2.1 Anatomy and Physiology Flashcards
What is the role of the GI tract and what are its requirements of its role ?
Absorption of nutrients (and drugs) and excretion of waste products
Requires:
- Breakdown large molecule (mechanical and chemical)
- Secretion of enzyme
- Transport mechanisms
- Secretion of compounds to aid absorption
What happens when the circular smooth muscle of the GI tract contracts ?
The lumen becomes smaller
What happens when the longatudinal smooth muscle contracts ?
Helps the movement of contents in lumen
What is peristalsis ?
Is a series of synchronised and wave-like smooth msucle contrations and relaxations that move food unidircetionally through the GI tract.
The contractions and relaxations of the smooth muscles causes the lumen to dialate and constrict.
What resides between the circular smooth muclee and the longitudinal smooth muscle and what is its function?
The nerve plexus (myenteric plexus)
This is a nerve network which co-ordinates the contraction-relaxation cycle at a local level
What are interstitial cells of cajal and what are their roles?
They serve as electrical; pacemacker and generates sponmtaneous electrical slow waves in the GIT. This helps co-ordinate contraction of GI smooth muscle.
They intergate signals from enteric nerves to smooth muscle
True/false. The top of the GIT contracts and the bottom relaxes to move food down the tract? The same thing applies to the small intestine.
True
What controls the mixing and propulation in the GIT and what are their local controls?
Enteric nervous system which has local controls of ACh, NA, 5-HT, NO and ATP
What does the autonomic nervous system act on ?
Enteric nerves and direct on smooth mucles
What does the parasympathetic nervous system release and what does it act on?
Releases ACh, acts on muscarinic receptors to stimulate contractions
Breifly summerise what happens when an ACtion potential arrives at the smooth mucle ?
- Action potential causes depolarisation
- Channels open within the membrane
- Ca2+ comes into the cell
- Vesicals containing ACh merge to the membreane
- ACh is released out of the menrin and acts on receptors on the mooth mucle
- This causes a contraction
What muscarinic receptor subtypes are on smooth mucle on the GIT?
M2: causes smooth mucle contraction
M3: which are on the smooth mucle too
What neurotransmitters (chemicals) can act on the pre-synaptic receptors on the nerve cells ? Do they stimulate or supress the release of ACh
Opioid acts on m- inhibit
Dopamine acts on D2receptor -inhibit
5-HT acts on 5-HT4 receptor - stimulate
In terms of smooth muscle opioid and dopamine causes SM to relax and 5-HT cause SM to contract
What are the two ways in which the GI motility can be controlled therapeutically ?
- Stmilation and antagonist of the muscarinic receptors
2. Stimulation or antagonist of the pre-synaptic receptors
Describe the three stages of mastication and salivation
- Grinding and breakup food for swallowing
- Mix food with saliva (enzymes)
- Stimulates taste buds
What are the 4 functions of the stomach?
- Storage of food
- Initiation of digestion of proteins and CHO
- Kill ingested bacteria (via acid)
- Formation of chyme, before transfer to small intestine
True/false? Stomach absorbs food not alcohol
False, stomach absorbs alcohol but not food
What does the duodenum recieve from the stomach?
Chyme
What enzymes are delivered to the duodenum from the acinar cells in the pancreas? And what do the enxymes breakdown?
Lipase- Fats Amylase- Carbohydrates Proteases- Protiens (trypsin, chymotrypsin,carboxypeptidases) Nucleases- Nucleic acids HCO3- Nutralises acids
Why might patients with cyctic fibrosis need PERT (pancreatic enzyme replacement therapy)?
Pancreatic sercretion depends on Cl- exchange and this is inpaired in patients with cystic fibrosis. This means that fat and protein digestion is imparied.
Can result in undernutrition
Where are most nutrients absorbed?
In the duodenum and jejunum
Where does B12 and Bile absorption occur?
Terminal ileum
What would happen if the small intestine was inflammed in terms of the absorption of nutrients ?
Inflamation causes flattening of the villi,
Reduces the surface area hence reduced the absorption of nutrients
What is the role of tight junctions ?
Limits the transport of contents between cells
If drugs can cross the elithelial cells that line the vili, where can they be absorbed ?
Lymphatic circulation as well as blood circulation
What is payers patches and what are their roles ?
Collection of sub-epithelial lymphoid follicles which acts as immune sensors .
Together with M cells, theyplay an important role in detecting pathogens in the GIT
How are fats digested?
By bile, which is a digestive fluid
What is bile made from?
Cholesterol
Where is bile synthesised?
Liver
Where is bile stored?
Gall bladder
Where is bile secreted ?
Duodenum
What does bile do?
Emulsifies fat and helps form micelles to aid fat absorption
What is entrohepatic recycling?
Reuptake of bile back into the liver
How much bile is produced a day?
1-2L
What chemicals are cholesterols synthesised into to make bile salts?
Cholesterol —> 7-hydroxycholestrol: —> cholate and chenodeoxycholate
What is the role of the portal vein and what is portal circulation?
Drains almost all of the blood from the digestive tract and empties directly into the liver
Portal circulation is the circulation of nutrient-rich blood between the gut and liver
Briefly describe the process of the transport of micelles in enterocytes and then into blood circulation
Miecelles (bile salts and fatty acid) are actively transported across the cells.
This is broken down into cholesterol and FA
Chylomicrons then transport this outside of the cell into blood circulation
Breifly describe the absorption of proteins and carbohydrates into enterocytes
Protiens are broken down into AA which is then transported into the cell via a Transpoter
Polysaccharides (aka carbohydrates) are broken down into glucose.
A symporter transports Na+ as well as glucose inside the cell
What is prenicious anemia caused by?
Lack of intrinsic factor that causes impaired uptake of vit B12
Breifly describe calcium uptake in enterocytes
Ca+ diffused into enterocytes via calcium channels.
This is passive diffusion
CaBP binds to Ca2+ and is transported out of the enterocyte via ATPase into the blood circulation
What prevents bacteria in large intestine from infecting small instestine ?
Ileocecal junction which is between the small and large intestine
What does colonic bacteria in the large intestine digest?
Non-starch polysacharrides - fibre and increases faecal bulk
True/False. More water and NA+ is extracted from the contents within the large intestine
True
Does digestion take place in the large intestine ?
NO
Breifly decribe the absorption of water through enterocytes
Osmosis
