Transport in Humans and Animals - Form 4 Chapter 10 Notes

Transport System

• Importance: Delivers essential substances (oxygen, nutrients) and removes waste products (carbon dioxide, nitrogenous wastes).
• Processes Involved:
  • Simple diffusion
  • Osmosis
  • Active transport
  • Cyclosis (胞质环流): Streaming of cytoplasm within cells.

Necessity of Transport System

• Each living cell needs essential substances and must expel waste.
• Unicellular organisms (e.g., Amoeba) accomplish this via diffusion through the plasma membrane.

Multicellular Organisms and Transport Systems

• Problem: Direct exchange is insufficient due to distance between substances and body cells.
• Solution: Development of internal transport systems.

Surface Area to Volume Ratio

• The bigger the organism, the smaller the total surface area to volume ratio.
• Implications: Less efficient exchange of materials and oxygen supply, slower metabolic rate (动物体积越大，表面积就相对小，氧气供应效率差，代谢率变得缓慢).

Activity: TSA/V Ratio and Diffusion Rate

• Problem Statement: How does the total surface area to volume ratio affect the diffusion rate of solutes?
• Hypothesis: The larger the TSA/V ratio, the faster the diffusion rate of solutes.
• Variables:
  • Manipulated: Side dimension of cubes
  • Responding: Percentage portion of the cube that changes color
  • Fixed: Concentration of 0.2 M NaOH solution, type of agar
• Materials: 1.0% agar-phenolphthalein, 0.2 M sodium hydroxide solution, plastic sheet, filter paper
• Apparatus: Petri dish, ruler, scissors, razor blade, stopwatch
• Procedure:
  1. Create cube-shaped molds of varying side dimensions (1 cm, 2 cm, 3 cm, 4 cm).
  2. Calculate total surface area and volume for each cube.
  3. Pour 1.0% agar-phenolphthalein into each mold and allow to set.
  4. Place each cube into a Petri dish with 50 ml of 0.2M sodium hydroxide solution, start stopwatch.
  5. After 5 minutes, remove each cube and estimate the percentage that changed color.

Key Observations and Improvements

• Relationship between cube size and TSA/V ratio: As cube size increases, TSA/V ratio decreases.
• Impact of TSA/V ratio on NaOH movement: Higher TSA/V ratio leads to faster NaOH diffusion.
• Improving Solute Movement: Increase the concentration of the sodium hydroxide solution.

Efficiency of Substance Exchange

Exchange occurs rapidly if:

• Large surface area in contact with the environment.
• Small organism volume (body size).
• Short distance between substances and body cells.
• High concentration gradient between substances and body cells.

Multicellular Organisms and Diffusion

• Large multicellular organisms have slow diffusion rates due to small TSA/V ratio. They overcome this by having transport systems.
• Flatworms have large TSA/V ratio due to their flat body, allowing efficient diffusion.

10.1 Types of Circulatory Systems

Open Circulatory System

• Haemolymph flows directly into the body cavity (haemocoel 血腔) and bathes the body cells.
• Direct exchange of materials between haemolymph and body cells.

Closed Circulatory System

• Blood flows in continuous closed blood vessels and is distributed throughout the body.
• Indirect exchange of materials occurs across the walls of blood capillaries.

Haemolymph

• Circulatory fluid in insects.
• Flows freely within the open body cavity (haemocoel 血腔).
• Direct contact with internal organs facilitates direct exchange of materials.
• Transports hormones, nutrients, salts, and metabolic wastes.
• Does not transport respiratory gases (oxygen and carbon dioxide).
• Lacks red blood cells, giving it a blue-green color.
• Flows slower than blood.

Open Circulatory System Mechanics

• One or more hearts pump haemolymph through blood vessels into the haemocoel.
• Haemolymph flows out from the heart into the haemocoel during heart contraction.
• Substance exchange occurs via diffusion in the haemocoel.
• Haemolymph diffuses directly into body cells.
• Slower compared to closed circulatory systems.
• During heart relaxation, haemolymph flows back into the heart through tiny openings called ostium 心门.
• Found in insects, crustaceans, molluscs.
• Insects need a tracheal system because the open circulatory system cannot distribute oxygen efficiently.

Differences between Open and Closed Circulatory Systems

Closed Circulatory System

• Found in all vertebrates and some invertebrates (molluscs, annelids).
• Blood flows within the heart and vessels.
• Never comes into direct contact with body cells.
• Two types: Single circulation and double circulation.

