Meat doesn’t grow on trees – so let’s cut them down

To mark the United Nations’ International Day of Forests on March 21st, this post briefly highlights the association between deforestation and arguably its  single largest cause – commercial livestock farming.



Beef consumption contributes to deforestation in the Amazon

In our modern world of dietary indulgence, where a person can order an entire platter of pork ribs, or a bucket of chicken wings, and receive it in matter of minutes, one can’t help but wonder just how did it become so easy to satisfy our cravings for all things meaty, and who or what is paying the real price for this convenience.

One doesn’t have to be an economist to understand the concept of ‘supply and demand’ – meaning that any increase in demand must be met by an increase in supply. So essentially, the livestock industry needs ensure that the supply is sufficient to satisfy consumer demands. This usually means scaling-up on existing production by acquiring more land space to house animals and grow food to feed them. Seeing that livestock already takes up around 45% of the global surface area 1, there is little space left to occupy – apart from rainforests.

The term “hamburger connection” was coined in 1981 to describe the United States’ then growing, and now firmly established love affair with beef 2. Cheap beef from cattle in Central American countries was produced and sold largely at the expense of their rainforests 2. In fact, over the past forty years, Central America alone  lost close to 40% of their rainforest  to cattle ranching alone 3. It wasn’t only US meat consumers enjoying cheap meat ranched on deforested land – in 2004-2005, approximately 1.2 million hectares of rainforest was cleared to grow the soybean crops that fed pigs and chickens in Europe 4. These figures are incorporated in the13 million hectares of global rainforest that has been cut down every year since 2000 5

The problem worsens as one travels further South, where the bulk of deforestation is taking place, and pasture land and feed crops make up the largest proportion of agricultural land 6. Brazil, believed to possess 62% of the Amazon rainforest, has already lost close to 80% of it; 70% of which was designated to cattle ranching 6.  Sadly but not surprisingly, this rate is increasing. From August 2012 to July 2013, Brazil reported a 35% increase in deforestation, as a space three times the size of New York City (2,338 sq km) was cleared 7.  The rate of deforestation in the Amazon was five times higher in 2013 than it was in 2012, which according to Reuters was “linked closely to soybean producers’ continual ‘indirect’ use of cattle ranchers’ deforested land.” 7


So what is all the fuss about deforestation anyway? Perhaps someone working in environmental health, or maybe a climatologist should be asked to comment. Up to 75% of Brazil’s greenhouse gas emissions is said to be caused by deforestation 8. From a global perspective, deforestation is responsible for a monumental 2.4 billion tonnes of carbon dioxide emissions every year 9, making it the largest contributor within the livestock sector. Deforestation also leads to considerable land degradation, which causes an estimated 75 billion tonnes of soil to be removed each year, at an average cost of US$400 billion dollars 6. Soil has a rich biodiversity of microbes that not only contributes to plant growth 10, but also determines much of the nutrient content of foods 10. During deforestation, organic matter is removed 10, leaving microbes with less of the carbon it needs to regulate nutrient delivery to plants 10, thus contributing to food and nutrition insecurity.

Deforestation, Climate Change, and Food Insecurity

Deforestation, Climate Change, and Food Insecurity

Environment scientists cite deforestation as one of the main causes of plant and animal species loss in tropical rainforests 11. This is hardly surprising when considering that just one quarter-pound hamburger imported from Latin America can destroy 165 pounds of living matter, including 20-30 plant species, 100 insect species, and dozens of bird, mammal, and reptile species. 12 It is even predicted that the number of birds threatened with extinction in the Amazon should triple within the next few decades 13. If current deforestation rates increase or even stays the same, species extinction will continue up to three decades after deforestation has ceased 13 – if it ever does.

Much of the ‘powers that be’ appear to be taking a “wait and see what happens” approach to deforestation and its impact on the environment and life as we know it. Unfortunately, much of the science is saying that by the time we begin to experience the real effects of deforestation, it may already be too late to prevent, reverse or halt any of the damage being done. In a sense, the real ‘power’ lies in the hands of the consumer, who can decide whether or not they want to learn more about how their diet contributes to deforestation, and whether or not they choose to do something about it.

