human reproduction male reproductive anatomy spermatogenesis and male hormones male reproductive...

Human Reproduction

• Male Reproductive Anatomy• Spermatogenesis and Male Hormones• Male Reproductive Technologies and Birth

Control• Female Reproductive Anatomy• Oogenesis and Female Hormones• Uterine and Ovarian Cycles• Development of the Fetus• Parturition and Lactation• Teratogens and Birth Defects • Reproductive Technologies

Reproduction

• ensures the survival of a species • Sexual reproduction produces offspring

with new and unique characteristics that

may increase their chance of survival.

Reproduction

• 2 types of gametes (sex cells)• Males: 1 billion sperm each day from the

ages 13-90• Females: born with 400, 000 eggs, 400

mature from ages 12 to 50 (menopause)• The average gestational period for a

human is 266 days.

Male Reproductive System

• The male reproductive structures are responsible for:

producing spermstoring spermdelivering sperm to the female


• Scrotum – holds the testes away from the body to keep

them cool. – Sperm production only occurs at

temperatures about 3 degrees below body temperature.

Male Reproductive SystemTestis

• descend about 2 months before birth• hang outside the internal body to maintain

a temperature of ~35OC to give sperm max survival ability

• 2 types of cells in the Testis:• 1) Interstitial cells- testosterone

producing cells• 2) Seminiferous tubules- cells that carry

out spermatogenesis (=making of sperm)


• Epididymis – holds sperm for about

2-4 days while they mature


Vas Deferens

• conducts sperm during ejaculation

• vasectomy: the vas deferens cut and tied

off, to prevent conduction of sperm.


• Ejaculatory Duct –propels semen and sperm through the urethra.

• Urethra –conduction of urine and semen out of the penis. – a sphincter muscle closes off the bladder,

preventing urine from exiting the urethra.


Penis • male organ for copulation. Beneath the skin,

lies the urethra surrounded by spongy protective tissue that expands to form the glans penis.

• Prepuce (foreskin) – is a loose sheath of skin covering the glans penis of uncircumcised males. The foreskin produces an oily secretion known as smegma.

Seminal Fluid-as sperm moves through the vas

deferens, it mixes with seminal fluid to help it do its job. This forms semen

Seminal fluid (semen) is produced by three different glands:

• 1) Seminal Vesicles – fluid high in fructose that provides food energy

sperm need to swim– Prostaglandins which cause contractions of

muscles in the female reproductive tract to help move sperm in

Seminal Fluid

• 2) Prostate Gland – milky white alkaline fluid that

neutralizes the acidity of the vagina

• 3) Cowper’s Gland – buffered fluid that cleanses and

neutralizes the acidity in the urethra

Spermatogenesis• Spermatozo

a – are the smallest cells in the body. They have very little cytoplasm in the head, and a large tail (flagellum).

The sperms head contains the DNA, the body contains tons of mitochondria to move the tail. Acrosome is an enzymes which helps sperm penetrate egg

Steps of Spermatogenesis• 1) Spermatogonia – undifferentiated germ cells that

have 46 chromosomes (2n)

• 2) Primary Spermatocytes – larger cells that undergo meiosis I (1n)

• 3) Secondary spermatocytes – cells that undergo meiosis II

• 4) Spermatids – cells with 23 chromosomes, that are ready to mature in the epididymis

• 5) Spermatozoa – mature sperm cells• 6) Sperm ready to go to the urethra!

Sertoli Cells- nourish sperm cells

Formation of sperm broken down:

Regulation of the Male

Reproductive

Hormones

TerminologyErection • parasympathetic nerve impulses dilate the arteries of the penis, allowing blood to flow rapidly into

the highly vascular penile tissue

• veins are compressed preventing blood from leaving the penis.

• Erection

Terminology

• Ejaculation – occurs when sexual stimulation forces semen to the urethra, where rhythmical muscle contractions cause the semen to be expelled/eject from the penis.

• Infertility – the inability to produce viable sperm.

