Unit 2Unit 2

Reproduction and Development

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Unit 1 IntroductionUnit 1 Introduction

We will be learning about the following topics: Structure/function of male/female reproductive

systems Hormonal control of male/female reproductive cycles Birth control methods Causes of infertility/reproductive technologies Process of fertilization and development

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Reproductive SystemReproductive System

Why is reproduction so important? Ensures the survival of a species

What is reproduction? Union of a male and female sex cell to form

new genetic combinations Survival of species depends on the varied

offspring

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The Importance of ReproductionThe Importance of Reproduction

Continuation of the species

Creation of diversity within the species Adaptation Change Mutation Survival of the fittest

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Types of ReproductionTypes of Reproduction

Sexual Sex cells from a male and a female fuse to

form a new organism Involves meiosis (formation of gametes)

Asexual Organism make a copy of itself Only one “parent” involved No meiosis Occurs in prokaryotic cells and some plants

via vegetative reproduction

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The The Reproductive SystemReproductive System

Gonads: organs that produce gametes and hormones

Ducts: receive and transport gametes

Accessory glands: secrete fluids into ducts

Perineal structures: collectively known as external genitalia

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Basic Human ReproductionBasic Human Reproduction

Separate male and female systems Male gonads called testes produce sperm cells

Sperm production begins at puberty and continues into old age

Approximately 1 billion produced each day

Female gonads called ovaries produce ova (ovum, sing.)

Ova are larger than sperm Female generally releases one ovum every 28 days

following onset of menstruation and continuing to menopause

Ova are developed prior to birth, approximately (400,000)

Sperm cell fertilizes an ovum in the oviducts of the female to form a zygote which implants (attaches) to the uterine wall where it grows and develops

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Development of the Male Reproductive Development of the Male Reproductive SystemSystem

Development of male reproductive begins at 12th week of embryonic development

Prior to this male and female embryos are similar

Testes descend into the scrotum during week 30-32 of male embryonic development

Scrotum is a sac-like pouch of skin that contains the testes and is locates below the pelvic region and outside of the body.

Scrotum is 92º F (33º C) while normal body temperature is 98.6º F (37º C)

Sperm production is optimal at this lower temperature

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Problems with testis descentProblems with testis descent

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Basic Anatomy - TestesBasic Anatomy - Testes

Testes Normally two Housed in the scrotum Produce sperm cells Tube called the vas deferens carries sperm

cells to the urethra for ejaculation

Two main cell types Seminiferous cells – produce sperm (site of

meiosis) Interstitial cells – produce testosterone

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Basic Anatomy - PenisBasic Anatomy - Penis

Male sexual organ and external organ of urination

No erectile bone – erection achieved by engorgement of spongy erectile tissue chambers

Corpus cavernosa (2) Corpus spongiosum (1) forms glans penis (tip)

Stimulation of erectile tissue due to parasympathetic nervous system

Arteries leading to penis dilate Veins leaving the penis constrict due to pressure

from arteries and enlarged spongy tissue Stimulation due to sexual arousal or other

factors – full bladder, friction, dreams, etc.

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The Male Reproductive SystemThe Male Reproductive System

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Male Reproductive SystemMale Reproductive System

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Functions of structuresFunctions of structures

Scrotum – pouch of skin that stores testes located below pelvic region

Vas Deferens – carries sperm from testes to urethra

Semen – fluid that contains sperm and other chemicals

Sertoli cell – nourishes developing sperm cells

Seminiferous tubules – found in each testis where sperm cells develop

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Functions of Structures…cont’dFunctions of Structures…cont’d

Epididymus – coiled tube located on each testis where sperm cells mature

Seminal vesicles – contain substances to help sperm survive (fructose and prostaglandins)

Prostate gland – contains a substance to protect sperm cells in vagina

Cowper’s Gland – secretes mucous rich fluids prior to ejaculation

Urethra – expels both semen and urine from penis (but never at the same time)

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Sperm Cells and SpermatogenesisSperm Cells and Spermatogenesis Formed in the testicles

Nucleus contains 23 chromosomes

Half carry a Y chromosome and half carry an X chromosome

Reduced cytoplasm = reduced energy store

Mitochondria surrounds flagellum

Acrosome at tip contains enzymes to aid penetration of ovum

Sertoli cells nurture developing spermSpermatogonia

(46 chromosomes)

Spermatocytes(23 chromosomes)

Sperm cells

meiosis 9-10 days

epididymis

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SpermatogenesisSpermatogenesis

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Sperm Cells – Interesting FactsSperm Cells – Interesting Facts

Can live 1-3 hours outside the body depending on temperature, moisture, etc.

