2. Nutrition
Process by which organisms obtain and utilize their food.
There are two parts to Nutrition:
1. Ingestion- process of taking food into the
digestive system so that it may be
hydrolized or digested.
2. Digestion- the breakdown of food (either
chemically or mechanically) in order to
utilize nutrients

3. Types of Nutrients
• Micronutrients- vitamins, minerals, & water
• Macronutrients- proteins, lipids, carbohydrates,
etc…

4. Human digestive
system

5. GI (gastrointestinal) tract = alimentary canal

6. Ingestion
• Mouth
– mechanical digestion
• teeth
– breaking up food
– chemical digestion
• saliva
– amylase
» enzyme digests starch
– mucin
» slippery protein (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

7. mouth
break up food
digest starch
kill germs
moisten food

8. Mouth
• Chemical and
mechanical
digestion.
• Food is chewed
(masticated)
mechanically.
• A bolus (lump) is
formed with
saliva and the
tongue.

10. TEETH
• The teeth, or dentes are accessory digestive organs located in
sockets of the alveolar processes of the mandible and
maxillae
• The alveolar processes are covered by the gingivae or gums,
which extend slightly into each socket. The sockets are lined
by the periodontal ligament or membrane which consists of
dense fibrous connective tissue that anchors the teeth to the
socket walls.
• A typical tooth has three major external regions: the crown,
root, and neck.

11. • The crown is the visible portion above the level of the gums.
Embedded in the socket are one to three roots.
• The neck is the constricted junction of the crown and root near
the gum line.
• Internally, dentin forms the majority of the tooth. Dentin consists
of a calcified connective tissue that gives the tooth its basic shape
and rigidity. It is harder than bone because of its higher content of
calcium salts (70% of dry weight).
• The dentin of the crown is covered by enamel, which consists
primarily of calcium phosphate and calcium carbonate. Enamel is
also harder than bone because of its even higher content of calcium
salts (about 95% of dry weight).
• In fact, enamel is the hardest substance in the body. It serves to
protect the tooth from the wear and tear of chewing. It also
protects against acids.

12. • The dentin of a tooth encloses a space. The enlarged part
of the space, the pulp cavity, lies within the crown and is
filled with pulp, a connective tissue containing blood
vessels, nerves, and lymphatic vessels.
• Narrow extensions of the pulp cavity, called root canals,
run through the root of the tooth. Each root canal has an
opening at its base, the apical foramen, through which
blood vessels, lymphatic vessels, and nerves extend.
• The blood vessels bring nourishment, the lymphatic vessels
offer protection, and the nerves provide sensation.
• Humans have two dentitions, or sets of teeth: deciduous
and permanent.
• The first of these—the deciduous teeth also called primary
teeth, milk teeth, or baby teeth—begin to erupt at about 6
months of age, and approximately two teeth appear each
month thereafter, until all 20 are present

14. Swallowing (& not choking)
• Epiglottis
– flap of cartilage
– closes trachea (windpipe) when swallowing
– food travels down esophagus
• Peristalsis
– involuntary muscle contractions to move food along

15. Pharynx
• The back of the
throat.
• Larynx- passage
for air, closes
when we
swallow.
• Is approximately
15cm long.

16. Digestive Glands
• Groups of
specialized
secretory cells.
• Found in the
lining of the
alimentary
canal or
accessory
organs.

17. esophagus
• The esophagus is the swallowing tube through
which food passes on its way from the mouth
to the stomach.
• The main function of this organ is to propel
food down into the stomach. There is also a
mechanism to prevent food from coming back
up or "refluxing" from the stomach into the
esophagus.

18. • The esophagus is a long, muscular tube that
also has two muscles (or sphincters) at the top
and bottom.
• All of these muscular areas must contract in
an exact sequence for swallowing to proceed
normally.

19. • series of involuntary
wave-like muscle
contractions which
move food along the
digestive tract
Peristalsis

20. STOMACH
• The human stomach is a muscular, elastic, pear-shaped
bag, lying crosswise in the abdominal cavity beneath
the diaphragm.
• The stomach is an expanded section of the digestive
tube between the esophagus and small intestine.
• The right side of the stomach is called the greater
curvature and the left the lesser curvature.
• The most distal and narrow section of the stomach is
termed the pylorus - as food is liquefied in the stomach
it passes through the pyloric canal into the small
intestine.

