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

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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

1. Excess amino acids cannot be stored
2. The liver deaminates the amino acids
3. Ammonia converted to urea
4. 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

1. A person is dehydrated
2. The plasma is very concentrated with salt
3. The pituitary gland releases more ADH
4. The kidney tubules are more permeable to water
5. Urine is less dilute

ADH in Over-Hydration

1. A person drinks a lot of water
2. The plasma is less concentrated with salt
3. The pituitary gland releases less ADH
4. The kidney tubules are less permeable to water
5. 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

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Dialysis Machines

1. Unfiltered blood is taken from the human
2. The blood is filtered in a dialysis machine
3. Waste Products pass from blood to dialysis fluid
4. 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

1. Drugs stimulate production of sex cells
2. Fertilisation takes place in the lab
3. Fertilised eggs grow into embryos.
4. 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