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Answer either A or B in the space below - Scottish Highers Human Biology - Question 14 - 2015
Question 14
Answer either A or B in the space below. Labelled diagrams may be used where appropriate. A Describe hormonal control of the menstrual cycle under the following he... show full transcript
Worked Solution & Example Answer:Answer either A or B in the space below - Scottish Highers Human Biology - Question 14 - 2015
Step 1
Describe hormonal control of the menstrual cycle under the following headings: (i) events leading to ovulation;
Answer
The menstrual cycle begins with the hypothalamus releasing Gonadotropin-releasing hormone (GnRH), stimulating the pituitary gland to secrete Follicle-stimulating hormone (FSH). FSH promotes the development of ovarian follicles, which produce estrogen. As estrogen levels rise, they stimulate the anterior pituitary to release Luteinizing hormone (LH). The peak of estrogen triggers a surge in LH, leading to ovulation. This process is governed by negative feedback; high estrogen levels inhibit FSH production, preventing further follicle development during this cycle.
Step 2
Describe hormonal control of the menstrual cycle under the following headings: (ii) events following ovulation.
Answer
After ovulation, the ruptured follicle transforms into the corpus luteum, which secretes progesterone and estrogen. Progesterone prepares the endometrium for potential implantation by enhancing its vascularization and maintaining its thickness. If fertilization does not occur, the corpus luteum degenerates, leading to a drop in progesterone and estrogen levels. This decrease triggers menstruation as the endometrium sheds, marking the end of the current cycle.
Step 3
Describe the cardiac cycle under the following headings: (i) the conducting system of the heart;
Answer
The cardiac cycle begins with the Sinoatrial node (SAN), the heart's natural pacemaker, which generates electrical impulses that cause the atria to contract. This impulse travels to the Atrioventricular node (AVN) located at the junction of the atria and ventricles. From the AVN, the impulse travels down the Bundle of His and divides into right and left bundle branches, spreading through the Purkinje fibers causing ventricular contraction, which pumps blood out of the heart.
Step 4
Describe the cardiac cycle under the following headings: (ii) nervous control of the cardiac cycle.
Answer
The autonomic nervous system regulates the cardiac cycle. The sympathetic nervous system activates the heart, increasing heart rate and contractility through the release of norepinephrine. In contrast, the parasympathetic system, mainly through the vagus nerve, slows down the heart rate by releasing acetylcholine. These systems work in a balanced manner, with sympathetic stimulation increasing heart activities during stress and parasympathetic control managing functions during rest.