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, myelinVitamins (e.g. C,D,E): small amounts for essential functions

Minerals: e.g. Ca, ZnWATERFibre

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

Ingestion: taking food INmechanical digestion (processing) (e.g.chewing)

chemical digestion (enzymatic hydrolysis)(Secretion) – of enzymes and mucous

Absorption – of nutrientsexcretion/egestion: elimination of waste products

Functions of the digestive system

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

Figure 24.1

The Components of the Digestive System

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

Oral (buccal) cavity (pharynx)

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 dig

estion

The pharynx

Smooth muscle shows rhythmic cycles of activityPeristalsis : waves that move a bolus (ball of food)Segmentation

Churn (mixing) and fragment a bolusLet’s watch!Peristalsis in action...

How does food move along the digestive tract?

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 VesselsPhotograph by Susumu NishinagaThis 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?

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

Oral (buccal) cavity/pharynx

The pharynx

• 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

6.1.5 Outline the function of the stomach

Structure of the stomach

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

very little absorption of nutrientsControl of enzyme (pepsin), acid (HCl) and hormone (gastrin) secretion is controlled by:1. Cephalic2. Gastric3. Intestinalfactors Control of gastric function

Digestion and absorption in the stomach

The Stomach

Figure 24.12b

The Stomach Lining

Figure 24.13c, d

• 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

6.1.5 Outline the function of the small intestine.

Figure 24.16a

Regions of the Small Intestine

Adaptations to increase surface area for absorption…• Plicae (folds) • Villi (fingerlike

projections)– Microvilli

Zooming in on the small intestine

Small intestine

Figure 24.17b, c

The Intestinal Wall

Figure 24.17d, e

The Intestinal Wall

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.

• Duodenal glands– produce mucus

• Ileum– lymph glands (Peyer’s patches)

Small Intestine

• Reabsorbs water and compact material into feces

• Absorb vitamins produced by bacteria

• Store faecal matter prior to defecation

Functions of the large intestine

The Large Intestine

Figure 24.18a-c

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).

• 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 pancreas

• Performs regulation of metabolism and blood and produces bile

• The liver has many different functions

The liver

The GallbladderBile 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 organStores bileHelps in digestion of fats