1. The Digestive System and Body Metabolism
Overview Of
Digestion
Chapter 14
The Digestive System and Body Metabolism
20 Cool Things
You Don’t Know
About the
Digestive System

3. Pill Cam

4. Digestive System
Takes in food, breaks it down into nutrient molecules and absorbs them into the bloodstream, then rids the body of indigestible remains

5. Anatomy of Digestive System
Alimentary canal –
digests food and absorbs digested fragments through its lining into the blood
GI, tract - continuous hollow tube: mouth, pharynx, esophagus, stomach, small and large intestine
Accessory digestive organs - assist: teeth, tongue, glands

6. Mouth (Oral Cavity) Food enters Mucus membrane-lined cavity
lips, cheeks, hard palate (anterior roof), soft palate (posterior roof)
uvula - fingerlike projection of soft palate

7. Mouth Tongue - attached to hyoid bone and styloid processes of skull
papillae containing taste buds on surface
Frenulum - secures tongue and limits its posterior movements
As food enters, it is mixed w/ saliva by tongue and chewed and swallowed
Taste

8. Salivary Glands - 3 pair Parotid glands - anterior to ears
mumps is inflammation of parotid glands
Submandibular and sublingual glands - empty secretions into mouth through ducts

9. Saliva Product of salivary glands, mixture of mucus and serous fluids
mucus moistens and binds food together into a mass (bolus)
serous part contains salivary amylase (enzyme for starch digestion)
Polls
Everywhere

10. Teeth Masticate (chew)
Deciduous (baby or milk) teeth - first set; formed from 6 months to 2 years
Permanent teeth - cause baby teeth to fall out b/t 6 and 12
32 permanent teeth
3rd molars (wisdom teeth) form b/t 17 and 25; sometimes absent or impacted in jawbone and must be surgically removed

11. Teeth by shape/function
Incisors - chisel-shaped, cutting
Canines - fanglike, tearing/piercing
Premolars (bicuspids)
Molars - broad crowns w/ rounded tips, grinding

14. Pharynx
Nasopharynx (respiratory), oropharynx (potesterior to oral cavity), and laryngopharynx (continuous w/ esophagus)
Peristalsis: Alternating contraction of muscles propel food into esophagus
Peristalsis

15. Esophagus Conducts food from pharynx through diaphragm to stomach
25 cm long

16. Walls of Alimentary Canal
Mucosa - innermost layer; moist membrane
Submucosa - blood vessels, nerve endings, lymph
Muscularis externa - inner circular, outer longitudinal smooth muscle
Serosa - outermost layer

17. Stomach C-shaped, left side, nearly hidden by liver and diaphragm
Peristalsis
C-shaped, left side, nearly hidden by liver and diaphragm
cardioesophageal sphincter - food enters from esophagus
fundus - expanded part
body – midportion
3rd oblique layer in muscularis externa to move, churn, mix, and pummel food
chemically breakdown proteins

18. Stomach Pylorus - funnel-shaped, terminal
Pyloric sphincter - goes to small intestine
25 cm long
when full, holds 4 liters of food
empty - collapses into folds (rugae)
Rugae on Dog Stomach

19. Stomach
Mucosa has gastric pits which lead into gastric glands that secrete gastric juice
chief cells - produce protein-digesting enzymes (pepsionogen)
parietal cells - produce HCl
Chyme is produced

20. Stomach - Food Breakdown
Secretion of gastric juice by sight, smell, and taste of food
presence of food and falling pH stimulate release of hormone gastrin that makes stomach produce enzymes, mucus, & HCl
2-3 liters gastric juice per day

21. Stomach: Food Propulsion
Peristalsis in lower half, and contractions squirt 3 ml of chyme into small intestine
takes 4 hrs for stomach to empty
Irritation (food poisoning) may activate vomiting

22. Small Intestine Major digestive organ
Muscular tube extending from pyloric sphincter to ileocecal valve
average length: 2 m (6 feet)
Hangs from coils suspended by mesentery
Large intestine encircles and frames it

24. Small Intestine - 3 subdivisions
Duodenum - curves around head of pancreas
Jejunum - extends from duodenum to ileum
ileum - terminal part that joins large intestine at ileocecal valve

