5. Cardiovascular System

Question 1

Blood

Answer 1

• Blood is a fluid type of connective tissue.
• Composed of plasma (55%) and cells (45%).
• Blood accounts for 7% of body weight. Average adult males have 5.6 L of blood & females 4.5 L.

Question 2

Blood Functions

Answer 2

• Contributes to homeostasis by transportingoxygen, carbon dioxide, nutrients, wastes and hormones.
• Helps regulate pH and temperature.
• Immune functionwith antibodies, phagocytes, clotting factors etc.

Question 3

Blood plasma

Answer 3

•Blood plasma is the yellow coloured liquid that remains when cells are removed from blood.

Consists of:
• Mostly water(91%).
• Proteins(7%).
• Mineral salts (0.9%).
• Nutrients.
• Organic waste materials.
• Hormones.
• Enzymes.
• Gases.

Question 4

Blood Plasma Proteins

Answer 4

•
All plasma proteins are synthesised by liver cells (hepatocytes).
•
The following account for the majority of plasma proteins:
1. Albumin
2. Globulins
3. Fibrinogen

Question 5

Albumin

Answer 5

• Smallest & most numerous plasma protein.
• Carrier of substances(lipids & steroid hormones).
• Maintains osmotic pressure.

Question 6

Globulins

Answer 6

Globulins: (38%)
• Immunity–Immunoglobulins (antibodies). IgE, IgM, IgA etc
• Transport iron, lipids and vitamins.

Question 7

Fibrinogen

Answer 7

Fibrinogen: (7%)
• Also called ‘clotting factor one’.
• Essential forblood clotting.

Question 8

Blood Plasma Nutrients

Answer 8

• Products of digestion pass into the blood for distribution to all body cells. These nutrients include:
• Simple sugars (carbohydrates) -mostly glucose.
• Amino acids (building blocks for proteins).
• Fats / oils -carried by proteins (i.e. HDL).
• Vitamins.
• The main mineral components are:
• Cations(positively charged ions): Sodium, potassium, calcium, magnesium.
• Anions (negatively charged ions): Chlorides, bicarbonates, phosphates.

Question 9

Cations

Answer 9

Na+= sodium
Ca+2= calcium
K+= potassium
Mg+2= magnesium

Question 10

Anions

Answer 10

Cl-= chlorine
HCO3- = bicarbonate
PO4 -2 = phosphate
SO4 -2 = sulphate

Question 11

Blood Plasma: Other

Answer 11

ORGANIC WASTE:
• Urea –produced from protein breakdown.
• Creatinine–by-product of muscle metabolism.
• Uric acid –from the breakdown of purines.
• Carbon dioxide-from cell metabolism.
HORMONES:
• Chemical messengers carried by the blood.
ENZYMES:
• Catalystsfor biochemical reactions in the body.
GASES:
• Oxygen (O2) & carbon dioxide (CO2).

Question 12

Blood Cells

Answer 12

1. Erythrocytes (Red blood cells)
2. Leukocytes (White blood cells)
3. Thrombocytes (Platelets)

Question 13

Haematopoiesis

Answer 13

• Haematopoiesis = production of all blood cells.
• All blood cells originate from pluripotent stem cells in the red bone marrow.
• During the first 2 months gestation, the embryonic yolk sacperforms haematopoiesis. Between months 2 and 9 of foetal life, the liver & spleen take over.
• In first few years of life all bone marrow is red and produces blood cells.
• In adults, haematopoiesis occurs in vertebrae, ribs, sternum, skull, sacrum, pelvis and proximal long bones (mostly femur).

Question 14

Erythrocytes (Red Blood Cells)

Answer 14

• Erythrocytes are biconcave & non-nucleated, giving the cells a larger surface area to transport oxygen.
• Erythrocytes have a life span of 90-120 days. They also have a strong & flexible cell membrane.
• Approx. 6-8 μm(micrometres) indiameter.
• The percentage of blood volume occupied by erythrocytes is called the‘haematocrit’.
• In females the haematocrit is roughly 42%, whilst in males it is approximately 47%.

Question 15

Erythrocyte Structure

Answer 15

• Erythrocytes are made up of haemoglobin molecules, which carry mostly oxygen & some carbon dioxide.
• Each erythrocyte has 280 million Hb molecules.
• One haemoglobin molecule consists of 4 polypeptide chains(‘globin’). Each chain is bound to a pigment called ‘haem’, which contains iron.
• Each haem group in haemoglobin can carry an oxygen molecule, thuseach haemoglobin can carry up to 4 oxygen molecules.

Question 16

Haemoglobin Structure

Answer 16

A haemoglobin molecule is made up of four polypeptide chains:
•Adult haemoglobin (HbA): composed of two α (alpha) and two β (beta) subunits.
•Foetal Haemoglobin (HbF): composed of two α (alpha) and two γ (gamma) subunits.

