Digestive System 2

What is the oesophagus and how long is it?

muscular tube extending from pharynx to stomach, behind trachea, 25cm

What are the main functions of the oesophagus?

transports food rapidly to stomach, protects against abrasion

How long does food take to travel through the oesophagus?

5 seconds for food, 1 second for fluid

What type of epithelium lines the oesophagus, and why?

thick stratified squamous epithelium, protects against abrasive food

How often is the oesophageal epithelium renewed?

every 7 days

What muscle is present in the upper third of the oesophagus?

skeletal muscle, allowing contraction and voluntary movement for swallowing

What covers most of the oesophagus externally?

fibrous adventitia, attaches it to neighboring structures

What is the stomach's shape, location and capacity?

j shaped enlargement of gut on left side, 1.5 litre capacity

What are the four regions of the stomach?

cardia, fundus, body, pylorus

What are rugae, and what is their function?

longitudinal folds of empty stomach lining that flatten as stomach expands

What is the function of the pyloric sphincter?

regulates release of stomach contents into small intestine

What are the stomach's main functions?

storage, secretion, protein digestion, limited absorption, protection, transport

What does the stomach secrete, and how much gastric juice is produced daily?

acid, enzymes, mucus, 2-3 litres of gastric juice per day

What is chyme?

mixture of food and gastric juice in stomach

Which enzyme digests proteins in the stomach?

pepsin

What substances can be absorbed by the stomach?

water, ions, some drugs including aspirin and alcohol

How does the stomach protect itself?

mucus protects its lining from its own acids and enzymes

How often do mixing waves occur in the stomach?

every 20 seconds

How does the stomach's muscularis externa differ from the usual gut wall?

three smooth muscle layers, inner oblique, middle circular, outer longitudinal

What are gastric pits and gastric glands?

gastric pits are mucosal openings lined by mucus secreting cells, gastric glands open into the pit

What do surface mucous cells secrete?

insoluble alkaline mucus that protects the stomach lining from acid and pepsin

What do gastric stem cells do?

divide to generate new epithelial cells

What do parietal cells secrete?

hcl, which kills microbes, and intrinsic factor which is required for b12 absorption

What do mucous neck cells secrete?

soluble acidic mucus

What do chief cells secrete?

pepsinogen and gastric lipase

What do enteroendocrine cells in the stomach secrete?

gastrin, which stimulates acid and pepsinogen secretion, increases stomach contractions and relaxes the pyloric sphincter

What is the developmental origin of liver cells?

hepatocytes are epithelial cells from embryonic endoderm

What are the major functions of the liver?

glycogen storage and release, red blood cell recycling, bile production and secretion, plasma protein synthesis, removal of toxins in blood

What three supplies must each hepatocyte have access to?

nutrient rich blood from intestine, oxygenated blood from systemic circulation, duct that drain bile towards gallbladder

What are the liver's two blood supplies?

hepatic portal vein, hepatic artery

What is a liver sinusoid?

blood channel between plates of hepatocytes where blood from hepatic portal vein and hepatic artery mix

What do fenestrated endothelial cells in liver sinusoids do?

allow watery components of blood through, no red blood cells

What is the space of Disse?

space between sinusoidal endothelium and hepatocytes where fluid can enter lymphatic drainage

What are bile canaliculi?

tiny channels between adjacent hepatocytes that collect bile

What is the role of tight junctions between hepatocytes?

separate bile canaliculi from surrounding spaces, prevent bile leakage

How are hepatocytes arranged in a liver lobule?

in plates facing central vein

What shape and approximate size is a liver lobule?

hexagonal in cross section, 2mm long, 1mm wide

What structures make up a portal triad?

branch of hepatic portal vein, branch of hepatic artery, bile duct

How does blood flow through a liver lobule?

enters from branches of portal vein and hepatic artery at the edges, flows through sinusoids, drains into central vein

How does bile flow through a liver lobule?

flows through hepatocytes through bile canaliculi towards bile duct

What carries blood away from a liver lobule?

central vein