DIGESTIVE SYSTEM IN HUMANS

2.2.2.2 Digestive system in humans

Why a person can swallow something while standing on their head - Once food enters the esophagus a series of wave-like muscular contractions in the walls of the esophagus (peristalsis) start and the food is pushed towards the stomach and other parts of the alimentary canal

Metabolism - All of the chemical and physical processes necessary for life

Anabolism - The chemical reactions of metabolism that build up complex substances from simple

materials, they require energy which comes from catabolism

Catabolism - A chemical reaction of metabolism which breaks down complex substances into simple ones and release energy

Biological importance of saliva - Contains the digestive enzyme salivary amylase which digests starch to

maltose, lubricates food for easier swallowing

Importance of bile - Salts in bile break down fats through emulsification, reacts with fat soluble vitamins (A,D,E,K) to make them water soluble, salts in bile neutralize HCl

Autolysis - Refers to the destruction of a cell through the action of its own enzymes i.e. self digestion Lipase - An enzyme which digests fats and oils

Catalysts - Substances that increase the speed of a chemical reaction and are used up in the reaction i.e. enzymes

Deanimation - The breakdown of unwanted amino acids in the liver by removal of nitrogen containing part

of the nucleus

Distase - An enzyme which digests stored starch in seeds

Emulsification - Breakdown of fats into droplets

Protease - An enzyme which digests protein

Trypsin - An enzyme produced by the pancreas which digests proteins converting them to amino acids

Enzymes which digest protein cannot digest starch because different enzymes can only break down specific types of substrates

Absorption - The movement of digested (soluble) food through the walls of the alimentary canal into the

blood stream

Amylase - A type of enzyme which digests carbohydrates,

Alimentary Canal (Gut) - A tube running from the mouth to the anus inside which digestion and absorption

take place

Assimilation - Utilization of digested food to build cells in the body

Bile - A greenish-yellow liquid made in the liver which is passed into the duodenum where its function is to aid in the digestion of fats

Cecum - A part of the intestine at the junction between the ileum and colon, serves no function in man but is

used for digestion of cellulose in herbivores

Chyme - The semi-fluid mass of partly digested food expelled by the stomach into the duodenum Cilium - An organelle found in eukaryotic cells which help to move nutrients or other cells along in the

organism

Colon - Part of the large intestine, its function is to absorb water and mineral salts from feces

Digestion - The process by which food is made soluble by the action of digestive juices (enzymes)

Dormancy - A resting, inactive condition in which metabolism almost stops

Duodenum - The part of the alimentary canal

between the stomach and the ileum Esophagus - The tube through which food passes

from the mouth to the stomach

Fatty Acids - Chemical components released when

fats are broken down during digestion Fermentation - The breakdown of sugar by

organisms such as yeast and bacteria which takes

place under anaerobic condition

Gastrointestinal Tract - Refers to the stomach and

intestines

Gall Bladder - A small bladder inside the liver where

bile is stored

Glycogen - A carbohydrate similar to starch. It is stored in the liver and muscles of mammals and then is converted into glucose as the body requires energy for metabolism

Hepatic Portal Vein - Vessel in which blood containing absorbed food is carried from the intestine to the liver

Lacteal - Part of the lymphatic system which extends through the centre of the villus. Its purpose is to absorb digested fat from the ileum

Larynx - The voice box

Mucus - A sticky fluid produced by goblets cells Pepsin - An enzyme produced by the stomach which

begins the digestion of proteins

Peristalsis - A wave-like contraction of the tubular organs such as the alimentary canal (gut) which propels the contents of the tube in one direction

Pharynx - An area at the back of the mouth immediately above the trachea and esophagus Rectum - The last part of the alimentary canal

Saliva - Fluids produced and released into the mouth by three pairs of salivary glands in response to food.

Contains the enzyme salivary amylase, mucin and minerals. Saliva is alkaline so the pH will be lowered Sphincter - A ring of muscle found in the walls of tubular organs such as the alimentary canal whose

contraction slows or stops movements of substances through the tube Stomach - A bag like organ at the end of the esophagus

Trachea - The wind pipe

Villi - Minute finger-like structures on the inner surfaces of the duodenum and ileum. These occur in the millions greatly increasing the surface area available for absorption

Liver - Detoxifies poisonous substances in the body such as alcohol, performs deamination to break down amino acids and form urea

Functions of the liver - Helps regulate blood sugar levels, stores fat to prevent starvation, deamination, storing vitamin A and D, stores iron from broken down erythrocytes (red blood cells)

Ileum - The region of the alimentary canal between the duodenum and colon where digestion is completed

and absorption takes place, small intestine. It also secretes intestinal juice

Intestinal Juice (Succus Entericus) - Juice containing proteins which help to break down food substance

as it passed through the ileum

Contents and roles of intestinal juice - Mucus, mineral salts, enzymes Mucus - Helps to lubricate the intestinal wall and prevents autolysis

Mineral Salts - Produced in order to neutralize the acid chyme from the stomach and to provide a more suitable pH for the action of enzymes in the intestine

Enzymes - Protease, enterokinase, nucleotidase, carbohydrase

Protease - Convert peptides into smaller peptides and amino acids and hydrolyses dipeptides into

amino acids

Enterokinase - A non-digestive enzyme which activates the trypsinogen produced by the pancreas

Nucleotidase - Converts nucleotides into sugars, organic bases and phosphoric acid

Carbohydrases - Amylase, maltase, lactase, sucrase

Amylase - Completes the hydrolysis of starch to maltose

Maltase - Hydrolyses maltose into glucose

Lactase - Hydrolyses lactose (the sugar in milk) into glucose and galactose Sucrase - Hydrolyses sucrose into glucose and fructose

Factors affecting the absorption of digested food in the ileum - Being well supplied with blood capillaries to ensure digested food substances are absorbed into the blood, must have a thin epithelial lining which is permeable to molecules like glucose which will increase the rate of diffusion of the digested food substances, the epithelial cells must be rich in mitochondria to provide energy for their activities since the absorption of some nutrients must be forced since absorption is taken against their concentration gradient, must possess a large surface area for absorption

Efficient absorption in the ileum through a large surface area is achieved in the following ways - It is long (almost 6m in humans), its walls are folded to provide large internal projections, the folds themselves have numerous villi, the epithelial cells lining the villi are covered with minute projections called microvilli