Transcript The Digestive System Chapter 16

The Digestive System
Function of the Digestive System
 Break down food into a “usable”
(absorbable) form
 Supply our cells with the nutrients they
need for energy, growth & repair
Elimination of waste products
Organs of the Digestive System
 Gastrointestinal tract (GI) – continuous
passageway which contains the food from the time
it enters the body, until it leaves; organs include:
 mouth (oral cavity), pharynx, esophagus, stomach,
small intestine, large intestine, rectum, anus
 Accessory organs - participate in digestive
processes; organs include:
 teeth, tongue, salivary glands, liver, gall bladder,
pancreas
Processes of Digestion
1. Ingestion
2. Movement along GIT
 Voluntary – e.g. swallowing
 Involuntary – e.g. peristalsis
3. Secretion – release of water, enzymes, acids,
buffers, mucous, etc. into GI tract for physical
(mechanical) & chemical digestive processes
Processes of Digestion
4. Digestion
 Mechanical processing – physical breakdown
of food; e.g. mastication, mixing waves
Chemical digestion – chemical breakdown of
food; disassembling of organic molecules into
their component parts; requires enzymes
 carbohydrates  monosaccharides
 proteins  amino acids
 lipids  fatty acids
Processes of Digestion
5. Absorption – movement of nutrients from GI tract
into blood capillaries (monosaccharides, amino
acids, H2O, vitamins, minerals)
6. Excretion (Defecation) – removal of waste
products from GI tract
Histology of the GIT
4 layers of tissue surround the
lumen of the GI tract
Mucosa
Submucosa
Muscularis externa
Serosa (a.k.a.
viseral peritoneum)
Mouth (oral cavity)
 Roof comprised of hard & soft palate; floor primarily comprised of
tongue
 Lips (labia)
Tongue that contains papillae (taste buds)
taste buds
 Salivary glands –
secrete saliva – made
of H2O, salts &
“salivary amylase”
Parotid duct
Parotid
gland
Sublingual
gland
Submandibular duct
Submandibular
gland
Teeth – involved in “mastication” (chewing)
 2 sets of teeth – deciduous & permanent
 4 types of teeth – incisors, cuspids
(canines), bicuspids (premolars), molars
Parts of a tooth –
 crown – portion of the tooth that
is visible; covered in enamel
 root – holds the tooth securely
in place
Pulp – made up of a rich supply
of blood vessels and nerves
Pharynx (throat)
Common passageway for air & food
 epiglottis protect airway when
swallowing (“deglutition”)
nasopharynx
uvula
oropharynx
epiglottis
laryngopharynx
Esophagus (gullet)
 collapsible tube that leads from pharynx to the stomach
 functions in “deglutition” through action of peristalsis
 lower esophageal sphincter (LES) is a ringlike muscle that controls the flow
between the esophagus and stomach (prevents stomach contents from flowing
back into the esophagus
Stomach - Gross Anatomy
Lower esophageal (cardiac) sphincter
Pyloric sphincter
Stomach - Histology
Rugae – folds of mucosa & submucosa to allow
for expansion of stomach
Mucosa of simple
columnar epithelium with
mucous cells
Gastric pit leading to
gastric glands
Stomach
 saclike organ composed of the fundus (upper, rounded
part), body (main portion), and antrum (lower part).
 Rugae are the folds in the mucosa lining the stomach.
Glands within those folds produces gastric juices that aid
in digestion and mucus that forms protective coating of the
lining of the stomach
Small Intestine - Anatomy
- connects stomach to large intestine; 15-20’ long;
- site for completion of chemical digestion & absorption of nutrients
- comprised of three regions:
Duodenum – 10” in length;
receives chyme from
stomach, secretions from
liver, gallbladder & pancreas
Jejunum – 8’ long; most
digestion & absorption
occurs here
Ileum – 12’ long; connects to
cecum of large intestine at
iliocecal valve (sphincter)
Small Intestine
:
Villi – small finger-like projections of
mucosal folds across surface of intestine
Plicae
circulares
Pancreas Feather shaped organ
located behind the stomach.
 Both endocrine (secretes
insulin & glucagon) &
exocrine gland (secretes
pancreatic juice)
Stomach
Tail
Body
Head
Duodenum
Pancreatic
duct
Pancreas
Pancreatic juice – mixture of enzymes & buffers (sodium
bicarbonate) secreted by acinar cells into pancreatic duct &
released into duodenum
Liver - Anatomy
 Largest organ within the body
 Comprised of 4 lobes
Liver & gall bladder
 Gall bladder – hollow
muscular sac under right lobe
of liver; stores &
concentrates bile; releases
bile through cystic duct
Right hepatic duct
Left hepatic duct
Liver - Functions
The liver has over 200 functions including (but not limited to):
storage of glycogen, fatty acids, fat-soluble vitamins &
minerals
 detoxification & removal of drugs, toxins & hormones
 phagocytosis of worn-out RBCs, bacteria & other
pathogens
Large Intestine
- Begins at the ilium & ends at the anus; 5’ long; 3” in diameter
- main functions – H2O reabsorption; absorption of some vitamins & minerals;
formation & temporary storage of fecal material
- no chemical (enzymatic) digestion
but some bacterial
Transverse
colon
- 3 regions: cecum, colon, rectum
Hepatic (rt.
Colic) flexure
Splenic (lt. colic)
flexure
Ascending
colon
Descending
colon
ileum
Ileocecal sphincter
Rectum
Anal canal
Cecum
Vermiform appendix
Rectum
Sigmoid
colonanal
Internal
Anal canal
sphincter
Rectum
External anal
sphincter
Anus
Role of the Large Intestines
Feces also known as stools are solid body
wastes expelled through the rectum and
anus.
 Gas produced by normal friendly bacteria.
The gas that is passes through the body
through the rectum is known as flatulence.

