1. Human Biology (BIOL 104) Talk Five: Digestion and Nutrition
Animal Nutrition and the Digestive System (Chapter 25)

2. (credit: Keith Weller, USDA ARS)
A balanced meal
There are three main food groupings to consider:
Carbohydrates
Proteins
Fats
Each of these are important and healthy in the correct proportions.
Carbohydrates provide energy – but we need the correct ones – remember fructose? To much of this induces fat production
Proteins 20 amino acids to make protein
12 amino acids humans can produce
8 we have to eat = “essential amino acids”
Copyright: OpenStax Biology for AP Courses, OpenStax, and Rice University
(credit: Keith Weller, USDA ARS)

3. (credit: Keith Weller, USDA ARS)
A balanced meal
It is harder to have all of theses eight essential amino acids if you are on a vegetarian or vegan diet
Fats are required in correct proportions for many roles in the human body, such as general protection of the internal organs, insolation, and nerve fibers.
Thoughts:
Malnutrition – what does it really mean?
Why are we not eating correctly?
what does time and economics have to do with basic human health?
Copyright: OpenStax Biology for AP Courses, OpenStax, and Rice University
(credit: Keith Weller, USDA ARS)

4. So, how do we digest food?
In the human digestive system, the process of digestion has many stages, the first of which starts in the mouth (oral cavity).
Digestion involves the breakdown of food into smaller and smaller components which can be absorbed and assimilated into the body.
The secretion of saliva helps to produce a bolus which can be swallowed in the esophagus to pass down into the stomach.
This initially results in the production of chyme which when fully broken down in the small intestine is absorbed into the blood.
Most of the digestion of food takes place in the small intestine. Water and some minerals are reabsorbed back into the blood, in the colon of the large intestine.
The waste products of digestion are defecated from the anus via the rectum.

5. Digestion occurs in 5 stages
1: Mechanical processing and motility
Teeth, the tongue, and various muscle layers start the process and send food on its journey
2: Secretion
Release of enzymes & chemicals for digestion and absorption
3: Digestion
Chemical breakdown of food – small molecules absorbed
4: Absorption
Nutrients move into the blood
5: Elimination
Undigested and unabsorbed residues excreted
Copyright: OpenStax Biology for AP Courses, OpenStax, and Rice University

6. The first step- Chewing and swallowing
Types
Mechanical (physical)
Chew
Tear
Grind
Mash
Mix
Chemical
Enzymatic reactions to improve digestion of
Carbohydrates
Proteins
Lipids
Copyright: OpenStax Biology for AP Courses, OpenStax, and Rice University

7. The first step- Chewing and swallowing
Teeth mechanically break down food into small pieces.
Tongue mixes food with saliva
Saliva contains amylase
helps break down starch.
Mucus
protects soft lining of digestive system
lubricates food for easier swallowing
Buffers
neutralizes acid to prevent tooth decay
Anti-bacterial chemicals
kill bacteria that enter mouth with food
Epiglottis is a flap-like structure at the back of the throat that closes over the trachea preventing food from entering it.
Copyright: OpenStax Biology for AP Courses, OpenStax, and Rice University

8. Taste Buds
As the food particles dissolve in the saliva they penetrate the cells of the taste buds located on the tongue and cheeks.
Humans can differentiate between
sweet
sour
salty
bitter
Copyright: OpenStax Biology for AP Courses, OpenStax, and Rice University

9. The Esophagus Approximately 10” long Functions include: Secrete mucus
Moves food from the throat to the stomach using muscle movement called peristalsis
A good way to describe peristalsis is an ocean wave moving through the muscle.
Has no role in chemical digestion – all it does is bring food (BOLUS) to stomach.
Sphincters – ring of muscle that encircle tubes.
Contraction closes tubes
Keeps acid in stomach – usually!
These diagrams don’t separate the esophagus from the mouth functions, you might want to talk about what happens in the mouth too.
Copyright: OpenStax Biology for AP Courses, OpenStax, and Rice University

10. The Stomach- Digestion and Storage
The stomach acts as a temporary storage site for food.
Food usually spends about 4 hours in the stomach.
It has ridges which allow it to expand to store about 1.5 litres of food.
The stomach is also the site of initial protein digestion.
From the wikimedia free licensed media file repository

11. The Stomach- Digestion and Storage
Millions of cells lining the stomach secrete various fluids known collectively as gastric fluids.
Gastric fluid consists of mucus, hydrochloric acid, pepsinogens and other substances.
Mucus coats and protects the lining of the stomach.
Hydrochloric acid kills any harmful substances that have been ingested and it also converts pepsinogen into pepsin.
Pepsin is a protein digesting enzyme that breaks large protein chains into smaller chains.
From the wikimedia free licensed media file repository

