1. 11.4 Sexual Reproduction
Essential idea: Sexual reproduction involves the development and fusion of haploid gametes

2. Bell Ringer
Outline the process of spermatogenesis

3. 11.4 Sexual Reproduction
Nature of science: Assessing risks and benefits associated with scientific research—the risks to human male fertility were not adequately assessed before steroids related to progesterone and estrogen were released into the environment as a result of the use of the female contraceptive pill. (4.8)
Understandings
Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation
Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm
Fertilization in animals can be internal or external
Fertilization involves mechanisms that prevent polyspermy
Implantation of the blastocyst in the endometrium is essential for the continuation of pregnancy
HCG stimulates the ovary to secrete progesterone during early pregnancy
The placenta facilitates the exchange of material between the mother and fetus
Estrogen and progesterone are secreted by the placenta once it has formed
Birth is mediated by positive feedback involving estrogen and oxytocin

4. 11.4 Sexual Reproduction Applications and Skills
Application: The average 38-week pregnancy in humans can be positioned on a graph showing the correlation between animal size and the development of the young at birth for other mammals
Skill: Annotation of diagrams of seminiferous tubules and ovary to show the stages of gametogenesis
Skill: Annotation of diagrams of mature sperm and egg to indicate functions

5. Retro Topic 6.6 Understandings
Insulin and glucagon are secreted by α and β cells in the pancreas to control blood glucose concentrations
Thyroxin is secreted by the thyroid gland to regulate the metabolic rate and help control body temperature
Leptin is secreted by cells in adipose tissue and acts on the hypothalamus of the brain to inhibit appetite
Melatonin is secreted by the pineal gland to control circadian rhythms
A gene on the Y chromosome causes embryonic gonads to develop and tests and secrete testosterone
Testosterone causes prenatal development of male genitalia and both sperm production and development of male secondary sexual characteristics during puberty
Estrogen and progesterone cause prenatal development of female reproductive organs and female secondary sexual characteristics during puberty
The menstrual cycle is controlled by negative and positive feed back mechanisms involving ovarian and pituitary hormones

6. Retro Topic 6.6 Applications and Skills
Application: Causes and treatment of Type I and Type II diabetes
Application: Testing of leptin on patients with clinical obesity and reasons for the failure to control the disease
Application: Causes of jet lag and use of melatonin to alleviate it
Application: The use in IVF of drugs to suspend the normal secretion of hormones, followed by the use of artificial doses of hormones to induce superovulation and establish a pregnancy
Application: William Harvey’s investigation of sexual reproduction in deer.
Skill: Annotate diagrams of the male and female reproductive system to show names of structures and their functions.

7. S Annotate diagrams of the male and female reproductive system to show names of structures and their functions
Male Reproduction
Be able to annotate for function:
Testis
Scrotum
Epididymis
Penis and erectile tissue
Urethra
Sperm duct
Seminal vesicle
Prostate gland
Bulbourethral gland

9. Functions: Male Reproductive System
Testis: produce sperm and testosterone
Scrotum: hold testes at lower than core body temperature
Epididymis: store sperm until ejaculation; cause sperm to become motile
Sperm duct: transfer sperm during ejaculation
Seminal vesicle: secrete fluid containing fructose and proteins
Prostate gland: secrete alkaline fluid with mineral ions
Urethra: transfer semen during ejaculation and urine during urination
Penis: penetrate the vagina for ejaculation of semen near the cervix
Bulbourethral gland: increases viscosity of ejaculate

10. Male Reproductive System Anterior View

11. Skill 6.6 Annotate diagrams of the male and female reproductive system to show names of structures and their functions
Annotations of the female reproductive system:
Ovary
Oviduct
Uterus
Cervix
Vagina
Vulva

13. Functions: Female Reproductive System
Ovary: produce eggs, estrogen, and progesterone
Oviduct (fallopian tubes): collect eggs at ovulation, provide a site for fertilization then move the embryo to the uterus
Uterus: provide for the needs of the embryo and then fetus during pregnancy. Formation of placenta
Cervix: protects the fetus during pregnancy and then dilate to provide a birth canal
Vagina: stimulate the penis to cause ejaculation and provide a birth canal
Vulva: protect internal parts of the female reproductive system

