Digestive system Flashcards
(48 cards)
1
Q
Osmosis
A
Water - Across a semi permeable membrane from a dilute solution to a more concentrated solution.
- isotonic - water in equilibrium
- hypertonic: more concentrated and will attract water from a more dilute solution
- hypotonic: less concentrated and will move away to a more concentrated solution
2
Q
Digestive system
A
- ingestion
- digestion
- absorption
- excretion
3
Q
Oxidation of food
A
We break down energy molecules to convert ADP yo ATP which stores energy in cells. We get about 40%. Rest lost as heat through body.
4
Q
Trace nutrition
A
Mainly H,O, N and C but we end other elements
Essential amino acids, 20, if we get 8 from food then liver can make the other 12.
Essential fatty acids - we need to eat linoleic and alpha-linolenic. We need these for building molecules and cell membranes.
5
Q
Vitamins
A
Come in different forms
- co-factors of enzymes: B and C vitamins
- transcription factors: D vitamins
- antioxidant: E vitamins
- clotting factor: K vitamins
6
Q
Vitamins A
A
Retinoids - lipid soluble and are stored in liver.
- retinal + opsin = rhodopsin. Vision
- retinoic acid: growth factor for skin and lining of certain areas e.g. nose. Important for T- cell differentiation
7
Q
B vitamins
A
Large family, mainly involved in cellular respiration pathways
- B1: thiamine - co-factor for several enzymes in the glycolysis pathway. Found in green vegetables and liver.
- B2: riboflavin - activation of other enzymes.
- B3: niacin - formation of NAD and NADP. Found in grains. Liver can synthesis B3 from B2, B6 and iron.
- B5: pantothenic acid
- B6: pyridoxin
- B7: biotin
- B9 Folate
- B12: cobalbamins - binds to intrinsic factor from the stomach, only way to be absorbed. For formation of red blood cells, central nervous system maintenance.
8
Q
Vitamins C
A
Know as ascorbic acid. Co-factor in many enzymatic reactions, involved in wound healing and collagen synthesis and can act as an antioxidant.
9
Q
Vitamin D
A
From sunlight and diet. Concentrated in liver. Involved in transcription factors and synthesis of certain calcium binding proteins. Can cause build up of calcium in the wrong places and premature atherosclerosis
10
Q
Vitamin E
A
Fat soluble antioxidants that protects cell membranes for reactive oxygen species
11
Q
Vitamin K
A
Helps clotting. Similar to naphthoquinones. Deficiency results in terminal bleeding, happens when gut microbes depleted.
12
Q
Alimentary canal
A
Long tube with specialised cavities
- outermost layer: smooth muscle
- innermost layer: mucosa
- nervous tissue and immune cells
13
Q
GI wall structure
A
- serosa
- longitudinal muscle
- circular muscle
- submucosa
- mucosal muscle
- mucosa
- epithelial lining
- lymph tissue
- mucosal glands
- submucosal glands
14
Q
Digestive track compartments
A
- mouth
- oesophagus
- stomach
- small intestine
- duodenum: 30cm
- jejunum: 1m
- ileum: 1.5m
- large intestine
15
Q
Eating
A
- mouth: chewing and mixing the food with saliva
- tongue: move food and swallowing
- oesophageal sphincter (and lower oesophageal sphincter)
16
Q
Stomach
A
- heavily folded so it can expand after a meal.
- different types of muscle for mixing with gastric secretion.
- names
- top part: fundus,
- middle part: body,
- lower part: antrum.
- fundus and body capable of receptive relaxation, relax to increase storage.
- antrum has strong contractions for mixing chyme
- pyloric sphincter tightly shut.
Small intestine sends signals to stomach
- fat in duodenum: CCK
- acidic chyme: secretin
- both CCK and secretin slow down gastric emptying by causing constriction of the pyloric sphincter.
17
Q
Mixing
A
Stretching of the stomach activated nerve cells and gastric is released and further stimulates stomach contractions
Fats are slowest to leave the stomach.
18
Q
Small intestine
A
Longest part of digestive track
Most absorption happens here
- proximal to distal (closer and further away from the stomach
- duodenum
- jejunum
- ileum
- peristalsis: short range contractions
- villus movement
- crypts of Lieberkühn and Brunner’s glands: bicarbonate ions to neutralise pH to protect small intestine and for digestive enzymes to function
Small intestine sends signals to stomach
- fat in duodenum: CCK
- acidic chyme: secretin
- both CCK and secretin slow down gastric emptying by causing constriction of the pyloric sphincter.
19
Q
Large intestine
A
- valve between terminal ileum and large intestine caecum: ileocaecal valve
- ascending colon
- transverse colon
- descending colon
- sigmoid colon
- rectum
- dries out wast and absorbs water and ions
- gut bacteria live here
- lots of immune cells.
- secretion of mucus.
- peristalsis and reverse peristalsis
- Haustral shuffling
20
Q
Digestive system: secretions
A
- saliva: enzymes for chemical digestion, antibodies and lubrication.
