Immune Memory
Textbook Diagram: graph of immune response to first and subsequent infections.
First Infection by a Particular Pathogen
The pathogen is detected.
Takes time for the specific immune system to ‘learn’ the correct antibody to make.
Antibody production is not immediate.
Peak antibody production is at about day 10 after infection.
After recovery some of the specific antibody producing cells remain alive.
Second and Subsequent Infections
Memory T cells from the first infection go immediately into a rapid multiplicative phase.
Antibody production is instant and in huge quantity.
The pathogen is eliminated so rapidly and completely that disease symptoms do not develop.
Memory T cells are the basis of vaccination.
Vaccination
A vaccine is specially prepared material that carries the antigen and is given to induce active immunity against a specific pathogen.
Suitable vaccines at most cause mild discomfort but give far faster and greater antibody production against infection such that no symptoms occur.
Types of Vaccines
Preparation of the dead pathogen.
Preparation of the live but weakened pathogen (cannot reproduce).
Preparation of a close but relatively harmless relative of the pathogen.
Preparation of parts of the pathogen that carry the antigen.
Examples of Vaccines
MMR: defence against measles, mumps and rubella.
3 in 1: defence against diphtheria, whooping cough and tetanus.
Immunisation
Immunisation is the protection against disease by vaccination or administration of antibodies.
Human Reproduction
Reproduction is the formation of new individuals of the same species.
Sexual reproduction is the only method of reproduction in our species.
Sexual reproduction involves the fusion of specialised haploid sex cells.
The fusion of sperm and egg cell is called fertilisation. Fertilisation results in the formation of a diploid zygote from which a new individual develops.
Reproductive Role of the Male
Production of sperm (male gametes)
Transfer of sperm into the female (insemination)
Reproductive Role of the Female
Production of egg cells (female gametes)
Reception of sperm
Provide favourable conditions for fertilisation, implantation and development of the baby
To give birth to the baby
Feed the baby by lactation
Male System
Textbook Diagram: male urinogenital system.
Testes
The primary sex organs.
Production of sperm (male haploid sex cells).
Sperm are produced by meiosis.
Secretion of the he male hormone, testosterone.
Epididymis
A long coiled tube that receives and stores the sperm.
The sperm mature in the epididymis.
Sperm Duct (Vas Deferens)
It is a muscular tube that transfers the sperm, by peristalsis, from the epididymis to the urethra.
Seminal Vesicle
Secretes a sugar-rich fluid that is also alkaline protecting the sperm in the acidic vagina.
Prostate Gland
Secretes a protective alkaline fluid that also stimulates sperm motility.
Cowper’s Gland
Secretes a protective alkaline fluid and mucus for lubrication.
Semen
A liquid mixture of sperm, fluids of seminal vesicles, prostate gland and Cowper’s gland.
The sperm, 50 to 300 million make up only about one thousandth of the volume of the semen.
Penis
Its function is to transfer sperm into the vagina of the female.
Three masses of erectile tissue, when engorged with blood, cause the penis to stiffen and become erect.
Urethra
Conveys urine and semen to the outside.
The sphincter muscle at the base of the bladder is contracted during sexual arousal.
This prevents the release of urine from the bladder — acidic urine would immobilise the sperm.
Sperm
Textbook Diagram: sperm structure.
Sperm is really just a haploid nucleus with a flagellum that propels it towards the egg cell.
The middle piece or neck contains mitochondria producing the ATP to supply energy for propulsion.
The head contains the nucleus with the genetic material.
It also has a large digestive enzyme sac, called the acrosome.
The digestive enzymes help the sperm to make their way to the surface of the egg cell.
Female System
Textbook Diagram: female reproductive system.
Ovaries
The ovaries are the primary sexual organs.
Produces the female gametes, the egg cells.
On average one egg cell matures every 28 days.
At ovulation the egg cell is released from the ovary.
Fallopian Tube (Uterine Tube)
The open funnel end close to the ovary captures the egg cell at ovulation.
Fertilisation of the egg cell usually occurs in the Fallopian tube.
The ‘fertilised egg’ is carried to the uterus.
