the reproductive system overall function –pair bonding via oxytocin –perpetuation of the species...

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

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

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

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.

…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.

Testes

• Two functions: – Spermatogenesis– Secretion of male sex hormone – testosterone

• Spermatogenesis:– Takes about 64 days– Occurs in seminiferous tubules– Surrounded by Sertoli cells

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

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

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

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

The penis consists almost entirely of three vascular compartments.

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

Ovary Has 2 Functions

• Oogenesis – production of ova

• Secretion of female sex hormones– Estrogen– Progesterone

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

It is best to understand the female reproductive function from 3 viewpoints:

• The ovum

• The hormones

• The endometrial lining

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

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

Now the endocrine story

• Early to mid-follicular phase:

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.

Look at this slide and the previous one together toget the full picture.

What can go wrong?

What normal physiologicevents alter this cycle?

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

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

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.

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

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

At menopause circulating levels of FSH and LH rise.

Why?