Topic 5: Transport in Humans Flashcards
Transport in Humans
Humans need a transport system as diffusion alone is inadequate for our cells in obtaining useful substances and removing excretory and toxic substances.
Components of Circulatory System
- Heart: A muscular pump that drives blood around the body.
- Blood (transport medium): A fluid tissue that carries various substances around the body.
- Blood vessels: Vessels that carry blood around the body; they are namely the artery, vein and capillary.
A. Main Blood Vessels of the Human Circulatory System
Double Circulatory System
The human circulatory system is a double circulatory system. In a double circulation, the blood flows through the heart twice in one circuit.
- Advantage: ensures that blood is pumped at low pressure to the lungs so that the blood can be properly oxygenated and the oxygenated blood can be pumped out at high pressure to all body cells at a fast rate
A. Main Blood Vessels of the Circulatory System
Pulmonary Circulation
Pulmonary circulation carries oxygenated blood from the lungs to the heart and deoxygenated blood from the heart to the lungs.
- Gaseous exchange happens in the lungs.
A. Main Blood Vessels of the Circulatory System
Systemic Circulation
Systemic circulation carries oxygenated blood from the heart to the rest of the body and deoxygenated blood from the rest of the body to the heart.
- Gaseous exchange (of oxygen and carbon dioxide) happens at the cells of the body.
- Hepatic blood vessels are connected to the liver.
- Renal blood vessels are connected to the kidneys
B. Function of Blood
What is Blood?
Blood is a fluid tissue because it contains cells suspended in the plasma (fluid).
B. Function of Blood
Components of Blood
- Plasma (55%)
- Red blood cells (eruthrocytes)
- White blood cells (leukopcytes)
- Platelets
B. Function of Blood
Main Functions of Blood
a) To transport oxygen, food substances (e.g. glucose, amino acids, fats and vitamins), waste materials (e.g. carbon dioxide), hormones, heat from one part of the body to another.
b) To protect the body by preventing the entry of foreign bodies and fighting infections.
C. Components of Blood
Plasma
- Plasma is the fluid part of blood. It consists of approximately 55% of blood volume.
- Plasma consists of 90% water and 10% dissolved substances.
- Dissolved in plasma are substances such as: mineral ions, digested food substances, metabolic waste products, plasma proteins, and hormones.
C. Components of Blood
Red Blood Cells (Erythrocytes)
- Produced in the bone marrow and broken down in the spleen.
- Lifespan of about 4 months
- Transports oxygen from the lungs to other parts of the body
C. Components of Blood
Adaptations / Structural Features of RBCs
- Haemoglobin (red pigment) present in cells
- Absence of nucleus
- Circular and biconcave shape
- Elastic and flexible cell surface membrane
C. Components of Blood
Haemoglobin (red pigment) present in cells
- Haemoglobin binds reversibly to oxygen to form oxyhaemoglobin, which helps to transport oxygen in the red blood cell around the body
- Each molecule of haemoglobin can bind up to four molecules of oxygen
C. Components of Blood
Absence of nucleus
More space available for more haemoglobin to be packed inside the cell cytoplasm and more oxygen to be transported
C. Components of Blood
Circular and biconcave shape
Increases the surface area to volume ratio of the cell, thus allowing quicker diffusion of oxygen in and out of the cell
C. Components of Blood
Elastic and flexible cell surface membrane
Cell can change its shape (e.g. bell shape, see above) while squeezing through small capillaries
C. Components of Blood
White Blood Cells (Leukocytes)
- WBCs are larger than RBCs.
- WBCs are less numerous than RBCs. (approx. ratio 700 EBC : 1 WBC)
- WBCs have a lifespan of only a few days.
- WBCs can be categorised into lymphocytes and phagocytes (for IP3 syllabus, covered in Topic 4)
C. Components of Blood
Platelets (Thrombocytes)
Not true cells but fragments of larger bone marrow cells called megakaryocytes.
They play an important role in blood clotting, by forming “sticky plugs” at wound sites.
Importance of blood clotting:
* prevents excessive loss of blood from the wound.
- prevents further entry of pathogens (virus and bacteria) through the wound.
C. Components of Blood
Mechanism of Blood Clotting
- Damaged tissue and platelets produce an enzyme called thrombokinase.
- Thrombokinase and calcium ions cause inactive prothrombin to become active thrombin.
- The thrombin enzyme uses fibrinogen to form insoluble fibrin threads that form a mesh to trap blood cells.
D. ABO Blood Groups
Blood Group A
Anti-B antibodies and A antigen
D. ABO Blood Groups
Blood Group B
Anti-A antibodies and B antigen
D. ABO Blood Groups
Blood Group AB
No anti-A and anti-B antibodies
A and B antigens
D. ABO Blood Groups
Blood Group O
Anti-A and anti-B antibodies
No A and B antigens
D. ABO Blood Groups
Agglutination
Agglutination is the clumping of red blood cells which is fatal.
