Transcript The Digestive System

The Digestive System
I. Introduction


Digestion is the process of altering the
physical state and chemical composition of
food, so that it can be absorbed.
The digestive tract is also called the
gastrointestinal tract or alimentary canal.
II. Digestive Organs






Oral cavity (mouth)
hard palate and soft palate form roof
Uvula – cone-shaped projection that keeps food
out of nasal cavity during swallowing
Tongue –mixes food particles with saliva and
moves food toward pharynx; also aides in
speech
Papillae – rough projections on surface of
tongue that help handle food and contain taste
buds (tip-salty/sweet; sides-sour; back-bitter)
Salivary glands – secrete saliva and are located
near the ears and tongue; saliva helps moisten
food particles and begins the chemical
digestion of carbohydrates
II. Digestive Organs (cont)
Teeth




break food into smaller pieces creating more
surface area for digestion
32 total; covered with enamel, the hardest
substance in the body
Begin physical digestion
Pharynx (throat)


connects oral cavity to esophagus
Esophagus




long tube (~25 cm) dorsal to trachea that delivers
food to stomach
made of smooth muscle
transports food by peristalsis (rippling contractions)
and secretes mucus
II. Digestive Organs (cont)








Stomach
J-shaped organ with a capacity of 1 liter or more
the stomach wall has folds called rugae
Main site of physical digestion, which is almost
completed in the stomach by the peristalsis waves
which churn the food
chemical digestion of proteins begins in the
stomach and is completed in the small intestines
gastric juice – combination of pepsin, pepsinogen,
hydrochloric acid, and mucus; pepsin begins the
digestion of protein; pepsinogen reacts with
hydrochloric acid and changes into pepsin
Little to no fat digestion takes place in the stomach.
Food leaves the stomach as a liquid called CHYME
II. Digestive Organs (cont)




Stomach
very limited amount of absorption occurs here;
water, some drugs (ex. Aspirin), and alcohol
The cardiac sphincter (lower esophageal
sphincter)– is located where the esophagus
connects to the stomach. It is a muscular valve
which prevents food and gastric enzymes from
being pushed back into the esophagus.
The pyloric sphincter – is located where the
stomach connects to the small intestine. It
prevents backwash from the Small intestine into
the stomach.
II. Digestive Organs (cont)







Liver
weighs ~3lbs. and is located in the upper right of
abdominal cavity
reddish-brown in color because it filters the blood,
and is divided into right and left lobes
functions in protein, carbohydrate, and lipid
metabolism
storage area for glycogen, iron, vitamins A, D, and B12
filters blood, destroying damaged RBCs and foreign
antigens
removes toxic substances such as alcohol from blood
II. Digestive Organs (cont)




Bile – is a yellowish-green enzyme that helps the
body digest fats by breaking the fats down
physically.
Fats and oils stick together and move away from
water this makes them difficult to digest because
the enzymes can not get around the fats.
Bile causes EMULSIFICATION to happen –
which means it separates the fats into tiny
droplets which can now be chemically digested.
Bile is made in the liver, stored in the gall bladder
(which is why it is green), and transported to the
pancreas and then the duodenum by the bile
duct.
II. Digestive Organs (cont)
Pancreas




lies posterior to greater curvature of stomach
secretes pancreatic juice into small intestine
pancreatic juice contains enzymes that digest
carbs, fats, nucleic acids, and proteins
II. Digestive Organs (cont)

Small intestine







between stomach and large intestine
many loops and coils
inner wall lined with villi – projections that increase
the surface area for absorption
secretes enzymes that break down food and
receives secretions from the pancreas and liver
completes digestion of nutrients in chyme
absorbs 90% of products of digestion
transports wastes into large intestine
II. Digestive Organs (cont)

Small intestine - Main site of chemical
digestion.




