Digestion

Mechanical and Chemical Breakdown of Ingested Food

3 Stages in Digestion

1.

 Digestion - breakdown of food into particles/molecules small enough to pass into the blood stream.

  2 types of digestion mechanical (Mastication) chemical (Enzymes) 2.

3.

Absorption of nutrients into the blood stream Elimination of indigestible nutrients

         

Organs and Glands of the Digestive System

Mouth Salivary Glands Esophagus Stomach Small intestine Liver Pancreas Gall bladder Intestinal Glands Large intestine

Enzymes of the Digestive System

    

Salivary amylase Pepsin

(proteins  (starch  sugar) peptones and proteoses)

Bile

(emulisification of lipids) Pancreatic Juice  

Amylase Trypsin

(polysacchardies  disacchardies) (peptones and proteoses  peptides) 

Lipase

(lipids  gylcerol and fatty acids) Intestinal Juice  

Peptidase Maltase

(peptides  amino acids) (Disaccharide  Monosacchardies)

The Mouth

    

Mechanical breakdown

of nutrients begins in the mouth by chewing (Mastication).  The purpose of chewing is to increase the surface area of food.

Chemical breakdown

of starch also begins in mouth. Starch is converted into glucose by salivary amylase (secreted by the salivary glands) This mixture of food and saliva is made into a mass of food called a bolus and then pushed into the pharynx by the tongue which triggers involuntary swallowing. The esophagus is a muscular tube whose muscular contractions ( peristalsis ) propel food to the stomach.

Peristalsis – the wave action of muscle that moves food through the digestive system.

The Stomach ( Churn, Churn, Churn)

    During a meal, the stomach gradually fills to a capacity of 1 liter, from an empty capacity of 50-100 milliliters.  At a price of discomfort, the stomach can distend to hold 2 liters or more.

The stomach secretes about 2 liters of gastric juices per day.

 Gastric juice contains hydrochloric acid, pepsinogen , and mucus Hydrochloric acid (HCl) lowers pH of the stomach to activate pepsinogen  pepsin. The acidic environment also helps to liquefy foods.  Pepsin is an enzyme that controls the hydrolysis of proteins into peptides. The stomach also mechanically churns the food. Chyme, (liquefied food) the mix of acid and food in the stomach, leaves the stomach and enters the small intestine.

The Small Intestine

 The small intestine is the major site for

digestion

and

absorption

of nutrients.

 98% of digestion and 100% of absorption of nutrients occurs in the small intestines.  Small intestine is made up of 3 parts  Duodenum  Jejunum  Ileum

From Stomach to Duodenum

 Chyme – Liquefied food  Acidic Chyme is pushed from the lower part of the stomach through the pyloric sphincter into the Duodenum (first part of small intestines).

 The stomach empties over a 1 to 2 hour period.

Small Intestines (Doudenum)

   Chyme is pushed out of the stomach into the small intestines. The acid chyme stimulates the Liver and the Pancreas.

The pancreas secretes digestive enzymes and stomach acid-neutralizing sodium bicarbonate.(2 pH  8 pH)  Enzymes - Lipase, Amylase, Trypsin The liver produces bile, which is stored in the gall bladder before entering the bile duct into the duodenum.  Bile emulsifies fats (breaks fats into little pieces)

Carbohydrate Digestion step by step

    The chyme is pushed into your small intestines (duodenum) which triggers the release of Pancreatic juice from the pancreas Amylase is one of the enzymes in the pancreatic juice which breaks down Polysaccharides into disaccharides Finally the intestinal glands release intestinal juice which includes the enzyme maltase. (jejunum)  Maltase breaks down the disaccharides into monosaccharide which are absorbed by the blood stream.

Monosaccharides are absorbed into blood stream and carried to the cells (ileum)

Protein Digestion Step by Step

     Proteins begin to be digested by Pepsin in the stomach while being liquefied by the acid HCL.

