1. The Digestive System

2. Overview of Digestion
Digestion is the mechanical and chemical breakdown of the foods we eat. We breakdown food mechanically with our teeth, and chemically with saliva and stomach acid. We do this so that we can alter this food so we can then absorb it through cell membranes.
nutrients and water=passable through a cell membrane.
A cheeseburger= not passable through a cell membrane.

4. Alimentary Canals
Consists of the mouth, pharynx, esophagus, stomach, small intestines, large intestines, and the anal canal. Also includes the salivary glands, liver, gallbladder, and pancreas.

5. Characteristics of the alimentary canals
Contains four distinct layers:
Mucosa
Submucosa
Muscular layer
Serosa

6. Mucosa
Contains some epithelial tissue on surface, underlying connective tissue, and in some regions, smooth muscle. Some areas develop folds that extend into lumens (passageways). More folds= more area for absorption.
May contain glands that secrete mucus and digestive enzymes.
Mucus is designed to protect the cells underneath it.

7. Submucosa
Contains loose connective tissue, blood vessels, lymph vessels and nerve tissues called a plexus.
plexus= network.

8. Muscular layer
Muscles are designed for movement, so the muscular layer is designed to move the tubes of the alimentary canals.
Two coats (layers) of smooth muscle and nerve tissues that form a nerve plexus.
Circular fibers- inner coat that causes the diameter of a tube to contract (gets smaller).
Longitudinal fibers- outer coat that cause a tube to shorten.

9. Serosa
Contains the visceral peritoneum (meaning that the serous membrane covers the organs).
Designed to protect other tissues, and make serous fluid for moistening and lubricating the organs.

10. Movement in the tubes
Two types:
Mixing
Propelling

11. Mixing
Smooth muscle moves rhythmically.
i.e. in the stomach.

12. Propelling
Peristalsis: works by causing a contraction of smooth muscle behind object being moved and the smooth muscle ahead of the object is relaxed. This motion propels objects forward throughout the digestive system.

13. Peristalsis

14. The mouth
The starting place of the digestive process. Undergoes mechanical (chewing) and chemical (adding saliva) breakdown.
Includes the mouth, lips, tongue, and palate.

15. The mouth: cheeks and lips
Cheeks: consist of the outer layers of skin. Contains subcutaneous fats (fat just below the skin) and muscles that are used in creating expressions. Inner layer of cheek (inside the mouth) consists of stratified squamous epithelium.

16. The mouth: lips
Highly mobile, surrounds the mouth. Contains skeletal muscle and sensory receptors to help judge texture and temperature.
Red lip color is due to lips having many blood vessels near the lip’s surface.

17. The mouth: tongue
Contains a membranous fold called the frenulum, that anchors the tongue to the floor of the mouth.
Mostly skeletal muscle. Contains rough bumps called papillae, which provide friction, letting the tongue manipulate and move food.
The hyoid bone is located at the base of the tongue. Contains lymphatic masses called lingual tonsils.

18. The mouth: palate
Roof of mouth. Hard palate located in anterior of palate. Soft palate located in the posterior of the palate. There is a muscular arch at the back of the mouth called the uvula. When we swallow, the uvula moves upward, closing the opening between the nasal cavity and the pharynx, stopping food from entering the nasal cavity.

19. The mouth: tonsils
Palantine tonsils: lymphatic tissue. Beneath the epithelial lining of the mouth. Contains lymphatic tissue.
Pharyngeal tonsils: Located above the border of the soft palate. Contains lymphatic tissue. A.k.a. adenoids

20. Slice and Dice!
When you have your tonsils removed, they are referring to removing the pharyngeal tonsils. When they swell, they block the passage of the pharynx to the nasal cavity.

21. The mouth: Teeth
In your lifetime, you will develop two sets of teeth. Primary (deciduous) teeth, and secondary (permanent teeth).
Primary teeth last from around age six months to four years. When the roots of the tooth are absorbed, the secondary teeth begin to dislodge the primary teeth from their sockets.
32 secondary teeth. (1 top row of 16, 1 bottom row of 16).

23. Function of teeth
Designed to break down food into smaller pieces mechanically.
Incisor- designed for ripping and tearing.
Cuspids- cone shaped, designed to tear at food.
Bicuspids and molars- somewhat flattened surfaces and designed to grind food.

24. Tooth anatomy Consists of two main parts:
Root= anchored to the alveolar process in the jaw.
Crown= the crown is the part of the tooth that we can see.
The place where the crown and root meet is called the “neck.”

25. (Please draw inside of tooth)

26. Salivary glands Contains serous cells and mucus cells.
Serous cells produce a watery like fluid that contains the digestive enzyme amylase.
(Amylose)

27. Mucus cells
The mucus cells form mucus that attaches to food when you chew and lubricates your food when you swallow.

28. Major salivary glands

29. Pharynx and esophagus
Connects the nasal and oral cavities with the larynx and esophagus. It comes in three parts:
Nasopharynx
Oropharynx
laryngopharynx

30. Nasopharynx- provides a passageway for air when breathing.
Oropharnyx- opens posterior to the soft palate into the nasopharynx. Passageway for food moving downward from the mouth.
Laryngopharynx- passageway to the esophagus.

