The Circulatory System Transports Materials Throughout the Body 5

What are the functions of blood?

• transporting oxygen and nutrients to all cells of the body

• transporting carbon dioxide and other waste products away from the cells

• transporting chemical messengers (hormones) to the cells

• maintaining the pH of body fluids

• distributing heat and maintaining body temperature

• maintaining water content and ion concentration of the body fluids

• protecting against disease-causing micro-organisms

• clotting when vessels are damaged, thus preventing blood loss

What is blood composed of?

• plasma - the liquid part, making up approximately 55% of the blood volume

• formed elements - the non-liquid part, making up 45% of the blood volume and consisting of erythrocytes (RBC), leucocytes (WBC) and thrombocytes (platelets)

What is plasma and its function?

• mixture of 91% water with 9% dissolved substances (nutrients, ions, gases, hormones, plasma proteins, wastes)

• pale yellow liquid component of blood that holds the blood cells

• function: to transport the components of blood (cells, nutrients, wastes, hormones, proteins, antibodies) throughout the body

what are erythrocytes and its function?

• most abundant cells in the blood → account for approximately 40-45% of its volume (haematocrit)

• biconcave shape (flattened in the middle of both sides)

• anucleated (no nucleus), which increases their flexibility and ability to move through blood vessels but limits their life span to only 120 days on average

  • allows more room for haemoglobin which can combine with oxygen and carbon dioxide to form oxyhaemoglobin and carbaminohaemoglobin

• produced in bone marrow and destroyed in liver and spleen

• function: to transport oxygen from the lungs to the cells throughout the body

What are leucocytes and its function?

• play an important role in protecting the body from infection by removing dead/injured cells and invading microorganisms

• make up only 1% of blood but larger than RBC

• life span of a few minutes during an infection but can live up to years without infection

What are the different types of leucocytes?

• granulocytes (granular cytoplasm and lobed nucleus) - phagocytes that are able to ingest foreign cells (e.g. bacteria)

  • neutrophils - most common type of WBC containing enzymes to digest pathogens

  • eosinophils - lead to inflammatory responses, responding to larger parasites (e.g. worms)

  • basophils - responsible for allergic reactions, producing heparin and histamine to defend the body against parasites and bacteria

• agranulocytes (agranular cytoplasm and spherical nucleus)

  • monocytes - biggest type of WBC, engulfing pathogens and aged/damaged cells by phagocytosis

  • lymphocytes - help to regulate the body’s immune system

What are thrombocytes and its function?

• small fragment of cells with no nucleus

• formed in the red bone marrow

• life span of 7 days

• function: adhere to the lining of an injured blood vessel and form a scaffold for the coagulation of blood to form a clot

Describe the transport of oxygen.

• oxygen is not very soluble in water, so only 3% of oxygen is carried in solution in the blood plasma

  • 97% is carried in combination with haemoglobin as oxyhaemoglobin

  • haemoglobin (Hb) + O2 ↔ HbO2

• combination of oxygen and haemoglobin is said to be a loose one because it can easily break down to release the oxygen

• presence of haemoglobin in RBC increases the oxygen carrying capacity of blood by about 60-70 times

• oxygen combines with haemoglobin when the oxygen concentration is relatively high

  • occurring in the capillaries in the lungs, where oxygen diffuses into the blood from the air in the alveoli

• oxyhaemoglobin breaks down when the concentration of oxygen is relatively low

  • as the cells of the body are continually using oxygen, the tissue fluid around the cells has a relatively low oxygen concentration

  • ∴ when the RBC flow through the capillaries between the body cells, they give up their oxygen, which diffuses into the tissue fluid and then into the cells

• oxygenated blood is bright red, deoxygenated blood is dark red

• RBC are well suited to their function of O2 transport because they:

  • contain haemoglobin, which is able to combine with O2

  • have no nucleus, so there is more room for haemoglobin molecules

  • are shaped like biconcave discs, increasing the surface area for O2 exchange and the thicker edges give a large volume that allows room for the haemoglobin molecules

Describe the transport of carbon dioxide.

