Blood Composition and Functions

• Blood makes up approximately 8% of human body weight.
• Blood contains erythrocytes, leucocytes, thrombocytes, and plasma.
• The volume percentage of blood cells in whole blood is about 45% in adults, known as hematocrit.
• The remaining volume is liquid plasma, consisting of water, plasma proteins, and electrolytes.
• Blood components consist of cells, cell fragments, and aqueous solution (plasma).

Blood Functions

• Transports gases like oxygen, carbon dioxide, and nitrogen, as well as nutrients for metabolism and its end products.
• Provides tissues with blood gases and nutrients.
• Transports waste products like carbon dioxide, urea, uric acid, and creatinine to eliminating organs like the lungs, liver, and kidneys.
• Carries chemical messengers such as hormones to target organs.

Acid-Base Balance

• Acid-base homeostasis is regulated by gas diffusion between alveoli and blood in the lungs.

Oxygen and Carbon Dioxide

• Blood transports oxygen from the alveoli to body cells.
• Oxygen diffuses into tissues, while carbon dioxide diffuses from the cells into the blood.
• Blood balances water between capillaries, intracellular and extracellular spaces.
• Blood helps maintain a constant body temperature.

Coagulation

• Blood contains dissolved coagulation factors, which are proteins.
• Coagulation factors are activated in a cascade to stop bleeding after blood vessel damage, leading to the formation of a thrombus.

Blood Cellular Components

• Erythrocytes transport oxygen from the lungs to tissues.
• Oxygen binds to the heme group of the hemoglobin in erythrocytes.
• Erythrocytes are round, biconcave shaped cells without a nucleus, and have a diameter of 8-10 µm.
• Leukocytes have a nucleus.
• Types of leukocytes include neutrophils, lymphocytes, monocytes, eosinophils, and basophils.
• The primary function of leukocytes is immune defense.
• Platelets are derived from megakaryocytes.
• Platelets function in hemostasis when blood vessel damage occurs.

Hormones and Receptors

• Endocrine glands secrete hormones into the bloodstream.

Steroids

• Steroid hormones are derived from cholesterol.
• They are produced by the adrenal glands and gonads.
• Steroid hormones are hydrophobic or non-polar, meaning they do not mix well with water.
• They travel through the bloodstream bound to transport proteins to reach their target cells.
• Steroid hormones can diffuse across the phospholipid membrane of target cells.
• Once inside the cell, they bind to a receptor to activate genes in the nucleus.

Non-Steroids

• Non-steroid hormones are either peptides or proteins.
• They are hydrophilic and do not require transport proteins.
• When non-steroid hormones reach a target cell, they bind to cell surface receptor proteins because they cannot pass through the phospholipid bilayer.
• Binding of non-steroid hormones to a receptor changes its shape.
• This activates proteins and enzymes that cause changes in gene expression within the cell.
• The hormone itself does not need to enter the cell to cause a change.

Amino-Acid Hormones

• Amino-acid hormones are derived from the amino acid tyrosine.
• Examples include thyroid hormones, epinephrine, and norepinephrine.