14. U6.6.6 A gene on the Y chromosome cause embryonic gonads to develop as testes and secrete testosterone
During the 6th week of embryogenesis, a gene on the Y chromosome (SRY – sex determining region of the Y) causes embryonic gonads to develop as testes and secrete testosterone
SRY gene codes for TDF (testis determining factor), a gene regulation protein which binds to specific DNA sites
TDF stimulates the expression of other genes that cause testis development

15. Testosterone causes prenatal development of male genitalia
U6.6.7 Testosterone causes prenatal development of male genitalia and both sperm production and development of secondary sexual characteristics during puberty
Testosterone is secreted from an early stage in fetal development (after the 8th week until the 15th week of pregnancy)
Testosterone causes prenatal development of male genitalia
At puberty, the secretion of testosterone increases
This stimulates sperm production (primary sex characteristic of males) and development of male secondary sexual characteristics during puberty
Secondary sex characteristics include enlargement of the penis, growth of pubic hair, deepening of the voice due to growth of the larynx

16. In the absence of SRY gene, embryonic gonads develop as ovaries
U6.6.8 Estrogen and progesterone cause prenatal development of female reproductive organs and female secondary sexual characteristics during puberty
In the absence of SRY gene, embryonic gonads develop as ovaries
Estrogen and progesterone (which are always present in pregnancy first secreted by mother’s ovaries and later by the placenta) cause prenatal development of female reproductive organs
At puberty secretion of these hormones increase and female secondary sexual characteristics develop
Enlargement of breasts and growth of pubic and underarm hair
Female pattern of fat deposition

17. U6.6.9 The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones
Follicular phase of ovarian cycle:
Group of follicles begin development in the ovary. In each follicle, an egg is stimulated to grow
Uterine (menstrual) cycle: (menstrual flow and proliferative phase) lining is repaired and starts to thicken
Luteal phase of ovarian cycle:
after egg is released at ovulation. Walls of follicle become the corpus luteum
Uterine(menstrual) cycle: secretory phase – continued development of the endometrium in preparation for implantation of an embryo

18. 4 Hormones control these developments
FSH
LH protein hormones from pituitary (anterior)
Estrogen (wall of follicle)
Progesterone (corpus luteum) steroid hormones from ovary

19. FSH rises to a peak at the end of menstrual cycle and stimulates development of follicles. Also stimulates secretion of estrogen by the cells in the follicle walls. Example of + feedback.
Estrogen peaks towards the end of the follicular phase. Stimulates repair and thickening of the endometrium after menstruation and an increase in FSH receptors, boosting estrogen production. When estrogen reaches high levels it inhibits the secretion of FSH (- feedback) and stimulates LH secretion
LH rises to a sudden and sharp peak towards end of follicular phase. Stimulates the completion of meiosis in the oocyte and partial digestion of follicle wall allowing it to burst open at ovulation. LH also promotes development of the wall of follicle after ovulation into corpus luteum which secretes estrogen (+ feedback) and progesterone
Progesterone levels rise at start of luteal phase, reach a peak and then drop back to a low level at the end of luteal phase. Promotes the thickening and maintenance of the endometrium. Inhibits FSH and LH secretion (- feedback).

21. A6.6.4 The use of IVF of drugs to suspend the normal secretion of hormones, followed by the use of artificial doses of hormones to induce superovulation and establish a pregnancy
Stage 1: Downregulation. Nasal spray of drug stops pituitary gland from secreting FSH and LH. Secretion of estrogen and progesterone therefore also stops.
Stage 2: Intramuscular injections of FSH in a much higher concentration and LH given daily for about 10 days, to stimulate follicles to develop. This is to mature far more follicles than usual follicles= superovulation
Stage 3: Injection of HCG to stimulate maturation when follicles are about 18 mm diameter
Stage 4: Harvesting eggs and fertilization while progesterone tablets placed in vagina to ensure that uterine lining is maintained

