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

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

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.

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.

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

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

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

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

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

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

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 J WERBA – IB BIOLOGY 11

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. J WERBA – IB BIOLOGY 12

CONTROL OF METABOLIC RATE & TEMPERATURE

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

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.

CONTROL OF APPETITE U.3

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

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

CONTROL OF CIRCADIAN RHYTHMS U.4

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.

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

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

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

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.

REPRODUCTIVE HORMONES

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.

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

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

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

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)

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)

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

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 1 7 14 28 time/days Menstruation Menstruation

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

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.

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)

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

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.

IN VITRO FERTILISATION (IVF) U.4

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.

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’.

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.

HORMONES, HOMEOSTASIS & REPRODUCTION Q1. Which words from the table below complete the sentence correctly? J WERBA – IB BIOLOGY 44

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] J WERBA – IB BIOLOGY 45

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? J WERBA – IB BIOLOGY 46

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] J WERBA – IB BIOLOGY 47