Lecture 1 Digestion and Absorption Physiology Review Flashcards
What is energy in terms of physiology?
Energy is the capacity to do work and comes from the macromolecules, which are converted to ATP as a useful form (energy currency)
- Other carriers also capture energy-yielding nutrients such as NADPH.*
- ATP cannot be stored, but balance between ATP and ADP/AMP is highly regulated*
How is most ATP created?
the oxidation of food fuels to CO2 and H2O; this is the exchange rate
Consists of substrate level oxidation and oxidative phosphorylation
What is energy primarily required for?
- Basal metabolism
- Thermic effect of food
- Physical activity
What else is produced with energy production?
The entire process of energy production also produces heat
Only a small fraction of total energy released from food is captured
What are the sources of heat production?
- Obligatory (Essential)
- Regulatory
How is ATP created?
In the mitochondria
Macronutrients go through separate processes but are eventually funnelled in the major reaction sequences, primarily leading to the CAC, ETC and finally ATPase.
What is substrate level phosphorylation?
Transfer of a phosphate group from a substrate directly onto ADP to produce ATP
Transferring from a higher energy molecule to one of lower energy
What is oxidative phosphorylation?
The process by which ATP synthesis is coupled to the movement of electrons through the mitochondrial electron transport chain and the associated consumption of oxygen.
It creates an electrochemical gradient in which 3 sites along electron transport chain transfer of H+ ions across membrane to generate ATP.
What is the rate-limiting step of oxidative phosphorylation?
Availability of ADP
What is the overall reaction of ATP synthesis?
How much ATP is produced from 1 mole of glucose?
38 ATP
What is the concept of ‘uncoupling’?
When there is a disruption to the normal functioning of the ETC mid-way which can decrease ATP production and result in more loss to heat
What does more loss to heat cause?
- increase in O2 consumption
- increase in oxidation of NADH & FADH without an increase in ATP production
What is the general conversion of energy from foodstuff?
- Total energy intake
- digestible energy intake
- Metabolizable energy
- The energy available to couple to work
- Energy actually used to accomplish work
- External work done on the environment
Much of this is lost as heat as it progresses through the process
What determines net ATP?
Efficiency of digestion, storage & metabolism processes determines net ATP
What are the components of the digestive tract?
- Primary: oral cavity, pharynx, esophagus, stomach, SI, LI
- Accessory: teeth, tongue, glandular organs (salivary glands, liver, gallbladder, pancreas)
What are the major functions of the GI tract?
- Digest complex molecules
- Absorb nutrients
- Barrier to entry of bacteria
Why is the stomach so acidic?
Activate zymogens, denatures proteins, kills bacteria
Helps break down food for easier digestion
How long is the SI?
10 ft or 3 m
Major functions of the SI?
- Bulk of absorption
- movement of solute, water and nutrients
Structure of the SI surface area
SI is a cylinder → circular folds of the mucosa → villi of mucosal surface → microvilli of absorptive epithelial cells of villi.
What part of the SI is the major site of absorption?
jejunum
What cells make up the epithelium of the SI?
Enterocyte
Very metabolically active and only 72 hour lifespan
How are water soluble nutrients transported out of the SI?
enter directly into capillaries
Includes amino acids, monosaccharides, glycerol, short chain fatty acids (SCFAs), electrolytes, water- soluble vitamins - quick to absorb and transport about 15-45 min
How are lipid soluble nutrients transported out of the SI?
transported via chylomicrons into lymphatics
Much slower absorption/ transportation
Types of nutrient movement across membranes
- Passive movement
- Carrier/ receptor-mediated movement
- facilitated, active, receptor-mediated
Describe general lipid movement to the lymph
Lots of packaging and shipping steps
What is a micelle?
What are bile acids?
Synthesized by the liver and emulsify dietary fats
4g pool cycled up to 12 x / day (metabolize 10-50g/day)
What are the primary bile acids?
Synthesized by the liver and emulsify dietary fats → break down larger fat globules in food into small droplets of fat.
- Smaller fat droplets are easier for the digestive enzymes from the pancreas to process and break down*.
- 4 g pool cycled up to 12 x / day (metabolize 10-50g/day)*
Nutrient absorption in the stomach
Stomach
water, alcohol, some minerals
Nutrient absorption in the SI
Small Intestine
most vitamins and minerals to varying degrees in the duodenum, jejunum & ileum
Nutrient absorption in the jejunum
Jejunum
Lipids, monosaccharides, amino acids, small peptides
Nutrient absorption in the ileum
Ileum
bile salts and acids
Nutrient absorption in the large intestine
Large intestine
water, electrolytes, as well as vitamin K, biotin, SCFAs from bacteria
What are the points of regulation in digestion and absorption?
- Digestion: gastric & pancreatic secretions, bile
- Absorption: surface area of the small intestine, motility, expression of transporters
How are digestion & absorption regulated?
- Enteric nervous system: GI innervated by SNS (inhibitory) and PNS (stimulatory) nerve cells
- Hormones/ regulatory peptides: can be endocrine, paracrine, and/ or neurocrine; most have multiple actions (mostly either inhibitory or stimulatory)
Hormones to know