Further reading:

Brighter Green

Case Study: Brazil Livestock

Deforestation: Disastrous consequences for the climate and for food security


  1. 1.      Thornton P, Mario Herrero M, Ericksen P (2011) Livestock and climate change. International Livestock Research Institute.
  1. 2.      Hecht SB. (1993) The Logic of Livestock and Deforestation in Amazonia. BioScience, Vol. 43, No. 10, pp. 687-695
  1. 3.       Food and Agriculture Organisation.  Cattle ranching and deforestation. Livestock Policy Brief 03
  1. 4.      Food and Agriculture Organisation: Livestock’s role in deforestation
  1. 5.      United Nations (2010) Deforestation in decline but rate remains alarming, UN agency says. United Nations News Centre.
  1. 6.      Steinfeld H, Gerber P, Wassenaar T et al. (2006) Livestock’s Long Shadow: Environmental issues and options. FAO/LEAD, Rome, Italy.
  1. 7.      Prada P, Barbara P (2013) Brazil data indicate increase in Amazon deforestation. Reuters.
  1. 8.      Tollefson J (2011) Brazil revisits forest code. Nature News
  1. 9.      McMichael AJ, Powles JW, Butler CW, Uauy R (2007) Food, livestock production, energy, climate change, and health. Lancet; 370: 1253–63
  1. 10.  Zhu YG (2009) Soil Science in the Understanding of the Security of Food Systems for Health. Asia Pac J Clin Nutr;18(4):516-519
  1. 11.  School of Natural Resources and Environment – University of Michigan; Modern Causes of Species Extinctions: habitat Destruction
  1. 12.  Julie Denslow and Christine Padoch, People of the Tropical Rainforest (Berkeley: University of California Press. 1988), 169.  cited by – McSpotlight – Beyond Beef:
  2. 13.  Wearn OR, Reuman DC, Ewers RM. (2012) Extinction Debt and Windows of Conservation Opportunity in the Brazilian Amazon. Science 337, 228; doi: 10.1126/science.1219013

The Lymphatic System

Here are the notes for the Lymphatic System lecture. You can download them from the box on the right

There is likely to be a class test on this topic next Wednesday (September 18th)

Any problems downloading please email me on



These notes will be covered in Tuesday’s lecture (April 23rd) – you can download the pdf version in the box to your right.


 Blood is considered a specialized form of connective tissue with cells suspended in a liquid extracellular matrix

  • origin in the bones 
  • Contains molecular fibers in the form of fibrinogen.
  • The blood cells present in blood are mainly red blood cells (also called RBCs or erythrocytes) and white blood cells, including leukocytes and platelets (also called thrombocytes).



Blood performs many important functions within the body including:

  • Supply of oxygen to tissues (bound to hemoglobin which is carried in red cells)
  • Supply of nutrients such as glucose, amino acids and fatty acids (dissolved in the blood or bound to plasma proteins)
  • Removal of waste such as carbon dioxide, urea and lactic acid
  • Immunological functions, including circulation of white cells, and detection of foreign material by antibodies
  • Coagulation, which is one part of the body’s self-repair mechanism
  • Messenger functions, including the transport of hormones and the signaling of tissue damage
  • Regulation of body pH (the normal pH of blood is in the range of 7.35 – 7.45)
  • Regulation of core body temperature
  • Hydraulic functions



  • Blood accounts for 7% of the human body weight, with an average density of approximately 1060 kg/m³, very close to pure water’s density of 1000 kg/m3.
  • The average adult has a blood volume of roughly 5 litres, composed of plasma and several kinds of cells (occasionally called corpuscles);
  • these formed elements of the blood are erythrocytes (red blood cells), leukocytes (white blood cells) and thrombocytes (platelets).
  • By volume the red blood cells constitute about 45% of whole blood, the plasma constitutes about 55%, and white cells constitute a minute volume.


Blood cells

Erythrocytes (Red Blood Cells)

  • 4.7 to 6.1 million (male), 4.2 to 5.4 million (female) 600 RBC for each WBC
  • Biconcave shape
  • In mammals, mature red blood cells lack a nucleus and organelles.
  • They contain the blood’s hemoglobin and distribute oxygen.
  • The red blood cells are also marked by glycoproteins that define the different blood types.
  • The proportion of blood occupied by red blood cells is referred to as the hematocrit, and is normally about 45%.

 Red cell formation:

  • occurs in the yolk sac, liver and spleen initially;
  • after birth formation occurs exclusively in bone marrow
  • The various cells of blood are made in the bone marrow in a process called haematopoiesis, which includes erythropoiesis, the production of red blood cells
  • During childhood, almost every human bone produces red blood cells; as adults, red blood cell production is limited to the larger bones: the bodies of the vertebrae, the breastbone (sternum), the ribcage, the pelvic bones, and the bones of the upper arms and legs.
  • 3 substances involved:
    • vitamin B12: DNA synthesis; cell growth and division
    • folic acid: DNA synthesis; cell growth and division
    • erythropoietin – hormone that controls rate of red blood cell formation
    • Iron: Hemoglobin synthesis

 Breakdown of RBCs:

  • more likely with age as cells become more fragile
  • Lifespan of the average RBC is 120 days
  • Over the years they experience wear and tear
  • Undergo phagocytic breakdown: Fe + haem + globin


