4.5.3 Hormonal coordination in humans
4.5.3.1 Human endocrine system
Negative Feedback
- Negative feedback is a key part of homeostasis
- When there is a change in the body’s internal environment, it is detected by receptors to return this change back to the set point
- The body then counteracts the change
Endocrine System
- The endocrine system works with the nervous system to maintain homeostasis
- This uses hormones, which are secreted into the bloodstream, then move through the blood to reach their target organ
- The endocrine system works by negative feedback
Functions of Pituitary Gland
- The pituitary gland exists as a structure in the brain
- It controls blood sugar, fertility, water levels, growth
- It works by secreting primary hormones that cause target organs to secrete secondary hormones
Hormones Secreted
- ACTH (Adrenocorticotrophic Hormone): stimulates the adrenal glands, leading to release of adrenaline
- Adrenaline is released during exercise
- ADH (Antidiuretic Hormone): stimulates the kidneys to control water levels in the blood
- Less ADH released when there is too much water
Endocrine Glands
4.5.3.2 Control of blood glucose concentration
Glucose Homeostasis
- Carbohydrates from food are broken down into glucose, which is used for respiration
- The pancreas is an endocrine organ in the abdomen that controls glucose levels
- E.g. glucose levels rise after eating, so the pancreas needs to reduce this
- Glucose is stored as glycogen
The Islets of Langerhans
- These cells work to produces the hormones insulin and glucagon
- There are two types of islet cells: alpha cells and beta cells
- Alpha cells produce glucagon
- Beta cells produce insulin
Glucagon and Insulin
- Glucagon converts glycogen into glucose
- It is important in starvation, and during exercise
- Insulin acts on the liver to reduce the blood glucose levels to convert glucose to glycogen
- More glucose is taken in the cells
Insulin and Diabetes Mellitus
- In Diabetes Mellitus, the body struggles to reduce the blood glucose level if it rises
- This can lead to high glucose levels in the blood – hyperglycaemia
Mechanism of Diabetes
Comparison of Age
Risk Factors
Diagnosis
Glucose Tolerance Test
- In this test, the person will be given a glucose drink
- The blood glucose is monitored over several hours
- In diabetics, glucose levels take much longer to return back to normal
Glucose Tolerance Test
Function of Glucagon
- The body’s mechanisms are in place to increase the blood sugar level if it gets too low
- Glucagon is a hormone produced by the alpha cells to increase the blood sugar level
- Glucagon converts glycogen into glucose, leading to an increase in the blood sugar level
Negative Feedback of Glucagon and Insulin
- When the blood sugar level decreases below the set point, glucagon is released
- When the blood sugar level increases too much above the set point, insulin is released
Exam Practice
4.5.3.3 Maintaining water and nitrogen balance in the body (biology only)
Osmoregulation
Osmoregulation in Homeostasis
- Osmoregulation: Control of blood water and mineral levels
- Water and nitrogen levels must be maintained in the body
- Osmosis: Movement of water down a gradient
- When water or salt levels change in the blood, there can be an osmotic effect
Osmoregulation in Plant Cells
Osmoregulation
- Plant cells can be turgid when full of water
- Guard Cells: Take up water, open the stoma of the plant and enable water loss via transpiration.
- Plant cells can be flaccid when empty of water
- This causes the cytoplasm to move away from the walls.
Osmoregulation in Red Blood Cells
- In a hypertonic solution, RBCs become crenated
- Net movement of water from cytoplasm of the RBC to the blood
- In a hypotonic solution, RBCs undergo haemolysis
- Net movement of water from the blood into the blood cells
Excretion of Water
Lungs
- When we breath out, water and CO2 leaves our lungs.
- You cannot control how much water vapour or CO2 is lost
Sweat
- Water and ions are lost via sweat, even when water levels are low
- You cannot control the loss of water and mineral ions in sweating
Urine
- This is the main source of water excretion
- You can partly control loss of water as urinating is a voluntary action.