It can occur when a) anti-A antibodies in the plasma bind with antigen A on the RBCs; b) anti-B antibodies in the plasma bind with antigen B on the RBCs
D. ABO Blood Groups
Universal Donor
Blood Group O
D. ABO Blood Groups
Universal Recipient
Blood Group AB
E. Blood Vessels
Categories of Blood Vessels
Arteries (which bring blood away from heart at higher pressure)
Veins (which bring blood towards the heart at relatively lower pressure)
Capillaries (blood vessels with one-cell thick walls)
E. Blood Vessels
Layers/Walls of Arteries and Veins
- The innermost layer is known as the endothelium.
- The middle layer consists of smooth muscle tissue and elastic fibres.
- The outer layer consists of connective tissues like collagen fibres.
E. Blood Vessels
Arteries
- Blood vessels that carry blood away from the heart
- All arteries transport oxygenated blood except the pulmonary artery.
- Blood flow in arteries is rapid and under high pressure.
- Thick muscular and elastic walls enable the arteries to withstand the high pressure of blood flowing though it.
- Thick elastic walls allow the arteries walls to stretch and recoil to push the blood along it in spurts, maintaining the high pressure of blood flowing through the artery.
- Smaller lumen when compared to a vein of the same external diameter.
- Arteries branch to form smaller arteries called arterioles.
- Arterioles branch to form many tiny blood vessels called capillaries.
E. Blood Vessels
Veins
- Blood vessels that carry blood towards the heart.
- All veins carry deoxygenated blood except the pulmonary vein.
- Blood flow in vein is slow and at low pressure.
- They have relatively thinner muscular and elastic walls as the pressure of the blood flowing though it is at low pressure.
- Semilunar valves are present to prevent the backflow of blood in the vein. These valves ensure that blood flows in one direction in the vein only. (Unidirectional flow of blood)
- Larger lumen when compared to an artery of the same diameter.
- Veins are located between large muscles of body. The contraction of these skeletal muscles (e.g. leg muscles) squeeze the veins and push the blood along, up towards the heart.
- Before capillaries leave an organ or tissue, they unite to form small veins called venules. Venules joined to form larger blood veins.
E. Blood Vessels
Capillaries
- Microscopic blood vessels that connect the arteries to veins and are found between cells of most tissues.
- Capillary walls are only one-cell thick and are partially permeable so that certain substances are able to diffuse through their walls quickly. (Muscular wall is absent)
- Capillaries branch repeatedly to provide a large surface area for the quick exchange of substances between blood and tissue cells.
- Smallest lumen compared to artery and vein.
- Blood flow is slow and pressure is falling.
- Valves are absent.
F. Blood Plasma and Tissue Fluid
Tissue Fluid
- Cells in the walls of capillary do not fit together exactly, forming small gaps in between, allowing plasma to leak out from the blood.
- The main force that pushes plasma out of the blood is hydrostatic pressure, which is the blood pressure against the capillary wall.
- Hence the minute spaces between tissue cells contain a colourless liquid called the tissue fluid (or interstitial fluid or intercellular fluid). Tissue fluid is a fluid that bathes the cells of our tissues.
F. Blood Plasma and Tissue Fluid
Components of Tissue Fluid
This tissue fluid contains dissolved food substances such as glucose and amino acids as well as waste products like urea and hydrogencarbonate ions.
- Proteins are not found in the tissue fluid as it is too large to pass through the gaps between the cells of the capillary walls.
- Phagocytes can squeeze through the gaps of the capillary walls to enter the tissue fluid, but not the red blood cells.
F. Blood Plasma and Tissue Fluid
Movement of Substances through Tissue Fluid
Oxygen and soluble food substances (e.g. glucose) diffuse quickly through the wall of capillaries from the blood plasma to the tissue fluids surrounding body cells, as the blood moves along the capillaries, down their concentration gradients.
Carbon dioxide and other waste products (e.g. urea) diffuse from the body cells into the tissue fluids, and subsequently into the blood plasma, to be carried away to various organs to be removed from the body, down their concentration gradient.
G. Structure and Function of the Heart
Structure of the Heart
- The heart is a muscular organ that functions to pump blood around the body, consisting of mainly cardiac muscles which contract and relax to circulate blood through the blood vessels.
- Four chambers (2 atria and 2 ventricles)
G. Structure and Function of the Heart
Right Side of the Heart
The right side of the heart received deoxygenated blood (low concentration of oxygen and high concentration of carbon dioxide) from the body (except lungs) and pumps it to the lungs.
G. Structure and Function of the Heart
Left Side of the Heart
The left side of the heart received oxygenated blood (high concentration of oxygen and low concentration of carbon dioxide) from the lungs and pump it to all parts of the body (except lungs).
G. Structure and Function of the Heart
Septum
The median septum between the left and the right side of the heart prevents oxygenated blood in the left side from mixing with deoxygenated blood in the right side.
