Human reproduction growth and development.By Rebecca AinsworthDiagram adapted from (human anatomy library, 2018)The male reproductive system produces, stores, nourishes and transports the reproductive cells gametes, also known as sperm. The structure and function of the male reproductive system are as followed:Scrotum: This bag of skin and muscle contains and protects the testes. Its job is to regulate temperature, making sure the sperm is kept at the right temperature for adequate production. The superficial location of the scrotums helps keep the sperm at a temperature of three degrees lower than the core body temperature of thirty-seven degrees. It does this by expanding when exposed to heat, allowing the testicles to cool and contracting in cooler climates, pulling the scrotum towards the body for warmth.Testis: The testes are two plum shaped glands which produce sperm and secretes testosterone. Organised within the testes are the seminiferous tubules, here is where the sperm is synthesised. Each measure at approximately four centimetres long by two and a half centimetres wide. Epididymis: Located at the back of each testis consists of a head, body and tail region. The epididymis stores and matures the sperm. The sperm mature as it passes through the long-coiled tube before ending up in the ejaculatory duct. The maturing process can take up to week.Ductus (vas) deferens: Is the sperm transport system which carries the ejaculatory sperm out of the epididymis and into the ejaculatory ducts.Bulbourethral gland: Secrete thick alkaline mucus that helps neutralise any urinary acids in the urethra.Rectum: Is part of the large intestine which connects the colon to the anus. It is where faeces collect before being excreted from the body.Seminal vesicle: Are leaf shaped tubular glands. They produce seminal fluid which mixes with the sperm. The white/ yellow fluid contains sugar fructose, proteins, citric acid, inorganic phosphorus, potassium and prostaglandins. Urinary bladder: Prostate gland: Is a chestnut-like organ which is located behind the pelvic bone. It is distal to the bladder and rests upon the rectum. The function of the prostate is to provide part of the fluid called seamen. The substance of the alkaline prostatic fluid help in sperm motility.Urethra: Tube which transports and discharges urine from the bladder to the vaginal opening.Corpora cavernosa: Are two chambers that run the length of the penis, filled with a sponge-like tissue that becomes engorged with blood allowing an erection to form.The female reproductive system is the complex structure of internal and external sex organs which matures at puberty, enabling to the production of gametes and the ability to nurture a growing foetus. The organs involved, and their function is as followed;Ovary: The ovaries produce and release female gametes and sex hormones such as oestrogen and progesterone. They are contained in a fibrous sack consisting of the cortex which houses the eggs and a medulla that contains most of the ovaries blood vessels and nerves.Uterus: This is the strong muscular sack made up of three layers; the inner lining (endometrium), middle muscular layer (myometrium) and the outer layer (perimetrium. Its function is to provide nourishment for the unborn foetus.Cervix: Acts as a passageway, having both a superior and inferior opening. These openings are blocked by a mucus plug except during menstruation and before ovulation to allow the prepared sperm to reach the secondary oocyte.Bladder: An elastic, muscular sac which urine from the kidneys is stored. Urine enters the bladder via the ureters and exits out of the urethra.Rectum: The terminal part of the large intestine through which waste products are stored until excretion.Vagina: A fibromuscular canal that provides a path for menstrual blood and foetus to leave the body. It receives the male sex organ and sperm. The lining of the vagina is lubricated by the vaginal mucus glands. Urethra: Tube which transports and discharges urine from the bladder to the vaginal opening.Clitoris: Located at the anterior apex of the vulva, the clitoris is highly sensitive to stimulation during sexual pleasure.Labium minora: Located on either side of the opening to the vagina the labium minora provides a thin, smooth protective structure around the clitoris, urinary and vaginal opening.Anus: composed of two sphincters, it is the opening of the rectum to the outside of the body.Labium majora: Are two prominent folds that part of the external female genitalia. Its job is to protect the softer tissues. The pubic hairs covering the labium majora provide a barrier against friction.Fallopian tubes: The location in which the secondary oocyte is fertilised. Fimbriae surround the