22. • The stomach is divided into 3 regions
• Fundus
• Body
• Antrum
• When the stomach is inactive the pyloric
sphincter is relaxed and open, and when the
stomach contains food the sphincter is closed.

23. Walls of the stomach
• There are 3 layers of smooth muscle fibers
• An outer layer of longitudinal fibers
• Middle layer of circular fibers
• Inner layer of oblique fibers
• The arrangement allows for the churning
motion as well as peristaltic movement.

24. Type of cells secretion notes
Surface Mucous Cells
(or "Mucous Surface Cells")
secrete a mucus
Neck Mucous Cells
(or "Mucous Neck Cells")
secrete a mucus whose acidity
is more neutral than that
secreted by the cells at the
surface of the stomach lining.
The mucus secreted by the
muscous neck cells has a more
neutral pH than that secreted
by the cells at the surface of
the stomach lining.
Chief Cells secrete pepsinogen Pepsinogen is an inactive
gastric enzyme which is
converted to pepsin, a protein-
digesting enzyme.
Parietal Cells secrete hydrochloric acid,
and an intrinsic factor
(involved in the absorption
of vitamin B12).
Hydrochloric acid assists in
the conversion of
pepsinogen to pepsin.

25. Type of cells secretion Notes
Gastric Juice: The secretions of the
surface mucous cells, neck
mucous cells, chief cells,
and parietal cells are
known collectively as
gastric juice.
(Hence gastric juice
includes mucous,
pepsinogen, hydrochloric
acid and intrinsic factor.)
G Cells - produce and secrete the
hormone gastrin.
Gastrin :
stimulates secretion of
gastric juice,
increases the
contractions of the
gastro-intestinal (GI)
tract, and
relaxes the pyloric
sphincter.

26. Function of stomach
• After food is chewed and moistened in the
mouth, it passes through the esophagus into the
stomach.
• Food is mixed with stomach acid and enzymes to
break the food down into smaller pieces. This
combination of food and stomach "juices" is
called chyme.
• The stomach also stores food temporarily,
releasing chyme in small amounts into the small
intestine, where it is further broken down into
nutrients to be absorbed into the body

27. Stomach
• Functions
– food storage
• can stretch to fit ~2L food
– disinfect food
• HCl = pH 2
– kills bacteria
– chemical digestion
• pepsin
– enzyme breaks down proteins
But the stomach is made out of protein!
What stops the stomach from digesting itself?
mucus secreted by stomach cells protects stomach
lining

28. stomach
kills germs
break up food
digest proteins
store food
sphincter
sphincter
mouth
break up food
digest starch
kill germs
moisten food

29. Gastric Juices
• Secreted by the stomach.
• Acidic (pH 1.5-2.5) (HCl).
• Pepsin- an enzyme that
breaks down large proteins
into amino acids.
• Food is further broken down
into a thin liquid called
chyme.

31. Accessory Organs
• Pancreas
• Liver
• Gall Bladder

32. Pancreas
• An organ which secretes both digestive
enzymes (exocrine) and hormones (endocrine)
• ** Pancreatic juice digests all major nutrient
types.
• Nearly all digestion occurs in the small
intestine & all digestion is completed in the SI.

33. • Digestive enzymes
– digest proteins
• trypsin, chymotrypsin
– digest starch
• amylase
• Buffers
– neutralizes
acid from
stomach

34. • The pancreas a retroperitoneal gland that is about 12–
15 cm (5–6 in.) long and 2.5 cm (1 in.) thick, lies
posterior to the greater curvature of the stomach.
• The pancreas consists of a head, a body, and a tail and
is usually connected to the duodenum by two ducts.
• Pancreatic juices are secreted by exocrine cells into
small ducts that ultimately unite to form two larger
ducts, the pancreatic Duct and the accessory duct
• The pancreatic duct (duct of Wirsung) is the larger of
the two ducts.
• In most people, the pancreatic duct joins the common
bile duct from the liver and gallbladder and enters the
duodenum as a dilated common duct called the
hepatopancreatic ampulla (ampulla of Vater).

