5.2 Alimentary system including process of digestion Flashcards
Alimentary/excretory Diagram attached
A. Pro-ventriculus
B. Rectal pad
C. Rectum
D. Malphigian tubule.
Where in the alimentary/excretory system might any disease forming organisms may be found, giving the name of the organ and relevant disease.
In the Ventriculus (mid-gut) you might find:
- American Foul Brood
- European Foul brood
- Nosema apis and Nosema cerana
In the Malphigian tubules you might find Malphigamoeba mellificae.
In the trachea you might find Acariposis woodi
What are the tree parts of the alimentary system?
FMH
- Foregut: pharynx, oesophagus, crop and proventriculus.
- Mid gut: ventriculus
- Hind gut: small intestine and rectum leading to the anus
Alimentary system functions (2)
P&W
- to store and filter nectar remove pollen, digest the pollen and nectar when required.
- to collect waste from the haemolymph and debris from digestion and recover salt and water
before passing on to the rectum.
What does the oesophegus do?
Circ and Longi
has inner layer of longitudinal and outer layer of circular muscles that move the
contents along by working against each other known as peristalsis.
What does the proventriculus do?
Four folds of the proventriculus work independently to extract pollen, form it into a bolus and
pass it into the Ventriculus.
What does the ventriculous do?
Main digestion occurs in the Ventriculus which is lined by epithelial cells surrounded by two
layers of cells, inner layer is circular and outer is longitudinal.
Epithelial cells are protected
internally by the peritrophic membrane.
What do the epithilial cells in the ventriculous do?
SucAmyProLips
They produce digestive enzymes. These include:
* Sucrase that breaks down sugars, ie sucrose into glucose + fructose
* Amylase that breaks down starches
* Proteases that breaks down protein in pollen into amino acids and
* Lipases that digest lipids into fatty acids and glycerol.
* Useful particles pass through the epithelial wall into the haemolymph which carries them to where
they are needed.
How does excretion work?
Waste material passes through the pyloric valve into the small intestine along with waste
material extracted by the Malpighian tubules. Then through the rectum before excretion via the
anus.
Describe the structure and function of the Ventriculus.
- U shaped within the abdomen with numerous transverse constrictions that form deep folds
creating a large surface area. - Epithelial wall consists of many cells that are continually breaking down and being replaced by
mitosis. - The wall is surrounded by circular muscles with longitudinal muscles outside them.
- The epithelial cells are protected from sharp objects such as pollen by the peritrophic
membrane made up of a jelly like material continually produced along the length of the
ventriculus. This membrane allows the soluble products of digestion to pass through but
hinders the passage of some pathogens. - The epithelial cells produce the digestive enzymes. These are released in many ways including
when the cells break down as mentioned above. - Carbohydrates are broken down into simple sugars mainly be sucrase (invertase) which is also
produced in the hypopharyngeal glands. Starch is broken down by amylase (diastase). Different
complex substances each require a specialised enzyme. - Proteins from pollen are broken down into their respective amino acids by proteases with a
different enzyme for each step of the process. - Lipids (fats) are broken down by lipases, produced in the ventriculus and resulting in fatty acids
and glycerol. - Material that is not absorbed into the haemolymph proceeds through the pyloric vale at the
posterior end of the ventriculus into the small intestine.
At which state does a worker larva defecate for the first time and why didn’t this occur before
this stage?
It occurs at the 5th moult as this is when the ventriculus joins with the proctodaeum. Before then
the two were divided.
How can a bee manage without a cleansing flight for several weeks in winter.
The rectum can expand to more or less fill the whole of the abdomen until the bee can take a
cleansing flight and deposit its load.
Ingestion explained
The process by which food is taken into the alimentary canal.
* In the mouth enzymes from the salivary and hypopharyngeal glands are added, including sucrase, glucose oxidase and amylase which start the digestive process.
* Nectar is then swallowed and moved down the oesophagus into the crop by the process of peristalsis.
In the crop it is mixed and stirred and then filtered by the proventriculus where pollen and other impurities are formed into a bolus and passed into the ventriculus.
Digestion explained
The process of breaking down the ingested material within the ventriculus so that it
can be absorbed and used by the honey bee.
* The process, starts in the mouth, continues in the ventriculus where more enzymes are produced by the epithelial cells.
* The bolus is surrounded by the jelly like peritrophic membrane which allows digestive enzymes to access the food while protecting the epithelial cells which are fragile.
* Enzymes enter the pollen through their pores and break down the protein into amino acids.
These pass through the peritrophic membrane to the epithelium to be absorbed into the haemolymph.
Absorption explained
The passing of soluble products of digestion through the wall of the Ventriculus into the haemolymph.
* The haemolymph then transports it to where it is needed.