Single Circulation (单循环)

• Found in fish.
• Blood passes through heart only once in a complete circulation.
• The fish heart has two chambers: one atrium and one ventricle, separated by an atrio-ventricular valve.
• Disadvantage: Blood is pumped only once, pressure cannot be maintained, leading to sluggish blood flow (心室一次泵血到鳃再到全身各处才流回心脏. 血压无法维持. 血流缓慢).
• Blood from the ventricle is pumped to gill capillaries for gaseous exchange, then to systemic capillaries.
• In systemic capillaries, oxygen diffuses into tissues, and carbon dioxide diffuses from tissues into the capillaries.

Double Circulation (双循环)

• Two sub-circuits:
  • Pulmonary circulation: Deoxygenated blood from right side of heart to lungs.
  • Systemic circulation: Oxygenated blood leaves left side of heart to all body parts except lungs.
• Blood passes through the heart twice in a complete circulation.
• More efficient than single circulation.
• Blood is pumped twice, maintaining pressure.
• Blood flows in large vessels (arteries and veins) before branching into smaller vessels (arterioles and venules) and capillaries, reducing blood pressure gradually and minimizing resistance.

Efficiency Comparison

• Double circulation is more efficient due to maintained pressure and less resistance, allowing faster oxygen delivery.
• Fish blood flow encounters more obstacles (gill and systemic capillaries), reducing blood hydrostatic pressure.
• Fish overcome this by having sinus venosus, a large lumen replacing veins and imposing less resistance.

Incomplete Double Circulation

• Found in amphibians and reptiles.
• Three-chambered heart: two atria and one ventricle.
• Two sub-circuits: pulmonary and systemic circulation.
• Incomplete circulation because deoxygenated and oxygenated blood mix (Disadvantage/weakness).
• Process:
  1. Deoxygenated blood from body to right atrium.
  2. Pulmocutaneous circulation to lungs and skin for gas exchange.
  3. Oxygenated blood from lungs and skin to left atrium via pulmonary vein.
  4. Blood from both atria enters one ventricle (some mixing occurs).
  5. Ventricle pumps blood through systemic circulations.
  6. Systemic circulation transports oxygenated blood to body tissues and returns deoxygenated blood to right atrium.

Complete Double Circulation (完全双循环)

• Found in birds and mammals.
• Four-chambered heart: two atria and two ventricles that are separated completely.
• Oxygenated and deoxygenated blood do not mix, allowing more efficient oxygen supply (心室完全隔离，含氧血和缺氧血不混合，输送氧气更有效率).
• Pulmonary Circulation:
  • Deoxygenated blood transported via pulmonary artery to lungs for gas exchange.
  • Oxygenated blood returns to left atrium and flows into left ventricle.
• Systemic Circulation:
  • Blood is pumped from heart via aorta to all body tissues.
  • Deoxygenated blood returns to right atrium via vena cava.

Human Circulation

• Complete double circulatory system.
• Four heart chambers (two atria, two ventricles).
• Oxygenated and deoxygenated blood do not mix.
• Hepatic portal vein transports deoxygenated blood containing nutrients from small intestine to liver.

Blood Vessels and Organ Connections

Types of Circulatory Systems Summary

• Open circulatory system: Insects.
• Closed circulatory system:
  • Single circulation: Fish.
  • Double circulation:
    • Incomplete double circulation: Amphibians, Reptiles.
    • Complete double circulation: Birds, Mammals.

Similarities in Circulatory Systems

• Found in all multicellular organisms.
• Consists of a heart to pump blood or haemolymph.
• Functions to transport nutrients and wastes.
• Has valves to ensure unidirectional blood flow.

Differences in Circulatory Systems

For closed circulatory system, blood is always contained in a continuous closed blood vessel and is distributed to the whole body. The exchange of substances that are essential to cells such as oxygen and nutrients occurs across the walls of blood capillaries.

10.2 Components of Circulatory System (循环系统的组成)

• Blood (血液): A type of connective tissue made up of plasma & blood cells; medium of transport (运输媒介).
• Vessels (血管): Consist of arteries, capillaries & veins; tubes that deliver blood (运输管道).
• Heart (心脏): Muscular pump that circulates blood to the whole body; provides power for blood circulation (运输动力泵).

Blood Composition (血液的化学成分)

• Plasma (55%): Liquid component, pale yellowish liquid.
• Blood cells (45%): Cellular components.

