Red blood cells (erythrocytes) carry oxygen using haemoglobin, an iron-containing protein. Mature human RBCs have no nucleus. They are made in the red bone marrow and live about 120 days; old cells are destroyed mainly in the spleen.
White blood cells (leucocytes) fight infection; lymphocytes make antibodies.
Platelets (thrombocytes) help blood clot. Their count falls sharply in dengue.
Plasma is the yellowish liquid part, about 90% water.
Blood group
Antigen on RBC
Can donate to
Can receive from
A
A
A, AB
A, O
B
B
B, AB
B, O
AB
A and B
AB only
All groups (universal recipient)
O
None
All groups (universal donor)
O only
Heart and circulation
The human heart has four chambers: two atria (receiving) and two ventricles (pumping). The left ventricle has the thickest wall because it pumps blood to the whole body.
Humans have double circulation: blood passes through the heart twice in one complete round (lungs, then body).
Arteries carry blood away from the heart; veins carry blood to the heart; capillaries link them.
Digestion
Where
What happens
Mouth
Saliva contains salivary amylase (ptyalin): starch begins to break down
Stomach
Hydrochloric acid kills germs and activates pepsin, which begins protein digestion
Liver
Makes bile; bile is stored in the gall bladder and emulsifies fats
Pancreas
Pancreatic juice with enzymes for proteins (trypsin), fats (lipase) and starch (amylase)
Small intestine
Digestion is completed; finger-like villi absorb digested food
Large intestine
Absorbs water; undigested waste is removed
Breathing and excretion
Gas exchange happens in the alveoli, tiny air sacs in the lungs surrounded by capillaries. The diaphragm helps in breathing.
Kidneys filter blood. Each has about a million nephrons, the functional units that form urine.
Urea is made in the liver and removed by the kidneys. When kidneys fail, dialysis (an artificial kidney) filters the blood.
Nervous system
Part
Main role
Cerebrum
Largest part; thinking, memory, intelligence, voluntary actions, senses
Cerebellum
Balance, posture, coordination of voluntary movements
Body temperature, hunger, thirst; links nervous and endocrine systems
Spinal cord
Reflex actions (e.g. pulling the hand from a hot object)
The neuron is the structural and functional unit of the nervous system. A reflex action is quick and automatic because it is handled by the spinal cord before the brain gets involved.
Glands and hormones
Gland
Hormone
Effect
Pituitary
Growth hormone and others
Master gland; controls other glands
Thyroid
Thyroxine
Metabolism; needs iodine (lack causes goitre)
Parathyroid
Parathormone
Calcium level in blood
Pancreas (islets of Langerhans)
Insulin (beta cells), glucagon (alpha cells)
Lower and raise blood sugar
Adrenal
Adrenaline
Fight-or-flight response
Testes / ovaries
Testosterone / oestrogen and progesterone
Sex characters and reproduction
The pancreas is both an exocrine gland (digestive juice through a duct) and an endocrine gland (hormones into the blood). Lack of insulin or poor response to it causes diabetes mellitus.
Sex of a child is decided by the father: mothers always pass an X chromosome, while a sperm carries either X (girl) or Y (boy).
