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What are the two ways that blastopore cells may develop?

Some ingress to form the primary mesenchyme, and some invaginate to form the archenteron

What forms the primary mesenchyme?

In embryo, some cells from the blastopore may ingress to form the primary mesenchyme

What forms the archenteron?

In embryo, some cells from the blastopore may ingress to form the archenteron

What forms the lower part of the anal cavity? (primordial anus)

The proctodeum

What is the proctodeum?

The primordial anus

What doe the archenteron eventually become?

The cavity that eventually forms the digestive tract

What eventually becomes the cavity that becomes the digestive tract?

The archenteron

What becomes the primordial mouth?

The stomodeum

What is the stomodeum?

The primordial mouth

What two embryological features are being pointed to in this image?

The stomodeum and blastopore

Which germ layer forms the internal lining of the GI tract and accessory organs of the digestive system?

The endoderm

What role does the endoderm play in the development of the digestive system?

It forms the internal lining of the GI tract and accessory organs

What is the distinction between the splanchnic and parietal hypomere?

The splanchnic hypomere is associated with the internal organs and the parietal hypomere is associated with the body wall.

Which germ layer develops the walls of the GI tract, visceral, and parietal membranes?

The mesoderm

What role does the mesoderm play in the development of the digestive system?

For the splanchnic hypomere, it forms the walls of the GI tract and the visceral membrane.

For the parietal hypomere, it forms the parietal membrane.

Label this diagram and, if applicable, describe each part.

Dorsal mesentery- attaches to the curve of the stomach, keeps the digestive organs separate from digestive wall

Epimere - dorsal mesoderm, epaxial muscles

Mesomere - intermediate mesoderm, kidney tubules and excretory glands

Hypomere - lateral mesoderm, heart, lymphatic system

What are the accessory organs in the digestive system?

• liver: forms from a diverticulum from the foregut

• gall bladder: develops froms a diverticulum which forms a bile duct

• pancreas: Forms from a diverticulum from the duodenum and migrates

What are the two gland types inside the pancreas?

Exocrine glands- acinar cells secrete digestive enzymes, ions, and water into the pancreatic duct which goes to the duodenum

Endocrine glands- cells called Islets of Langerhan secrete hormones into blood vessels (primarily insulin and glucagon)

What do the exocrine glands in the pancreas do?

Acinar cells secrete digestive enzymes, ions, and water into the pancreatic duct which goes to the duodenum

What do the endocrine glands in the pancreas do?

Islet of Langerhan cells secrete hormones into blood vessels (primarily insulin and glucagon)

What is the difference between insulin and glucagon?

insulin lowers your blood sugar and glucagon raises it

Which gland in the pancreas doesn’t have a duct and secretes hormones like insulin and glucagon?

Endocrine glands

Which gland in the pancreas secretes ions, digestive enzymes, and water into the pancreatic duct?

Exocrine gland

What is the purpose of the mesentery in the development of the digestive system?

It anchors the intestines to the abdominal wall to prevent them from twisting or collapsing.

It carries blood vessels, nerves, and lymphatics to the intestines.

What are the major cavities that we need to know?

The pleural cavity, pericardial cavity, and peritoneal cavity

What is the pleural cavity?

• embryological origin

• location

• purpose

• layers

Embryological origin

Lateral plate mesoderm

Location

Surrounds each lung, located between the lungs and the chest wall

Purpose

It keeps the lungs against the chest wall, allowing for more efficient expansion during inhalation

Layers

Visceral pleura: covers the lungs

Parietal pleura: lines inner chest wall and diaphragm

Which cavity exists between the lungs and the chest wall?

Pleural cavity

What are the two layers of the pleural cavity and what do they do?

The visceral pleura lines the lungs and the parietal pleura lines the chest wall and diaphragm. They both create negative pressure to allow for more efficient expansion during inhalation.

What is the Pericardial cavity?

• embryological origin

• location

• purpose

• layers

Embryological origin

Lateral plate mesoderm

Location

The space between the two layers of the serous pericardium surrounding the heart.

Purpose

Reduces friction from heartbeats and protects the heart from over exertion

Layers

Visceral pericardia is directly adhered to the heart muscle

Parietal pericardia lines the inner surface of the fibrous pericardium

What is the Peritoneal cavity?