Excretion of Proteins
Introduction
- Proteins contain nitrogen
- When proteins are digested, they break down to amino acids by protease enzymes
- Excess amino acids cannot be stored
- The liver deaminates the amino acids
- Ammonia converted to urea
- The urea is excreted
Functions of the Kidney
Controlling Ion Levels
- Kidneys decide the amount of ions we excrete in the urine
- E.g. sodium
Excreting Urea
- Kidneys remove urea from the body in urin
- This urea is a product of breakdown of proteins
Water Control
- Kidneys control how much water is lost in urine
Nephron Reabsorption
Nephron Reabsorption
Production of Urine
Interpreting Data
Proteins
- Proteins should have a concentration of 0 in the urine
Anti-Diuretic Hormone (ADH)
Pituitary Gland
- ADH is released by the pituitary gland
- The target organ is the kidneys
Water Control
- ADH is a key factor in deciding water content of the blood
- Overly hydrated → Urinate Frequently
- Dehydrated → Urinate Less
- Water levels are detected in the brain
- This controls how much ADH is released by the pituitary gland
ADH in Dehydration
- A person is dehydrated
- The plasma is very concentrated with salt
- The pituitary gland releases more ADH
- The kidney tubules are more permeable to water
- Urine is less dilute
ADH in Over-Hydration
- A person drinks a lot of water
- The plasma is less concentrated with salt
- The pituitary gland releases less ADH
- The kidney tubules are less permeable to water
- rine is more dilute
ADH in Special States
- Alcohol: Reduces ADH Production
- Urea: Normally constant in urine during changes in water content
Renal Dialysis
- Kidney failure leads to a build up of toxins
- Humans may need treatment for kidneys
Dialysis Machines
- Unfiltered blood is taken from the human
- The blood is filtered in a dialysis machine
- Waste Products pass from blood to dialysis fluid
- A countercurrent system is used
Negatives of Dialysis
- Painful Process: Impact on Quality of Life
- Hassle: Regular visits to hospital
- Diet: Control intake of amino acids and salts
Exam Practice
4.5.3.4 Hormones in human reproduction
Changes During Adolescence
- Reproductive hormones are released during adolescence and lead to many changes
- This is called puberty
Changes During Adolescence
- Secondary Sex Characteristics: can be used to differentiate gender but not involved in reproduction
- Production of Sex Cells: needed for reproduction
Testosterone in Males
- Main reproductive hormone for males
- Produced in the Leydig cells of the testes
- Testosterone stimulates the production of sperm in males
Changes caused by Testosterone
- Hair Growth Increases
- Muscle Growth Increases
- Voice Deepens and Breaks
- Sperm production begins
- Penis and testes develop
Oestrogen in Females
- Main reproductive hormone for females
- Produced in the ovaries
- Oestrogen causes ovulation. This is the release of an egg from the ovaries
- During puberty, eggs begin to mature
- This means that they can take part in the menstrual cycle
Changes caused by Oestrogen
- Underarm and pubic hair growth
- Sexual organs develop
- Breasts form
- Hips widen
- Voice gets slightly deeper
Menstrual Cycle: Key Stages
Menstrual Cycle: Key Events
Luteinising Hormone (LH)
- Released mainly during day 14
- Produced by pituitary gland
- Key in ovulation
Follicle Stimulating Hormone (FSH)
- Released mainly during days 2-3
- Produced by pituitary gland
- Key in maturation of egg – stimulates the egg
Oestrogen
- Released mainly during days 4-15
- Produced by ovaries
- Key in growing uterus lining
- Key in ovulation – oestrogen stimulates a surge in LH to cause release of egg
Progesterone
- Released mainly during days 15-27
- Produced by follicle in the ovaries
- Key in maintaining uterus lining
- Key in end of menstrual cycle – fall in progesterone at day 28 vital
Hormones Work Together in the Menstrual Cycle
- Release of FSH stimulates release of Oestrogen
- High Oestrogen levels are high, they suppress FSH