35. Composition and Functions of Pancreatic Juice
• Each day the pancreas produces 1200–1500 ml of
pancreatic juice, a clear, colourless liquid consisting mostly
of water, some salts, sodium bicarbonate, and several
enzymes.
• The sodium bicarbonate gives pancreatic juice a slightly
alkaline pH (7.1–8.2) that buffers acidic gastric juice in
chyme, stops the action of pepsin from the stomach, and
creates the proper pH for the action of digestive enzymes in
the small intestine.
• The enzymes in pancreatic juice include a starch digesting
enzyme called pancreatic amylase
• several protein digesting enzymes called trypsin,
chymotrypsin , carboxypeptidase and elastase the
principal triglyceride-digesting enzyme in adults, called
pancreatic lipase and nucleic acid – digesting enzymes
called ribonuclease and deoxyribonuclease.

36. Liver
• Function
– produces bile
• bile stored in gallbladder until needed
• breaks up fats
– act like detergents to breakup fats

37. • The liver is the heaviest gland of the body,
weighing about 1.4 kg (about 3 lb) in an average
adult.
• The gallbladder is a pear-shaped sac that is
located in a depression of the posterior surface of
the liver. It is 7–10 cm (3–4 in.) long and typically
hangs from the anterior inferior margin of the
liver
• The liver is divided into two principal lobes—a
large right lobe and a smaller left lobe by the
falciform ligament.
• Histologically, the liver is composed of several
components

38. • Hepatocytes
• Bile canaliculi
• Hepatic sinusoids
• Hepatic lobule
• Portal lobule

40. • Role and Composition of Bile
• Each day, hepatocytes secrete 800–1000 ml of
bile, a yellow, brownish, or olive-green liquid.
• It has a pH of 7.6–8.6 and consists mostly of
water, bile salts, cholesterol, a phospholipid
called lecithin, bile pigments, and several ions
• The principal bile pigment is bilirubin. The
phagocytosis of aged red blood cells liberates
iron, globin, and bilirubin (derived from heme)
• The iron and globin are recycled; the bilirubin is
secreted into the bile and is eventually broken
down in the intestine.
• One of its breakdown products—stercobilin—
gives feces their normal brown color

41. • Bile is partially an excretory product and partially
a digestive secretion.
• Bile salts, which are sodium salts and potassium
salts
• of bile acids (mostly chenodeoxycholic acid and
cholic acid), play a role in emulsification, the
breakdown of large lipid globules into a
suspension of small lipid globules.
• The small lipid globules present a very large
surface area that allows pancreatic lipase to more
rapidly accomplish digestion of triglycerides.
• Bile salts also aid in the absorption of lipids
following their digestion.

42. Functions of the Liver
• Carbohydrate metabolism
• Lipid metabolism
• Protein metabolism.
• Processing of drugs and hormones.
• Excretion of Bilirubin
• Synthesis of bile salts
• Storage
• Phagocytosis
• Activation of vitamin D.

43. Gall bladder
• Pouch structure located near the liver which
concentrates and stores bile
• Bile duct – a long tube that carries BILE. The
top half of the common bile duct is
associated with the liver, while the bottom
half of the common bile duct is associated
with the pancreas, through which it passes on
its way to the intestine.

45. pancreas
produces enzymes to
digest proteins & starch
stomach
kills germs
break up food
digest proteins
store food
mouth
break up food
digest starch
kill germs
moisten food
liver
produces bile
- stored in gall bladder
break up fats

46. Small Intestine
• Most chemical digestion
takes place here.
• Simple sugars and proteins
are absorbed into the inner
lining.
• Fatty acids and glycerol go
to lymphatic system.
• Lined with villi, which
increase surface area for
absorption, one cell thick.

47. Small intestine
• The small intestine is continuous with the
stomach at the pyloric sphincter and leads to
the large intestine at the ileocaecal valve.
• In the small intestine the chemical digestion
of the food is completed and most of the
absorption of the nutrients takes place.
• The small intestine consists of 3 main section

49. • Duodenum
• Jejunum
• Ileum
• The duodenum is about 25cm long
• Secretions from the gall bladder and the
pancreas are released into the duodenum
through the common structure, the
hepatopancreatic sphicter.

50. • The jejunum is the middle section of the small
intestine and about 2 meters long.
• The ileum is about 3 meters long and controls
the flow of materials to the 1st part of large
intestine.

51. Intestinal juices
• About 1500ml of intestinal juice are secreted
daily by the glands.
• Water, mucus, mineral salts
• The pH of the intestinal juices is usually
between 7.8 and 8.0

52. Function of small intestine
• Onward movement of its contents by
peristalsis
• Secretion of the intestinal juice, also inc by the
parasympathetic stimulation.
• Completion of chemical digestion of
carbohydrates, protein and fats in the
enterocytes of the villi.
• Protection against infection by microbes that
have survived the antimicrobial action of hcl.