Blood Components

• Plasma (血浆) (55%)
• Blood cells (血球细胞) (45%)
  • Red blood cells / Erythrocytes (红血球)
  • White blood cells / Leucocytes (白血球)
  • Platelets / Thrombocytes (血小板)

Function of Blood (TRP)

• Transport (运输): Nutrients, wastes, enzymes, hormones, oxygen to body cells.
• Regulation (调节): Body temperature.
• Protection (防御): Fight against diseases, clot the blood.

Detailed Blood Functions

Blood Separation

The blood can be separated into 2 layers:

• Plasma (upper layer, forms 55% of blood volume).
• Blood cells (lower layer, forms 45% of volume).

Plasma Constituents (血浆的构成部分)

Plasma consists of:

• 90% water.
• 10% transported substances:
  • Plasma proteins
  • Inorganic ions
  • Dissolved substances (nutrients, metabolic wastes, respiratory gases)
  • Hormones & enzymes

Constituents of Plasma & Major Functions of Constituents

• Water H2O: Act as a solvent for respiratory gas, ions, digestive products, and excretory substances.
• Ions (K+,Na): Maintain blood pH and osmotic balance.
• Plasma proteins
  • Fibrinogen (纤维蛋白原): Play role in blood clotting.
  • Albumin (白蛋白): Controls blood osmotic pressure.
  • Globulin (免疫球蛋白): Is a type of antibody that is involved in the body’s defence.
• Solutes
  • Nutrients: Important for energy, growth, and maintenance of health.
  • Excretory substances: Are toxic substances that need to be disposed of from the body.
  • Oxygen: Is required in the respiration of cells.
  • Hormones: Control physiological activities in the body.
  • Enzymes: Are involved in cell metabolic processes.

Plasma vs. Serum

• Serum is plasma with its clotting factors removed (plasma without fibrinogen) (血清不含有纤维蛋白原).
• Plasma contains fibrinogen, while serum does not.
• Serum does not contain anticoagulant, suitable for blood chemical analysis (血液化学成分分析).

Production of Blood Cells

• All blood cells are manufactured by stem cells in the bone marrow of ribs, sternum, vertebrae, etc.
• Blood cells enter the blood vessels after maturation.
• Different types of blood cells have different life spans: Erythrocytes (120 days), Leucocytes (less than 5 days), Platelets (less than 7 days).

Destruction of Blood Cells

• Blood cells are destroyed in the liver and spleen through phagocytosis, where they are engulfed by macrophages.

Genesis of Erythrocytes (Erythropoeisis)

• Formation starts with haemocytoblast, a stem cell in bone marrow.
• Haemocytoblasts differentiate into common myeloid progenitor cells, which produce proerythroblasts, myeloblasts, and megakaryocytes.
• Proerythroblasts become erythroblasts and eventually normoblasts with iron uptake and haemoglobin synthesis.
• Normoblasts lose nucleus as they become reticulocytes. Some reticulocytes are released into blood and mature into erythrocytes.

Destruction of Erythrocytes (Haemolysis)

Erythrocytes

• 5 million/mm3 of blood.
• Characteristics:
  • Tiny in size (8 µm).
  • Biconcave disc shape (双凹圆盘状).
  • No nucleus, mitochondria, or ribosomes.
  • Elastic plasma membrane.
  • Contain numerous (250 millions) haemoglobin molecules.

Erythrocyte Structure and Function

• Small & Biconcave disc shape: Thinner in center to allow large surface area to volume ratio for rapid diffusion of oxygen (增大扩散表面积).
• Elastic plasma membrane: Allows squeezing into narrow capillaries (可挤过狭窄微血管进行物质交换).
• Large number of haemoglobin: Each haemoglobin contains a heme group with an iron atom, the binding site of oxygen. Haemoglobin combines with oxygen to form oxyhaemoglobin in high oxygen partial pressure conditions.
• No nucleus :so that more space for haemoglobin can be fit in to carry more oxygen.可容纳更多血红蛋白

Structure of Haemoglobin (血红蛋白)

• A haemoglobin molecule is made of four polypeptide subunits (2 alpha chains and 2 beta chains).
• Each subunit contains a heme group, and each heme group consists of an iron atom.
• Each iron atom can bind with one molecule of oxygen.

Anaemia (贫血病)

• A person lacking iron in diet may suffer from anaemia.
• Without iron atom, the number of haemoglobin and red blood cells will be reduced.

Leucocyte (白细胞)

• 7000 /mm3 of blood.
• Characteristics:
  • Contains a nucleus.
  • Colorless (do not contain haemoglobin).
  • Larger in size than erythrocytes but fewer in number.
  • Irregular in shape, can change shape and diffuse through capillary walls into interstitial fluid.

