1. Topic 6: Human Health and Physiology 6.1 Digestion

3. 6.1.1 Explain why the digestion of large food molecules is essential Some terms: Ingestion – the process of bringing food into the digestion system Egestion – the passing out of food that has not been digested Digestion – the mechanical or chemical breakdown of food Digestion is essential because the materials we eat are far too big to pass across the wall of the digestive system into the blood stream. The first stage of digestion is mechanical digestion (chewing in the mouth and churning in the stomach) This process increases the surface area of the food for the enzymes to act The next step is chemical digestion (enzymes breaking down food)

4. 6.1.1 Explain why the digestion of large food molecules is essential Our diet consists mainly of: Carbohydrates (sugars and starches) – Broken down into monosaccharides like glucose Lipids (fats and triglycerides) – Broken down into fatty acids and glycerol Proteins – Broken down into amino acids

5. 6.1.2 Explain the need for enzymes in digestion Enzymes are needed to speed up the process of the chemical breakdown of food (catabolic reactions) Enzymes lower the activation energy required for this process Allow reactions to happen effectively at 37°C (body temperature) And here is some good enzyme review from Topic 3 https://www.dropbox.com/s/svg1mg1mm8gf7n9/Top ic%203.6%20Enzymes.ppt

6. 6.1.3 State the source, substrate, products and optimum pH conditions for one amylase, one protease and one lipase There are three types of enzymes that breakdown the three kinds of macronutrients 1.amylase – break down carbohydrates 2.protease – break down proteins 3.lipase – break down lipids (fats)

7. 6.1.4 Draw and label a diagram of the digestive system

9. Two views of the gall bladder, liver, pancreas and small intestines (duodenum) association.

10. 6.1.4 Draw and label a diagram of the digestive system

11. 6.1.5 Outline the function of the stomach, small intestines and large intestines Stomach 1.Stores the meal in the lumen (a) 2.The muscles of the stomach breakdown food mechanically 3.Produces proteases (protein enzymes) to breakdown proteins (e) 4.Immune defense – – the walls of the stomach contain gastric glands that secrete hydrochloric acid (b) – keeps the pH between 1.5 and 2.0 – the low pH also kills harmful pathogens 5.The stomach also secrets mucus to protect it from the acidic environment and prevents autolysis (self-digestion) (c)

12. 6.1.5 Outline the function of the stomach, small intestines and large intestines Small intestines The two main functions of the digestion system are digestion and absorption Both happen here in the small intestines The bolus of food are moved along the small intestines by muscular contractions called peristalsis

13. 6.1.5 Outline the function of the stomach, small intestines and large intestines Digestion The food mixture (chyme) enters the small intestines from the stomach The chyme meets with bile and pancreatic enzymes Bile is a basic salt that breaks down fat into small droplets (emulsification) The emulsified fat has more surface area for the lipase to work Bile also neutralizes the acidic chyme that comes from the acidic environment of the stomach Other enzymes such as amylase and protease break down starches and proteins

14. 6.1.5 Outline the function of the stomach, small intestines and large intestines Absorption The structure of the small intestines are folded and made up of many small finger-like projections called villi. Both structures help to greatly increase the surface area of the small intestines. The products of digestion (amino acids, monosaccharaides, fatty acids, glycerol, vitamins and minerals) are absorbed across the layer of epithelial cells into the blood stream. The epithelial cells have microvilli to further increase surface area. The products of digestion need to be actively transported across the membrane (requires energy – ATP)

15. 6.1.5 Outline the function of the stomach, small intestines and large intestines Large Intestines Its main function is absorption of liquids and minerals The structure of the large intestines does not contain villi, but has many folds to increase surface area When the food byproducts have reached the large intestines, most of the useful material has been absorbed

16. 6.1.5 Outline the function of the stomach, small intestines and large intestines What remains is indigestible material, dead intestinal cells, bacteria, glucose, salts, minerals and many liters of water The water, glucose and salts are vital and are absorbed back into the body What remains is the feces which is egested from the body. 50% of the feces is composed of bacteria Salt and glucose is actively transported across the membrane and water follows by osmosis

17. 6.1.6 Distinguish between absorption and assimilation Absorption – taking the byproducts of digestion across the membrane of the small intestines or large intestines into the blood or the lacteals Assimilation – using the byproducts of digestion for different functions in the organism (energy, building blocks)

18. 6.1.7 Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion The structural adaptations include: 1.Villi and microvilli to increase surface area 2.One-cell thick epithelial layer for a short diffusion pathway 3.Rich blood supply to quickly carry away products of digestion and maintain concentration gradient 4.Lacteals to absorb and transport lipids

19. 6.1.7 Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion Absorption The small intestine’s main purpose is the absorption of the products of digestion It is very efficient due to its large surface area The surface area is enhanced by: a.folds in the small intestines (ileum) - SA increased 3X b.Villi are one-cell thick for easy absorption and transport – SA increased 10X c.micro villi – SA increased 10X This allows for greater absorption

20. 6.1.7 Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion Transport Inside the villi are networks of capillaries that will transport the products of digestion to different parts of the body Lacteals (or lymph vessels) are responsible for transporting lipids It is also important that the capillaries carry the products away from the site of absorption in order to maintain concentration gradients

21. Watch this to see if you understand everything.