What do humans need to live? Humans make energy using: food oxygen Animals build bodies using: food for raw materials amino acids, sugars, fats, nucleotides ATP energy for synthesis food ATP O2 mitochondria

Getting & Using Food Ingest Digest Absorb Eliminate taking in food mechanical digestion breaking up food into smaller pieces chemical digestion breaking down food into molecules small enough to be absorbed into cells enzymes Absorb absorb nutrients across cell membranes diffusion active transport Eliminate undigested material passes out of body

Digestive System ABSORPTION – Nutrient molecules absorbed from gut into bloodstream INGESTION – Act of taking in food and drink into body ELIMINATION – Ridding the body of undigested food waste DIGESTION BREAKDOWN – Chemical and Physical

Mechanical/Physical Digestion -food is broken down -more surface created Examples: Chewing with teeth -churning food in stomach -No new molecules are produced

Chemical Digestion -food molecules are broken down -produce brand new smaller molecules. -requires digestive enzymes and water as a substrate (hydrolysis reactions.)

In many parts of the digestive tract both types of digestion are happening simultaneously. For example: in the stomach.

Fig. 12.1

Human digestive system After chewing and swallowing, it takes 5 to 10 seconds for food to pass down the esophagus to the stomach, where it spends 2 to 6 hours being partially digested. Final digestion and nutrient absorption occur in the small intestine over a period of 5 to 6 hours. In 12 to 24 hours, any undigested material passes through the large intestine, and feces are expelled through the anus.

Mouth Functions mechanical digestion chemical digestion (saliva) teeth break up food chemical digestion (saliva) amylase enzyme digests starch mucus protects soft lining of digestive system lubricates food for easier swallowing buffers neutralizes acid to prevent tooth decay anti-bacterial chemicals kill bacteria that enter mouth with food All that in spit!

Fig. 12.2a

Tonsils at the back sides of the mouth protect against infections. Tonsillitis results when the tonsils become inflamed; the infection can spread to the middle ears. Three pairs of salivary glands (parotid, sublingual, submandibular) send saliva (containing salivary amylase for digestion of starch to maltose) into the mouth.

mouth break up food digest starch kill germs moisten food

Swallowing (& not choking) Epiglottis flap of cartilage closes trachea (windpipe) when swallowing food travels down esophagus Peristalsis involuntary muscle contractions to move food along

Peristalsis in Esophagus The ESOPHAGUS Peristalsis in Esophagus The esophagus is a muscular tube that conducts food through the thoracic cavity and diaphragm into the stomach. Peristalsis begins in the esophagus; this collapsed tube moves the bolus of food downward after swallowing occurs. Heartburn is a burning pain when acidic stomach contents enter the esophagus. Peristalsis is a rhythmic contraction that pushes food through the digestive tube. When peristalsis occurs with no food present, it produces a sensation of a lump in the throat. When vomiting occurs, a contraction of the abdominal muscles and diaphragm propels the contents of the stomach upward through the esophagus.

PERISTALSIS

Stomach Functions disinfect food food storage digests protein hydrochloric acid = pH 2 kills bacteria food storage can stretch to fit ~2L food digests protein pepsin enzyme Still, the epithelium is continually eroded, and the epithelium is completely replaced by mitosis every three days. Gastric ulcers, lesions in the stomach lining, are caused by the acid-tolerant bacterium Heliobacter pylori. Ulcers are often treated with antibiotics. Pepsin is secreted in an inactive form, called pepsinogen by specialized chief cells in gastric pits. Parietal cells, also in the pits, secrete hydrochloric acid which converts pepsinogen to the active pepsin only when both reach the lumen of the stomach, minimizing self-digestion. Also, in a positive-feedback system, activated pepsin can activate more pepsinogen molecules. But the stomach is made out of protein! What stops the stomach from digesting itself? mucus secreted by stomach cells protects stomach lining

Stomach Functions 1. Storage of a meal – most expanded structure along the alimentary canal

2. Mechanical Digestion of food – Stomach is very muscular and it squeezes to churn and mix food to physically break it down

3. Chemical Digestion of food – Adds PEPSIN enzyme to start chemically breaking proteins into small peptide chains

4. Protection against Germs – HCl helps activate enzymes but it also helps kill many of the bacteria that we ingest.

GASTRIC GLANDS -produce gastric juice which consists of mucous, HCl, Pepsinogen and water. In the presence of HCl the Pepsinogen converts to active Pepsin. This Pepsin is a PROTEASE enzyme, breaking proteins into smaller peptide chains

mouth break up food digest starch kill germs moisten food stomach kills germs break up food digest proteins store food sphincter sphincter

This is where all the work is done! Small intestine Functions digestion digest carbohydrates amylase from pancreas digest proteins trypsin & chymotrypsin from pancreas digest lipids (fats) bile from liver & lipase from pancreas absorption nutrients move into body cells by: diffusion active transport This is where all the work is done! About every 20 seconds, the stomach contents are mixed by the churning action of smooth muscles. As a result of mixing and enzyme action, what begins in the stomach as a recently swallowed meal becomes a nutrient-rich broth known as acid chyme. At the opening from the stomach to the small intestine is the pyloric sphincter, which helps regulate the passage of chyme into the intestine. A squirt at a time, it takes about 2 to 6 hours after a meal for the stomach to empty.