25. Small Intestine Chemical digestion begins
Small amount of food processed at a time - controlled by pyloric sphincter
Pancreatic enzymes from pancreatic duct and bile from bile duct enter duodenum

27. Small Intestine - 3 structures that increase absorption
Microvilli - tiny projections that give fuzzy look (brush border)
Villi - fingerlike projections that give velvety appearance
Circular folds - deep folds of both mucosa and submucosa

29. Small Intestine: Food Breakdown and Absorption
Takes 3-6 hours
By end, digestion is complete and most absorption has occurred
Microvilli have brush border enzymes to break down sugars and complete protein digestion

30. Food Breakdown and Absorption
Pancreatic juice digests starch, proteins, fats, and nucleic acids; contains bicarbonate to neutralize chyme
When chyme enters, it stimulates hormones secretin and cholecystokinin to release bile

31. Food Breakdown and Absorption
Bile is necessary for absorption of fats and fat-soluble vitamins K,D,A
At end, all that remains is water, indigestible food and bacteria which enters large intestine
Food propulsion - peristalsis

33. Large Intestine Larger in diameter, shorter in length (1.5 m)
Extends from ileocecal valve to anus
Dries out indigestible food by absorbing water, eliminates residue as feces

34. Large Intestine Subdivisions
Cecum - saclike, first part
Appendix - wormlike structure hanging from cecum; ideal bacteria location - appendicitis
Colon - ascending, transverse, descending, and sigmoid
Rectum
Anal canal - ends in anus which opens to exterior; has external voluntary sphincter and internal involuntary sphincter

35. Large Intestine
Lots of goblet cells to produce mucus to act as lubricant to ease passage of feces

36. Large Intestine: Food Breakdown and Absorption
Residue is there hours
Bacteria metabolize nutrients and release gases (methane, hydrogen sulfide)
500 ml of gas produced each day

37. Food Breakdown and Absorption
Absorption limited to vitamins, some ions, and most of remaining water
Feces - solid product delivered to rectum; undigested food residue, mucus, bacteria, and some water

38. Large Intestine: Propulsion and Defecation
Peristalsis and mass movements (long, slow-moving, powerful contractile waves that move over colon 3-4 times daily to push contents toward rectum)
occur after eating; fiber increases strength of contraction

39. Propulsion and Defecation
When feces in rectum, defecation reflex causes rectum to contract and anal sphincters to relax
Diarrhea - food rushes through before water is absorbed, can result in dehydration and electrolyte imbalance
How fast food
Travels thorough.

40. Propulsion and Defecation
Constipation - food residue remains too long and too much water is absorbed; due to lack of fiber, poor bowel habits, or laxative abuse
A constipated body

41. Other Accessory Digestive Organs – Pancreas
Soft, pink, triangular gland extending from spleen to duodenum
produces enzymes that break down food and neutralize acidic chyme from stomach, produces hormones insulin, glucagon

42. Liver Liver - largest gland in body; under diaphragm on right 4 lobes
produces bile which leaves liver through common hepatic duct

43. Gallbladder
Small, thin-walled green sac in the inferior surface of liver
When digestion is not occurring, bile is stored and concentrated by removal of water
bile stored too long, it crystallizes forming gallstones
Yellow-green, watery solution of bile salts, bile pigments (bilirubin), cholesterol, phospholipids, and electrolytes
bile salts emulsify fats to provide more surface area

45. Disease: Jaundice Bile pigments enter bloodstream
Can result from hepatitis (inflammation of liver from viral infection of contaminated water or blood transfusion) or cirrhosis (severe damage from drinking excess alcoholic beverages)

46. Nutrition and Metabolism
Most foods used as metabolic fuels (transformed into ATP); some nutrients build cellular molecules
Energy value measured in kilocalories (kcal) or Calories (C)

47. Nutrition
Nutrient - substance in food used to promote normal growth, maintenance and repair
Carbohydrates, lipids, proteins - bulk of food; vitamins, and minerals in minute amounts

48. .
Water - 60% of volume of food
Most foods are combination of nutrients from 5 food groups (grains, fruits, vegetables, meats, and milk products)