• around 7-8% is dissolved in the plasma and carried in solution

• around 22% combines with the globin part of haemoglobin to form carbaminohaemoglobin

• around 70% is carried in the plasm as bicarbonate ions (HCO3 -)

• as the blood flowing through the capillaries between the body cells, CO2 diffuses into the plasma due to the difference in CO2 concentration

• some CO2 dissolves into plasma, some combines with haemoglobin, but most reacts with water to form carbonic acid, which then ionises into hydrogen and bicarbonate ions

• the alveoli are surrounded by a dense network of capillaries where the CO2 dissolved in the plasma diffuses out of the blood into the air in the alveolus

• the carbaminohaemoglobin breaks down and CO2 molecules released also diffuse into alveolus

Describe the transport of nutrients and waste.

• nutrients and waste (except CO2) are dissolved and transported in the blood plasma

• nutrients are the essential elements and molecules that are obtained from the food we eat

• inorganic nutrients are transported as ions (Na+, Ca2+, K+, Cl-, I-)

• organic nutrients dissolved in the blood plasma include:

  • glucose

  • vitamins

  • amino acids

  • fatty acids

  • glycerol

• metabolic wastes are substances produced by the cells that cannot be used and would be harmful if allowed to accumulate

• most important organic wastes that are transported in solution are:

  • urea

  • creatinine

  • uric acid

What does blood clotting do?

blood clotting helps to minimise blood loss from broken vessels and prevent entry of infecting micro-organisms after an injury that causes damage to blood vessels

Describe the what occurs during blood clotting for small tears.

1. vasoconstriction

   • muscles in the walls of the small arteries that have been injured/broken constrict immediately to reduce blood flow and blood loss

2. platelet plug

   • internal walls of blood vessels are normally very smooth but any damage creates a rough surface to which the platelets stick

   • sticking platelets attract others, building a plug at the site of injury because they are exposed to collagen (a protein found in the connective tissue located just outside the blood vessel)

   • the plug also helps to reduce blood loss

   • the platelets release substances that act as vasoconstrictors, which enhance and prolong the constriction of the damaged vessels

Describe what happens during blood clotting for more serious injuries.

1. vasoconstriction

2. coagulation

   • for more serious injuries

   • complex process involving a large number of clotting factors which are present in the blood plasma

   • these reactions result in the formation of threads of an insoluble protein called fibrin, forming a mesh, called a blood clot/thrombus, that traps blood cells, platelets and plasma

   • the threads stick to the damaged blood vessels and hold the clot in position

What is the process that happens after coagulation?

clot retraction

• slower process after the formation of the clot

• network contracts pulling the edges of damaged blood vessels together, causing a fluid known as serum to be squeezed out

• the clot then dries, forming a scab that prevents entry of infecting micro-organisms

Describe the heart and its functions.

• the pump that pushes the blood around the body

• located between the 2 lungs in the mediastinum, behind and slightly to the left of the sternum

• a conical shape, approximately 12cm long, 9cm at its widest point and 6cm thick

• completely enclose in the membrane of pericardium, which holds it in place but also allows it to move as it beats and prevents the heart from overstretching

• wall of heart is made up of cardiac muscle

• septum - separates the left and right sides of the heart

Describe the flow of blood through the heart, body and lungs.

• the right side collects blood from the body and pumps it to the lungs

• the left side receives blood from the lungs and pumps it to the rest of the body

• the right atrium receives blood from the body and passes it to the right ventricle

• the right ventricle pumps blood to the lungs

• the left atrium receives blood from the lungs and passes it to the left ventricle

• the left ventricle pumps blood to the body

• walls of the left ventricle is thicker as it needs to be much stronger to pump the blood through the blood vessels supplying the body

• atria collect blood from the body and lungs while the ventricles pump blood out of the heart to the lungs and body

What do valves in the heart do?

ensure that the blood can only flow in one direction

What are the atrioventricular valves?

