Gastrointestinal Tract III (IV) Flashcards
Accessory organs of the small intestine with a function in digestion
liver: production
gall bladder: storage of bile
pancreas: enzyme and bicarbonate secretion
The liver
- largest gland in body
- has thin capsule of dense connective tissue
- weighs 1200g - 1600g
- high metabolic activity
gross anatomy of the human liver
- consists of four primary lobes: right, left, caudate, quadrate
- falciform ligament: separated larger right and smaller left lobes, suspends liver from diaphragm and attached the liver ventral body wall
- round ligament: remnant of foetal umbilical vein
Hepatic blood circulation
- blood supply of the liver unusual because it has a dual blood supply
liver receives: - arterial blood from the hepatic artery
- from the hepatic portal vein (from small intestines) - all toxins are taken out at the liver before the blood goes back
- branched of hepatic portal vein and hepatic artery empty together and mix in the liver sinusoids
blood leaves liver: - through hepatic vein -> inferior vena cava
Hepatic arterial circulation
- liver received approx. 30% arterial blood from the hepatic artery
- highly oxygenated
Hepatic (liver tissue) portal system
- liver receives 70% venous blood from organs of the gastrointestinal tract and spleen through the hepatic portal vein
- contains nutrients absorbed from the GI tract
- Oxygen poor
Blood supply of the liver - the liver as a filter
- Liver functions as a filter to remove potentially harmful xenobiotics
- Xenobiotics: chemical compounds that are foreign to a living organism = not normally naturally produced by or expected to be present within the organism
Microscopic anatomy of the liver
- Liver lobules: hexagonal structural and functional units
- Hepatocytes (liver cells) filter nutrient-rich blood, produce bile
- central vein located in longitudinal axis
- central vein for the blood vessels and nerves
Hepatocytes = liver cells
- make up about 80% of the cells in the liver (others can be white blood cells)
- filter and process nutrient-rich blood
- increased rough and smooth ER, golgi, peroxisomes and mitochondria
Hepatocyte functions
- produce 900mL bile/day
- produces blood nutrients
- store fat-soluble vitamins (fat storage)
- perform detoxification
portal triad
- not necessarily a triad at each corner of the hexagon, but it was what called when it was thought to have 3
5 parts in each corner of portal triad contain
- branch of hepatic artery, which supplies oxygen (from the heart)
- branch of hepatic portal vein, which brings nutrient-rich blood from intestine
- bile duct, which receives bile from bile canulicali
- lymphatic vessels
- a branch of the vagus nerve
Microscopic anatomy of the liver
- liver sinusoids (liver blood vessels): leaky capillaries between hepatic plates
- blood enters liver lobules through branched of hepatic portal vein and hepatic artery empty together and mix in the sinusoids
Stellate macrophages
- hepatic macrophafes = kupffer cells
- line walled of liver sinusoids
- star-shaped, phagocytic
- phagocytose invading agents
- remove debris and old red blood cells
Bile
- dark green/yellow fluid due to chemicals within and their composition
- produced by the liver hepatocytes
- collected in lobule canulicali (= bile capillaries)
Bile consists of
- water = 97%
- bile salts = 0.7%, fat emulsification and absorption
- bilirubin = 0.2%
- fats (cholestrol) = 0.5%
- electrolytes (the rest)
Bile enterohepatic circulation
- 95% of secreted bile salts are recycled
1. reabsorbed into blood by ileum
2. returned to liver via hepatic portal blood -> only 5% newly synthesised
3. re-secreted in newly formed bile - after being produced, stored in gall bladder. Then once eating occurs, the bile is released and goes through pancreatic duct into the ileum
Function of bile in digestion
- fat is water repellent, but enzyme responsible for fat digestion (lipase) is water soluble
- bile salts emulsify (mix of water and oils to the point where it looke like one) fats in the intestine
- they surround fat droplets to from micelles, providing a greater surface area for pancreatic lipase to break down the fat
