Download The Digestive System

Biology 12 - The Digestive System - Chapter Notes
In a nutshell...
• The body uses a variety of small molecules (amino acids, fatty acids,
glucose) for its metabolic needs. Food is mechanically and chemically
broken down into these molecules during digestion, after which they can be
taken up by body cells through the separate process of absorption.
• Food travels in a one-way path from mouth to esophagus to stomach to
small intestine to large intestine to anus.
• Organs and structures in the digestive system are specialized for specific
functions in digestion.
• Digestive enzymes are specific hydrolytic enzymes that have a preferred
temperature and pH.
• Proper nutrition is necessary to health.
•
DIGESTION: the ___________________________________ of
ingested food _________________________________ small
enough to move through epithelial cells and into the internal
environment.
•
•
ABSORPTION: the passage of ____________________________________________________, which
distributes them through the body.
ELIMINATION: the __________________________________________________ from the body.
We will look at DIGESTION first.
•
During digestion, protein are broken down into ____________________, carbohydrates into
_____________, fat to ______________l and _________________, nucleic acids to
__________________.
•
Digestion is an EXTRACELLULAR (______________________) process. It occurs within the gut (a tube
that runs from mouth to anus).
•
Digestion is achieved through the cooperation of a number of body parts and organ systems, and its
coordination depends on the actions of several key HORMONES. Let’s first look at the parts of the
digestive system:
Jeong – Student— Page 3
Mouth
besides emitting pearls of wisdom, your
Incisors
mouth is where
_______________________..
• the mouth receives food, chews it up,
Canine
moistens it, and starts to digest any starch in
the food.
Premolars
Hard Palate
Structure
Molars
• divided into an anterior hard palate (contains
several bones) and a posterior soft palate,
Soft Palate
Uvula
which is composed of muscle tissue. That
thing that hangs down in the back of your
Tonsil
throat people think is their tonsils is really the
uvula, and is the end part of soft palate. (the
tonsils lie on the sides of the throat).
• sense of hunger is due to the combined
sensations of smelling and tasting of food.
Olfactory (scent) receptors in the nose, and
taste buds on the tongue, remind you that
you’re hungry.
Teeth
• a normal adult mouth has 32 teeth. The
purpose of teeth is to chew food into pieces
that can be swallowed easily.
• different teeth types aid this: 8 incisors for biting, 4 canines for tearing, 8 flat premolars for grinding,
and 12 molars for crushing. (wisdom teeth are final molars which may or may not erupt properly) -- if not,
they must be removed surgically).
•
•
There are three sets of SALIVARY GLANDS that produce SALIVA:
1. ___________________ (below ears)
2. ___________________ (below tongue)
3. ___________________ (under lower jaw).
•
•
You can locate the duct opening of these with your tongue (parotid - by
second upper molar, sublingual and submandibular flaps are under the
tongue).
When you chew food, you moisten and lubricate it with _______________.
Saliva contains ___________________________ ___________________
_____________________________________
a) Salivary Amylase: a ____________________________ that breaks down starch in the presence of
water. _______________ is broken down to ________________ (a disaccharide of glucose), which is
later broken down to ___________________________________.
•
b) Lingual (____________________________) lipase: starts the digestion of the
___________________ in the mouth by ________________ dietary triglycerides forming
_________________________________________.
It also _______________ the __________________________ of food, preparing it for chemical digestion
and swallowing.
•
Thus, _________________________________, even before the food is swallowed. Once food has been
chewed, it is called a _________________.
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•
Food is then passed through the back of the mouth when you swallow. The _________________ that it
enters is called the ___________________, which is simply the region _____________________________
where swallowing takes place.
•
Swallowing is a __________________________ (requires no conscious thought).
•
To prevent food from going down your air passages, some clever
maneuvering is necessary. Note that it is impossible to breath and swallow at
the same time. What is happening?
•
when you swallow, the following happens in order to block air passages:
1.
the SOFT PALATE MOVES BACK to cover openings to nose
(nasopharyngeal openings).
2.
