Essential Human Anatomy and Physiology Principles
Mitosis
Mitosis is a type of cell division in which one parent cell divides to form two genetically identical daughter cells, maintaining the same number of chromosomes as the parent cell. It occurs in somatic (body) cells and is essential for growth, repair, and replacement of worn-out cells. Mitosis takes place in four main stages:
- Prophase: Chromosomes become visible and the nuclear membrane disappears.
- Metaphase: Chromosomes align at the equator of the cell.
- Anaphase: Sister chromatids separate and move toward opposite poles.
- Telophase: Two new nuclei are formed and the cytoplasm divides.
Mitosis helps in tissue growth, wound healing, and asexual reproduction in some organisms.
Meiosis
Meiosis is a special type of cell division that occurs in reproductive organs to produce gametes such as sperm and ova. In meiosis, one parent cell divides twice to form four daughter cells, each containing half the number of chromosomes of the parent cell. This reduction is important for maintaining the normal chromosome number after fertilization. Meiosis occurs in two stages: Meiosis I (homologous chromosomes separate) and Meiosis II (sister chromatids separate). It plays an important role in genetic variation, sexual reproduction, and heredity.
Classification of Tissues
Tissues are groups of similar cells that work together to perform a specific function. Human body tissues are classified into four main types:
- Epithelial: Forms coverings and linings; functions in protection, absorption, and secretion.
- Connective: Supports and binds body parts (e.g., bone, blood, adipose).
- Muscular: Responsible for movement (skeletal, smooth, and cardiac).
- Nervous: Forms the brain, spinal cord, and nerves for impulse transmission.
Composition and Functions of Blood
Blood is a specialized fluid connective tissue composed of plasma (55%) and formed elements (RBCs, WBCs, and platelets). It transports oxygen, nutrients, and hormones while removing waste products. Blood also maintains body temperature, pH, fluid balance, and provides immunity through white blood cells and antibodies.
Structure of Skeletal Muscle
Skeletal muscle is a voluntary, striated muscle attached to bones. It consists of long, cylindrical, multinucleated fibers. Key structures include:
- Connective layers: Epimysium, perimysium, and endomysium.
- Cellular components: Sarcolemma (membrane) and sarcoplasm (cytoplasm).
- Functional units: Myofibrils containing sarcomeres with actin and myosin filaments.
Mechanism of Respiration
Respiration consists of two phases:
- Inspiration: The diaphragm and external intercostal muscles contract, increasing thoracic volume and drawing air into the lungs.
- Expiration: Muscles relax, decreasing thoracic volume and forcing air out.
Gas exchange occurs in the alveoli, where oxygen enters the blood and carbon dioxide is expelled.
Cardiac Cycle
The cardiac cycle is the sequence of events in one heartbeat, lasting about 0.8 seconds. It includes:
- Atrial systole: Atria contract to fill ventricles.
- Ventricular systole: Ventricles contract to pump blood into the aorta and pulmonary artery.
- Complete cardiac diastole: Chambers relax and refill.
Conductive System of the Heart
This network regulates heartbeat rhythm: the SA node (pacemaker) initiates impulses, which travel to the AV node, through the bundle of His, and finally into Purkinje fibers to trigger coordinated ventricular contraction.
Lymphatic System
The lymphatic system maintains fluid balance and immunity. It consists of lymph vessels, nodes, the spleen, thymus, and tonsils. It drains excess tissue fluid, produces lymphocytes to fight infection, and absorbs fats from the small intestine via lacteals.
Structure and Functions of the Cell
The cell is the basic unit of life, consisting of the plasma membrane, cytoplasm (containing organelles like mitochondria and ribosomes), and the nucleus (DNA control center). Cells are essential for energy production, protein synthesis, tissue repair, and homeostasis.
The Retina
The retina is the light-sensitive layer at the back of the eye. It contains rods (dim light/black-and-white vision) and cones (color/bright light vision). It converts light into nerve impulses transmitted to the brain via the optic nerve.
Systemic and Pulmonary Circulation
Blood circulates through two primary pathways:
- Pulmonary Circulation: Moves deoxygenated blood from the heart to the lungs for oxygenation and back.
- Systemic Circulation: Distributes oxygenated blood from the heart to the entire body and returns deoxygenated blood to the heart.