Can anyone help me to answer these Bio questions

1) As heart rate( i.e. heartbeat rate) is related to the circulatory system in mammals, the cardiac muscles of the heart are responsible for contraction under myogenic control (i.e. without need for nerve supply) to maintain basic requirement of life.

Furthermore, the heart rate is also under neurogenic and hormonal control.

For the nervous control, the rate and force of contraction of heart are regulated by a group of neurones in the cardiovascular centre in the medulla. E.g. when the body is under stressed, it sends off impulses to stimulate SA node in the heart. Hence the heart rate increases.

For the hormonal control, during different body condition, blood volume and composition will change.The change of blood volume is detected by stretch receptors in the walls of venae cava and the change of composition is detected by chemoreceptors in the carotid and aortic bodies. Hormones like adrenaline and acetylcholine, thyroxine will be released according to different conditions.


2) Kidney plays a very important role in regulating water content inside the body. And osmoregulation is also under hormonal control. E.g. when increased amount of water is uptaken, the water potential in body fluid is higher than normal. It is detected by the osmoregulators in hypothalamus. Lesser ADH (hormone) is released from posterior pituitary, smaller proportion of water is reabsorbed in renal tubules of kidney. Hence a larger volume of dilute urine is produced. It helps to restore the osmotic concentration of body fluid by lowering the plasma solute potential.


3) C. Materials are exchanged between the foetus and mother at the placenta. The exact site of exchange is through the foetal capillaries. Red Blood cell is too large in size to pass through. And it is very important to separate the blood cells to avoid imcompatibility of blood groups between the maternal blood and foetal blood!

1)唔好太明白你問咩...應該係medulla oblongata
3)應該係c....總之blood cell一定唔可以