Digestion (Option D)
Exocrine glands
• - Releases their secretion into:
• 1) Surface of the body (e.g
sweat glands, sebaceous
glands, mammary gland, Molls
gland)
2) lumen of digestive gut
(digestive gland)
• Examples of digestive glands include:
Glands
Salivary
glands
Gastric glands
Pancreatic
glands
Intestinal
glands
Enzymes
Saliva which contains
amylase
gastric juices which
includes hydrochloric
acid and proteases
pancreatic juices
which include lipase,
protease and
amylase
Peptidase
carbohydrases
Action
Breaks down starch
Breaks down protein
Breaks down
polypeptide
Breaks down dipeptide,
disaccharides
Structure of a Typical Exocrine Gland
1)Exocrine glands are composed of secretory cells which form an acinus (plural =
acini)
2) The acini are surrounded by a basement membrane
3) Held together by tight junctions between secretory cells
4) The secretory cells has ER and golgi network for material secretion and are rich in
mitochondria
5) Exocrine products are released (via secretory vesicles) into a duct
Objective : To understand secretion of digestive juices and stomach acid
Two mechanisms
Nervous mechanism
Hormonal mechanism
Sight and smell
Entry of the food
Detection of food by stretch receptor in the stomach lining
Brain
Brain triggers the release of digestive hormones to achieve sustained
gastric stimulation.
LEPTIN AND THYROXIN
Objective : To understand secretion of digestive juices and stomach acid
Hormonal mechanism
secretin, gastrin, cholecystokinin
stomatostatin
Gastrin
Gastrin secretion is inhibited
If the pH is too low;
Stimulation of
release of HCL
Secretin and somatostatin
When the food is passed to small intestine duodenum release
Bile
Secretin & cholecystokinin
HCO3
Objective : To understand secretion of digestive juices and stomach acid
Explain the hormonal mechanism of secretion digestive juices 4marks
Gastrin is secreted in to blood stream by gastric pits.
It stimulates the release of stomach acid.
If stomach pH is too low, gastrine secretion is inhibited by sercetin and somatostatin.
Duodenum releases two hormones; secretin and chlecystokinin.
These causes liver to relase bile and pancreas to release pancreatic juice which contain HCO3
ions. This neutralizes the stomach acid.
Objective : To understand secretion of digestive juices and stomach acid
Stomach acid functions
[1] Assistance in digestion of food
By dissolving chemical bonds in the food.
[2] Activation of proteases
[3] Prevents pathogenic infections
By destroying microorganisms in the ingested food.
H
Objective : To understand secretion of digestive juices and stomach acid
Proton inhibitor pump
Certain medications and diseases
increase secretion of H+ ions.
This lowers the pH of the stomach.
PPis are the drugs which bind to proton
pump and inhibit the H+ ion secretion.
People using PPIs have more chances of
gastric infections due to reduced acid
secretion.
https://www.youtube.com/watch?v=E8B97QS0aeA
T
Intestinal Villi
• Digested food has passed
through the
• Stomach
Small
intestine
• Small intestine is highly folded
into villi (singular: villus)
• Villi increases the available
surface area for material
absorption
• Features of Villi
• Microvilli –increases surface area
for absorption
• Rich blood supply – Dense capillary
network rapidly transports
absorbed products
• Single layer epithelium – Minimises
diffusion distance between lumen
and blood
• Lacteals – Absorbs lipids from the
intestine
• Intestinal glands –release digestive
juices
• Membrane proteins – Facilitates
transport of digested materials into
epithelial cells
Identification of villus epithelium cells
from electron micrographs
• Tight Junctions
• Tight junction between two adjacent cells,
creates an impermeable barrier
Identification of villus epithelium cells
from electron micrographs
• Microvilli- increase surface area of the plasma
membrane, allowing for more absorption to
occur
Identification of villus epithelium cells from
electron micrographs
• Mitochondria
• Intestinal villi will possess large numbers of mitochondria to
provide ATP for active transport mechanisms
Identification of villus epithelium cells
from electron micrographs
• Pinocytotic Vesicles
• Pinocytosis (‘cell-drinking’) is the non-specific uptake of fluids and
dissolved solutes
Objective : To understand digestive infection & role of fiber in the diet
Objective : To understand digestive infection & role of fiber in the diet
Fiber
Dietary fiber
Indigestible food from plants and fungi;
Especially cellulose, chitin etc.
Lack of cellulase
Humans lack this enzyme which can digest cellulose
Water
Nutrients
Bacteria
Some herbivores like cow have special bacteria which
digest the cellulose.
Objective : To understand digestive infection & role of fiber in the diet
https://www.youtube.com/watch?v=Ujr0UAbyPS4
Roughage
the coarse indigestible constituents
of food or fodder
Keeps the movement on :
Provide the bulk in intestine to keep the material moving though gut.
Absorption
Roughage absorb the water.
This keeps bowl movement soft and easy to pass through
Bile pigment Epithelial cells
Lignin
Cellulose
Human flora (Bacteria)
Objective : To understand digestive infection & role of fiber in the diet
Importance of fiber rich food.
Constipation reduction
Less possibility
Of colon and rectal cancer
Weight management
Slows the absorption rate
Objective : To understand digestive infection & role of fiber in the diet
Questions:
[1] Explain the importance of fiber in diet
[2] State the meaning of roughage
[3] Mention the egested material in humans.
[4] Discuss why humans can not digest cellulose where has some
herbivores can.
Objective : To understand digestive infection & role of fiber in the diet
Digestive infections
Stomach ulcer
Stomach ulcers are inflammed and damaged areas in the
stomach wall, typically caused by exposure to gastric acids
• Helicobacter pylori is a bacterium that can survive the acid
conditions of the stomach by penetrating the mucus lining
• H. pylori anchors to the epithelial lining of the stomach,
underneath the mucus lining
• An inflammatory immune response damages the epithelial
cells of the stomach – including the mucus-secreting goblet
cells
• This results in the degradation of the protective mucus lining,
exposing the stomach wall to gastric acids and causing ulcers
• The prolonged presence of stomach ulcers may lead to the
development of stomach cancer over many years (20 – 30
years)
• H. pylori infections can be treated by antibiotics (previously,
stomach ulcers were considered stress related and not
treatable
)
Objective : To understand digestive infection & role of fiber in the diet
Cholera Toxin
Vibrio Cholerae
Step1
Ganglioside receptor
cAMP is produced
Osmosis
https://www.youtube.com/watch?v=cHr3cRsc
0MU
Diarrhea & dehydration