2. Chapter 6: Nutrition in Humans

3. Digestion The apple is too complex for your body to absorb directly.
It needs to be digested first.
Digestion is the physical and chemical breaking up of food into smaller components.

4. Physical Digestion
Physical digestion: mechanical break-up of food into smaller particles.
Achieved through
Chewing action of the teeth and tongue
Churning action in the stomach
What is the purpose?
Increases surface area to volume ratio so that digestive enzymes can act on food more efficiently.

5. Chemical Digestion
Chemical digestion: break-up of large molecules in food into smaller soluble molecules which can be absorbed.
Achieved through
Digestive enzymes in digestive system
Eg. Starch Maltose
What is the purpose?
To get smaller soluble molecules which the body can absorbed.
Amylase

6. Digestion
What will be the consequences if a dog swallow a whole hot dog without chewing? The hot dog will not be digested completely even when it is goes through the dog’s digestive system.
You may find traces of the hot dog in the dog’s fecaes.

7. Passage of food 1. Mouth 2. Oesophagus 3. Stomach 4. Small Intestine
5. Large Intestine
6. Anus

8. Mouth and buccal cavity
Ingestion is the taking in of food into the body through the mouth
Mastication or chewing is the process by which food is crushed and ground by teeth.

9. Mouth and buccal cavity
Purposes of chewing
Reduced food sizes for swallowing
Increases surface area for enzymes to work on
Chewing stimulates salivary glands to secrete saliva
Saliva contains salivary amylase
Salivary amylase digests starch to maltose
Digestion is the process of breaking down complex insoluble food substances into simple soluble food substances.

10. Pharynx Air Pharynx Epiglottis Oesophagus Glottis Larynx
During swallowing, the larynx is raised and the glottis is covered by the epiglottis.
During breathing, the larynx is lowered and the glottis is open.

11. Question- Can we eat food upside down?
Yes, the muscles in our body push the food to where it should go.
Yes, but we cannot drink upside down.
No, gravity will pull the food out.
Dick
Harry
Tom

12. Answer - Can we eat food upside down?
Muth
Answer - Can we eat food upside down?
Video as proof:
Yes, Dick is correct - we can eat and drink upside down!!
Peristalsis is the rhythmic contraction of smooth muscles to propel contents through the digestive tract

13. Muth
Oesophagus
1. Mouth
2. Oesphagus
Oesophagus - Organ which consists of a muscular tube through which food passes from the pharynx to the stomach

14. Muth Oesophagus Peristalsis in oesophagus Longitudinal muscles
Wall here dilates
Circular muscles
Wall here constricts (circular muscles contract and longitudinal muscles relax)
Circular muscles relax
Longitudinal muscles constract

15. Digestion of different food
Muth
Digestion of different food
Region of digestion
Secretion
Source
Enzyme
Action
Mouth
Saliva
Salivary glands
Salivary amylase
Starch to maltose
Stomach
Gastric juice
Gastric glands
Pepsin
Proteins to polypeptides
Rennin
caseinogen to casein

16. Digestion of different food
Small intestine
Bile
Liver -
Bile salts emulsify (NOT chemically digest) fats
Pancreatic juice
pancreas
Amylase
Starch to maltose
Trypsin
Proteins to polypeptides
Lipase
Fats to fatty acids and glycerol
Intestinal juice
Intestinal glands
Enterokinase
Trypsinogen to trypsin
Maltase
Maltose to glucose
Lactase
Lactose to glucose and galactose
Surcase
Sucrose to glucose and fructose
Erepsin
Polypeptides to amino acids

17. Muth Summary Ingestion Mastication Digestion Peristalsis 1. Mouth
2. Oesophagus
3. Stomach
4. Small Intestine
5. Large Intestine
6. Anus

18. Muth
Absorption
Products of digestion are absorbed throughout the small intestine.
Epithelium
Lacteal
Blood capillaries
Highly magnified epithelial cell
fold
To liver
Microvilli
Circular muscles
Small intestine with portions cut off to show folds and villi
Longitudinal muscles
Magnified section of a villi

19. Absorption
Jejunum
Q. How is the small intestine adapted for absorption of digested food substances?
Large surface area.
Inner walls have numerous folds.
Inner walls have villi – small finger-like projections.
Microvilli found on villi.
Thin walls for digested food substances to diffuse through (epithelium is only one cell thick)
Lacteal transport fats and blood capillaries transport sugars and amino acids away from intestine to maintain concentration gradient for absorption.
Ileum