  1. Squeezing through capillaries of active tissues damages RBCs
  2. Macrophages phagocytize damaged RBCs
  3. Hemoglobin is broken down into heme and globin
  4. Heme is broken down into iron and biliverdin
  5. Iron is either reused in synthesis of new haemoglobin or stored in the liver as ferritin
  6. Some biliverdin (green pigment) is converted to bilirubin (orange pigment)
  7. Both biliverdin and bilirubin are excreted in bile
  8. Globin is broken down into amino acids that are either metabolized by macrophages or released into the plasma


White blood cells (also called leukocytes)

  • 4,000-11,000 leukocytes
  • White blood cells are part of the immune system; they destroy and remove old or aberrant cells and cellular debris, as well as attack infectious agents (pathogens) and foreign substances.
  • The cancer of leukocytes is called leukemia.
  • The various cells of blood are made in the bone marrow in a process called haematopoiesis,
  • which includes myelopoiesis, the production of white blood cells and platelets.

White Blood Cells are divided into:

  • Granulocytes: contains visible granules in cytoplasm
    • Neutrophils – first to arrive at infection site (54% to 62% of leukocytes)
    • Eosinophils – moderate allergic reactions & defend against parasitic worm infections  (1% to 3% of leukocytes)
    • Basophils – release histamine and heparin (<1% of leukocytes)
  • agranylocytes: contains no granules
    • lymphocytes- single large nucleus (25% to 33% of leukocytes)
      • recognizes foreign substances (bacteria and cancer cells)
    • monocytes (3% to 8% of leukocytes)
      • mobile and phagocytic
      • circulating precursors of macrophages (exist as monocytes before they turn into macrophages)


Thrombocytes (platelets)

  • 200,000-500,000 thrombocytes
  • Platelets are responsible for blood clotting (coagulation).
  • They change fibrinogen into fibrin.
  • This fibrin creates a mesh onto which red blood cells collect and clot, which then stops more blood from leaving the body and also helps to prevent bacteria from entering the body.


  • About 55% of whole blood is blood plasma,
  •  a fluid that is the blood’s liquid medium, which
  •  by itself is straw-yellow in color.
  • The blood plasma volume totals of 2.7-3.0 litres in an average human.
  • It is essentially an aqueous solution containing 92% water, 8% blood plasma proteins (albumins, globulins, fibrinogen), gases (oxygen, carbon dioxide, nitrogen) and trace amounts of other materials.
  • Plasma circulates dissolved nutrients, such as, glucose, amino acids and plasma lipids (fatty acids, cholesterol, phospholipids — dissolved in the blood or bound to plasma proteins),
  • Removes waste products, such as, carbon dioxide, urea and lactic acid.

Functions of plasma proteins

  • Maintain Colloidal osmotic pressure
  • Acts as transport medium for fat, fatty acids, hormones, calcium, iron, etc.
  • Y-globulins- act as antibodies
  • Fibrinogen + globulins- acute phase reactions
  • Regulate the pH of blood (acting as buffer)
  • Acts as reserve supply of amino acids in the blood


Electrolytes – important in maintaining plasma pH and osmotic pressure

  • Sodium, Potassium, Calcium, Magnesium
  • Chloride, Bicarbonate, Phosphate, Sulphate

 Other important components include:

  • Serum albumin
  • Blood clotting factors (to facilitate coagulation)
  • Immunoglobulins (antibodies)
  • Various other proteins
  • Various electrolytes (mainly sodium and chloride)

 The term serum refers to plasma from which the clotting proteins have been removed.


  • Hemoglobin determines the color of blood in vertebrates.
  • Each molecule has four heme groups, and their interaction with various molecules alters the exact color.
  • In vertebrates and other hemoglobin-using creatures, arterial blood and capillary blood are bright red as oxygen impacts a strong red color to the heme group.
  • Deoxygenated blood is a darker shade of red; this is present in veins, and can be seen when blood is taken from the vein (blood donation; venous blood samples)


General medical disorders

 Disorders of volume

  • Injury can cause blood loss through bleeding[19].
  • A healthy adult can lose almost 20% of blood volume (1L) before the first symptom, restlessness, begins,
  • and 40% of volume (2L) before shock sets in.
  • Thrombocytes are important for blood coagulation and the formation of blood clots which can stop bleeding.
  • Trauma to the internal organs or bones can cause internal bleeding, which can sometimes be severe.

Disorders of circulation

  • Shock is the ineffective perfusion of tissues, and can be caused by a variety of conditions including blood loss, infection, and poor cardiac output.
  • Atherosclerosis reduces the flow of blood through arteries, because atheroma lines arteries and narrows them. Atheroma tends to increase with age, and its progression can be compounded by many causes including smoking, high blood pressure, excess circulating lipids (hyperlipidemia), and diabetes mellitus.
  • Coagulation can form a thrombosis which can obstruct vessels.
  • Problems with blood composition, the pumping action of the heart, or narrowing of blood vessels can have many consequences including hypoxia (lack of oxygen) of the tissues supplied.
  • The term ischaemia refers to tissue which is inadequately perfused with blood, and
  • infarction refers to tissue death (necrosis) which can occur when the blood supply has been blocked (or is very inadequate).


