Digestive System II SBI3U

How Do Animals Obtain Energy? Autotrophs: Take energy from the environment in the form of sunlight or inorganic chemicals Use the energy to create energy- rich molecules. Examples: plants and algae

How Animals Obtain Energy: Heterotrophs: Take in autotrophs as a food source. Depend on autotrophs for the energy and raw materials they need Heterotrophs obtain energy by breaking down organic molecules obtained from the autotrophs Examples: all animals, most fungi, bacteria and protozoa.

Autotrophs and Heterotrophs

Animals (i.e. heterotophs) Have adapted mechanisms to search, obtain and take in their food. Animals obtain food from any of the following 4 mechanisms.

Feeding Mechanisms 1) Filter Feeding: Use a « filter basket » to obtain organisms suspended in the water. Siphons water into its mouth and filters it to obtain its food. Examples: Tube worms, clams, whales

Filter Feeding in Sponges Video

Feeding Mechanisms 2) Substrate Feeding: Live within or on their food source and eat their way through it. Examples : Earthworms, caterpillars

Feeding Mechanisms 4) Bulk Feeders: Most vertebrates (including humans). Ingest large pieces of food or swallow it whole. Different animals may use tentacles, pincers and claws to eat.

Feeding Mechanisms 3) Fluid Feeders: Suck or lick fluids (ex. blood or sap) from plants or animals. Their mouth parts are adapted to pierce through skin or leaf tissue. Examples: spiders, bees, butterflies.

Digestive Tract In order for the cells to obtain nutrients, the digestive system needs to break them down into small, soluble units. The small units of nutrients diffuse into cell membranes and into the circulatory system.

Alimentary Canal Most animals have a digestive tract also known as « Alimentary Canal » Alimentary Canal: tube where food in processed, beginning at the mouth and ending at the anus. There are various organs along the alimentary canal that process the food.

Alimentary Canal Pouch like structure that softens and stores food Example: Earthworm Churns and grinds the food

Similarities and Differences The function of the alimentary canal is the same for all animals. The length differs according to feeding habits. Herbivores and Omnivores have longer digestive tracts than Carnivores.

Stages of Digestion No matter the feeding mechanisms all animals undergoe the same 4 stages of digestion. a) Ingestion b) Digestion c) Absorption d) Elimination

Stages of Digestion Ingestion: Taking in the food Digestion: Breakdown of food (mechanical and chemical) into small molecules Absorption: diffusion of small molecules into the circulatory system Elimination: removal of undigested solid waste from the body.

10.2 The Human Digestive System The digestive tract has numerous organs with specific functions. Each organ helps to breakdown food. Label the diagram on your handout

DIAGRAM OF DIGESTIVE SYSTEM: Mouth Esophagus Liver Stomach Pancreas Gallbladder Small Intestine Large Intestine Rectum Appendix Anus

Digestive system Mechanical Digestion: physical breakdown of large pieces of food into smaller pieces. Chemical Digestion: chemical breakdown of nutrients into smaller molecules by hydrolysis and enzymatic action.

STEP 1: Ingestion Mouth Mechanical digestion: Teeth break down food into small pieces. Chemical digestion: Amylase (enzyme) breaks down the bonds in carbohydrates.

Saliva is secreted from 3 pairs of salivary glands. The secretion of saliva is triggered before you have food in your mouth. Smell or sight trigger the glands.

Role of Saliva (Chemical Digestion) Enzyme (amylase) breaks down starches (carbohydrates) into simple sugars. Dissolves water-soluble food particles. Stimulates taste buds. Lubricates the food so it can be swallowed.

When the mouth has created a bolus of food, the tongue pushes it toward the back of the throat. The esophagus (the hollow muscular) tube that leads to your stomach) lies next to the trachea (the tube that leads to the lungs). Epiglottis – flap/valve that covers the trachea when swallowing so food doesn’t go down the wrong tube. Food stretches the walls of the esophagus and moves downward through waves of contractions called “peristalsis”.

Esophagus Glands in the lining produce mucus which keeps the tube moist and facilitates movement of food/swallowing. Video

Esophagus When the bolus of food reaches the bottom of the esophagus the esophageal sphincter opens. Usually it remains closed to prevent acidic juices from flowing up into the esophagus ( acid reflux/heartburn). When you swallow, the muscles relax, opening the sphincter and allowing the food to enter the stomach.