49. Obesity Rates
in the US.

51. Dietary Sources of Major Nutrients - Carbohydrates
From plants except lactose and glycogen in meats
sugar - fruit, sugar cane, milk
starch - grains, legumes, root vegetables
cellulose - most vegetables

52. Lipids
Neutral fats: saturated in animal products, unsaturated in seeds, nuts, vegetable oils
Cholesterol - egg yolk, meats, and milk
Phospholipids

53. Proteins
Animal products, eggs, milk
Amino acid polymers
legumes, nuts, and cereals are low in one or more essential amino acids

54. Vitamins
Organic nutrients, small amounts
No one food contains all required vitamins, need balanced diet
Most function as coenzymes: act w/ enzymes for task

55. Minerals
Requires adequate supplies of 7: Ca, P, K, S, Na, Cl, and Mg; trace amounts of others
Fats/sugars have none, cereals and grains poor sources
In veggies, legumes, milk, meats

56. Metabolism
All chemical reactions necessary to maintain life
Catabolism - substances broken down, energy released and captured to make ATP
Anabolism - larger molecules built from smaller ones

57. Metabolism
Carbohydrates (glucose) - broken down to make ATP
Fats - build cell membranes, myelin sheaths, insulate, ATP
Proteins - structural materials hoarded by body cells

58. Carbohydrate Metabolism
Carbs - preferred fuel to produce ATP from glucose (blood sugar): energy from bonds broken binds phosphate to ADP to make ATP
Carbon atoms leave as CO2 and hydrogen combines w/ oxygen to make water

59. Carbohydrate Metabolism - Homeostasis of blood glucose
Hyperglycemia - high levels; excess stored as glycogen and converted to fats
Hypoglycemia - low levels; liver breaks down stored glycogen and releases glucose to blood

60. Fat Metabolism
Liver - make ATP, synthesize lipoproteins, clotting protein and cholesterol for membranes or steroid hormones
Form myelin sheaths and fatty cushions around organs
Most concentrated form of enegy

61. Fat Metabolism
To be used for ATP synthesis, it must be broken down into acetic acid; when not enough glucose, acetone accumulates in blood making it acidic (acidosis/ketosis)
no carb diets, diabetes, and starvation

62. Protein Metabolism
Proteins - bulk of cell structures; broken down into amino acids for enzymes, membranes
Cells use ATP to actively transport amino acids (8 of the 20 are not made by cells - essential amino acids)

63. Protein Metabolism
Amino acids make ATP when protein is in excess or no fats or carbs
amine groups are removed as ammonia which is toxic so it combines w/ CO2 to form urea

64. Central Role of Liver
Manufactures bile, detoxifies drugs and alcohol, degrades hormones, makes substances vital to body, metabolism
We have more liver tissue than needed, so if damaged, it regenerates rapidly and easily

65. General Metabolic Functions
Liver maintains blood glucose levels
After high carb meal, glucose is removed from blood and converted to glycogen (glycogenesis) and stored in liver

66. General Metabolic Functions
As body cells remove glucose from blood, liver breaks down stored glycogen (glycogenolysis)
gluconeogenesis - make glucose from fat and protein

67. General Metabolic Functions
Hormones insulin, thyroxin, and glucagon control blood sugar
Fats are oxidized for energy, broken down into acetic acid or stored as fat reserves
Makes cholesterol and secretes its breakdown products as bile

68. General Metabolic Function
Albumin - most abundant protein; holds fluids in bloodstream
insufficient albumin causes fluid to go from blood to tissues (edema)
Synthesize amino acids and detoxify ammonia

69. Cholesterol Metabolism and Transport
Cholesterol - structural base for steroid hormones and vitamin D; major building block of plasma membranes
15% from diet, 85% made by liver
Broken down and secreted in bile salts, which leave as feces

70. Cholesterol Metabolism
Insoluble in water, so transported bound to lipid-protein complexes - lipoproteins
Low-density lipoproteins (LDLs) - transport cholesterol/lipids to body cells; if too much deposited on arteries - “bad lipoproteins”