There are 3 sections to the small intestines:
Duodenum which is the first section and is 25 cm
long. Pancreatic enzymes and bile are released
into the small intestine in this section.
Jejunum is the second section and is about 2.5m
(8 ft) long and passes imperceptibly into the
Ileum, which is the final section and is about 4m
(12 ft).
II. Digestive Organs (cont)
large intestine






also called colon
reabsorbs water, vitamins and electrolytes
last stages of chemical digestion occur here through
bacterial, rather than enzymatic action
forms and stores feces (FYI - feces is ~75%water and
the odor results from bacteria products; feces is
composed of water, salts, bacteria (such as E. coli), and
undigested food)
feces formation/defecation: peristaltic waves occur only
2-3 times a day in the large intestine; the waves produce
mass movements, usually after a meal
II. Digestive Organs (cont)

Large intestine is made up of 3 sections as well –

The first is the ascending colon which connects to
the small intestine and has the appendix coming
off of it.
The second is the transverse colon.
The third is the descending colon.


Rectum – expandable organ for temporary storage of
feces
Anus – final exit lined with keratinized epidermal tissue
Enzymes of the digestive system
ENZYME
SOURCE
DIGESTIVE ACTION
Amylase
Salivary
glands,
pancreas
Begins digestion of carbs;
polysacc to disacc
pepsin
stomach
Begins digestion of protein
lipase
Small
intestine and
pancreas
chemical
digestion of lipids;
triglycerides to fatty acids
and glycerol
Enzymes of the digestive system
bile
Liver
Physical digestion of fats
proteolytic enzymes:
ex. trypsin
Pancreas
Breaks down proteins into
peptides
peptidases
sucrase, maltase,
lactase
Small intestine Breaks down peptides into
amino acids
Small intestine
Breaks down disacc into
monosacc
Digestive System Key Terms





Peristalsis: waves of rhythmic contractions
that aid in digestive processes
Rugae: folds in the stomach
Chyme: partially digested food mixed with
stomach acid (stomach to intestines)
Sphincter: ring-like muscles that maintain
constriction ( like valves)
Villi: projections of a membrane that
increases surface area
Digestive System Key Terms







Bolus: chewed up food
Mastication: the act of chewing
Enzymes: proteins that act as catalysts in
the body
Amylase: enzyme that breaks down
carbohydrates
Pepsin: enzyme that breaks down protein
Lipase: enzyme that breaks down fats
Gallbladder: small organ that stores bile
Nutrition

Nutrition is the process by which the body
takes in and utilizes necessary food sources
(nutrients).
Metabolism

Cellular Metabolism:



The chemical and physical reactions that take
place in the cell.
Normally involves an enzyme to synthesize or
break down molecules (CHO, Lipid, PRO) for cell
use.
Example: Mitochondria making energy for the
body.
Nutrients

Carbohydrates:





Organic
Supply energy for cellular processes
Sources: starch from grains, veggies; glycogen
from meat; disaccharides from cane sugar;
monosaccharides from honey and fruits
Cellulose- sugar that cannot be digested, provides
bulk (called fiber) which assists movement thru
digestive system
RDI (Recommended Daily Intake) 125-175 grams
Nutrients

Lipids:





Organic
Supply energy for cellular processes and building
cellular structures
Fats, oils
Sources: Meats, eggs, milk, lard, seeds, nuts,
plant oils
Saturated fats should account for no more than
10% of diet
Nutrients

Proteins:





Organic
Made of amino acids
Imp. Components of enzymes, clotting factors,
keratin in skin and hair, collagen in connective
tissue, muscle components (actin/myosin)
hormones, antibodies
Sources: Meat, fish, poultry, cheese, nuts, milk,
eggs, cereals, legumes
RDI is about 0.8 g per kilogram of body weight
Nutrients

Vitamins





Organic
Essential nutrients that must come from foods
RDI varies for each vitamin
See table 25-4, 25-5 in the Anatomy book
Examples: A, B, C, K, Folic Acid
Nutrients

Minerals:







Inorganic
Essential for human metabolism
Plants extract minerals from soil, we eat the plants,
therefore we get the minerals.
Most concentrated in teeth and bones
Play vital role in nerve impulse conduction, muscle fiber
contraction, blood coagulation (CA, NA, K, etc)
Table 25-3 in Anatomy book for more info
Examples: Zinc, Iron, Sodium, Potassium, Calcium,
Phosphorus
Metabolism



