Liver, pancreas & gallbladder Flashcards
Define excretion
The removal of waste products of metabolism from the body’s excretory organs
e.g., lungs excrete carbon dioxide
Kidney excretes urea
What is the function of the liver?
- It acts as a store, stores excess glucose as glycogen and fat soluble vitamins
- It detoxifies toxic substances e.g., NH3
- It produces bile for fat emulsification
- It produces plasma proteins
- It degrades old RBC
- Involved in carbohydrate, fat & protein metabolism
Describe the structure of the liver
The liver has 4 primary lobes that are separated by falciform. The liver is suspended above the diaphragm
It has 3 main blood vessels, hepatic vein, hepatic portal vein & hepatic artery.
Bile leaves the liver through left & right hepatic duct which travels to the duodenum
The hepatic portal vein receives nutrient rich oxygenated blood from abdominal tract and transports it to the liver
Hepatic artery supplies oxygenated blood to the liver
Hepatic vein transports deoxygenated blood from the liver to the inferior vena cava
Liver structure continued
Lobules are divided by connective tissue containing portal tracts. At each corner of the lobule portal triads are found that contain 3 basic structures of: bile duct, hepatic artery & hepatic portal vein. Liver sinusoids found between hepatocyte plates
Blood from hepatic artery & portal vein pass through sinusoids into the central vein which divides into hepatic veins which drain the liver
There is a 2-way exchange between sinusoids & hepatocytes
Hepatic macrophages (Kupffer cells) found which remove debris e.g., bacteria, break down RBC (haemolysis)
Bile flows through bile canniculi which run alongside hepatocytes and into portal triad.
Blood and bile flow in opposite directions
What are the functions of the hepatocytes?
- Secrete 900ml of bile daily
- Process nutrients e.g., glucose to glycogen
- Store fat soluble vitamins
- Rid body of ammonia by deaminating it and converting it to urea
Space of disse is the space between the hepatocyte and the sinusoid, containing blood plasma. - Where Kupffer cells are found, contains hepatocytes microvilli which increase the SA for absorption of blood plasma
Define haemolysis
Haemolysis: is the breakdown of RBC as they have a lifespan of 120 days, the Fe prosthetic group is recycled. The Hb is broken down to form bilirubin a yellowish pigment, this is carried out via Kupffer cells. Haemoglobin is broken into haem & globin; globin is broken down further to amino acids.
Haem is broken down into Fe & bilirubin, Fe gets recycled, and the bilirubin is excreted from the liver via the bile canniculi towards the duodenum.
Describe the structure of the gallbladder
It consists of 3 components: fundus, neck & body
Inside Layer: The inside of the gallbladder is comprised of columnar epithelium cells. This is very similar to the intestines and the stomach.
Lamina Propria: The next layer is a layer of loose connective tissue called the lamina propria. Together the propria lamina and the columnar epithelium make the mucous membrane.
Smooth Muscle: The next layer in the structure of the gallbladder is a layer of smooth muscle. Smooth muscle is involuntary muscle that lines most autonomous organs. Around the muscle is a layer of connective tissue aptly called the peri muscle.
Serosa: The outermost layer of the gallbladder is the serosa. This is the lining of the gallbladder that contains blood vessels.
Describe the change that occurs in the gallbladder when it empties
When the gallbladder is empty its mucosa folds (like stomach) & then expands once it fills. It expels bile via the cystic duct in the neck of the gallbladder due to contraction of muscle walls. Bile then flows into the bile duct.
Describe the components of bile
Bile is a yellow green alkaline substance; it neutralises the HCL in the stomach
Bilirubin is a yellow waste product of haem which is absorbed via the hepatocytes, excreted to bile & metabolised by small intestine. Bile breaks down to form faeces colour pigment
Bile salts (cholesterol derivatives) they are recycled in the enterohepatic circulation mechanism
Bile pigments (Bilirubin)
Cholesterol
Triglycerides
Electrolytes
Phospholipids
Describe the function of the pancreas
The pancreas is an exocrine (80%) and endocrine gland (20%)
- It secretes hormones of glucagon & insulin
- It also produces digestive enzymes e.g., pepsin via pancreatic acini
Pepsin is produced in it’s inactive form to prevent digestion of the pancreas itself
It produces an alkaline mix with enzymes that neutralises chyme
Ducts in pancreas transport acini secretions and pancreatic juice
Describe the structure and function of pancreatic juice
Pancreatic juice is made from Water, Bicarbonate ions, Electrolytes. Pancreatic enzymes (amylase, lipase, proteases, nucleases)
It is needed to breakdown food as it contains digestive enzymes
Describe the regulation of bile & pancreatic secretion
Hormones & neural stimuli both trigger the secretion of bile & pancreatic juices e.g., CCK & secretin
The presence of bile salts is a major stimulus.
Bile salts are returned to the liver via enterohepatic circulation. the return of bile salts triggers the release of bile.
When no digestion is occurring bile backs up to the cystic duct into the gallbladder to be stored, Bile does not enter the SI until the gallbladder contracts
Describe the mechanism
- CCK release triggered by fats & proteins in chyme, secretin released via acidic chyme, both enter circulation
- CCK induces secretion of enzyme-rich pancreatic juice, secretin causes HCO3- PJ secretion, vagus nerve weakly stimulates cephalic & gastric phases
- Bile salts return to liver via EC, stimulating bile secretion
- Gallbladder contracts via CCK, vagus nerve stimulates weak gallbladder contractions
- CCK causes the hepatopancreatic sphincter to relax which releases bile & PJ into duodenum
