Transcript Digestive system

Functions of the digestive system
Ingestion- bringing in food/nutrients
 Mechanical processing- mechanically
breaking food down, chewing, etc.
 Digestion- chemically breaking food down
 Secretion- release of nutrients
 Absorption- movement of nutrients to the
blood stream
 Excretion- removal of waste

Organization of Digestive Tract
 The
digestive tract is lined w/
mucous membranes to protect the
epithelium of the digestive tract, and
to help food move through
 Stratified in areas of high stress, like
the mouth and simple in the small
intestine where absorption takes
place
Movement of Digestive Materials
 Peristalsis-
waves of muscular
contractions that move a bolus, along
the digestive tract
 Segmentation- cycles of contraction
that churn and fragment bolus
Control of Digestive Functions
Neural Mechanisms- sensory neurons in
the digestive tract stimulate motor
neurons to control the smooth muscle of
the digestive tract
 Hormonal control- a lot of digestion is
controled by hormones, there are atleast
18 involved in digestion

Oral Cavity
 The
tongue- mechanical processing
of food
 Salivary glands- 3 pairs, produce 11.5 liters of saliva a day
 Lubrication and moistening
 Salivary amylase- digests complex
carbohydrates
 Teeth- mechanical digestion
Digestive Tract
Pharynx- Passageway from the mouth to
the esophagus
 Esophagus- hollow muscular tube, which
moves food through using peristalsis
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Stomach

Four Regions
Cardia- superior portion that connects w/ the
esophagus, contains lots of mucous glands
to protect stomach lining
 Fundus- upper curve of the stomach
 Body- largest region, gastric glands release
acid and enzymes, mixes food
 Pylorus- last section, connects to the
duodenum

Gastric Glands
Parietal cells- secrete HCl to keep
stomach pH at 1.5-2.0. Acidic
environment kills most microorganisms,
breaks down proteins, breaks down plant
cell walls, activates pepsin (protein
digesting enzyme)
 Chief cells- Secrete pepsin

Pyloric glands
Mostly produce mucous
 Produces hormone gastrin, which
stimulates secretion of the parietal and
chief cells, as well as contractions of the
stomach walls to mix and stir contents

Regulation of gastric activity
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Cephalic phase- prepares stomach for arrival of
food, stimulates mucous, acid, and enzyme
activity
Gastric phase- begins w/ the arrival of food, 3-4
hours while ingested foods are processed
Intestinal phase- controls rate of chyme leaving
stomach and entering the duodenum
Small Intestine
Absorption of nutrients
 Duodenum- “mixing bowl”, mixes chyme
and digestive secretions from pancreas
and liver
 Jejunum- most chemical digestion and
absorption
 Ileum- connects to the large intestine

Pancreas

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
organ posterior to the stomach, secretes
enzymes and buffers into the duodenum
Secretes insulin and glucagon to control blood
sugar levels
Secretes pancreatic juice- consists of an
alkaline solution to neutralize acidity of the
chyme and enzymes to complete digestion
Liver
 Divided
into two lobes, left and right
 Hepatocytes- adjust circulating levels
of nutrients
 Secretes bile, which helps break
down fats
Physiology of the liver

Metabolic regulation- regulates
composition of blood before it is sent to
the rest of the body
 Carbohydrate metabolism- if blood
glucose drops, hepatocytes break down
glycogen into glucose. If blood glucose
increases, hepatocytes remove glucose
and store it as glycogen or store it as
fat
Liver physiology cont.
Lipid metabolism- regulate circulating
levels of fats
 Amino acid metabolism
 Removal of waste
 Vitamin storage- fat soluble vitamins
are stored (A, D, E, and K)
 Mineral storage and Drug inactivation

Liver Regulation
Remove debris and pathogens from the
blood
 Plasma proteins- regulate osmotic
pressure of the blood
 Removal of toxins
 Synthesis and secretion of bile- emulsifies
fats so they can be digested
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Gallbladder

Stores bile, which can become more
concentrated the longer it remains in the
gall bladder
Large Intestine
Cecum- first section of large intestine,
connects to the ileum
 Colon

Ascending
 Transverse
 Descending
 Sigmoid colon
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Physiology of the large intestine
Reabsorption of water
 Absorption of vitamins- K (used by the
liver to make clotting factors, Biotin
(glucose metabolism), Vitamin B5 (used
for making steriod hormones)
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These are made by bacteria living in the
colon