The ‘fertilised egg’ reaches the uterus in about six days.
Sperm have been known to survive in the Fallopian tube for at least six days.
Uterus (Womb)
The uterus is the site of menstruation, implantation, development of the embryo and labour.
A new uterine lining (endometrium) develops each cycle to receive and nourish the early embryo.
The bulk of the uterine wall is composed of muscle.
The strong contractions of the uterine muscles expel the baby at birth.
Cervix
The cervix is a narrow opening between the uterus and vagina.
A solid mucus plug protects the uterus from pathogens.
This mucus softens at the time of ovulation to allow the entry of sperm.
Vagina
It receives the penis during sexual intercourse.
The sperm, in the semen are deposited here (insemination).
It is the passageway for menstrual flow and childbirth.
During the maturation of the Graafian follicle one specialised cells undergoes meiosis.
Just one functional haploid cell that becomes the female gamete (ovum or egg cell).
The mature Graafian follicle ruptures at the surface of the ovary ejecting the egg cell (ovulation).
Sperm Journey seminiferous tubule of testis >> epididymis >> spermduct >> urethra >> vagina >> cervix >> uterus >> Fallopian tube
Egg Cell Journey ovary >> body cavity >> Fallopian tube
Secondary Sexual Characteristics
These are the features that distinguish the sexually mature individual from the immature. They appear at puberty as a result of new higher levels of oestrogen in females and testosterone in males.
Male Secondary Sexual Characteristics
hair growth on the face, underarm, chest and pubic region
enlarged larynx producing a deeper voice
wider shoulders
greater skeletal musculature
taller
Female Secondary Sexual Characteristics
hair growth in the pubic region and underarm
enlarged breasts
wide hips
greater fat deposits under the skin
taller
Menstrual Cycle
The menstrual cycle is the repeating series of changes in the uterine lining of a fertile female if fertilisation and implantation does not happen. This cycle ranges from 24 to 35 days, commonly 28 days.
Events of the Female Reproductive Cycle
Day 1 to day 5
Day 1 is the first day of menstruation.
The corpus luteum of the previous cycle has disintegrated.
The levels of oestrogen and progesterone declined greatly.
Low progesterone level leads to the menstruation.
Menstruation is the breakdown and discharge of the outer layer of the uterine lining.
Low oestrogen and progesterone levels permit the secretion of FSH (follicle stimulating hormone) by the pituitary gland.
Day 6 to day 13
FSH stimulated the formation and maturation of a Graafian follicle.
The maturing follicle secretes oestrogen.
Oestrogen inhibits FSH secretion preventing other follicles maturing.
Oestrogen also stimulates repair of the uterine lining.
Oestrogen brings about a surge of LH (luteinising hormone) just before ovulation.
Day 14
The surge of LH stimulates ovulation.
Ovulation is the release of the egg cell from the mature Graafian follicle at the ovary’s surface.
The egg cell is drawn into the Fallopian tube.
Day 15 to day 26
A corpus luteum (yellow body) develops from the ‘empty’ Graafian follicle.
The corpus luteum secretes progesterone and oestrogen.
These hormones stimulate the final maturation of the uterine lining.
High levels of theses hormones also inhibit FSH and LH secretion from the pituitary.
If implantation does not take place by day 26 the corpus luteum disintegrates.
Day 26 to day 28
The degeneration of the corpus luteum causes he levels of oestrogen and progesterone to decline rapidly.
The degenerated corpus luteum becomes a small scar in the ovary.
The usual first sign that pregnancy has occurred is that menstruation does not happen.
Implantation is the embedding of the blastocyst (early developing embryo) into the uterine lining (endometrium).
Implantation occurs about six days after fertilisation.
The developing embryo releases a hormone into the mother’s blood.
This hormone maintains the corpus luteum.
The surviving corpus luteum continues to secrete progesterone and oestrogen.
As a result the endometrium (uterine lining) does not break down and the pregnancy continues.
Conception is fertilisation followed by successful implantation.
Development up to Implantation
Textbook Diagram: development from zygote to blastocyst.
Cleavage — increase in the number of cells by division but no overall increase in size.