22. A6.6.5 William Harvey’s investigation of sexual reproduction in deer
He was taught the “seed and the soil” theory of Aristotle, according to which the male produces a seed, which forms an egg when it mixes with menstrual blood. The egg develops into a fetus inside of the mother
Deer are seasonal breeders and only become sexually active in autumn
Harvey examined the uterus of female deer during mating season by slaughtering and dissecting them expecting to find eggs developing in the uterus immediately after mating
He only found evidence of anything happening in females 2 or more months after the start of the mating season
Led him to the belief that Aristotle’s theory was false

24. Spermatogenesis Spermatogenesis: production of mature sperm cells
A continuous and prolific process in the adult male. Each ejaculation of a human male contains million sperm cells
Occurs in the seminiferous tubules of the testis. See figure in your textbook.
The stem cells that give rise to sperm are called spermatogonia (singular: spermatogonium). They are located at the periphery of each seminiferous tubule (furthest from the lumen of the tubule: aka germinal epithelium).
Spermatogonia reproduce via mitosis and produce large numbers of spermatogonia. These are 2n cells. In humans 2n = 46 chromosomes.

25. Spermatogenesis
Spermatogonia differentiate (become more determined) into spermatids (sperm cells) and then to spermatozoa (swimming sperm with a tail piece).
This differentiation process begins with growth.
Spermatogonia develop into primary spermatocytes which sometime appear as the largest cells in the seminiferous tubules. They have entered Meiosis 1 which means that the DNA has been replicated and the cells will go through the tetrad stage with crossing over, metaphase 1 which leads to separation of homologous chromosomes during anaphase 1 and telophase 1 which results in 2 haploid cells (n = 23 but each chromosome made up of 2 sister chromatids attached at the centromere)

26. Primary spermatocytes divide and becomes secondary spermatocytes, which will appear to be smaller and closer to the lumen of the seminiferous tubule. Secondary spermatocytes are in the process of going through Meiosis II.
At the end of Meiosis II, there are 4 spermatids that are haploid (n)
Spermatids then differentiate into mature spermatozoa, or sperm cells. This involves their association with Sertoli cells (also called nurse cells). Sertoli cells transfer nutrients to the spermatids

31. Seminiferous tubule
Flagella of spermatozoa
Spermatogonium

32. Seminiferous Tubules

33. Homunculus

34. Anatomy of a sperm
About 50 um long

35. Differentiation of Sperm
Differentiation of sperm includes:
Nucleus shrinks by losing water and the chromosomes become closely packed into a small volume
All RNA is eliminated, leaving only the DNA
Nucleus changes shape to become elongated and narrow
Golgi apparatus gives rise to the acrosome
Acrosome contains a supply of hydrolytic enzymes which are used to dissolve the egg membranes during fertilization

36. Differentiation continued
The nucleus and acrosome form the head of the new sperm cell
The centrioles that were involved in meiosis give rise to the flagellum
The mitochondria become concentrated in the mid-piece region and form one continuous body which becomes twisted spirally around the axial filament and one of the centrosomes
The axial filament is the main part of the tail or flagellum of the sperm cell or spermatozoon
Protein fibers strengthen the tail piece
Most of the cytoplasm is discarded during the later stages of spermatogenesis
The sperm cell still has a plasma membrane or cell membrane

37. Finishing Spermatogenesis
Testicular tissue includes seminiferous tubules which have a basement membrane around them, interstitial cells which secrete androgens especially testosterone, and blood vessels
Sperm cells make their way to the epididymis where they acquire their motility
This process, from spermatogonia to motile sperm, takes days in human male

38. Role of Hormones in Spermatogenesis
FSH (pituitary hormone): acts on seminiferous tubules to increase spermatogenesis by stimulating primary spermatocytes to undergo the first division of meiosis and form secondary spermatocytes
LH (pituitary hormone): stimulates interstitial cells (also called Leidig cells) to make androgens (testosterone) which in turn stimulate sperm production
Testosterone (from interstitial cells): stimulates the development of secondary spermatocytes into mature sperm. Responsible for primary and secondary sex characteristics

