Blood

Intermediate 2 Biology

Unit 3 : Animal Physiology

Composition of Blood

• Blood contains

– Red blood cells

– White blood cells

– platelets

– plasma

Plasma

• Watery, yellowish fluid • Suspended in plasma

– Proteins e.g. Antibodies

• Transports water-soluble substances to within diffusion distance of living cells. – Glucose – Amino acids

• Carbon dioxide transported as bicarbonate ions (as CO2 with water to form an acid which can cause problems)

Red Blood Cells

• Very small and numerous

• Flexible – squeeze through tiny capillaries to deliver oxygen to cells

• Biconcave disc shape – large surface area in relation to volume

• No nucleus

• Cytoplasm rich in haemoglobin

Haemoglobin

• Haemoglobin combines with oxygen to increase the oxygen-carrying capacity of blood.

• Association

– Haemoglobin combines with oxygen when the oxygen concentration is high

• Dissociation

– Haemoglobin rapidly releases oxygen when oxygen concentration is low

Association and dissociation

haemoglobin oxygen oxyhaemoglobin +

Association

(in lungs)

dissociation

(in tissues)

Oxygen affinity

• Haemoglobin has a high affinity for oxygen when oxygen concentration in the environment is high

• Haemoglobin has a low affinity for oxygen when the oxygen concentration in the environment is low.

• Affinity – Tendency to combine with oxygen

oxygen dissociation curve

• Partial pressure of oxygen (pO2) – Measure of concentration of oxygen – Measured in kPa

• The oxygen dissociation curve shows saturation of haemoglobin at different partial pressures of oxygen (pO2).

• High pO2 – haemoglobin saturated with oxygen • Low pO2 – oxyhaemoglobin gives up its oxygen to

respiring cells (dissociates)

oxygen dissociation curve

Respiring cells

• Actively respiring cells have a low oxygen tension (2.7kPa)

• Alveolar air has a high oxygen tension (13kPa)

• In lungs haemoglobin is loaded with oxygen – It moves along a concentration gradient from the

alveolar air (High oxygen concentration) to the blood (low oxygen concentration)

• In respiring tissues oxygen is unloaded – Diffuses from a high concentration in the blood to a

low concentration in the respiring cells.

White Blood Cells

• White blood cells

– Contain a nucleus

– Can change shape and squeeze through capillary walls

• Types of white blood cell include

– Monocytes

• Phagocytosis

– Lymphocytes

• Antibody production

Phagocytosis

• Bacteria are engulfed and destroys by phagocytic cells, e.g. monocytes or macrophages

• Stages of phagocytosis – Bacteria releases a chemical and the phagocyte moves towards

it – The phagocyte adheres to the bacteria – The cell membrane changes shape and engulfs the bacteria in a

phagocytic vacuole – Lysosomes fuse with the vacuole releasing powerful digestive

enzymes – Bacteria is digested – Products of digestion are absorbed into the cytoplasm of the

phagocyte

Phagocytosis

• Dead bacteria and phagocytes can accumulate at the site of infection forming pus.

• Macrophages can be found in liver, spleen and lymph

Immunity

• Immunity – An organism’s ability to resist infection

• Phagocytosis is an example of non-specific

immunity – Providing protection against a range of

microorganisms

• Antibody production is an example of a specific immune response – Each antibody is specific to a particular antigen – Thee antibody and antigen are complementary

Antigens

• An antigen is a protein molecule that is recognised as “foreign” by the body’s lymphocytes

VIRUS

antigens

Antibody

• Y-shaped molecule

• Produced by lymphocytes

• Receptor sites are specific to an antigen

• When an antibody attaches to its complementary antigen, the antigen is rendered harmless

Immunological memory

• Primary response – Infection by disease-causing organism – Latent period when the lymphocytes respond and start to

produce antibodies – Often person suffers symptoms of the disease

• Secondary response – Exposure to the same antigen – Memory cells remain in blood from first infection and as a

result antibodies • Produced more rapidly • Produced at a high concentration • Remain in the bloodstream for a longer time

Primary and secondary response

Immunity

• Natural acquired immunity

– The person has been exposed to the disease-causing organism

– Memory cells remain in bloodstream

• Artificially acquired immunity

– Vaccinations contain a small dose of the antigens

– Lymphocytes are stimulated to produce antibodys

– Memory cells remain in bloodstream