Cleavage begins immediately after fertilisation.
By mitotic cell divisions the zygote forms into a solid ball of about 100 cells.
This small solid ball of cells is called the morula.
Blastocyst Formation
Growth continues by cell division.
Water is absorbed forming a hollow ball of cells with a special group of cells at one end.
The hollow ball is called the blastocyst.
The outer layer of cells is the trophoblast.
The internal group of cells is called the inner cell mass.
The liquid-filled cavity is the blastocoel.
The blastocyst is the structure that implants into the endometrium.
Embryonic Period - up to the end of week 8.
The inner cell mass forms the three primary cell layers ectoderm, mesoderm, endoderm.
Each primary cell layer gives rise to specific new tissues and organs.
Ectoderm: skin epidermis and nervous system.
Mesoderm: skeleton, muscles.
Endoderm: lining of gut, pancreas, thyroid and lungs.
The trophoblast contributes to the formation of the placenta. The placenta is fully operational by the third month.
Foetal Period: week 8 to birth
The tissues and organs of the embryo are brought to maturation.
A foetus is an embryo that resembles a developed individual.
Pregnancy ends with the birth of the foetus.
Pregnancy lasts on average 38 weeks after fertilization or 40 weeks after the last menstruation.
The Placenta
Textbook Diagram: Foetus in the uterus
Functions of the Placenta
Protection of the Embryo
hinders the entry of pathogens from the mother
allows the entry of antibodies from the mother (passive induced immunity)
keeps the embryo separated from the mother’s higher blood pressure
prevents exchange of red blood cells avoiding the deadly possibility of agglutination
Gas Exchange
supply of O2 from the mother
excretion of CO2 from the embryo to the mother’s blood
Nutrient Supply
glucose, amino acids, lipids, vitamins and minerals pass to the embryo from the mother’s blood
Endocrine
secretes a variety of hormones including oestrogen and progesterone
the hormones maintain the pregnancy
the hormone prepare the mother’s body for birth and lactation
Excretion
metabolic wastes, CO2 and urea, pass from embryo into the mother’s blood
Transfer of materials by diffusion and active transport is very efficient because the blood of the embryo and mother are very close and there is a very large surface area, 14 m2. (Your skin is 2 m2)
The placenta is connected to the embryo by the umbilical cord.
Two arteries and a large vein are present in the umbilical cord.
The arteries carry blood from the foetus to the placenta.
The vein carries blood from the placenta to the foetus.
The placenta is unique — the only organ made from tissue contributed by two different individuals.
Birth
Dilation Stage
Gradual widening of the cervix.
The cervix must be wide enough to allow safe passage of the head into the vagina.
The pituitary gland secretes oxytocin hormone.
Oxytocin stimulates the contraction of the uterine muscles.
The contraction of these muscles brings about the dilation of the cervix.
The amniotic sac ruptures and the amniotic fluid escapes by way of the vagina.
Emergence Stage
the baby passes from the uterus through the cervix and along the vagina to the outside
the umbilical cord is clamped closed near to the baby
the cord is cut on the far side of the clamp
Placental Stage
the placenta is detached from the uterine wall
expulsion of the placenta and foetal membranes from the mother
Lactation
Lactation is breastfeeding the baby with milk.
The placenta produced very high levels of oestrogen and progesterone.
After the birth of the baby these hormone levels fall rapidly.
This decline allows the pituitary to secrete prolactin hormone.
Prolactin stimulates the glands in the breasts to produce milk.
The suckling of a baby at the breast stimulates the mother’s pituitary to release prolactin.
The regular presence of prolactin maintains milk production.
Suckling also stimulates the pituitary to secrete oxytocin.
Oxytocin causes the milk ducts to contract ejecting the milk from the breast.
Advantages of Lactation
Human milk has a lot of advantages for the baby’s growth and development.
Human milk is nutritionally balanced for a developing human baby.
It also contains a wide variety of beneficial chemicals that include mother’s antibodies.
These antibodies protect the child against common pathogens.
Human milk also contains chemicals favourable for brain growth and development.
Human milk also encourages the growth of mutualistic bacteria in the large intestine.