39. Production of Semen
Epididymis: sperm undergo a maturation process while they are stored in here and become able to swim
Seminal vesicles (2) and prostate gland: produce and store fluids and expel them during ejaculation. Fluid mixes with sperm and increases the volume of the ejaculate. Fluid from the seminal vesicles contains nutrients for the sperm including fructose and mucus which protects the sperm in the vagina. Fluid from prostate gland contains mineral ions and is alkaline so protects the sperm from the acid conditions in the vagina
Cowper’s gland aka Bulbourethral Gland produces a high viscosity solution

40. Cross Section of Mammalian Ovary

41. Mammalian Ovary Microscope Image

42. Mammalian Egg Mammalian egg is about 110 um in diameter
Zona pellucida- clear membrane that surrounds egg before implantation
Surrounded by follicle cells which are ovulated together with secondary oocyte
Corona radiata

44. Structure of the Egg Haploid nucleus (n) Two centrioles
Cytoplasm contains droplets of fat (yolk). The egg cell has more cytoplasm than any other human cell. The mitochondria of the zygote are all derived from the cytoplasm of the egg cell. The egg cell destroys the helical mitochondria of the sperm after fertilization.
Periphery of egg contains cortical granules which are small vesicles that participate in the fertilization reaction and help form the bar to polyspermy

45. Structure of the Egg
Sometimes see 1st polar body that may have divided underneath the plasma membrane
Clear layer of gel surrounds egg composed of glycoprotein called the zona pellucida
Layer of follicle cells surround egg called the corona radiata

46. Oogenesis

47. Oogenesis Oogenesis: the production of ova or egg (ovum is singular)
In the female embryo, the primordial germ cells differentiate into oogonia which in turn develop into primary oocytes. By birth, a female’s lifetime supply of primary oocytes is present in her ovaries. Each primary oocyte is arrested at Prophase of Meiosis I. Starting at puberty, a single primary oocyte (2n) completes Meiosis I each month, developing into a secondary oocyte.

48. Oogenesis
The meiosis divisions in oogenesis involve unequal cytokinesis, with the smaller cells becoming polar bodies.
The secondary oocyte completes Meiosis II only if a sperm cell enters it. After Meiosis II, the haploid nuclei of the sperm and the mature ovum fuse.
In the ovary, oogonia (2n) divide by mitosis to form more oogonia (2n).

49. Oogenesis
5. Oogonia grow into larger cells called primary oocytes (2n) which start the first division of Meiosis but stop during Prophase I. A primary oocyte and a single layer of follicle cells around form a primary follicle. At birth, baby girls contain about 400,000 primary follicles
6. Every menstrual cycle, a few primary follicles start to develop, completing the first division of meiosis and forming 2 haploid nuclei (sister chromatids attached to the centromere). Since the cytoplasm does not divide equally, you get a large secondary oocyte and a small polar body or cell (n).

50. Oogenesis
7. Secondary oocyte starts Meiosis II but stops in Prophase II. Follicle cells proliferate (mitosis) and follicular fluid is forming. As the egg approaches maturity, an eccentric (not in the center) cavity appears in the mass of the follicle cells. This cavity is filled with fluid secreted by the cells of the follicle. The follicle at this stage is known as a Graafian follicle. Follicle cells actively assist the growth of the oocyte by secreting substances (RNA, yolk) which are taken up by the oocyte. The membrane that develops between the oocytes and the follicle cells in the space occupied by the interdigitating microvilli of the oocyte is called the zona pellucida (clear zone). According to the IB syllabus, you will see this around the primary oocytes.

