Answer:
C. Aldosterone increases sodium reabsorption by increasing the number of Na+-K+ ATPase pumps in the luminal membrane of the proximal tubule.
Explanation:
The terminal part of distal convoluted tubules has two different types of cells: principal cells and intercalated cells. These cells are also present throughout the collecting duct. The principal cells serve to reabsorb Na+ and secrete K+ and have receptors for aldosterone and antidiuretic hormone (ADH).
The function of intercalated cells reabsorb HCO3 - and K+ and to secrete H+. Angiotensin II stimulates the adrenal cortex to release aldosterone which in turn stimulates the principal cells in the collecting ducts to reabsorb more Na+ and secrete more K+. The increased reabsorption of Na+ facilitates reabsorption of more water to increase blood volume and blood pressure.
Answer:
The myosin filament or more precisely the myosin head can now bind to the actin forming the cross bridges followed by a power stroke during which actin slides over myosin.
Explanation:
The muscle contraction can be explained by sliding filament theory bu Huxley and Huxley. The two muscle proteins which take part in muscle contraction are myosin and actin.
Myosin: It is a hexameric protein. Each monomer is called meromyosin. Each meromyosin has two important parts, a globular head with a short arm and a tail. The head forms cross bridges with the actin filament. Myosin head acts as ATPase enzyme. When ATP binds, head acts as enzyme hydrolyzing the ATP to produce energy. The head also has the site for binding of actin.
Actin filament: It contains three proteins, filamentous actin, tropomyosin and troponin. Filamentous actin contains active site for myosin binding but at rest, tropmyosin covers the myosin binding site. This prevents the cross bridge formation. Tropomyosin are held in place by troponin molecules.
When calcium is available, the binding of calcium to a TpC sub-unit of troponin causes the shifting of tropomyosin-troponin complex. Now actin can attach to myosin head and slide over myosin.
The actin filaments slide over the myosin filament by the the formation of cross bridges and during this process the I-band gets reduced whereas the A band remain the same. The lengths of actin and myosin filaments remain unchanged.
Answer:
Explanation:
A polar orbit is one in which a satellite passes above or nearly above both poles of the body being orbited (usually a planet such as the Earth, but possibly another body such as the Moon or Sun) on each revolution. It therefore has an inclination of (or very close to) 90 degrees to the body's equator.
Answer:
c. causes cells to swell and burst, whereas apoptotic cells shrink and condense
Explanation:
These two mechanism are responsible for death of cells in multi cellular organisms.Apoptosis is naturally occurring process which is well organised and programmed.It is ensures the automatic death of old and worn out cells, needed for certain cellular developments. This is demonstrated by DNA fragmentation,cell shrinkage,and the break down of the nuclear walls.It can be initiated through two pathways of intrinsic and extrinsic,The latter leads to death from internal factors,while in the former is when external factor causes the death .
However,when cell death is influenced by external factors(toxins) in the cell environments,which lead to unpredictable or unregulated process leading to cell death ,the process is called Necrosis.it is demonstrated with the swelling and busting of the cell.and characterised with inflammation. It is an accidental death which causes injuries to the cells and tissues.
