Alimentary Canal - Insect Anatomy

True or False: the whole alimentary canal makes up epithelium

True

What makes up a single layer of cells?

Epithelium

What cuticle lining is secreted by epithelial cells in the foregut and hindgut?

Intima

Which part of the alimentary canal is endodermal in origin? Which is ectodermal in origin?

The midgut

Foregut and hindgut is ectodermal

What are the functions of the forgut?

Food acquisition, storage, and initial digestion

Name all the main parts of the alimentary canal foregut (7)

Preoral cavity

• Cibarial cavity and salivarium

Buccal cavity

Pharynx

Esophagus

Crop

Proventriculus

Stomodeal valve

Name the functions of the alimentary canal

Digestion (fore and midgut)

Absorption (mostly midgut)

Excretion (hindgut)

Water, ionic balance

Ecdysis, storage, enzyme production and secretion

Explain the two types of muscles in the alimentary canal

Extrinsic muscles are attached to the exoskeleton

Intrinsic muscles are only within the canal and weak

• 2 layers: circular and longitudinal

The ______ cavity is in front of the hypopharynx and the _______ is behind the hypopharynx in the preoral cavity

Cibarial

Salivarium

What chamber is just inside of the mouth?

Buccal cavity

What is the pharynx?

Swallowing mechanism or pharyngeal pump

What muscles does the pharynx have?

Extrinsic muscles arise on frons and vertex

What is the difference of muscles when the pharnyx is subdivided?

Ant. pharynx has extrinsic muscles in front of the brain

Post. pharynx muscles origin on the vertex (behind the brain)

True or False: the esophagus has extrinsic muscles

False - simple tube with no extrinsic muscles

What is a simple enlargement of the esophagus?

Crop

What is the function of the crop

Storage and digestion by saliva and midgut digestive fluids

Which part of the alimentary canal has teeth?

Proventriculus

What is the function of the proventriculus?

Grinding/physical digestion - analogous to gizzard

may also serve as valve

What is it called when the stomodeal valve is externally differentiated?

Cardia

What is the function of the stomodeal valve?

Controls food passage - may allow backward passage of digestive fluids

What part projects into the midgut?

Stomodeal valve

What are the functions of the midgut?

enzyme production, digestion, absorption, exocytosis (merocrine secretion)

What is merocrine secretion

Cell vacuoles are released through the fusion of the vacuole membrane with the cell membrane

True or False: there are no muscles in the midgut

False. Intrinsic muscles poorly developed, no extrinsic muscles.

What part of the alimentary canal has microvilli on the lumen surface?

Midgut

What part of the alimentary canal do cells rapidly get replaced or are metabolically active?

Midgut

Where is the ventriculus and caeae located?

Midgut

What is a simple tube that bears microvilli on inner surface and increase surface area for absorption?

Ventriculus

How many rings does caecae have?

1-3

What is the function of midgut cells?

Secrete digestive enzymes and ions that regulate pH; absorb nutrients

What are the three major types of midgut cells?

Columnar epithelium (enterocytes) - bear microvilli

Endocrine cells (enteroendocrine) - secrete hormones to regulate midgut

Regenerative cells (stem cells) - in groups called nidi or lie within regenerative crypts

What are the specialized midgut cells that create high concentration of potassium in gut lumen - changes pH?

Goblet cells

What are the functions of peritrophic membrane?

Protect midgut (from abrasion)

Semipermeable

Conserve enzymes - countercurrent flow

What is the peritrophic membrane composed of?

Chitin microfibrils and proteins in a proteoglycan matrix

What is type 1 and type 2 secretion in peritrophic membrane?

Type 1 - whole midgut

Type 2 - anterior midgut

What is the filter chamber?

Functions to concentrate food in the midgut and is divided into 2-4 sections

What are the functions of the hindgut?

Excretion and modification of waste for excretion

Maintain homeostasis (osmoregulation)

• water absorption and conservation, ionic balance, absorption of useful ions

What muscles are present in the hindgut?

Extrinsic muscles

• “suspensory” muscles

• dilators (excretion)

What are the two valves in the hindgut?

Pyloric valve - formed from post. part of midgut

Proctodeal valve - formed from the ant. part of hindgut

What is the pylorus?

Where malpighian tubules meet hindgut

Valve at ant. part and not always clearly set off

Where does the malpighian tubules open?

Open at the pylorus, independently or grouped into a common opening

What are the functions of malpighian tubules?

Removes waste from hemolymph

Produce “primary urine”

sometimes produce silk

How does the malpighian tubules work?

Tips free in hemolyph - moved by a muscle

Absorb blood non-selectively

• plasma (non-cellular), small particles, ions

• proton pump

• cotransporter → antiporter

Resorb useful components (use ion pump, diffusion less)

What are the functions of the anterior intestine

Modify wastes for excretion - reabsorb ions, water; acid-base balance

How can the anterior intestine be differentiated into?

Anterior ileum

Posterior colon

What is another word for posterior intestine?

Rectum

What is the function of the posterior intestine?

Water and ionic balance

What are the rectal pads in the posterior intestine?

Columnar epithelial cells

Tracheated in Dragonfly immatures (Branchial basket)

True or False: there are no muscles present in the posterior intestine

False

What collects metabolic waste from blood and creates primary urine?

Malpighian tubules

What excretion type is used by aquatic insects?

Ammonia

________ excretion is cheap metabolically, requires a lot of water, and is toxic

Ammonia

The excretion type that requires less water and is less toxic but more metabolically expensive is ______ excretion

Urea

_______ excretion is the most metabolically expensive but relatively not toxic

Uric acid

What are symporters?

A type of cotransporter where 2 molecules transported across cell membrane at same time

What cotransporter has molecules moving in different directions in its concentration gradient?

Antiporters

What are protein pumps used to export or import small molecules

Cotransporters

What can be obligate or facultative and helps in digestion by producing materials the insect would otherwise be deficient in like amino acids

Digestive symbionts