Absorption in Small Intestines Absorption through villi & microvilli finger-like projections increases surface area for absorption SMALL INTESTINES 6 meters long, but can stretch to cover a tennis court

Fig. 12.6 Small Intestine

It’s all about surface area 1.Plicae 2. Villi 3. Microvilli

VILLI Microvilli

Its All About Active Transport Products of Carbohydrate and Protein Digestion are actively transported from small intestine into the villus. These simple sugars and amino acids are taken into the capillary bed in the villus and transported to the Liver. Products of Fat digestion are absorbed into the central lymphatic vessel called a LACTEAL

Duodenum  Jejenum  Ileum

DUODENUM Functions The Duodenum is only about 45 cm (18 inches long) but it plays a couple of very important roles: 1. Receives incoming Stomach Chyme, Pancreatic Juices and Bile from Liver and Gall bladder. 2. Secretes digestive juces/enzymes from duodenal glands

mouth break up food digest starch kill germs moisten food stomach kills germs break up food digest proteins store food liver produces bile - stored in gall bladder break up fats small intestines breakdown food - proteins - starch - fats absorb nutrients pancreas produces enzymes to digest proteins & starch

Accessory Organs PANCREAS LIVER GALL BLADDER

Pancreas Produces digestive enzymes Buffers digest proteins trypsin, chymotrypsin digest starch amylase digest lipids lipase Buffers neutralizes acid from stomach small intestine pancreas

PANCREAS Function -produces a variety of hydrolytic digestive enzymes that help chemically finish off the digestion of Carbohydrates, Fats and Proteins.

Pancreatic Juice INGREDIENTS: Sodium Bicarbonate – NaHCO3 LIPASES PANCREATIC AMYLASE TRYPSIN – same function as PEPSIN NUCLEASES (work on Nucleic Acids)

Pancreatic Endocrine Function When blood sugar is getting too high. The pancreas produces and secretes INSULIN into the bloodstream

Pancreatic Endocrine Function When blood glucose levels start getting too low, the Pancreas will produce and secrete the hormone GLUCAGON. Glucagon will travel through the bloodstream to tell muscle and liver cells to break down their stored Glycogen back into glucose and send it back into the blood, to raise blood sugar levels

mouth break up food digest starch kill germs moisten food stomach kills germs break up food digest proteins store food pancreas produces enzymes to digest all foods

Liver & Gall Bladder Produces bile breaks up fats gallbladder only stores bile that’s why you can have your gall bladder removed bile contains colors from old red blood cells collected in liver = iron in RBC rusts & makes feces brown

Fig. 12.11

Gall Bladder Function -sits inferior (below) the liver. -stores bile that was produced in the liver. -secretes this bile into the Duodenum. -bile helps emulsify fats to create more surface area so that hydrolytic lipases (fat enzymes) can break the fat down chemically.

mouth break up food digest starch kill germs moisten food stomach kills germs break up food digest proteins store food liver produces bile - stored in gall bladder break up fats pancreas produces enzymes to digest proteins & starch

Large intestines (colon) Function re-absorbs water use ~9 liters of water every day in digestive juices if don’t reabsorb water would die of dehydration > 90% of water re-absorbed not enough water re-absorbed diarrhea can be fatal! too much water re-absorbed constipation reabsorb by diffusion

Large Intestine Functions 1. Receives undigested waste and helps absorb fluid (water) from those wastes back into the bloodstream, to help keep us from dehydrating. 2. Helps compact and form feces. 3. Harbours helpful bacteria which can further break down wastes to free up minerals and some bacteria will help produce and free up some vitamins, such as Vitamin K

You’ve got company! Living in the large intestine is a community of helpful bacteria Escherichia coli: E. coli digest cellulose digests fruits & vegetables produce vitamins vitamin K & B vitamins BUT generate gases by-product of bacterial metabolism methane, hydrogen sulfide STINKY! PEE-YOO!

Large Intestine/Colon Fig. 12.8 Large Intestine/Colon

mouth break up food digest starch kill germs moisten food stomach kills germs break up food digest proteins store food liver produces bile - stored in gall bladder break up fats small intestines breakdown food - proteins - starch - fats absorb nutrients pancreas produces enzymes to digest proteins & carbs large intestines absorb water

Appendix Vestigial organ

mouth break up food digest starch kill germs moisten food stomach kills germs break up food digest proteins store food liver produces bile - stored in gall bladder break up fats small intestines breakdown food - proteins - starch - fats absorb nutrients pancreas produces enzymes to digest proteins & carbs large intestines absorb water appendix

So don’t forget to wash your hands! Rectum Last section of large intestines eliminate feces what’s left over? undigested materials mainly cellulose from plants called roughage or fiber keeps everything moving & cleans out intestines masses of bacteria So don’t forget to wash your hands!

Fig. 12.9