  • Insufficient red cell mass
  • (anemia) can be the result of bleeding, blood diseases like thalassemia, or nutritional deficiencies; and
  • may require blood transfusion.
  • Several countries have blood banks to fill the demand for transfusable blood.
  • A person receiving a blood transfusion must have a blood type compatible with that of the donor.

Types of anaemia:

–          Aplastic – caused by toxic chemicals; result in damaged bone marrow

–          Hemolytic – caused by toxic chemicals/radiation; result in destroyed blood cells

–          Iron deficiency – caused by dietary lack of iron; result in haemoglobin deficient

–          Sickle cell – caused by defective gene; result in red blood cells abnormally shaped

–          Thalassemia – caused by defective gene; result in red blood cells short-lived/haemoglobin deficient

–          Pernicious anemia – caused by inability to absorb vitamin B12; result excess of large, fragile cells –

N.B – Vitamin B12 is absorbed from the small intestine- needs intrinsic factor produced in the stomach- and stored in the liver.  Deficiency of intrinsic factor causes pernicious anaemia – can cause permanent brain damage

 Disorders of coagulation

Hemophilia is a genetic illness that causes dysfunction in one of the blood’s clotting mechanisms. This can allow otherwise minor wounds to be life-threatening, but more commonly results in hemarthrosis, or bleeding into joint spaces, which can be crippling.

Ineffective or insufficient platelets can also result in coagulopathy (bleeding disorders).

Thrombophilia (hyper-coagulable state) results from defects in regulation of platelet or clotting factor function, and can cause thrombosis.

 Infectious disorders:

Blood is an important vector of infection. Owing to blood-borne infections, bloodstained objects are treated as a biohazard.

–          HIV, the virus which causes AIDS, is transmitted through contact between blood, semen, or the bodily secretions of an infected person.

–          Hepatitis B and C are transmitted primarily through blood contact.

–          Bacterial infection of the blood is bacteremia or sepsis.

–          Viral Infection is viremia.

–          Malaria and trypanosomiasis are blood-borne parasitic infections.


Carbon monoxide poisoning

–          Substances other than oxygen can bind to hemoglobin, and can cause irreversible damage to the body.

–          Carbon monoxide is extremely dangerous when carried to the blood via the lungs by inhalation,

–          Carbon monoxide irreversibly binds to hemoglobin to form carboxyhemoglobin,

–          less hemoglobin is free to bind oxygen, and less oxygen can be transported in the blood.

–          Can cause suffocation insidiously (creeps up).

–          A fire burning in an enclosed room with poor ventilation presents a very dangerous hazard since it can create a build-up of carbon monoxide in the air.

–          Some carbon monoxide binds to hemoglobin when smoking tobacco.


Medical Treatments

 Blood products

–          Blood for transfusion is obtained from human donors by blood donation and stored in a blood bank.

–          There are many different blood types in humans, the ABO blood group system, and the Rhesus blood group system being the most important.

–          Transfusion of blood of an incompatible blood group may cause severe, often fatal, complications, so crossmatching is done to ensure that a compatible blood product is transfused.

–          Other blood products administered intravenously are platelets, blood plasma, cryoprecipitate and specific coagulation factor concentrates.


Intravenous administration

–          Many forms of medication (from antibiotics to chemotherapy) are administered intravenously, as they are not readily or adequately absorbed by the digestive tract.

–          After severe acute blood loss, liquid preparations, generically known as plasma expanders, can be given intravenously, either solutions of salts (NaCl, KCl, CaCl2 etc…) at physiological concentrations, or colloidal solutions, such as dextrans, human serum albumin, or fresh frozen plasma.

–          In these emergency situations, a plasma expander is a more effective life-saving procedure than a blood transfusion, because the metabolism of transfused red blood cells does not restart immediately after a transfusion.



  • In modern evidence-based medicine bloodletting is used in management of a few rare diseases, including haemochromatosis and polycythemia.
  • However, bloodletting and leeching were common unvalidated interventions used until the 19th century, as many diseases were incorrectly thought to be due to an excess of blood, according to Hippocratic medicine.




















Blood Types

These notes will be covered in Monday’s (April 22nd) lecture. Download the pdf version in the box to your right.


