Physiology - Cellular Flashcards
What lipids does the plasma membrane consist mostly of?
Phospholipids and cholesterol
What is the plasma membrane?
A fluid lipid bilayer embedded with proteins
What appearance does the plasma membrane have on an electron microscope?
Trilaminar
Describe the head of a phospholipid
Negatively charged, polar, hydrophilic
Describe the tail of a phospholipid
Uncharged, non-polar, hydrophobic
What contributes to the fluidity and stability of the membrane?
Cholesterol
Name the 3 types of membrane porteins that are insterted within or attached to the lipid bilayer
Integral proteins - embedded in the lipid bilayer (receptors)
Transmembrane proteins - extend through the membrane (e.g. transporters, channels)
Peripheral proteins - do not penetrate the membrane (more common intracellularly) (e.g. receptor-associated enzymes)
What is there a small amount of located on the outer surface of cells?
membrane carbohydrate
What layer do glycoproteins and glycolipids together form?
The glycocalyx
What do some transmembrane proteins form?
Water-filled highly-selective ion channels
What are calcium channel blockers used to manage?
Hypertension and abnormal heart rhythms
What disease is directly linked to genetic mutations in channels?
Cystic Fibrosis
What do carrier or transport proteins exhibit?
Substrate specificity - accept only a particular molecule (or ion) or group of closely related molecules.
Where are docking-marker acceptors located and what do they do?
Located on the inner membrane surface
Interact with secretory vesicles leading to exocytosis of the vesicle contents
Name a membrane bound enzyme?
Protein kinase C
Rececptors are commonly found on the outer surface and bind specific molecules such as?
Hormones
Name two types of cell adhesion molecules (CAMs)
- Cadherins
2. Integrins
What do cadherins do?
Help hold cells within tissues together
What do integrins do?
Span the plasma membrane acting as a link between extra and intracellular environments
What serve as self-identify markers?
Membrane carbohydrates
Name the three types of cell junctions
- Desmosomes
- Tight junctions
- Gap junctions
What are desmosomes?
Adhering junctions that anchor cells together, especially in tissues subject to stretching.
What are tight junctions?
They join the lateral edges of epithelial cells near their lumenal (apical) membranes. They can be tight or leaky.
What are gap junctions?
Gap junctions are communicating junctions that allow the movement of charge carrying ions and small molecules between two adjacent cells.
What are the two properties that influence whether a particle can permeate the plasma membrane without assistance?
Solubility of the particle in lipid
Size of the particle
Molcules and ions that can penetrate the membrane are passively driven across the membrane by two forces - what are they?
- Diffusion down a concentration gradient
2. Movement along an electrical gradient
Give the 5 factors in Fick’s law of diffusion
- The magnitude of the concentration gradient
- The surface area of the membrane across which diffusion is taking place
- The lipid solubility of the substance
- The molecular weight of the substance
- The distance through which diffusion must take place
What type of charged area do cations tend to move towards?
More negatively charged areas
How is an electrical gradient formed?
When there is a difference in charge between two adjacent areas
What are aquaporins?
Water channels
What is osmolarity?
The concentration of osmotically active particles present in a solution
What is tonicity?
The effect a solution has on cell volume - tonicity has no units
Describe carrier mediated transport
Substance binds onto a specific carrier which undergoes a conformational change which transports the substance.
What three characteristics determine the kind and amount of material transferred across the membrane?
- Specificity - each carrier is specialised to transport a specific substance or a few closely related chemical compounds (cysteinuria)
- Saturation - transport maximum (Tm) (renal glucose re-absorption)
- Competition - e.g. an amino acid carrier can transport both Gly and Ala. The presence of both diminishes the rate of transfer for either.
What is another term form carrier mediated transport?
Facilitated diffusion or active transport
Does facilitated diffusion need energy?
Noi
Does active transport need energy?
Yes
What kind of concentration gradient does facilitated diffusion occur along?
From high to low
What two forms does active transport come in?
- Primary active transport
2. Secondary active transport
What is primary active transport?
Energy is directly required to move a substance against its concentration gradient
What is secondary active transport?