Types of Leucocytes

• Divided into 2 basic types based on granules in cytoplasm:
  • Granulocytes – neutrophils, eosinophils, basophils.
  • Agranulocytes – monocytes, lymphocytes.

Granulocytes

• Have granular cytoplasm (有颗粒).
• Have lobed nucleus (耳垂状核).
• Have amoeboid movement.
• Include neutrophils, eosinophils, basophils.

Agranulocytes

• Non-granular cytoplasm (无颗粒).
• Nuclei are not lobed (无耳垂状).
• Divided into 2 types:
  • Monocytes (单核球).
  • Leucocytes (淋巴球).

Functions of Granulocytes

• Neutrophils: Most common (70%), engulf bacteria through phagocytosis.
• Eosinophils: 2 – 4%, release enzymes to fight inflammation in allergy reactions, kill parasitic worms.
• Basophils: Rarest (~ 1%), secrete heparin (肝素) to prevent blood clotting.

Functions of Agranulocytes

• Monocytes: Largest leucocytes, 5 – 8%, ingest bacteria through phagocytosis.
• Lymphocytes: 25% of all leucocytes, produce antibodies to destroy pathogens.

Functions of Leucocytes

Functions & Adaptations of Leucocytes

1. Engulf pathogens that invade the body by phagocytosis (吞噬病菌):
   • Have irregular shape to allow the cells to squeeze through blood capillary.
   • Have enzymes in cytoplasm to digest pathogens.
   • Cell membrane is sensitive and can detect pathogens.
2. Produce antibodies to stimulate immune response (产生抗体, 启动免疫反应):
   • Large nucleus contains many copies of genes to control the production of antibody.
   • defend the body against disease 抵抗疾病

Types of Lymphocytes

Thrombocytes/ Platelets

• Not cells, tiny fragments of large cells (megakaryocytes) from bone marrow.
• Characteristics:
  • Colorless.
  • Irregular shape.
  • Without nucleus.
  • About 2 -3 µm.
  • Live for 6 – 7 days.

Functions of Platelets

• Involved in blood clotting in wounds (使伤口处血液凝固).
• Maintain the integrity of blood vessel wall (维持血管的完整性).

Blood Vessels

• 3 main types:
  • Artery (动脉).
  • Capillary (微血管).
  • Vein (静脉).

Sequence of Blood Flow

Structure of Blood Vessels (血管的构造)

• Arteries: Thick walls, smaller lumen; more/thick smooth muscle + elastic fibers; less elastic fibers/thin.
• Veins: Thin walls, larger lumen; less smooth muscle + elastic fibers; more elastic fibers/thick, elastic.
• Capillaries: Very thin walls, extremely small lumen, only one cell passes at a time.

Structure of Arteries and Veins

• Have 3 layered walls:
  • Fibrous connective tissue (external layer).
  • Smooth muscles and elastic fibers (middle layer) - thick.
  • Endothelium tissues (inner layer) - single flatten cells.

Artery Structure and Function Adaptation

• Thick muscular wall: Can withstand high-pressured blood.
• Elastic wall full of fibrous tissue (elasticity弹性): Can stretch to allow blood to flow in surges (pulse) & prevent bursting of vessel wall, also recoil to maintain blood pressure.
• Small lumen: Can withstand high-pressured blood.

Capillary Structures

• Function: Carry blood from arterioles to venules.
• Form capillary network in body, allow exchange of materials w/ body cells & blood via diffusion.
• No valves. Lumen is very small (Diameter = 7 – 9 µm).
• Wall is one-cell thick.
• Do not have elastic fibers, smooth and connective muscles.

Capillary Structure Adaptation

• Very Thin Wall and Permeable: Facilitates rapid diffusion.
• Lacks Muscles or Elastic Fibers:

How is the structures of capillaries adapted to exchange substances?

• To allow the exchange of materials with body cells through diffusion easily.
• The wall is very thin, as thick as one cell & permeable
• To facilitate diffusion of substances to occur rapidly.

Vein Structure and FunctionAdaptation

• Thin Wall: Carries blood at low pressure with slow flow.
• Less Elastic Fibers: Expands less due to no pulse.

HEART

• ~ 300 g, as big as a fist.
• Located between lungs in the thorax cavity.
• Function: Muscular pump sending blood throughout the body.
• Enveloped by a membrane called pericardium (围心膜).

