Food provides the energy and nutrients that the body needs to stay alive and be healthy. Before the body can make use of it, the food has to be broken down to release the nutrients (digested). The nutrients are then absorbed into the bloodstream and taken to the cells where they can be used. Introduction

Digestion Digestion is the breakdown of large macromolecules into smaller components by the action of digestive enzymes. CHO CHO  begins in mouth, continues in small intestine (pancreatic juice and small intestinal enzymes). Fats Fats  digested primarily in small intestine: – liver (bile); – enzymes in pancreatic juice & small intestine. Protein Protein  begins in stomach; continues in small intestine with enzymes in pancreatic juice & small intestine

Mastication Saliva: Saliva: –α- Amylase breaks down starch to sugars. – Mucus to lubricate the food for easier swallowing. – Lysozyme to kill bacteria. Digestion in the Mouth

Digestion in the Stomach Stomach secretes gastric juice and HCl. Gastrin Gastrin stimulates flow of stomach enzymes and HCl. Gastric Inhibitory Peptide Gastric Inhibitory Peptide (GIP) inhibits the secretion of stomach enzymes and acid.

Pepsinogen Secreted by chief cells & activated by HCl and pepsin. Pepsin digests proteins into peptides and amino acids.

Hydrochloric acid (HCl) Secreted by parietal cells. Denatures protein. Turns pepsinogen into pepsin & provide a medium of low pH favoring pepsin action. Partially digests dietary protein. Kills many swallowed virulent organisms. Promotes the secretion of pancreas & bile. Promotes the absorption of calcium & ferrous.

Duodenum Duodenum – Primary site of digestion Jejunum Jejunum – Some digestion Ileum Ileum – Little digestion Digestion in the Small Intestine

1.Pancreatic juice: 1.Pancreatic juice: Bicarbonate and digestive enzymes. Bile. 2. Bile. Intestinal cells: 3. Intestinal cells: Digestive enzymes. Digestion in the Small Intestine

Bicarbonate (HCO 3  ): Neutralize HCl & provide a weak basic medium favoring digestive enzyme action. Pancreatic enzymes: It contains: - Proteases. - Lipases. - Amylase. - Nucleases. Pancreatic Juice

Pancreatic Zymogens - Trypsinogen. - Chymotrypsinogen. - Procarboxypeptidase. - Prophospholipase.

enteropeptidase (enterokinase) Trypsinogen Trypsin enteropeptidase, trypsin Chymotrypsinogen Chymotrypsin trypsin Procarboxypeptidase Carboxypeptidase trypsin Prophospholipase Phospholipase Activation of Pancreatic Zymogens

Secretin: Stimulates the secretion of bicarbonate. Cholecystokinin (CCK): Stimulates the release of enzyme rich pancreatic fluids. Hormonal Regulation of Pancreatic secretion

Bile secretion (mainly bile salts) Fat emulsification. Lipid absorption. Absorption of fat-soluble vitamins.

Hormonal control of Bile secretion Cholecystokinin: Cholecystokinin: Stimulates contraction of gallbladder and flow of bile.

Enterokinase: Enterokinase: the only one secreted. Oligopeptidases, oligosaccharidases Oligopeptidases, oligosaccharidases those are contained in the epithelial cells. Enzymes of the Small Intestine

Digestion in the Small Intestine  Pancreatic enzymes  Pancreatic enzymes play the major digestive function:  Complete digestion of starch (pancreatic α- amylase).  Complete digestion of protein (trypsin, etc.).  Digestion of fat (lipases).  Digestion of nucleic acids (nucleases).  Enzymes from the brush border:  Break down disaccharides into simple sugars.  Complete some protein digestion.

Sites of Absorption Oral cavity & Stomach: little Duodenum & Upper jejunum: most nutrients Ileum: bile salts & Vit. B 12 Colon: water & electrolytes

Sites of Absorption

Types of Absorption Passive Diffusion: – Intestinal wall is permeable to the nutrients. – Going from higher to lower concentration (i.e. down concentration gradient). – No energy expended. Facilitated Diffusion: – A carrier shuttles substances into the absorptive cells. – Going from higher to lower concentration (i.e. down concentration gradient). – No energy expended. Active Transport: – Going from lower to higher concentration (i.e. against concentration gradient). – Uses a carrier and ATP.

