Endocrine System

 

Introduction

Learn all about the human endocrine system. 

There are a total of 4 learning objectives, each learning objective contains information and questions to help prepare you for the upcoming lesson.

 

 

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1. Describe the functions of the endocrine system

What is the purpose of the endocrine system?

Endocrine System

The endocrine system is composed of ductless glands which produce hormones, the body’s chemical messengers.

Each gland produces specific hormones and Hormones control and affect many body functions and organs, as well as behaviour.

The function of the endocrine system is closely linked to that of the nervous system.

  • contribute to the reproductive process
  • produce and secrete hormones to regulate body activities
  • maintain the body during times of stress
  • all of the above

Hormone

A hormone is a chemical messenger, which is secreted directly into the blood by a particular gland. Some hormones are made of protein (e.g. insulin), whilst others are steroids (adrenocorticoid hormones), glycoproteins (FSH, LH, TSH), and derivatives of single amino acids, (T4, T3).

Hormones are produced in the gland and are then transported to the area/organ they control or affect.

Endocrine Gland

Endocrine glands are ductless gland which produces hormones.

Ductless means that there is no separate canal or tube to transport the hormones to the blood. Hormones travel straight into the bloodstream from the gland.

Hormones and Endocrine System

Hormones and Endocrine System affects the behaviour and function of different areas of the body and of the body overall, e.g. hormones are responsible for correct growth, changes during puberty, the menstrual cycle, pregnancy, the menopause, responses to stress and danger and the proper functioning of the kidneys and digestive system.

If too much of a hormone is produced it is known as hyper-secretion;

Too little is known as hypo-secretion.

Fill in the blanks

  • Pineal Gland
  • Pituitary gland
  • Parathyroid and Thyroid gland
  • Adrenal gland

2. Describe the names and effects of hormones (1)

The Pituitary Gland (Master Gland)

Anterior lobe hormones

Adrenocorticotrophin (ACTH)
Function: controls adrenal cortex
Malfunction: see adrenal cortex.

Melanocyte-stimulating hormone (MSH)
Function: stimulates production of melanin in basal layer of the skin.

Human growth hormone (HGH)
Function: regulates height and growth; main controller along with genes of final height of a person
Malfunctions: hypersecretion causes gigantism or acromegaly; hyposecretion causes dwarfism.

Thyrotrophin (TSH)
Function: controls thyroid gland
Malfunctions: see thyroid gland.

Gonadotrophins (gonad/sex organ hormones)
Function: control sexual development and organs (ovaries and testes)

Follicle-stimulating hormone (FSH)
Function: stimulates ovaries to produce oestrogen and to ovulate in women and stimulates sperm production in men.

Luteinising hormone (LH)
Function: stimulates ovaries to produce the corpus luteum from ruptured follicle and produce progesterone.

Interstitial cell-stimulating hormone (ICSH)/ luteinising hormone in men
Function: stimulates sperm production and secretion of testosterone.
Malfunctions (of gonadotrophin): Polycystic ovarian syndrome, Endometriosis Fibroids

Prolactin or lactogenic hormone (LTH)
Function: production of milk during lactation.

Which of the following secretes the adrenocorticotrophic hormone (ACTH)?

  • anterior lobe of pituitary
  • posterior lobe of pituitary
  • adrenal medulla
  • adrenal cortex

Posterior lobe hormones

Antidiuretic hormone (ADH or vasopressin)
Function: regulation of water absorption in kidneys
Malfunctions: hyposecretion: diabetes insipidus; hypersecretion: oedema (swelling).

Oxytocin
Function: contracts mammary glands when suckling begins, to release milk secreted into ducts; contraction of muscles of uterus to begin childbirth and during it.

Which hormone is responsible for increasing water reabsorption in the kidney tubules?

  • luteinising hormone (LH)
  • aldosterone
  • anti-diuretic hormone (ADH)
  • oxytocin

Which of the following hormones stimulates the uterus during labour?

  • prolactin
  • oestrogen
  • progesterone
  • oxytocin

Pineal Body

Hormone:
Melatonin (derived from serotonin)
Function: controls body rhythms – responds to sunlight
Malfunctions: jet-lagged feeling; depression, SAD – seasonal affective disorder.

Thyroid Glands

Hormones:
Thyroxin, and Triiodothyronine (produced in response to TSH from anterior lobe of Pituitary Gland)
Functions: stimulate tissue metabolism; maintain BMR (basic metabolic rate).
Malfunctions: hypersecretion known as Graves disease or thyrotoxicosis (hyperthyroidism — increase in metabolic rate, heart rate, anxiety, intolerance of heat plus raised temperature, frequent bowel action); hyposecretion — body systems slow below normal speed, cretinism (at birth) or myxoedema (disorder caused later in life by untreated cretinism), goitre – thyroid enlargement.

Calcitonin
Function: maintenance of calcium and phosphorus balance.
Malfunction: hypersecretion causes lowering of blood calcium level by inhibiting loss of calcium from bone.