20. Absorption Q. How does absorption take place in the intestines?
Sugars and amino acids diffuse or actively transported into blood capillaries
Glycerol and fatty acids diffuse into epithelium where they combine to form minute fat globules which enter the lacteals.
Water enters by osmosis
Water is mainly absorbed in ileum, partly in colon.
Mineral salts either diffuse or are actively transported into blood capillaries in ileum and colon

21. Absorption
Q. What is the difference between active transport and diffusion?
Active transport uses energy from respiration to transport substances against a concentration gradient, BUT diffusion is an energy-free process as transport of substances is down a concentration gradient.

22. Undigested and unabsorbed food
Q. What happens to undigested and unabsorbed food?
The undigested and unabsorbed matter is stored temporarily in rectum before it is discharged as faeces through the anus.
Egestion or defecation is the process of removing undigested food from the body.
Rectum
Anus

23. Inv 6.1 – How are carbohydrates absorbed?
Visking tubing represents the small intestine epithelial.
Distilled water represents the blood which carries away absorbed food substances away from intestine.
Expected result is that starch will remain in the visking tubing as the starch molecules are too big.
Glucose will diffuse through the visking tubing into the distilled water due to presence of concentration gradient.
Cotton thread
Visking tubing
Boiling tube
Solution of starch and glucose
Distilled water

24. Summary Questions
Q1. Mastication of food takes place in the buccal cavity. T/F
Q2. Chewing stimulates the salivary glands to release salivary maltase. T/F
Q3. Starch is the only food substance that is digested in the mouth. T/F
Q4. Peristalsis is the rhythmic, wave-like contractions of the gut walls. It only take place along the oesophagus. T/F
Q5. Bile contains lipase for the digestion of fats. T/F
Q6. The abundant blood capillaries found in the small intestine transport away glucose, starch, amino acids and water away from the small intestine. T/F
Q7. Most of the water in our body is absorbed along the large intestine. T/F

25. Transport and utilization of sugars
What happens to glucose and amino acids absorbed in the small intestine?
Carried by blood to the liver through the hepatic portal vein.
Then carried by blood away from the liver to other parts of the body when glucose and amino acids are needed through the hepatic vein.
Excess glucose is converted by liver and stored as glycogen.
Excess amino acids are deaminated.
Hepatic artery
Hepatic vein
Liver
Hepatic portal vein
Mainly sugars and amino acids
Blood capillaries
Small intestine

26. Functions of Liver 1. Regulation of blood glucose concentration
2. Production of bile
3. Iron storage
4. Protein synthesis
5.Deamination of amino acids
6. Detoxification

27. Functions of Liver 1. Regulation of blood glucose concentration
2. Production of bile
3. Iron storage
4. Protein synthesis
5.Deamination of amino acids
6. Detoxification

28. Functions of Liver 1. Regulation of blood glucose concentration
2. Production of bile
3. Iron storage
4. Protein synthesis
5.Deamination of amino acids
6. Detoxification
Note that gall bladder stores bile but does not produce bile.

29. Functions of Liver Spleen RBC is destroyed where Brought to
Haemoglobin transported to
1. Regulation of blood glucose concentration
2. Production of bile
3. Iron storage
4. Protein synthesis
5.Deamination of amino acids
6. Detoxification
Haemoglobin is broken down in liver and iron released is stored.

30. Functions of Liver Amino group Carbon residue An amino acid
Ammonium ion R
1. Regulation of blood glucose concentration
2. Production of bile
3. Iron storage
4. Protein synthesis
5.Deamination of amino acids
6. Detoxification
NH2 – CH - COOH
Amino group
Carbon residue
Ammonia (toxic)
Glucose
Urea (non-toxic)
Glycogen

31. Functions of Liver
This process of converting harmful substances into harmless ones is called detoxification.
Harmful substances include benzoic acid
and picric acid.
Liver also contains an enzyme (alcohol dehydrogenase) to break down alcohol.
Excess alcohol consumption may lead to gastric ulcers and cirrhosis.
1. Regulation of blood glucose concentration
2. Production of bile
3. Iron storage
4. Protein synthesis
5.Deamination of amino acids
6. Detoxification