5. Cardiovascular System P1 Flashcards
The three parts of the cardiovascular system
- heart
- blood
- blood vessels
Blood
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 5.6L of blood and females 4.5L.
Functions of the blood
- Contributes to homeostasis by transporting oxygen, carbon dioxide, nutrients, wastes and hormones.
- Helps regulate pH and temp.
- Immune function with antibodies, phagocytes, clotting factors etc.
Blood plasma
Blood plasma is the yellow coloured liquid that remains when cells are removed from blood.
What does blood plasma consist of?
- Mostly water (91%)
- Proteins (7%)
- Mineral salts (0.9%)
- Nutrients
- Organic waste materials
- Hormones
- Enzymes
- Gases
Blood plasma proteins
The majority of plasma proteins are synthesised by liver cells (hepatocytes).
Plasma proteins:
• Albumin
• Globulins
• Fibrinogen
Albumin
- Smallest and most numerous plasma protein
- Carrier of substances (lipids and steroid hormones)
- Maintains osmotic pressure
Globulins
- Immunity - immunoglobulins (antibodies); secreted by B cells
- Transports iron, lipids and vitamins
Fibrinogen
- Also called ‘clotting factor one’
* Essential for blood clotting
Blood plasma nutrients
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 in blood plasma
- Cations (positively charged ions): sodium, potassium, calcium, magnesium
- Anions (negatively charged ions): chlorides, bicarbonates, phosphates
Blood plasma 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
Blood plasma hormones
• Chemical messengers carried by the blood
Blood plasma enzymes
Catalysts for biochemical reactions in the body
Blood plasma gases
- Oxygen (O2)
* Carbon dioxide (CO2)
The types of blood cells
- Erythrocytes (red blood cells)
- Leukocytes (white blood cells)
- Thrombocytes (platelets)
Haematopoiesis
= production of ALL blood cells
All blood cells originate from pluripotent stem cells in the red bone marrow.
During the first two months gestation, the embryonic yolk sac performs haematopoiesis. Between months 2-9 of foetal life, the liver and spleen take over.
In the 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).
Erythrocytes
Erythrocytes are bi-concave and non-nucleated, giving the cells a larger surface area to transport oxygen.
Life span of 90-120 days.
They have a strong and flexible cell membrane.
Approx 6-8 micrometres in diameter.
Haematocrit
The percentage of blood volume occupied by erythrocytes.
In females the haematocrit is roughly 42%, males 47%
Erythrocyte structure
Erythrocytes are made up of haemoglobin molecules, which carry mostly oxygen and 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, thus each haemoglobin can carry up to four oxygen molecules.
Haemoglobin structure
A haemoglobin molecule is made up of 4 polypeptide chains:
- Adult haemoglobin (HbA): composed of 2 a (alpha) and 2 b (beta) sub-units.
- Foetal haemoglobin (HbF): composed of 2 a (alpha) and 2 y (gamma) sub-units.
Why is blood red?
- Blood appears red due to the interaction of iron and oxygen within haem units.
- The chemical bonds between iron and oxygen reflect light.
Erythropoiesis
The formation of erythrocytes occurs in the red bone marrow.
- Immature erythrocytes have nuclei and 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
Process of erythropoiesis
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 and pregnancy.
- Premature newborns 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.
Haemolysis
Haemolysis describes the destruction of erythrocytes to release haemoglobin into plasma.
- An erythrocyte normally lives 90-120 days. About 1% break down each day.
- Haemolysis is carried out by specialised macrophages (phagocytic cells) found in many tissues; especially the spleen, bone marrow and liver.
- The globin amino acids and iron are recycled.
- Bilirubin is a yellow coloured pigment formed from the breakdown of haem. Bilirubin is excreted in bile and urine.
Haemolysis and bilirubin
The pigment bilirubin is formed from the breakdown of haem.
• Bilirubin is predominantly 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.
The 2 major blood group systems
ABO and rhesus
Where are blood group antigens located?
On the surface of erythrocytes
ABO system
- Based on 2 glycolipid antigens called A and B.
- Those whose erythrocytes display antigen A have blood group A. Antigen B are blood group B. Both A and B are AB. Neither antigen are O.
- Blod plasma contains antibodies that react with A or B antigens if the two are mixed. Anti-A antibody reacts with antigen A etc.
Transfusion reaction
The antigen-antibody complexes formed activate an immune response that causes erythrocyte membranes to rupture.
Universal donor
Blood group O-
because erythrocytes have neither A or B antigens for antibodies to attach to.
Universal recipient
Blood group AB+
because the recipient blood plasma contains no antibodies against either A or B antigens that could be donated.
Rhesus blood group
Rhesus antigen (rhesus factor) is another surface antigen found on erythrocytes.
Those that have (Rh) antigen are Rh positive, those lacking Rh antigens are Rh negative.
