B3 Biology

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B3 – Using Biology

The Kidneys and ADH

A kidney is made up of a pelvis, renal cortex and medulla. It has many nephrons. Nephrons are sections of capillaries and tubules that clean blood. There are two types of filtration that happen in the kidney, these are ultrafiltration and selective reabsorption. Ultrafiltration happens at high pressures between the glomerulus and Bowman’s capsule. Large molecules such as blood cells and proteins stay in the blood whereas smaller molecules such as glucose, urea, ions and water are pushed through. The substances move through the first convoluted tubule where selective reabsorption begins. All the glucose is reabsorbed and sufficient water is reabsorbed, depending on the concentration of ADH. The liquid continues to be pushed through the nephron via the Loop of Henlé to the second convoluted tubule. Anything left at the end of the second convoluted tubule is moved along the ureter to the bladder where it stored before excretion through the urethra.

ADH stands for Anti-Diuretic Hormone and is secreted by the pituitary gland in the brain – it changes the permeability of the walls of the tubules in the nephrons so more or less water can be reabsorbed. When the concentration of water in the blood is low, more ADH is secreted by the pituitary gland to make the walls more permeable and more water is reabsorbed. When normal levels have been reached, the pituitary gland stops secreting ADH in negative feedback. When we are over-hydrated, less ADH is secreted so walls become less permeable and we excrete more water.

Kidney Treatments

Kidney failure is a major problem and can be treated/cured by either dialysis or a transplant.

The three steps of dialysis are:

1.       Take “dirty” blood from patient

2.       Put blood through dialysis machine where it flows through dialysate (separated by a partially permeable membrane. The waste moves from areas of high to low concentration so urea, ions and excess water is lost. Glucose and salts stay in the blood because the dialysate contains the same concentration as the blood

3.       Give the clean blood back

Dialysis is good because it does treat kidney failure patients and stops them from dying, however, it does not indefinitely cure the disease. Only a transplant can cure it forever and even that does not always work. The patient who has had a transplant must take frequent immunosuppressant drugs so their body does not reject the foreign organ. It is also hard to find an exact tissue match.


Female sex cells are called ova. They are adapted for their job because they contain a haploid nucleus that because diploid with a sperm cell. It also has lots of cytoplasm which contains nutrients and its jelly coat turns to a structure that stops other sperm cells entering after fertilisation. A fertilised ovum is called a zygote.

Sperm cells are either male or female. They have a tail for swimming, an acrosome containing digestive enzymes to break the jelly coat of…


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