The gallbladder definition
- a thin-walled muscular sac
- attached to visceral layer of the liver = on ventral liver surface
- received and stored bile from the liver via the hepatic and then cystic duct
- muscular contractions released bile via cystic duct, which flows into the bile duct
the gallbladder
- lined by a simple columnar epithelium
- functions to store and concentrate bile by absorbing water and ions
- can store 50-100mL in humans
- contains many honeycomb folds that allow it to expand as it fills
Functions of a healthy liver: metabolism
carbohydrates, amino acids and fats
Functions of a healthy liver: energy homeostasis via
glycogenesis, glycogenolysis, gluconeogenesis, ketogenesis, repackaging excess FA
Functions of a healthy liver: synthesis and secretion of
albumin, plasma proteins, clotting factors, transport proteins, insulin-like growth factoe-1, cholestrol, bile salts, glutathione
Functions of a healthy liver: storage of
glycogen, vitamin A, vitamin B12, iron, copper
Functions of a healthy liver: purification transformation and clearance of:
toxins, drugs, hormones, ammonia -> urea, bilirubin
the pancreas
- no distinct capsule, but covered by a thin layer of loos connective tissue
- location: mostly retroperitoneal, deep to greater curvature of stomach
- head is encircled by duodenum
- tail touches spleen
Exocrine functions of pancreas (basic)
produces pancreatic juice
Endocrine functions of pancreas (basic)
- secretion of insulin and glucagon by pancreatic islet and cells = islets of Langerhans
- clumps of secretory cells supports by reticulin fibres, and containing fenestrated capillaries
- delicate capsule arounf each islet
- paler than the surrounding exocrine cells due to less rough endoplasmatic reticulum
- isles do not have an acinar organisation
- endocrine pancreas is made up of clusters of cells called islets of langerhans
the endocrine pancreas - islets of Langerhans
- islets cells: 3 secretory cell types:
- 20% alpha - secrete glucagon
- 75% beta - secrete insulin
(insulin stimulates the synthesis of glycogen, protein and fatty acids)(facilitates the uptake of glucose into cells and activated glucokinase in liver) - 5% delta - secrete somatostatin
(locally acting hormone which inhibits other endocrine cells)
The exocrine pancreas
- closely packed serous acini= clusters of secretory cells
- produce zymogen granules containing proenzymes
- secrete an enzyme rich alkaline fluid into the duodenum via the pancreatic duct
- the alkaline pH is due to the presence of bicarbonate ions, and helps to neutralise the acid chyme from the stomach, as it enters the duodenum
- the enzymes digest proteins, carbohydrates, lipids and nucleic acids
- > ducts: secrete to duodenum via main pancreatic duct
- > smaller duct cells produce water and bicarbonate
Secretions of the exocrine pancreas
- secretions of the acini empty into ducts lined with a simple low cuboidal epithelium, which becomes stratifies cuiboidal in the larfer ducts
what is secreted of the exocrine pancreas
- proteases: digests proteins, secreted in inactive form to prevent self-digestion
- lipases: digests fats
- amylase: digest carbohydrates
- bicarbonate: neutralises chyme
Structure of the enzyme - producing tissue of the pancreas
DIAGRAM
Pancreatic juice composition and role in digestion
- 1200-1500mL produced daily containing: watery, alkaline solution (pH 8), electrolytes, primarily HCO3-
1. neutralises gastric acid and acidic chyme in duodenum
2. enzymes to break down protein (protease), fat (lipase), starch (amylase) and nucleic acids (nucleases
3. suppresses gastric acid secretion
Enzyme-producing tissue of the pancreas - histology
DIAGRAM
Activation of pancreastic proteases in SI
DIAGRAM
Bile and pancreatic secretions into the small intestine
- bile duct and pancreatic duct unite in wall of duodenum
- fust together in the bulblike structure called heaptopancreatic ampulla
- ampulla opens into duodenum via volcano-shaped majoy duodenal papilla
- hepatopancreatic sphincter controls entry of bil and pancreatic juice into duodenum
Control of secretion
- bile and pancreatic juice secretions are both stimulated by neural and hormone controls
