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The Reproductive System
Overall Function– Pair bonding via oxytocin– Perpetuation of the species– Genetic recombination
• Each person can make about 8 million kinds of gametes
• Each gamete contains half the genetic material for the new individual formed at conception
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Infertility
• Defined as no successful pregnancy after 1 year of trying
• About 10-15% of couples in industrialized countries are “subfertile”
• Less is known about less developed countries
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Types of Infertility
• Primary – no successful pregnancies
• Secondary – 1 or more babies, then trouble with subsequence pregnancies
• Male and Female Factors:– About 30% of cases involve just the man– About 50% just the woman– About 20% involve both partners
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Infertility rates are rising…
Causes are mostly related to maternal age:
- More women are deferring childbearing
- There are more older women in the population
Also, as more options become available, more couples are seeking treatment for infertility.
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…but there are more solutions
• About half of all sub-fertile couples eventually have a successful pregnancy
• This is largely thanks to reproductive technologies – more on that later.
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Testes
• Two functions: – Spermatogenesis– Secretion of male sex hormone – testosterone
• Spermatogenesis:– Takes about 64 days– Occurs in seminiferous tubules– Surrounded by Sertoli cells
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Sertoli Cells
• Create Sertoli cell barrier– Protects developing sperm from toxins– Also isolates sperm from immune system
• Nourishes developing sperm, secrete luminal fluid– Fluid contains androgen binding protein,
keeps testosterone levels high
• Involved in endocrine regulation of sperm production
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Pathway of the Sperm
• Testes – produced in seminiferous tubules
• Epididymus – final maturation & storage
• Vas deferens – transport from testes to penis. Secretions added from– Seminal vesicles – fructose, prostaglandins,
fluid– Prostate – alkaline secretions, sperm clotting– Bulbourethral glands – mucus
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Roles of Testosterone
• Developmental Effects– Development of male genitalia– Needed for secondary sex characteristics– Protein anabolism, bone growth, and
eventually, cessation of bone growth
• Regulation of reproduction in adult males– Stimulates spermatogenesis– Maintains accessory repro organs & sex drive
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Erection
• A spinal reflex, afferent pathways in genital region
• Efferent pathways are parasympathetic nerves to vascular compartment of penis– When activated, promote relaxation of
arteriolar smooth muscle, allowing more blood to enter
– Process mediated by nitric oxide
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The penis consists almost entirely of three vascular compartments.
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Common Male Factors in Infertility
• “Plumbing” problems– Failure of Emission– Blockage of the Epididymis– Retrograde Ejaculation
• Immunologic Infertility – anti-sperm antibodies
• Endocrine Problems– Low levels of FSH and LH– Low levels of testosterone
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Ovary Has 2 Functions
• Oogenesis – production of ova
• Secretion of female sex hormones– Estrogen– Progesterone
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Oogenesis
• Female baby has about 1 million ova at birth, but only about 400 reach full maturity.
• The rest under go a process called “atresia”, a type of programmed cell death
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It is best to understand the female reproductive function from 3 viewpoints:
• The ovum
• The hormones
• The endometrial lining
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First, let’s look at the ovum’s viewpoint:• The oocyte is contained within a follicle, which is
surrounded by granulosa cells.• When a follicle begins to develop, the oocyte
increases in size, and granulosa cells proliferate– Outer layer called theca forms and surrounds
follicle– Fluid-filled space called antrum forms around
ovum– This stage is called an antral follicle
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The menstrual cycle, from the perspective of an ovum
• At the start of the follicular phase, several antral follicles begin to enlarge and undergo further development
• After about 1 week, the dominant follicle is selected. It continues to enlarge and becomes a mature (Graafian) follicle
• Ovulation occurs when the wall of the follicle (and ovary) ruptures, releasing ovum. Occurs on about day 14.
• After releasing the ovum, the remnant of the follicle develops into a gland-like structure called the corpus luteum
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Now the endocrine story
• Early to mid-follicular phase:
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Now the Endocrine Story:
Here are the feedback loops,but you need to look at this process over the courseof the menstrual cycle forit to make sense.
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Look at this slide and the previous one together toget the full picture.
What can go wrong?
What normal physiologicevents alter this cycle?
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Roles of Estrogen:Developmental Effects
1. Stimulates growth of external genitalia
2. Stimulates secondary sex characteristics at puberty
3. Stimulates bone growth, and then cessation of bone growth, prevents osteoporosis
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Roles of Estrogen in Adult Female
1. Stimulates ovary and follicle growth, maintains reproductive tract
2. Induces progesterone receptors in uterus
3. Has a negative feedback effect on hypothalamus and anterior pituitary, preventing maturation of additional follicles during luteal phase
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Female Sexual Response and Sexual Dysfunction
• Normal female sex drive relies on testosterone, so low levels of testosterone can reduce sex drive
• As we saw in males, normal sexual function depends on sufficient blood flow to the genitals. Blood flow can be improved by creams containing prostaglandin E1.
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Spinal Cord Injury and Female Sexual Function
• About 50% of women with SCI retain sexual responsiveness. If sacral reflex loops are intact, then sexual function will be preserved.
• However, injury to the T11 – L2 regions, which is the source of sensory and sympathetic innervation to the genitals is associated with loss of sexual function
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Menopause
• Fertility peaks in women in their mid-20’s, and begins to decline gradually after age 30.
• Menopause results from a decrease in number of follicles, and in the sensitivity of remaining follicles to gonadotropins
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At menopause circulating levels of FSH and LH rise.
Why?