• embryological origin

• location

• purpose

• layers

Embryological origin

Lateral plate

Location

Lines the abdominopelvic region

Purpose

Allows for friction-free movement of abdominal organs

contains antibodies and leukocytes to prevent infection

Layers

Visceral peritoneum covers the organs

Parietal peritoneum lines the abdominal wall

Which cavity surrounds the heart?

Pericardial cavity

What are the two layers of the pericardial cavity?

Visceral pericardia is adhered to the actual heart muscle and parietal pericardia lines the fibrous outer layer

Which cavity lines the abdominopelvic region and what are the layers

The peritoneal cavity

Visceral peritoneum lines the organs, parietal peritoneum lines the abdominal wall

What are the four “Tunics” of the digestive tract?

Mucosa, submucosa, mucularis externa, and serosa

Label

What is the mucosa tunic of the digestive tract? What is its purpose?

It is the innermost layer, extending from mouth to anus.

It is made of epithelial tissue.

It is responsible for absorption of nutrients and secretion of enzymes, mucus, and hormones.

What is the submucosa tunic of the digestive tract? What is its purpose?

It is between the mucosa and mucularis externa, and is made of connective tissue, blood vessels, and nerves.

The layer of nerves is responsible for regulation and secretion of glands. The nerves send signals to the glands based on what is/isn’t being absorbed.

The connective tissue provides support for the tract and allows for flexibility.

The blood vessels support the mucosa and transport absorbed nutrients.

What is the mucularis externa tunic of the digestive tract? What is its purpose?

It is comprised of smooth muscle, circular muscle, and longitudinal muscle.

It is responsible for the contractions of the GI tract, moving the food throughout it.

What is the serosa tunic of the digestive tract? What is its purpose?

It is made out of loose and dense connective tissue.

It secretes lubricant around your organs so that there is less friction when the organs move around.

Which tunic of the digestive tract secretes lubricant to prevent friction?

The serosa

Which tunic of the digestive tract is responsible for moving the food throughout?

Mucularis externa

Which tunic of the digestive tract provides structure for the mucosa, transports absorbed nutrients, and tells glands when to secrete?

Submucosa

Which tunic of the digestive tract absorbs nutrients and secretion of mucus, enzymes, and hormones?

Mucosa

What kind of epithelial tissue does the mouth/pharynx have to have and why?

Stratified squamous because of the amount of food that passes through it.

What kind of epithelial tissue does the stomach have to have and why?

Simple columnar because it needs to protect the rest of your organs from stomach acid, bacteria, etc.

There is a lot of mucus secreted because of the acid.

What kind of epithelial tissue do the intestines have to have and why?

Simple columnar with microvilli, because it aids in the moving of food.

What are the bones that make up the oral cavity?

Dermal bones make up the lower portion of the oral cavity and the chondrocranium makes up the upper portion

Describe what goes into tooth development

Dermal papillae

This is your gum line

Fleshy, highly vascularized connective tissue

Ameloblast

• comes from the ectoderm and creates tooth enamel

• enamel does not regrow

Odontoblast

• creates dentin

• comes from mesoderm

• dentin is the bottom part of your tooth

What are the two kinds of tooth shape?

Homodont and heterodont

What are the terms for whether or not teeth get replaced when lost?

Polyphyodonty- teeth get replaced when lost (like sharks)

Diphyodonty- teeth do not get replaced when lost

What are the different kinds of tooth attachment? Example species

Acrodont- not deep in the gum line, less bleeding when teeth break or are lost. Sharks, fish

Pleurodont- partially in the gum line, amphibians and lizards

Thecodont - goes deeply into the jaw, lots of vascularized tissue involved. archosaur lineage, mammals

Vomerine - actually fuse with the jaw fish, amphibians generally covered by a layer of mucus

Which type of tooth attachment has the tooth fused to the jaw?

Vomerine

Which kind of tooth attachment is deeply rooted in the gum tissue?

Thecodont

Which kind of tooth attachment is partially entrenched in the gum tissue

Pleurodont

Which kind of tooth attachment is on the surface of the gum tissue

Acrodont

What are teeth that are replaceable called?

Polyphyodonty

What are teeth that do not get replaced when lost called?

Diphyodonty

What are the three main glands in the oral cavity?

Mucus, salivary, and venom

What are mucus glands in the oral cavity?

