The Main Roles of the kidneys areThe Removal of urea from the blood, The Adjustment of ions in the blood and The Adjustment of water content in the blood
A healthy kidney produces urine by: First filtering the blood through ultrafiltration. Then reabsorbing all the sugar, dissolved ions and as much water as the body needs.It then releases urea, excess water and ions as urine.
Ultrafiltration: This is when a high pressure is built up which squeezes water, urea, ions and sugar out of the blood and into the Bowman's capsule. The membrane between the blood vessels and the Bowman's capsule act like filters, so big molecules like protein and blood cells cannot squeeze out. They stay in the blood. Reabsorption: As the liquid flows along the nephron, useful substances are absorbed back into the blood. All the sugar is reabsorbed through the process of active transport, against the concentration gradient. Sufficient ions are reabsorbed by active transport, but excess ions are not. Sufficient water is reabsorbed. Release of Wastes: The remaining substances (including urea) continue out of the nephron, into the ureter and down to the bladder as urine.
The Kidneys Part 2
If the kidneys don't work properly, waste substances build up in the blood and you lose the ability to control the levels of ions and water in your body. You get problems in the heat, bones, nervous system, stomach, mouth etc. Eventually this results in death People who suffer from kidney failure may be treated either by using a kidney dialysis machine or by having a healthy kidney transplant. Treatment by dialysis restores the concentrations of dissolved substances in the blood to normal levels, and removes waste substances. It has to carried out at regular intervals. In a dialysis machine the person's blood flows between particularly permeable membranes, surrounded by dialysis fluid. The dialysis fluid contains the same concentration of dissolved ions and glucose as healthy blood. This ensures that glucose and useful mineral ions are not lost. Only waste substances, such as urea and excess ions and excess water diffuse into the dialysis fluid.Problems:Many patients have to have a dialysis session three times a week and each session takes 3-4 hours. This can be time consuming and inconvenient. Dialysis may cause blood clots or infections. Kidney transplants are the only cure to kidney diseases. A disease kidney is replaced with a healthy one from a donor. However, the donor kidney maybe rejected. The recipient's antibodies may attack the antigens on the donor organ as they do not recognise them as part of the recipient's body.Antigens are proteins on the surface of cells.Precautions are taken to prevent rejection of the transplanted kidney.A donor kidney with a 'tissue-type' similar to that of the recipient is used. The tissue type is based on antigens.The recipient is treated with drug that suppresses the immune system so it won't attack the transplanted kidney.
The Kidneys Part 3
Kidney Dialysis machines are:
· Expensive to run.
· Not pleasant experience.
· Inconvenient and time consuming.
· Have long waiting lists.
· Have possibility of rejection.
· Drugs that suppress the immune system can make people vulnerable to other illnesses.
The special features of egg cells
The special features of egg cells:
Their cytoplasm contains lots of nutrients so it can feed the growing embryo.
The egg cell contains a Haploid Nucleus so that when the egg fuses with a sperm it will have a full set of chromosomes.
Straight after fertilisation, the eggs membrane changes it's structure to stop any more sperm getting in. This makes sure the offspring end up with the right amount of DNA.
The special features of sperm cells
The special features of sperm cells:
Sperm are small and they have a tail (Flagellum) to help them swim to the fertilised egg in the uterus.
Sperm have lots of mitochondria in their middle section to provide them with the energy (From respiration) needed to swim this distance.
Sperm also have an Acrosome at the front of the head, where they store the enzymes they need to digest their way through the membrane of the egg cell. Sperm contain a haploid nucleus- This means that they only have one copy of each chromosome.
The Menstrual cycle
The Menstrual cycle has four stages:
Stage 1 Days 1-4 The lining of the uterus breaks down and is released causing bleeding.
Stage 2 Days 4-14 The lining of the uterus builds up again into a thick spongy layer of blood vessels ready to recieve a fertilised egg.
Stage 3 Day 14 An egg is released from the ovary (Ovulation).
Stage 4 Days 14-28 The lining of the uterus is then mantained. If no fertilised egg has landed on the uterus wall by day 28 the lining of the uterus starts to break down and the whole cycle starts all over again.
The menstrual cycle is controlled by four hormones:
FSH (Follicle-stimulating hormone): Causes a egg follicle to mature in one of the ovaries. Stimulates oestrogen production.
Oestrogen: causes the lining of the uterus to thicken and grow. A high level stimulates an LH surge (a rapid increase).
LH (Luteinising Hormone): The LH surge stimulates ovulation at day 14 the follicle ruptures and the egg is released. Stimulates the remains of the follicle to develop into a structure called a corpus luteum which secretes progesterone.
Progesterone: Maintains the lining of the uterus. Prevents the production of FSH and LH. When the level of progesterone falls, and there is a low oestrogen level, the uterus lining breaks down. A low progesterone level allows FSH to increase and then the whole cycle starts again.