The Gastrointestinal System LO Flashcards
Describe the functions of a liver cell with special reference to bile secretion, metabolism of carbohydrates, proteins and lipids
- production of bile - helps carry away waste and breakdown fats in the small intestine during digestion
- production of certain proteins for blood plasma
- production of cholesterol and special proteins to help carry fats through the body
Identify the constituents and functions of bile
- bile contains: bile salts, cholesterol, bilirubin, water, mineral salts, mucus,
- bile salts: emulsify fats into smaller droplets making cholesterol and fatty acids soluble enabling their absorption along with fat soluble vitamins
- excrete cholesterol
- excretes bilirubin to avoid jaundice
Describe the structure of carbohydrates, proteins and fats and their function in the body
Structure
- carbohydrates: chain of carbons each attatched to an oxygen molecule
- proteins: amino acid sequence, can be primary, secondary, tertiary, quaternary
- fats: glycerol backbone and three fatty acids
Function
- carbohydrates: body’s primary source of energy
- proteins: repair cells and make new ones
- fats: give your body energy and support cell function
Discuss the digestion of carbohydrates
Carbohydrates
- converted to sugars
- long chains of sugars
- broken down by enzymes
- into single sugar units
- only monosaccharides can be absorbed
Describe the lock and key hypothesis of enzyme action
- Enzyme has specific active site
- Enzyme and substrate are complementary
- Bind to form enzyme substrate complex
Discuss three phases of gastric secretion
Phase 1: cephalic phase
- occurs in response to stimuli received by the senses
- reflex in origin and is mediated by the vagus nerve
- gastric juice secreted in response to vagaries stimulation
- either directly by electrical impulses or indirectly by stimuli received through the senses
Phase 2: gastric phase
- mediated by vagus nerve and the release of gastrin
- acid continues to be secreted in response to distension and the peptides and amino acids from proteins
- chemical action of free amino acids and peptides excite the liberation of gastrin from the antrum into circulation
- there are chemical, mechanical and hormonal factors contributing to the gastric secretory response
Phase 3: intestinal phase
- not fully understood due to complex stimulatory and inhibitor process
- amino acids and peptides in circulation promote gastric acid secretion
- secretion of gastric acid is important inhibitor of gastrin release
- if pH of astral content falls below 2.5 gastrin is not released
- some of the hormones released from small intestine are byproducts of digestion (glucagon, secretin)
Discuss lipid metabolism, identifying the roles of fatty acids, triglycerides, phospholipids and cholesterol within the body
Lipid metabolism - fat ingested by the body is emulsified into smaller particles by bile salts and then lipase is secreted by the pancreas and small intestine hydrolysing the triglycerides into free fatty acids monoglycerides
Role of ……..
….triglycerides - energy store for later use
….phospholipids - prevent accumulation of fat in the liver
….cholesterol - helps body make cell membranes and hormones
Discuss carbohydrate metabolism to include monosaccharides, disaccharides, polysaccharides
- Monosaccharides are the simplest form of carbohydrates and are composed of a single molecule or subunit.
- Disaccharides are composed of two monosaccharides linked together
- Polysaccharides are composed of three or more monosaccharides linked together
- Therefore, carbohydrates are broken down into disaccharides or monosaccharides
Define the term glycolysis
The breakdown of glucose by enzymes, releasing energy and pyruvic acid
Define the term glycogenesis
The formation of glycogen, the primary carbohydrate stored in the liver and muscle cells of animals from glucose
Define the term gluconeogenesis
The process of making glucose from its own breakdown products or from the breakdown products of lipids or proteins
Identify the role of insulin and glucagon in carbohydrate metabolism
Insulin - lowers blood glucose by increasing glucose transport in muscle and adipose tissue and stimulates the synthesis of glycogen, fat and protein
Glucagon - promotes hepatic conversion of glycogen to glucose and inhibits glucose breakdown and glycogen formation
Discuss protein metabolism
1) in small intestine dietary proteins are broken down into amino acids by digestive enzymes
2) amino acids are transported in the portal circulation from the small intestine to the liver and then into general circulation, making it available to all body cells
3) from the amino acids available the cells chose those required for their own needs
Describe the functions of the mouth
- physical breakdown of food
- initial digestive enzymes released
- infection control
Describe the functions of the oesophagus
- rapid transport of bolus to stomach through the thorax
Describe the functions of the salivary glands
- three main ones: parotid, submandibular, sub-lingual
- release digestive enzymes
- oral hygiene
- lubricate food bolus
Describe the functions of the stomach
- storage facility
- to produce chyme
- physical and chemical breakdown
- produce acid
- unravels proteins
- activates enzymes
- disinfects stomach contents
Describe the functions of the duodenum
- start of small intestine
- pancreas and liver join here
- acidic chyme is neutralised here
- water enters duodenum through gut walls - dilutes chyme
- digestive enzymes enter here
Describe the functions of the liver
- mainly composed of cells called hepatocytes
- produces bile
- synthesises proteins like albumin/clotting factors
- detoxifies blood
- energy storage (glycogen)
Describe the structure and function of the gallbladder
- connected above the liver and below the duodenum
- stores and concentrates bile (which comes from liver)
- connects the GI tract through a system of tubes
- contracts when fat is detected in the duodenum
- releases bile into the duodenum
Describe the functions of bile
Contains bile salts - help to emulsify fats into smaller droplets
Contains cholesterol - helps excrete cholesterol from the body
Contains bilirubin
When red blood cells die bilirubin is released and needs to be excreted from body - if not excreted can lead to jaundice
Describe the functions of the pancreas
Endocrine function
- produces insulin/glucagon
- very small bit of pancreas
Exocrine function
- produces enzymes for digestion
- most of pancreas
Describe the functions of the jejunum
- final digestion
- nutrient absorption
- water and electrolyte absorption
Describe the functions of the large bowel
- final water absorption
- temporary storage
Rectum/anus
- defaecation
Discuss the digestion of proteins
- converted to amino acids
- long chains of amino acids (polypeptides)
- broken down by protease enzymes like pepsin
Discuss the digestion of fats
- requires bile and enzymes
- bile - breaks fat up into smaller droplets (emulsify)
- lipases - break fat molecules into smaller units