Cardiac Blood Supply

• Coronary arteries transport oxygenated blood to supply oxygen & nutrients to cardiac muscle cells.
• Coronary veins transport deoxygenated blood away from heart.

4 chambers of the Heart

• Right atrium (右心房): Receives deoxygenated blood from vena cava -> Channels deoxygenated blood from all parts of body to the right atrium of heart
• Right ventricle (右心室): Pumps deoxygenated blood to the lungs -> Carries deoxygenated blood from the right ventricle of heart to the lungs
• Left atrium (左心房): Receives oxygenated blood from lungs -> Carries oxygenated blood from the lungs to the left atrium of heart
• Left ventricle (左心室): Pumps oxygenated blood through the aorta to all parts of the body -> Carries oxygenated blood from the left ventricle of heart to the all parts of body

Chamber Thickness

Which chambers are thicker?

• Ventricles are thicker than atria, because they need to pump blood out of the heart.
• Left ventricles thicker than right, because it has to generate stronger contraction force to pump blood out of the aorta to the whole body while the right ventricle only has to pump blood to lungs.

Blood Vessels Connected to the Heart

1. Vena Cava (上、下腔静脉): Channels deoxygenated blood from all parts of the body to the right atrium of heart.
2. Pulmonary artery (肺动脉): Carries deoxygenated blood from the right ventricle of heart to the lungs.
3. Pulmonary vein (肺静脉): Carries oxygenated blood from the lungs to the left atrium of heart.
4. Aorta (主动脉): Carries oxygenated blood from the left ventricle of heart to the all parts of body.

Valves

• Tricuspid valve: Prevents blood from flowing back into right atrium.
• Bicuspid valve or Mitral Valve: Prevents blood from flowing back into left atrium / Bicuspid valve. Consists of two leaflets.
• Aortic valve: Prevents blood from flowing back into left ventricle
• Pulmonary valve: Prevents blood from flowing back into right ventricle

10.3 Mechanism of Heart

• The heart acts as a muscular pump that pumps blood to the whole body.
• Made up of cardiac muscles -> the heart is myogenic 肌原性, so that the heart can contract & relax spontaneously without the need to receive signal by nerve impulses.
• Cardiac muscle cells are interconnected, join together by intercalated discs 闰盘 – allow rapid spread of nerve impulses through the heart & stimulates the cardiac muscle cells to contract simultaneously and uniformly.

Contractile States:

• Cardiac diastole: When cardiac muscles of ventricles relax, to receive the blood from atria (心脏舒张期).
• Cardiac systole: When cardiac muscles of ventricles contract, to pump the blood out of the heart (心脏收缩期).

Normal Blood Pressure

• Normal blood pressure 120/80 mmHg
• Systolic pressure (收缩压): The highest recorded pressure in the artery when ventricles contract.
• Diastolic pressure (舒张压): The lowest recorded pressure in the artery when ventricles relax.

Heartbeat

• initiated and coordinated by sinoatrial (SA) node 窦 房结/ pacemaker 起搏器
  • cluster of specialised heart muscle cell, set the rate of contraction
  • located in the wall of right atrium generate electrical impulses causing heart muscles of atria to contract & pump blood to ventricles.

Electronic pacemaker

• Function to artificially take over the role of sinus-atrial node if it's not working properly.
• It sends small electrical charges to stimulate heartbeat.

Blood Circulation

The produced force that enables blood to circulate 血液循环的原动力 in humans is generated by:

• The pumping of the heart, and
• The contraction of the skeletal muscles.

Contraction of Skeletal:

• Contraction of skeletal muscles around the veins the force produced by pumping of the force of the heart is insufficient for blood continues to flow through the veins and return to heart. Besides, the blood from lower limbs flow against the force of gravity. Skeletal muscles presses and constricts the veins, causing the blood is pushed along through the veins Blood flow back to the heart requires the contraction of skeletal muscles around the veins. Due to prolonged relaxation of the skeletal muscles on legs, the blood flow back to the heart becomes blocked and starts to pool in veins (venous insufficiency静脉曲张).

Regulatory Mechanism of Blood Pressure

• Blood pressure:
  • Force that blood exerts on the walls of the blood vessels, measure in mm Hg by sphygmomanometerNormal = 120 (systolic pressure) / 80 (diastolic pressure) mm Hg
  • Control by cardiovascular centre at medulla oblongata Negative feedback mechanism:
    • baroreceptors / pressure receptor located in the aortic arch and carotid arteries effectors are cardiac muscle and smooth muscle of artery

10.6 Cardiovascular Diseases

Cardiovascular diseases may occur due to:

1. High level of low-density lipoprotein (LDL, or “bad cholesterol”) in blood, that are deposited and clog the blood vessels (胆固醇堵塞血管).
2. Deficiency in vitamins and minerals (antioxidants), that can reduce the LDL level.