Metabolism - the series of processes by
which food is converted into the energy and
products needed to sustain life
On the cellular level, metabolism is the
process of making ATP.
Why is ATP so important?
Metabolism

ATP- Adenosine triphosphate:




The version of energy useful to cells
ATP  ADP (triphosphate to diphosphate)- loss
of the phosphate releases energy
Lost phos. recharges (like a battery) and bonds
with an ADP to make an ATP: Energy must be
available in the cells for this to occur
Cellular Respiration provides the energy to
regenerate ATP, ATP provides the E for cellular
activities.
Metabolism

Carbohydrate Pathways





Carbohydrates are many sugars hooked together.
These pathways break them into individual glucose
molecules
CHO used as energy or converted to glycogen or fat
Glucose molecules absorbed from sm. Intestine into
blood stream and delivered to body cells
Insulin helps transfer glucose across the cell
membrane
3 Steps of Cellular Respiration = 1 Glycolysis, 2
Kreb’s Cycle, and 3 Electron Transport Chain (ETC)
combined
Metabolism

Glycolysis:




Process that breaks down the glucose into pyruvic
acid
Occurs in the cytoplasm (all cells)
Product is pyruvic acid which is moved to the
mitochondria
Net Yield 2 ATP
Metabolism

Kreb’s Cycle (Citric Acid Cycle):



Occurs in membrane of the mitochondria, involves
the pyruvic acid made in glycolysis
High E compounds made (8 NADH and 2 FADH2)
which donate electrons to the electron transport
system (ETS)
Net Yield 2 ATP
Metabolism

Electron Transport System:


ATP produced when NADH and FADH2 release
hydrogen atoms generating energy
Net Yield around 32 ATP
**Note: A total of 36 ATP are generated from
the energy in 1 molecule of Glucose.**
2 from glycolysis + 2 from Kreb’s cycle + 32
from ETS
Digestive System Disorders
Digestive System Disorders

Crohn’s Disease - is an autoimmune disease
where the immune system attacks the
gastrointestinal tract, producing inflammation.
Heartburn (acid reflux) – when
stomach juices regurgitate back into the
esophagus through the cardiac sphincter.
This causes a burning sensation that has
nothing to do
with your heart.
Gallstones - form when bile stored in
the gallbladder hardens into pieces of
stone-like material.
The largest gallstone
on record was
removed from an
80-year old woman
in 1952 and
weighed 6.29 kg
(13.84 pounds).
Digestive System Disorders

Ulcers (peptic) – an erosion of the mucous or wall
of the stomach or small intestine. Extremely painful
because of the acidic wearing down of the walls of
your GI tract.

Hernia - is a protrusion of
a tissue or part of an organ
through the muscle tissue
or the membrane by which
it is normally contained.
Irritable bowel syndrome (IBS) - is a
blanket term for a variety of diseases causing
discomfort in the gastro-intestinal tract. It is
also called spastic colon, characterized by
chronic abdominal pain, discomfort,
bloating, and
alteration of bowel
habits in the
absence of any
organic cause.
Digestive System Disorders

Cirrhosis – liver disease where the liver
tissue is replaced by scar tissue. Typically
caused by alcoholism or hepatitis.

Jaundice - is a yellowish discoloration of the
skin typically caused by excess bilirubin or
the breakdown of red blood cells.
Colon polyps - A colon polyp is a
growth on the surface of the colon.
Some colon polyps are benign
(not cancerous), but
some are cancerous.
Globally, cancer of the colon
and rectum is the third leading
cause of cancer in males and
the fourth leading cause of
cancer in females.
Digestive System Disorders



Lactose intolerance - the inability to digest
significant amounts of lactose, the major
sugar found in milk. Lactose intolerance is
caused by a shortage of the enzyme lactase.
Cystic Fibrosis – causes the blockage of the
pancreatic duct due to the build up of
hardened mucous.
Hemorrhoids - are abnormally swollen veins
in the rectum and anus.