31. Swallowing food In three stages:
Stage one: food is chewed and mixed with saliva, and formed into a bolus by the tongue.
Stage two: food stimulates receptor in pharyngeal opening. Triggers swallowing reflex.

32. (stage two continued)
1. the soft palate rises (so food doesn’t go up your nose.)
2. Hyoid and larynx are elevated. A flap called the epiglottis covers the trachea, preventing food from entering the lungs.
3. Tongue pushes against soft palate, sealing off oral cavity from pharynx.
4. The longitudinal muscles contract and pharyngeal wall contracts.
5. Muscles in the pharynx relax opening epiglottis.
6. A peristaltic wave begins in the pharyngeal muscles and forces food into the esophagus.

33. Stage three
Peristalsis transports food from epiglottis to the stomach.
(swallowing temporarily inhibits breathing so you do not inhale food while eating!)

34. Esophagus Straight collapsible tube around 25 centimeters long.
Food comes from the pharynx, down the esophagus to the stomach.
Some mucus glands are found in the submucosa of the esophagus. (creates a lubricant)
When peristaltic waves stop, the esophageal sphincter releases relaxes and lets food fall into the stomach.

35. The stomach
Hangs inferior to the diaphragm in the upper left portion of the abdomen. Has a capacity of roughly one liter of material. Can expand to accommodate some more material if needed.
What happens when the stomach gets too much food in it?

36. Reverse peristalsis

37. The stomach continued Little food is absorbed here.
Mechanical digestion occurs through the churning and folding the stomach does when food is in it.
Chemical digestion occurs when the food mixes with juices in the stomach.

38. The stomach The stomach is divided in four parts: Cardiac region
Fundic region
Body region
Pyloric canal

39. The stomach
At the end of the pyloric canal, a sphincter called the pyloric sphincter prevents stomach acids from going into the intestines.

40. Break it down!
In the stomach, there are many pits that are designed to be openings that let acids into the stomach, these are called the gastric glands.
Three types of gastric glands:
Mucous glands- make mucus for stomach lining.
Chief cells and parietal cells- form gastric juice .

41. The most important enzyme
Pepsin- the precursor to pepsin, pepsinogen, is secreted by chief cells in the stomach. When the pepsinogen comes in contact with HCl, which is created by the parietal cells, it changes into pepsin.
Pepsin can start breaking down almost any proteins you get in your diet.

42. Regulation of gastric secretions
Gastric juice is made constantly, but there are some triggers that can set off it’s production.
When you taste, see, or smell food, your body gives off a chemical called acytlcholine from nerve endings. Acytlcholine stimulates the gastric glands to produce more pepsinogen and HCl.

43. Stopping gastric juice production
When food enters the small intestines, the hormone cholecystokinin is released, which gives a signal to the gastric glands to halt their production of gastric juice.

44. Components of gastric juice
Pepsinogen- inactive form of pepsin
Pepsin- protein splitting enzyme that digests nearly all types of dietary proteins.
Hydrochloric acid- provides the acid environment needed to turn pepsinogen into pepsin.
Mucus- provides a high viscosity alkaline protective layer on the inside stomach wall.
Intrinsic factor- aids in vitamin B12 absorption.

45. Regulation of gastric secretions
Gastrin- hormone released from stomach, increases secretory activity of gastric glands.
Cholecytokinin- decreases gastric motility as small intestines fill.

46. What is absorbed in the stomach
When it comes to absorption, the stomach is not the place where the most of it occurs.
Only some water, small amounts of salts, fat soluble drugs, and alcohol are absorbed in the stomach.
Don’t give alcohol to
children.

47. Mixing and emptying
When food is mixed with stomach acid, our product is called chyme.
Peristalsis pushes the food to the pyloric sphincter, which then relaxes and allows food into the duodenum (first part of small intestines).

48. It is at this point that most of the secondary digestive organs, like the liver and pancreas, add their digestive juices to the mix to help further break down food.

49. Pancreas
In contact with the duodenum, this C-shaped organ secretes pancreatic juice which contains pancreatic amylase, pancreatic lipase (breaks down triglycerides), and nulease, which breaks down nucleic acids into nucleotides.

50. Liver
Located in the upper right corner of the abdominal cavity. Helps maintain proper glucose levels by breaking down carbohydrates.

51. Functions
Carbohydrate metabolism- polymerizes glucose to glycogen, breaks down glycogen into glucose, and converts noncarbohydrates to glucose.
Lipid metabolism- oxidizes fatty acids, synthesizes lipoproteins, phosolipids, and cholesterol.
Protein metabolism- deaminates amino acids; forms urea, converts one amino acid into another amino acid.

52. Storage- stores gylcogen, iron, and vitamin A, D, and B12.
Blood filtering- removing damaged RBCs and pathogens.
Detoxification secretion- removes toxins from blood, secretes bile.

53. Gallbladder
Pear shaped sac located inferior side of the liver’s surface.
The gallbladder is one storage spot for extra bile so that it can be used at a moments notice later on.