  • A blood type (also called a blood group) is a classification of blood based on the presence or absence of inherited antigenic substances on the surface of red blood cells (RBCs).
  • These antigens may be proteins, carbohydrates, glycoproteins, or glycolipids, depending on the blood group system, and some of these antigens are also present on the surface of other types of cells of various tissues.
    • Blood types are inherited and represent contributions from both parents. A total of 29 human blood group systems are now recognized by the International Society of Blood Transfusion (ISBT)
    • Across the 29 blood groups, over 600 different blood group antigens have been found, but many of these are very rare or are mainly found in certain ethnic groups.


  • Almost always, an individual has the same blood group for life; but very rarely an individual’s blood type changes through addition or suppression of an antigen in infection, malignancy or autoimmune disease.


  • An example of this rare phenomenon is the case Demi-Lee Brennan, an Australian citizen, whose blood group changed after a liver transplant.


  •  Another more common cause in blood type change is a bone marrow transplant.
    • If a person receives a bone marrow from someone who is a different ABO type (ex. a type A patient receives a type O bone marrow), the patient’s blood type will eventually convert to the donor’s type.



  • Early transfusion experiments (late 1600s) used lamb blood
  • Human blood was used in 1800s with unpredictable results – some were cured, while some were killed when their kidneys failed under the strain of dealing with clumping blood cells because of incompatible blood types
  • The two most significant blood group systems were discovered during early experiments with blood transfusion: the ABO group in 1901and the Rhesus group in 1937.
  • Development of the Coombs test in 1945, the advent of transfusion medicine, and the understanding of hemolytic disease of the newborn led to discovery of more blood groups

ABO Blood Group

Based on the presence or absence of two major antigens on RBCs membranes: Antigen A and Antigen B

A person’s RBCs have one of four antigen combinations:

–          Antigen A only (Type A)

–          Antigen B only (Type B)

–          Antigen A and Antigen B (Type AB)

–          None (Type O)





  • ABO blood group antibodies are synthesised in plasma approx 2 – 8 months after birth
  • They are called “Anti-“because they are “against”. E.g. Anti-A means “against A”
  • These antibodies can bind to antigens on the surface of incompatible transfused red blood cells (or other tissue cells), often leading to destruction of the cells by recruitment of other components of the immune system.
  • These naturally occurring antibodies are of the IgM class, and as was described above, IgM antibodies have the capability of agglutinating (clumping) red cells within the blood vessels, possibly leading to death.
  • The associated anti-A antibodies and anti-B antibodies are usually “Immunoglobulin M”, abbreviated IgM, antibodies. ABO IgM antibodies are produced in the first years of life by sensitization to environmental substances such as food, bacteria and viruses.
  • When IgM antibodies bind to the transfused cells, the transfused cells can clump.




  • Transfusion medicine is a specialized branch of hematology that is concerned with the study of blood groups, along with the work of a blood bank to provide a transfusion service for blood and other blood products.
  • It is vital that compatible blood is selected for transfusions and that compatible tissue is selected for organ transplantation.
    • A test called the Antibody Screen is always performed on patients who may require red blood cell transfusion, and this test will detect most clinically significant red cell antibodies.
    • If a unit of incompatible blood is transfused between a donor and recipient, a severe acute immunological reaction, hemolysis (RBC destruction), renal failure and shock are likely to occur, and death is a possibility.
    • Patients should ideally receive their own blood or type-specific blood products to minimize the chance of a transfusion reaction.
    • Risks can be further reduced by cross-matching blood, but this may be skipped when blood is required for an emergency.
    • Cross-matching involves mixing a sample of the recipient’s blood with a sample of the donor’s blood and checking if the mixture agglutinates, or forms clumps. If agglutination is not obvious by direct vision, blood bank technicians usually check for agglutination with a microscope.



  • Agglutination occurs due to a reaction between RBC surface molecules (antigens) and protein antibodies travelling in the plasma
  • Mismatched blood transfusion produces signs of agglutination, including

–          Anxiety

–          Breathing difficulty

–          Facial flushing

–          Headache

–          Severe pain in neck, chest and lumba area

–          Red blood cells burst, releasing free hemoglobin. Hemoglobin is then phagocytised by macrophages, breaking it down into heme and globin. Some of the heme is recycled, while the rest is converted to the orange pigment bilirubin. Excess build-up of bilirubin causes the yellow skin observed in jaundice. 







Blood group compatibility

In persons with:

–          Type A you find Anti-B antibodies (because antigen B is absent), so they should not receive type B or type AB blood transfusion

–          Type B you find Anti-A antibodies (because antigen A is absent) so they should not receive type A or type AB blood transfusion

–          Type AB you find no antibodies (because antigen A and B are present) so they can receive a transfusion from any blood type (universal recipients), although its best to use the same type AB

–          Type O you find  both Anti-A and Anti-B antibodies (because both A and B are absent), so they can only receive type O transfusion, but in theory, type O can be given to any blood type (universal donors)

–          the terms universal donor and universal recipient are an over-simplification, because they only consider possible reactions of the recipient’s anti-A and anti-B antibodies to transfused red blood cells, and also possible sensitisation to RhD antigens. The possible reactions of anti-A and anti-B antibodies present in the transfused blood to the recipients RBCs are not considered, because a relatively small volume of plasma containing antibodies is transfused.


