Created By :- Pathan A.J. Mahatma gandhi vidyalay,manchar,tal : ambegaon, dist : pune STD:10TH science and technology

HUMAN DIGESTIVE SYSTEM Section II

HUMAN DIGESTIVE SYSTEM Ingestion Taking food into the alimentary canal Digestion The chemical and physical process where large molecules are broken down to small molecule, so that the body can use them to build and nourish cells, and to provide energy. Chemical digestion involves a chemical change from one sort of molecule to another. Mechanical digestion involves the teeth and churning movements of the alimentary canal.

HUMAN DIGESTIVE SYSTEM Absorption The uptake of a substance into the cells of an organism’s body. Assimilation The incorporation of absorbed food into various parts of the body Egestion The removal of indigestible food from the body

The Human Digestive System

Structures Alimentary canal is a muscular tube, running from mouth to anus Oral cavity Mouth Teeth tongue Oesophagus Stomach Length of time taken for food through the alimentary canal varies depending on the person. On average it takes approx. 10hrs to reach the large intestine. From there it can be released quickly or else it might wait more than a day, depends partly on the amount of fibre in the diet.

Structures Liver Pancreas Small intestine Large intestine Anus Bile duct Pancreas Small intestine Duodenum ileum Large intestine Colon Rectum Anus Length of time taken for food through the alimentary canal varies depending on the person. On average it takes approx. 10hrs to reach the large intestine. From there it can be released quickly or else it might wait more than a day, depends partly on the amount of fibre in the diet.

Functions Mouth Ingestion of food here Bolus formed here. Bolus is a ball of food formed after chewing. Physical digestion Tongue and teeth use to masticate the food Mastication = mechanical grinding action of teeth Chemical digestion Saliva released contains salivary amylase which breaks down carbohydrates

Functions of the digestive system Oesophagus Carry the food from mouth to stomach Peristalsis – rhythmic waves of contraction by smooth muscles in the wall of the canal that move the food

Functions Stomach Physical digestion Chemical digestion Churning of the stomach helps break down the food Chemical digestion Hydrochloric acid released Protease breaks down proteins Cardiac sphincter - controls entrance of food into stomach from oesophagus Stomach - fully distended, human stomach holds 2-4 litres of food - glucose and alcohol are absorbed in stomach - takes about 4 hours to empty stomach

Accessory Digestive Organs

Functions Liver Bile duct = bile (yellowish-green watery liquid) used in mechanical digestion of lipids Large fat droplets broken down, increasing the surface area = emulsification contains NO enzymes largest internal organ processes food by the Hepatic Portal Vein delivered from digestive tract

Functions Liver Functions of: maintenance of a constant glucose level in bloodstream detoxification of drugs & alcohol production of bile (acts as emulsifier – begins fat breakdown destruction old RBC & converts haemoglobin to bilirubin regulation of cholesterol & other fats Hepatic portal system: drains blood from digestive tract Metabolic functions: storage, synthesis, chemical processing largest internal organ processes food by the Hepatic Portal Vein delivered from digestive tract

Liver - Assimilation Defined as the incorporation of absorbed food into various parts of the body The hepatic portal vein delivers the sugars and amino acids to the liver. The liver ensures the right nutrients are sent to the right cells so that various bodily functions can occur eg. Amino acids are made into new proteins for growth & repair OR glucose which is used for respiration

Accessory Organs: Aid Digestion and Absorption Pancreas: exocrine functions Produces pancreatic juice contains digestive enzymes: Amylase Protease lipase Secretes sodium bicarbonate to neutralize the stomach acids Gallbladder: stores bile

Functions Small Intestine Functions: Digestion: neutralize acid from stomach, add digestive enzymes and bile, break proteins, carbohydrates and lipids to absorbable materials Absorption: 95% of food absorbed here Pyloric sphincter - sphincter separating the stomach and small intestine regulates the passage of material from stomach to small intestine Small intestine - surface area of small intestine is 300 m2; about the size of a double tennis court - about 5 m long

Small Intestine Very long ~5 metres (adult), more time for the food to be absorbed Highly folded, increases the surface area for absorption Hepatic portal vein carries the amino acids and sugars to the liver, where they are sorted and redirected to be used by the body or if in excess stored. Excess sugar stored as GLYCOGEN Excess amino acids deaminated (broken down) to GLYCOGEN and UREA Sugars (eg.glucose & fructose) used for cellular respiration Amino acids used for growth, repair or replacement of cells

Small Intestine Two parts Duodenum Ileum Food is mixed with Bile Pancreatic juice Ileum Intestinal juice Maltase Protease (peptides to amino acids) Where absorption occurs Inner surface folded and covered in villi

Structure of the small intestine

Villi Function Structure Increase the surface area that can absorb food Structure Capillary network Blood - to collect the sugars and amino acids Lacteal (lymph vessels) collect the fatty acids and glycerol One cell thick Goblet cells Produce mucus which protect lining of gut Lacteal carries the fatty acids and glycerol to the base of the neck where they join the vena cava. Fats not used immediately for energy are stored under the skin or around vital organs

Absorption of Proteins and Carbohydrates

Absorption of Fats

Major enzymes of digestive system Carbohydrates Amylase Mouth & duodenum Substrate = starch Product = maltose Proteins Protease Stomach (pepsin) & duodenum (trypsin) Substrate = proteins & polypeptides Product = polypeptides (Stomach) & amino acids Lipids Lipase Duodenum & ileum Substrate = emulsified fats Product= fatty acids and glycerol Ileum enzymes = maltase – maltose = glucose Sucrase – sucrose = glucose and fructose Lactase = lactose = glucose and galactose Peptidase = polypeptides = amino acids

Functions Large Intestine Anus Functions: absorbs nutrients and water, and eliminates waste Substances found in large intestine = mostly water, dead bacterial cells, cellulose fibers, other indigestible materials, lubricated by mucus Anus Where egestion of waste occurs Pyloric sphincter - sphincter separating the stomach and small intestine regulates the passage of material from stomach to small intestine Small intestine - surface area of small intestine is 300 m2; about the size of a double tennis court - about 5 m long

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