- gastric juices:
- HCl - kills bacteria, and enzymes - pepsins that only function at low pH (ogen - inactive and is activated by the HCl). HCl inhibits salivary alpha-amylase.
- gastrin (which stimulates secretion of HCl and pepsinogen - negative feedback). Hormone produced by the stomach in response to antrum distension. Increased by insulin, which is stimulated by blood glucose levels - extraction of food.
- intrinsic factor
- mucus
- localised bicarbonate ions (HCO3-) which neutralise layer by the lining.
- pancreatic juices:
- bile
- intestinal juices
21
Q
Digestive system: gastrointestinal hormones
A
Endocrine cells in the lining of the stomach and small intestine (enteroendocrine or enterogastrones).
22
Q
Digestive system: gastrointestinal enzymes
A
Mostly peptidases (enteropeptidases)
23
Q
Digestive system: accessory organs
A
- saliva glands
- liver
- pancreas
- gall bladder
24
Q
Small intestine: duodenal brush border.
A
Villi projections increase surface area.
secretions:
- enteropeptidases (enteric system - gastrointestinal track): various digestive enzymes
- peptidases: digest proteins
- oligosaccharidases: digest carbohydrates
- enterogastrones (hormones secreted by the intestine): slow down gastric peristalsis
- secretin: stimulates release of digestive salts from pancreas (and bicarbonate ions in response to acidic chyme).
- cholecystokinin (CCK): stimulates release of digestive enzymes from pancreas (stimulated from fats in the stomach).
- bicarbonate ions
25
Fats, bile and the liver
- lipids leave stomach mostly undigested. hydrophobic.
- emulsification: live produces bile (stored in gall-bladder) and released into the small intestine and acts to brake up surface area of lipid so digestive enzymes can break them down.
- CCK stimulates liver to increase bile production to aid in digestion
26
Structure of pancreas
Exocrine function of the pancreas: produce pancreatic juice
- just below the stomach send has a duct leading to the duodenum (small intestine).
- exocrine portion called acini, arranged in ring like structure (one acinar many acini).
27
Pancreatic juice
- acini produce the enzymatic components of the pancreatic juice
- proteases (inactive): trypsinogen
- lipases
- pancreatic alpha-amylase (second one, fist one from saliva was destroyed in the stomach by pepsin and pH.
- ribonuclease and deoxyribonuclease: digest nucleic acids like RNA and DNA
- ions including bicarbonate ions: neutralise the acidic chyme.
- best stimulus: acidic chyme in duodenum stimulates the secretion of secretin.
- CCK produced in response to fats
28
Liver
Large organ. Each dark dot is a nucleus. In the middle is the portal triad, where bile leaves the liver and goes to the gall bladder
Blood to the liver
- oxygenated blood from a branch of the aorta - by the hepatic artery.
- second blood supply via the hepatic portal vein. The hepatic portal vein takes blood from the digestive track along the intestines and sends it to the liver.
- capillaries in the liver are fenestrated (not very closely stuck together) so the hepatocyte - the liver cells: are in close contact with the blood plasma all the time
- live stores glycogen (a polymer of glucose)
- liver breaks down proteins (protein catabolism): turns ammonia into urea.
- synthesises 12 amino acids and many plasma proteins, including clotting factor.
- stores glycogen, fat-soluble vitamins and iron
- lipid metabolism
- wast management:
- detoxification
- catabolism of haemoglobin from used red blood cells.
Produces bile for digestion: bilary canaliculi between hepatocytes (liver cells), drain into bile ducts, then to the small intestine.
Portal triad - branch of portal vein, branch of hepatic artery and branch of bile duct.
29
Bile
Involved in digestion and absorption of lipids. Bile emulsified the lipids (breaks them up).
- ruminant: cholesterol, which is taken back up by the hepatocytes
- bilirubin: is a breakdown product from haem and gives the bile its colour (yellow-green).
- bile is stimulated by gastrin and CCK (CCK is produced in response to fats in the duodenum).
- bile is recycled: bile gets reabsorbed with the liquids and fatty acids into the hepatocytes. 10 - 20% of bile is not reabsorbed and is excreted along with the faeces.
- only way to excrete cholesterol is through the faeces.
- between meals bile is stored in the gall-bladder and it concentrates the bile 5-20 times, so more efficient.
30
Absorption
Carbohydrates - absorbed in the duodenum and the upper jejunum (easy to break down and absorb).
- we can only absorb 3 mono-saccharides: fructose, glucose and galactose.
Proteins - 50% absorbed in duodenum and 50% in the ileum as they get into smaller bits down to a single amino acid.
Liquids - mostly absorb by mid-jejunum but depends on access to bile.
Water
Ions
Trace nutrients
31
Carbohydrates: at brush border
Duodenum - villi - micro-villi facing into the lumen: resembles a brush
We can only absorb carbohydrates at the brush border - fructose, glucose and galactose
- lactose = sucrose + galactose. Galactose can be absorbed.