Can live 5-7 days in the cervix

Up to 500 million sperm cells per ejaculation. Below 40 M is considered infertile

Average ejaculation is 1 teaspoon (5 ml) in volume

Can be stored for many years in cryogenic storage systems

Used in artificial insemination

Tadpole like shape

Head, mid-piece, and tail

Fertility rates depend on number and motility

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Seminal FluidSeminal Fluid

Secretions from three glands make up seminal fluid

Seminal vesicle secretions (60%)

Fructose Prostagladins

Prostate secretions (30%) Alkaline buffer (basic)

Cowper’s gland (bulbourethral gland)

Pre-ejaculatory fluid

Hormonal Control Hormonal Control of the Male of the Male

Reproductive Reproductive SystemSystem

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Topics - Hormonal Control of the Topics - Hormonal Control of the Male Reproductive SystemMale Reproductive System

Where testosterone is produced

Functions of testosterone

Structures that control the production of sperm and testosterone

Hormones involved in the control of production of sperm and testosterone

Describe how production is regulated (negative feedback system) to maintain homeostasis of testosterone

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Where Testosterone is ProducedWhere Testosterone is Produced

In interstitial cells in testes

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Functions of TestosteroneFunctions of Testosterone

Stimulates spermatogenesis (production of new sperm cells)

Promotes development of secondary sex characteristics

Maturation of testes and penis Increase in sex drive Facial/body hair Growth of larnyx (deepening of voice) Secretion of body oils (acne)

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Structures that control the production of sperm and Structures that control the production of sperm and testosteronetestosterone

Hypothalamus

and Pituitary

Gland

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Hormonal Control of Male Reproductive Hormonal Control of Male Reproductive SystemSystem

GnRH (Gonadotropin-releasing hormone) produced in hypothalamus

At the pituitary, GnRH stimulates the synthesis and secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH)

FSH stimulates production of sperm cells in seminiferous tubules of testes

LH stimulates production of testosterone by interstitial cells (Leydig cells) of testes

Negative FB Loop: The hypothalamus detects high levels of testosterone whichlowers GnRH production in the pituitary which in turn lowers LH secretions. Thisresults in lower levels of testosterone production.

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Hormones Involved…Hormones Involved…

In the production of sperm:

Follicle Stimulating Hormone (FSH)

Acts on the Sertoli Cells in the testes (seminti to produce sperm cells

In the production of testosterone:

Luteinizing Hormone (LH)

Acts on the interstitial cells in the testes to produce testosterone

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Negative Feedback ControlNegative Feedback Control

Required to maintain constant levels of testosterone and sperm

Hypothalamus → GnRH → Pituitary → LH → Interstitial cells → testosterone produced

Hypothalamus → GnRH → Pituitary → FSH → Sertoli Cells → Sperm produced

If sperm/testosterone too high → system shuts off to decrease levels set level

If sperm/testosterone is too low → system turns on to increase levels to set level

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Hormonal Feedback/Regulation of Male Reproductive Function

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Female Female Reproductive Reproductive

SystemSystem

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Female Reproductive System DevelopmentFemale Reproductive System Development

Development of female reproductive begins at 12th week of embryonic development

Prior to this male and female embryos are similar

Paired ovaries form near the kidneys during embryonic development and remain in the abdominal region

Ovaries contain ova, or “eggs”

Ovaries also produce female sex hormones Estrogen Progesterone

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Female Reproductive System Internal (X-Female Reproductive System Internal (X-Section)Section)

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Female Reproductive System - External Female Reproductive System - External AnatomyAnatomy

Separate openings to the outside for products of the urinary and reproductive systems

Urethra Vagina

Clitoris develops from the same embryonic tissue as the penis and consists of erectile tissue

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Basic Anatomy - Female Reproductive Basic Anatomy - Female Reproductive SystemSystem