Question 17

Erythropoiesis

Answer 17

• The formation of erythrocytes occurs in the red bone marrow.
• Immature erythrocytes have nuclei & organelles which they lose as they mature (loss of nucleus causes indent in cell).
• The following nutrients are required for erythrocyte formation:
• Vitamin B12
• Folate (vitamin B9)
• Iron
• Hypoxia stimulates the secretion of the hormone ‘erythropoietin’ (EPO) from the kidneys, which stimulates erythropoiesis in the bone marrow.
• Causes include high altitude, haemolysis, blood loss & pregnancy.
• Premature new-born’s often exhibit anaemia, partly due to inadequate EPO.
• During first weeks of life, the liver produces EPO. The liver is less sensitive than the kidneys to hypoxia.

Question 18

Haemolysis

Answer 18

• Haemolysis describes the destruction of erythrocytes to release haemoglobin into plasma.
• An erythrocyte normally lives for 90 to 120 days. About 1% of erythrocytes break down each day.
• Haemolysis is carried out by specialised macrophages(phagocytic cells) found in many tissues; especially the spleen, bone marrow & liver.
• The globin amino acids and iron are recycled.
• Bilirubinis a yellow coloured pigment formed from the breakdown of ‘haem’. Bilirubinis excreted in bile and urine.

Question 19

Haemolysis and Bilirubin

Answer 19

• The pigment ‘bilirubin’ is formed from the breakdown of haem.
• Bilirubin is predominately formed in the spleen, bone marrow and liver. Once formed, bilirubin is described
as being ‘unconjugated’. Bilirubin must be conjugated in the liver for it to be effectively excreted in the GIT.
• Conjugated bilirubin is mostly excreted in faeces (staining brown).

Question 20

Blood Groups

Answer 20

• There are two major blood group systems: ABO and Rhesus.

* Blood group antigens are located on the surface of erythrocytes.

Question 21

ABO System

Answer 21

• Based on two glycolipid antigens called A& B.
• Those whose erythrocytes display antigen A have blood group A. Antigen B are blood group B. Both A & B are AB. Or neither antigen are O.
• Blood plasma contains antibodies that react with A or B antigens if the two are mixed. Anti-A antibody reacts with antigen A etc.
• In a transfusion reaction, the antigen-antibody complexes formed activate an immune response that causes erythrocyte membranes to rupture.

Question 22

Blood Group O-

Answer 22

•

Blood group O-= ‘Universal dOnor’because erythrocytes have neither A or B antigens for antibodies to attach too.

Question 23

Blood group AB+

Answer 23

‘Universal recipient’ because the recipient blood plasma contains no antibodies against either A or B antigens that could be donated.

Question 24

Rhesus Blood Group

Answer 24

• Rhesus antigen (rhesus factor) is another surface antigen found on erythrocytes.
• Those that have Rhesus (Rh) antigens are ‘Rhesus positive’ & those lacking Rh antigens are Rh negative.
• Inheritance of the rhesus factor is via a rhesus dominant gene (85% of people are rhesus positive).
• Anti-Rhesus Antibodies are produced in rhesus negative individuals only if they come into contact with the rhesus antigen (not normally in blood).
• Can come into contact in pregnancy orincompatible blood transfusion.

Question 25

Rhesus Blood Group: Pregnancy

Answer 25

• In Pregnancy, the only way antibodies are developed against the Rh antigen is through placental sensitisation or transfusion. • This only occurs if the mother is Rh- and the unborn baby is Rh+ (inheriting the father's rhesus antigen). • Normally maternal and foetal blood cells do not mix, but this can occur at delivery, if there is an ante-partum haemorrhage, or in subsequent pregnancies. • The most common problem with Rh incompatibility is ‘haemolytic disease of the newborn’(see later). • An injection of anti-Rh antibodies binds to and inactivates foetal Rh antigens. • These antibodies administered medically are often referred to anti D antibodies.

Question 26

Leukocytes

Answer 26

• Leukocytes function to defend the body from microbes (i.e. bacteria, viruses, fungi) & foreign particles. • Leukocytes account for 1% of blood volume. • Leukocytes contain nuclei (unlike erythrocytes). Leukocytes can be classified as: 1. Granulocytes -> have secretory granules in their cytoplasm. 2. Agranulocytes ->have no granules in their cytoplasm.

Question 27

Granulocytes

Answer 27

Neutrophils (60%) Basophils/Mast Cells (1%) Eosinophils (2-4%)

Question 28

Neutrophils

Answer 28

Primary functions: •Phagocytosis-ingest & destroy microbes. •These cells die forming part of the pus. Mode of action: •Phagocytosis: lysosomes digest microbes. •1st to migrate to site of infection (<1 hour). Involved in: •Infection, tissue damage, leukaemia, inflammatory diseases (i.e. rheumatoid arthritis), heavy smoking, excessive exercise.

