Feedback and the osetrus cycle

Feedback and the osetrus cycle

1. Homeostatic control systems, such as those that regulate body core temperature in mammals, usually involve negative feedback - deviations from the norm or set point trigger responses that restore the system back to its original level. And, as in temperature regualtion, there are often seperate mechanisms controlling deviations in different directions, such as dual system provides a greater degree of body control and means that the body is not over reliant on one set of responses.

2. Sometimes a homeostatic mechanisms break down and negative feedback does not occur. Deviations from the norm are not corrected. Even worse, the deviations may be made larger. This results in a process called postive feedback in which a small change in output causes a futher change in the same direction. postive feedback is usually harmful becuase it tends to produce unstable conditions

3. Females mammals go through a cycle called the oestrus cycle which includes a period of heightened sexual activity. Oestrus refers to the time in the cycle when she becomes sexually receptive and attractive to males. It occurs just before ovulation, when the female is most fertile

4. Probably the most familar oestrus cycle is that of humans who, like most of their primate relatives, are exceptional amoung mammals; they are sexually receptive thoughout the year, and they mensturate

5. The uterus lining in all mammals undergoes a similar pattern of thickening during a reprodcutive cycle. However, if fertilisation does not occur, the uterine lining of primates breaks down and is discharged with blood through the vagina, whereas the uterus lining of non-menstruating mammals is reabsorbed and there is no extensive bleeding

6. The reproductive cycle of non-primate mammals is known as the oestrus cycle because oestrus is the most promonent event in it. It lasts from 5 to 60 days depending on the species. The primate reproductive cycle is also called the menstrual cycle because of the prominance of menstruation

7. In humans a regualr sequence of changes is controlled by the interaction of several hormones, the chief of which are follicle-stimulating hormone (FSH), luteinising hormone (LH), progesterone, and oestrogen. The cycle has three main stages;

   • 1. The follicular phase; where a follicle develops
     • 2. The ovulatory phase; an egg is released into the uterus
       • 3. The lueteal phase; where a corpus leuteum is formed