Food Ingestion and Digestion
Animals require nutrients, including major ones such as organic carbon and nitrogen, vitamin, minerals and certain amino acids that cannot be synthesized in vivo. The nutrients are taken in the form of food. Food processing include ingestion--taking the food, digestion--breaking down the food into small unit that can be absorbed, absorption-- nutrient molecules are absorbed into body and blood stream, and elimination--undigested waste is passed out of the digestive tract. Chemical digestion (breaking down macromolecules into its smaller building units) and absorption mainly occurs in small intestine.
Respiration
Respiration is a process inhaling oxygen and exhaling carbon dioxide. Gas exchange occurs in lung through diffusion mechanism. Capillaries in lung take in oxygen and release carbon dioxide.
Circulation
Cardiovascular system contains heart, vein, artery and capillary. Blood Circulation is divided into two parts: pulmonary circuit and system circuit. In pulmonary circuit, Heart pumps CO2-riched blood to lung, then the blood releases CO2 and uptakes O2 in the lung, the O2-riched blood returned back to heart eventually. In systemic circuit, Heart pumps O2-riched blood to tissues, the blood releases O2 for tissue to use and uptakes CO2 generated by the tissue and send the CO2-riched blood returns back to heart. A cardiac cycle includes three steps of alternating relaxing and contraction of heart: diastole, atria systole and ventricular systole.
Body Defense
Blood carries nonspecific defense proteins (interferon and complete) and cells (neutrophils, monocytes, macrophages, Natural killer cells). The body defense can be categorized into nonspecific defense and immune response. An inflammatory response is the major component of nonspecific response. It is initiated by tissue injury, then chemical signals such as histamine is released, histamine triggers local blood vessels dilation, and migration of phagocytes to the infected area, exhibiting swelling and redness phenotype. Phagocytes consume bacteria and cell debris and the wound is repaired. Resistance to specific invaders is called an immune response, which contains two interactive immune responses: The humoral immune response: antibodies in blood system, it involves B cells and antibodies, which recognize antigens; some antibodies are soluble proteins that travel free in blood and lymph, others are integral membrane proteins on B cells. When a pathogen invades the body, it may be detected by and bind to an antibody on B cell. This binding and other system component activates the B cell, which makes multiple soluble copies of an antibody with the same specificity. The antibody then attacks the invaders and kills them. The cellular immune response: detect antigens that reside within or on cells. Main component is T cells which destroy virus-infected or mutated cells. T cell receptors recognize and bind specific antigens on cell surface and lyse the infected cells.
Development and Reproduction
The reproductive and development process involves the following steps: sperm and ova formation via meiosis, zygote formation, embryo development, and child born process and growth stages. Once becoming an adult, one can produce more offspring by same procedure. There are three important steps for embryo development: cleavage, gastrulation and organ formation. During cleavage, cells divide rapidly and form a ball-like structure called blastula. During gastrulation, three layers are formed, ectoderm, endoderm and mesoderm. Then the embryo continues to develop to form organs. From Endoderm form the following organs/tissues: digestive tract, liver, pancreas, thyroid, parathyroid, thymus, lining of bladder. Ectoderm forms the skin and central nervous system. Mesoderm forms internal organs, skeletal/muscular system.
Sense and Nervous System
The sensory process is a process in which a stimuli from outside becomes a signal to the body. Briefly it involves a sensory receptor which converts the stimuli to an electrical signal, and the sensory neurons then transmit the signal to the central nerve system, which is processed and passed to a motor neuron and finally reach an effector to cause an action. There are three types of neurons playing important roles in this process: Sensory Neurons - Send impulses towards the CNS, away from the peripheral system. Interneurons - Neurons lying entirely within the CNS. Motor Neurons - These nerve cells carry signals from the CNS to the cells in the peripheral system. Neurons communicate at synapse. Action potential can regenerate itself along the neuron. The potential arrives at the synaptic cleft and release neurotransmitter; Neurotransmitter then binds to receptor on the receive neuron. The binding opens ion channel in the receive neuron and generates new action potential.
