The Digestive System Part 2 Objectives:

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Presentation transcript:

The Digestive System Part 2 Objectives: 1. Explain the anatomy of the digestive system 2. Explain the difference between mechanical and chemical digestion and where each occurs 3. State the organ that begins the chemical digestion of each of the macromolecules. 4. Follow the path of a spaghetti and meat ball dinner through the digestive system.

The Stomach Mechanical digestion occurs here – physical mixing and grinding of food particles Chemical digestion occurs here – acids, hormones, and enzymes released to break food down further

The Pathway of Food 1. The bolus enters the cardia section of the stomach – just under the diaphragm and heart (hence the name) Stomach grinds down bolus and mixes it with acids and enzymes – bolus becomes chyme 2. Chyme moves to the upper round section of the stomach called the fundus Chyme is further ground, mixed, and held for 40-60 minutes Enzymatic digestion occurs (acid here is only at 30% strength so it won’t interfere with enzymes)

The Pathway of Food 3. Chyme moves to the large middle section called the body Peristalsis mixes and churns chyme Area where digestion begins HCl and pepsin at work – stops enzymatic action 4. Antrum is the last part of the stomach before the pylorus The majority of stomach digestion is done here Food held a long time and released to the duodenum in a slow and methodical manner

Parts of the Stomach

Small Intestine - Functions 1. Chemical Digestion neutralize acid from stomach add digestive enzymes and bile break proteins, carbohydrates and lipids into absorbable materials 2. Absorption - 95% of food absorbed here

Small Intestine - Structure Regions: (stomach connects via pyloric sphincter) Duodenum – 20-35 cm long Jejunum – 3 m long Ileum – 4 m long Mucosa adaptations: villi containing blood and lacteal capillaries (absorbs digested lipids) = maximizes absorption

Small Intestine

Accessory Organs Pancreas: digestive role Secretes digestive enzymes into small intestine: lipases break down lipids, carbohydrases (like amylase and lactase) break down carbohydrates proteases (like trypsin and pepsin) break down proteins produces hormones to regulate blood sugar (insulin and glucagon) produces bicarbonate ions to neutralize HCl after digestion Liver Produces bile (acts as emulsifer – begins fat breakdown) Metabolic functions: storage of glycogen (tightly packed glucose); protein synthesis; chemical processing – detoxification (alcohol, drugs) Gallbladder: stores bile

Break down of the Macromolecules (AMYLASE) CHO’s ------digested to------ MONOSACCHARIDES (starch) (glucose) (PEPTIDASE) PROTEIN -------digested to--------- AMINO ACIDS (BILE) (LIPASE) FATS ---emulsified----digested to --- GLYCEROL & FATTY ACIDS

Accessory Organs pancreas

Absorption of Proteins and Carbs (circuatory system)

Absorption of Fats This mechanism of absorption is a little different because lipids cannot go directly into the blood since they are not soluble. mechanism of entry into circulation!

Large Intestine

Large Intestine (Colon) Functions: absorbs nutrients and water, and produces/eliminates waste Structure: cecum: cecum receives chyme from the small intestine (via ileocecal valve) appendix = VESTIGIAL STRUCTURE - the shrunken remainder of the cecum ceca in herbivores are large and contain mutualistic bacteria that help digest cellulose Why still there? – protect beneficial bacteria … and not a huge selective pressure for elimination Colon: ascending, transverse, descending, sigmoid

Colon … continued Rectum: Last 20 cm of colon End of digestive tract Passes feces from large intestine to the anus Anus: Pair of circular muscles called anal sphincters Controls defecation

Control of Digestive System The nervous and hormonal systems act on digestion before we even eat: seeing, smelling and tasting food stimulates gastric secretions Regulation dependent on volume and content of food Nervous system: stretch receptors in stomach

These gastric juices start the digestion of protein Hormones: Swallowing stimulates production of gastric juices, ex. the hormone gastrin stimulate gastric juices to be released before food gets to stomach. These gastric juices start the digestion of protein Hormones: Gastrin: stimulates release of gastric juice Secretin: stimulates pancreas to secrete water and bicarbonate Cholecystokinin (CCK): signals pancreas to secrete digestive enzymes

Speed of Digestion The speed of digestion is under homeostatic control. It also varies with food type - A larger meal activates more receptors which stimulates stronger stomach muscle contractions and faster emptying - Fatty meal: digestion slows down in response to a hormone from the small intestine (enterogasterone) to allow more time for fat digestion (we feel full longer after a fatty meal)

What do the parts do? Mouth Gullet Stomach Small intestine Large intestine Rectum Anus Teeth grind food, saliva added. Muscles squeeze food down. Food mixed with strong acid. Absorbs all nutrients. Water is absorbed. Faeces are formed and stored. Faeces are egested.

Plenary How is the small intestine structured to allow maximum absorption? Why should we ensure that we eat fiber? What is the function of the liver, pancreas and gall bladder? Why are they technically not considered to be digestive organs. Name three enzymes involved in chemical digestion, state which macromolecule they breakdown.

Your Task Read Complete Trace the path of a spaghetti and meat ball dinner from ingestion to absorption.