• Impotency – the inability to achieve a sustained erection. Cure: Viagra© and Cialis ©

Male Reproductive Hormones

• GnRH : gonadotropic releasing hormone– released from hypothalamus– stimulates the anterior pituitary to release LH and

FSH

• LH : luteinizing hormone– stimulates the interstitial cells (cells in between

seminiferous tubules) of the testes to produce testosterone

• Testosterone – responsible for male secondary sex characteristics (pubic hair, armpit hair, thick jaws, voice changes, muscle mass, broad shoulders, aggression) required for sperm production

• FSH: follicle stimulating hormone– stimulates production of sperm in the

seminiferous tubules



• Inhibin– produced by Sertoli cells when sperm count is

high– Sends feedback to inhibit FSH and GnRH

Sperm Production

Female Reproductive Structures

• The female reproductive structures are responsible for

• reception of sperm• producing an egg• nourishing and protecting the fetus• delivering the baby

Female Reproductive Structures

Female External Structures (Vulva)

• Labia majora – large, fatty, hair covered folds that protect the genitals

• Labia minora – smaller folds of skin inside the labia that are kept moist by secretions

• Clitoris – small shaft of erectile tissue

Female Internal Structures

• Vagina – intercourse : accepts the penis– birth canal during labor– pH is generally acidic


• Cervix – Thick muscular tissue – plugs closed with mucous during

pregnancy– prevents material from getting into

the uterus, and holds the baby in

Female Internal Structures• Uterus (womb)

– pear shaped muscular organ (5 cm wide) – houses the developing fetus during pregnancy (30

cm wide)– strong contractions help push the baby out during

birth– main body is known as the fundus– Inner layer of the uterus is called the

endometrium. Here there is tons of blood vessels, tissue, and mucous. If no fertilization occurs it is expelled from the uterus (=menstration)

• Hysterectomy: removal of the uterus


• Ovaries – produce the ovum from follicles

found in the outer cortex


• Oviducts /Fallopian tubes – conduction of the ovum (egg) from

the ovaries to the uterus– where fertilization usually takes

place (sperm meets the eggs)– If egg implants here = ectopic

pregnancyfrequency


• Fimbriae – small fingerlike projections at the ends

of the oviducts that sweep to draw the egg into the fallopian tube


Tubal Ligation- sterilization is females, fallopian tubes are severed and thus sperm and egg can not join.

Ovarian Structures

• Follicle – cells that support and protect the ovum– secrete estrogen to mature the ovum– become a corpus luteum following

ovulation.

• Ovum – egg cell, viable for about 24 hours after release.

Ovarian Structures

• Corpus Luteum – cells remaining after a follicle has

ruptured during ovulation– secretes progesterone and some

estrogen for about 3 months if fertilization and pregnancy occurs

– deteriorates after about 14 days if fertilization does not occur.

Oogenesis

Regulation of the Female Reproductive Hormones

• GnRH – stimulates the anterior pituitary to produce FSH and LH

• FSH – stimulates development of the follicle and the production of estrogen within the ovary

Regulation of the Female Reproductive Hormones

• LH – causes ovulation, development of the corpus luteum which secretes progesterone

Reproductive Hormones

• Estrogen – secreted by the follicles in the ovaries– causes maturation of the egg– stimulates growth of the endometrium

(uterus lining)– Female secondary sex characteristics– Inhibits FSH

Reproductive Hormones

• Progesterone – secreted by the corpus luteum – continues preparation of

endometrium – inhibits both FSH and LH to prevent

ovulation– prevents uterine contractions– firms the cervix

P 525 Fig 6

The Uterine

and Ovarian Cycles

(Menstrual

cycle)

Day 1-5: Menstruation/Flow Phase

– Estrogen and progesterone levels are low– endometrium is sloughed off and shed

(menstration)

Day 1-13: Follicular Phase – Increased FSH secreted from ant. pit. promotes

development of the follicle to day 6 or 7.– follicle releases estrogen, which promotes growth

of the endometrium. Estrogen peaks at day 12 to mature the new follicle. Day 13 there is a very small spike in LH and FSH as well

Day 14: Ovulation – An increase in LH and FSH causes the follicle to

rupture (=ovulation) and let the ovum to be released

– FSH is lowered

Day 15 – 22: Luteal Phase– LH promotes formation of the corpus luteum from

the left over ruptured empty follicle– corpus luteum produces progesterone, inhibits

GnRH, LH and FSH, preventing subsequent ovulation.

