True/False

The statements that are False are explained below.

1. Actually, this is true, but only to the extent that epinephrine and glucagon stimulate lipolysis. Glycogenolysis does not represent gluconeogenesis because the glucose produced is from a complex carbohydrate (glycogen).

3. Actually, this is true, but only in starvation where stress or infection might be expected. Cortisol does not respond specifically to declines in blood sugar.

7. Positive feedback occurs when high levels of a hormone indirectly stimulate even greater secretion of the hormone. When low levels of a hormone stimulate secretion it is referred to as the removal of negative feedback. In an automotive analogy, puting your foot on the brake is negative feedback, taking your foot off the brake is the removal of negative fedback and pressing on the gas pedal is positive feedback.

8. Positive feedback in the female menstrual cycle occurs in the follicular phase when rising levels of estrogens stimulate the hypothalamus and anterior pituitary, leading to further release of gonadotrophins (FSH and LH).

 

Terminology

Meiosis

(a)This is a process that occurs in the gonads. It involves two sequential cell divisions that results in the production of four daughter cells (gametes) each having one of each kind of chromosome and therefore half the normal (diploid) number found in ordinary cells. In humans, meiosis occurs in adult testes or ovaries (under the proper influence of gonadotrophic hormones) and results in sperm or ova with 23 chromosomes. Details of meiosis can be found in your textbook.

(b) Meiosis must occur in order to generate sufficient numbers of haploid gametes for sexual reproduction. The fertilization of an ovum by a single sperm thus restores the normal diploid number of chromosomes (46) and creates a viable and genetically unique zygote with half its genetic material from the mother and half from the father. Without meiosis, there would be no haploid sperm or ova produced, no sexual reproduction and thus the end of life on earth that utilizes sexual reproduction, a process that endows offspring with genetic variation and thus adaptability and susceptibility to natural selection

Corpus luteum

(a) This is a yellow body formed from those cells of the mature (Graafian) follicle that do not leave the ovary at ovulation. Promoted by the surge of LH, they begin secreting progesterone and estrogens during the luteal phase of the menstrual cycle. Unless fertilization occurs, the corpus luteum will disintegrate and levels of progesterone and estrogens will fall, causing the sloughing of the endometrium (menstruation). Should fertilization occur, the corpus luteum is stimulated by human chorionic gonadotrophin (hCG) from the early placenta and is maintained for up to three months until the placenta takes over steroid production.

(b) The importance of this structure is to provide the hormones necessary to maintain the endometrium and promote glycogen deposition there during the "secretory phase"of the uterus each month. If the corpus luteum were to fail, the endometrium would be sloughed which would prevent implantation or abort gestation.

Glycogenolysis

(a) This is the breakdown of glycogen which releases glucose into the blood. The liver is the main depot for glycogen (although some is found in but used by muscle), and is targeted by such hormones as glucagon and epinephrine that are released in the postabsorptive period. Cortisol, from the adrenal cortex, is also necessary for glycogenolysis. This source of glucose (glycogen) can sustain the human body for only about __________ hours.

Incidentally, glycogen, per se, is never found in the blood.

(b) Without prompt or adequate glycogenolysis, the body would have to immediately rely on lipid and protein breakdown for energy in the early postabsorptive periods. Both of these sources are slow and proteolysis is damaging as it can reduce muscle mass, decrease immunity and deplete digestive enzymes. Glycogenolysis provides necessary glucose for the body and especially the brain during the usually short postabsorptive periods between meals.

 

Situational

(A) Patients with panhypopituitarism would develop intolerance to cold . Without their anterior pituitary, no TSH would be formed and the thyroid would not release T3 or T4. These two thyroid hormones stimulate cell metabolism (oxygen and glucose consumption), and so foster heat production which helps maintain body temperature.

(B) Yes, without the adenohypophysis, there would be no ACTH and hence no secretion of cortisol from the adrenal cortex. Cortisol helps provide glucose and amino acids for cell repair and mitosis. Ironically, high levels of cortisol can also produce intolerance to infection as the hormone can be immunosuppressive when artificially elevated.

(C) Yes, without the anterior pituitary, no FSH or LH could be released. The ovaries would cease to function and the menstrual cycle would stop. Without estrogens and progesterone from the ovaries, secondary sexual characteristics would regress and the woman would effectively enter menopause immediately. This development could be forestalled with daily sex hormones (HRT).