THE ENDOCRINE SYSTEM

Question 1

The endocrine system

Answer 1

The endocrine system is a collection of glans that produce and secrete hormones. Hormones are signal
molecules that are transported to target organs by the circulatory system.

Question 2

Types of hormones

Answer 2

• Steroid – lipid based (cholesterol). They are nonpolar and usually bind to nucleic receptors. They also have a relatively long effect on the body. They can easily enter cells, but they act quite slowly because it takes time to be produced.
• Protein – they are water soluble and usual bind to membrane receptor. They act via secondary messengers. They can’t enter cells easily, therefore causing for a cascade of secondary messengers.

Question 3

Feedback loops:

Answer 3

the endocrine system is regulated by feedback loops.
1. Negative feedback – the system acts to contradict a change (reduces the initial stimulus), like blood
sugar and insulin.
2. Positive feedback – the system acts to increase a change (amplifies the initial stimulus), like breast
feeding and oxytocin.

**This system mostly contains a list of organs and glens that secrete hormone into the blood.

Question 4

Hypothalamus

Answer 4

An area in the brain involved in all the major axes of the systems. It is a master regulator. Hormones that
are secreted form the hypothalamus are protein based, and are called releasing hormones.

Question 5

Axis – feedback loops between the hypothalamus:

Answer 5

1. Hypothalamic to Anterior Pituitary – thyroid axis.
2. Hypothalamic to Anterior Pituitary – adrenal axis.
3. Hypothalamic to Anterior Pituitary – gonadal axis.

Question 6

Axis pathway:

Answer 6

1. The hypothalamus sends a releasing hormones to the anterior pituitary.
2. The anterior pituitary secretes a stimulating hormone into the blood circulation.
3. The stimulating hormone can enter bind to its target organism (direct), or bind to another gland which causes to a release of another hormone (tropic).

Question 7

Releasing hormones of the hypothalamus:

Answer 7

• Corticotrophin releasing hormone (𝐶𝑅𝐻)
• Gonadotropin releasing hormone (𝐺𝑁𝑅𝐻)
• Thyrotropin releasing hormone (𝑇𝑅𝐻)
• Growth hormone releasing hormone (𝐺𝐻𝑅𝐻)
• Prolactin inhibitory factor (𝑃𝐼𝐹)

Question 8

Corticotrophin releasing hormone (𝐶𝑅𝐻)

Answer 8

Is a peptide hormone involved in the stress response. Its main function is the stimulation of the pituitary synthesis of 𝐴𝐶𝑇𝐻, as part of the axis.

Question 9

Gonadotropin releasing hormone (𝐺𝑁𝑅𝐻)

Answer 9

Responsible for the release of follicle-stimulating hormone (𝐹𝑆𝐻) and luteinizing hormone (𝐿𝐻) from the anterior pituitary. Part of the gonadal axis.

Question 10

Thyrotropin releasing hormone (𝑇𝑅𝐻)

Answer 10

Stimulates the release of thyroid-stimulating hormone or (𝑇𝑆𝐻). Part of the thyroid axis.

Question 11

Growth hormone releasing hormone (𝐺𝐻𝑅𝐻)

Answer 11

It is the releasing hormone of growth hormone (𝐺𝐻).

Question 12

Prolactin inhibitory factor (𝑃𝐼𝐹)

Answer 12

Promotes the growth of breast tissue and stimulates and sustains milk production in postpartum mammals.

Question 13

Pituitary Gland

Answer 13

A small gland located beneath the hypothalamus. It is divided into two lobes:

• Anterior lobe
• Posterior lobe

Question 14

Anterior lobe

Answer 14

receives releasing hormones from the hypothalamus and secretes stimulating hormones. In the hypothalamus there is a capillary bed, and in the anterior lobe of there is a second capillary bed (portal system).
- 𝐶𝑅𝐻 → 𝐴𝐶𝑇𝐻 (stimulates adrenal).
- 𝑃𝐼𝐹 → 𝑃𝑟𝑜𝑙𝑒𝑐𝑡𝑖𝑛 (inhibition stimulates breast milk production and secretion).
- 𝐺𝑁𝑅 → 𝐿𝐻 (stimulates ova/sperm production), 𝐹𝑆𝐻 (stimulates ovaries and testes).
- 𝑇𝑅𝐻 → 𝑇𝑆𝐻 (stimulates thyroid).
- 𝐺𝐻𝑅𝐻 → 𝐺𝐻 (stimulates done growth).
* Decrease 𝐺𝐻 levels in children is called
“dwarfism”.
* Increased 𝐺𝐻 levels in children is called
“gigantism”.
* Increased 𝐺𝐻 levels in adults is called
“acromegaly”.

Question 15

Posterior lobe

Answer 15

Does not receives hormones; 𝐴𝐷𝐻 and oxytocin are transported in axons, stored in the posterior pituitary and released into the blood.
- Antidiuretic (𝐴𝐷𝐻) – vasopressin that promotes retention of water in the kidneys when
the body is hydrated, results in high concentrated urine. This hormone is secreted due to
low blood pressure.

• Oxytocin – stimulates contraction of the uterus in childbirth, Brest milk ejection in females
  and mammy gland cells.

Question 16

Thyroid Gland

Answer 16

Located in front of the trachea. Regulated by the hypothalamus and pituitary (thyroid axis) Its main
hormones are:
- Thyroid hormones (𝑇3-triiodothyronine, 𝑇4-thyroxine) – these are regulators of metabolism and heart rate in the body. They are regulated by the thyroid axis (𝑇𝑅𝐻 → 𝑇𝑆𝐻 → 𝑇3, 𝑇4). These hormones inhibit 𝑇𝑅𝐻 and 𝑇𝑆𝐻 (negative feedback).
- Calcitonin –hormone that lowers blood calcium.