71. Cholesterol Metabolism
High-density lipoproteins (HDLs) - transport cholesterol from tissue cells to liver for disposal in bile; high levels are good
Both types necessary; ratio determines whether cholesterol will go to arterial walls

72. Body Energy Balance
When fuel is burned, it consumes O2 and generates heat
Energy intake = total energy output (heat + work + energy storage)

73. Body Energy Balance
Energy intake - liberated during food oxidation
Energy output - lost as heat (60%) + used to do work (driven by ATP) + stored as fat or glycogen

74. Regulation of Food Intake
When energy intake and energy outflow are balanced, body weight is stable
Food intake controlled by rising or falling blood levels of nutrients, hormones, body temp. and psychological factors

75. Basal Metabolic Rate
Carbs & proteins yield 4 kcal/g, fats yield 9 kcal/g
Basal metabolic rate (BMR) - amount of heat produced by body per unit time at rest; energy supply for breathing, heartbeat, and kidney function

76. Basal Metabolic Rate
Avg. adult has BMR of kcal/hr; influenced by surface area, gender, age, and thyroxin production (more thyroxin produced by thyroid gland, higher O2 consumption and ATP use and metabolic rate)

77. Basal Metabolic Rate
Hyperthyroidism - excessive rate, lose weight despite increased hunger and food intake, bones and muscles weaken
Hypothyroidism - slow rate, obesity, diminished thought process

78. Total Metabolic Rate
When active, more glucose must be oxidized to provide more energy for activities
Total Metabolic Rate (TMR) - total amount of kcal body must consume to fuel all activities

79. Total Metabolic Rate
When total calories = TMR, weight is constant
If eat more, excess calories appear as fat deposits
If active w/o enough food, break down fat reserves and even tissues to satisfy TMR

80. Body Temp Regulation
Heat warms tissues and blood keeping them at homeostatic temps
Reflects balance b/t heat production and heat loss, controlled by hypothalamus, regulated b/t ºF

81. Heat-Promoting Mechanisms
When cold, heat is conserved by vasoconstriction of blood vessels and shivering makes blood route to vital body organs causing temp of skin to drop
if extended, skin cells w/o O2 die leading to frostbite

82. Heat-Promoting Mechanisms
Hypothermia - extremely low body temp from prolonged exposure to cold; vital signs decrease, person becomes drowsy and can progress to coma and death as metabolic rate stops

83. Heat Loss Mechanisms
Most loss occurs through skin by radiation (when body temp increases, blood vessels dilate and heat radiates off surface) or evaporation (too hot - perspiration off skin’s surface; effective unless humid)

84. Heat Loss Mechanisms
Hyperthermia (elevated body temp) depresses hypothalamus and positive-feedback cycle occurs: soaring body temp increases metabolic rate, which increases heat production

85. Heat Loss Mechanisms
Heat stroke - skin hot and dry - fatal unless immersed in cool water and given fluids
Heat exhaustion - collapse during vigorous activity due to excessive loss of fluids (dehydration), causing low blood pressure, fast heart rate and cool, clammy skin

86. Heat Loss Mechanisms
Fever - controlled hyperthermia - results from infection, cancer, or allergies; pyrogens are released to hypothalamus that set thermostat at higher level
chills - reset lower - sweat
too high - protein denatures

87. Developmental Aspects
5th week - alimentary canal forms
cleft palate/lip - child unable to suck properly
tracheoesophageal fistula - connection b/t esophagus and trachea - causes drool, cyanosis during feedings

88. Development Aspect
Cystic fibrosis - blockage of pancreatic ducts so that fats and fat-soluble vitamins are not digested or absorbed
PKU - inability of tissue cells to use phenylalanine (amino acid) causes brain damage

89. Developmental Aspects
Newborn: rooting & sucking reflex
Appetite decreases in elementary age and increases in adolescence
Gastroenteritis - inflammation of GI tract due to contaminated food
Appendicitis - common in teens

90. Developmental Aspects
Middle age - metabolic rate decreases 5-8% every 10 yrs
ulcers & gallbladder problems
Old age - activity of GI tract declines, taste and smell decrease
cancer of stomach and colon