12. The Stomach- Digestion and Storage
Movement of food into and out of the stomach is controlled by circular muscles known as sphincters.
One at the top of the stomach allows food from the esophagus to enter and prevents food from going back up into the esophagus.
Another located at the bottom slowly releases partially digested food into the small intestine.
Alcohol and some water are absorbed here – food is not.
The partially digested food is called chyme.
From the wikimedia free licensed media file repository

13. Copyright: OpenStax Biology for AP Courses, OpenStax, and Rice University
The Intestines
The intestines are named for their diameter, not length.
The small intestine is up to 7 m in length but only 2.5 cm in diameter.
The large intestine (also known as the Colon) is only 1.5 m in length but 7.6 cm in diameter.

14. The small intestine
Copyright: OpenStax Biology for AP Courses, OpenStax, and Rice University
Where much of the digestion and absorption of food takes place.
It receives bile juice and pancreatic juice through the hepato-pancreatic duct, controlled by a sphincter
The small intestine is where most chemical digestion takes place.
Most of the digestive enzymes that act in the small intestine are secreted by the pancreas and enter the small intestine via the pancreatic duct

15. The small intestine Approx 20 feet in length
First 25 cm – Duodenum
A duct brings Bile (from Liver and Gallbladder)
emulsifies fat – disperses in water
A duct brings Pancreatic Juice from Pancreas. Contains
NaCHO3 – neutralizes chyme
enzymes to complete food digestion.
The small intestine contains Villi –absorb nutrients.
Sugars & amino acids enter blood capillaries
Glycerol and fatty acids enter lymph nodules
Almost 90% of our daily fluid intake is absorbed in the small intestine.
Copyright: OpenStax Biology for AP Courses, OpenStax, and Rice University

16. Small Intestine
Copyright: OpenStax Biology for AP Courses, OpenStax, and Rice University
Nutrients from the food pass into the bloodstream through the small intestine walls.
Absorbs:
80% ingested water
Vitamins
Minerals
Carbohydrates
Proteins
Lipids
Secretes digestive enzymes

17. Segmentation in the Small Intestine
Unlike peristalsis, which predominates in the esophagus, segmentation contractions occur in the large intestine and small intestine, while predominating in the latter
When the contractions of the intestinal wall move chyme in both directions to allow mixing with the secretions of the intestines.
From the wikimedia free licensed media file repository

18. The small intestine - Villi
Increases surface area of small intestine
Each villus contains a capillary network along with a lacteal.
The lacteal is a vessel of the lymphatic system.
End products of protein and carbohydrate digestion enter the capillary network.
End products of fat digestion are absorbed into the lacteal.
Copyright: OpenStax Biology for AP Courses, OpenStax, and Rice University

19. The small intestine - Villi
The Hepatic Portal Vein takes all absorbed nutrients (except large fat molecules) from villi to the liver for further processing and storage.

20. The large Intestine 4-1/2 feet long
Absorbs water, salts and some vitamins
Stores indigestible material for defecation
Contains the:
Cecum (blind end of ascending colon).
Appendix located here.
Colon- Ascending, Transverse, Descending and Sigmoid.
The sigmoid Colon enters Rectum (last 20 cm of large intestine, where it opens at the Anus.
Feces: ¾ water and ¼ solid
Copyright: OpenStax Biology for AP Courses, OpenStax, and Rice University

21. The large Intestine Functions Bacterial digestion
Ferment carbohydrates
Protein breakdown
Absorbs more water
Concentrate wastes
Solid materials pass through the large intestine.
These are undigestible solids (fibers).
Water is absorbed.
Vitamins K and B are reabsorbed with the water.
Rectum- solid wastes exit the body.
Copyright: OpenStax Biology for AP Courses, OpenStax, and Rice University

22. The large Intestine – You’ve got company!
Living in the large intestine is a community of helpful bacteria
Escherichia coli (E. coli)
produce vitamins
vitamin K; B vitamins
generate gases
by-product of bacterial metabolism
methane, hydrogen sulfide

23. The Accessory Organs The liver
Copyright: OpenStax Biology for AP Courses, OpenStax, and Rice University
The liver
The largest internal organ in humans and it plays a very important role in digestion of fats and detoxifying blood.
Produces bile, a digestive juice that is required for the breakdown of fatty components of the food in the duodenum.
The liver also processes the vitamins and fats and synthesizes many plasma proteins.
From digestion, vitamin A, D, E, and K are stored here.
iron from the breakdown of red blood cells also stored

24. The pancreas secretes digestive juices
The pancreas secretes digestive juices. The chyme produced from the stomach is highly acidic in nature; the pancreatic juices contain high levels of bicarbonate, an alkali that neutralizes the acidic chyme.
Additionally, the pancreatic juices contain a large variety of enzymes that are required for the digestion of protein and
carbohydrates.
The gallbladder is a small organ that aids the liver by storing bile and concentrating bile salts.
When chyme containing fatty acids enters the duodenum, the bile is secreted from the gallbladder into the duodenum.
The Accessory Organs
Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2).