Inheritance of the Rh
Inheritance of the rhesus factor is via a rhesus dominant gene (85% of people are rhesus positive).
Anti-rhesus antibodies
They are produces in rhesus-negative individuals only if they come into contact with the rhesus antigen.
Can come into contact in pregnancy or incompatible blood transfusion.
Rh and pregnancy
In pregnancy, the only way antibodies are developed against the Rh antigen is through placental sensitisation or transfusion.
This only occurs is the mother is Rh- and unborn baby is Rh+ (inheriting the father 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’.
Why is an injection of anti- Rh antibodies needed and what do they do?
Often referred to as anti-D antibodies. Binds to and inactivates foetal Rh antigens.
Needed because:
1) Rh+ father
2) Rh- mother carrying her first Rh+ fetus. Rh antigens from the developing fetus can enter the mothers blood during delivery.
3) In response to the fetal Rh antigens, the mother will produce anti-Rh antibodies.
4) If the woman becomes pregnant with another Rh+ fetus, her anti-Rh antibodies will cross the placenta and damage fetal red blood cells.
The 8 blood groups
- O+
- O-
- AB+
- AB-
- B+
- B-
- A+
- A-
Leukocytes
Leukocytes function is to defend the body from microbes like bacteria, viruses, fungi, and foreign particles
Account for 1% of blood volume and contain nuclei.
Leukocytes classifications
- Granulocytes: have secretory granules in their cytoplasm
* Agranulocytes: have no granules in their cytoplasm
Name the granulocytes
- Neutrophils
- Basophils / mast cells
- Eosinophils
Neutrophils
60%
Primary functions:
• phagocytosis (ingest and destroy microbes
• these cells die forming part of the pus
Mode of action:
• phagocytosis: lysosomes digest microbes
• first to migrate to site of infection (<1 hr)
Involved in:
• infection, tissue damage, leukaemia, inflammatory diseases (i.e RA), heavy smoking, excessive exercise
Basophils / mast cells
(1%)
In blood = basophils
In tissue = mast cells
Primary functions:
• Key cells in inflammation
• Release histamine and heparin
Mode of action:
• Release histamine and heparin from granules
• Histamine dilates blood vessels.
• Non phagocytic
Eosinophills
(2-4%)
Primary functions:
• Eliminates parasites
• Promote inflammation - allergic reactions
Mode of action:
• Phagocytosis
• Migrate to allergic site
Involved in:
• Parasitic infections, atopic (extrinsic asthma, allergies
Name the agranulocytes
- Monocytes / macrophages
* Lymphocytes
Monocytes / macrophages
(6%)
In blood = monocytes
In tissue = macrophages
Primary functions:
• Inflammation and repair
• Phagocytosis - ingest and destroy cellular debris and pathogens
• Activate other immune cells via antigen presentation
Mode of action:
• Phagocytosis and chemotaxis (attracts other components of the immune system)
• Secretes cytokines; e.g. interleukin 1 - promotes fever, produces globulins and activates T-lymphocytes
Lymphocytes
(30%)
B- lymphocytes
T- lymphocytes
Natural killer (NK) cells
Primary function:
• Abundant in blood and lymphatic tissue where B- & T- lymphocytes are critical for immunity against specific antigens and the production of immunological memory
Mode of action:
• B- lymphocytes activate immune response via antibody formation
• T- lymphocytes and NK cells kill invading pathogens
Thrombocytes
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 (thrombocytes).
- Produced under the influence of thrombopoitin (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.
Thrombocytes - storage molecules
Platelets contain ‘storage’ granules. These are tiny sacs that release proteins and 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.
Four stages of a blood clot
1) Vasco constriction
• 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.
2) Platelet plug formation
• Platelets contact and stick to the damaged wall. They are activated and release binding proteins. vWF is needed for this stage.
•These changes lead to platelet aggregation and cause platelets to become sticky (positive feedback)
3) Coagulation
• Clotting factors form a clot thereby reinforcing the plug. The enzyme ‘thrombin’ in produced which converts fibrinogen into fibrin.
• Fibrin forms long, sticky threads - producing a mesh in the clot. Erythrocytes become caught up in the web and a clot forms.
4) Fibrinolysis
• Breakdown of a clot. The enzyme plasmin can dissolve a clot by digesting fibrin threads and inactivating fibrinogen and thrombin
Blood clotting - vitamin K
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 and 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 like natto.
Anti-coagulants
• 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 four clotting factors)
• Aspirin (suppresses thromboxane)
Anti-coagulant herbs:
• Ginko, garlic, ginger, turmeric
Nutrients:
• Vitamin E
• Essential fatty acids (EFAs)
All blood cells originate from a haematopoietic stem cell and will then develop through either…
Myeloid or lymphoid cell line
What blood cells originate from myeloid linage
All blood cells, other than lymphocytes and natural killer cells originate from myeloid linage.
