1. Digestive System

2. 6.1 Digestive Functions
The food we eat is a combination of a huge assortment of molecules
Our system Breaks these molecules down via physical and chemical digestive processes to obtain forms that can be absorbed and used in our body
The parts that can not be used are released

3. The digestive functions are:
Ingestion
Physical and chemical digestion
Absorption
Defecation

4. 6.2 Digestive Structures
Imagine the digestive system as a long tube (around 7 m long) contained within the body
Food enters one end, the mouth, is processed throughout its length; nutrients absorbed, and wastes are released from the other end, the anus

5. Much of the treatment that food is exposed to comes from the specializations of this tube, the alimentary canal (gastrointestinal tract)
Its muscular walls control the movement of materials through it; glands along its walls release water, enzymes, and some hormones; specialized structures absorb nutrients

6. The pancreas and the liver are attached to the alimentary canal and produce secretions that are used in the digestive process
Both of these secretions enter at the duodenum

7. Pancreas The pancreas is located behind the stomach
It is specialized both as an endocrine and exocrine gland

8. It is an endocrine gland because it produces and secretes the hormones insulin and glucagon from cells called islets of Langerhans into the blood stream
Insulin lowers blood sugar levels by increasing cell’s ability to use it and promoting its storage in the form of glycogen by the liver

9. Glucagon allows the liver to release glucose from glycogen when blood sugar levels drop
Together, these hormones help regulate the blood’s level of glucose

10. The pancreas is an exocrine gland because it produces the digestive juice called pancreatic juice, which it releases to the duodenum through the pancreatic duct
Pancreatic juice is a combination of water, sodium bicarbonate, lipase, trypsinogen (which becomes trypsin), nucleases, and pancreatic amylase

11. Liver The liver is the bodies largest internal organ
It is located behind the diaphragm
The liver is richly supplied with blood, and has the following functions:

12. 1) Regulate the glucose level in blood
Glucose should comprise about 0.1% of blood plasma
If the level is too high, glucose will be converted to and stored as glycogen by the liver
If it is too low, glycogen breaks down into glucose

13. 2) Produce urea
Body cells produce ammonia, a toxic by-product from the metabolism of amino acids and nucleotides
It is transported though blood to the liver where it is converted into, the less toxic, urea
Urea is removed from the blood by the kidneys during urine formation

14. 3) Detoxify blood
The liver destroys other toxins in the blood (like alcohol)
The liver metabolizes alcohol into fatty acids, which increases the fatty nature of liver tissue
Removes and stores fat-soluble vitamins, which have toxic effects on cells when in high concentrations

15. 4) Produce bile
Bile is stored in the gall bladder until a hormone signals its release
Bile emulsifies fat clusters into smaller pieces
This increases their surface area, increasing the efficiency of the lipase enzyme, which chemically breaks them down into fatty acids and glycerol

16. 5) Produce blood proteins (globulins)
Albumin (helps maintain osmotic pressure)
Fibrinogen
Prothrombin (needed for blood clotting)

17. 6) Destroy old red blood cells
RBC have an average life span of 4 months (millions die every day)
The liver disassembles the dead RBC and recycles the useful components
For example, iron from hemoglobin is returned to bone marrow for the manufacture of new RBC; the rest of the hemoglobin is worn out and added to bile to be excreted through the digestive system

18. Review The function of the gall bladder is to Store bile
Synthesize lipids
Produce enzymes
Stimulate the release of pancreatic juice

19. Review The function of the gall bladder is to Store bile
Synthesize lipids
Produce enzymes
Stimulate the release of pancreatic juice

20. Glucose is stored in the liver as
Fat
Starch
Protein
Glycogen

21. Glucose is stored in the liver as
Fat
Starch
Protein
Glycogen

22. The release of insulin is triggered by
Low levels of blood sugar
High levels of blood sugar
Low amounts of sugar in one’s diet
High amounts of sugar in one’s diet

23. The release of insulin is triggered by
Low levels of blood sugar
High levels of blood sugar
Low amounts of sugar in one’s diet
High amounts of sugar in one’s diet

24. One function of the liver is the production of
Urea
Lipase
Mucus
Hydrochloric acid

25. One function of the liver is the production of
Urea
Lipase
Mucus
Hydrochloric acid

26. Which of the following pancreatic secretions doesn’t enter the duodenum?
Insulin
Lipase
Trypsin
Bicarbonate ions

27. Which of the following pancreatic secretions doesn’t enter the duodenum?
Insulin
Lipase
Trypsin
Bicarbonate ions

28. Processes of Digestion
Mouth
Stomach
Small intestines
Colon (Large intestines)

29. 6.3 Mouth
First, food is chewed up (physical digestion), increasing the surface area so that chemical digestion can take place faster.
Salivary glands release saliva (water and salivary amylase, also known as ptyalin) through ducts into the mouth
Water is used as a lubricant to aid in swallowing food and as a reactant in hydrolytic reactions that occur during digestion

30. Salivary amylase (or ptyalin) breaks the bonds between the sugar molecules of starch to begin its chemical conversion to maltose

31. The tongue is a muscle that rolls chewed food into lumps (bolus) and pushes them to the back of the mouth for swallowing
Swallowing is a reflexive action resulting from contractions of the two layers of smooth muscles that line the pharynx and esophagus

32. The pharynx is a common passageway for both food and air
In order to prevent food materials from going down the trachea, the epiglottis covers it

33. The muscle contractions called peristalsis move each bolus down the esophagus
There is a constriction called the cardiac sphincter at the base of the esophagus that must relax and open before the food materials can enter the stomach