25. From the wikimedia free licensed media file repository
Human Nutrition
The provision to obtain the essential nutrients necessary to support life and health.
In general, people can survive for two to eight weeks without food, depending on stored body fat and muscle mass.
Poor nutrition is a chronic problem linked to poverty, poor nutrition understanding and practices, and deficient sanitation and food security.
From the wikimedia free licensed media file repository

26. From the wikimedia free licensed media file repository
Human Nutrition
Malnutrition globally provides many challenges to individuals and societies.
Lack of proper nutrition contributes to worse class performance, lower test scores, and eventually less successful students and a less productive and competitive economy.
Malnutrition and its consequences are immense contributors to deaths and disabilities worldwide.
Promoting good nutrition helps children grow, promotes human development and advances economic growth and eradication of poverty.
From the wikimedia free licensed media file repository

27. From the wikimedia free licensed media file repository
Vegetarian diets
Need to make sure you get enough protein
20 amino acids to make protein
12 amino acids humans can produce
8 we have to eat = “essential amino acids”
Grains (like corn) have 6 amino acids (orange box)
missing 2
Beans (like soybean & red beans) have 6 amino acids (green box)
missing different 2
mix beans & grains for complete group of amino acids
rice & beans
taco/tortilla & beans
tofu & rice
peanut butter & bread
From the wikimedia free licensed media file repository

28. Vegetarian diets
By Stephreyn85 - Own work, CC BY-SA 3.0,

29. Vitamins
Organic compounds needed by the body in small, but essential amounts
Cannot be synthesized by the body in sufficient amounts
Function in a variety of ways in metabolic reactions
Thirteen known vitamins
Water-Soluble Vitamins Versus Fat-soluble Vitamins

30. Water-Soluble Vitamins
Pantothenic acid
Biotin
B12 (cyanocobalamin)
Folic acid
B6 (pyridoxine)
C (ascorbic acid)
B1 (thiamin)
B2 (riboflavin)
Niacin

31. Copyright ©The McGraw-Hill Companies; used with permission
Fat-soluble Vitamins
Copyright ©The McGraw-Hill Companies; used with permission

32. Vitamins Vit A- Antioxidant: healthy eyes, hair, bones
Vit D – Steroid: bones and teeth
Vit E – Antioxidant: healthy unsaturated fats
Vit K – Clotting blood
Vit C – Antioxidant: Capillaries, bones teeth
Vit B1 – coenzyme for cellular respiration
Vit B6 – coenzyme for hormones and hemoglobin
Vit B12 – coenzyme for synthesis of nucleic acid
Biotin – coenzyme for metabolism of ammino acids and fatty acids

33. From the wikimedia free licensed media file repository
Minerals
Essential inorganic elements
Involved in a variety of metabolic processes
Major minerals versus trace minerals
From the wikimedia free licensed media file repository

34. Essential dietary minerals
Chlorine: as chloride ions along with Sodium
Magnesium: required for processing ATP and related reactions
builds bone, causes strong peristalsis, increases flexibility, increases alkalinity.
Phosphorus: required component of bones; essential for energy processing Approximately 80% is found in inorganic portion of bones and teeth. Phosphorus is a component of every cell, as well as important metabolites, including DNA, RNA, ATP, and phospholipids.
Also important in pH regulation. Food sources include cheese, egg yolk, milk, meat, fish, poultry, whole-grain cereals, and many others.
Potassium: a very common electrolyte (heart and nerve health). With sodium, potassium is involved in maintaining normal water balance, osmotic equilibrium, and acid-base balance.
In addition to calcium, it is important in the regulation of neuromuscular activity. Food sources include bananas, avocados, vegetables, potatoes, legumes, and mushrooms.

35. Trace minerals
Cobalt required for biosynthesis of vitamin B12 family of coenzymes
Copper required component of many redox enzymes, including cytochrome c oxidase
Chromium required for sugar metabolism
Iodine required for important organs as breast, stomach, salivary glands, thymus etc.
Iron required for many enzymes, and for hemoglobin and some other proteins
Manganese required for the processing of oxygen
Nickel present in urease
Zinc required for several enzymes such as carboxypeptidase, liver alcohol dehydrogenase, carbonic anhydrase

36. The End!