Pregnancy (ABO Group)

  • Many pregnant women carry a fetus with a different blood type from their own, and the mother can form antibodies against fetal RBCs.
  • Generally, agglutination in the fetus during pregnancy does not occur because Anti-A and Anti-B antibodies cannot cross the placenta due to their size
  • However, sometimes these maternal antibodies are IgG, a small immunoglobulin, which can cross the placenta and cause hemolysis of fetal RBCs, which in turn can lead to hemolytic disease of the newborn, an illness of low fetal blood counts which can be temporary or treatable but can occasionally be severe, depending on the antibody causing the hemolytic disease of the newborn.


Rhesus (Rh) Blood Group

  • The Rh blood group consists of several antigen types, the most common being antigen D.
  •  If RBC surface membranes contain antigen D or other Rh antigens, the blood tests Rh-positive.
  •  If there are no Rh antigens on the membrane surface, the blood tests Rh-negative.
  • The D antigen is considered highly immunogenic, meaning that a person who is D negative is very likely to make Anti-D when exposed to the D antigen (through either transfusion or pregnancy).
  • A RhD negative patient who does not have any anti-RhD antibodies (never being previously sensitized to RhD positive RBCs) can receive a transfusion of RhD positive blood once, but this would cause sensitization to the RhD antigen, and a female patient would become at risk for hemolytic disease of the newborn.
  • Anti-D antibodies only form in Rh-negative persons in response to RBCs with Rh antigens being present. If an Rh-negative person receives an initial transfusion of Rh-positive blood, Anti-D antibodies will be produced and the person will become sensitised, yet there may be no serious consequences at that time. However, if the person receives a second transfusion, agglutination may occur.
  • If an Rh-negative individual is exposed to a Rh-positive antigen, the immune system will produce antibodies that can specifically bind to that particular blood group antigen, and an immunological memory against that antigen is formed.
  • The individual will have become sensitized to Rh-positive blood group antigen.


 Pregnancy (Rh Group)

If an Rh-negative woman is pregnant with a Rh-positive fetus, the first pregnancy may have no serious consequences unless:

–           there is a tearing of the placental membrane at the time of birth, or

–          the pregnancy ends before birth, or

–          during an invasive prenatal test,

then some of the Rh-positive fetal blood may enter maternal circulation and stimulate maternal Anti-Rh antibodies. If this woman becomes pregnant with a second Rh-positive fetus, anti-Rh antibodies (hemolysins) can cross the placental membrane and destroy fetal RBCs. This causes the disease erythroblastosis fetalis – haemolytic disease of the newborn, which is currently very rare 

Prevention of the formation of Anti-D by D negative mothers is accomplished by a medication called RhIg, given at about 28 weeks of gestation and after delivery, if the infant is determined to be D positive.

   Rh-negative is quite rare.



Blood Products

  • In order to provide maximum benefit from each blood donation and to extend shelf-life, blood banks fractionate some whole blood into several products.
  • The most common of these products are:

–           packed RBCs,

–           plasma,

–          platelets,

–          cryoprecipitate, and

–          fresh frozen plasma (FFP).

  • FFP is quick-frozen to retain the labile clotting factors V and VIII, which are usually administered to patients who have a potentially fatal clotting problem caused by a condition such as advanced liver disease, overdose of anticoagulant, or disseminated intravascular coagulation (DIC).
  • Units of packed red cells are made by removing as much of the plasma as possible from whole blood units.
  • Clotting factors synthesized by modern recombinant methods are now in routine clinical use for hemophilia, as the risks of infection transmission that occur with pooled blood products are avoided.


Muscle Tissue

This topic is quite brief and will be covered in Wednesday’s (April 17th) lecture. You can download the lecture notes in the BOX to the right

Remember the tutorial on Thursday will cover some example questions that may come in both the test and the final end of semester exam

General characteristics

  • Muscle tissue contracts (shortens and thickens),
  • moves structures attached to it (contractile)
  • Sometimes called muscle fibers – elongated
  • Three major types of muscle tissue are skeletal, smooth, and cardiac


