physiology test 2 Flashcards
what are phospholipids made of
diglyceride + phosphoric acid. Found in egg yolk
what is the structure of sterols
contain four C rings. Mostly in animal tissues and egg yolk.
how are dietary lipids generally digestion
Esterases cleave ester bonds
o Lipase
o Phospholipase (pancreas)
o Cholesterol esterase (pancreas)
what are the 3 ways that fat is emulsified
force
emulsion
hydrolysis
how is fat emulsified by force
chyme passing through pyloric sphincter physically breaking down fat droplets
how is fat emulsified by emulsion
Bile acids synthesised by cholesterol in liver
Sterol ring is retained and OH groups added
Hydrophobic side chains replaced by group containing carb. Acid
Bile acids ionised to bile salts
how is fat emulsified by hydrolysis
In intestinal lumen
Lingual lipase & Gastric lipase
Hydrolyses at sn-3
Directly absorbed into portal vein
Pancreatic lipase: hydrolysesTAG –> 2 diacylglycerols –> 2 monoacylglycerol
Colipase: Hydrophobic regions associate with lipid droplet.
how are phospholipids digested
Phospholipase A2 from pancreas
Hydrolyse phospholipids
Produces lysophosphatidylcholine + FFA
how are sterols digested
Free cholesterol DOESN’T need to be digested
Cholesterol ester needs breakdown (cholesterol ester hydrolase)
list all the possible products of lipid digestion
Lyso-phosphatidylcholine
2-monoacylglycerol
Free cholesterol
Fatty acids
Phytosterols
Fat soluble vitamins
describe the structure of the large intestine mucosa
2 muscle layers (circular and longitudinal)
Incomplete longitudinal muscle layer – forms bands
Has ‘pouches’ called haustra
Simple columnar epithelium cells
No folds
Straight, tubular crypt glands in cell wall
list the 3 motility processes of the large intestine
haustral contractions
mass movements
defecation reflex
describe the motility of the large intestine through haustral contractions
Basoelectrical rhythm by pacemaker cells, lower frequency
Alternating contraction/relaxation (flattening) of haustra pouch
Mixing contents back and forth (non propulsive)
Absorption and storage
Local control – intrinsic nerve plexuses mediate contractions
describe the motility of the large intestine through mass movements
Contraction of large colon segments
Coordinated by ENS reflexes:
Gastrocolic (stomach distension). Clears contents in prep for new meal
Duodenocolic (duodenum stimuli e.g. chyme)
describe the motility of the large intestine through the defecation reflex
Internal anal sphincter (smooth muscle) and external anal sphincter (external0
Rectal distention initiated reflex
Relaxation of both sphincters
Controlled by local (intrinsic/extrinsic NS) and parasympathetic reflexes (vagal nerves)
Conscious control: afferent input into cerebrum
briefly explain constipation
Longer retention of contents –> excess water absorbed from faeces
Appendicitis may occurs with faecal obstruction
o Abdominal pain
o Inflammation
o Bacterial infection
what are some things absorbed in the large instines
Salt, water and electrolytes, short chain FA, vitamins
Na+ active absorbed (pump)
Cl- passive absorbed
Water osmosis
what are chylomicrons
Long chain fatty acids packaged into chylomicrons in SI enterocytes
Enter circulation vis lymphatics
Lipid composition modified in circulation
Concentration of chylomicrons decreases after time after fat dense meal – due to lipoprotein lipase action (LPL)
what are the products of lipoprotein lipase (LPL) action
hydrolyses TAG
Products taken up by adipocytes, myocytes, mammary gland epithelial cells (lactation)
Chylomicrons lose phospholipids, free cholesterol and apolipoproteins due to circulating HDL (now becomes chylomicrons remnants)
explain VLDL and LDL metabolism
Secretin of VLDL:
o Contains Apo B100, cholesterol, cholesterol ester
o TAG
Once release into circulation, VLDL acquires other apolipoproteins from HDL
Hydrolysis in capillaries: FAs released from LPL action
In circulation for days, exchanges lipid component with other lipoproteins
LDL taken up by endocytosis
describe HDL metabolism
Synthesised in liver as Apo A1
Acquires lecithin cholesterol acyl transferase in circulation – allows HDL to continue collecting cholesterol as it moves through tissues
HDL can counteract some atherosclerotic plaque through reverse cholesterol transport
HDL delivers cholesterol to liver – binds to SR-B1 on hepatocyte surface
Liver can maintain cholesterol homeostasis, and put cholesterol into bile (for elimination)
what are some interventions for high cholesterol levels
Statins – make less cholesterol in liver
Cholestyramine – medication binds bile acids and prevents reabsorption
Ezetimibe – medication interferes with dietary cholesterol uptake from NPC1l1 transporter
Plant sterols – replaces cholesterols in mixed micelles and interferes with intestinal absorption
why does the liver need cholesterol
Liver needs most cholesterol for bile production
Regulates intracellular cholesterol homeostasis in hepatocytes
what happens if cholesterol levels in the liver is too low
LDL receptors on cell membrane can bring in cholesterol from circulation
Can make cholesterol from acetyl CoA
what happens if cholesterol levels in the liver is too high
Liver acts to decrease cholesterol
explain water movement
Transcellular mechanism – across cells via aquaporins
Paracellular path – between cells via solute driven diffusion
Water movement dependant on osmotic gradients
Maintained by active solute transport.