– Estrogen levels continue to be high which continues the thicken the endometrium

- ovum eventually implants into the endometrium

• If no fertilization and implantation occurs by day 22, the corpus luteum degenerates, then progesterone levels drop, estorgen levels drop, and the endometrium begins to break down

• Many birth control pills are high in progesterone which prevents ovulation

• cancer

• No Fertilization corpus luteum degenerates, estrogen and progesterone levels drop, and menstruation occurs.

The Uterine Cycle

Menstrualcycle

Fertilization

Fertilization-union of sperm (1n) and secondary oocyte (1n) in the fallopian tube

– Only one spermatozoa will fertilize an egg

– Now called a zygote (2n)

– http://www.uchsc.edu/ltc/fert.swf

Early Embryonic Development

12 hours: Zygote formed –fertilized egg, divides by cleavage, mitosis with no increase in size

• 36 hours: 1st division (2 cells)• 40hours: 4 cells• 60h: 8 cells

Day 3: Morula – solid ball of cells the same size as the fertilized egg (32 cells)


Day 4-5: Blastocyst forms:• hollow ball of 64 cells filled with

fluid,• outer layer forms the chorion, inner

layer forms the embryo• Implants to endometrium day 6-10

Implantation (around day 6)

• embryo embeds itself in the endometrium.

• To save itself from being shed, blastocyst produces HCG (human chorionic gonadotropic hormone): maintains the corpus luteum for about 2-3 months.

***Reminder: corpus luteum produces progesterone and estrogen to maintain the endometrium and prevent ovulation

• HCG detected in blood or urine with a pregnancy test

• hCG Pregnancy Test ELISA

Gastrulation


Day 7-12: Gastrula forms• the blastocyst pushes in

(invaginates) and forms the 3 primary germ layers

• the hollow space forms a primitive gut

3 Germ Layers created are:

Ectoderm – nervous system and epidermis of the skin

(hair, nails,retina, lens, inner ear, lining of the nose, mouth, anus and tooth enamel)

Neurula- notochord/neural tube forms from the ectoderm layer (forms in 3rd to 4th week)

Germ Layers

Germ Layers

Mesoderm – skeleton, muscles, reproductive organs

(connective tissue,cartilage, blood, blood vessels, kidneys)

Endoderm –lining of the digestive and respiratory system, endocrine glands

(trachea, bronchi, lungs, gallbladder, urethra, liver, pancreas, thyroid,bladder)

• Gastrulation

• BERP: Overview

Embryo at 4 weeks

Extra Embryonic Membranes

Placenta • The chorion cells and the endometrium

cells fuse to form the placenta• forms around the fetus

• exchange of gases, delivery of nutrients and removal of wastes for the fetus

• no direct blood shared between the mother and the fetus

• Produces progesterone and estrogen at about 4 months



• Amnion – inner membrane filled with fluid to provide protection, maintain temperature, swallowing (amniotic sac)

• Chorion-outer membrane, contributes to placenta

• Extraembryonic coelom – fluid filled space between amnion and chorion


• Allantois – collects nitrogenous wastes and forms the umbilical cord and placenta blood vessels

• Yolk Sac – surrounds embryo, first site of blood cell formation (until liver is formed), becomes part of the primitive gut

How Old Are You?

Gestational age

-calculated from the first day of the mother’s last menstrual period.

–length of pregnancy is 40 weeks

How Old Are You?

Fertilization age –actual age of the fetus- estimated to be about two weeks before the

date of the last menstrual period.

