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

2. Digestion….

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

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

5. 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

6. How much of each do you need?

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

10. 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….

11. Chemical digestion

12. 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

13. Draw and label a diagram of the human digestive system.

14. 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

15. 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

20. The Components of the Digestive System
Figure 24.1

21. 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

24. Digestion begins in the mouth…

25. Digestion begins in the mouth…

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

27. The pharynx

28. 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...

29. Peristalsis
Figure 24.4

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

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

32. The Structure of the Digestive Tract
Figure 24.3

33. 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.

34. Why do we need enzymes for digestion?

35. 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

36. The pharynx

37. 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

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

40. 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

41. The Stomach
Figure 24.12b

42. The Stomach Lining
Figure 24.13c, d

43. 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

44. Regions of the Small Intestine
Figure 24.16a

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

46. The Intestinal Wall
Figure 24.17b, c

47. The Intestinal Wall
Figure 24.17d, e

48. 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.

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

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

51. The Large Intestine

52. 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

53. 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

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

55. 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