Energy is required but is not used directly to produce “uphill” movement. The carrier does not split ATP instead it moves a molecule “uphill” by using secondhand energy stored in the form of an ion concentration gradient (usually Na+ gradieny)
What does the sodium-potassium pump transport in and out of the cell?
Transports 3 sodium out and 2 potassium in
What are the 3 important roles for the sodim-potassium pump?
- Helps establish sodium and potassium concentration gradients across the plasma mebrane of all cells
- Helps regulate cell volume by controlling concentration of solutes inside the cell
- The energy used to drive the pump indirectly serves as the energy source for secondary active transport
What is the definition of secondary active transport?
The transfer of a solute across the membrane is always coupled with the transfer of the ion that supplies the driving force (typically sodium)
What are the two mechanisms by which secondary active transport can occur?
- Symport (co-transport) - the solute and sodium move in the same direction (e.g. glucose absorption at the apical membrane of enterocytes)
- Antiport (exchange or countertransport) - the solute and sodium move in opposite directions (sodium into, solute out of the cell). E.G. cells exchange sodium and protons by means of antiport, important in regulation of intracellular pH.
What are the two methods of vesicular transport?
Endocytosis and exocytosis
What two functions can exocytosis allow?
Secretion of enzymes, protein hormones
Way of adding carriers, channels or receptors to the plasma membrane (e.g. GLUT4 and insulin)
What is the seperation of opposite charges across the membrane called?
The membrane potential (Em) - units: mV (1/1000 volt)
Name two types of excitable cells
Nerve and muscle
What is produced when excitable cells produce rapid, transient changes in their membrane potential when excited?
Action potentials
What is constant in non-excitable cells?
The resting membrane potential
Is the concentration of sodium ions high or lower in extracellular fluid?
Higher
Is the conentration of potassium ions high or lower in intracellular fluid?
Higher
Is the intracellular protein anion (A-) ion concentration higher or lower in intracellular fluid?
Higher (extracellular is 0)
Is the concentration of Chloride ions higher or lower in extracellular fluid?
Higher
What direction is the concentration gradient for K+ and Na+?
K+ is outward
Na+ is inward
At resting potential the membrane is 100x more permeable to which ion?
More permeable to K+ than Na+
What ion is the plasma membrane impermeable to?
The large negatively charged (anionic) intracellular proteins (A-)
What direction is the electrical gradient for K+ going in?
Inward
What is the equilibrium potential for K+?
-90 mV
What two opposing forces act on potassium ions?
- The concentration gradient (tending to move K+ out of the cell)
- The electrical gradient (tending to move K+ into the cell)
What can the equilibrium potential for any given ion be calculated using?
The Nernst equation
State the Nernst equation?
Eion = (61log10) [ion]o/[ion]i
What direction is the electrical gradient for Na+ moving?
Moving Na+ out of the cell
What is the equilibrium potential for Na+?
+60 mV
What is the value of the resting membrane potential?
-70 mV
What can be used to calculate the resting membrane potential (Em)?
The Goldman-Hodgkin-Katz equation (GHK)
What type of current does the sodium-potassium pump generate?
Hyperpolarising current
In skeletal muscle: how much does the hyperpolarising current caused by the sodium-potassium pump add to the resting membrane potential?
2-3 mV
Changes in resting membrane potential are linked to the secretion of what from pancreatic B-cells?
Insulin
What prevents plasma fatty acids getting to the brain?
The blood-brain barrier
At what level of glucose would a patient be classed as hypoglycaemic?
<2.5 mmol/l of glucose
In the absorptive and post-absorptive states: what hormones control [glucose]p?
Insulin and glucagon from the pancreas
In emergencies what hormones control [glucose]p?
Adrenaline (adrenal gland)
During starvation what hormones control [glucose]p?
Cortisol (adrenal) and growth hormone (pituitary)
Pancreatic Islets of Langerhans: What do alpha cells release, What do beta-cells release and what do D-cells release?
alpha-cells release glucagon
beta-cells release insulin
D-cells release somatostatin
What ensues if the pancreas is removed or islets destroyed?
Diabetes mellitus [glucose]p is very high (>12 mmol\l) + glycosuria
In the absorptive state: what happens to [glucose]p levels, [insulin]p levels and [glucagon]p levels?