Skeletal Muscle Tissue

  • Forms muscles that attach to bones
  • Can be controlled by conscious effort (voluntary muscle tissue)
  • Long (up to 40 mm in length)
  • Narrow (less than 0.1mm)
  • Have alternating light and dark cross-markings called striations
  • Each cell has many nuclei
  • Function: Moves the head, trunk, limbs, enable us to smile, write, talk, sing, chew, breathe

 muslce tissue - skeletal

Smooth Muscle

  • Called smooth muscle because its cells lack striations (alternating light and dark cross-markings)
  • Shorter than skeletal muscles
  • Spindle shaped
  • Each cell has a single nucleus, which is centrally located
  • Comprises the walls of hollow internal organs – stomach, intestines, urinary bladder, uterus, blood vessels
  • Involuntary muscle – cannot be stimulated to contract by conscious effort
  • Functions: Moves food through the digestive tract, constricts blood vessels, empties urinary bladder  

muscle tissue -  SmoothMusc3_400X_rev

Smooth Muscle Tissue

Cardiac Muscle Tissue

  • Only found in the heart
  • Makes up the bulk of the heart
  • Cells are striated (alternating light and dark cross-markings), branched, joined end-to-end and interconnected in complex networks
  • Each cell has only one nucleus
  • Intercalated disc – intercellular junction – where one cell touches another
  • Controlled involuntarily – can continue to function without nervous stimulation (heart still pumps in brain dead people)
  • Function: Pumps blood through the heart chambers and into the blood vessels

cardiac muscle

Cardiac Muscle Tissue

Connective Tissue

It is always a good idea to read through the notes in advance so that any questions you might have you can ask the lecturer.

Remember, the lecture is the best place to ask questions and have them explained to you (even if the lecturer does not know the answer he or she can find out) so it is always in your best interest to attend.

General Characteristics

Connective tissues are the most abundant type of tissue in the body.

Functions of Connective tissues:

  1. Bind structures
  2. Provide support and protection
  3. Serve as frameworks
  4. Fill spaces
  5. Store fat
  6. Produce blood cells
  7. Protect against infection
  8. Help repair tissue damage

Connective tissue is made up of major cell types called Fixed Cells and Wandering Cells:

  • Fixed cells – stay in the specific tissue type for a long period (fibroblasts, mast cells)

–          Fibroblasts:  Large, star-shaped cells; secrete proteins into extracellular matrix to produce fibers. Most common type of fixed cell

–          Mast cells: large and widely distributed in connective tissues; release heparin (prevents blood clotting), and histamine (promotes reactions associated with inflammation and allergies)

  • Wandering cells – move through and appear in tissues temporarily, usually in response to infection (macrophages)

–            Macrophages: Almost as numerous as fibroblasts; originate as white blood cells; specialised to carry out phagocytosis (remove foreign particles from tissues – scavenger cells)



Connective tissues have a large amount of extracellular matrix (EM) between them. The extracellular matrix is made up of:

  •  protein fibers (collagenous, elastic, reticular)

–          Collagenous – thick threads of the protein collagen (major structural protein); flexible but only slightly elastic; great tensile strength (can resist large pulling forces); hold structures together (ligaments – connects bones to bones; and tendons – connects muscles to bones); found in dense connective tissue

  collagenous fibers



–          Elastic – made up of spring-like protein called elastin; sometimes called yellow fibers; easily stretched and will resume original shape and ngth when force is removed; found in boy parts subject to stretching – vocal cords, air passages of respiratory system

–          Reticular – thin collagenous fibers; highly branched and form supporting networks in a variety of tissues (e.g spleen)

  • a ground substance (made up of non-fibrous protein and other molecules) – binds, supports and provides a medium for substances to be transferred from the blood to the tissue cells
  • fluid – The consistency of the extracellular matrix varies from fluid to semi-solid to solid

Classification of Connective Tissues

  1. Connective tissue proper
  •  Loose connective tissue (areolar, adipose, reticular)
  • Dense connective tissue (dense regular, dense irregular, elastic)

2.          Specialised connective tissue

  •  Cartilage
  • Bone
  • Blood
  1. Connective tissue proper:

Loose connective tissue

–          Areolar – forms thin delicate membranes throughout the body; made up mainly of fibroblasts; located some distance apart from each other; cells separated by ground substance that contains many protein fibers secreted by fibroblasts

 Areolar Connective Tissue


–          Adipose (fat) – develops when certain cells (adipocytes) store fat in their cytoplasm as droplets; become adipose tissue when adipocytes become so abundant that they crowd out other cells; lies beneath the skin, in spaces between muscles around kidneys, behind eyeballs etc.