Question 17

Functions of Thyroid gland

Answer 17

1.Metabolism regulation – maintains normal blood pressure, heart rate, muscle tone and
reproductive functions.

2. Calcium blood level regulation.

Question 18

Hypothyroidism

Answer 18

• Low thyroid production = low metabolic rate
• Can be due to Hashimotos Disease
• Symptoms =weight gain, dry hair & skin, cold intolerance
• Complimants =Bradycardia

Question 19

Hyperthyroidism

Answer 19

• High thyroid production = overactive metabolisam
• Can be due to Graves Disease
• Symptoms =weight loss, moist hair & skin, heat intolerance
• Complimants =Tachycardia

Question 20

Parathyroid Gland

Answer 20

Four small glens located on the backside of the thyroid. This is an independent endocrine organ (not part of an axis). They produce a hormone called 𝑃𝑇𝐻.
𝑃𝑇𝐻 functions:
* Increases blood calcium levels by increasing reabsorption from the 𝐺𝐼𝑇
* Resorption of bones in order to resale calcium into the blood.
* Reabsorption of calcium from the kidneys.

Question 21

The release of PTH hormones in stimulated by..

Answer 21

By hypocalcaemia – low levels of calcium ions in the blood.
 𝑃𝑇𝐻 works alongside vitamin 𝐾 in calcium abosoption.
 Calcium is vital for muscle contraction and nervous transmission. Therefore, calcium levels have to be
regulated constantly.

Question 22

Pancreas

Answer 22

Located behind the stomach; it has an exocrine function as part of the 𝐺𝐼𝑇, and an endocrine function in the regulation of blood sugar levels.
** The pancreas is an independent endocrine organ

Question 23

Pancreas -Endocrine

Answer 23

Endocrine – secretes hormones inside of the pancreas like:
 Insulin – decrease glucose levels in the blood.
 glucagon – increase glucose levels in the blood

Question 24

Pancreas - Exocrine

Answer 24

Exocrine – secretes enzyme outside of the pancreas and into the duodenum like:
 Trypsin – breaks down proteins.
 Lipase – breaks down lipids.
 Amylase – breaks down carbohydrates.
 Ribonuclease and deoxyriboclease – break down nucleic acids.

Question 25

The Langerhans islets

Answer 25

The Langerhans islets, which are the part of the pancreas that contain its endocrine cells, contain two types of cells:
* 𝛼 cells – produce and secretes glucagon that elevates glucose levels in the blood, by causing the
liver to breakdown glycogen.
* 𝛽 cells – produce and secretes insulin that lowers glucose levels in the blood, by causing the cells
to absorb glucose.

Question 26

Pathology of the pancreas:

Answer 26

1. Diabetes mellitus type 1 – auto immune disease in which the pancreas doesn’t produce insulin, causing hyperglycemia.
2. Diabetes mellitus type 2 – disease in which insulin receptor are resistant to insulin, causing hyperglycemia. (Hyperglycemia can result in rapid heart rate).

Question 27

Adrenal Glands

Answer 27

Two glens located on top of the kidneys (one on each side). They are composed of outer layers (cortex) and
inner layers (medulla).
They are composed of outer layers (cortex) and inner layers (medulla).
Secrets the following hormons:
*Corticosteroids
*Catecholmines
*Cortisol

Question 28

Corticosteroids

Answer 28

produces in the cortex and regulates salt/water balance.

• Mineralocorticoids – increase glucose levels (steroid hormones). Also help regulate the homeostasis of sodium and potassium.
  * Aldosterone is a mineralocorticoid.
• Glucocorticoids – has sexual functions like (androgens – testosterone)

Question 29

Catecholmines

Answer 29

Produced in the medulla.
* Adrenaline (epinephrine) and noradrenaline (norepinephrine) help the body cope with stress by increasing the heart rate and blood pressure.

Question 30

Cortisol

Answer 30

Glucocorticoid hormone that response to stress.
It is responsible to:
* Immune system suppressor – inhibits pain, fever and illness.
* Increased glucose level in the blood.

Question 31

Gonads

Answer 31

The gonads are the testicles in the males and the ovaries in the females; both of them are the site of gamete production (sperm and oocytes). They are also the site of sex hormones production:
* Produced estrogen and progesterone in females.
* Produces testosterone in males.
Both are regulated by the gonad axis (𝐺𝑁𝑅 → 𝐿𝐻,
𝐹𝑆𝐻 → Estrogen, Progesterone and Testosterone).

**Testosterone, estrogen and progesterone are pressing in both males and females, but in different
amount.

Question 32

Gonads in females

Answer 32

𝐿𝐻 and 𝐹𝑆𝐻 cause the proliferation of follicles, and the production of estrogen and progesterone. These
hormones are responsible for secondary sexual features, and for the growth of the uterine lining, preparing it for receding a fetus.

Question 33

The role of progesterone:

Answer 33

1. Maintains pregnancy.

2. Promotes uterine lining.

Question 34

The role of estrogen:

Answer 34

1. Development of sexual female characteristics such as female productive organs and breast.
2. Menstrual cycle.
3. Conception.

Question 35

Gonads in males

Answer 35

𝐿𝐻 and 𝐹𝑆𝐻 support spermatogenesis, and the production of testosterone, which is responsible for
secondary sexual features.

Question 36

The role of testosterone:

Answer 36

1. Promotes facial hair growth.
2. Promotes boldness.
3. Promotes muscle growth.
4. Voice thickness.
5. Increase sexual drive.
6. Other development of male characteristics.

Question 37

Pineal Gland

Answer 37

A gland located deep within the brain. Secretes melatonin which helps regulate the wake-sleep cycle of the body.