicuspid valves.
• The first heart sound (lub) is associated with the closure of the tricuspid and bicuspid valves.

Semilunar Valves

• Ventricular pressure increase causes the semilunar valves of the pulmonary artery (right side) and the aorta (left side) to force open.
• Allowing blood in the ventricles to flow through these vessels and into the circulatory pathways.

Ventricular Diastole

• The ventricles relax (ventricular diastole) and ventricular pressure falls causing the closure of semilunar valves which prevents blood from flowing back into the ventricles.
• The second heart sound (dub) is associated with the closure of the semilunar valves.

Joint Diastole

• Ventricular pressure declines and tricuspid and bicuspid valves are pushed open.
• Pressure in the atria forces the valves to open, emptying blood into the ventricles leading the ventricles and atria again in an relaxed (joint diastole) state and the cycle repeats.
• The SAN generates a new action potential which repeats the events.
• Each cardiac cycle produces two sounds: the first sound is lub and the second heart sound is dub.

Blood Pressure

• Force of blood against the arteries.
• Normal blood pressure measures to be 120 – 140 / 70 – 90 mm Hg along with the normal pulse rate 60 – 80 per min.

Sphygmomanometer

• For blood pressure measurement through sphygmomanometer.

Systolic Blood Pressure

• The reading recorded when the pressure is exerted on the arteries and blood vessels while the heart is beating.
• Normal reading of 90-120mm Hg.

Diastolic Blood Pressure

• The reading recorded when the pressure is exerted on the walls of arteries between heartbeats when the heart is relaxed.
• Normal reading of between 60 – 80 mm Hg.

What is Hypertension

• Abnormally high blood pressure with a high psychological stress.
• Patients suffering from this disorder will have their blood pressure reading greater than 140 over/90 mm.

Causes of Hypertension

• Acute stress and unfavorable environmental factors
• Other lifestyle factors include: inactive habits, high sodium (processed foods), tobacco and alcohol use.

Effects of Hypertension

• Itself asymptomatic, and may lead to cardiovascular system damage.
• Leads to the increased development of plaques narrowing the blood vessels, in the illness atherosclerosis.

Treatment and Precautions for Hypertension

• Weight loss treatment programs like diet and exercise.
• A well-balanced diet (whole grains, fruits, vegetables, low-fat dairy products).
• Avoid LDL cholesterol (low-density lipoprotein).
• Reduce sodium intake.
• Increase intake of calcium and vitamin D.

Pulse Rate

• Pulse Rate the expansion and elastic recoil of the walls of the artery during ventricular systole.

Heart Beat

• the time taken by one systole followed by immediate diastole of the heart.
• Pulse can be felt in the wrist below the base of the thumb and neck.

Explore the relationships between blood, tissue fluid, and lymph. Understand their roles in material exchange, defense mechanisms, and overall circulatory function. Learn about open vs. closed circulatory systems and fluid volumes.