Glucose rises
Insulin rises
Glucagon falls
What does insulin favour - catabolism or anabolism?
Anabolism
What does insulin stimulate the conversion of?
Glucose into glycogen
Fatty acids into triglycerides
Amino acids into protein
Insulin is the hormone of the…
Fed-state
What does glucagon favour - catabolism or anabolism?
Catabolism
What does glucagon stimulate the conversion of?
Glycogen to glucose
Triglycerides into fatty acids
Glucagon is the hormone of the…
Hungry-state
In what 3 ways does insulin lower [glucose]p?
- Stimulating the uptake of glucose from the blood into muscle and fat cells
- Activating the enzymes in the liver and muscle which convert glucose to glycogen
- Insulin also promotes the incorporation of amino acids into protein in muscle and promotes lipogenesis in adipose tissue
How does insulin promote glucose uptake into muscle and fat?
Insulin causes glucose transporter proteins (GLUT4) to be inserted into the plasma membrane of muscle and fat cells from intracellular stores
What 5 things promote insulin secretion?
- Increased glucose (beta-cells)
- Increased amino acids
- Increased parasympathetic activity
- Glucagon
- GIP
What 2 things inhibit the secretion of insulin?
- Decreased glucose
2. Increased sympathetic activity (e.g. exercise)
How is diabetes mellitus detected?
Oral glucose tolerance test
What is glycosuria?
Glucose appearing in urine
How does severe diabetes affect urinary output?
Glycosuria, increased urinary volume, dehydration and consequently thirst
How does severe diabetes affect cells?
The inability of cells to utilise glucose causes a compensatory increase in lipolysis to generate fatty acids as an energy source
How does severe diabetes affect liver function?
Metabolism of fatty acids generates acetyl CoA. Liver is unable to process the extra acetyl CoA through citric acid cycle. Ketone bodies are formed.
What do ketone bodies do to blood pH and what does this initiate?
These lower blood pH “metabolic acidosis”, initiating compensatory hyperventilation “acid drop” breath
Type I diabetes: child or adult onset?
Childhood onset
Type I diabetes: Amount of insulin secreted?
Little/no insulin secretion
What defect causes type I diabetes?
Defect in B-cell function
What develops if type I diabetes is not treated?
Ketosis
Type II diabetes: Child or adult onset?
Adult
Type II diabetes: amount of insulin secretion?
Normal or exceed normal
What defect causes type II diabetes?
Defect in insulin sensitivty
What three things stimulate the release of glucagon?
- Decreased blood glucose (direct effect on alpha-cell)
- Amino acids (raises [glucose]p after protein meal)
- Sympathetic nerve activity (e.g. exercise)
What 2 things inhibit the release of glucagon?
- Raised blood glucose
2. Insulin
In what 4 ways does glucagon raise [glucose]p?
- Increasing liver glycogenolysis
- Inhibiting liver glycogen synthesis
- Promoting liver gluconeogenesis
- Also promotes lipolysis in liver and adipose tissue
What prevents hypoglycaemia after a rich protein meal?
Glucagon
If we starve for long periods what happens to fats and protein?
Fats are metabolised
Protein is catabolised. Protein catabolism has serious consequences such as muscle wasting
What 3 layers is the adrenal cortex made from?
- Zona glomerulosa
- Zona fasciculata
- Zona reticularis
What does the zona glomerulosa release?
Aldosterone
What does the zona fasciculata release?
Cortisol
What does the zona reticularis release?
Sex hormones
What does the medulla of adrenal gland release?
Adrenaline (in storage granules)
What are adrenaline and cortisol released in response to?
Stress
What 4 things does adrenaline do?
- Raises [glucose]p
- Stimulates glycogenolysis
- Stimulates gluconeogenesis
- Released during short-term emergencies
What 4 things does cortisol do?
- Raises [glucose]p
- Stimulates protein catabolism
- Stimulates gluconeogenesis
- Also stimulates lipolysis
(not important for rapid mobilisation of fuel)
Where is the growth hormone secreted from?
Anterior lobe of pituitary glanfd
In response to starvation what 3 things does the growth hormone do?
- Decrease glucose uptake by muscle “glucose sparing” action
- Mobilises glucose from liver
- Also promotes lipolysis in fat cells