TRACHEA (WINDPIPE) MOVES UP under a flap of tissue called the
epiglottis, blocking its opening. When food goes down the "wrong way" it
goes into the trachea, and is then coughed back up.
3.
opening to LARYNX (larynx = “voice box”) is called the “glottis.” This opening is COVERED when
the trachea moves up (you can see this by observing the movement of the Adam's Apple (part of the
larynx) when swallowing). It gets ______________________ ___________________ called the
____________________.
•
food then has _________________ to go ---> _________________ _______________________
•
Esophagus: a ______________________________ that extends from ____________________________.
Made of several types of tissue.
•
The inner surface lined with _____________________________. This layer
is attached by connective tissue to a layer of ____________________
containing both _______________________________________ muscle.
•
Esophagus
food moves down the esophagus through ____________________
_____________________________________________________________
. If peristalsis occurs when there is no food in the esophagus, you will feel
that there is a “lump” in your throat.
•
Food bolus reaches the end of the esophagus and arrives at the _________
______________ connecting to the stomach. (sphincters function like _____________). Made of muscles
that encircle tubes, open them when they relax, close them when they contract).
•
Normally, this _________________________________________ out of stomach, but when _____________
occurs, a ____________________________ causes the sphincter to relax and the contents of the stomach
are propelled outward.
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BEFORE WE BEGIN…..
Hormones of the Digestive System
Hormone _______________:
Location & target:
– produced and released in the _________________
- released into the blood and targets the stomach to ___________________
________________
Trigger:
- stimulated by the presence of ____________________________ in the
stomach (detected by chemoreceptors)
- other stimulants include: ________________________________________
Hormone __________________:
Location & target:
- secreted by cells in ____________________
- stimulates the __________________________________
- stimulates the ______________________________
- stimulates the ________________________________________ into the
duodenum
Trigger:
- acidic contents from the stomach – ___________________
- secretin is turned off when the pH level returns to normal
Hormone ____________________________:
Location & target:
- secreted by cells in ___________________________________
- stimulates _______________________________ into the intestine
- stimulates pancreas to release _____________________ into the intestine
- (acts to give signal to the brain – that’s enough food for now)
Trigger:
- _________________________ food from the stomach
Hormone ___________________________________
Location & target:
- produced in the ______________________
- ________________________________________________________
- ________________ emptying of the stomach contents into duodenum,
allowing more time for digesting to occur in the small intestine
Trigger:
- chyme containing high amounts of carbohydrate, proteins, and fatty acids
Stomach
Jeong – Student— Page 6
STOMACH
• is a _____________________________________ that lies on left side of
the body beneath the diaphragm.
•
_______________ to hold about half a gallon (~1.5 liters) of solids and/or
Cardiac
Sphincter
Stomach
liquids in an average adult.
Functions include:
1) ___________________________________________ of food (2~6 hours)
Pyloric
Sphincter
2) ______________________________________ food (physical digestion)
• three layers of muscle contract to churn and mix its contents
• “hunger pains” are felt when an empty stomach churns.
3) _________________ fluids called gastric juices.
•
•
the mucus lining of the stomach contains inner GASTRIC GLANDS which produce GASTRIC JUICE.
Gastric juice contains:
a) _______________
b) ___________ (hydrochloric acid) – creates acidic environment pH 2 to kill bacteria in food and help
break it down. HCl also ____________________________
c) ____________________ and HCl combine, and ______________ pepsinogen into ____________,
an active HYDROLYTIC ENZYME that ____________________________ into smaller chains of
amino acids called _________________________________. (further on in the digestive tract they
are broken down individual amino acids by other enzymes. This is the reaction that takes place.
protein + H2O
pepsin
---------------------->
peptides
d) _______________ secreted by mucosal cells. It _________________________________ from
being digested by Pepsin and HCl. If HCl does penetrate, pepsin starts to digest the stomach lining
---> forms an ___________ (an open sore on the wall of the stomach). Too much gastric juice
can cause ulcers, as can too much nervous stimulation (i.e. stress), since this will cause oversecretion of gastric juices). However, the #1 cause of ulcers is actually a bacterial infections
(Helicobacter pylori) that impair the ability of cells to produce mucus. Thus, most ulcers can now be
cured with antibiotics.
