Lecture 2 - Digestion/Absorption Physiology, Intro to Energy Flashcards
What is food? Why do we need it?
Energy
There are different formats of food, some are essential
To maintain health and avoid certain diseases
Can humans exist without energy?
No
What is the body’s energy currency?
ATP; easier to use than macronutrients. Transferable
Which nutrients have energy?
CHO, PRO, Lipids, alcohol, vitamins and minerals (can elicit energy)
What are the physiological processes requiring energy?
Everything
Kreb’s cycle, glycolysis, bowel movements
Exercise, movement, getting from A to B, rest, etc.
How is most ATP created?
Most ATP is created by oxidation of food fuels to CO2 and H2O
- done through substrate level oxidation and oxidative phosphorylation
Why do we need nutrients?
We need them for energy
Energy = the capacity to do work
Carbohydrates, lipids, proteins, alcohol = Potential energy
Nutrients must be converted to ATP (“captured”) - the major energy currency of the cell
What are the three things energy is required for? **
- Basal Metabolism - normal processes of growth and maintenance; most of heat production
- Thermic effect of food (TEF) - assimilation or use of dietary fuels
- Physical activity (EEPA)
Energy released from energy-yielding nutrients is ‘captured’ by…
ATP and other carriers (i.e. NADPH)
Can ATP be stored?
ATP cannot be stored, but balance between ATP and ADP/AMP is highly regulated like casino chips!
The process of energy production also produces…?
Heat (only a small fraction of total energy released from food is captured and actually usable by us)
What are the 3 sources of heat production?
- Obligatory processes
- Regulatory processes
- Some heat produced via thermogenesis from TEF and EEPA
Explain Obligatory (essential) heat production
- Released from anabolic and catabolic reactions (using and synthesizing ATP)
- Produced by fundamental molecular transport processes (e.e. reactions involved in absorption, digestion, storage of nutrients (Na/K pump, H+ pump for ETC)
Explain Regulatory heat production
- Reactions involved in homeostasis of body temperature and overall body maintenance
- Also essential but regulated. Dependent on the environment (e.g. -25 vs 21)
What are the major function(s) of the GI tract?
Digest complex molecules
Absorb nutrients
Barrier to entry of bacteria
What does saliva have in it?
Antibacterial properties: thiocyanate, lactoferrin, lysozyme
Amylase (breaks down starch into sugar)
What are the movements in the stomach?
Propulsion, grinding, retropulsion
Does the stomach participate in digestion?
Yes it is part of digestion through mechanical means but is not really an absorptive organ and not much chemical digestion occurs
What do glans in stomach secrete?
They secrete gastric juices containing water, electrolytes, and enzymes
Examples:
- Parietal (oxyntic) cells —> HCl, IF (B12 absorption)
- Neck (mucous) cells —> HCO3-, mucous
- Chief cells —> pepsinogens
- Enteroendocrine cells —> hormones
Why is the stomach so acidic?
Activates zymogens, denatures proteins, kills bacteria
How long is the small intestine?
10ft or 3m
What occurs in the small intestine?
Bulk of absorption; movement of solute; water and nutrients
What is the surface area of the small intestine? Why is this important?
200m2.
Surface area and type facilitates absorption and transport
What is the major site of absorption?
Jejunum
What is the lifespan of the enterocyte? Why is this important?
Lifespan is 72 hours so it is very metabolically active, and it costs a lot of energy because they only last 3 days
How are water-soluble nutrients transported? What are these water-soluble nutrients?
Water-soluble nutrients enter directly into capillaries, feeding the portal vein (directly to liver)
- includes amino acids, monosaccharides, glycerol, short chain fatty acids (SCFAs), electrolytes, water-soluble vitamins
- Quite quick. About 15 minutes after digesting glucose
How are lipid-soluble nutrients transported?
Lipid-soluble nutrients are transported via chylomicrons into lymphatics
- CMs too large to enter blood capillaries therefore enter lymphatic capillaries via fenestrations of lacteals; eventually enter blood circulation via lymphatic vessels (thoracic duct)
- Fat takes 4 hours (peak) or longer to absorb
- can accumulate
Where is Somatostatin located and what do they do?
Located in pancreatic (D)-cells and intestinal cells
- Inhibits gastric secretions and motility and pancreatic exocrine and gall bladder secretions
What does gastrin do and how does it act?
Gastrin is released by G-cells in antrum of the stomach and proximal small intestine
- acts in stomach to increase secretion of gastric acid, motility, pepsinogen release
What is secretin released by and what does it do?
Secretin secreted by S-cells in duodenum in response to acidic chyme. It stimulates release of pancreatic juice (HCO3-) and enzymes
What is cholecystokinin (CK) secreted by and what does it do?
Secreted by I-cells in proximal small intestine and by enteric nerves in the ileum and colon
- stimulates release of pancreatic juice and enzymes and gall bladder contraction
What does ghrelin, motilin, PYY, GIP, GLP do?
What are the 5 sites of nutrient absorption?
- Stomach: water, alcohol, some minerals
- Small intestine: most vitamins and minerals to varying degrees in duodenum, jejunum, and ileum
- Jejunum: lipids, monosaccharides, amino acids, small peptides.
- Ileum: bile salts and acids
- Large intestine: water, electrolytes, as well as vitamin K, biotin, SCFAs from bacteria
