1. HORMONES, HOMEOSTASIS & REPRODUCTION
Hormones are used when signals need to be widely distributed.
Topic 6.6
IB Biology
Miss Werba

2. TOPIC 6 – HUMAN PHYSIOLOGY
6.1
DIGESTION & ABSORPTION
6.2
THE BLOOD SYSTEM
6.3
DEFENCE AGAINST INFECTIOUS DISEASE
6.4
GAS ECHANGE
6.5
NEURONS & SYNAPSES
6.6
HORMONES, HOMEOSTASIS & REPRODUCTION

3. THINGS TO COVER U.1 U.2 U.3 U.4 U.5 U.6 U.7 U.8 Statement Guidance
Insulin and glucagon are secreted by β and α cells of the pancreas respectively to control blood glucose concentration.
U.2
Thyroxin is secreted by the thyroid gland to regulate the metabolic rate and help control body temperature.
U.3
Leptin is secreted by cells in adipose tissue and acts on the hypothalamus of the brain to inhibit appetite.
U.4
Melatonin is secreted by the pineal gland to control circadian rhythms.
U.5
A gene on the Y chromosome causes embryonic gonads to develop as testes and secrete testosterone.
U.6
Testosterone causes pre-natal development of male genitalia and both sperm production and development of male secondary sexual characteristics during puberty.
U.7
Oestrogen and progesterone cause pre-natal development of female reproductive organs and female secondary sexual characteristics during puberty.
U.8
The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones.
The roles of FSH, LH, estrogen and progesterone in the menstrual cycle are expected.

4. THINGS TO COVER A.1 A.2 A.3 A.4 A.5 S.1 Statement Guidance NOS 1.8
Causes and treatment of Type I and Type II diabetes.
A.2
Testing of leptin on patients with clinical obesity and and reasons for the failure to control the disease.
A.3
Causes of jet lag and use of melatonin to alleviate it.
A.4
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.
A.5
William Harvey’s investigation of sexual reproduction in deer.
William Harvey failed to solve the mystery of sexual reproduction because effective microscopes were not available when he was working, so fusion of gametes and subsequent embryo development remained undiscovered.
S.1
Annotate diagrams of the male and female reproductive system to show names of structures and their functions.
NOS
1.8
Developments in scientific research follow improvements in apparatus — William Harvey was hampered in his observational research into reproduction by lack of equipment. The microscope was invented 17 years after his death.

5. THE ENDOCRINE SYSTEM
The endocrine system consists of glands that release hormones that are transported in the blood.
Produces slow responses

6. HOMEOSTASIS
Homeostasis involves maintaining the internal environment between narrow limits
Feedback loops control homeostasis
Feedback can be positive or negative
Negative feedback:
more common
has a stabilising effect
changes are reversed

7. CONTROL OF BLOOD GLUCOSE
Control of blood glucose concentration involves the insulin and glucagon hormones
Secreted by the pancreas
Insulin  secreted by β cells  lowers blood glucose levels
Glucagon  secreted by α cells  raises blood glucose levels

8. CONTROL OF BLOOD GLUCOSE
 cells secrete insulin, glucose glycogen
Detected by hypothalamus
Blood glucose concentration falls
Blood sugar rises
Normal blood glucose level (90mg/100mL)
Blood glucose concentration rises
Blood sugar falls
α cells secrete glucagon, glycogen glucose
Detected by hypothalamus

9. DIABETES The failure to control blood glucose level
Leads to hyperglycaemia, abnormally high levels of glucose in the blood
The kidney cannot reabsorb all of the glucose any longer, so it is excreted in the urine.
Urine volume increases  leads to thirst
Muscle tissue is broken down  leads to weight loss
May impair vision
May lead to kidney failure
There are two types of diabetes

10. DIABETES Type I diabetes: Early onset (usually childhood)
Due to loss of insulin secreting cells in the pancreas
No insulin produced (autoimmune?)
Controlled by regular insulin injections; pancreas transplant
Potential for stem cell therapy – researchers have successfully produced human beta cells from embryonic SC and are now doing animal trials in order to test their use as a treatment for diabetes

11. DIABETES Type II diabetes: Late onset (usually adulthood)
Commonly associated with being overweight for a long period of time
Caused by reduced sensitivity of the insulin target cells  they don’t take up sufficient glucose to reduce the levels in the blood
Controlled through dietary measures, increased activity and/or medication
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12. CONTROL OF METABOLIC RATE & TEMPERATURE
Control of metabolic rate and temperature involves the thyroxin hormone
Secreted by the thyroid
Release is controlled by the hypothalamus in the brain
Prolonged exposure to cold will stimulate the hypothalamus to trigger the release of thyroxin from the thyroid gland
Metabolic rate will increase, generating heat as a by product.
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13. CONTROL OF METABOLIC RATE & TEMPERATURE