- sucrose = fructose and glucose, which can both be absorbed.
- starch/glycogen = individual glucose molecules
32
Absorption of carbohydrates (secondary active transport)
Fructose - absorbed by GLUT-5, transports fructose from the lumen into the cell, down concentration gradient. When cell is full of fructose, GLUT-2 on the absolute rail side (facing the blood) transports it into the blood.
Glucose and galactose can be taken off the small intestine AGAINST the concentration gradient.
SGLT-1 (Sodium-Glucose-Linked-Transporter molecule 1) can transport either glucose or galactose access the cell membrane only if sodium (NA+) is being transported (due to low concentration gradient in the cell - free ride).
Glucose/galactose can leave the cell by the protein GLUT-2 towards the blood (same exit as fructose).
Sodium pump helps keep low concentration of sodium in cell. Used ATP.
33
ATP in sodium-potassium pump (active transport)
Expels 3 sodiums and takes in two potassiums.
Pump in the cell membrane open to the inside of the cell and ready.
1. Three sodium ions are taken from inside the cell into the pump. That triggers a small change in shape of the protein and it associates with ATP.
2. The ATP is broken down into ADP. The loss of this phosphate bond releases some energy and allows the protein to change shape again. The lost phosphate group associates with the pump.
3. The associated phosphate causes the protein to change shape even more so it is now open to the outside and the sodium ions are sent out.
4. The pump is now open, empty and associated with phosphate and ready to start second half of cycle.
5. Two potassium (K+) arrive and causes the release of the phosphate group, causing the protein to change shape towards the inside of the cell.
34
Large intestine
Colonic bacteria
All monosaccharides absorbed by the end of the small intestine.
Some starch that makes it into the small intestine will be used as food for microbes in the gut
35
Malabsorption syndromes
- lactose intolerance: can’t break down lactose into sucrose and galactose, then sucrose into glucose and galactose, then it doesn’t get absorbed. Enters the large intestine and excites the bacteria causing gases, cramping, distention and diarrhoea.
- glucose-galactose malabsorption syndrome: hereditary. Gene for SGLT-1 (protein that allows glucose/galactose into the cell) faulty, so no transport, therefore can’t absorb glucose/galactos.
36
Absorption of proteins
Most of digested protein is absorbed, including all the enzymes secreted in digestive track.
Proteases secreted by pancreas are inactive and the enteropeptidases in the brush border of the duodenum and jejunum activate them, particularly the pancreatic trypsin (trypsinogen into trypsin).
37
Protein absorption defects
Trypsinogen deficiency - hereditary, rare, faulty trypsinogen gene.
Cysteinuria - cysteine in the urine, kidney stones
Prolinuria - proline and hydroxyproline in urine.
38
Digestion and absorption of fats
Lipids causes the release of CCK. CCK causes bile to be released into the duodenum. Bile emulsify the fat so the pancreatic lipase can get at it. Then the fatty acids enter the lacteals as chylomicrons.
A chylomicron is a combination of fatty acid and monoglycerides and some cholesterol ester.
The chylomicron can then be absorbed by passing into the lacteals, which are lymphatic vessels found in the villi, and combine to form lymphatic vessels and eventually empty the fatty acid into the blood stream.
39
Malabsorption syndromes: lipids
- bile deficiency
- intestinal mucosal atrophy
- pancreatic insufficiency
40
Large intestine: ion and water absorption and vitamin K
- water absorption happens all along the intestine. Highest rate of sodium absorption is in the jejunum, followed by the ileum.
- absorption of sodium can be increased by the presents of sugars or neutral amino acids in the small intestine.
- colon can absorb water against concentration gradient
- there is a net absorption of potassium in the jejunum and the ileum. Excessive loss of potassium can be caused by diarrhoea and can affect excitable cells e.g. heart muscle
- glucocorticoid and somatostatin (hormones) can be used to increase water absorption.
41
Water loss and intake
- ingestion
- saliva
- gastric secretions
- bile
- pancreatic juices
- intestinal secretions
- small intestine absorption
- large intestine: absorbed sodium and water against strong osmotic gradient.
42
What is the purpose of the tongue in eating?
Moves food around the mouth, to the teeth and eventually to the back
43
What is a sphincter?
A ring of muscle constricting movement between one part of the body and another
44
Stomach secretes: HCl, pepsinogen (inactive). HCl coverts pepsinogen into pepsin. Pepsin is a protease, an enzyme that beaks down protein bonds. Also secretes: mucus, bicarbonate ions and glycoproteins (for vitamin B12)
What digestive enzyme does the stomach produce?
Pepsin
45
The fact that the stomach secretes gastrin means that the stomach acts as?
An endocrine gland
46
Why is the stomach content acidic?
The stomach secretes HCl to activate pepsinogen
47
CCK released in response to?
Fats in the duodenum
48
Secretin released in response to?
Drop in pH in small intestine
