Case study 1 HBS202 SP1 2021 - Answer template PDF

Preview

Summary

HBS 202 Advanced Systems Physiology A SP1 2021 Case Study 1 : Endocrine Physiology...

Description

Case study 1 Endocrine Physiology

HBS202 Advanced Systems Physiology A SP1 2021

Name: Han Ngoc Thi Julie Le Student ID: 20394202 1. Draw a diagram of the HPG axis including the key hypothalamic, pituitary and gonadal hormones involved as well as feedback loops (3 marks).

-/+

Hypothalamus

GnRH

+

FSH & LH

+

-/+

Case study 1 Endocrine Physiology

HBS202 Advanced Systems Physiology A SP1 2021

Ovary

Estrogen, Progesterone

2. Using the hormones that you have identified in your diagram (and also including leptin), complete the following table for each (6 marks):

Hormone

Type of hormone

Transport

Receptor

2nd

(peptide/lipid/ami

in

location

messenger

ne)

blood

(cell

pathway

the

membrane vs intracellula GnRH

Peptide

(Gonadotropi

Dissolved

r) Cell

cAMP

in plasma

membrane

Ca2+ pathways

n-releasing hormone) FSH (Follicle stimulating

and

Peptide

Dissolved

Cell

cAMP

in plasma

membrane

pathway

Case study 1 Endocrine Physiology hormone) LH

HBS202 Advanced Systems Physiology A SP1 2021 Peptide

(luteinizing hormone) Estrogen

Progesterone

Leptin

Lipid

Lipid

Peptide

Dissolved

Cell

cAMP

and

in plasma

membrane

Ca2+

Bound to

Intracellula

pathways cAMP

carrier

r

pathway

proteins Bound to

intracellula

cAMP

carrier

r

cGMP

proteins Dissolved

Cell

pathways cAMP

in plasma

membrane

pathways

and

3. What is the difference between the negative and positive feedback exerted by the gonadal hormones, and how are the levels of the other HPG hormones affected in either case? (3 marks) Throughout most of the menstrual cycle, estrogen and progesterone provides negative feedback to the hypothalamus and anterior pituitary gland to decrease/inhibit production of FSH, LH, estrogen and progesterone, and maintain their levels. Positive feedback is exerted by estrogen to the hypothalamus and anterior pituitary gland during follicular phase which increases the production of estrogen by the ovaries, leading to ovulation. During positive feedback, levels of FSH and LH increases, stimulating follicles in the ovaries to mature and stimulates remaining mature follicle to release its oocyte and develop into a corpus luteum respectively. 4. Leptin plays a permissive role in puberty. Explain what this means? (1 mark) Leptin is not a primary factor for the onset of puberty but rather a permissive factor on the onset of puberty, where it depends on the individual’s development and act as a metabolic gate for pubertal maturation to proceed.

5. Given that leptin acts at the hypothalamus, how do you think it enhances reproductive maturation and timing of puberty? (2 marks)

Case study 1 Endocrine Physiology

HBS202 Advanced Systems Physiology A SP1 2021

The presence of leptin signals the hypothalamus of the nutritional status and the degree of fat and energy stores. The timing of puberty can be reflected by body weight more so than chronological age, suggests that meeting a certain level of leptin triggers neuroendocrine cascade, resulting in the onset of puberty. Leptin accelerates secretion of GnRH, increasing secretion of LH and FSH, which are essential for reproductive maturation.

6. Given the action of leptin and your understanding of hormone-receptor interactions, how do you think this ratio changes when approaching puberty i.e. is it more free:bound hormone or vice versa? Why do you think that this is the case? (2.5 marks) When approaching puberty, leptin bound hormones (attached to soluble receptors) become more free in the blood; less leptin are attached to soluble receptors. More free bound leptin can act as a signal to the body to increase production of sex hormones while also increasing body fat level. Increase body fat, therefore increase leptin level triggers the onset of puberty and maintain normal reproductive maturation. However, obese children have high leptin levels where leptin circulates in free form and thus resistant to free leptin.

7. What would be the effect of a GnRH antagonist? How would this affect LH, FSH and gonadal hormone levels when administered? (2.5 marks) GnRH antagonist binds to the GnRH receptors in the pituitary gland, blocking the secretion of LH and FSH, which simultaneously inhibits release of gonadal hormones, thus levels of LH, FSH and gonadal hormones are reduced....