Week 19 Flashcards
What is digestion?
Digestion is the conversion of the food we eat into a form that can move through our GIT epithelial cells. This process can be described by two forms of digestion mechanical (chomp chomp) and chemical (enzymes)
Where are carbohydrates digested?
Starts in the mouth but mainly Small intestine
Where are proteins digested?
Stomach and duodenum
Where are lipids digested?
Small intestine
What are the three main divisions of the small intestine?
Duodenum
Jejunum
Ileum
What are the five patterns of digestion in the small intestine?
- No digestion- the substance is freely absorbed by the small intestine eg glucose
- Luminal hydrolysis of polymer to monomers- polymeric substance digested by enzymes into monomers
- Oligomer hydrolysis to monomers by brush border enzymes- brush border enzymes convert oligometric substrate into monomers before absorption
- Intracellular hydrolysis- oligomers broken down inside cell.
- Luminal hydrolysis and intracellular resynthesis- digested, absorbed, reassembled.
What are some macronutrients absorbed into the small intestine and their digestive pathways associated?
- Glucose - no digestion needed.
- Protein - luminal hydrolysis of polymers to monomers (Amino acids)
- Sucrose- brush border hydrolysis of oligomer to monomers (glucose + fructose)
- Peptide- intracellular hydrolysis
- Triacylglycerol - luminal hydrolysis followed by intracellular resynthesis
Where is carbohydrates digested predominately?
- Mouth (salivary amylase)
2. Duodenum (pancreatic amylase)
Where and how is carbohydrate absorbed?
Proximal duodenum
- Glucose and galactose absorbed with co-transport of sodium ions (micronutrient)
- Fructose passively absorbed.
Where is proteins digested?
- Stomach (pepsin + HCl) (makes small peptides)
2. Small intestine (pancreatic enzymes) (makes small peptides)
Where and how are proteins absorbed?
Small intestines
1. Small peptides are freely absorbed 2. Brush border enzymes convert peptide to amino acids for absorption.
Where is fats digested?
- Mouth (salivary lipase) (enzymes are water soluble so can only act on the outer edge of a lipid drop)
- Duodenum- (pancreatic lipase and bile salts)
Where and how are fats absorbed?
- Small intestine- pancreatic lipase + bile salts to emulsify fats into smaller droplets to allow increased access by enzymes.
What are micronutrients?
Vitamins and minerals
What is a key factor for absorption of a micronutrient?
Solubility
What are the fat soluble vitamins?
A,D,E,K - absorbed with lipids as part of the chylomicron
What are the water soluble vitamins?
B,C - absorbed by active transport or specific transport proteins.
What are some macroscopic factors affecting absorption rates in the small intestine?
- Long (6m)
2. Huge Surface area (with many plicae (folds) and villi)
What are some microscopic factors affecting absorption rates in the small intestine?
- Brush border microvilli (in the mucosa layer)
- Goblet cells mucous secretion (mucosa layer)
- Inner circular and outer longitudinal muscles
What are some macroscopic factors affecting absorption rates in the large intestine?
- 1.5m long
2. Major site of water absorption, concentration and faeces storage
What are some microscopic factors affecting absorption rates in the large intestine?
- No villi
- Straight crypts
- Simple columnar epithelium
- High number of goblet cells (mucous secretion)
- High immune cell density
How is water absorbed in the large intestine?
- Sodium is actively pumped in from the lumen
2. Water passively follows
What are some vitamins absorbed in the large intestine?
Vitamins produced by colonic bacteria:
1. Vitamin K, vitamin B12, thiamine B1, riboflavin B2. 2. These are absorbed by specific transporters or via lymph (Vit K)
What structures increase surface area in the small intestine?
- Plicae (folds)
2. Villi
What substances are absorbed from the large intestine?
- Sodium- to draw water in
2. Vitamins K,B12,B1,B2.
What is the general relationship between motility and absorption?
- Motility up = absorption decrease
Motility decrease = absorption increase
What is the source, target and action of Gastrin?
Source = G cells, antrum of stomach Target = parietal cells in body of the stomach Action = increase H+ ion secretion (more stomach acid)
What is the source, target and action of Somatostatin?
Source = D cells in stomach and duodenum, cells of pancreatic islets
Target = Stomach, Intestine, Pancreas, Liver
Action =
Stomach- reduces gastrin release
Intestine- increases fluid absorption/ decreases secretion
Pancreas reduces endocrine/exocrine secretions
Liver- reduces bile flow
What is the source, target and action of VIP?
