Lesson 2: The Human Alimentary Canal

The Human Alimentary Canal … includes the entire tube from the mouth all the way to the anus

Human Alimentary Canal  Mouth  Pharynx  Esophagus  Stomach  Small intestine  Large intestine  Rectum  Anus

Accessory Organs  Salivary glands Secrete saliva  Liver Secretes bile  Gallbladder Stores and concentrates bile  Pancreas Secretes digestive enzymes …Organs that are involved in digestion but that food does not pass directly through

Types of Digestion  Physical Digestion: Food is physically broken down Example – Teeth chew food  Chemical Digestion: Food is broken down by acids, bases or enzymes in the human alimentary canal Example – HCl in stomach

Mouth (Oral Cavity)  Site of Ingestion  Salivary Amylase breaks carbohydrates into simpler sugars ??? What type of digestion takes place in the mouth? Physical? Chemical?

Saliva  Produced by salivary glands at back of mouth and under tongue  Saliva includes Salivary amylase (enzyme) Bicarbonate (buffer) Mucins (bind food into bolus) Water

Salivary Glands  Accessory Organ found at back of mouth and under tongue  Releases salivary amylase into the mouth

Swallowing Tongue forces food into pharynx Epiglottis closes off the trachea to prevent choking (breathing temporarily stops) Bolus moves into oesophagus Once chewed, food is called a bolus

Pharynx (The throat)  No physical or chemical digestion occurs here  Links in with the respiratory system

Esophagus  Function: to transport food from mouth to the stomach  Food considered a BOLUS at this stage wet ball of chewed food How does the bolus get from the mouth to the stomach?

Peristalsis Peristalsis: waves of muscular contraction that move food along the human alimentary canal

Stomach  Muscular sac-like organ  Lined with a thick protective mucus  The stomach lining secretes Gastric Juices that contain: Hydrochloric Acid Pepsinogen (inactive form of pepsin) Mucus Discuss the types of digestion occurring in the stomach…

Chemical Digestion in the Stomach  Pepsinogen is activated by the acid HCl in the stomach and becomes pepsin  Pepsin chemically digests protein into amino acids

Physical Digestion  Food is mixed and moved by waves of stomach contractions (peristalsis)  Becomes Chyme – thick liquid made of partially digested food and stomach juices

Small Intestine  Over 6.5 meters long  Duodenum First 10 cm of small intestine

What happens in the small intestine? 1. Pancreatic juices neutralise acidic chyme 2. Digestion is completed in duodenum Liver secretes bile, via gallbladder, which emulsifies fats Pancreas secretes various enzymes which complete the breakdown of protein, carbs and fats 3. Absorption takes place of digested products into bloodstream

LIVER  produces bile which breaks up the larger fats (emulsification) GALLBLADDER  stores the bile until needed

Large Intestine  Function: to absorb water into blood  Also the site of vitamin K production  End section: rectum & anus

Stages of Digestion 1. Ingestion – the process by which food is taken into the body 2. Digestion - the process of breaking up complex substances into simpler substances. 3. Absorption – the process by which digested food diffuses into blood 4. Assimilation - the conversion or incorporation of absorbed simple food into the complex substances that are useful in our bodies 5. Egestion - the elimination of undigested food (faeces) from the body YOU DECIDE! Look at your diagram of the Digestive System. Where does each stage of digestion take place? Hint: Some stages take place at multiple locations…

Warning: Do not confuse Egestion with Excretion Egestion – removal of undigested food (faeces) via the anus Excretion – removal of waste products of metabolism (like urine, carbon dioxide, sweat)