Membranes Biochemistry Flashcards
What is meningitis?
Infection of meninges of the brain
Usually due to vital/bacterial infection
What are the meninges?
Membranes that cover brain neuronal tissue
Why are the meninges important?
Closely associated with blood brain barrier
What is the blood brain barrier?
Selectively permeable membrane that regulates passage of small + large molecules into microenvironment of neurons of brain
What are all the blood brain barriers?
Blood-retina barrier Blood-spinal cord barrier Blood-cerebrospinal fluid barrier Arachnoid barrier Blood-brain barrier
What type of barrier is the blood-brain barrier?
Physical barrier to molecule penetration into brain
What is able to cross the BBB?
Pain killers (analgesics)
Anaesthetics
Antibiotics
What doesn’t cross the BBB?
Antihistamines
Chemotherapy drugs
Drugs that cause vomiting + nausea
What is the most important membrane?
GI tract
Why is GI tract most important membrane?
Drug molecules need to be absorbed so they enter systemic circulation
What happens when a patient takes a tablet?
Tablet enters stomach + dissolves
Absorbed in intestines
Enters circulation
Reaches action site
What must the drug be to be absorbed?
Drug must be in reasonable soluble form
What happens if a drug fails to be H2O soluble?
Cannot be absorbed from small intestine into systemic circulation
= therapeutic failure
Why may a drug be H2O insoluble?
Tablet may not disintegrate (formulation problem) Drug formulated in tablet granules = H2O insoluble
What factors effect drug solubility of drugs?
Several polar groups - OH
Able to dissociate - eg. COOH
Poor electrolyte
Why is having polar groups important for drug solubility?
Greater H bonding
= increases H2O solubility
Why is being able to dissociate important for drug solubility?
Create proton + negative drug ion
When are drugs poor electrolytes?
DO NOT dissociate readily
What are examples of weak electrolytes?
Acetic acid Ammonium Phosphoric acid Carbonic acid GOOD SOLUBILITY BUT POOR DISSOCIATION
Describe small intestine
Villi
Supplied with blood
Receive lymph supply
Rudimentary nerve supply
What is the gut wall structure?
Mucous coat
Submucous coat
Muscular coat
Serous coat
Describe mucous coat
Surface epithelium with glands
Loose fibrous tissue with capillaries + lymphatic vessels
Muscularis mucosae
Lymphatic tissue
What is villi linked to?
Epidermis
What does epidermal cells have?
Small finger like protuberances
= increase SA for absorption
What is structure of cell membrane?
Phospholipid bi-layer
What is structure of phospholipid bi-layer?
H2O soluble polar head = outside
Fatty acid chain = inside
What drug property factors affect absorption of drugs?
Lipid/H2O solubility
Molecular size
Degree of ionisation
Chemical structure
How do drugs pass through cell membrane?
Passive diffusion
What do drugs need to be to penetrate cell membrane?
Slightly hydrophilic to penetrate hydrophilic head
Slightly lipophilic to penetrate lipophilic head
Why is paracetamol more likely to pass through cell membrane compared to Rifampicin?
Paracetamol = small Rifampicin = large
What makes a drug more likely to pass through cell membrane?
Contain functional groups that donate or accept H+
What does ionised form of a drug attract?
H2O = H2O soluble
When is ionised form of a drug useful?
Enter hydrophilic area of membrane
What happens when ionised form of a drug enters fatty acid section of membrane?
Ionisation reverses = drug becomes fat soluble
What are the physical properties of membrane that affect drug absorption?
SA
Thickness
Conc gradient
^^^FICK’S LAW ^^^
What happens in filtration?
Drug molecules pass through pore in membrane
Dissolved in bloodstream
Under increased pressure
How does drug molecule pass through pore of membrane?
Force via dynamic pressure through pore
What pressures are involved?
Hydrostatic
Osmotic
What is the glomeruli?
Small sections of kidney
What happens to blood vessels in kidney?
Blood supply under pressure
= blood vessels narrow
Increased blood pressure
= H2O soluble drugs forced out of blood vessels
What happens to micro blood vessels in kidney?
Fluid forced out of micro blood vessels
THEN further forced through pores of membrane
Cells form Bowman’s capsule
Fluid collects + passes to bladder
Why do anti-inflammatory pain killers have an effect upon kidney filtration?
Cause narrowing of blood vessels
= glomeruli vasoconstricts
= pressure + vol of blood to glomeruli reduced
= reduction in filtration
Why is proportion of fluid reabsorbed by osmosis?
Blood vessels exert high osmotic pull
Describe active transport across membrane
Transported by pore or protein Requires energy to open OR close pore Against conc gradient Energy from glucose + ATP Pumps = move molecules against conc gradient
What is endocytosis?
Process of cell ingesting material by enveloping it in proportion of cell membrane
What is phagocytosis?
Endocytosis of large particles
What is pinocytosis?
Brings fluid containing dissolved substances
What is receptor-mediated endocytosis?
Endocytosis by portion of cell membrane that contains receptors specific to certain substance