They are in the epithelial layer of the buccal cavity. They lubricate food and are also used for filter feeding

They help maintain a healthy oral cavity by neutralizing toxins

What are salivary glands?

They are only present in tetrapods because we chew

They moisten food and produce amylase which breaks down complex carbohydrates

What are venom glands?

They can produce hemotoxins or neurotoxins

Neurotoxins destroy nerves and hemotoxins destroy organs, red blood cells, etc

They immobilize prey and are also used defensively

Venom also has digestive enzymes to help start the digestive process early

Describe the tongue of fish

• derived from the floor of the mouth/pharynx

• “soft’ tongue

• may develop keratinized teeth

Describe the tongue of tetrapods

• muscular tongue

• derived from hypobranchial musculature

• rests on the hyoid apparatus

Label

• nerve fibers

• supporting cell

• oral epithelium

• taste pore

• taste cell

• taste hair

What are some special tongues?

Frog

lingual feeding - uses tongue to catch prey

Snake

Jacobson’s organ - tongue is used to pick up chemicals and jacobson’s organ identifies the smell

Woodpecker

Hyoid apparatus allows woodpecker to protrude its tongue

What is the pharynx?

• extension of the mouth

• embryological source of many organs

• source of gill slits

What is the esophagus?

• reduced in anamniotes

• muscular tube that connects the mouth to the stomach

• in crocodilians and birds, there is an extension of the esophagus called the crop that keeps an excessive amount of food from entering the esophagus

What is the stomach?

• originally functioned as a storage organ which would gradually release food into the intestine

• now has a second phase of digestion that involves chemical and mechanical digestion

• develops from the foregut (endoderm)

What is found along the lining of the stomach?

Gastric pits above gastric glands

What is a gastric gland? What cells are within them and what do they do?

• simple columnar epithelium

Mucous cells

• secrete alkaline mucin which forms a protective layer against the gastric acid of the stomach

• neutralizes acidity

• contains tight junctions to prevent acid from going into muscle tissue

Mucous neck cells

• beneath mucous cells

• secrete acidic mucin

• believed to act as a protective barrier from the alkaline mucin

D cells

• main stomach enteroendocrine cells

• secrete somatostatin which prevents gastric acid secretion

• main function is to inhibit HCl secretion

G cells

• secrete gastrin which stimulates gastric acid secretion

• works to stimulate HCl secretion

Parietal cells

• secrete HCl and intrinsic factor

• HCl (gastric acid) acts to cleave pepsinogen

• Intrinsic factor stimulates absorption of B12

Chief Cells

• secrete pepsinogen

• cleaved by HCl to create pepsin

• pepsin denatures proteins

What is the purpose of mucous cells in the gastric pit?

• form outermost layer

• secretes alkaline mucin, which creates a protective layer against gastric acid

• neutralizes acidity

• has tight junctions to prevent acid or food particles from reaching muscle tissue

What is alkaline mucin?

A protective mucus secreted by mucous cells that protect the gastric pit and stomach lining from gastric acid

What is HCl?

Gastric acid

What are Mucous neck cells and what do they do?

They are beneath the mucous cells in the gastric pit. They produce acidic mucin. Function unknown but assumed to produce protective layer from alkaline mucin

What are D cells? What do they do?

• main stomach enteroendocrine cells

• inhibits secretion of HCl (gastric acid) by producing somatostatin

What are G cells? What do they do?

G cells act in opposition of D cells.

They produce gastrin which stimulates the production of HCl.

What are parietal cells? What do they do?

Parietal cells are in the gastric pit and they are the cells that the D and G cells act upon. They secrete gastric acid and intrinsic factor.

Gastric acid cleaves pepsinogen to make pepsin which denatures proteins.

Intrinsic factor stimulates the absorption of B12.

What are chief cells? What do they do?

Secrete pepsinogen, which is cleaved by gastric acid to become pepsin, which denatures proteins.

How do proteins get denatured?

When a protein loses its shape, it loses its function. Different denaturing agents can corrupt the shape of a protein. In the stomach, the denaturing agents are pepsin and gastric acid.

What are the four major parts of the stomach?

Cardiac region

fundus

body

Pyloric region

Label the regions of the stomach

What is the cardiac region of the stomach?

• portion surrounding the opening from the esophagus into the stomach

What is the fundus of the stomach?

• farthest from the pyloric sphincter

• enlarged part above the cardiac orifice and is inferior to the diaphragm