* Digested food include
monosacarides, lipids and amino acids.
* Some absorption of water and food minerals occurs in the small intestine.
Excretion explained
The removal of any indigestible material from the body. It is carried out via the rectum.
* Waste products are collected from the Haemolymph by the Malphigian tubules.
* Each tubule has a single wall lined with microvilli.
* Each tubule is served by a good supply of tracheoles and widely separated muscle fibres.
* Waste product is filtered through the tubule wall at its upper end.
* They pass through the wall into the lumen in the centre.
* Filtration is passive and while waste is collected some water and mineral salts are reabsorbed back into the haemolymph to prevent dehydration. This occurs at the lower part of the tube.
* When what is left reaches the intestinal connection it passes into the digestive system and is
passed to the outside of the body via the small intestine and the rectum.
What is Peristalsis?
Contractions of the muscles (both longitudinal and circular) that push food through the oesophagus into the abdomen in waves
Structure of the fat body
Trophocytes (fat cells) found throughout the pupa, larvae and adult bee. Form the major part of the fat body. Important sites of protein synthesis and the proteins found in the haemolymph are produced here
Oenocytes - found in larval, pupae and adult beefound in high concentrations over the wax glands and reach a maximum size when the wax glands are at their peak of production.
The structure of the fat body
Fat body consists of thin sheets or ribbons, usually one or two cells thick, or of small nodules suspended in the hemocoel by connective tissues and trachea.
The fat body is generally found in
the abdomen.
Within the honeybee there are three key fat bodies:
- trophocytes
- oenocytes
- urate cells
Name the three key fat body cells:
- Trophocytes (fat cells)
- Oenocytes
- Urate cells
What are Urate cells?
Urate cells exit in the larva and pupa, they store nitrogenous waste in the form of uric acid. Once
the adult Malpighian tubules form, the role of the urate cells disappears and so do the cells.
What are trophocytes?
Fat cells contained within and forming the major part of the fat body.
The fat bodies of the larva die off and are (almost) completely replaced with new fat bodies in the adult.
During the larval life the tropphocytes (fat cells) build up, they contain oil globules, glycogen and protein.
During the pupa stage the fat bodies disintegrate releasing their content into the haemolymph.
In the adult bee the fat cells contain fat and protein, the mix differs by age and season:
* - young worker mainly fat globules
* - older bees protein levels increase due to not feeding young
* - mainly protein in fat body
What are oenocytes?
Found within the fat body Oenocytes are generally responsible for lipid processing and detoxification. In the worker honeybee they are found in great quantity above the wax glands and in the queen are part of the
yolk production for eggs.
Foregut
- The cells of the foregut are flattened and undifferentiated as they are not involved in absorption or digestion.
- The cuticular lining is unsclerortized and consists only of endocuticle and epicuticle. The foregut comprises 4 regions:
1. - The pharynx
2. - Oesophagus
3. - Crop
4. - Proventriculus
The oesophagus
A narrow tube passing through the petiole. It is surrounded by an inner layer of longitudinal muscles and an outer layer of circular muscles
The antagonistic action of these muscles causes the contents to be moved towards the crop, this movement is called peristalsis.
The inner wall of the oesophagus is lined with a thick cuticular intima (the innermost coating or membrane of a part or organ) which allows for the expansion caused by peristalsis.
The crop
The extendable part of the foregut
Main digestion powerhouse
The Ventriculus
- Considered the true stomach of the honeybee.
- Forms a U shape within the abdomen
- Has numerous transverse constrictions that form deep internal folds.
- When dissecting a bee the colour of the Ventriculus can be brown, this is due to the colour of the contents, usually it is pearly white when empty.
- The epithelial wall of the Ventriculus is continuous throughout the midgut
- Surrounded by muscles circular surrounded by longitudinal (opposite to oesophagus).
- The epithelium cells are many and are continually increasing through mitotic division.
- Cells are cast off and degenerate releasing
digestive enzymes and absorption nutrients. - Other cells prevalent are enteroendocrine, which
secrete hormones which regulate the function of the midgut and intestinal stem cells, form which
differentiated cells are derived. - The peritrophic membrane separates the volume of the midgut from the epithelial wall, it comprises
proteoglycan gel on a framework of chitin microfibrils. - It is produced by the epithelial cells throughout the midgut. It allows passage of digestive enzymes to the ingested food and digested food to pass through the epithelial to the haemolymph.
- The enzymes produced by the epithelial include sucrose (breaks down sugars), amylase (breaks
down starch), proteases (breaks down protein in pollen to amino acids), lipases (digest lipids to
produce fatty acids and glycerol).
Absorption into the haemolymph is across enterocytes in the epithelial.
Diagram of Alimentary system
