The Developmental Origins of the Gut and Accessory Organs Flashcards
What is the gut?
A tube with accessory tubes that aid in digestion.
What are the accessory organs of the gut?
The salivary glands, liver, gall bladder and pancreas.
What organs arise from the gut but are not involved in nutrient extraction?
The lung and thyroid
What do the mouth parts arise from?
The branchial arches
What structures other than mouth parts do the branchial arches form?
Structures in the ear, head and neck.
What is the developmental stage of the human embryo at 32 days?
The four branchial arches are arranged symmetrically with the laryngeal pouch between.
What does the laryngeal pouch develop into?
The laryngeal groove
What does each segment of the branchial arches contain?
Cells that will develop into nerves, connective tissue and arteries surrounded by mesodermal tissue.
What kind of tissue is found on the outside of each branchial arch?
Ectodermal tissue
What kind of tissue is found on the inside of each branchial arch?
Endodermal tissue
What is the valley between the outside of each branchial arch called?
A cleft
What is the valley between the inside of each branchial arch called?
A pouch
What do the pouches give rise to?
The auditory tube, thymus and thyroid.
What do the clefts give rise to?
The skin of the ear, neck and eardrum.
What does the gut develop as?
An endodermal tube
What surrounds the endoderm of the gut and forms muscle and connective tissue?
The splanchnic mesoderm.
What provides nutrients to the embryo before the development of the placenta?
The yolk sac.
When does the foregut start to move and develop?
In week 4
What developmental activities are occurring in week 6?
The formation of the trachea. The stomach is fully developed and the dorsal and ventral pancreas are developing.
When does the hepatic bud that will become the liver form?
Week 4
What happens in week 5?
The hepatic bud develops more and starts to differentiate cells into hepatic cells.
What happens in week 6?
- The buds of the endoderm form the pancreas
- The secretion of enzymes and endocrine secretion hormones begins
- The pancreas is attached the the gut by the pancreatic duct
- The pancreatic buds converge to form one organ with acini and Islets of Langerhans
What does the dorsal pancreatic bud form?
The exocrine pancreas
How does the dorsal pancreas change in week 6?
It elongates and grows around the ventral pancreatic duct.
What are the 5 main regions of the gut?
- The mouth and salivary glands
- The pharynx and oesophagus
- The stomach
- The small intestine (duodenum, ileum and jejunum)
- The large intestine (colon, rectum and anus)
What initiates the process of digestion?
Chewing
Where does most digestion occur?
In the lumen of the small intestine.
What is the function of the large intestine?
Removes water and electrolytes
Where are most nutrients absorbed?
In the small intestine
What are the four layers of the gut wall?
The mucosa, submucosa, muscularis externa and the serosa.
What is the function of the mucosa?
It lines the lumen and is highly folded to increase surface area. It is the absorptive surface of the gut and contains mucus.
What is the function of the submucosa?
It is a thick layer of connective tissue that provides structural support and elasticity.
What is the structure of the muscularis externa?
It consists of an inner ring of circular smooth muscle and an outer ring of longitudinal muscle and is innervated by the myenteric nerve plexus.
What is the structure and function of the serosa?
An outer layer of connective tissue that secretes liquid that lubricates organs.
What are the sections of the stomach?
The oxyntic and pyloric mucosae.
What cells are found in oxyntic gastric pit and glands?
- Mucus cells that secrete HCO3 rich mucus
- Chief cells that secrete pepsinogen that is cleaved to initiate protein digestion
- Parietal cells that secret HCl
- Enterochromaffin-like cells (ECL) that secret histamine which stimulates HCl production
What cells are found in the pyloric pit?
- ECL cells
- G cells which secrete gastrin which promotes motility and stimulates other cells
- D cells which secrete somatostatin in response to acid and inhibits parietal, G and ECL cells.
What are the villi of the small intestine lined with?
Enterocytes and goblet cells.
What is the function of enterocytes?
They participate in nutrient absorption and fluid secretion.
What is the site of enterocyte regeneration?
The Crypt of Lieberkühn
What creates mass movement in the large intestine?
Simultaneous contraction of the ascending and transverse colon.
What mixes matter in the large intestine?
Slow haustral contractions
What induces the defecation reflex?
Distension of the rectum, relaxation of the internal sphincter and increased pressure on the external anal sphincter.
What are the primary functions of the colon?
- Absorption of Na, Cl and H2O to condense ileocecal material to stool
- Absorption of short chain fatty acids
- Secretion of K, HCO3 and mucus
- Periodic elimination of faeces
What is the largest organ in the peritoneal coelom?
The liver
What are the functions of the liver?
- To neutralise toxins
- Glycogen storage and glucose homeostasis
- Secretes albumin for blood plasma
- Bile synthesis
- Fe and Cu recovery
How is the liver connected to the gut?
By the hepatic and cystic duct
What are the sources of blood for the liver?
The hepatic artery and hepatic portal vein
What is a liver lobule?
A unit of liver
What is each liver lobule fed by?
A branch of the hepatic artery and portal vein.
What does each lobule contain?
A bile canaliculi.
What are hepatic plates?
A unit of a lobule
What metabolises nutrients in hepatic plates?
Cords of hepatocytes
What are the functions of hepatic plates?
Site of glycogen synthesis and maintenance of blood plasma glucose.
What cells produce bile?
Hepatocytes
What does bile secretion in the gut result in?
It emulsifies fats and aids lipid absorption.
What are Kupffer cells?
A type of macrophage found in the sinusoid that neutralise bacteria and microbial debris.
Where is the pancreas located?
Along the duodenum
Where does glucose homeostasis occur?
In the pancreas
What hormones does the pancreas secrete?
Gastrin, somatostatin and digestive enzymes
How is the pancreas connected to the gut?
Through the pancreatic duct
What is the function of the exocrine pancreas?
The drainage of glands into the duodenum
What do duct cells secrete?
Bicarbonate which neutralises digestive juices.
What is the function of acinar cells?
To secrete digestive enzymes
What do Islets secrete?
Metabolic hormones
What does secretin induce?
Bicarbonate secretion from the pancreatic duct.
What does neutralisation of stomach acid result in?
Release of cholecystokinin (CKK) which induces release of digestive enzymes from the acini.
What are the major digestive enzymes?
Pancreatic lipase, trypsinogen, sterol esterase and pancreatic amylase.
What is the endocrine pancreas organised into?
Islets of Langerhans
What do alpha cells produce?
Glucagon
What do beta cells produce?
Insulin
What do delta cells produce?
Somatostatin in response to acidification of blood.
