Introduction and Erythrocytes
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7 functions of the circulatory system
1. Transport - nutrients and waste
2. Hormone transport
3. Protection - antibodies and whilte blood cells
4. Prevents blood loss via clotting
5. Maintains fluid balance
6. Maintains pH
7. Regulates temperature
Amount of blood in adults
4-6 litres of blood
2 main components of blood
Plasma and formed elements
Describe blood plasma?
Clear extraceullrar fluid
Contains plasma proteins (8%)
Other 2% = hormones, wastes and gases
This is the matrix
Describe formed elements of blood?
Red Blood cells
White blood cells
List the 3 main categories of plasma proteins?
Albumins - 60%
Most abundant plasma protein (plasma)
Contributes to viscocity & plasma osmotic presssure
Influences blood pressure - flow and fluid balance
A plasma protein (plasma)
Provides immune system functions
3 types - alpha, beta and gamma globulins
- Plasma protein (plasma)
- Precursor to fibrin threads that help form blood clots
How are plasma proteins formed?
All are formed by the liver, except globulins that are produced by plasma cells)
What are the non-protein elements of blood plasma?
These form 2% of the plasma
- amino acids - from dietary protein or tissue breakdown
- nitrogenous wastes (urea) - these are the toxic end products of catabolism and normally removed by the kidneys
- Nutrients - glucose, vitamins, fats, minerals etc
- Oxygen and carbon dioxide
- Electrolytes - Na+ makes up 90% of plasma cations
What is blood viscosity?
Resistance to flow and is basically the stickness of the fluid
How many more times viscous is blood than water
What does an increase in RBC count mean for blood flow and blood pressure?
Increased RBC = increased resistance to flow = increased viscosity = increased blood pressure and volume and more strain on the heart
Define blood osmolarity?
It refers to the total molarity of dissolved particles (RBCs, Na+, protein)
What does a high osmolarity mean for blood pressure?
It causes fluid absorption into blood and raises blood pressure
What does a low osmolarity mean for the body?
- A low osmolarity causes fluid to remain in tissues and may result in edema
- (e.g. from protein deficiency)
Describe the structure of a RBC (erythocyte)
1. Disc shaped cell of 7.5um diameter and 2um thick at the rim
2. Lacks organelles like mitrochondria and is anucleate
3. Contains cytoskeletion proteins (spectin and actin) that give membrane resilience
4. RBCs contain hemoglobin (red pigment molecule) they are little more than bags of hemoglobin
What are the functions of eythrocytes?
1. Transport of oxygen to tissues and carbon dioxide to the lungs
2. Increased surface area/volume ratio of a RBS increases diffusion rate of these gases
3. Majority of oxygen (98.5%) in blood is transported within the RBC attached to the hemoglobin molecules
4. There are 280 million Hb molecules in a single RBC
What is hemoglobin?
Hb is an iron/protein pigment molecule found in the blood
Describe the structure of hemoglobin?
Consists of heme groups and globins
1. Heme groups - conjugate with each protein chain, the hemoglobin molecule can carry 4 O2, binds to O2 to iron component at its centre
2. Globins - 4 protein chains, 2 alpha and 2 beta chains each around 140 amino acids long
What indicates the amount of oxygen that blood can carry?
A combination of RBC count and hemoglobin concentration
What is hemocrit?
- The %age of whole blood volume composed of RBCs
- Men = 42-52%
- Women = 37-48%
What is the hemoglobin concentration of whole blood?
- Men = 13-18g/DL
- Women = 12-16g/DL
What is the red blood cell count of men and women?
- Men = 4.6-6.2 million/ul
- Women = 4.2-5.4 million/ul
Why are RBS and hemoglobin values lower in women?
- - aldersterone stimulates RBD production and there is less in women
- - women have periodic menstrual losses
What equipment can be used to show the % volume of RBCs
How long does and erthrocyte live for?
Where are RBCs produced?
In red bone marrow (a soft network of connective tissue bordering on wide capallaries called sinusoids)
What is the production of RBCs called (in red bone marrow)?
How long does erythropoiesis take?
3-5 days, and results in the loss of the nucleus and most organelles and the synthesis of hemoglobin
What does the loss of nucleus and ribosomes mean for the RBC
No nucleus or ribosomes means that the RBC cannot repair itself
What is the rate of RBC production?
2.5 million RBCs per second
How long does the development of the RBC take?
- 3-5 days
- In this time there is a reduction in cell size, increase in cell number, synthesis of hemoglobin, and loss of nucleus
How does RBC production begin?
With the pluripotent stem cell
Describe the disposal of RBC's?
1. RBCs lyse in narrow channels in spleen (RBC graveyard)
2. Macrophages in spleen engulf and destroy the dying erthyrocytes
3. Heme and globin portion is split
4. The iron core of heme is salvaged and stored in the liver and remainder leaves the body in faeces
5. The globins are hydrolyzed into amino acids
Describe how erythrocyte homeostais is maintained?
- 1. Negative feedback control - drop in RBC count causes hypoxemia
- 2. Increased erthropoietin (EPO) outout from kidneys stimulates bone marrow
- 3. RBC count increases in 3 to 4 days
The stimulus for erythropoiesis is low levels of Oxygen, increase in exercise, loss of lung tissue in emphysema
What is polycythemia?
A blood condition in which there is an abnormally high RBC count and/or hematocrit
What are the common causes of polycythemia?
- Bone marrow abnormalities
- Dehydration (transient increase in hematocrit)
- Living at high altitude
- Blood doping and EPO use by athletes
What can polycythemia cause?
Increases in blood viscosity can lead to increased blood volume and blood pressure
What is anemia?
A blood condition in which there is an abnormally low RBC count or decrease in the quality of hemoglobin
What are the common causes of anemia?
- Bone marrow abnormalities
- Blood loss
- Inadequate dietary intake or iron
- Lack of vitamin B12 absorption
- Production of abnormal hemoglobin (sickle cell disease)
What can anemia cause?
- Tissues suffer from oxygen deprivation (tissue hypoxia) resuklting in shortness of breath and lethargy
- Compensatory increased cardiac output to offset the reduced oxygen carryimg effect of anemia which may lead to cardiac failure
Describe a sickle cell RBC?
Stiff sticky crescent shaped RBC's which rupture easily and "dam up" in small blood vessels
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