Download Ingestion Digestion Absorption elimination

Ingestion
Digestion
Absorption
elimination
Ingestion (human)
• In the mouth – food is broken down
physically by the teeth and chemically
by saliva
• Saliva is a mixture of water and amylase, an
enzyme that breaks down starch. Saliva
lubricates the food so it can be swallowed and
makes it possible to taste the food we eat
• Teeth – incisors for cutting, canines for
tearing, premolars for grinding, molars for
crushing
• In the esophagus – after leaving the mouth,
food descends the esophagus – the tube
between the mouth and the stomach
• The food stretches the walls of the esophagus,
activating peristalsis – a series of muscular
contractions and relaxations that resemble
waves, that move food along to the stomach
(even if you do a headstand!!)
Questions about ingestion
1. What are the functions of saliva?
2. How does chewing help in the digestion of
food?
3. What are amylase enzymes and why are they
necessary?
Digestion (human)
• Stomach - Site of food storage and the
digestion of proteins
• The stomach is in the shape of a “J” and can
hold 1.5L of food
• The cells lining the interior of the stomach
secrete fluids that help with digestion (gastric
juices). The stomach secretes 500 mL of
gastric juices after every meal.
• Gastric juices – fluids that help with digestion,
including:
– Mucosal lining - provides a protective coating for
the cells of the stomach
– HCl (hydrochloric acid) - kills harmful substances
ingested with food
– Pepsinogen - becomes pepsin, a digestive enzyme
• The pH of the stomach is between 1.5 and 3.0
• The mucosal lining is basic and protects the
cells lining the interior of the stomach from
being broken down.
• Small intestine – Where the majority of
digestion takes place.
• In humans, it is 7m long and 2.5cm wide (the
large intestine is 1.5m long and 7.6cm wide)
• The majority of digestion happens in the first
25-30cm of the small
intestine, which is called
the duodenum
• Pancreas – a digestive organ that secretes a
bicarbonate ion solution into the small
intestine that neutralizes the HCl and
denatures pepsin so the cells lining the
intestine are not damaged by the gastric juices
• The pancreas also secretes enzymes which
break down food
– proteins trypsin and erepsin
– carbohydrates: amylase
and disaccharidases
– lipids: lipase
• Liver – digestive organ that produces bile,
which is used to break down lipids
• Bile is stored and concentrated in the gall
bladder
• Bile is released into the small intestine to
physically break down lipids so they can be
chemically digested by enzymes (lipases)
Questions on digestion
1. How are the cells of the small intestine
protected from stomach acids? Explain the
mechanism and the chemicals involved.
2. In cases of extreme obesity, a section of the
small intestine can be removed. What effect
do you think this would have on the patient?
Absorption and elimination (human)
• The majority of absorption happens in the small
intestine. The intestinal walls are covered with
villi, projections that increase the surface area of
the walls to maximise absorption of nutrients.
Villi are themselves covered with microvilli to
create even greater surface area
• When they are absorbed across the intestinal
walls, nutrients enter the circulatory system and
are delivered throughout the body
• The colon – (large intestine) stores waste for the
time it takes the body to absorb water, salts and
vitamins
• Cellulose (fiber) cannot be broken down by our
bodies but it provides volume to our solid waste.
Once the volume of waste reaches a certain
quantity, a signal is sent to the nervous system,
which initialises defecation.
• Elimination removes toxic waste from our bodies.
The more cellulose we eat, the more defecations
we will have and the less time the toxins remain
in our bodies
Questions on absorption and
elimination
1. What is the function of the colon in the
digestive system?
2. Why is cellulose considered to be an
important part of your diet?
3. Describe what the inside of the small
intestine looks like and how this structure
increases the efficiency of its operation.