G. Structure and Function of the Heart
Heart Valves
Heart valves ensure that blood flows unidirectionally (in one direction), hence preventing back-flow of blood.
- Semilunar valves (found in pulmonary artery and aorta)
- Atrio-ventricular valves
- bicuspid valve (between left atrium and right ventricle)
- tricuspid valve (between right atrium and left ventricle)
G. Structure and Function of the Heart
Why are the walls of the ventricles thicker and more muscular than the walls of the atria?
The muscular walls of ventricle contract to pump blood to the rest of the body (a further distance), so the walls are thicker and more muscular to exert a higher pressure, ensuring blood reaches all areas of the body. However, the muscular walls of atria contract to pump blood only to the ventricles (short distance), so the walls are thinner and less muscular, as blood can be pumped at a lower pressure.
G. Structure and Function of the Heart
Why are the walls of the right ventricle thinner and less muscular than the left ventricle?
The right ventricle pumps blood to the lungs, which is a shorter distance from the heart. Hence, less pressure is required to be exerted when the right ventricle contracts. However, the left ventricle has to pump blood around the whole body (further distance), whcih requires higher pressure.
H. The Cardiac Cycle
The Cardiac Cycle
The cardiac cycle refers to the events that occur during a single heartbeat.
H. The Cardiac Cycle
Systole
The systole phase refers to the contraction of the walls of the chambers of the heart.
H. The Cardiac Cycle
Diastole
The diastole phase refers to the relaxation of the walls of the chambers of the heart.
H. The Cardiac Cycle
Atrial Systole
- Muscles surrounding both atria contract, forcing blood into the ventricles.
- The tricuspid and bicuspid valves open to allow blood to pass through.
- Semilunar valves close to prevent backflow of blood into the vena cava and pulmonary vein.
H. The Cardiac Cycle
Ventricular Systole
- Muscles surrounding both ventricles contract and the pressure in the ventricles rises.
- Blood from the ventricles are pumped out of the heart, into the pulmonary artery and aorta
- The tricuspid and bicuspid valves close to prevent backflow of blood into the atria.
- The semilunar valves in the pulmonary artery and the aorta open to allow blood to pass through.
H. The Cardiac Cycle
Diastole
- Muscles surrounding both atria and ventricles relax and the pressure in all chambers fall.
- Blood enters the relaxed atria and ventricles.
- The tricuspid and bicuspid valves open to allow blood to pass through.
- The semilunar valves in the pulmonary artery and the aorta close to prevent backflow of blood into the ventricles.
I. Pressure Changes in the Left Side of the Heart
Pressure Changes during Atrial Systole
- Atrial pressure is higher than ventricular pressure.
- Bicuspid valve is open to allow blood to flow.
- Blood therefore flows from left atrium to left ventricle, down its pressure gradient.
- Aortic pressure higher than ventricular pressure. Semi-lunar valves close to prevent backflow of blood from aorta into left ventricle
I. Pressure Changes in the Left Side of the Heart
Pressure Changes during Ventricular Systole
- Ventricular pressure rises such that it is higher than aortic pressure.
- Semi-lunar valves open to allow blood to flow through.
- Blood flows from left ventricle into the aorta
- Meanwhile, atrium undergoes diastole and begins to be filled with blood. Bicuspid valve closes to prevent backflow of blood from ventricle to atrium. (“Dub” sound)
I. Pressure Changes in the Left Side of the Heart
Pressure Changes during Ventricular Diastole
- Ventricular pressure decreases until it is lower than aortic pressure.
- Semi-lunar valves close to prevent backflow of blood from aorta into left ventricle. (“Lub” sound)
- Ventricular pressure decreases further until it is lower than atrial pressure.
- Bicuspid valve opens to allow blood to flow.
- Blood therefore flows from left atrium to left ventricle, down its pressure gradient.
J. Coronary Heart Disease
Coronary Heart Disease
- The coronary arteries supply oxygen and nutrients to the heart muscles.
- These may become narrowed and eventually, blocked by a build-up of fatty deposits (plaque) containing cholesterol, resulting in coronary heart disease.
- If a coronary artery is blocked, the blood supply to part of the heart muscle is cut off. As a result, those heart muscle cells are deprived of oxygen and nutrients, thus cannot respire and dies. That part of the heart cannot continue to contract, causing a heart attack.
J. Coronary Heart Disease
Causes of Coronary Heart Disease
- Diet high in cholesterol and saturated animal fats
- Lack of exercise - sedentary lifestyles increase the risk of coronary heart disease
- Stress and smoking (increases blood pressure and the narrowing of artery walls through buildup of plaque)
J. Coronary Heart Disease
Preventive Measures Against Coronary Heart Disease
- Diet: reduce intake of cholesterol and saturated animal fats
- Regular physical exercise (strengthens heart and maintains the elasticity of arterial walls)
- Manage stress and avoid smoking
