Digestive System & Diet

All organisms need to obtain energy from essential nutrients. Heterotrophs get energy from other organisms.

Plants are Autotrophs, they make food from simple substances They use the process of photosynthesis to make food.

What is Diet? Diet is everything you eat and drink

Different food groups Carbohydrates –Starches –Sugars –Fiber Proteins Fats & lipids Vitamins & Minerals Water

Healthy Diet

Canada’s Food Guide

Vegetarian Food Pyramid

How much do you need? Food provides nutrients for –Energy –Material for growth and repair –Health Energy is measured in Joules (J) Number of joules/day depends on: –Age –Gender –Occupation/activity level

Specialized digestive systems Simple animals such as jellyfish and flatworms have a digestive sac with a single opening into a gastrovascular cavity This opening serve as both an entrance for food and as an exit for waste material Food goes to gastrovascular cavity  break down by chemical  nutrients absorbed by cell  digestion continue inside cells  nutrients diffuse to other cells

More complex digestive system They have different opening for food intake and waste (i.e. earthworm) Food ingested through mouth  muscular pharynx  esophagus  crop (temporary storage)  physical breakdown of food by the gizzard  go to the intestine for further breakdown  small molecules are absorbed by the cells around the intestine  undigested wastes eliminate through the anus

Human digestive system The human digestive system is referred to as gastrointestinal tract (GI tract) It is about 7-9 m long (longer than the human being

The 5 processes.... Ingestion: taking in food (eating) Digestion: breaking down food into simpler substances. Absorption: digested food passes into the blood. Assimilation: Digested food is used by cells of the body. Egestion: Elimination of waste undigested food.

What happens to the food you eat? Food is made of complex insoluble macro- molecules. Has to be broken down into small soluble micro-molecules (glucose, amino acids, fatty acids and glycerol) Breaking down food into small soluble molecules is called DIGESTION.

Digestion Two types –Mechanical –Chemical Mechanical –Teeth –Muscular contractions Chemical –Enzymes

Digestive system A long tube starting at the mouth and ending at the anus

The digestive system consists of A tube lined with glandular cells that secrete digestive juices and enzymes Associated organs –Liver –Pancreas –Gall bladder –Salivary glands

Mouth Incisors and canines are specialized for grabbing and cutting food Pre-molars and molars are flattened teeth specialized in grinding and crushing food Type of teeth an animal has is directly related to its diet.

Mouth Mechanical digestion –Teeth break food into smaller pieces that increases the surface area for digestion –Saliva creates a basic pH of about 8 & moistens food allowing soluble chemicals to dissolve. Chemical digestion –3 pairs of Salivary glands produce the enzyme AMYLASE – this begins the breakdown of STARCH –Saliva also dissolves food so we can taste

Salivary Glands Chewed food is mixed with saliva from 3 pairs of salivary glands, the food is now called a BOLUS

Buccal Phase: tongue moves upward and backward against the hard and soft palate to push the bolus into the Oropharynx Pharyngeal stage: involuntary movements push the bolus through the pharynx and into the esophagus. The brain signals the uvula to close the nasopharynx and the epiglottis to seal the larynx. The upper esophageal sphincter relaxes to allow the bolus to move into the esophagus and contracts to reduce back flow into the pharynx Swallowing

Swallowing Esophageal stage: the bolus is pushed by the peristalsis, involantary wave like contractions of the muscle of the esophagus. Once the bolus reach the end of the esophagus it reaches the stomach.

Peristalsis

The Stomach Food enters the stomach through a valve known as the gastroesophageal Sphincter The stomach churns the food like a blender. Food is liquefied and now is known as CHYME Food stays in the stomach for several hours

Stomach The 4 layers of the stomach Innermost layer (mucosa): secretes gastric juice a mixture of digestive enzymes, acid and mucus. 2 nd layer (submucosa): layer of connective tissue contains nerves and blood vessels 3 rd layer (muscularis): smooth muscles, contract frequently, churning and mixing the food with gastric juice to produce chyme Outermost layer (serosa): holds the stomach in place and secretes lubricating fluid to eliminate friction between organs

The stomach “Epithelial cells line inner surface of the stomach, and secrete about 2 liters of gastric juices per day. Gastric juice contains hydrochloric acid, pepsinogen, and mucus; ingredients important in digestion. Secretions are controlled by nervous (smells, thoughts, and caffeine) and endocrine signals. The stomach secretes hydrochloric acid and pepsin. Hydrochloric acid (HCl) lowers pH of the stomach so pepsin is activated. Pepsin is an enzyme that controls the hydrolysis of proteins into peptides. The stomach also mechanically churns the food. Chyme, the mix of acid and food in the stomach, leaves the stomach and enters the small intestine.”pepsinogen

Acid reflux Gastroesophageal sphincter does not close completely Acid from the stomach enters the esophagus Cause burning sensation in the lower throat (heartburn or acid reflux) Cause: overfilled stomach, smoking,

Stomach ulcer Stomach acid is strong enough to kill most bacteria in the stomach Helocobacter Pulori survive by secreting acid neutralizing enzymes  prevents mucus producing cells from producing mucus to protect stomach lining The strong acid will open a sore called stomach ulcer Ulcer bleed and can be very painful and dangerous