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UGA / Entomology / ENTO 3645 / How is food digested?

How is food digested?

How is food digested?

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School: University of Georgia
Department: Entomology
Course: Medical Entomology Lecture
Term: Spring 2019
Tags:
Cost: 25
Name: ENTO 3645 Class Notes Week 3
Description: These are the class notes for week 3 of class.
Uploaded: 01/24/2019
7 Pages 53 Views 3 Unlocks
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ENTO 3645 – Week 3 Lecture Notes  


How is food digested?



1/22 – Lecture 2 Slides  

*These notes will be an aid to the slides posted on ELC.  

Slide 20 

• Circular muscles – surround organs and move food down – peristalsis  Slide 21 

• Food is chewed up in the mouth, then enters the pharynx to the esophagus.  • The esophagus goes into the crop – a food storage place.  

• Proventriculus – a valve.  

• No digestion or absorption of nutrients happen in the crop.

• All the way up to the proventriculus is lined with exoskeleton

• Parasites have a hard time getting through the proventriculus.  

• Midgut – where digestion and nutrient absorption occurs.  


Where does digestion and nutrient absorption occur?



• This process is different in humans, because we digest in our stomach and absorption  occurs in the small intestine – not in one place like insects do.  

• The midgut is not lined with exoskeleton – it has a delicate surface covered by microvilli  – these increase surface area for absorption of nutrients.  We also discuss several other topics like What is the measurement sign for luminous intensity?

• Gastric caecum also increase surface areas, but also store parasites that aid in the  digestion of food.  

Slide 22 

• The pumps work in a coordinated way and take advantage of the exoskeleton being able  to expand/narrow.  

• The muscles that line the cibarial pump will pull in blood.  

• They will feed on blood or nectar (sugar) for different purposes.


Where should tracheal tubes be located?



Don't forget about the age old question of How did political revolution transform europe?

• Mosquitoes have a large crop that Is isolated.  

• A sugar meal can be put into the dorsal diverticula to still allow blood to come into the  midgut.

Slide 23 

• Section through an unfed mosquito (black and white).

• The posterior mid gut fills up with blood and it takes three days to convert it to eggs.  • Typical a mosquito will take a blood meal and not have another until she lays eggs (80- 140)

Slide 24 

• The surface area of the gut is huge compared to mosquitoes.

• Insects bring food into the gut and digest out side of the cells it by secreting digestive  enzymes into the lumen.  

• Ticks take the food into phagolysosomes to digest it in the cells.  

• Parasites are actively taking in the phagolysosomes.  

Slide 25  

• The tubes extend into the hemolymph.

• They are open at the end that empties into the gut.  

• They pull in nitrogenous waste from the hemolymph.  

• They are also pulling in potassium and water.  

• In the rectum there are rectal glands that resorb the water and potassium out of the  waste material.  

• The epicuticle helps insects from drying out – so this is another way for their body to  retain water.  If you want to learn more check out How did women's roles change during the war?

Slide 26 

• Oxygen can diffuse in and CO2 can diffuse out.

• You can think of these as snorkels.  

• Diffusion through these narrow tubes is not efficient, so the air sacs open up area  between muscles to help pull in air.  

• 99.9% insects do not have hemoglobin.  

• Tracheal tubes need to be located near places that need oxygen.  

• This could be a factor that limits the size of insects, because their isn’t an efficient  transport of oxygen.  

• Another factor for why insects are small could be that insects tend to occupy niches that  select for small body sizes (like in the bark of trees).  

Slide 27  

• There’s a single blood vessel – the aorta that feeds into the heart.  

• It opens up in the head.  If you want to learn more check out How is naturalistic observation facilitated?

• Ostium are openings in the aorta that allow hemolymph to come in and be pushed to  the head and go through the body.  

• This is essential for moving waste, hormones, and nutrients and preventing stagnation. Slide 28  Don't forget about the age old question of What's an example of contrived problem?