10-12 cm in length oviducts, or Fallopian tubes, connect ovaries to the uterus

Released ovum travels along oviducts via cilia

Fertilization of ovum occurs in oviduct

Oviducts join at uterus, or womb

Uterus is connected to vagina by the cervix

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The UterusThe Uterus

Composed of three main tissues:

1. Perimetrium – fibrous elastic tissue that surrounds the uterus and holds it place with ligaments

2. Myometrium – muscular lining that supports a fetus and also contracts during child birth

3. Endometrium – forms the placenta for the developing fetus. Released if no fertilization takes place – menstruation.

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Main Structures and FunctionsMain Structures and Functions

The ovaries produce the cells that become ova (eggs).

A released oocyte moves into the oviduct (or Fallopian tube) where it may be fertilized if sperm are present.

If fertilized, it completes meiosis and becomes an ovum.

If an embryo results it will attach to the lining of the uterus to complete its development.

The cervix is the opening from the uterus into the vagina. Holds fetus in place during pregnancy.

The vagina is the canal for entry of the penis and exit of menstrual flow and serves as the birth canal.

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OvariesOvaries

Each ovary contains hundreds of thousands of follicles

Follicles are the structure in the ovaries that produces the eggs and, in particular, the female sex hormones, estrogen and progesterone

Each follicle contains an oocyte An oocyte is a cell that has begun the process of

meiosis and can eventually produce an ovum (egg)

FSH and LH from the anterior pituitary create changes in the ovary during various phases of the ovarian cycle

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FolliclesFollicles

Primary follicles consist of a primary oocyte surrounded by granulosa cells

Outer layer of connective tissue surrounding the follicles is called the theca

Theca secretes androgens that are converted to estrogen in the granulosa cells

Secondary follicles secrete estrogen and nurture the secondary oocyte

Eventually forms an ovarian follicle (Graafian follicle) that ruptures and releases the ovum

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Follicle Stages in the OvaryFollicle Stages in the Ovary

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Hormones and the OvaryHormones and the Ovary

FSH causes development of the follicle during the first half of the menstrual cycle

After ovulation the follicle becomes the corpus luteum under the influence of LH

Negative feedback regulates hormone levels

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Uterine (Menstrual) CycleUterine (Menstrual) Cycle

Day 1-5: Menstruation - shedding of uterine lining - due to low hormone levels

Day 6-13: Proliferative Phase -FSH stimulates follicle which in turn secretes estrogen. Estrogen causes the endometrium to thicken.

Day 14: Ovulation

Day 15-28: Secretory Phase – LH promotes the formation of the corpus luteum within the ruptured follicle - which in turn produces progesterone, which in turn stimulates the endometrium to secrete thick nutrient-rich fluids (ready for implantation).

If no implantation then the corpus luteum degenerates as LH levels fall. Progesterone levels also fall and endometrium is no longer maintained – menses begins and cycle repeats.

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No FertilizationNo Fertilization

LH levels fall during the luteal phase

Corpus luteum degenerates

Progesterone levels fall

Uterine lining (endometrium) is no longer maintained due to low levels of progesterone

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FertilizationFertilization

Fertilization occurs in the upper portion of the oviduct and implantation occurs on the uterine wall

Embryonic cell divisions begin and the embryo produces the hormone HCG

HCG maintains the corpus luteum so that progesterone continues to be released

Uterine lining continues to thicken so the embryo can survive

HCG → human chorionic gonadotropin

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Critical Hormones in ReproductionCritical Hormones in Reproduction

FSHFSH - secreted by the anterior pituitary. Stimulates the development of an ovarian follicle in a female or the production of sperm in a male.

LHLH - produced by the anterior pituitary gland. Stmulates the development of the corpus luteum in females and the production of testosterone in males.

EstrogenEstrogen - Female sex hormone, which, along with progesterone, maintains the primary sex organs and stimulates development of the female secondary sex characteristics.

ProgesteroneProgesterone -Female sex hormone secreted by the corpus luteum of the ovary and by the placenta.

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Reproductive Reproductive Health IssuesHealth Issues

Fibroid Tumors

Ovarian and Cervical Cancer

Bartholin Cysts

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Fibroid TumorsFibroid Tumors

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Ovarian CancerOvarian Cancer

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ResourcesResources

Female Reproduction