51. Ovary and Graafian Follicle

55. Ovulation Mature follicle bursts
Egg is still a secondary oocyte when it is ovulated

56. Fertilization and Completion of Meiosis
After fertilization, the secondary oocyte completes the 2nd division of meiosis to form an ovum
First and 2nd polar bodies do not develop and degenerate

57. Comparing Spermatogenesis and Oogenesis
Begins with proliferation of cells by mitosis
Involves cell growth before meiosis
Involves 2 divisions of meiosis
Millions produced daily
Begins with proliferation of cells by mitosis
Involves cell growth before meiosis
Involves 2 divisions of meiosis
1 every 28 days

58. Comparing Spermatogenesis and Oogenesis
Released at ejaculation
Sperm formation starts during puberty
Continues throughout adult life of men
4 sperm produced per meiosis
Reduced amount of cytoplasm
Released at ovulation around day 14 of menstrual cycle.
Early stages occur during fetal development
Becomes irregular and then stops at menopause
1 egg produced per meiosis
Increased amount of cytoplasm

59. Decline in Male Fertility
Newsweek 1/25/15 Douglas Main, BPA Disrupts Sperm Development, Linked to Declining Male Fertility
The Wall Street Journal 7/15/13 Shirley Wang, The Decline in Male Fertility
In general, men produce upward of 60 million sperm/ml of semen. As long as the count is greater than 40 million/ml, men are considered fertile but below that threshold and particularly under 20 million/ml, their ability to help conceive drops
While there are regional variations, sperm counts and quality have been declining over the past 50 years
One 2013 study of more than 26,000 French men found that sperm concentrations have dropped by nearly 2%/year from

60. Hypothesis
1. Increasing exposure to endocrine-disrupting chemicals (especially substances that mimic the effects of estrogen). Bisphenol A (BPA), an endocrine disruptor found in many plastics, can linings and receipts, and which mimics the effects of estrogen may play a role
Corroboration from animal studies (mice exposed for a short period of time)
Link between higher BPA levels in men’s urine and low sperm counts
Presence of estrogen and progesterone in the environment as a result of the female contraceptive pill

61. Other Hypothesis
One of the most robust links with decreased sperm count is maternal smoking during pregnancy
May influence the number of Sertoli cells produced which impacts the production of sperm.
Male’s current marijuana use also linked to lower sperm count.
Sedentary jobs
Sitting for over 2 hours at a time has been linked with lower sperm counts.
Hot water
Frequent hot baths which increase scrotal temperature, are known to affect sperm count.

62. Fertilization

63. External Fertilization
Sea Urchin Fertilization
It takes place outside of the body
Females release unfertilized eggs and males put their sperm over the eggs
Other examples include salmon and other fish, frogs and other amphibians

64. Internal Fertilization
Mammalian Fertilization
Male passes his sperm into the female’s body and fertilization takes place inside
Other examples: pythons and other reptiles, albatrosses and other birds

65. Fertilization
The sperm is attracted to the egg as the result of chemicals produced by the outer zone of the egg (corona, zona pellucida).
The sperm migrates through the coat of follicle cells and binds to receptor molecules in the zona pellucida of the cell. This binding induces the acrosome reaction in which the sperm releases hydrolytic enzymes into the zona pellucida
With the help of these enzymes, the sperm reaches the plasma membrane of the egg and membrane proteins of the sperm bind to receptors on the egg membrane
The plasma membranes fuse, making it possible for the contents of the sperm cell to enter the egg

66. Fertilization
Fusion of the plasma membranes of the sperm and egg causes the cortical granule reaction caused by the flow of calcium ions triggered by the fusion
The cortical granule reaction involves small vesicles called cortical granules moving to the plasma membrane of the egg and fusing with it, releasing their contents by exocytosis
Enzymes released during the egg’s cortical reaction harden the zona pellucida, which now functions as a block to polyspermy. This occurs because enzymes from the cortical granules cause cross-linking of glycoproteins in the zona.

