Biology - Human Reproduction

Gonad

an organ that produces sex cells in animals

Testes

produce sperm and testosterone

• meiosis occurs in the tubules

• cells between the tubules make testosterone

Epididymis

matures and stores sperm

Sperm Ducts

carry sperm to the urethra in the penis

Urethra

allows the passage of either urine or sperm

Associated Glands

seminal vesicles, the prostate gland, Cowper’s glands

• produce seminal fluid that feeds the sperm and allows them to swim

Semen

a fluid containing sperm and seminal fluid

Puberty

the beginning of sexual maturity

FSH

made by the pituitary gland, stimulates sperm production

LH

made by the pituitary gland, causes testosterone production to increase greatly

Testosterone

causes:

• the primary male characteristics (growth of penis and descent from testes and bone cavity)

• the secondary male characteristics (increased body hair, enlargement of the larynx, muscle and bone growth)

Secondary Sexual Characteristics

features that distinguish males from females, apart from the sex organs themselves

Infertility

the inability to produce offspring

Male Infertility

• can be due to the production of low numbers of sperm

• can be caused by lack of hormones, smoking, drugs, mumps or chemicals

Ovulation

the release of an egg from the Graafian Follicle in the ovary

Ovaries

produces egg and female hormones

Graafian Follicle

produces the female hormone oestrogen

After Ovulation

the empty Graafian Follicle becomes the corpus luteum, which makes progesterone and some oestrogen

Funnel of the Fallopian Tube

catches the egg; then cilia and muscles push it along the tube

Uterus

a muscular structure with a spongy lining (called the endometrium) that is enriched with blood vessels to nourish the embryo

Vagina

allows the entry of sperm and the exit of the baby at birth

Menstrual Cycle

a series of events that occurs every 28 days on average in the female if fertilisation has not taken place

Menopause

when ovulation and menstruation stop happening in a female

Menstruation

the discharge of the lining of the uterus (the endometrium) and the unfertilised egg

Days 1-5

menstruation; meiosis occurs in the ovary, forming a new egg in the Graafian follicle

Days 6-14

the endometrium thickens (due to oestrogen)

Day 14

ovulation (i.e. an egg is released from the Graafian follicle in the ovary)

Days 14-28

the endometrium continues to develop; the egg dies by day 16 if it is not fertilised

Oestrogen and Progesterone

• in the menstrual cycle they both cause the development of the endometrium and they both inhibit egg formation

• at puberty they cause secondary female traits such as breast enlargement, widening of the pelvis, increase in body fat, body growth and production of hair

Female Infertility

• is often due to the failure to ovulate

• can be caused by a lack of LH

• is treated by injections of LH or by in-vitro fertilisation

FSH

made by the pituitary gland between days 1 and 5; it stimulates egg development

Oestrogen

made by the Graafian follicle on days 5 to 14; causes the endometrium to develop, inhibits secretion of FSH, and stimulates secretion of LH

LH

made by the pituitary gland on day 14; stimulates ovulation and causes the corpus luteum to form

Progesterone and Oestrogen

made by the corpus luteum on days 14 to 28; they continue the enlargement of the endometrium, inhibit the secretion of FSH and LH, and inhibit uterine contraction

Fibroids

• benign tumours of the uterus

• can cause heavy and prolonged periods, pain, miscarriage, or infertility

Copulation

the act of sexual intercourse

Orgasm

the physical and emotional sensations experienced at the peak of sexual excitement

Ejaculation

the release of semen from the penis

Insemination

the release of semen into the vagina, just outside the cervix

Chemotaxis

the sperm swim towards the chemical released by the egg

Fertilisation

occurs when the nucleus of the sperm fuses with the nucleus of the egg, forming a diploid zygote

Implantation

the embedding of the fertilised egg into the lining of the uterus

In-Vitro Fertilisation

involves removing eggs from an ovary and fertilising them outside the body

Placenta

separates the blood of the embryo and the mother

Functions of the Placenta

the exchange of materials between the embryo and mother

• oxygen, food, antibodies, drugs, some hormones and microorganisms enter the embryo

• carbon dioxide, salts and urea enter the mother

Morula

a solid ball of cells formed from a zygote by mitosis

Day 1

fertilisation occurs

Day 3

rapid mitosis to form a solid ball of cells called a morula

Day 5

the formation of a hollow blastocyst

Day 7

implantation, which is the burrowing of the blastocyst into the endometrium

Day 10

the blastocyst forms three germ layers

By the Fourth Week

heart, brain and umbilical cord form

About the Fourth Week

chorion and mother’s blood vessels in the endometrium make the placenta

Fifth Week

internal organs start to form

By the Eighth Week

all the organs and systems are formed; the shape is now recognisably human and the embryo is called a foetus

By the Twelfth Week

bones are replacing cartilage; the foetus sucks its thumb and kicks its feet

Blastocyst

a hollow ball of cells formed from a morula

Germ Layers

basic layers of cells in the blastocyst from which all adult tissues and organs will form

Ectoderm

skin, nails, hair, nervous system

Endoderm

muscles, skeleton, excretory system, respiratory system, circulatory system, reproductive system

Endoderm

inner lining of digestive, respiratory, and excretory systems; liver and pancreas

Coelom

heart, lungs and kidneys

Gestation

the length of time spent in the uterus from fertilisation to birth

Stage 1 of Birth

contractions of the uterus push the head of the foetus towards the cervix; the amnion bursts and amniotic fluid is released

Stage 2 of Birth

the head of the baby is forced out through the vagina

Stage 3 of Birth

the afterbirth (placenta and foetal membranes) are expelled from the vagina

Main Hormones at Birth

• progesterone drops, allowing for the uterus to contract

• oxytocin (produced by the pituitary) stimulates uterine contractions

Lactation

the secretion of milk by the mammary glans of the female

Prolactin

produced by the pituitary of the mother after birth; stimulates milk production

Benefits of Breastfeeding

• ideal nutrients

• antibodies to fight infection

• sterile

• improves recovery in mother

• reduces risk of breast cancer

Birth Control

refers to methods taken to limit the number of children that are born

Contraception

the deliberate prevention fo fertilisation or pregnancy