0709-Input-Output: The Alimentary and Excretory Systems

Lecture for Year 1 Semester 1 medical student PPSD session on 5th September 2007 by Professor Omar Hasan Kasule Sr.


Food is needed for energy, growth, repair, and maintenance of the body. Only some of the ingested food is used to sustain the body the rest is eliminated in the feces. The alimentary canal is a tube outside the body in direct contact with the external environment. Some food ingested at the mouth exits at the anus without entering the body. Digested food is absorbed by the intestines to enter the internal environment. The alimentary canal has a role in balancing the internal and external environments. It takes material from the environment, processes it, and returns it to the environment. Human appetite for food (a requirement for survival) is so strong that prayer is delayed when food is presented. Nutritional habits reflect underlying visions, beliefs, and cultural experiences. The alimentary system can be looked at as the final pathway for human corruption because food security is the underlying but often unstated purpose behind crime, corruption, treachery, amassing of wealth, aggression, and many other transgressions. Some people eat to get energy for righteous life activities. Others may eat for enjoyment or to get energy for evil.



Digestion takes place in the mouth, the stomach, and the intestines. Humans have to eat at intervals because of limited internal food storage. The limited storage enables them to engage in activities of human civilization without having to eat continuously. Besides its digestive function, the stomach acts to warn humans of impending starvation by its hunger pangs.



The alimentary system separates the nutritious food to be absorbed from the non-nutritious one to be eliminated as waste. It protects the environment by detoxifyting ingested toxins or detoxifying metabolic products before elimination into the ecosystem. Feces are considered filth (najasat) largely because of their content of infective and toxic material. Proper disposal of excreta at both the individual and community levels is a mark of civilizational development. Fecal hygiene is a pre-requisite for many humans to live together (civilized existence) because it prevents infectious and toxic disease.



The complex human food in all its varieties is in the final analysis reduced to a few chemical compounds after digestion (amino acids, glucose, and fatty acids). They are all finally reduced to Acetyl CoA that enters the Krebs cycle. The main purpose of the metabolic processes is to generate energy from food. The liver is the chemical intermediary between the alimentary system and the rest of the body. It is responsible for maintenance of the body's chemical and metabolic homeostasis. It is the great factory involved in both anabolism and catabolism. The liver is also the great protector of the body by detoxifying toxic substances from the alimentary tract.



The diseases of over-nutrition are obesity, diabetes mellitus, ischemic heart disease, and atherosclerosis. The prophet taught the rule of the thirds as a guide for food intake: one third for solid food, one third for water, and one third empty. He taught that people do not eat until they are hungry and when they eat they do not fill their belly. Three levels of food intake can be described: necessary, sufficient, and excess. The necessary is for maintenance of life and health. The sufficient is for psychological satisfaction. The excess is harmful. Obesity is a result of excessive intake without matching physical exercise.



The excretory system consists of the kidneys, ureters, bladder, and urethra. The system forms and voids urine and ensures fluid and electrolyte balance It ensures homeostatic control of the body by controlling and maintaining the volume, pH, and ionic composition of plasma. The kidney is the most important organ in homeostasis fulfilling the physical laws relating to equilibrium and balance. Urine is filth. Measures must be taken to avoid being soiled by urine and teaches measures to safeguard against urine. Washing of hands and the external excretory organs is required after urination. The use of the right hand is forbidden because the right hand is to be reserved for eating. Urination on the street or public places is forbidden

ŠProfessor Omar Hasan Kasule, Sr. September 2007