67. Calcium Release due to Fertilization

68. Following Fertilization
Mitosis follows
The nuclei from the sperm and egg do not fuse together
Instead, both nuclei carry out mitosis, using the same centrioles and spindle of microtubules
A two-cell embryo is produced

69. Early Embryonic Development
Pregnancy (gestation): condition of carrying one or more developing embryos in the uterus.
It is preceded by conception (fertilization of an egg by a sperm) and ends with birth of the offspring
Human pregnancy averages 266 days from conception

70. Early Development
Fertilization occurs in the oviduct and cleavage (cell division) begins in about 24 hours (mitosis without growth).
As cleavage continues, the zygote develops into a solid ball of cells called a morula passing down the oviduct to the uterus
The embryo reaches the uterus in 3-4 days and develops into a hollow ball of cells called a blastocyst. This stage develops about 1 week after fertilization
The blastocyst implants into the endometrium in the next 5 days

71. Early Development

72. Human Blastocyst

73. Early Development: Cleavage

74. Sea Urchin Development

75. Frog Early Development

76. More Early Development
During implantation, the blastocyst bores into the endometrium which grows over the blastocyst
For the first 2-4 weeks of development, nutrients are obtained directly from the endometrium
Embryonic tissues begin to mingle with the endometrium to form the placenta which functions in respiratory gas exchange, nutrient transfer, and waste removal for the embryo
Blood from the embryo passes through the umbilical artery to the placenta and returns through the umbilical vein

79. Bell Ringer
Outline the process of oogenesis

80. Early Human Development

81. HCG and Role in Pregnancy
Human chorionic gonadotropin (HCG) is an embryonic hormone that maintains progesterone and estrogen secretion by the corpus luteum to prevent menstruation which would end the pregnancy
The fetus also develops around itself an amniotic sac containing amniotic fluid
The fetus floats in this fluid and is supported by it

82. Hormones
HCG is an embryonic hormone that signals its presence and controls the mother’s reproductive system (secreted from the embryo)
HCG acts like pituitary LH to maintain secretion of progesterone and estrogens by the corpus luteum through the first trimester (1/3 of pregnancy). Therefore its secretion prevents menstruation and spontaneous abortion of the embryo.
Levels in maternal blood are so high that some is excreted in the urine, where it can be detected in pregnancy tests, the basis of which are monoclonal antibodies
Progesterone and estrogen are necessary throughout pregnancy to stimulate the development of the uterine lining
Corpus luteum does degenerate in the middle of pregnancy, but by then the placenta has taken over the role of secreting estrogen and progesterone

83. Structure of Placenta
Disc-shaped organ, containing embryonic and maternal blood vessels which grows to about the size of a dinner plate (185mm in diameter and 20 mm thick) and weighs somewhat less than 1 kg
The uterus with its placenta still exhibits 2 layers
Outer muscular layer which is used during childbirth, called the myometrium
Inner lining of the uterus, the endometrium, into which the placenta grows
Next slide is not too pretty…

84. Human Placenta

85. Human Placenta (less scary)

86. Placenta Circulation
Note: Umbilical arteries are blue, umbilical veins are red!

87. Blood Flow in Placenta
The placenta has numerous small projections called placental villi that give a large surface area for gas exchange and the exchange of other materials. Within the villi are fetal capillaries. Fetal blood flows through the capillaries in the villi
Between the villi are inter-villous spaces where maternal blood flows brought by uterine arteries and carried away by uterine veins
Arteries- takes blood away from the heart (arteries away)
Veins- takes blood to the heart (veins have valves)

88. Blood Flow in the Placenta
Deoxygenated fetal blood flows from the fetus to the placenta along two umbilical arteries while oxygenated fetal blood flows back to the fetus from the placenta along the umbilical vein
Maternal blood enters the placenta in uterine arteries, flows through blood pools in the endometrium, and leaves via uterine veins.
Embryonic or fetal blood, which remains in vessels, enters the placenta through arteries and passes through capillaries in fingerlike chorionic villi, where oxygen and nutrients are acquired
Fetal blood leaves the placenta through veins leading back to the fetus
Materials are exchanged by diffusion, active transport, selective absorption between the fetal capillary bed and the maternal blood pools
Mother’s blood and fetus blood never mix

89. Overview: Functions of the Placenta
Receives from the maternal circulation: oxygen, glucose, lipids, water, minerals, vitamins, antibodies, hormones
Sends into the maternal circulation: carbon dioxide, urea, hormones, water
Note: Maternal BLOOD does not flow along the umbilical cord or through the fetus