53. • Secretion of the hormones cholecystokinin
and secretin.
• Absorption of nutrients.

54. Small intestine
• Function
– chemical digestion
• major organ of digestion & absorption
– absorption through lining
• over 6 meters!
• small intestine has huge surface area = 300m2 (~size
of tennis court)
• Structure
– 3 sections
• duodenum = most digestion
• jejunum = absorption of nutrients & water
• ileum = absorption of nutrients & water

55. Duodenum
• 1st section of small intestines
– acid food from stomach
– mixes with digestive juices from:
 pancreas
 liver
 gall bladder

56. stomach
kills germs
break up food
digest proteins
store food
mouth
break up food
digest starch
kill germs
moisten food
pancreas
produces enzymes to
digest proteins & starch

57. Absorption in the SI
• Much absorption is thought to occur directly through the wall
without the need for special adaptations
• Almost 90% of our daily fluid intake is absorbed in the small
intestine.
• Villi - increase the surface area of the small intestines, thus
providing better absorption of materials

58. Absorption by Small Intestines
• Absorption through villi & microvilli
– finger-like projections
– increase surface area for absorption

59. VILLI

60. Large intestine
• The large intestine is about 1.5 meters long,
beginning at the caecum and terminating at
the rectum and anal canal deep in the pelvis.
• Its lumen is about 6.5cm in diameter, larger
than the small intestine.
• The colon is divided into
• Caecum
• Ascending colon

61. • Transverse colon
• Descending colon
• Sigmoid colon
• The caecum is the 1st part of the colon
• It is a dilated region which has a blind end
inferiorly and is continuous with the asending
colon superiorly.

62. • The ascending colon passes upwards from the
caecum to the level of the liver where it
curves to the left at the hepatic flexure.
• The transverse colon that extends across the
abdominal cavity in the front of the
duodenum and the stomach to the area of the
spleen and curves downwards.

63. • The descending colon passes down the left
side of the abdominal cavity then curves
towards the midline.
• The sigmoid colon is a s shaped curve in the
pelvis that continues downwards to become
rectum.
• The rectum is about 13cm long it leads from
the sigmoid colon and terminates in the anal
canal.

64. • The anal canal is short about 3.8cm long in
adults and leads from the rectum to the
exterior.

65. function of large intestine, rectum,
anal canal
• Absorption
• Microbial activity
• Mass movement
• defecation

66. Large intestines (colon)
• Function
– re-absorb water
• use ~9 liters of water every
day in digestive juices
• > 90% of water reabsorbed
– not enough water absorbed
» diarrhea
– too much water absorbed
» constipation

67. • 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.

68. 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

69. Appendix
Vestigial organ

70. Rectum
• Last section of colon
(large intestines)
– eliminate feces
• undigested materials
– extracellular waste
» mainly cellulose
from plants
» roughage or fiber
– masses of bacteria

71. Digestive Homeostasis Disorders
• ULCERS – erosion of the surface of the
alimentary canal generally associated with
some kind of irritant

72. • CONSTIPATION – a
condition in which the
large intestine is emptied
with difficulty.
• Too much water is
reabsorbed
• and the solid waste
hardens
Digestive Homeostasis Disorders

73. Digestive Homeostasis Disorders
• DIARRHEA – a gastrointestinal
disturbance characterized by
decreased water absorption and
increased peristaltic activity of the
large intestine.
• This results in increased, multiple,
watery feces.
• This condition may result in severe
dehydration, especially in infants

74. Digestive Homeostasis Disorders
• APPENDICITIS – an inflammation of the
appendix due to infection
• Common treatment is removal of the
appendix via surgery

75. Digestive Homeostasis Disorders
• GALLSTONES – an accumulation of
hardened cholesterol and/or calcium
deposits in the gallbladder
• Can either be “passed” (OUCH!!) or
surgically removed

76. Digestive Homeostasis Disorders
• ANOREXIA NERVOSA - a psychological
condition where an individual thinks they
appear overweight and refuses to eat.
• Weighs 85% or less than what is
developmentally expected for age and height
• Young girls do not begin to menstruate at the
appropriate age.

77. Digestive Homeostasis Disorders
• HEART BURN – ACID from the stomach
backs up into the esophagus.