Parathyroid Glands

Hormone:
Parathormone

Functions: maintenance of calcium level in plasma; stimulates calcium re-absorption in kidneys; activates Vitamin D.

Malfunctions:

  • Hypersecretion – hyperparathyroidism: Softened bones and thus spontaneous bone fractures;
  • Hyposecretion — hypoparathyroidism: abnormally low blood calcium levels; tetany (spasms in hands and feet caused by over-contraction in muscles); convulsions (from over-stimulated nerves).

Thymus

Hormone:

Thymic Factor (TF), Thymic Humoral Factor (THF)Thymosine, Thymopoietin

Functions: Part of immune system, appear to promote development of T Lymphocytes in the thymus gland.

Malfunction: lowered immunity and/or stress.

3. Describe the names and effects of hormones (2)

Where are the islets of Langerhans situated in?

Pancreas

Hormones:
Insulin and Glucagon

Function: helps glucose enter cells thus regulating blood sugar levels.

Malfunctions:

  • Hyposecretion: diabetes mellitus (high blood sugar level and high urine production); fatigue; weight loss; coma;
  • Hypersecretion: hypoglycaemia (low blood sugar level) including symptoms of hunger, sweating; in serious cases may lead to coma.

  • liver
  • ovaries
  • kidneys
  • pancreas

Which of the following hormones increases blood circulation and heart rate?

Adrenal medulla
The adrenal medulla functions to support the sympathetic nervous system.

Hormones:

  • Adrenaline and noradrenaline
    Function: often known as the stress hormones, they prepare the body for ‘fight or flight’ by speeding up heart rate, slowing digestive and urinary systems, increasing blood pressure and blood sugar level. 

Adrenal cortex

Hormones:

  • Mineralocorticoids – aldosterone (steroids)
    Function: regulates salts in body, especially sodium chloride and potassium.
    Malfunctions: hypersecretion — kidney failure, high blood pressure, too much potassium in blood causing abnormal heart beat; hyposecretion: Addison’s disease; muscular atrophy and weakness; body systems slow down.
     
  • Glucocorticoids (steroids) (cortisol and cortisone)
    Functions: produced in response to ACTH (from pituitary, anterior lobe); metabolises carbohydrates, fats and proteins.
    Malfunctions: hypersecretion —Cushing’s syndrome; stunted growth, moon-shaped face, muscular atrophy, hypertension, diabetes mellitus.
     
  • Sex hormones (steroids); female: oestrogen and progesterone, (some normal in male); male: testosterone (small amounts secreted in the ovaries in females)
    Functions: sexual development and maturity; ovulation; hair growth in pubic and axillary (armpit) areas.
    Malfunctions: many, including hirsutism, amenorrhoea (hypersecretion of testosterone in women); muscle atrophy and breast growth (hypersecretion of oestrogen in men); hyposecretion: Addison’s disease.

  • noradrenaline
  • adrenaline
  • insulin
  • testosterone

The glucocorticoids are secreted by?

  • adrenal medulla
  • pancreas
  • adrenal cortex
  • pineal gland

Which hormone is involved with the development of the placenta?

Ovaries

Hormones:
Oestrogen and Progesterone (female sex hormones, small amount produced in male testes)

Functions: responsible for female sexual characteristics e.g. breast growth, widening of hips, pubic and axillary hair growth.

Malfunctions: Cause unknown. In women can lead to polycystic ovarian syndrome (known as Stein-Leventhal syndrome); in males can lead to muscle atrophy and breast growth.

  • prolactin
  • progesterone
  • follicle-stimulating hormone (FSH)
  • oestrogen

Which hormone is a male sex hormone?

Testes

Hormone:
Testosterone (male sex hormone, small amount produced in female ovaries)

Functions: responsible for male sexual characteristics thus sperm production, changes at puberty — voice breaking, pubic, facial and axillary hair growth, increased muscle mass.

Malfunctions: though a low level of testosterone is normal in females, hypersecretion can lead to virilism, hirsutism and amenorrhoea.

  • Oestrogen
  • Progesterone
  • Melatonin
  • Testosterone

Video of Endocrine System

4. Describe diseases and disorders of the endocrine system.

Addison’s syndrome

Cause: hyposecretion of adrenocortical hormones (sex, growth and salt regulation hormones).

Effects: muscular atrophy and weakness; hypotension; gastric problems like vomiting, changes in skin pigmentation, irregular menstrual cycle and dehydration.

Hypersecretion of testosterone in women can lead to what condition?

Amenorrhoea

Cause: can be caused by hypersecretion of testosterone (in females), stress; radical weight loss, anaemia.

Effect: absence of menstruation.

  • amenorrhea
  • polycystic ovary syndrome
  • gynaecomastia
  • menopause

Cushing’s syndrome

Cause: hypersecretion of adrenocortical hormones (sex, growth and salt regulation hormones) i.e. the opposite of Addison’s syndrome.