PATHOLOGY OF THE GI
TRACT
Disorders of the stomach and
esophagus
GERD (gastroesophageal reflux disease)
upward flow of stomach acid into the
esophagus
 Dysphagia: difficulty in swallowing
 Pyrosis (“heart burn”) burning sensation caused
from return of acidic stomach contents to the
esophagus

Disorders of the stomach and
esophagus (cont)

Peptic ulcers: lesion of the mucous
membranes of the digestive system
 Gastric
ulcers occur in stomach
 Duodenal ulcers occur in the upper part of the
small intestines (most common form)
Eating Disorders
Anorexia: lack or loss of appetite for food
 Bulimia: characterized by episode of binge
eating followed by inappropriate behavior
such as self-induced vomiting or misuse of
laxatives
 Pica: persistent eating of nonnutritional
substances such as clay.

Disorders of the Intestines
Diverticulitis: inflammation of a pouch or
sac occurring in the lining or wall of the
intestines
 IBD (inflammatory bowel disease): chronic
inflammatory disease of the GI tract

 Crohn’s
disease: chronic autoimmune
disorder causing scarring and thickening of
the walls of the intestines.
Disorders of the Intestines
Intestinal obstruction: complete stoppage
or serious impairment to the passage of
intestinal contents.
 Diarrhea: dia (through) rrhea (flow);
abnormal frequency of loose or watery
stools that can lead to dehydration
 Constipation: decrease in frequency of the
passage of stools

Hepatitis
Inflammation of the liver usually caused by
a virus but may also be caused by a toxic
substance.
 There are 5 varieties of hepatitis: A, B, C,
D, E

Diagnostic Procedures
Enema: a solution is placed into the
rectum and colon to clear the bowels in
preparation for a procedure
 Hemoccult: lab test for hidden blood in
stools
 Colonoscopy: direct visual examination of
the inner surface of the colon

Pharmacology
Laxatives: medications or foods given to
stimulate bowel movements
 Acid blockers: which are taken before
eating, block the production of acid
 Antiemetics: prevents or relieve nausea
and vomiting.
