Hormonal coordination in humans

5.3.1 Human endocrine system

Endocrine system

• Composed of gland which secrete chemicals called hormones into bloodstream
• Hormone transported in bloodstream to target organ where it produces an effect
• Effect slower but longer compare to nervous system

What is a hormone? (1)

Chemical messenger produced by endocrine gland

 

Pituitary gland	Acts as ‘master gland’ Secretes hormones into blood in response to body conditions (Some hormones act on other glands to stimulate other hormones to produce different hormones) In men – stimulate ovaries In women – stimulate testes
Thyroid gland	Produce thyroxine Controls metabolic rate Controlled by negative feedback
Adrenal gland	Produce adrenaline Prepares body for stressful situations / ‘fight or flight’ response Increase heart rate & delivery of O2 & glucose to brain & muscles
Pancreas	Secretes insulin Controls level of glucose in blood
Ovary	Produce & release eggs Produce oestrogen Causes changes at puberty & control menstrual cycle
Testis	Produce sperm Produce testosterone Cause changes at puberty & stimulates sperm production

Hyperthyroidism – caused by an overactive thyroid gland

Suggest what would happen in the body of a person with hyperthyroidism. (3)

• Too much thyroxine is released into blood
• Which raises basal metabolic rate (BMR)
• Causing increase formation of glycogen, rate of respiration, breakdown of proteins

5.3.2 Control of blood glucose concentration

Which organ in the body monitors the concentration of glucose (sugar) in the blood? (1)

• Pancreas

Explain how insulin controls blood glucose levels in body (3)

• If too high, pancreas produces insulin to cause glucose move from blood into cells
• In liver & muscle cells, excess glucose is converted to glycogen for storage
• If too low, pancreas produces glucagon to break down glycogen to convert into glucose & released into blood in a negative feedback cycle

During the race, the cyclist’s blood glucose concentration began to decrease. Describe how the body responds when the blood glucose concentration begins to decrease. (3)

• Pancreas detects low blood glucose
• Produces glucagon
• So glycogen is converted to glucose

	Description	Treatment
Type 1 diabetes	Pancreas fails to produce sufficient insulin Characterized by uncollected high blood glucose levels	Insulin injections to replace insulin that isn’t made Pancreas transplant (Dis – pancreas could be rejected)
Type 2 diabetes	Body cells no longer respond to insulin produced Risk – obesity	Carbohydrate controlled diet Exercise

Insulin cannot be taken as a tablet. Why? (1)

• It digested / broken down

Other than using drugs or insulin, give two methods of treating diabetes. (2)

• Control or change diet
• Exercise
• Pancreas transplant

Give one symptom of diabetes (1)

• High normal blood sugar & remains high

Give one way in which a diabetic may be advised to change their diet. (1)

• Small meals

How does this change in diet help diabetic? (1)

• Prevent high blood sugar

A high concentration of glucose in blood can harm body cells as a result of osmosis. Explain why. (4)

• Water movement out of cell from dilute to concentrated solution through partially permeable membrane
• Cell shrink

5.3.3 Maintaining water and nitrogen balance in the body (biology only)

• Water leaves body through lungs during exhalation
• Water, ions & urea lost from skin in sweat
• Excess water, ions & urea are removed through kidneys in urine

What happens to body cells if kidneys produce very little urine? (1)

• Cells swell

If body cells lose/gain too much water by osmosis, they don’t function efficiently

The digestion of proteins from diet

• Excess amino acids deaminated & form ammonia
• Ammonia is toxic so converted to urea in liver
• Urea filtered by kidney & released into blood
• Urea in urine stored in bladder for safe excretion

How urine is produced by kidneys. (5)

• Urea filtered by kidney & released into blood
• Reabsorption of all glucose, some ions by active transport & water by osmosis as needed by body back into blood
• Urea present in urine

Functions of kidneys in maintaining water balance of body

• Filtration – high pressure in blood forces small molecules (glucose, urea, ions, water) out of blood into tubules
• Selective reabsorption – all glucose for respiration & enough water & ions to make con in body constant, no urea reabsorbed
• Formation of urine – anything remaining in tubules forms urine & passes down into bladder

How to keep water concentration constant?