Standing gradient:
o Sodium moves through enterocyte into lateral space (space between cells)
o Creates high osmotic pressure in lateral space
o Water then enters driven by high osmotic pressure
o Osmotic pressure decreases, hydrostatic pressure increases
o Water is flushed into capillaries
where is calcium stored
99% skeleton
list some dietary sources of calcium
- Nuts
- Dairy
- Broccoli
- spinach
- Baked beans and legumes
- Dried figs
list some functions of calcium
o Muscle contraction
o Nerve conductivity
o Enzyme activation
o Blood clotting
o neurotransmitter secretion
how is calcium absorbed
Alimentary absorption (gut) or renal absorption (more effective)
Obligatory loss of calcium through skin, sweat, faeces
Insoluble calcium salts are solubilised in low pH – stomach
SI has 2 transport mechanisms:
o Transcellular. Carrier mediated active transport. 60% absorption. saturable
o Paracellular absorption: passive diffusion. Non saturable. Jejunum and ileum
what are the transporters involved in calcium absorption
Calcium transporter 1 (CaT1). Moves Ca across brush border
Calbindin. Systolic binding protein. Moves Ca through enterocyte
Calcium ATP-ase pump
what are some factors affecting calcium absorption
1 – 24 dihydroxy vitamin D
o Upregulates CaT1 and calbindin
o Improved calcium absorption
Rate of transit through intestine
Life stages:
o Infants, children, adolescences pregnant and lactation increases absorption
o Decreased with age and lower oestrogen levels
Diet
o Protein and sugars, and vitamin D increase
o Free fatty acids and fibre decrease
list some functions of iron
Haemoglobin synthesis and oxygen transport
DNA synthesis
Electron transport
how is iron absorbed
Transporters across luminal membrane from 2 active transporters:
Haem via HAEM CARRIER PROTEIN 1(hydrolysed prior from proteases)
Hydrolysed in cell to ferrous iron
Non haem via DIVALENT METAL TRANSPORTER 1
Ferric iron concerted to ferrous iron at brush border from duodenal cytochrome b
2 fates after absorption: used immediately or absorbed
what is the fate of iron if it’s needed for immediate use
ferroportin transports Fe2+ across basolateral membrane
Fe2+ oxidised to Fe3+
Binds to transferrin for transport in blood
what is the fate of iron if it’s needed for storage
Stored in epithelial cells as ferritin (short term)
Excreted in faeces with epithelial turnover (3 days)
list some factors affecting iron absorption
Ascorbic acid (promotes) – converts ferric iron to ferrous iron and chelated iron in gut lumen
Organic acids – citric acid enhances absorption
Inhibited by polyphenols (vegetables, some grains, tannin in tea
phytates
list some dietary sources of iodine
marine food
eggs
variety of meats
grains and legumes
Iodine: organic form, amino acid bound
Iodide: free form. Mostly in thyroid gland, some circulating
list some functions of iodine
Key constituant of thyroid hormones
Involved with thyroxine
Essential for normal growth and development
what is the process of iodine absorption
Iodine releases and reduce to iodide before absorption
Rapidly absorbed din stomach and duodenum
Absorbed active transport at enterocyte apical surface by sodium-iodide transporter
Exit across basolateral surface into bloodstream by chloride channel (CLC-2)
Exit across basolateral surface into bloodstream by chloride channel (CLC-2)
Thyroid follicular cells actively take up free iodide immediately from blood
what are the 3 states of energy balance
- Constant body weight
- Unused energy stored.
- Body must use stored energy to supply needs
what are the 3 key nuclei involved in hypothalamic control of energy balance
o Arcuate nucleus
o Lateral hypothalamic area
o Paraventricular nucleus