• The accessory glands are where the fluid component of the semen is produced.

• Many females will mate once in her life, because they can take in enough semen to  fertilize her eggs for the rest of her life.  

• If you extract the accessory glands from males and inject them into unmated females  she will begin to not mate anymore.  

• Spermatheca – where the sperm is stored from mating.  

Slide 29 

• Each segment of the body has its own ganglia.  

• The mouth parts were derived from fusing ancestral segments and having their limbs  turn into specialized parts.  

• Subesophageal ganglion controls mouth movements.

• Thoracic ganglia control leg and flight muscles in the corresponding part of the thorax.  • The caudal ganglion controls the genitalia.  

Slide 30  

• Side view

Slide 31  

• View from the top.

• The middle/top area contains areas for learning and memory.

Slide 32  

• Mechanoreceptors – the insect will know when they are disturbed, the hairs move.  • Other hairs are rigidly fused = chemosensory hairs.  

Slide 33  

• The hairs are covered with pores. Don't forget about the age old question of Where is glycogen stored from?

• The interior of the hair is filled with hemolymph.

• The nerves have odor receptor proteins on their surface.  

• When an odor receptor binds, there’s a protein shape change that causes and action  potential and the insect knows what scent it is.  

• Each nerve will produce only one kind of odor receptor.  

1/24 – Lecture 2 Slides  

*These notes will be an aid to the slides posted on ELC.  

Slide 33

• The odor proteins were first found in antennas.  

Slide 34  

• There’s a lens that focuses the light into the center of the structure to the nerve cell.  • Within the nerve there’s the rhabdom – an endoplasmic reticulum that makes a stacked  structure.

• The photon of light will go through the stack to be absorbed by a photoreceptor, cause  an action potential, and signal the brain that there is light.  

• Each ommatidium points in a different direction, so they know where the light is coming  from, and there are also color receptors.  

• Primary and secondary pigment cells keep the photons from crossing into adjacent  ommatidium.  

• The ommatidium can only see what is straight in front of it/in line with it, so the array of  the ommatidium create an image.  

• Many insects can see more colors than we can.  

• Butterflies and bees can see special markings on plants that we can’t see.  • The eyes of a wild type fruit fly will be black. White eyed flies have a mutation that  blocks the formation of a functional enzyme that makes the pigments. Since the  pigment isn’t made, the photons can come from any direction and they are basically  blind.  

• In order to develop model for disease transmission, you need to know how long the  insects live. The pigments in the eyes are synthesized continuously, so the older the  insect, the more pigment there will be. So you can use lab insects to predict the age of  wild insects.  

• The amount of ommatidia in insects is less than humans, so their images are more  pixelated. In many cases they don’t need detail but instead a sense of movement. • Some insects use their vision to find females.  

• They are sensitive to movement across their field of view.  

Slide 35  

• Hormones – a messenger that is produced at one place in the body and has its use in  another place of the body. They are transported.  

• The concept of hormones was discovered by people studying insects.  • As insects grow, they molt and change form/change their exoskeleton.  • The guy that discovered hormones was interested in this, so he had insects that were at  

different molting stages. He cut a hole in each insect and glued them together with  beeswax so that their hemolymph could be exchanged. He was trying to find how  insects know when to molt/what stage to molt to.  

• It was thought that there might be an internal clock that can tell. In this case the two  insects would be independent of each other and would still molt according to their path.

• Another possibility is that there was some kind of secretion that was produce and  determines the phase of the molt. In this case, both of the insects would molt to the  same change if connected. This is what happened. The insect molting to a larvae molted  normally, but the insect destined to molt to an adult molted to a large larvae. • Diapause – a physiological pause that occur during winter.  

• The hormones are of interest, because if we can manipulate them then we can control  insects. Ex: if we can manipulate reproduction hormones, then we can prevent them  from reproducing.  