If water concentration in blood too high

• Detected by osmoreceptor in hypothalamus
• Less ADH (anti-diuretic hormone) released by pituitary gland
• Less water reabsorbed from kidney tubules to blood
• Less water in blood

If water concentration in blood too low

• Detected by osmoreceptor in hypothalamus
• More ADH released by pituitary gland
• More water reabsorbed from kidney tubules to blood
• More water in blood

Treatments for kidney failure

Organ transplant		Use kidney dialysis
Advantages	Disadvantages	How it work Unfiltered blood taken from blood vessel in arm Blood pump keep blood moving Mixed with blood thinners / anti-coagulant to prevent clotting Inside dialysis machine, blood & dialysis fluid separated by partially permeable membrane. Blood flows in opposite direction to dialysis fluid, allowing exchange occur Excess ions & water diffuse across partially permeable membrane Clean blood flows through bubble trap to get rid of bubbles Clean blood returns to blood vessel in armDialysis fluid Same concentration of glucose & ions – no net movement of glucose out of blood No urea – steep concentration gradient from blood down to fluid – more urea leaves blood Advantages  Available to all patients No need for immune-suppressant drugs Disadvantages Limit salt & protein intake Risk of blood clot Regular dialysis sessions
Keep blood concentration constant Prevent high blood pressure Cheaper in long term	Long term drug use Hazards of operation Shortage of donors

 

Explain why transplanted organ may be rejected. (3)

• WBC produce antibodies, which attack antigens on transplanted organ

How to prevent kidney from being rejected? (1)

• Tissue typing donor kidney

5.3.4 Hormones in human reproduction

During puberty reproductive hormones cause secondary sex characteristics to develop.

What is ovulation? (1)

• Release of egg from ovary
• At puberty eggs begin to mature & one is released every 28 days

Follicle stimulating hormone (FSH)	Stimulates egg maturation in ovary Stimulates ovary to produce oestrogen
Oestrogen	Stimulate release of eggs
Luteinising hormone (LH)	Inhibits FSH Stimulates release of egg Causes uterus lining to develop, while progesterone maintains it
Progesterone	Maintain uterus lining Inhibits release of FSH & LH

Describe how FSH, LH & oestrogen are involved in control of menstrual cycle. (3)

• FSH – stimulate egg maturation
• LS – stimulate egg release
• Oestrogen – inhibits FSH

The mini-pill is a contraceptive that only contains progesterone hormone.

Explain why missing a dose of mini-pill would reduce success rate of mini-pill. (4)

• Missing a dose cause drop in progesterone level
• So FSH & LH not inhibited anyone
• Egg is matured & released

5.3.5 Contraception

How oral contraceptives / hormonal methods of contraception prevent eggs mature?

• Contraceptive pill contains oestrogen (stop FSH) & progesterone (stop FSH & LH) – stop ovulation
• Injection, implant or skin patch release progesterone – inhibit maturation & egg release for a no of months/years (how long and how effective?)

Advantage – reliable

Disadvantage – doesn’t protect against STDs

How can non-hormonal methods of contraception control fertility?

• Barrier methods eg condoms & diaphragms – prevent sperm reaching egg
• Spermicidal agents – kill or disable sperm
• Intrauterine devices (IUD) – prevent implantation of embryo or release of hormone
• Abstaining from intercourse when egg is in oviduct (natural method)
• Sterilisation (surgical methods)

In women – female sterilisation – oviducts are cut to prevent egg from reaching uterus

In men – vasectomy – sperm tubes are cut to prevent sperm from leaving penis

Disadvantage – x prevent STDs

Why issues around contraception cannot be answered by science alone?

• The Catholic church teaches that all contraception is unethical, except natural methods

Condom prevents STDs

Describe benefits & possible problems that may result from use of hormones to regulate human reproduction. You should refer to fertility drugs & contraceptives in your answer. (4)

	Advantages	Disadvantages
Oral contraceptives	Prevent egg release Regulate menstrual cycle	Prolonged use may prevent later ovulation Cause headache
Fertility drugs	Can stimulate egg release	Multiple births

 

 

 

 

 

 

Source: https://www.bbc.co.uk/bitesize/guides/zpwjk2p/revision/7

5.3.6 The use of hormones to treat infertility (HT only)

Name 2 hormones used in IVF treatment. (2)

• FSH & LH

Why are fertility drugs given to some women? (1)

• To stimulate egg production to help them get pregnant

Describe the process of IVF. (4)

• FSH & LH given to mother to matures & release eggs
• Egg collected from mother’s ovary & mixed by sperm from father in the lab. Fertilisation occurs.
• Fertilised egg divides & develop into embryos
• When they’re tiny balls of cells, one or two embryos are inserted into mother’s uterus

Disadvantages of IVF treatment (4)

• Low success rate / more likely to have faulty chromosome if too old
• Emotionally & physically stressful
• Multiple births cause possible harm to mother & babies
• Expensive

The committee which regulates IVF treatment now advises that only one embryo is used in each treatment. Suggest one reason for this. (1)

• So fewer multiple births
• Multiple births cause possible harm to mother & babies

5.3.7 Negative feedback (HT only)

Details in…

5.3.2 Control of blood glucose concentration

5.3.3 Maintaining water and nitrogen balance in the body (biology only)