- Oestrogen stimulates release of LH when oestrogen levels are high
- Progesterone inhibits LH and FSH
- As Oestrogen and Progesterone drop, inhibition of FSH ends
Key Stages of Menstrual Cycle
Events of Menstrual Cycle
4.5.3.5 Contraception
Contraception
- Interventions that can stop pregnancy from occurring
- These can be hormonal or non-hormonal
- These can be before sexual intercourse or after fertilisation
Hormonal Interventions
- Alter the hormonal balance of the body
- Pros: effective, as they alter environment to prevent fertilisation
- Cons: weight gain, acne, changes in blood pressures
Oral Contraceptives (The Pill)
- Contains oestrogen and progesterone
- Used to stop FSH
- Egg maturation cannot take place
- Ovulation cannot occur
Progesterone
- Progesterone can inhibit maturation and release of eggs
- Can be injected, implanted or slow-release skin patch
- Stops egg maturation and release of eggs
- 92-99% success rate
Barrier Methods
- These can stop fertilisation
- Condoms prevent the sperm entering the female
- Diaphragms prevent the sperm entering the cervix
Intrauterine Devices
- Intrauterine devices stop the implantation of an embryo
- Coils stop implantation of embryo
- Copper is released which changes chemical makeup of mucus
Spermicidal Agents
- Spermicidal agents kill sperm cells
- Spermicides can kill or disable sperm
- Some people have allergies
Abstaining from Intercourse
- Abstaining means avoiding intercourse during certain timings of menstrual cycle
- Needs to be planned carefully
Surgical
- Surgical methods are often permanent methods of contraception
- Sterilisation in females
- Vasectomy in males
4.5.3.6 The use of hormones to treat infertility (HT only)
Fertility Drugs
- FSH and LH can be used to stimulate egg maturation
- Without FSH, it is difficult for fertilisation
- Fertility drugs allow maturation of eggs
In Vitro Fertilisation (IVF)
- IVF involves fertilising an embryo, in vitro or in glass
- Used in women who have blocked oviducts and men with sperm issues
- Offered to women under 43, who have tried and failed to become pregnant after two years of regular unprotected sex [NHS]
In Vitro Fertilisation (IVF)
IVF
- Drugs stimulate production of sex cells
- Fertilisation takes place in the lab
- Fertilised eggs grow into embryos.
- Embryos are implanted back into the mother
Con: Low Success Rate
- Not always 100% successful
- This can add to stress
Con: Physical and Emotional Stress
- Can lead to emotional strain for women who put all their hopes into treatment
Con: Multiple Births
- Can be difficult for babies and the mother
- This can manifest as twins, triplets and even more
4.5.3.7 Negative feedback (HT only)
Adrenal Glands and Adrenaline
- Adrenaline is a hormone produced by the adrenal glands
- Released in situations when body needs more oxygen
- E.g. when an animal is being hunted
Adrenaline: Increased Heart Rate
- Pumps more blood around the body for muscles
Adrenaline: Glucose Production
- Increase breakdown of glycogen into glucose in liver
Adrenaline: Vasoconstriction in Gut
- Blood redirected to muscles and brain, for increased oxygen delivery
Adrenaline: Pupil Dilation
- Make the individual more alert
Adrenaline: Bronchioles Widen
- Increased ventilation to get more air for faster gas exchange
Summary of Adrenaline
- Increased Heart Rate
- Glucose Production
- Vasoconstriction in the gut
- Pupil dilation
- Bronchioles widen
Thyroid Glands and Thyroxine
- Thyroid Gland: Endocrine gland in the throat
- Thyroxine: Controls the basal metabolic rate
Hypothyroidism
- Definition: Too little thyroxine, reducing the basal metabolic rate
- This causes:
- Weight Gain
- Reduced Heart Rate
- Loss of Appetite
- Reduced Fertility
Hyperthyroidism
- Definition: Too much thyroxine, increases the basal metabolic rate
- This causes:
- Weight Loss
- Palpitations
- Irregular Menstrual Cycles in Females
- Irritability
Goitre
- Swelling in the neck
- Caused by hyperthyroidism and hypothyroidism
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