DIGESTIONIn humans

Objectives Looking at the processing of nutrients.

You should be able to identify features of effective systems in heterotroph’s

Mechanical breakdown What is this?

Where does this occur?

Why is it important?

Chemical Breakdown What protein is used here?

Where does it occur?

There are three main types...

Chemical Digestion - Digestive EnzymesAmylase

StarchGlucose

Protease

Protein

Amino Acids

Glycerol

Fatty Acid

Fatty AcidFatty Acid

Glycerol

Fatty Acid

Fatty Acid

Fatty Acid

Lipase

Fat Fatty Acids and Glycerol

Ingestion Oral cavity/Mouth Both mechanical and chemical

digestion begin here Food in the oral cavity triggers nervous

reflex that triggers salivary glands. More than 1L of saliva is secreted in a

human per day. In saliva is:

Mucin, protects mouth from abrasions, helps you swallow.

Buffers, stop tooth decay Salivary Amylase, digestive enzyme that

breaks down starch. Mouth shapes food into a ball called

Bolus which is pushed into the pharynx.

• The pharynx is an intersection between the oesophagus & the windpipe.

Digestion Peristalsis squeezes a

bolus along the narrow oesophagus through involuntary waves of smooth muscle contractions.

Starch is continually hydrolysed as it moves towards the stomach.

DigestionStomach : stores food and performs

preliminary digestion is located on the LHS of the abdominal

cavity, it breaks up food and delivers it to the duodenum

It is extremely elastic and has accordian style folds allowing it to hold up to 2L.

The epithelium lining stomach secretes gastric juices that:

Have a high concentraion of HCl (pH of 2).

Could digest iron nailsDisrupts extra cellular matrixKills bacteria Include pepsin, breaks down protein.

Food will remain in the stomach for up to 6 hours until it resembles a ‘soupy’substance known as chyme.

Digestion

Small intestines is the organ where: Most hydrolysis takes place of macromolecules Most absorption of nutrients into the blood.

In humans: 6m long. It is the longest section of the alimentary canal. Called ‘small’ because of diameter.

There are three defined regions in the small intestine:1 the duodenum2 the jejunum3 the ileum.

Digestion Secretions from the pancreas enter the duodenum at the top of

the small intestine. These secretions, known as pancreatic juice, contain a mixture of

amylase, trypsin, lipase and bicarbonate Bicarbonate neutralised acid from stomach chyme and stops

pepsin and protease from working Bile, produced by the liver, passes down the bile duct and into the

duodenum. If there is no food to digest in the small intestine bile is stored in the gall bladder. It’s involved in the mechanical breakdown of fats.

Lipases are enzymes that are produced by the pancreas and act on the fat droplets. They chemically break down fat into fatty acidsand glycerol.

Trypsin this enzyme acts on the long chain polypeptides and breaks them down to shorter-chain peptides.

From the duodenum, food enters the jejunum and the ileum where digestion of allfood nutrients continues.

Absorption

The small intestines have the surface area of a tennis court.

High SA/V ratio from villi & microvilli. Passive & Active transport used to

absorb materials like glucose, amino acids, fatty acids & glycerol

Materials flow from capillaries & lacteal into hepatic portal vessel .

Liver Detoxifies/removes

Drugs Alcohol

Stores Gycolgen Vitamins (A, D, E, K) Fe and other minerals Cholesterol

Activates vitamin D Fetal RBC production Phagocytosis Metabolizes absorbed food

molecules Carbohydrates Proteins Lipids

Large Intestines Are Involved In Water Reabsorption

Made up of two parts: colon and rectum It compacts undigested food material, such as

dietary fibre, and to absorb water and some salts back into the body.

This waste material, faeces, is eliminated from the body through the anus.

Words to know Oesophagus Amylase Salivary gland Saliva Peristalis Stomach Gastric Juices Chyme Pancreas Amylase

Lipase Small

intestine Liver Colon Anus Faeces Bile Bile duct Gallbladder