90. More about the Exchange of Materials Across the Placenta
(Refer to diagram of HL review guide)
Fetal portion of the placenta is called the chorion
The chorion forms the placental barrier controlling what passes in each direction
Chorion has villi (fingerlike projections) and the villi have microvilli which increase the surface area for the exchange of materials

91. Chorion
Close to the villus surface are mitochondria which provide ATP for active transport
Cytoplasm of the chorion produces estrogen and progesterone and secretes them into the maternal blood
Maintains corpus luteum, prevents menstrual flow, and maintains endometrium of the uterus
Within the chorion is a freely permeable basement membrane
There is also connective tissue inside the villus and there are capillaries with very thin walls of single cells that carry fetal blood
These capillaries are close to the villus surface so that there is only a small distance separating maternal and fetal blood

92. Childbirth
Labor is induced and regulated by interplay among estrogen, oxytocin, and prostaglandins. Progesterone also has a role.
Progesterone levels, which were high in the mother during pregnancy, abruptly fall signaling an end of pregnancy
This allows oxytocin to be secreted from the pituitary gland
High estrogen levels during the last weeks of pregnancy trigger formation of oxytocin receptors on the uterus
Oxytocin (from the fetus and maternal pituitary) stimulates the smooth muscles of the uterus to contract
Oxytocin also stimulates prostaglandin secretion by the placenta (enhances muscle contraction)
Physical and emotional stresses caused by the uterine muscle contractions stimulate secretion of additional oxytocin and prostaglandins. This is an example of positive feedback

93. Childbirth Cervix relaxes and dilates
Amniotic sac ruptures and amniotic fluid is released (water breaking)
Baby pushed out through cervix and vagina
Umbilical cord cut
Placenta delivered

94. A 11.4.1 Body mass vs. Birth mass

95. Animal size vs. duration of gestation

96. Scales are both logarithmic
Humans have a 283 day gestation and 65 kg body mass
Although there is a positive correlation overall between body mass and duration of gestation, there are examples of species that have the same length of gestation but body masses differing by more than 2 orders of magnitude
Animals with a relatively long gestation have offspring more advanced in their development when they are born than animals with a short gestation time in relation to adult body mass
Log10283 = 2.45; log1065 = 1.8

97. Retro 6.6
Hormone: Chemical messengers secreted by endocrine glands into the blood and transported by the blood to specific target cells. Long distance signaling molecules

98. U Insulin and glucagon are secreted by α and β cells in the pancreas to control blood glucose concentrations
Glucose homeostasis: maintained by insulin and glucagon
A rise in blood glucose above the set point (about 90mg/100mL in humans) stimulates the pancreas to secrete insulin, which triggers its target organs to take up excess glucose from the blood
Once the excess is removed and blood glucose concentration dips below the set point, the pancreas responds by secreting glucagon, which acts on the liver to raise the blood glucose levels

99. A 6.6.1
Type I – early onset
Inability to produce sufficient quantities of insulin
Autoimmune disease arising from the destruction of beta cells in islets of Langerhans by the body’s own immune system
May have viral trigger; also a genetic component to risk (HLA type)
Frequent testing of blood and injections of insulin. Some implantable insulin pumps.

100. Type 1 Diabetes

101. A 6.6.1
Type II – late onset
Inability to process or respond to insulin because of a deficiency of insulin receptors on target cells
Onset is slow. Main risk factors are sugary, fatty diets, prolonged obesity due to habitual overeating and lack of exercise, together with genetic factors that affect energy metabolism
Weight loss, exercise, dietary adjustments to reduce foods with high sugar content and starches that break down quickly
Drugs that stimulate pancreas to produce more insulin; injected insulin if needed

102. Type 2 Diabetes

103. U Thyroxin is secreted by the thyroid gland to regulate the metabolic rate and help control body temperature
Thyroid gland is a butterfly shaped gland located in your neck. The major hormone produced, thyroxin, is formed from the amino acid, tyrosine, and iodine and exists in 2 forms, T4 and T3, based on number of iodine atoms
T4 converted to T3. T3 acts as a transcription regulator
Thyroxin leads to an increase in metabolism by targeting all cells but mainly liver, muscles, and brain
Thyroxin also helps to regulate internal body temperature
An increase in metabolic rate produces more heat from the increased chemical reactions. So an increase in thyroxin will lead to an increase in body temperature and vice-versa.