Slide 36  

• Incomplete metamorphosis – the adult stage looks similar to the ones that preceded it.  • Different insects can have different numbers of nymph stages, but 5 is pretty common.  • Complete metamorphosis – a series of immature stages that look very different from  the adult.

• In order to transition from the larvae stage to the adult, the insect has a pupa stage.  • Fitness is directed related to size with insects in that the larger the insect, the more eggs  they will most likely have.  

• It is thought that the selective advantage for complete metamorphosis is that the adults  are not in competition for food with the larvae, because they feed on different  resources.  

• Many insects have complete metamorphosis.  

• In either case, the insect has to control the molting process (when they will molt and  into what).  

Slide 38/The Regulation of Molting page of ELC 

• Eventually, the insect cannot grow anymore inside the exoskeleton, so it molts to  continue growing. The flexible membrane in between sclerites are pulled apart. This will  then carry action potentials to the brain that it is stretched as far as it can go. This signal  tells the insect to begin molting.  

• Ecdysis – the removal of the exoskeleton.

• The first hormone generated is PTTH, a peptide hormone – this is secreted from the  corpus cardiacum. It travels through the hemolymph and targets the molt gland. The  gland is not connected to the brain. This triggers the release of ecdysone into the  hemolymph that is taken into epithelial cells. The ecdysone has a nuclear receptor that  when bound will separate the living epithelial cells from the dead exoskeleton cells and  fluid will fill the area.  

• The new exoskeleton is very flexible. When the new one is under the old, the old will  remove (ecdysis) and is stimulated by molting hormones. The insect will swallow air into  its gut and flex its muscles to hit sutures in the old exoskeleton to split it open and crawl  out (a tough process).

• Once they are out they can make the new exoskeleton large enough for room to grow  and as it hardens it get darker.

• The action of ecdysone Is modified by the presence of JH (juvenile hormone) that is  processed in the corpus allatum. The JH receptor is present in the epidermal cells. The  receptor modifies the response to ecdysone. In the early molts, the insect will produce a  lot of JH. At each molt the amount of JH drops.

• In the case of complete metamorphosis there will be some JH that will lead to the pupa  stage, then there will be no JH the next molting stage and the adult will be formed.  • If you mess with JH, then the insect won’t ever reach the adult stage and won’t be able  to reproduce. This takes longer.  

• JH Is a hormone that has one function as the insect is developing and goes away when  the insect is an adult, but eventually it comes back for egg function.  

Lecture 2 Slides 

Slide 1  

• Nest parasites – feed on nest maker usually when their asleep.

• They need sensory information to tell when the prey is there.

• In general, olfaction is important for all arthropods – especially for CO2 detection  because we exhale it. They will use the CO2 receptors in their antennae to orient  themselves toward the source.  

• Heat blocks the CO2 receptor and dilutes its affect. It also blocks the lactic acid receptor.  It also has repellent activity.  

Slide 2  

• Only about 5% of our skin is blood vessels, so the mosquito inject saliva into our skin  while trying to suck blood.

• A problem for mosquitos is that our blood vessels will open when we’re hot and close  when we are old, so when closed they are hard to find.  

• Also, when we are injured our body attempts to stop the bleeding.  

• These are hemostatic responses.

• In the blood, there are specialized cells called platelets that response to the injury  signals by aggregating and forming a platelet plug to cause the blood vessel to constrict.  This process happens in seconds.  

• Mosquitoes will inject their saliva and it counteracts all of these responses. • Whenever there is an on signal to a process there has to be an off signal. This means  that there has to be something to stop the platelets: AMP.  

• Collagen is a protein that lines our blood vessel, but is hidden in the endothelium.  Platelets will only be in contact with these when the endothelium is torn.  • Platelets will release TXA2 and 5-HT (serotonin) that will cause the blood vessels to  constrict: vasoconstriction.

• The saliva of the mosquito will counteract the affects of the vasoconstrictors.  • Coagulation is more important in larger blood vessels. All blood-feeders make  anticoagulants.

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