Arteriosclerosis (动脉硬化)

• The result of old age;
• Occurs when calcium is deposited on the plaque and causes the artery to become hard and lose its elasticity;
• Restricts blood flow to body tissues.

Atherosclerosis (动脉粥样形成)

• Formation of plaque on the artery walls, due to deposition of cholesterol, lipid, dead muscle tissues, and coagulated platelets -> make the blood vessels thin and narrow (使血管堵塞变窄).
• Narrowed arteries are unable to circulate the required oxygenated blood to the body cells.

Hypertension (高血压)

• Occurs because arteriosclerosis makes the lumen of an artery to become narrow, thus obstructing blood flow. Because the blood is difficult to flow through the narrowed lumen of artery, the heart needs to work harder. This condition increases blood pressure (hypertension), results risk of cardiovascular disease.

Thrombosis (血栓塞)

• When vessels become narrow and blood flows too slowly, clotting factors may accumulate and blood clot is formed.
• Such a clot is called a thrombus, or embolus if it moves -> block narrow artery result to the risk of oxygen tissue.

Heart and Brain Risk:

• When clot forms in a coronary artery (artery that supplies blood to the heart), restricting the oxygen supply to cardiac muscle tissues. This lead to heart attack/ myocardial infraction (心肌梗塞)
• If clot blocks blood flow to the brain, stroke occurs when arteries in the brain are blocked or even burst. Brain cells may die.

Symptoms of Coronary Disease 冠心病 Angina (Chest Pain) Myocardial infarction Cardiac sudden death

Angina (心绞痛）: Is caused by partial blockage of the coronary artery. Heart attack (myocardial infarction): total blockage of the coronary artery.

Stroke (中风）: Occurs when brain cells die because they fail to get supply of oxygen and nutrients. Because arteries in the brain are blocked or even ruptured (脑动脉硬化导致动脉栓塞或血管爆裂引发脑溢血).

Lack of exercise

Practices to reduce the risk of cardiovascular diseases

• restrict the intake of animal fats and cholesterol;
• consume sufficient dietary fibre;
• do not smoke;
• exercise regularly.

Treatments for a patient who suffers from heart failure:

1. Medication
   • Taking antihypertensive drugs (降压药), to relax blood vessels and lower blood pressure
   • Examples: Angiotensin-converting enzyme (ACE) inhibitors (血管紧张素转换酶抑制剂), Diuretics (潴钾利尿剂) (water pills)
2. Surgery
   • Coronary bypass surgery (冠状动脉搭桥术)Taking a healthy blood vessel from your leg, arm or chest and connecting it below and above the blocked arteries, to improve blood flow to your heart muscle.
3. Nanotechnology.
   • Nanoparticles are designed to resemble high-density lipoprotein cholesterol (HDL) (“good” cholesterol) to help reduce the plaque in the lumen

10.4 BLOOD CLOTTING

Blood clotting is the mechanism to stop or minimise blood loss from damaged blood vessels. Prevents excessive blood loss, entry of microorganisms and foreign particles, maintains blood pressure.

Clotting factors (凝血因子).

• Normal condition, blood flow is prevent from clotting by anticoagulants (抗凝素) such as heparin Involve the release of clotting factors e.g.fibrinogen, prothrombin, thromboplastin, calcium ions, vitamin K

Mechanism of blood clotting = Clumped platelets, damaged cells and clotting factor form thrombokinase -> thrombokinase (in the presence of Ca2+ and vitamin k) converts prothrombin into thrombin -> thrombin converts fibrinogen to fibrin. Clotting Pathway: Fibrin forms a mesh of fibres across the wound and prevents loss of blood.

Impaired blood clotting mechanism:

• Hemophilia (血友病) = hereditary disease in which blood unable to clot due to lack of certain clotting factors. Excessive bleeding due to small wounds or bruises (瘀伤) can result in death
• Thrombosis (血栓) = a blood clot that attached in any vessels such as ateriosclerosis and cause damage in blood vessels (because damage endothelial or/arteriosclerosis caused it), or sluggish blood flow that causes clotting factors to accumulate.
• Embolism (血栓塞): The clot blood is caused by thrombrosis become drifted and and stuck, its embolus.