Erythrocyte Function and Life Cycle

Question 1

components of blood

Answer 1

• Plasma (~55%)
• Buffy Coat (<1%) - white blood cells (leukocytes) and platelets (thrombocytes)
• Red blood cells (~45%)

Question 2

what is the haematocrit/packed cell volume

Answer 2

• the ratio of RBCs to the total blood volume
• males - 40-52% (0.4-0.52)
• females - 36-47% (0.36-0.47)
• red cell volume/ total blood volume

Question 3

functions of formed elements

Answer 3

red blood cells - transport
white blood cells - immunity
platelets - haemostasis
all - homeostasis

Question 4

what is complete/full blood count

Answer 4

• calculates the cellular or formed elements of blood
• 99% of the formed elements of blood
• red cell count : males - 4.3-5.9x10^12/L, females - 3.5-5.0x10^12/L

Question 5

average blood volumes

Answer 5

• 70ml/kg
• males - 5-6 litres
• females - 4.5-5.5 lites

Question 6

red blood cells

Answer 6

• biconcave discs
• 7-8 micrometres diameter
• 2.5 micrometres wide
• develop in bone marrow
• no major organelles
• no DNA
• produce ATP through glycolysis
• 5.4 million/microlitres (men)
• 4.8 million/microlitres (female)
• squeeze through micro-vessels by changing shape
• survive 120 days
• broken down by reticuloendothelial

Question 7

Erythrocyte function

Answer 7

• 95% haemoglobin
• oxygen transporting protein
• haemoglobin - 4 peptide chains - each linked to an iron carrying haem molecule
• one haemoglobin molecule can carry 4 oxygen molecules
• 130-180 g/L (males)
• 115-165 g/L (females)
• low blood Hb referred to as anaemia
• iron is a vital component of haem
• facilitation of carbon dioxide transport
• control of acid-base equilibrium in blood

Question 8

Erythropoiesis

Answer 8

• embryonic RBCs produced in the yolk sac
• in fetus - primarily moves to liver but also spleen and lymph nodes
• approx. one month before birth exclusively in bone marrow
• bone marrow of all bones until 5 years.
• after this, most bones stop except humerus, tibia and fibia
• after membranous bones, sternum, ribs and vertebrae
• 2-3 million made every second
• less productive with age

Question 9

Erythropoiesis - erythrocyte production

Answer 9

process from pluripotental haemotopoietic stem cells
- pluripotential cells differentiate into erythroid cells (proerythroblasts)
- committed, divide and mature into normoblasts
- nuclear material extruded, ER
- reabsorbed forming reticulocyte
- mature within 1 day - erythrocyte

• formed in bone marrow
• 2-3 million/second
• vitamin B12 and folate essential for maturation, cell division
• iron essential for haemoglobin

Question 10

control of erythropoiesis

Answer 10

• kidneys receive 20-255 resting CO
• stimulus - hypoxia
• detector - kidney
• effector - EPO

Question 11

what is anaemia

Answer 11

• deficiency of haemoglobin in the blood either because too few red blood cells or not enough haemoglobin reducing oxygen carrying capacity of blood

Question 12

anaemia - signs and symptoms

Answer 12

• fatigue, lethargy or weakness
• shortness of breath
• palpitations
• headache
• dizziness
• pallor of the eyes, lips, skin and nails
• poor condition of nails, lips and tongue
• hair loss
• tachycardia, heart murmurs, cardiac enlargement and heart failure (severe)
• jaundice

Question 13

possible causes of anaemia

Answer 13

• abnormalities of erythropoiesis (decreased iron, vitamin B12, folic acid, EPO, bone marrow disorder/aplasia)
• deficiencies of erythrocytes (haemolysis, blood loss, hypersplenism)

Question 14

Macrocytic Anaemia

Answer 14

• erythrocytes will be abnormally large (macrocytes)
• increased MCV and MCH
• rupture easil only last 40-60 days causing jaundice
• find megaloblasts (abnormal precursors)
• haemoglobin normal - too few erythrocytes
• happens when - reductions in vitamin B12 or folate, pernicious anaemia (reduced secretion of intrinsic factor)

Question 15

Microcytic Anaemia

Answer 15

• iron deficiency - iron demands exceed the supply
• decreased MCH and MCV
• erythrocytes will contain less haemoglobin
• erythrocytes produced mmuch smaller than normal
• happens when - reduced iron intake - dietary deficiency

Question 16

Sickle Cell Anaemia

Answer 16

• genetic condition
• primarily effects people of East African origin and African Americans
• abnormal haemoglobin synthesised
• long crystals cause cells to elongate (sickle appearance rather than biconcave)
• cells rupture easily
• cause blood flow to back up

Question 17

tests that may help to confirm iron deficiency

Answer 17

• serum iron - level of iron in blood, result usually decreased
• total iron-binding capacity - measurement of the protein (transferrin) that carries iron through the blood will be increased
• transferrin saturation index - ratio of serum iron to iron binding capacity - result of less than 15% may indicate iron deficiency
• ferritin - reflects the amount of stored iron in your body and is usually low in anaemia - considered to be most specific unless infection or inflammation are present

Question 18

Polycythemia

Answer 18

• secondary/ compensatory polycethemia - when tissue becomes hypoxic due to lack of oxygen in breathed air or disease
• EPO stimulates an increase of erythrocytes
• physiologic polycethemia - high altitudes 6-7 million/mm3
• mechanisms controlling circulatory system balance one another out, therefore not generally a problem
• ploycythemia vera - pathological genetic condition 7-8 million/mm3 (normal - 5 million)
• increase in haematocrit increases blood volume and viscosity
• vascular system becomes engorged and many blood capillaries become plugged due to increased viscosity of blood
• normally blood viscosity is 3 times of water, in polycythemia vera its 10 times
• people with polycythemia vera often have a ruddy complexion with bluish tint