The absence of a nucleus means that the red blood cells can carry more

Blood as a tissue

COMPOSITION OF BLOOD

Plasma.

The liquid part of blood. Mainly water but also containing;

(a) Salts - sodium hydrogencarbonate, acts as a buffer (helps prevent changes in pH)

(b) Proteins - fibrinogen, antibodies, hormones

(c) Digested foods - amino acids, glucose and fats

(d) Excretory products - e.g. urea

Red Blood Cells

Also known as red blood corpuscles or erythrocytes. Bi-concave discs with no nucleus. Made in the bone marrow, live for approximately 180 days. Destroyed in the spleen at rate of 200,000 million per day. 5.5 million per mm3 of blood. Contain the respiratory pigment haemoglobin, made of a protein with an iron group. In areas of high oxygen concentration (the lungs) forms a temporary compound called oxyhaemoglobin. Breaks down to release the oxygen in areas of low oxygen concentration (respiring tissues).

White Blood Cells (leucocytes)

Typical animal cell shaped. 4,000 to 13,000 per mm3. Three basic types

Type	Appearance	Description	Site of production	Mode of action
Granulocytes		Lobed nucleus. Granular cytoplasm.	bone marrow	Destroy bacteria by ingestion (phagocytosis)
Lymphocytes		Large round nucleus. Clear cytoplasm.	lymph nodes and spleen	Make antibodies or kill infected cells.
Monocytes		Oval or kidney shape nucleus. Clear cytoplasm.	Lymph nodes	Ingest foreign particles.

All white blood cells are involved in the body's defence mechanisms.