• between the atria and ventricles

• flaps of thin tissue with the edges held by chordae tendineae, that attach to the heart on papillary muscles

• when the ventricles contract, the blood catches behind the flaps and they billow out like a parachute, sealing off the opening between the atria and the ventricles → blood must then leave the heart through arteries and not flow back into the atria

• tricuspid valve - between the right atrium and ventricle with 3 cusps

• mitral (bicuspid) valve - between the left atrium and ventricle with 2 cusps

What are the semilunar valves?

• second set of valves that stop blood from flowing back into the ventricles when ventricles relax

• 3 cusps

• when blood flows into the artery, the cusps are pressed flat against the artery wall

• when blood tries to flow back into the ventricle, the cusps fill out and seal off the artery, ensuring that the blood only flows in one direction

• pulmonary valve - between the right ventricle and pulmonary artery with 3 cusps

• aortic valve - between the left ventricle and the aorta with 3 cusps

What are arteries and its functions?

• blood vessels that carry blood away from the heart

• aorta - largest artery that takes blood from the left ventricle to the body

• pulmonary artery - takes blood from the right ventricle to the lungs

• have thick, muscular, elastic walls containing smooth muscle and elastic fibres

  • when the ventricles contract and push the blood into the arteries, the walls of the arteries stretch to accommodate the extra blood

  • when the ventricles relax, the elastic artery walls recoil, keeping the blood moving and maintaining the pressure

• vasoconstriction - the muscle in the artery walls contract to reduce the diameter of the artery and thus reduce blood flow to an organ

• vasodilatation - the muscle in the artery walls relax to increase blood flow to an organ

  • wastes such as CO2 acts as vasodilators

  • blood flow may be controlled to allow for the changing needs of the body

• the very large arteries that receive blood pumped by the ventricles divide into smaller arteries then into arterioles, which supply blood to the capillaries

What are capillaries and its functions?

• link between arteries and veins

• microscopic blood vessels that form a network to carry blood close to nearly every cell in the body, enabling the cells to get their requirements from the blood and pass their waste into the blood

• have only 1 layer of cells, making them suitable for their function as it allows substances to pass easily between the blood and surrounding cells

What are veins and its functions?

• carry blood towards the heart

• capillaries join into venules (small veins), which then join up to make larger veins

• inferior/superior (anterior/posterior) vena vaca - bring blood from the body to the right atrium

  • superior brings blood from above the heart, inferior brings blood from below

• pulmonary veins - bring blood from the lungs to the left atrium (4 pulmonary veins → 2 from each lung)

• have thin, relatively inelastic walls with little muscle because of the constant, relatively low blood pressure due to the blood losing most of its pressure as it flows through the capillaries

  • many veins therefore have valves to prevent the blood from flowing backwards

What is blood?

blood is the transport medium that delivers oxygen and nutrients to cells and carries away their wastes

What are the 2 ways that the blood flow to and from the cell are able to change to cater for the changes in requirements of cells?

• changing the output of blood from the heart

• changing the diameter of the blood vessels supplying the tissues

What is the cardiac cycle?

sequence of events that occur in one complete beat of the heart

What are the 2 stages of the cardiac cycle?

• systole - pumping phase, when the heart muscles contract

• diastole - filling phase, when the heart muscles relax

• for the short time the atria and ventricles are is diastole, the atria fills with blood and the ventricles also receive blood as the valves are open

• atrial systole (the contraction of the atria) then follows and forces the remaining blood into the ventricles

• the atria then relaxes and refills while the ventricles contract in ventricular systole

What is cardiac output?