Effects: muscular atrophy and weakness, hypertension, moonshaped face, redistribution of body fat, sometimes mental illness, osteoporosis.

Increased thirst, increased output of urine, weight loss, and thin skin with impaired healing capacity are all signs of?

Diabetes Mellitus

  • TYPE 1
    Cause: Auto-immune disease results in pancreas being unable to produce insulin
    Effects: Symptoms include high blood glucose level, excessive thirst, high urine output, tiredness and weight loss. Cannot be cured but can be controlled by regular (2-4/day) insulin injections.
  • TYPE 2
    Cause: The body cells do not respond properly to insulin and the pancreas may not produce enough. Linked closely to obesity.
    Effects: Symptoms are as Type 1, but may not be as obvious and take longer to develop. Can be controlled by a healthy diet and physical activity. Tablets or insulin injections may also be required.

Diabetes Insipidus

Rare form of diabetes caused by a deficiency of the pituitary hormone vasopressin, which regulates kidney function.

  • hyperglycaemia
  • hypoglycaemia
  • diabetes
  • gynaecomastia

Endometriosis

A condition resulting from the appearance of endometrial tissue outside the womb and causing pelvic pain, especially associated with menstruation

Polycystic ovarian syndrome

Also known as Stein-Leventhal syndrome

Cause: not known.

Effects: irregular menstrual cycle, due to stimulation, multiple growth of follicular ovarian cysts and sometimes infertility, enlarged ovaries and often high levels of oestrogen; 50% of patients are obese and become hirsute; age range of sufferers is usually 16-30.

Pre-menstrual syndrome

Physical and emotional symptoms that occur in the one to two weeks before a woman’s period. Symptoms often vary between women and resolve around the start of bleeding. 

Stress

Stress is a threat to the body and the body responds to it like any other danger – the adrenal medulla releases adrenaline and noradrenaline to help us with the fight or flight response.

The physical manifestations of the arrival of adrenaline in the body are faster heart rate and breathing, sweating (hence sweaty palms when we are frightened or nervous), a glucose rush from the liver and heightened senses (like hearing and sight).

Prolonged stress may cause amenorrhoea in women and low production of sperm in men.

Revision

What is the purpose of the endocrine system?

  • contribute to the reproductive process
  • produce and secrete hormones to regulate body activities
  • maintain the body during times of stress
  • all of the above

Which of the following secretes the adrenocorticotrophic hormone (ACTH)?

  • anterior lobe of pituitary
  • posterior lobe of pituitary
  • adrenal medulla
  • adrenal cortex

Which endocrine gland responsible for secreting the thyroid-stimulating hormone (TSH)?

  • anterior lobe of pituitary
  • posterior lobe of pituitary
  • thyroid
  • parathyroids

Which of the following hormones stimulates the uterus during labour?

  • prolactin
  • oestrogen
  • progesterone
  • oxytocin

Hyposecretion of the thyroid gland in an adult can lead to which disorder?

  • Addison’s disease
  • Cretinism
  • Myxoedema
  • Cushing’s syndrome

Which hormone controls adrenal cortex?

  • noradrenaline
  • adrenaline
  • glucocorticoids
  • adrenocorticotrophin

Which of the following hormones increases blood circulation and heart rate?

  • noradrenaline
  • adrenaline
  • insulin
  • testosterone

Which hormone is responsible for increasing water reabsorption in the kidney tubules?

  • luteinising hormone (LH)
  • aldosterone
  • anti-diuretic hormone (ADH)
  • oxytocin

Where are the islets of Langerhans situated in?

  • liver
  • ovaries
  • kidneys
  • pancreas

The glucocorticoids are secreted by?

  • adrenal medulla
  • pancreas
  • adrenal cortex
  • pineal gland

Which hormone is a male sex hormone?

  • Oestrogen
  • Progesterone
  • Melatonin
  • Testosterone

Which hormone is involved with the development of the placenta?

  • prolactin
  • progesterone
  • follicle-stimulating hormone (FSH)
  • oestrogen

Hypersecretion of testosterone in women can lead to what condition?

  • amenorrhea
  • polycystic ovary syndrome
  • gynaecomastia
  • menopause

An increased metabolic rate, weight loss, sweating and restlessness are all symptoms of?

  • cushing’s syndrome
  • thyrotoxicosis
  • myxoedema
  • diabetes mellitus

Endocrine glands in the body have a feedback mechanism which is coordinated by which gland?

  • pineal
  • pituitary
  • adrenals
  • thyroid

The conversion of glucose to glycogen is controlled by which hormone?

  • oxytoxin
  • thyroxin
  • adrenalin
  • insulin

The hormone parathormone regulates the metabolism of?

  • carbohydrates
  • calcium
  • protein
  • fats

Which of the following is not secreted by the thyroid gland?

  • calcitonin
  • triodothyronine
  • thyroxine
  • melatonin