Lec 1 - Reproductive system

Control of body functions

The nervous and endocrine system act together to coordinate functions of all body systems. The nervous system acts through nerve impulses (action potentials) conducted along axons of neurons. At synapses, nerve impulses trigger the release of neurotransmitters. The

endocrine system act through hormones, a mediator molecule that is released in one part of the

body but regulates the activity of cells in other parts of the body.

Function of hormones

These processes help maintain internal homeostasis by regulating the chemical composition and volume of body fluids, metabolism and energy balance, muscle

contraction, glandular secretion, and aspects of immune function. They also play key roles in controlling growth and development, regulating reproductive systems.

Hypothalamus:

is a neuroendocrine organ that maintains homeostasis by integrating neural and hormonal signals to regulate functions such as reproduction, stress, body temperature, hunger, thirst, and sleep.

Posterior pituitary

stores and releases the peptide hormones oxytocin and antidiuretic hormone (ADH), which are synthesised in the hypothalamus. Oxytocin stimulates smooth muscle contraction, particularly during childbirth and milk ejection.

Anterior pituitary

Neurosecretory neurons in the hypothalamus produce releasing and inhibiting hormones that are transported to the anterior pituitary via the hypophyseal portal system, where blood flows directly between capillary beds. These hormones then act on specific groups of anterior

pituitary cells to regulate their secretory activity. Gonadotrophs produce the two gonadotrophins; Follicle Stimulating Hormone (FSH) and Luteinising Hormone (LH).

key reproductive hormones

Water Soluble (Peptides and proteins) - Gonadotrophin releasing hormone (GnRH): Hypothalamus, Anterior

Follicle-stimulating hormone (Anterior pituitary) , Luteinising hormone (Anterior pituitary)

Oxytocin (Posterior pituitary)

Features of hormone regulation

Hormone levels are regulated by complex homeostatic mechanisms involving positive and negative feedback loops that amplify and coordinate endocrine activity. Negative feedback is the most important of these, commonly operating through signalling pathways between the hypothalamus, pituitary, and target organs.

Pituitary hormones that regulate gonadal activity

Follicle Stimulating Hormone (FSH) and Luteinising Hormone (LH). Bind to receptors in the ovary and testis. Promote the synthesis of sex steroid hormones and gametogenesis.

The principle sex steroid hormones

Androgens - Testosterone is the main secretory product of the testis, and associated with the development and maintenance of male characteristics and fertility. Testosterone & 5α Dihydrotestosterone

Some key properties

• Male sex development

• Secondary sex characteristics

• Spermatogenesis

• Libido (sexual drive)

• Muscle development

Oestrogens - Main role is in development and maintenance of female characteristics and fertility. Oestradiol, Oestrone, Oestriol.

The main site of oestrogen production is the granulosa cells of the growing follicle.

Some key properties

• Female sex development

• Secondary sex characteristics

• Regulation of the menstrual cycle

• Growth of the endometrium

• Bone growth

Progestagens - the major steroidal hormone of the corpus luteum and of the placenta. Associated with the preparations for pregnancy and its maintenance.

Sex Determination & Differentiation

Determination - Commitment of the bipotential gonad to a testis or an ovary. The Sex-determining Region on the Y

chromosome (known as the SRY gene) provides the pathway for testes to develop. The presence of a testis determines the sexual fate of the embryo, against the basic feminine trend. In the absence of SRY, the embryo develops into a female.

Differentiation - The phenotypic development of genital structures due to the action of hormones produced following gonadal development.

The internal genitalia

Male differentiation - Müllerian duct regression occurs under the control of Anti-müllerian hormone (AMH). Testosterone secreted by the testis actively maintain the Wolan ducts. The Wolan ducts develop into the epididymis, vas deferens and seminal vesicles. The testis descends from its internal position to the scrotum, usually after the 7th month.

Female differentiation - Female differentiation of the genital tract lags behind male organogenesis. The Wolan ducts begin to regress slowly from about 10 weeks. The Müllerian ducts persist and develop to give rise to the fallopian tubes, uterus, cervix, and upper vagina.

The external genitalia

The male and female external genitalia develop from a single bipotential precursor.

Male differentiation - Fusion of the urethral folds enclosing the urethral tube forming the shaft of the penis. Labioscrotal swellings fuse in the midline forming the scrotum. The genital tubercle (glans area) expands forming the glans penis.

Female differentiationThe urethral folds and labioscrotal swellings remain separate, thus forming the labia minora and majora. The genital tubercle (glans area) forms the clitoris.

Puberty

The physical, emotional, and sexual transition from childhood to adulthood, occurring gradually but marked by distinct milestones. After the reproductive system develops in the embryo, it becomes relatively inactive during childhood, and puberty represents its reactivation, leading to secondary sexual maturation and reproductive capacity. Gonadotrophin levels remain very low until puberty begins.

Endocrine changes during puberty

An increase in plasma LH levels is the first endocrine sign of puberty and is the result of an increase in GnRH release. Gonadotrophin secretion (both LH and FSH) occurs in early puberty at night during sleep. In late puberty, daytime LH pulses also increase. Sex steroids rise in response to the increase in plasma LH.

Secondary sexual characteristics

Characteristics develop at different chronological ages in different individuals the sequence in which the changes occur are quite characteristic for each sex staging criteria (Tanner stage) allows abnormalities to be detected, and comparisons made between individuals.

Menopause

The menopause is the consequence of the ovaries running out of follicles and occurs between 50 and 52 years of age. The last episode of natural menstrual bleeding signifies the end of her reproductive life and is referred to as the menopause.

Postmenopausal oestrogen production. By ~ one year after the menopause the ovary has essentially ceased producing hormones (ovarian senescence). Oestrogen production reduces to less than one-tenth of previous. Oestrogen (oestrone) arises mainly from production in the stromal cells of adipose tissue. Oestrone is a weak oestrogen.

Clinical Symptoms Women Experience during Perimenopause

Vasomotor - hot flushes, night sweats

Genitourinary symptoms - atrophic changes, vaginal dryness

Bone metabolism - osteoporosis

Behavioural/Psychological changes - depression, tension, anxiety, mental confusion, loss of libido

Most of these symptoms of the menopause may be prevented or arrested by oestrogen treatment (known as menopausal hormone therapy)