Source = ENS neurons
Target = small intestine, pancreas
Action = small intestines - decreases smooth muscle relaxation and increases small intestine secretions
Pancreas- increases secretions
What is malabsorption?
A defect in the digestion and absorption of food nutrients.
What is the different types of malabsorption issues?
- Can effect a single nutrient- lactose intolerance
2. Can effect multiple nutrients- coeliac disease
What is the common presentations of malabsorption issues?
- Diarrhoea (steatorrhea)
2. Weight loss
What can malabsorption lead to?
Malnutrition and anaemia.
What are some systemic effects of malabsorption?
Malnutrition Weight loss Growth retardation Oedema Anemia Muscle cramps (loss of calcium) Osteoporosis Bleeding deficiencies
What are some GIT localised effects of malabsorption?
Diarrhoea
Impaired carbohydrate/electrolyte absorption - leading to osmotic diarrhoea
Unabsorbed fats lead to mucosa irritation
Pale, bulky, frequent stool with foul odour.
What is the consequences for inadequate intake of carbohydrate?
- Tissue wasting
2. Metabolic acidosis resulting from accelerated fat use for energy requirements
What are the two types of dietary fatty acids?
Saturated (no double bonds)
Unsaturated (double bonds etc)
What is meant by an essential fatty acid?
They cannot be synthesized in the body and have to be supplied though diet.
What is a characteristic of all essential fatty acid structure?
They are all polyunsaturated.
What is the consequence of essential fatty acid deficiency
- Poor growth
- Skin legions
- depression
What is meant by essential amino acid?
Cannot be made by body must be supplied by diet
What are conditionally essential amino acids?
Needed only in certain situations, illness, pregnancy etc
What is the difference between complete and incomplete food proteins?
Complete- has all essential amino acids (usually animal origin)
Incomplete- lacks one or more essential amino acids (usually plant origin)
What are the consequences of inadequate protein intake?
- Weight loss
- Tissue wasting
- Growth retardation in children
- Anemia
- Oedema
Define vitamin
Organic compounds that catalyze/support a number of biochemical reactions
Define minerals
Inorganic elements/compounds that are part of metabolic reactions or provide structural support in body tissues.
What is a coenzyme?
Small organic molecules that temporarily bind to enzymes and are essential to that enzymes functioning. Coenzymes are a form of cofactors.
What are all B-vitamins?
Co-enzymes or precursors to coenzymes.
What are the consequences of folate deficiency?
- Anemia
- Gastrointestinal problems
- Spina bifida risks in newborns (open spine)
- Neural deficits
- Vascular disease
What are the consequences of Vitamin B12 deficiency?
- Macrocytosis (large red blood cell size)
- Peripheral neuropathy
- Ataxia (uncoordinated muscle movements
- Depression
- Weakness
- Smooth tongue
What are some consequences of Vitamin C deficiency?
- Scurvy (degeneration of skin, teeth, blood vessels)
- Weakness
- Delayed wound healing
- Impaired immunity
- Gastrointestinal upset (extreme deficiency)
- Kidney stone (extreme deficiency)
- Gout (extreme deficiency)
What is Vitamin C for?
Critical co-factor in hydroxylation of collagen and proline residues
As collagen is main structural protein in connective tissues leads to things like scurvy if there is a deficiency.
What are some consequences of Vitamin A deficiency?
- Night blindness
- Dry, scaling skin
- Increased infection
- Immune dysfunction
- For extreme deficiency- headache, irritability, vomiting, hair loss, blurred vision, liver and bone damage.
What are some consequences of Vitamin D deficiency?
- Rickets (bone deformities in children)
- Soft bones in adults
- Poor muscle tone
- Joint pain
- Vulnerable to infections
- Increased cancer risk
- In extreme cases- brain, cardiovascular and kidney damage, calcification of soft tissues, fatigue, weight loss.
What is Anaemia?
Anaemia is a condition that develops when your blood lacks enough healthy red blood cells or haemoglobin.
What are some consequences in Iron deficiency?
- Iron deficiency anemia
- Weakness
- Impaired immunity
- Impaired cognition in children
- Fatigue
- In extreme cases- liver damage, hemochromatosis.