34. 6.4 Stomach
The stomach is a large J-shaped organ with walls that have three layers of muscle that churn food material , causing the release of gastrin (a hormone that travels from the cells of the stomach walls into the blood stream
As gastrin circulates the body, it affects the stomach and causes the release of gastric juices

35. Gastric juice contains water as well as HCl and pepsinogen
At this point the bolus becomes known as acid chyme (runny)
The HCl creates an environment with a low pH to kill any bacterial growth that may be in the food and reacts with pepsinogen, converting it to pepsin (which converts proteins into polypeptides)

36. Pepsin is secreted as pepsinogen because a cell would not survive the production of it in its active form
The inner walls of the stomach also produce mucus to protect themselves from the acid chyme
Bacterial infection of the mucosal lining by Helicobacter pylori can lead to an ulcer

37. Review
Which of the following digestive enzymes is NOT correctly matched with its substrate?
Lipase – fat
Pepsin – protein
Trypsin – nucleic acid
Salivary amylase - starch

38. Review
Which of the following digestive enzymes is NOT correctly matched with its substrate?
Lipase – fat
Pepsin – protein
Trypsin – nucleic acid
Salivary amylase - starch

39. The part of the digestive tract where starch first undergoes chemical digestion is the
Mouth
Stomach
Small intestine
Large intestine

40. The part of the digestive tract where starch first undergoes chemical digestion is the
Mouth
Stomach
Small intestine
Large intestine

41. When salivary amylase enters the stomach, it becomes
Basic
Acidic
Buffered
denatured

42. When salivary amylase enters the stomach, it becomes
Basic
Acidic
Buffered
denatured

43. Which region has openings for both the trachea and esophagus?
Throat
Pharynx
Stomach
epiglottis

44. Which region has openings for both the trachea and esophagus?
Throat
Pharynx
Stomach
epiglottis

45. Which of the following correctly matches a digestive enzyme with its source?
Pepsin – pancreas
Bile – gall bladder
Trypsin – stomach
Amylase - pancreas

46. Which of the following correctly matches a digestive enzyme with its source?
Pepsin – pancreas
Bile – gall bladder
Trypsin – stomach
Amylase - pancreas

47. 6.5 Small Intestines
The pyloric sphincter is similar to the cardiac sphincter, except it is located at the posterior of the stomach where it controls the passage of the liquid acid chyme into the duodenum (the first part of the small intestines)
The duodenum is specialized by the presence of chemoreceptors (chemical sensitive nerve endings that are able to detect the different biochemicals in the food material), that regulate which secretions are released

48. When signaled to, the gall bladder releases the fat emulsifier bile and the pancreas releases pancreatic juice
The biocarbonate ions (HCO3-) “over-neutralize” the acid chyme and buffer it at a pH of about 8.3
The enzymatic components of pancreatic juice are active at this alkaline pH

49. Lipase converts emulsified lipids into fatty acids and glycerol
Trypsin breaks many peptide bonds to convert various lengths of polypeptides into shorter peptide units
Pancreatic amylase breaks remaining starch into maltose
Nuclease converts some of the nucleic acids into nucleotides and nucleotidases (which break nucleotides into their component molecules)

50. All of these enzymes are active in the duodenum
The duodenum also produce and secrete its own enzymes
Disaccharidases (maltase and lactase)
Peptidase (to break remaining polypeptides into amino acids)
nuclease

51. The longest part of the small intestines is called the ileum (absorbs the products of digestion)
It has a large surface area and is lined with specialized structures for absorption by active trasnport
These structures are called villi

52. The epithelial cells lining the villi are equipped with mitochondria to produce the required ATP
Internally, each villus has a capillary bed and a lacteal (an absorptive end of the lymphatic system)
The products of fat digestion are reconstructed into neutral fats by the epithelial cells before they enter the lacteals, the rest of the products of digestion enter the blood stream

54. 6.6 Colon
The undigested food move from the ileum through the ileo-caecal valve (another sphincter) to the large intestine (colon)
The first segment of the colon is the caecum, then the appendix (a vestigial structure)

56. The major roles of the colon are to absorb a great amount of the water and store E. coli
E. coli is a bacterium that metabolizes some of what our body cannot (waste material)
Their metabolism releases minerals and manufactures some vitamins and
amino acids

57. These nutrients (from E
These nutrients (from E. coli) get absorbed along with water into the circulatory system
The bacteria begin the decomposition of the waste materials and convert them to feces with a changed color, smell, and texture

58. The last part of the colon is the rectum that stores feces until defecation
It ends with the anal sphincter, which controls defecation

59. Review The bacterium E. coli is normally abundant in Food Feces
Bile salts
Stomach juices

60. Review The bacterium E. coli is normally abundant in Food Feces
Bile salts
Stomach juices

61. Which of the following is absorbed into lacteals?
Glucose
Fatty acids
Nucleotides
Amino acids

62. Which of the following is absorbed into lacteals?
Glucose
Fatty acids
Nucleotides
Amino acids

63. Which digestive organ is the appendix attached to?
The stomach
The gall bladder
The large intestine
The small intestine

64. Which digestive organ is the appendix attached to?
The stomach
The gall bladder
The large intestine
The small intestine

65. The removal of a large section of the colon is likely to affect the
Release of bile
Digestion of fats
Absorption of glucose
Water balance in the body

66. The removal of a large section of the colon is likely to affect the
Release of bile
Digestion of fats
Absorption of glucose
Water balance in the body

67. Which of the following structures does NOT produce digestive enzymes?
Stomach
Pancreas
Small intestine
Large intestine

68. Which of the following structures does NOT produce digestive enzymes?
Stomach
Pancreas
Small intestine
Large intestine