Transcript Digestion without diagrams

The Digestive System
This lesson brought to you
courtesy of
Human Anatomy and Physiology
4th Edition
by
Elaine Marieb
Don’t write the red writing.
Digestive Processes (Functions)
• Ingestion – Taking food in.
• Propulsion – The process that moves food
through the digestive tract (also known the
alimentary canal). The movement that does
this is called peristalsis.
• Mechanical Digestion – Physical processing
of food that makes digestion by enzymes
easier.
• Chemical Digestion – catabolic (breaking
down) steps that involve enzymes.
More Digestive Processes
• Absorption – absorbing broken down
food products into the bloodstream or
lymph.
• Defecation – Elimanation of indigestible
substances via the anus.
Smooth Muscle Movements
• Peristalsis
– wave of smooth muscle contractions that
move food down the alimentary canal
• Reverse peristalsis
– A more technical way of saying: vomiting,
throwing up, chucking, technicolour yawning,
spewing, revisiting lunch or blowing chunks –
sorry for stretching the point, I just had to get
that out my system….which, incidentally, is a
really bad way to apologize for throwing up
on someone
Mouth and related organs
• What processes does the mouth
perform?
• Teeth
• Tongue
• Cheeks
• Hard Palate
• Soft palate
– uvula
Pharynx
• In the part of the throat where
involuntary swallowing begins.
• Basically a bridge between the mouth
(oral cavity) and the esophagus.
• Is connected to the nose and indirectly
to the middle ear – hence the need for
ear, nose and throat doctors.
Epiglottis
• Is a flap that covers the trachea when we
swallow and prevents food from blocking
our airway.
Pancreatic and Intestinal
enzymes
• As a general rule pancreatic enzymes
break long chain molecules smaller chains
or MUCH smaller chains and the intestinal
enzyme break them up into their basic
components e.g. proteins into amino
acids.
Esophagus
• Is the tube that carries food from the
pharynx to the stomach.
Stomach function
• It breaks proteins down into large
polypeptides.
• Mechanical Digestion of food
• The stomach acid helps to kill off most
bacteria and well as denaturing the
protein.
• May detect if the food has gone off/is
toxic and induce vomit reflex.
Small Intestine
• The tube that exits the stomach.
• It has 3 parts: the duodenum, jejunum
and ileum
The duodenum
• Smallest part of small intestine (about 25cm)
• Contains ducts from the pancreas and the gall
bladder.
• Major site of digestion where fats, lipids,
proteins and nucleic acids (DNA) are broken
down by enzymes in Pancreatic juices.
• Fats are emulsified by the bile which makes
their digestion faster (emulsification = fats
become small droplets = larger surface area
for enzymes to act upon)
The jejunum and the ileum
• Major sites for absorption of nutrients
are
– Jejunum 2.5 m
– Ileum 3.6 m
• Heavy modified to increase surface
area.
Surface Area Increasing
Structures
• There are circular folds (plicae cirulares in
Latin) in the small in intestine that are about
1cm deep.
• On the circular folds are 1mm high finger like
projections called villi (singular villus). Each of
these contains blood and lymph vessels to
absorb nutrients.
• Each cover each villus has mircovilli on there
absorptive cells, these are also covered in
enzymes called Brush Border Enzymes that
break down nutrients.
Large Intestine
• Is mostly responsible for reclaiming
water from the indigestible leftovers. It
also recovers some electrolytes.
• What might happen to someone who
has diarrhea (watery feces)?
Rectum and Anus
• The Rectum is the final part of the
digestive tract.
• The anus is the opening at the end of
the digestive tract. It is surrounded by a
circular muscle called the anal sphincter
which allows you to refrain from
defecation until it is convenient.