• To calculate due date: LMP –3 months + 7 days

• calculator

Trimesters

• 1rst : until end of third month

• 2nd: 4-6months

• 3rd : 7-9 months

Developmental Milestones

• 1 week – fertilization, cleavage, blastocyst

• 2 weeks – implantation, chorion secretes HCG, 3 germ layers form


• 3 weeks – nervous system is evident, heart begins to form (2 tubes), heart beats around day 22

• 4-5 weeks – limb buds appear, eyes, ears and nose develop, umbilical cord is attached to placenta


• 6-8 weeks – fetus is recognizable as a human, all organ system are developed, reflexes begin (size = 1.5”, 0.5 g)

• 8th week = fetus

• 9-16 weeks – heartbeat is audible with a stethoscope, bone replaces cartilage, eyelashes formed, fetus can suck and swallow (size = 6”, 0.5 lb)


• 17-28 weeks – movement is felt by mother, eyelids open (size = 12”, 3lb)

– Week 28: premature baby has 10-20% chance of survival


• 32 weeks: fetus moves to head down position and lungs mature – (has 50% survival rate if born)


• after about 32 weeks significant weight gain

• 40 weeks: full term (size = 21”, 7.5 lbs)

• See summary chart on page 534

Virtual Development

Conception to Birth, Anatomical Travelogue

Visible Embryo

Teratogens• Teratogens - chemical substances or

infections that cause specific birth defects

Teratogens

-Thalidomide-prescribed for morning sickness in the late 50’s and early 60’s

-rubella during the first 12 weeks of pregnancy: eye problems, hearing problems and heart damage.

Parturition: Birth

Hormones:-relaxin: made by placenta, loosens pelvis ligaments

-prostaglandins – contractions

-oxytocin from Post. Pit - contractions

Parturition

Stage 1 – dilation and effacement(thinning) of the cervix, mucous plug dislodges, uterine contractions open the cervix

Stage 2 – delivery of the baby, cervix is dilated to about 10 cm, intense contractions every 1-2 min push the baby down the birth canal

Stage 3 – delivery of the placenta

Parturition

• The average labor lasts about 12 hours, but can range from 1 hour to 36 hours.

• caesarean section may be required. – involves removing the baby from an incision

in the front of the abdomen.

Lactation

• prolactin stimulates the glandular tissue in the breasts to produce fluids, colostrum, and milk.

• Colostrum is a rich fluid containing mostly sugar and proteins. This first milk is believed to play a role in early immunity.

Lactation

• Regular suckling stimulates the pituitary gland to release oxytocin– causes weak uterine contractions to return it

to its pre pregnancy shape– causes “let down” of milk – 1.5 L of milk each day

Reproductive Technologies

and Health• Pap Smear – a sample of cervical cells

are taken and examined for abnormal growth (cancer)

• Ultrasound – uses sound waves to view the baby in the womb

Ultrasound Scan Fetal Video Clips


and Health• Amniocentesis – sampling of the cells

from the amniotic fluid at about 16 weeks to check for genetic abnormalities

Amniocentesis Flash Animation - Mountain View Bay Area Sunnyvale Cupertino Palo

Alto Standford


and Health• Chorionic Villus Sampling – sampling

of cells from the chorion at about 5 weeks to check for genetic abnormalities

http://www.pbs.org/wgbh/nova/miracle/windows.html

Fertility Technologies

• IVF – in vitro (in glass) fertilization – fertilizing the egg in a petri dish, and implanting the embryo 2-4 days later

Life Changine Science - Program 3: IVF

• AID – artificial insemination by donor, sperm is artificially placed in the vagina.


• Egg Screening – testing and selecting eggs to be fertilized, fertility drugs produce eggs that are collected using a needle biopsy

• TSE – testicular sperm extraction– removal of sperm via biopsy (not ejaculation)

• ICSI – intracytoplasmic sperm injection– sperm head is injected directly into the egg


• GIFT – gamete intra-fallopian transfer – sperm and egg are transferred to the

fallopian tube for fertilization

• AH – assisted hatching– a chemical solution is dripped over the egg

to allow the sperm to penetrate more easily


• Embryo Transfer – implantation of an embryo (at blastocyst stage) into the womb or fallopian tube, may be frozen or unfrozen

• Fertility Drugs – induce ovulation, usually many ova are produced at one time, often results in multiples

human reproduction male reproductive anatomy spermatogenesis and male hormones male reproductive...

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