e) ______________ – an _____________________________. (makes milk into a semisolid, slowing
down the movement of milk to allow efficient digestion – very important in babies)
4) ______________________________ of food into the small intestines:
• after 2 - 6 hours (depending on the type of food), the food has been turned into a semi-liquid food mass
called ____________________, and the stomach empties into the first part of the small intestine (called
the duodenum). This emptying is _____________________________________________ at the bottom of
the stomach.
Jeong – Student— Page 7
Small Intestine: The Food Processor
•
In our story, only some digestion has thus far taken place.
___________ of _________________________ of most
nutrients occur in the _______________________.
•
Divided into three zones: the
_____________________________________________.
•
Small intestine is about ____________________ (~20 feet),
compared to 1.5 m (~ 5 feet) for large intestine.
•
The _____________________ of small intestine called the
_________________. The duodenum plays a major role in
digestion. It is here that _________________ SENT FROM
THE ___________________________ break down
___________________, and secretions of the duodenum
itself also break down other nutrients
LIVER & GALL BLADDER - producing and secreting bile:
______________________: A small, pear-shaped muscular sac,
located under the right lobe of the liver
- aids in digestion by _________________________________________
•
_________________________________________. This will
stimulate the release of the ______________ into the blood, causing
the gall bladder to release ______________
•
Bile is sent to the duodenum via a duct from the
_______________________ (where bile is stored).
•
bile is a thick green liquid (it gets its green colour from
____________________________________________________
(another function of the liver).
•
bile contains _______________________ called BILE SALTS which
break FAT into _____________________________.
•
Due to the hydrophobic nature of fat molecules, they cling together –
making it _______________________ (a hydrolytic enzyme) to
breakdown fat. The problem is solved by using bile. __________
consists of molecules that have ______________________ and
________________________ (can dissolve in lipid) characteristics.
The bile molecules therefore place themselves in between the fat
and water. In this way the fat droplets remain suspended in water
rather than merging together. In the digestive stract emulsification
allows lipase to gain access to the fat molecules and thus facilitates
in digestion)
Jeong – Student— Page 8
Pancreas & Pancreatic Juice:
• ___________________ stimulates the release of the hormone __________________________________
into the blood
• Secretin targets ________________ to release Pancreatic juice into duodenum through a duct
Pancreatic Juice contain:
a) _________________________________ (NaHCO3)
•
NaHCO3 makes the juice highly alkaline (pH ~ 8.5). It ______________________________________
and make the small intestine pH basic
Pancreatic Juice contain ___________________________ which include:
a) ___________________: digest proteins into peptones and amino acids
b) _______________________________: digest starch into simple sugars and glucose
c) ________________: digest triglycerides to glycerol and fatty acids
d) ____________________: digest nucleic acids into nucleotide
e)
•
_____________ in the small intestine again trigger the release of ____________ from the pancreas for more
____________________________________.
Endocrine Functions of the Pancreas
Note: the pancreas also has an endocrine function. It produces the _________________________________.
Insulin is a hormone that ___________________________________. It causes ___________ to be _________
________ by cells. It is produced by different cells (β
β cells in “islets of Langerhans”) in the pancreas than the
ones that make pancreatic juice.
- Insulin is _________________________________________________, and it __________________________
throughout the body.
- Insulin also helps in ___________________________________________ which is ____________ in the liver
for future use.
- People who don’t produce insulin or enough insulin, or who lack insulin receptors on target cells, will suffer
from diabetes.
_________________: a hormone that stimulates the ______________________________________ therefore
increases your blood sugar level.
- When levels of sugar in your blood declines, your pancreas produces glucagon, which stimulates the liver to
_____________________________________________. As a result, your blood glucose levels return to normal.
Glucagon works opposite to insulin: Glucagon has the effect of raising blood glucose concentrations.
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