8.5 Digestion, Absorption & Transport of Macronutrients Flashcards
What is lactose broken into?
Galactose and glucose
What does amylase break polysaccharides into?
- Maltose
- Glucose Oligomers
Describe the action of an SGLT1 transporter
- Na/K pump pumps sodium out of cell, creating concentration gradient
- Two sodium ions transport back into the cell via active transport, and this energy is harnessed to move glucose through the transporter into the cell against its conc gradient
H>ow does water respond to the uptake of monosaccharides?
Follows out of lumen into enterocytes and bloodstream
What is co-lipase?
Protein that binds to and anchors lipase to the surfae of emulsion droplet
Briefly describe lipid digestion
- Bile salts emulsify large lipid droplets
- Pancreatic lipase breaks into monoglycerides and free fatty acids (with co-lipase)
- Packaged into micelles (with bile salts and lecithin)
- Released near cell
- Cross membrane and enter cell, where they are resynthesised to triglycerides
- Coated with lipoprotein to form chylomicrons, which enter central lacteal (too big for capillaries)
What are the two sources of protein in our digestive tract?
- Exogenous: dietary
- Endogenous: digestive enzymes, proteins shed from villi tips
Draw a map of protein digestion
Document
What enzymes in the brush border of the small intestine break down small peptides?
Aminopeptidases
What intracellular enzymes break down peptides?
Intracellular peptidases
Draw a diagram of the movement of ions and sugars into and out of an enterocyte
Document
Which enzyme catalyses fructose phosphorylation?
Ketohexokinase
Describe fructose metabolism
- Fructose is phosphorylated by Khk
- Phosphorylated fructose is cleaved and converted into glucose glycerate and organic acids
Where does the bulk of fructose metabolism occur?
The small intestine
Which can store more glucose: hepatocytes or muscle?
Muscle
Will glucose enter muscle in the absence of insulin? Why does this make sense?
No; there will be no GLUT4 transport proteins, which the cells rely on for transportation.
Where does the thoracic duct drain into?
Usually, the left subclavian vein
What enzyme in capillary walls breaks down chylomicrons that have entered circulation from the thoracic duct? What happens next?
Lipoprotein lipase. This enzyme then cleaves the triglycerides to fatty acids and glycerol within a few minutes.
What happens to fatty acids and glycerol that are taken up into adipose cells?
Recombined to triglycerides for storage
What happens to fatty acids and glycerol that are taken up into muscle cells?
Stored or oxidised immediately
What happens to the remnants of chylomicrons following their breakdown?
Captured by the liver, endocytosed, and degraded
What is in the core of a lipoprotein?
Triglycerides and cholesteryl esters
What is on the surface of lipoproteins?
- Phospholipid
- Unesterified cholesterol
- Apolipoproteins
What are the four types of lipoproteins?
- Chylomicrons
- VLDL
- LDL
- HDL
Density relates to proportion that is protein
What are the two kinds of lipoproteins? Where are they synthesised, and what is their function?
- Chylomicrons (enterocytes)
- VLDLs (liver)
- Function: deliver energy-rich triglycerides to cells in the body
When LDLs deliver cholesterol to cells, how is it taken up, and what is it used for?
- Taken up by receptor-mediated endocytosis
- Used for steroid hormones, cell membrane synthesis etc.
How does the liver remove LDL and other lipoproteins from circulation?
Receptor-mediated endocytosis