Types of Absorption

The digestion products, sugars, fatty acids, glycerol, amino acids, and dipeptides are able to enter the intestinal wall. The amino acids and sugars then pass from the villi wall into the bloodstream and go to the liver. Most of the fatty acids and monoacylglycerol are then re- esterified and incorporated into chylomicrons and go to the lymphatic system from where they enter the bloodstream. The nutrients are then transported in the blood to all the cells of the body. In this way the cells get the nutrients they need. Absorption in the Small Intestine

Absorption of water, minerals, and vitamins (leaving a mass in a semi-solid state). Almost everything of nutritional value has been utilized by time it reaches the large intestines -- leaving only waste (cellulose, pectins, etc..). Feces contains some water, dead mucosal cells, bacteria, non-absorbed remains of digestion (inorganic matter and lipid). Absorption in the Large Intestine

METABOLISM Metabolism is the sum of all biochemical reactions occurring in living cells. These reactions can be divided into two main groups: – 1) ANABOLISM – 2) CATABOLISM

Involves the synthesis of complex molecules from simpler molecules which requires energy input. Involves the breakdown of complex molecules into simpler molecules involving hydrolysis or oxidation and the release of energy.

Regulation of metabolism Metabolic processes are regulated by Many factors, most important are: 1- Enzymes 2- Coenzymes 3- Hormones 4-Feed back mechanism 5-Homeostasis

Enzymes are proteins that catalyze (i.e. accelerate) and control the rates of chemical reactions. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, the products. Almost all processes in a biological cell need enzymes in order to occur at significant rates.

ENZYME AS BIOLOGICAL CATALYSTS: Enzymes are biological catalysts produced by living cells. Enzymes lower the amount of activation energy needed. They speed up the rate of biochemical reactions in the cell but remain unchanged at the end of the reactions. Most enzymes are globular protein molecules.

The chemicals which an enzyme acts on is called its substrate. The enzyme combines with its substrate to form an enzyme-substrate complex. The complex than breaks up into product and enzyme. A metabolic pathway is a number of reactions catalysed by sequence of enzymes.

How do enzymes work? substrate: molecules upon which an enzyme acts. The enzyme is shaped so that it can only lock up with a specific substrate molecule. enzyme substrate > product

There are approximately 3000 enzymes which have been characterised. These are grouped into six main classes according to the type of reaction catalysed. At present, only a limited number are used in enzyme electrodes or for other analytical purposes.

IEC Classification of Enzymes Group Name Type of Reaction Catalyzed Oxidases or Dehydrogenases Oxidation-reduction reactions Transferases Transfer of functional groups HydrolasesHydrolysis reactions Lyases Addition to double bonds or its reverse IsomerasesIsomerization reactions Ligases or Synthetases Formation of bonds with ATP cleavage

A non protein component of enzymes is called the cofactor. If the cofactor is organic, then it is called a coenzyme. Coenzymes are relatively small molecules compared to the protein part of the enzyme. Many of the coenzymes are derived from vitamins. The coenzymes make up a part of the active site, since without the coenzyme, the enzyme will not function.

In the graphic on the left is the structure for the coenzyme, NAD+, Nicotinamide Adenine Dinucleotide. Nicotinamide is from the niacin vitamin. The NAD+ coenzyme is involved with many types of oxidation reactions where alcohols are converted to ketones or aldehydes.

Vitamin Coenzyme Function niacin nicotinamide adenine dinucleotide (NAD + ) oxidation or hydrogen transfer riboflavin flavin adenine dinucleotide (FAD) oxidation or hydrogen transfer pantothenic acid coenzyme A (CoA) Acetyl group carrier vitamin B-12 coenzyme B-12 Methyl group transfer thiamin (B-1) thiaminpyrophosphate (TPP) Aldehyde group transfer

Insulin Glucagon Adrenaline Glucocorticoids Growth Hormones Thyroxin These also are regulators of metabolism : Stimulating or inhibiting certain reactions.

4-Feed back mechanism When a certain substance increases in its level in the blood, a certain message goes to the brain. The brain will then send a message to the special organ that forms this substance to stop producing it.

5-Homeostasis Keeping the internal environment(blood,C S F)constant (i.e. the level of its constituents constant) inspire of the changes of the outside environment and the chemical changes taking place inside