14. CONTROL OF METABOLIC RATE & TEMPERATURE
-ve feedback of thyroxin, no thyroxin produced, reduced metabolism, sweating, vasodilation, hair or feathers lie flat, behaviour changes
Detected by hypothalamus
Increase in body temp
Body temp falls
Normal body temperature (37°C)
Body temp rises
Decrease in body temp
thyroxine produced by thyroid, increased metabolism, no sweating, piloerection, vasoconstriction, shivering, behaviour changes
Detected by hypothalamus

15. CONTROL OF APPETITE Control of appetite involves the leptin hormone
U.3
Control of appetite involves the leptin hormone
Secreted by the adipose (fat) cells
It regulates the amount of fat stored in the body in order to regulate energy levels
When the adipose tissue reaches a certain level, leptin is released.
It acts on the hypothalamus that then inhibits appetite and increases metabolism.

16. CONTROL OF APPETITE
U.3

17. OBESITY Clinical obesity = BMI over 30 kg m-2
Obese patients generally have higher leptin levels than a non-obese person.
This does not match expectations.
One hypothesis is that in these cases, there is a fault in the leptin-receptor on the cells of the hypothalamus.
Leptin injections will therefore not work to reduce hunger.
mutated leptin gene

18. CONTROL OF CIRCADIAN RHYTHMS
U.4
Control of circadian rhythms involves the melatonin hormone
Secreted by the pineal gland in the brain
The secretion of melatonin follows a regular pattern to control the sleep/wake cycle
High secretion at night, low during the day
Maintained by the natural light-dark cycle
On average, children release more melatonin than adults

19. CONTROL OF CIRCADIAN RHYTHMS
U.4

20. JET LAG Caused by rapid travel across time zones
Travelling disrupts the normal circadian rhythms
The brain resets to the new rhythm
The more time zones that have been crossed, the longer it will take to reset.
Melatonin tablets can be used to alleviate jet lag – but their efficacy has not been proven since dosage and timing are highly variable.
Spending some time looking at the moon has also been known to help recovery from jet lag.

21. MALE REPRODUCTIVE SYSTEM
ANNOTATE!
bladder
vas deferens
seminal vesicles
prostate gland
Cowper’s gland
urethra
scrotum
penis
epididymis
testis (pl. testes)

22. MALE REPRODUCTIVE SYSTEM
Testis: produces sperm & testosterone
Scrotum: keeps testes at a lower temperature
Epididymis: temporary storage of sperm during maturation
Vas deferens: transfers sperm during ejaculation
Seminal vesicle: produces some of the fluid making up semen
Prostate gland: produces some of the fluid making up semen
Penis: enters vagina to release semen near cervix during ejaculation
Erectile tissue: fills with blood to produce an erection
Urethra: transports urine and semen

23. FEMALE REPRODUCTIVE SYSTEM
ANNOTATE!
Fallopian tube (oviduct)
funnel
ovary
ovarian ligament
uterus
endometrium
uterine wall
cervix
vagina
vulva

24. FEMALE REPRODUCTIVE SYSTEM
Ovary: releases one secondary oocyte once a month; releases progesterone and oestrogen
Oviduct: picks up secondary oocyte at ovulation; site of fertilisation; responsible for transporting the blastocyst to the uterus
Uterus: place where foetus grows
Endometrium: lining of the uterus which is shed and replaced during menstruation; site of implantation of the blastocyst
Cervix: neck of uterus; plugged by mucous during pregnancy
Vagina: region where semen is deposited during intercourse; birth canal.

25. REPRODUCTIVE HORMONES

26. REPRODUCTIVE HORMONES
During foetal development, the gonads develop close to the kidney.
A gene on the Y chromosome causes embryonic gonads in the male to develop as testes and move into the scrotum.
The testes start to secrete testosterone. This causes the external genitalia to develop.

27. TESTOSTERONE Functions: pre-natal development of male genitalia
development of male secondary sexual characteristics during puberty
stimulates the final stages of spermatogenesis (sperm production)

28. OESTROGEN and PROGESTERONE
U.7
Functions:
pre-natal development of female genitalia
development of female secondary sexual characteristics during puberty

29. HORMONES & MENSTRUATION
There are 4 hormones involved in controlling the monthly cycle:
FSH – Follicle Stimulating Hormone
LH – Luteinising Hormone
Progesterone
Oestrogen
Pituitary
gland
Ovary

30. HORMONES & MENSTRUATION
Pituitary gland (in the brain) releases FSH:
stimulates the growth of the follicle
stimulates oestrogen production by the follicle
The growing follicle (in the ovary) releases oestrogen:
increases endometrium thickness
inhibits FSH production (-ve feedback)
stimulates LH production (+ve feedback)