• how quickly the blood flows around the body depends on how fast the heart is beating and how much blood the heart pumps with each beat

• heart rate - number of times the heart beats per minute

• stroke volume - volume of the blood forced from a ventricle of the heart with each contraction

• cardiac output - the amount of blood leaving one of the ventricles every minute

  • influenced by heart rate & stroke volume

• cardiac output (mL/min) = stroke volume (mL) x heart rate (beats/min)

Who discovered the ABO and Rh blood group system and when?

• in 1901, Karl Landsteiner discover ABO blood group system by mixing samples of blood from different people

• in 1940, he discovered the Rh blood system

What are antigens and antibodies?

• antigens - sugar and protein molecules that coat the surface of RBC that are able to stimulate the immune system

• antibody - protein produced by the immune system

• antigen and its antibody combine to form a complex and cause a reaction

Describe the ABO blood groups.

• 2 sugar antigens involved in ABO classification

  • antigen A

  • antigen B

• on the surface of the RBC, a person may have:

  • antigen A

  • antigen B

  • both antigens

  • neither antigens

• the body’s ability to make the antigens and a person’s ABO blood group is determined by their DNA and is therefore inherited

• anti-A - antibody that reacts against antigen A

• anti-B - antibody that reacts against antigen B

• a person’s immune system is able to recognize its own antigens and won’t produce antibodies for them but will produce antibodies for antigens that are non-self

Describe the Rh blood groups.

• Rhesus blood group system is also based on antigens that occur on the surface of the RBC

• Rh antigens are proteins

• a person with Rh antigens is said to be Rh positive

• a person without Rh antigens is said to be Rh negative and can produce anti-Rh

What are the main functions of the lymphatic system?

• to collect some of the fluid that escapes from the blood capillaries due to relatively high pressures and return it to the circulatory system

• the body’s internal defence against disease-causing organisms

What does the lymphatic system consists of?

• network of lymph capillaries joined to larger lymph vessels/lymphatic vessels/lymphatics

• lymph nodes, which are located along the length of some lymph vessels

What is lymph?

• excess fluid in the tissues returned to the blood by the lymphatic system

• does not circulate as the lymphatic system is a one-way system carrying fluid away from the tissues

What are the lymph vessels and its functions?

• originate as lymph capillaries which are slightly larger and more permeable than blood capillaries

  • capillaries unite to form larger vessels

• proteins and disease-causing organisms in the intercellular fluid can easily pass through the walls of the lymph capillaries into the lymph

• network of lymph vessels join to form 2 lymphatic ducts that empty the lymph into large veins in the upper chest

• lymph is moved through the lymphatic vessels as a result of smooth and skeletal muscles and valves

  • smooth and skeletal muscle layers are able to contract, providing additional force

  • as there is no central pump, there is no force driving the direction of the flow of the lymph, so the larger vessels have valves that close when the pressure drops, preventing the back flow of lymph

Describe lymph nodes/glands and its functions.

• occur at intervals along the lymphatic vessels

• most numerous in the:

  • neck

  • armpits

  • groin

  • around the alimentary canal

• nodes are bean-shaped and range in length 1 - 25mm, surrounded by a capsule of connective tissue that extends into the node, forming a network

  • within the framework are masses of lymphoid tissue, containing cells of lymphocytes, macrophages and plasma cells

  • spaces between the cells of the lymphoid tissue are criss-crossed by a network of fibres

How does lymph enter the circulatory system?

lymph enters through vessels on the convex side of the node, filters through the spaces and passes through vessels on the opposite side, passing through several nodes before entering the circulatory system

What is the role of the lymphatic system in defence against disease?

• lymph entering the lymph node contains cell debris, foreign particles and micro-organisms that have penetrated the body’s external defences

• larger particles are trapped in the meshwork of fibres as the lymph flows through the spaces in the nodes

• macrophages - large phagocytic cells that destroy the particles, ingesting the particles by phagocytosis

  • projections from the macrophage surround the particle and take it into the cell, where it is destroyed by enzymes within 10-30 min

• lymph nodes may be swollen during an infection because of the increase in formation of lymphocytes