54. Regulating bile release
Bile doesn’t get released into the blood stream all willy-nilly. When cholecytokinin stimulates the gallbladder, the gallbladder contracts and releases bile into the duodenum.

55. The small intestine
Runs from the stomach to the large intestines. Long, with many folds inside of it, called villi.
Why do you think there are many folds in the small intestines? Why is the small intestines so long?

56. Parts of the small intestines
Duodenum- the beginning of the small intestines, which about 25 cm long and 5 cm wide. Anterior of right kidney.
Jejunum- middle of the small intestines.
Ileum- end of small intestines, empties into the large intestines.
Mesentery- suspends the small intestines from the posterior of the abdominal wall. The mesentery contains a plexus of nerves and blood vessels.

57. Inside the small intestines
As we stated earlier, there are a series of folds called villi that increase the surface area of the inside of the small intestines, further allowing more absorption of nutrients and water.

58. Intestinal villi
Found mostly in the duodenum and the proximal portion of the jejunum. Contains blood vessels and lymphatic capillaries called lacteal.
How can cancer in the small intestines affect the rest of the body?

59. Secretions of the small intestines
Peptidase- breaks down peptides into amino acids.
Sucrase, maltase, lactase- breaks down disaccharides into monosaccharides.
Lipase- Breaks down fatty acids and glycerol.
Enterokinase- converts tripsinogen into tripsin.

60. Movement in the small intestines
Like the stomach, the small intestines moves food through peristalsis.
At the end of the small intestines, there is a sphincter called the ileocecal sphincter which blocks off the end of the small intestines from the beginning of the large intestines.
In some cases a peristaltic rush may occur, pushing the materials from the small intestines into the large intestines, preventing the absorption of nutrients… guess what happens next…

62. The Large intestines
Named so because they have a larger diameter than the small intestines. About 1.5 meters long, starts at the ileocecal sphincter and ends at the rectal sphincter.
Made of four parts:
Cecum
Colon
Rectum
Anal canal

63. The cecum
Beginning of the large intestines. Has a dilated pouch-like structure that hangs just below the ileocecal sphincter.
Lateral to the cecum, the vermiform appendix can be found. It has no known digestive functions, but contains lymphatic tissues.

65. The colon The colon has four main parts: Ascending Descending
Transverse
Sigmoid

66. Before the rectum, but after the descending colon, the S-shaped bend in the intestines is called the sigmoid colon.

67. The rectum
Lies next to the sacrum, about 5 cm long, becomes the anal canal.

68. The anal canal
8 distinct folds called anal columns exist on the anal canal. The distal end is the opening we know as the anus.
There are two anal sphincters, internal and external, composed of skeletal muscle, and are under voluntary control, that prevent the “loss” of material in the anal canal until it is ready to be discharged.

69. Large intestines Structure
Made of the same tissues as the rest of the alimentary canal. Unlike the small intestines, it lacks villi.
Longitudinal muscles form three distinct bands, rather than having a uniform layout of muscle.

70. Large intestines function
The large intestines have little to no digestive functions. The only major secretion of the large intestines is mucus. Chyme does not digest or absorb here. The beginning of the large intestines absorbs little water, and the rest of the large intestines is designed to store that wasted material (feces) at its distal end.

71. Movement in the large intestines
2-3 major peristaltic waves. Mixing and movement similar to rest of digestive system.

72. Defecation reflex
A defecation reflex is initiated when a person takes and holds a deep breath, and contracts then relaxes the walls of the anal canal.
When the rectum distends, a peristaltic wave moves feces out of the rectum, and expels it from the digestive system.

73. Feces 75% water Brown because of bile in the feces
Pungent aroma from the compounds produced by the bacteria in the intestines.

74. Nutrients and Nutrient requirements
Carbohydrates- organic compounds used to store energy and for cellular respiration.
Starch, glucose, glycogen, disaccharides, and monosaccharides.
Cellulose is indigestible, and referred to as “fiber” in your diet.

75. Lipids Fats, oils, and fat-like substances (fatty acids).
Primarily in animal origins. (saturated fats)
Seeds, nuts, plant oils. (unsaturated fats)
Cholesterol is not found in plant origins. If it is in your plant based meal, then it was most likely added to it.
Essential fatty acids- fatty acids the body cannot make or convert one FA to another. You must get these from an outside source.

76. Proteins
Amino acid polymers that provide a wide variety of functions. Includes enzymes, clotting factors, keratin, elastin, and collagen.
Proteins are found in most animal based sources as well as peanuts and other legumes.
Essential A.A.- amino acids the body cannot make or convert one A.A. to form another. You must get these from an outside source.

77. Vitamins
Organic compounds that are not carbohydrates, lipids, or proteins, but the body still needs adequate amounts of in order to still function.
Fat soluble: A,D,E,K
Water soluble: B,C

78. Minerals
Minerals are elements (other than carbon) are essential in human metabolism. Most minerals are concentrated in the bones and teeth.
Major minerals: potassium, phosphorus, calcium, sulfur, chlorine, sodium, and magnesium.