104. Disorders of the Thyroid
Hyperthyroidism
Over production of thyroid hormones leads to high body temperature, profuse sweating, weight loss, irritability, and high blood pressure. Graves’ disease is leading cause
Hypothyroidism
Under production of thyroid hormone which can lead to lethargy and weight gain, forgetfulness and depression, feeling cold all of the time, constipation. Can be caused by an inadequate supply of iodine, or an autoimmune disease that attacks the thyroid (Hashimoto’s thyroiditis)

105. Grave’s Disease

106. U Leptin is secreted by cells in adipose tissue and acts on the hypothalamus of the brain to inhibit appetite
Appetite regulating hormones are secreted by various organs and tissues and act on the hypothalamus that controls the “satiety center”
Understanding this satiety pathway came about from the discovery of mutants (ob and db genes) in mice that caused them to be chronically obese

107. Leptin
Leptin is a hormone secreted by fat storage cells (adipose cells)
As levels of adipose tissue increase, leptin suppresses appetite
When body fat decreases, leptin levels fall, and appetite increases
Helps to regulate body weight
ob+ allele produces the satiety factor, now understood to be the hormone, leptin, in fat cells
db+ allele encodes the leptin receptor in membranes of cells in the hypothalamus
When ob/ob mice injected with leptin, appetite declined, energy expenditure increased and body mass dropped by 30% in a month

108. A 6.6.2 Leptin is also made in humans
Moved to clinical trials of 73 obese volunteers, only 47 of which finished the trial.
Double blind study (neither researchers nor volunteers knew what the subjects were injecting)
Results in humans showed varied results although on average, humans on highest dose lost the greatest amount of weight…which quickly found them again when the trial was over
Only small fraction of human obesity due to lack of leptin. Most due to lack of response by target cells. So, increasing leptin levels have no effect on levels of obesity
Route of administration: injections. These were not well tolerated by the subjects (35% drop out rate)

109. U 6.6.4 Melatonin is secreted by the pineal gland to control circadian rhythms
Melatonin is a hormone made by the pineal gland, a small gland in the brain
It is a modified amino acid
Melatonin helps control your sleep and wake cycles
Circadian rhythms: rhythms of behavior/ biochemistry that fit a 24 hour cycle

110. Production of melatonin under the control of the hypothalamus
Sequence of events leading to release:
Ganglion cells in the retina detect whether it is light or dark and send impulses to the supra-chiasmatic nuclei (SCN) in the hypothalamus
Supra-chiasmatic nucleus functions as a biological clock
Neurons in the SCN control secretion of melatonin by the pineal gland
Regulates functions related to light and to seasons marked by changes in day length
Primary functions relates to biological rhythms associated with reproduction

111. Melatonin production
Normally, melatonin levels begin to rise in the mid-to-late evening, remain high for most of the night, and then drop in the early morning hours.
Light affects how much melatonin the body produces
During the shorter days of winter, the body may produce melatonin either earlier or later in the day than usual. This change can lead to symptoms of seasonal affective disorder (SAD) or winter depression

112. A 6.6.3
Melatonin secretion decreases with age which explains how sleep patterns become more irregular as we grow older
Circadian rhythms are disrupted by travelling rapidly between time zones. Symptoms include: sleep disturbance, fatigue, headaches, irritability. This pattern = jet lag.
SCN and pineal set rhythm to the timing of day and night at point of departure. Only lasts a few days. Exposure to light at destination resynchronizes circadian rhythm.
Melatonin can be used to prevent or reduce jet lag.
Taken orally at the time when sleep should ideally start. Works best when travelling East, crossing 5 or more time zones.