Plan for this week Complete Digestion (p.24 – 33 of IGCSE book) Wednesday – dissection and microscopy lab Thursday – Test on Drugs and the Brain

Digestion….

The Digestive System 6.1.1 Explain why digestion of large food molecules is essential. 6.1.2 Explain the need for enzymes in digestion. 6.1.3 State the source, substrate, products and optimum pH conditions for one amylase, one protease and one lipase. 6.1.4 Draw and label a diagram of the digestive system. 6.1.5 Outline the function of the stomach, small intestine and large intestine. 6.1.6 Distinguish between absorption and assimilation. 6.1.7 Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion.

Before we begin…. WHAT do we need to eat? (a rough guide)

Essential components of the diet Carbohydrates (sugars and complex carbohydrate): ENERGY Proteins: enzymes, structure, muscle, growth, repair, immune function (antibodies) Fats: ENERGY, cell membranes, myelin Vitamins (e.g. C,D,E): small amounts for essential functions Minerals: e.g. Ca, Zn WATER Fibre

How much of each do you need?

So why do we have a digestive system? Does all food need to be digested?

Digestion makes food (nutrients) easier to absorb… Mechanical Digestion: Breakdown by TEETH, and by the churning movements of the GI system (peristalsis) Chemical digestion: Enzymes and acid….

Chemical digestion

Functions of the digestive system Ingestion: taking food IN mechanical digestion (processing) (e.g.chewing) chemical digestion (enzymatic hydrolysis) (Secretion) – of enzymes and mucous Absorption – of nutrients excretion/egestion: elimination of waste products

Draw and label a diagram of the human digestive system.

Simple digestion: Intracellular food processing Paramecium Food is ingested through endocytosis and forms food vacuole Food vacuole fuses with lysosome,which contains digestive juices Nutrients absorbed through membrane Vacuole refuses with membrane and waste is eliminated through exocytosis

Simple digestive systems: Extracellular food processing Food breakdown and absorption occur in compartments that are continuous with outside of organism Gastrovascular cavity: food enters + waste exits through a single opening Cnidarians (ex. Hydra) have this

The Components of the Digestive System Figure 24.1

Oral (buccal) cavity (pharynx) Its functions include: analysis of material before swallowing (touch, temperature, and taste receptors in tongue) mechanical processing by the teeth and tongue Lubrication (with water/mucous) limited digestion (salivary amylase) Production of a food bolus for transportation to the stomach (via oesophagus) by peristalsis The pharynx provides a common pathway for air, food and liquids

Digestion begins in the mouth…

Digestion begins in the mouth…

Step by step through the digestive tract explore the digestive tract UPenn animation animation of organs of digestion

The pharynx

How does food move along the digestive tract? Smooth muscle shows rhythmic cycles of activity Peristalsis : waves that move a bolus (ball of food) Segmentation Churn (mixing) and fragment a bolus Let’s watch! Peristalsis in action...

Peristalsis Figure 24.4

Digestion is achieved through both chemical and mechanical breakdown 6.1.1 Explain why digestion of large food molecules is essential. 6.1.2 Explain the need for enzymes in digestion. 6.1.3 State the source, substrate, products and optimum pH conditions for one amylase, one protease and one lipase.

Why do we need enzymes for digestion? Stephen Taylor intro to digestion/enzymes zoom into amylase...

The Structure of the Digestive Tract Figure 24.3

Small Intestine Blood Vessels Photograph by Susumu Nishinaga This colored scanning micrograph shows a cast of blood vessels from the external wall of the small intestine. Measuring about 22 feet (6.7 meters) in length, the small intestine performs most of the major digestion and absorption of nutrients. The walls of the small intestine are lined with millions of projections called villi, which absorb and transmit nutrients into the bloodstream.

Why do we need enzymes for digestion?

Oral (buccal) cavity/pharynx Its functions include: analysis of material before swallowing (touch, temperature, and taste receptors in tongue) mechanical processing by the teeth and tongue lubrication limited digestion (salivary amylase) Production of a food bolus for transportation to the stomach (via oesophagus) by peristalsis The pharynx provides a common pathway for air, food and liquids

The pharynx

6.1.5 Outline the function of the stomach yum!....digestion from the inside Storage of undigested food Hydrochloric acid lowers pH to 2, killing bacteria and denaturing proteins Mechanical breakdown of food through muscular action Chemical breakdown of food with acids and enzymes (pepsin begins protein digestion) Produces chyme

Structure of the stomach Rugae: rough ridges which allow grinding of food (mechanical digestion)

Digestion and absorption in the stomach very little absorption of nutrients Control of enzyme (pepsin), acid (HCl) and hormone (gastrin) secretion is controlled by: Cephalic Gastric Intestinal factors Control of gastric function

The Stomach Figure 24.12b

The Stomach Lining Figure 24.13c, d

6.1.5 Outline the function of the small intestine. Important digestive and absorptive functions pancreas, liver & gall bladder secrete enzymes and juices into small intestine Small intestine divided into three sections: Duodenum Jejunum Ileum

Regions of the Small Intestine Figure 24.16a

Small intestine Adaptations to increase surface area for absorption… Plicae (folds) Villi (fingerlike projections) Microvilli Zooming in on the small intestine

The Intestinal Wall Figure 24.17b, c

The Intestinal Wall Figure 24.17d, e

Microvillae Microvilli (MV) are minute finger like projections of the luminal (L) plasma membrane and serve the purpose of significantly increasing surface area (as much as 30-fold) in regions specialized for absorption, such as here in the small intestine.

Small Intestine Duodenal glands Ileum produce mucus lymph glands (Peyer’s patches)

Functions of the large intestine Reabsorbs water and compact material into feces Absorb vitamins produced by bacteria Store faecal matter prior to defecation

The Large Intestine

The Pancreas The pancreas and gland cells of the small intestine secrete digestive enzymes that chemically break down complex food molecules into simpler ones. These enzymes include trypsin (for protein digestion), amylase (for carbohydrate digestion), and lipase (for lipid digestion). Figure 24.18a-c

The pancreas Pancreatic duct penetrates duodenal wall Endocrine functions (hormones) Insulin and glucagons Exocrine functions (digestive enzymes) Pancreatic juice containing many enzymes are secreted into small intestine

The liver Performs regulation of metabolism and blood and produces bile The liver has many different functions

The Gallbladder Bile liquid is created in the liver and stored in the gallbladder. Bile emulsifies (breaks into small particles) lipids (fats), which aids in the mechanical digestion of fats. Gall bladder: Hollow, pear-shaped organ Stores bile Helps in digestion of fats