Week 6 Flashcards
Facts about Pancreas
Around 12-15cm long
Three regions: head, body tail
What two ducts connect the pancreas to the duodenum?
Main pancreatic duct
Accessory duct
What is the pancreas’s exocrine function?
The pancreas contains clusters of glandular epithelial cells where 99% of these clusters are acini. Cells in the acini produce and secrete the components of pancreatic juice
What do acini secrete?
Inactive versions of digestive enzymes - zymogens and proenzymes
Bicarbonate ions that raises the pH of chyme
Facts about pancreatic juice
1-1.5L produced daily
PH between 7.1-8.2
The flow of pancreatic juice
Flows into intercalated discs to the interlobar duct
Then drains into the main pancreatic duct and delivered to duodenum.
Digestive enzyme secretion activated by cholecystokinin where bicarbonate secretion is activated by secretin
Enzymes of pancreatic juice and their function
Pancreatic amylase- carbohydrate digestion
Trypsin, chymotrypsin, carboxypeptidase - Protein digestion
Ribonuclease and deoxyribonuclease - nucleic acid digestion
Two main secretory cells + two others
Alpha islet cells (17%) - Secrete glucagon
Beta islet cells (70%) - secrete insulin
Delta cells (7%) - Secrete somatostatin, inhibit secretion of glucagon and insulin
Fcells (6%) - Secrete pancreatic peptide, inhibits somatostatin
Role of glucagon
Promote glycogenolysis and glyconeogenesis (increases blood sugar concentration, promotes release of fatty acids)
Main target is liver and adipose tissue
Role of Insulin
Promotes glucose uptake into skeletal muscle and adipose tissue via GluT4
Promotes glycogenesis in muscle and liver
Increases amino acid uptake and protein synthesis
Increases formation of triglycerides
Main functions of the Liver
Metabolism
Detoxification
Excretion
Synthesis
Storage
Phagocytosis
Activation of Vit D
What is the liver made up of?
Hepatocytes
Bile canaliculi
Hepatic sinusoids
Stellate reticuloendothelial cells
The role of hepatocytes in the liver
Main cell in liver (80%)
Form hepatic laminae
The role of Bile canaliculi
Network of ducts between hepatic laminae
Carry bile secreted by heaptocytes to bile ducts
These ducts converge into common hepatic duct
Bile can be stored in gall bladder
The role of hepatic sinusoids
Convey oxygen rich blood from branches of hepatic artery to central veins.
Blood flows towards the central vein while bile flows in the opposite direction
Key bile components and their function
Bilirubin - Main bile pigment derived from haem
Bile salts - Responsible for emulsifying lipids and also aid absorption via formation of micelles
The Liver’s role in metabolising carbohydrates
Maintains glucose concentration:
- Stores glucose molecules as glycogen
- Breaks down glycogen to glucose
- Conversion of some amino acids and lactic acid to glucose
- Converts fructose and galactose to glucose
The liver’s role in metabolising lipids
Converts excess carbohydrates and proteins into triglycerides
Synthesise cholesterol and phospholipids
Produces lipoproteins for transportation of triglycerides and cholesterol to other cells
Liver’s role in metabolising proteins
Deamination of amino acids
Transamination
Conversion of ammonia to urea
Synthesis of most plasma proteins
Liver detoxification Pathways - Phase 1
Driven by specific enzymes
Involves oxidation, perioxidation and reduction
Process produces less harmful substances
Liver detoxification pathways - Phase II
Converts phase I metabolites into water soluble form
Involves powerful antioxidants such as gluthione
Allows excretion in urine
Liver as storage
Glycogen
Vitamins A, B12, D, E, K
Minerals including iron and copper
Liver’s role in activating Vit D
Converts inert Vit D from sun, foods or supplements to calcidiol
Then processed in kidneys to form active form of Vit D - Calcitriol
Absorptive state vs post-absorptive state
Recently digested and absorbed nutrients are available, including glucose
No new nutrients available, metabolic needs of the cells must be met by mobilising nutrients stored in the body
Absorptive state metabolic reactions
Glucose: 50% is oxidised and used for ATP production, 40% converted to triglycerides and stored mainly in adipocytes, 10% converted to glycogen in liver and skeletal muscle.
Lipids: triglycerides and fatty acids are stored in adipocytes which are delivered by chylomicrons
Proteins: Amino acids absorbed for the manufacture of proteins, deaminated by the liver to produce keto acids
Regulation of absorptive state
Insulin secretion increases after a meal.
Insulin metabolic effects
GluT4 production and entry of glucose in skeletal muscle and adipocytes
Anabolism of glucose to glycogen
Formation of triglycerides in adipocytes and liver
Amino acid absorption and protein synthesis
Functions of postabsorptive state
Cells still require glucose for ATP production
Maintaining a blood glucose concentration of 5mmol/L
Glucagon can promote glucose release from liver’s glycogen stores
Cortisol and glucagon promote gluconeogenesis
Postabsorptive State Reactions
Glucose production - gluconeogenesis
Glucose sparing - reactions that help preserve the body’s glucose reserves
Postabsorptive state regulation
Glucagon
Cortisol
Epinephrine and norepinephrine
Ketone bodies
Are made when the body is starved, Produce mainly hepatocytes
Steps of ketogenesis
- Lipolysis: Breakdown of triglycerides into free fatty acids and glycerol.
- Beta-oxidation: Free fatty acids are converted to acetyl-CoA.
- Ketone body formation: Acetyl-CoA is converted to acetoacetate, which can be further reduced to beta-hydroxybutyrate or spontaneously convert to acetone.
Significance of ketogenesis
Ketogenesis provides an alternative energy source during periods of low carbohydrate availability, helps preserve muscle protein, and is important in metabolic health.
How is ketogenesis upregulated ?
Glucagon
Cortisol
T3 and t4
Catecholamines
Average basal Metabolic rate
1200-1800kcal/day
Energy homeostasis
BMR 60%
Physical activity 30-35%
Food induced thermogenesis 5-10%