Question 29

Basophils/Mast Cells

Answer 29

Primary functions: • In blood = basophils • In tissue= mast cells • Key cells in ‘inflammation’. Release histamine & heparin. Mode of action: Release histamine & heparinfrom granules. • Histamine dilates blood vessels. • Not phagocytic. Involved in: • Inflammatory diseases (i.e. inflammatory bowel diseases), allergies, infections, hypothyroidism, leukaemia.

Question 30

Eosinophils

Answer 30

``` Primary functions: • Eliminate parasites. • Promote inflammation–allergic reactions. Mode of action: • Phagocytosis. • Migrate to allergic site. Involved in: • Parasitic infections, atopic (extrinsic) asthma, allergies. ```

Question 31

Agranulocytes

Answer 31

Monocytes / Macrophages (6%) | Lymphocytes (30%)

Question 32

Monocytes / Macrophages (6%)

Answer 32

Primary functions: • In blood = monocytes. • In tissue = macrophages. Inflammation & repair • Phagocytosis-ingest & destroy cellular debris & pathogens. • Activate other immune cells via antigen presentation. Mode of action: • Phagocytosis & chemotaxis(attracts other components of the immune system). • Secrete cytokines e.g. Interleukin 1 –promotes fever, Produces globulins & activates T-lymphocytes.

Question 33

Lymphocytes (30%)

Answer 33

Primary functions: • B-lymphocytes. • T-lymphocytes. • Natural killer (NK) cells. • Abundant in blood & lymphatic tissue where B and T lymphocytes are critical forimmunity against specific antigens and the production of immunological memory. Mode of Action: • B-lymphocytesactivate immune response via antibodyformation. • T-lymphocytes& NK cells kill invading pathogens (NK do this non-specifically).

Question 34

Thrombocytes (Platelets)

Answer 34

* Thrombocytes are small non-nucleated discs produced in the red bone marrow. * Thrombocytes develop from megakaryoblasts that transform into megakaryocytes. These huge cells break down into 2000-3000 fragments -> these are thrombocytes. * Produced under influence of thrombopoietin (mostly from liver) and have a life span of 10 days. * Involved in blood clotting and prevent blood loss from damaged blood vessels by forming a platelet plug.

Question 35

Thrombocytes: Function

Answer 35

* Platelets contain ‘storage’ granules. These are tiny sacs that release proteins & adhesion molecules such as clotting factors. * When activated, platelets release the contents of these granules in order to initiate clotting and eventually, healing. * Platelet activation also initiates the production of thromboxane which is a vasoconstrictor that helps to strengthen a blood clot.

Question 36

4 Stages of Blood Clotting

Answer 36

1. Vasoconstriction 2. Platelet plug formation 3. Coagulation 4. Fibrinolysis

Question 37

Vasoconstriction

Answer 37

* When arterioles are damaged, the smooth muscle contracts immediately. * When collagen is exposed in vascular endothelium, thromboxane is released which causes vascular spasm and attracts platelets.

Question 38

Platelet Plug Formation

Answer 38

* Platelets contact and stick to the damaged wall. They are activated and release binding proteins. vWFis needed for this stage. * These changes lead to platelet aggregation and causes platelets to become sticky (positive feedback).

Question 39

Coagulation

Answer 39

* Clotting factors form clot thereby reinforcing the plug. The enzyme ‘thrombin’ is produced which converts fibrinogen into fibrin. * Fibrin forms long, sticky threads that produce a mesh in the clot. Erythrocytes become caught up in the web and a clot forms.

Question 40

Fibrinolysis

Answer 40

•Breakdown of a clot. The enzyme plasmin can dissolve a clot by digesting fibrin threads and inactivating fibrinogen and thrombin.

Question 41

Blood Clotting: Vitamin K

Answer 41

* Vitamin K is a fat soluble vitamin responsible for making four clotting factors (does not cause clotting itself). * Vitamin K1 is found in dark green vegetables & tomatoes. * Vitamin K2 is better absorbed and remains in the body for longer. This is synthesised by intestinal bacteria and is also found in fermented foods.

Question 42

Anti-Coagulants

Answer 42

• Heparin–a natural anti-coagulant produced by the body, produced by mast cells and basophils. Drugs: • Warfarin (vitamin K antagonist and hence blocks synthesis of 4 clotting factors). • Aspirin-anti-coagulant (suppresses thromboxane).

Question 43

Blood Cells

Answer 43

• All blood cells originate from a haematopoietic stem cell. •Cells will then develop through either the myeloid or lymphoid cell line. •All blood cells, other than lymphocytes (and natural killer cells) originate from myeloid linage.