The Human Digestive System

Functions of digestive system1)Ingestion of food2)Mechanical digestion3)Chemical digestion4)Move food along alimentary canal5)Absorb digested food into blood and lymph6)Eliminate material that is not absorbed.

Overview

• Mechanical Digestion: – Teeth and jaws– Tongue– Peristalsis

Chemical Digestion:- enzymes from bile- stomach- small intestine- Large intestine

Parts of the Human Digestive System

The Mouth

• Teeth:– Incisors – for cutting (fruit)– Canines – for tearing (meat)– Pre-molars – for crushing– Molars – for crushing

• Tongue – moves food around the mouth–Forms it into a bolus ready for swallowing.

• Saliva – provides moisture so food is easier to swallow

– contains amylase to start breaking down starch.

Teeth (mechanical digestion)

Incisors – four in each jaw-Have a thin, sharp edge for cutting

Canines – two in each jaw-thin, pointed edge for piercing food. Thicker than incisors, so more support for tearing.

-Pre-molars (4 in each jaw)and molars (6 in each jaw)– large, strong teeth. Upper and lower sets lock together to crush food.

Structure of teeth

• Crown – the part of the tooth above the gum.

• Root – The part of the tooth that anchors it to the jaw.

• Enamel is the hardest substance produced by the body. Once worn away it can not be replaced.

Stomach

• Food enters from oesophagus; sphincter stops food from going back up.

• Stomach acid (HCl) continues to breakdown the nutrients. Pepsin works to break down the proteins.

• Peristalsis churns the food and stomach acid together so they form chyme.

• Pyloric sphincter regularly releases small amounts of chyme into the duodenum.

Stomach

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Tissue layers• Most parts of the digestive system have four

tissue layers.• Mucosa – the inner lining. Characterised by a

large amount of fingerlike projections to increase surface area.

• Sub-mucosa – contains the vessels for the circulatory and lymphatic systems.

• Muscularis – layer of muscle tissue that enable the organ to expand and contract as food passes through. Is responsible for peristalsis.

• Serosa – the outside covering.

Small Intestine

• The small intestine secretes intestinal juice to continue chemical digestion.

• Bile is secreted by the liver and pancreatic juice from the pancreas. These mix with the chyme in the duodenum.

• Food is mixed and moved along by segmentation.

• Nutrients are absorbed by active transport, diffusion or osmosis.

Structure of the small intestine

Functions of the liver

Blood glucose regulation: creates or breaks down glycogen to ensure the right level of carbohydrates in the blood.Deamination: excess proteins are converted to carbs and the waste is sent to the kidneys.Fat conversion: excess glycogen becomes stored as fat.Bile formation: to assist in the break down of fats.Production of plasma proteins and blood-clotting factors.Toxin and hormone breakdown.Storage: Iron, Vitamin A, Vitamin D

Enzymes• Enzymes are specifically designed to break certain food

molecules down into smaller building blocks. They usually only work on a certain type of bond.

• Enzymes operate best in a certain set of conditions eg temperature, pH

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Large Intestine

• Water is reabsorbed by the body. • Waste products are moved through to the

rectum and expelled through the anus.• The appendix has no apparent function in

humans. However if it becomes infected and ruptures, it can lead to death.

Large Intestine

Digestion of proteins

Protein

(pepsin and stomach acid)

Peptides

(peptidases)

Amino acids

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Digestion of Carbohydrates

• Begins with salivary amylase.• Carbohydrates stay in the stomach for a relatively

short amount of time.• Pancreatic amylase continues to shorten the length of the saccharide chains until they can be absorbed by active transport.

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Digestion of Fats

• Fats stay in the stomach for up to 8 hours.• Bile salts separate the fats into small droplets.• Lipase breaks down the fat molecules.

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