ovary, guiding the oocyte into the fallopian tube. After getting fertilised at the infundibulum the fertilised egg then passes around the curved section called the Ampullar region before reaching the isthmus which opens into the uterine cavity. Diagram adapted from (Anatomy body charts, 2018)The process of ovulation and menstruation occur due to the interplay between the pituitary gland, the ovaries and the uterus. The menstrual cycle can be split into two phases, Follicular phase happens from day one to day fourteen. From day fourteen to twenty-eight is known as the luteal phase. At the start of the typical twenty-eight-day cycle, the hypothalamus creates GnRH (gonadotropin-releasing hormone) sending it into the network of blood vessels which surround the pituitary gland. This stimulates the cells of the pituitary gland causing it to secrete FSH (follicle stimulating hormone), which then travels through the bloodstream to reach the ovaries. At the ovaries, FSH stimulates the development of ovarian follicles. Each of the developing follicles consists of an immature oocyte, cells that secrete Oestrogen and fluid. Most of these follicles degenerate by day seven, leaving only a single dominant follicle to grow that nourishes the developing egg inside it. Rising levels of FSH helps the egg mature in preparation for its release during ovulation. The Oestrogen released by the follicle helps in the regeneration of the endometrial lining of the uterus. The surge of Oestrogen into the bloodstream at day twelve reaches the hypothalamus resulting in the increased secretion of GnRH and stimulating the production of LH (Luteinising hormone) by the pituitary gland. The rise of LH causes the follicle to bulge, acting as a trigger for the rupture of the follicle, releasing a secondary oocyte and ovulation to occur at around twelve to fourteen days of the cycle. After the egg is released, it is picked up by suction and is swept away by the fimbriae into the opening of the fallopian tube. From here it takes approximately five to six days to travel through the fallopian tube before reaching the uterus. The rupture of the follicle creates a structure known as corpus luteum, which triggers the release of progesterone. Progesterone causes important changes in the endometrium lining of the uterus, making it thicker in preparation for it supporting the development of a fertilised egg. The secretion of progesterone is maintained for several days. If the egg is successfully fertilised it will implant in the uterus, making the women pregnant. If the egg isn’t fertilised, then it will begin to dissolve and the levels of Progesterone and Oestrogen fall. Not becoming pregnant means the thicker wall of the uterus isn’t needed resulting in the uterine lining shedding, this is known as a period, starting the menstrual cycle again.Diagram adapted from (Human Anatomy Library, 2018)Fertilisation occurs between days 11-16 of the menstrual cycle when a solitary sperm (male gametes) penetrates the zona pellucida which surrounds the mature oocyte (female gametes). DNA is released into the focal point of the egg creating 23 sets of chromosomes, shaping a zygote. During the journey of the sperm through the fallopian tube, the egg discharges chemotaxis which draws in the sperm. The single sperm goes through an acrosome reaction, achieving fertilisation by puncturing the eggs cells membrane. At the point of entering a cortical reaction is triggered, hardening the zona pellucida to stop any more sperm getting inside. Day 4 post fertilisation the singular cell will have divided into a cluster of 16 cells, now becoming the morula. The morula will continue to divide until a formation known as a blastocyst consisting of 32+ cells is created. This subsequently forms the embryo and by day 7 the shedding of the zona pellucida results in implantation into the growing uterine wall.On completion of implantation, the woman’s body will now go through the stages of pregnancy. Pregnancy normally lasts 40 weeks starting from the woman’s last menstrual period, this is split into three phases called trimesters. The first trimester lasts from weeks 1-13, second is from week 14-26 and the third covers weeks 27-40.During the first trimester, the corpus luteum in the ovary produces most of the hormones, oestrogen and progesterone which contributes to the support of the embryo and development of the placenta. However, the corpus luteum degenerates early in the second trimester making the placenta the main hormone producer. Oestrogen is responsible for most of the physiological changes that occur during pregnancy. The normal menstrual cycle no longer takes place, oestrogen suppresses the release of the hormones follicle stimulating hormone (Fsh) and luteinising hormone(LH) stopping ovulation. High levels of oestrogen also help the growth of the foetus organ systems, such as the foetal lungs and liver. Oestrogen and human chorionic somatotropin (hCS) work together to stimulate maternal tissue growth, enables development of the foetus and the maturation of the breasts preparing for lactation and breastfeeding. The change in oestrogen levels at the start of pregnancy is often a contributing factor of symptoms such as exhaustion, nausea, vomiting and headaches.More energy is required during gestation, the growth of the anterior pituitary gland causes an increase in production of thyrotropin. Thyrotropin effects the thyroid gland and increases metabolic rate and appetite, helping the body cope with the additional calories needed for foetal growth. Human chorionic somatotropin is secreted by the placenta modifies the metabolic state of the body during pregnancy to facilitate the energy supply of the foetus. Anti-insulin actions of human chorionic somatotropin may also account for gestational diabetes that develops in 10% of pregnancies. The average weight gain during pregnancy is between 25-35 pounds. A breakdown of the total weight is foetus 7-8pounds, placenta and amniotic fluid 6 pounds, breast 3-4 pounds, uterus 4 pounds, at 3-10 pounds there is fat and blood volume 4 pounds. The hormone relaxin is responsible for joints and ligaments ability to be more flexible, to enable easy passage of the foetus through the birth canal. The increased flexibility can lead to waddling gait and other joint pain.More blood and plasma are needed in the body to ensure effective levels of nutrients and oxygen are supplied to the foetus and mum, blood volume increases by 40-50%. During pregnancy, the risk of venous thromboembolism (VTE) is higher due to the rise of coagulation produced by the liver. Extra blood puts more pressure on the heart, making heart rate rise by 10-20 more beats a minute causing increased cardiac output. Normally, the heart beating faster, and increased blood volume would result in high blood pressure, but progesterone causes blood vessels to dilate, resulting in lower blood pressure.The respiratory system also adapts to pregnancy due to intra-abdominal pressure caused by the growing uterus. Shortness of breath is experienced in the third trimester, as the uterus grows it pushes the diaphragm 4 centimetres upwards compressing the lungs. This causes the functional residual capacity to decrease; however, the total lung capacity is unaffected. Towards the end of pregnancy, the pressure from the uterus eases when the foetus descends into the pelvis. However, the new location of the uterus applies extra force to the urinary bladder leading to frequent urination.Initiation of labour starts with the rise of oestrogen and the secretion of oxytocin from the pituitary gland. These high levels of the two hormones cause the uterus to contract, the uterus releases prostaglandins leading to the decrease in progesterone. Towards the end of the third trimester, the body triggers an inflammatory response using surfactant proteins to stimulate the softening of the cervix, preparing for dilation. Labour is separated into three stages; the first stage begins at the start of contractions to the complete opening and thinning of the cervix usually lasting 6-12 hours. Gradual, mild contractions are the latent phase of stage 1 and will be the beginning of the cervix dilating. Once the cervix reaches 3cm, stage one moves onto the active stage where the intensity and frequency of contraction will increase to every three to four minutes, lasting up to 90 seconds. More vigorous contractions move the head of the baby downwards, applying pressure against the cervix. The pressure results in the rupture of the amniotic sac, known as ‘waters breaking’. At 7-10cm the last phase of stage one is the transition stage, where engagement of the infant’s head occurs, and contractions are more frequent and intense. Delivery of the baby happens at stage two typically lasting 1-2 hours. On the way down through the birth canal, the baby will make several position adjustments. Flexion presses the foetal chin against its chest as the head meets the resistance from the pelvic floor, the fetal shoulders will then turn 45 degrees during internal rotation. Crowning will follow the extension of the foetus, leading to the birth of the baby. After the birth, the umbilical cord will be clamped and cut separating the baby from the placenta. The last stage of labour will be the delivery of the placenta, an injection of a drug (syntocinon) is given to stimulate placental detachment. The drug speeds up the process, lessening the event of postpartum haemorrhage occurring.