 Adipose Connective Tissue




–          Reticular – made up of thin reticular fibres in a 3D network; helps provide framework of some internal organs (liver, spleen)

reticular connective tissue



Dense connective tissue

–          Dense regular – made up of thick, closely packed collagenous fibers, a network of elastic fibers, and a few cells (mainly fibroblasts); binds body structures as part of tendons and ligaments; blood supply to dense regular tissue is poor, hence sprains take considerable time to heal

dense regular connective tissue2



–          Dense Irregular –  thicker, interwoven and more randomly organised than dense regular (allows tissue to sustain tension from different areas); located in the dermis (inner skin layer)

dense irregular connective tissue



–          Elastic – mainly made up of yellow elastic fibers in parallel strands or branching networks; have collagenous fibers and fibroblasts between these fibers; found in the attachment between the bones of the spinal column & within the walls of certain hollow internal organs (large arteries and some portions of the heart)

elastic tissue



2.                Specialised connective tissue

–          Cartilage – rigid connective tissue; provides support/frameworks/attachment, protects underlying tissues, forms structural model for many bones; abundant and largely made up of collagenous fibers in  a ground substance (extracellular matrix –contains large volume of water); cartilage cells (chondrocytes) occupy small chambers (lacunae) and are found within the extracellular matrix; lacks direct blood supply – cartilage cells obtain nutrients from surrounding cells via diffusion (this is why torn cartilage heals slowly); three types of cartilage:

  •  Hyaline cartilagemost common; looks like white glass – very fine collagenous fibers in extracellular matrix; found on the end of bones in many joints, in soft part of the nose; important in development and growth of many boneshyaline cartilage




  • Elastic cartilage  – more flexible than hyaline – extracellular matrix has dense network of elastic fibers; provides framework for external ears and parts of the larynx  

elastic cartilage

                                                ELASTIC CARTILAGE



  • Fibrocartilage – very tough tissue – many collagenous fibers; shock absorber for structures subjected to pressure – forms pads between individual bones of the spinal column, cushions bones in the knees and pelvic girdle




–          Bonemost rigid connective tissue; hardness due to mineral salts between cells (calcium phosphate/calcium carbonate); supports body structures internally; protects vital structures (brain and thorax); contains red marrow, which forms blood cells; stores and releases inorganic chemicals (calcium, phosphorus); every bone cell is fairly close to nutrient supply – materials move rapidly between blood vessels and bone cells  – injured bne heals more rapidly than injured cartilage; interior portion consists of spongy bone, which lightens the weight of the bone and provides spaces for bone marrow


 Bone TissueBone Tissue



–          Blood made up of cells suspended in a fluid extracellular matrix called plasma; include red blood cells – transport gases, white blood cells – fights infection and platelets (cellular fragments) – involved in blood clotting; formed in red marrow (hollow parts of certain bones); red blood cells function entirely in the blood vessels; white blood cells migrate from blood to connective tissues   

Blood Tissue




  • Adipocyte: An adipose, or fat cell.
  • Adipose connective tissue: Tissue with closely packed cells that have large central fat droplets and peripheral nuclei, and a sparse gel-like matrix with fibers. Functions as an energy reserve, insulation against heat loss, support and protection of organs. Located in hypodermis under the skin, in breasts, around kidneys, behind eyeballs, and widely distributed as body fat.
  • Articular cartilage: Hyaline cartilage covering bone ends at movable joints.
  • Cartilage: A type of connective tissue consisting of chondrocytes in lacunae, embedded in a dense network of collagen and elastic fibers and an extracellular matrix of chondroitin sulfate.
  • Cartilage bone: Bone formed by the calcification of hyaline cartilage structures.
  • Chondritis: Inflammation of cartilage.
  • Chondroblast: A dividing cartilage-forming cell, derived from mesenchyme, that secretes a cartilaginous matrix and fibers, becomes enclosed in a lacuna, then differentiates into a chondrocyte.
  • Chondroclast: A giant multinucleated cell involved in the resorption of calcified cartilage.
  • Chondrocyte: Mature cartilage cell that occupies a lacuna within cartilage matrix.
  • Costal cartilage: Hyaline cartilage that forms the anterior continuation of a rib; articulates with the sternum.
  • Hyaline cartilage: Tissue with many chondrocytes that lie in lacunae, amorphous but firm matrix, and thin collagen fibers. Functions in providing support, flexibility, and smooth surfaces for joint movements. Located in cartilages of the trachea, larynx, and nose; costal cartilages of the ribs; articular cartilages of long bones; embryonic and fetal skeleton.
  • Hypodermis: Subcutaneous tissue deep to the skin; consists of adipose and areolar connective tissue
  • Leptin: hormone secreted by Adipose tissue; suppresses appetite; increases energy expenditure
  • Marrow: Soft, spongelike material in the cavities of bone; red bone marrow produces blood cells; yellow bone marrow contains adipose tissue that stores triglycerides.
  • Renal fascia: Outermost sheath of dense fibrous connective tissue that surrounds the adipose capsule and anchors the kidneys.
  • Resistin: hormone secreted by Adipose tissue; antagonizes insulin’s action on fat, muscle, and liver cells.
  • Subcutaneous layer: A continuous sheet of areolar connective tissue and adipose tissue between the dermis of the skin and the deep fascia of the muscles. Also called the superficial fascia.