Lecture 5 Endocrinology part 2 Flashcards
What are we doing now?
Sex Hormones & Pregnancy
Growth Hormones
Calcium regulation and bone
Learning Outcomes
*Outline the main hormones and cell types involved in the endocrine regulation of reproductive physiology
*Explain the major aspects of male reproductive physiology & its endocrine control of Spermatogenesis
*Describe the occurrence and causes of male infertility
Gonads
Spermatogenesis
Spermatogenesis process
*Spermatogoniumare stem cells that produce spermatocytes by process of meiosis
*Secondary spermatocytes contain HALF amount of DNA and mature finally into spermatozoa
Sertolicells
FUNCTIONS:
*Joined by tight junctions forming blood–testis barrier
*Nourishes spermatocytes, spermatids, and sperm Phagocytose excess spermatid cytoplasm as they developProduce fluid for sperm transport
ENDOCRINE FUNCTION:
*Secrete the hormone inhibin
*regulate the effects of testosterone and FSH(follicle-stimulating hormone)
Leydig Cells
Testosterone
*Is an androgen
*Synthesised from cholesterol (acts via nuclear hormone receptor)
*Secreted by Leydigcells of testes
*In prostate the enzyme 5α-reductase converts testosterone to dihydrotestosterone (DHT)
PHYSIOLOGICAL EFFECTS
*Stimulates descent of testes before birth
*Part of negative feedback loop to control sperm production
*Controls secondary male features such as
*Beard growth
Voice deepeningAnabolism
Why do you think hormones become so prominent during puberty?
What are the events that occur in the target cell that cause the effects that we see as a result of the hormone?
Why Do Hormones Become So Prominent During Puberty?
Puberty is a developmental stage during which the body undergoes significant physical, emotional, and reproductive changes, transforming a child into a sexually mature adult. The prominence of hormones during puberty is crucial because they serve as chemical messengers that regulate the physiological changes necessary for growth and maturation. There are several reasons why hormones become so important during this phase:
Activation of the Hypothalamic-Pituitary-Gonadal (HPG) Axis:
The onset of puberty begins when the hypothalamus in the brain releases gonadotropin-releasing hormone (GnRH).
GnRH stimulates the pituitary gland to secrete luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which then act on the gonads (testes in males and ovaries in females) to produce sex hormones (testosterone, estrogen, and progesterone).
Role in Sexual Maturation:
Hormones like testosterone in males and estrogen in females are responsible for the development of secondary sexual characteristics such as the growth of facial hair, deepening of the voice, breast development, and the onset of menstruation.
They also stimulate the growth of reproductive organs (e.g., the testes and ovaries) to prepare the body for reproductive functions.
Growth Spurts and Physical Changes:
Growth hormone (GH) plays a major role in the rapid growth spurts in height, muscle mass, and bone density that are commonly observed during puberty.
Hormones help regulate changes in body composition, such as increased lean muscle mass in boys and increased body fat distribution in girls.
Emotional and Psychological Changes:
Puberty is also associated with significant emotional and psychological changes, often driven by hormones like testosterone and estrogen.
These hormones affect the brain, leading to mood swings, increased emotional sensitivity, and changes in behavior.
Triggering Reproductive Capability:
Hormones orchestrate the development of the body’s ability to reproduce, including the production of sperm in males and the release of eggs in females.
The menstrual cycle in females is regulated by hormones like estrogen and progesterone, which prepare the uterus for potential pregnancy.
Events in the Target Cell That Cause Hormonal Effects
When a hormone reaches its target cell, a series of specific events occur that lead to the observable effects. These events depend on the type of hormone (steroid or non-steroid) and its receptor mechanism. Here are the main steps involved in hormone action on target cells:
Hormone Binding to Receptor:
Hormones bind to specific receptors located either on the surface of the cell membrane (for non-steroid hormones) or inside the cell (for steroid hormones).
The hormone-receptor interaction is highly specific, ensuring that only target cells with the appropriate receptor are affected.
Signal Transduction Pathway:
For steroid hormones (like testosterone and estrogen), the hormone-receptor complex directly enters the cell’s nucleus and binds to DNA, leading to the activation or suppression of specific genes. This process affects the production of proteins that trigger changes in the cell’s function.
For non-steroid hormones (like growth hormone or insulin), the hormone binds to a cell-surface receptor, which triggers a signal transduction pathway. This pathway often involves a series of molecular interactions that amplify the hormone’s signal, leading to cellular responses.
Activation of Second Messengers:
In the case of non-steroid hormones, binding to the cell-surface receptor often activates second messengers like cyclic AMP (cAMP), calcium ions (Ca2+), or inositol trisphosphate (IP3).
Second messengers amplify the hormone’s signal and initiate a cascade of intracellular events that lead to physiological responses, such as enzyme activation, ion channel opening, or changes in gene expression.
Gene Expression and Protein Synthesis:
Hormone signaling often leads to the activation or repression of specific genes within the cell’s DNA.
This change in gene expression results in the production of proteins that drive various cellular activities and physiological changes, such as cell growth, metabolism, or secretion of other molecules.
Physiological Effects:
The end result of hormone action on target cells is the physiological changes we see during puberty, such as growth, sexual maturation, changes in mood, and increased metabolic activity.
These effects can be fast-acting (like adrenaline’s effect on heart rate) or slower and more sustained (like testosterone’s effect on muscle growth).
Why Hormones Are Important During Puberty
Coordinated Development: Hormones ensure that the changes of puberty occur in a coordinated manner, leading to the synchronized development of different bodily functions.
Adaptation to Adult Roles: These hormonal changes also prepare the individual for adult roles, both in terms of physical reproduction and psychological maturity.
Regulation of Long-Term Processes: Hormones regulate long-term processes that are essential for maintaining the body’s homeostasis and adaptation to new conditions.
In summary, hormones become prominent during puberty because they are the key regulators of the physical, sexual, and emotional changes that define this developmental stage. The events they trigger in target cells lead to changes in gene expression, protein synthesis, and cellular function, resulting in the observable effects associated with puberty.
Spermatozoa structure
*Contains 23 chromosomes
*Acrosome contains enzymes which help it penetrate the secondary Oocye→fertilisation
*Middle piece contains
*Neck contains centrioles that produce microtubules for the rest of the tail
*Principal and end pieces enable motility
What regulates Spermatogenesis?
Only has a releasing hormone: Gonadotropin-releasing hormone (GnRH)
*Stimulates gondaotrophs to secrete the gonadotropins:
➢Luteinising hormone (LH)
➢Follicle Stimulating hormone (FSH)
*Inhibin production is stimulated by testosterone
Hormonal regulation of Spermatogenesis
*GnRH stimulates production of Luteinising Hormone (LH) and Follicle Stimulating Hormone (FSH) by gonadotroph cells in anterior pituitary. *LH stimulates testosterone secretion from Leydig cells (relatively quickly).
*FSH & Testosterone stimulate androgen binding protein (ABP) production (FSH = slower).
*FSH stimulates release of inhibin by Sertoli Cells.
*Testosterone negatively regulates gonadotroph cell production of LH.
*Testosterone decreases release of GnRH from the hypothalamus.
*Inhibin negatively regulates gonadotroph cell production of FS
Male reproductive system -Summary
Explain the major aspects of male reproductive physiology & its endocrine control of Spermatogenesis
Male reproductive system -Summary
Outline the main hormones and cell types involved in the endocrine regulation of reproductive physiology