The chyme is pushed into your small intestines (duodenum) which triggers the release of Pancreatic juice from the pancreas Trypsin is one of the enzymes in pancreatic juice which continues the breakdown of proteins into Peptide bonds Finally the intestinal glands release intestinal juice which includes peptidase which breaks peptide bonds into amino acids. (jejunum) Those amino acids are absorbed into the blood stream and carried to the cells (ileum)

Digestion of Lipids

 The chyme is pushed into your small intestines (duodenum) which triggers the release of Pancreatic juice from the pancreas and bile from your gall bladder.

 Bile emulsifies (chews) the lipids to increase surface area  Lipase that is found in pancreatic juice hydrolyses lipids into a glycerol and 3 fatty acids  The products are absorbed by the small intestines and carried to the cells for use. (jejunum and ileum)

Enzymes and were they are Used

     Salivary amalyase (starch  Pepsin (proteins  sugar) Polypeptides)

MOUTH STOMACH

Bile (emulisification of lipids)

DUODENUM

Pancreatic Juice

DOUDENUM

 Amylase (polysacchardies  disacchardies)   Trypsin (peptones and proteoses  Lipase (lipids  peptides) gylcerol and fatty acids) Intestinal Juice

JUJUMIN and ILEUM

 Peptidase (peptides  amino acids)  Maltase (Disaccharide  Monosacchardies)

Villi and MircoVilli

   The small intestine is lined with vill and microvilli The purpose of villi and microvilli are to increase surface area in the small intestines. Increase the speed at which nutrients are absorbed  The small intestines a 6 meter long tube has a surface area of 300 square meters or the surface area of a 500-600m long tube. Each villus has a capillary network supplied by a small artery. Absorbed nutrients pass through the microvilli into the capillary (blood stream), usually by passive transport (diffusion).

The Large Intestine

      The large intestine colon, and rectum. is made up by the cecum, appendix , Digested food is pushed from the small intestines into the large intestine. No digestion takes place in the large intestines Material in the large intestine is mostly indigestible residue and liquid. Water, and salts are absorbed, the remaining contents form feces (mostly cellulose, bacteria, bilirubin). Bacteria in the large intestine, such as

E. coli

, produce vitamins (including vitamin K) that are absorbed.

There are 3 parts to the Colon 1. Ascending Colon 2. Transverse Colon 3. Descending Colon

The Liver and Gall Bladder

 The Liver makes Bile and stores it in the gall bladder.

  The Gall bladder sends bile to the small intestine when the acidic chyme from the stomach. Bile contains bile salts, which emulsify fats, making them susceptible to enzymatic breakdown. The liver also stores excess glucose in the form of glycogen.

The Pancreas

 When the acidic chyme is pushed out of the stomach into the small intestines. IT simulates the pancreas to send pancreatic juice, which neutralizes the chyme, begins digestions of Carbohydrates, Lipids and continues digestion of protein.  Pancreatic juice also contains Lipase which digested emulsified Lipids

Stomach HCl

    Hydrochloric acid does not directly function in digestion:  it kills microorganisms that cause food poisoning.

  lowers the stomach pH to between 1.5 and 2.5 activates pepsinogen (to pepsin) Pepsin is an enzyme that starts protein digestion. HCl inhibits further carbohydrate breakdown started by salivary amylase. HCl aids in the liquefaction of masticated food Epithelial cells secrete mucus that forms a protective barrier between the cells lining the inside of the stomach and the stomach acids.

Ulcers

    Peptic ulcers fails and the HCl eats away at the lining of the stomach. result when the protective mucus Bleeding ulcers result when tissue damage is so severe that bleeding occurs into the stomach.

Perforated ulcers are life-threatening situations where a hole has formed in the stomach wall. At least 90% of all peptic ulcers are caused by

Helicobacter pylori (bacteria)

ulcers. . Other factors, including stress and ibuprofen, can also produce