Acid Reflux Video

STEP 2: DIGESTION Stomach Muscular, J-shaped organ Left side of the abdominal cavity below the diaphragm (muscle that separates the heart, lungs and ribs from abdominal cavity). Performs both chemical and mechanical digestion

Stomach The walls of the stomach are folded so that it can expand after a meal. The glands on the stomach wall release « gastric juice » which consists of HCl, salts, enzymes, water and mucus (for chemical digestion) when food is present. The wall is covered in a mucus coat which protects it from the acid released from the gastric juices.

Stomach Enzyme (pepsin) is released and remains inactive until HCl is secreted from the glands (when food is present). Pepsin hydrolyzes proteins to produce polypeptides.

Stomach The HCl breaks down food and destroys foreign bacteria in the food. Stomach contracts and relaxes to churn the food (mechanical digestion). The churning of the food helps to break it up and mix it with the gastric juices. The mixing and churning of the food creates chyme. Once the process has finished the pyloric sphincter opens to move food into the small intestine.

Pyloric Sphincter

Stomach While food is still being processed in the small intestine, the chyme is stored (temporarily) in the stomach. Once the processed food has moved to the large intestine, the chyme is released from the stomach. The stomach is surrounded by nerves that regulate this.

STEP 2: DIGESTION Small Intestine Further breaks down the nutrients so that they can be absorbed. Intestinal glands secrete trypsin and chymotrypsin (proteases: enzymes that digest large polypeptides). Made up of 3 parts: Duodenum, Jejunum, Illeum

Duodenum Receives secretions from the gallbladder and pancreas to further breakdown nutrients. Breaks down proteins, fats and carbohydrates with the help of proteases, lipases and carbohydrases (enzymes). Walls contain folds to increase the surface area to increase absorption.

The folds are covered by tiny, finger-like projections, “villi” and each villus is covered with microvilli (this is where the nutrients are absorbed into the bloodstream through diffusion). A capillary network is within the villi and collects the nutrients.

The gall bladder and pancreas secrete enzymes as food passes through the duodenum.

Jejunum 2.5 m long. Contains more folds than the duodenum. Breaks down the remaining proteins and carbohydrates so that they can be absorbed.

Ileum 3 m long. Has fewer villi than the duodenum and jejunum. Absorbs nutrients and pushes undigested material into the large intestine.

STEP 3: ABSORPTION Small Intestine and Large intestine

STEP 3: ABSORPTION Large Intestine Large intestine is 1.5 m in length The large intestine (a.k.a colon) reabsorbs fluids and electrolytes Absorbs 90% of water back into the blood. Bacteria live here producing vitamin K /B and folic acid and break down undigested matter. Any undigested material that remains is called feces. Fecal matter is stored here for elimination through the rectum.

STEP 4: ELIMINATION Rectum Main component of feces: Cellulose: makes up plant cell walls, cannot be digested by humans. Living and dead bacteria Water Toxic wastes are removed People who don’t eat enough cellulose (plant material and fibre) have fewer bowel movements and are at risk of colon cancer.

Accessory Organs

Pancreas Secretes about 1 L of pancreatic fluid into the duodenum each day. Pancreatic Fluid contains enzymes: pancreatic lipase - chemically digests lipids (fats) pancreatic amylase – digests carbohydrates (starch and glycogen) peptidases – digests peptides Bicarbonate – alters pH of chyme so that enzymes can be activated. (pH 1 to pH 8)

Liver Largest internal organ in the human body. Releases bile (greenish-yellow fluid made up of bile pigments and salts) Bile is sent to the gallbladder where it is temporarily stored. The bile pigments (waste products from when liver destroys old red blood cells) are not needed for digestion, and are eliminated from the intestine as waste.

Bile Fats are insoluble in water and remain suspended in the chyme. The bile salts break up the fat droplets so they can disperse through the chyme. The enzymes break the droplets apart (the greater surface area makes it easier for enzymes to break down the fats in the small intestine). Video http://www.youtube.com/watch?v=Z7xKYNz9AS0

Digestive Enzymes Induced Fit Model Enzymes: proteins that help speed up chemical reactions. (ex. hydrolysis) Digestive Enzymes Induced Fit Model The substrate and enzyme have complimentary shapes. Thus making them fit perfectly with one another. Therefore, the enzyme is highly specific to its substrate.

Factors that affect enzyme activity Temperature: Enzymes have an optimal temperature at which they work best. Most human enzymes have an optimal activity at 37˚ If the temperature is too high the chemical bond in the enzyme breaks thus denaturing the enzyme

Factors that affect enzyme activity 2) pH: Enzymes have an optimal pH at which they work best. Pepsin, is only active when it is immersed in a low (acidic) pH (ex. in stomach). Trypsin works best at a pH of 6 to 8 (ex. in small intestine).