Plan for this week
• Complete Digestion (p.24 – 33 of IGCSE
book)
• Wednesday – dissection and
microscopy lab
• Thursday – Test on Drugs and the Brain
Digestion….
The Digestive System
6.1.1 Explain why digestion of large food molecules is essential.
6.1.2 Explain the need for enzymes in digestion.
6.1.3 State the source, substrate, products and optimum pH conditions for one
amylase, one protease and one lipase.
6.1.4 Draw and label a diagram of the digestive system.
6.1.5 Outline the function of the stomach, small intestine and large intestine.
6.1.6 Distinguish between absorption and assimilation.
6.1.7 Explain how the structure of the villus is related to its role in absorption and
transport of the products of digestion.
Before we begin….
• WHAT do we need to eat? (a rough guide)
Essential components of the diet
Carbohydrates (sugars and complex carbohydrate):
ENERGY
Proteins: enzymes, structure, muscle, growth,
repair, immune function (antibodies)
Fats: ENERGY, cell membranes, myelin
Vitamins (e.g. C,D,E): small amounts for essential
functions
Minerals: e.g. Ca, Zn
WATER
Fibre
How much of each do you need?
So why do we have a digestive system?
Does all food need to be digested?
Digestion makes food (nutrients)
easier to absorb…
• Mechanical Digestion: Breakdown by
TEETH, and by the churning movements of the
GI system (peristalsis)
• Chemical digestion: Enzymes and acid….
Chemical digestion
Functions of the digestive system
Ingestion: taking food IN
mechanical digestion (processing) (e.g.chewing)
chemical digestion (enzymatic hydrolysis)
(Secretion) – of enzymes and mucous
Absorption – of nutrients
excretion/egestion: elimination of waste products
Draw and label a diagram of the human digestive
system.
Simple digestion: Intracellular food
processing
•
•
•
•
•
Paramecium
Food is ingested through
endocytosis and forms food
vacuole
Food vacuole fuses with
lysosome,which contains
digestive juices
Nutrients absorbed through
membrane
Vacuole refuses with
membrane and waste is
eliminated through
exocytosis
Simple digestive systems: Extracellular
food processing
•
Food breakdown and absorption occur in
compartments that are continuous with
outside of organism
• Gastrovascular cavity
•
:
food enters + waste exits through a single
opening
Cnidarians (ex. Hydra) have this
The Components of the Digestive System
Figure 24.1
Oral (buccal) cavity (pharynx)
Its functions include:
– analysis of material before swallowing (touch,
temperature, and taste receptors in tongue)
– mechanical processing by the teeth and tongue
– Lubrication (with water/mucous)
– limited digestion (salivary amylase)
– Production of a food bolus for transportation to the
stomach (via oesophagus) by peristalsis
The pharynx provides a common pathway
for air, food and liquids
Digestion begins in the mouth…
Digestion begins in the mouth…
Step by step through the digestive tract
• explore the digestive tract
• UPenn animation
• animation of organs of
digestion
The pharynx
How does food move along the digestive
tract?
Smooth muscle shows rhythmic cycles of activity
Peristalsis : waves that move a bolus (ball of food)
Segmentation
Churn (mixing) and fragment a bolus
Let’s watch!
Peristalsis in action...
Peristalsis
Figure 24.4
Digestion is achieved through both
chemical and mechanical breakdown
6.1.1 Explain why digestion of large food molecules
is essential.
6.1.2 Explain the need for enzymes in digestion.
6.1.3 State the source, substrate, products and
optimum pH conditions for one amylase, one
protease and one lipase.
Why do we need enzymes for digestion?
• Stephen Taylor intro to digestion/enzymes
• zoom into amylase...
The Structure of the Digestive Tract
Figure 24.3
Small Intestine Blood Vessels
Photograph by Susumu Nishinaga
This colored scanning micrograph shows a cast of blood vessels from the external wall of the
small intestine. Measuring about 22 feet (6.7 meters) in length, the small intestine performs
most of the major digestion and absorption of nutrients. The walls of the small intestine are
lined with millions of projections called villi, which absorb and transmit nutrients into the
bloodstream.
Why do we need enzymes for digestion?
Oral (buccal) cavity/pharynx
Its functions include:
– analysis of material before swallowing (touch,
temperature, and taste receptors in tongue)
– mechanical processing by the teeth and tongue
– lubrication
– limited digestion (salivary amylase)
– Production of a food bolus for transportation to the
stomach (via oesophagus) by peristalsis
– The pharynx provides a common pathway for air,
food and liquids
The pharynx
6.1.5 Outline the function of the stomach
• yum!....digestion from the inside
• Storage of undigested food
• Hydrochloric acid lowers pH to 2,
killing bacteria and denaturing
proteins
• Mechanical breakdown of food
through muscular action
• Chemical breakdown of food with
acids and enzymes
(pepsin begins protein digestion)
• Produces chyme
Structure of the stomach
Rugae: rough ridges which allow grinding of food (mechanical digestion)
Digestion and absorption in the
stomach
very little absorption of
nutrients
Control of enzyme (pepsin),
acid (HCl) and hormone
(gastrin) secretion is
controlled by:
1. Cephalic
2. Gastric
3. Intestinal
factors
Control of gastric function
The Stomach
Figure 24.12b
The Stomach Lining
Figure 24.13c, d
6.1.5 Outline the function of the small
intestine.
• Important digestive and
absorptive functions
•
pancreas, liver & gall bladder
secrete enzymes and juices into
small intestine
• Small intestine divided into
three sections:
– Duodenum
– Jejunum
– Ileum
Regions of the Small Intestine
Figure 24.16a
Small intestine
Adaptations to increase
surface area for
absorption…
• Plicae (folds)
• Villi (fingerlike
projections)
– Microvilli
Zooming in on the small
intestine
The Intestinal Wall
Figure 24.17b, c
The Intestinal Wall
Figure 24.17d, e
Microvillae
Microvilli (MV) are minute finger like
projections of the luminal (L) plasma
membrane and serve the purpose of
significantly increasing surface area (as much
as 30-fold) in regions specialized for
absorption, such as here in the small intestine.
Small Intestine
• Duodenal glands
– produce mucus
• Ileum
– lymph glands (Peyer’s patches)
Functions of the large intestine
• Reabsorbs water and compact material into feces
• Absorb vitamins produced by bacteria
• Store faecal matter prior to defecation
The Large Intestine
The Pancreas
The pancreas and gland cells of the small
intestine secrete digestive enzymes that
chemically break down complex food
molecules into simpler ones.
These enzymes include trypsin (for protein
digestion), amylase (for carbohydrate
digestion), and lipase (for lipid digestion).
Figure 24.18a-c
• Pancreatic duct
penetrates
duodenal wall
The
pancreas
• Endocrine functions (hormones)
– Insulin and glucagons
• Exocrine functions (digestive enzymes)
– Pancreatic juice containing many enzymes are
secreted into small intestine
The liver
• Performs regulation of metabolism and blood
and produces bile
• The liver has many different functions
The Gallbladder
Bile liquid is created in the liver
and stored in the gallbladder. Bile
emulsifies (breaks into small
particles) lipids (fats), which aids
in the mechanical digestion of fats.
Gall bladder: Hollow, pear-shaped
organ
Stores bile
Helps in digestion of fats