31. HORMONES & MENSTRUATION
Pituitary gland releases LH:
stimulates ovulation (+ve feedback)
stimulates corpus luteum formation
stimulates oestrogen and progesterone production by the corpus luteum
The corpus luteum (in the ovary) produces progesterone:
maintains endometrium
inhibits FSH production (-ve feedback)
inhibits LH production (-ve feedback)

32. HORMONES & MENSTRUATION
If fertilisation of egg occurs, the zygote releases a hormone (hCG) which maintains the corpus luteum
If fertilisation does not occur:
the corpus luteum degenerates
FSH inhibition by progesterone is lost
the pituitary will start producing FSH again to stimulate another follicle

33. Pituitary Gland (Anterior Lobe)
HYPOTHALAMUS
FSH LH
Pituitary Gland (Anterior Lobe)
Inhibits FSH
Stimulates LH
Inhibits FSH & LH
Growing follicle
Ovulation
Corpus luteum
Ovaries
OESTROGEN
PROGESTERONE
Builds up endometrium
Maintains endometrium
time/days
Menstruation Menstruation

34. HORMONES & MENSTRUATION
FSH
OESTROGEN LH
PROGESTERONE
Source
Pituitary
Ovary (follicle)
Ovary (corpus luteum)
Functions
Stimulates follicle growth
Stimulates oestrogen secretion
Stimulates progesterone secretion
FSH surge stimulates ovulation
Stimulates thickening of endometrium
Promotes secondary sexual characteristics (eg. breast development, widening of hips)
Stimulates LH secretion
Inhibits FSH secretion
LH surge stimulates ovulation
Stimulates corpus luteum formation
Inhibits ovulation
Maintains endometrium
Inhibits FSH secretion
Inhibits LH secretion

36. IN VITRO FERTILISATION (IVF)
U.4
IVF = in vitro fertilisation
‘in vitro’ literally means ‘in glass’
In this procedure, the egg and the sperm meet outside the female’s body.
First “test tube baby” was Louise Brown, born in 1978.

37. IN VITRO FERTILISATION (IVF)
U.4
Process:
Drugs are used to suspend the normal secretion of hormones.
Drugs are used to down-regulate the menstrual cycle:
FSH injected  stimulates development of multiple follicles and induce superovulation
hCG injected  causes follicles to mature
Eggs are harvested/extracted (from the mature follicles/ovaries)

38. IN VITRO FERTILISATION (IVF)
U.4
Process:
Semen sample collected and processed to concentrate it.
Healthy sperm is selected.
Semen is brought into contact with the egg to allow fertilization:
sperm is directly injected into egg when low numbers or motility are a factor
semen is mixed with eggs in a dish/outside the body

39. IN VITRO FERTILISATION (IVF)
U.4
Process:
Incubated at 37°C to allow embryos to develop
Dish examined to choose healthiest embryo (eg. karyotyping and/or gene probes);
More hormones are used to prepare the mother’s uterus (eg. progesterone, hCG)
Embryo(s) are placed in uterus/oviduct, using a catheter or frozen so that they can be used later
Pregnancy test/scan used to assess success.

40. IN VITRO FERTILISATION (IVF)
U.4

41. TECHNOLOGY ENABLES DEVELOPMENTS IN RESEARCH
NOS 1.8
Developments in scientific research follow improvements in apparatus.
William Harvey was hampered in his observational research into reproduction by lack of equipment. The microscope was invented 17 years after his death.

42. WILLIAM HARVEY’S RESEARCH
Harvey investigated human circulation (Topic 6.2) and sexual reproduction.
He observed growth in fertilised hens’ eggs, as these were large and easy to obtain and observe. He made connections between a drop of blood on the yolk and the growth of new chick.
He observed that deer needed to mate before any offspring could be produced. Observations of the uteruses of some of these deer showed that the embryo only appeared a couple of months after mating. This led to false conclusions about the lack of importance of the male ‘seed’.

43. WILLIAM HARVEY’S RESEARCH
William Harvey failed to solve the mystery of sexual reproduction because effective microscopes were not available when he was working.
Fusion of gametes and embryonic development remained undiscovered.
Sperm were first observed in 1677.
Harvey had passed away in 1657.

44. HORMONES, HOMEOSTASIS & REPRODUCTION
Q1. Which words from the table below complete the sentence correctly?
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45. HORMONES, HOMEOSTASIS & REPRODUCTION
Q2. Distinguish between type I and type II diabetes. [3] Q3. Explain the principle of homeostasis with reference to the control of blood glucose. [9]
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46. HORMONES, HOMEOSTASIS & REPRODUCTION
Q4. The hormones progesterone and LH were measured in a woman’s blood over 40 days. When did her menstrual bleed start?
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47. HORMONES, HOMEOSTASIS & REPRODUCTION
Q5.
Outline the roles of FSH in the menstrual cycle. [2]
FSH is secreted by the pituitary gland. During pregnancy, FSH secretion is inhibited. Suggest how FSH secretion could be inhibited during pregnancy. [1]
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