Endocrine System

Question 1

What are the actions of the endocrine system mediated by?

Answer 1

Hormones

Question 2

What regulatory systems does the endocrine system control?

Answer 2

• Regulation of cellular metabolism
• Maintenance of homeostasis
• Sexual development and reproduction
• Growth and development from childhood to adult
• Modulating long term behaviour (mood, sleep)

Question 3

What are the three classes of hormones, based on their structure?

Answer 3

Proteins - chains of amino acids (usually injected)
Steroids - modified cholesterol fat structure (oral administration)
Amino acid derivatives - start with amino acids which have turned into signals; thyroid hormone, catecholamines

Question 4

What do glands develop from?

Answer 4

Epithelial cells

Question 5

What are the three (+1) types of glands/secretion?

Describe them both

Answer 5

Exocrine

• when you are secreting something to the outside of your body
• the epithelial cells are arranged as ducts/tubes
• the ducts lead to the lumen of the organ (e.g.: sweat gland open onto the skin, pancreatic duct opens into the duodenum)

Endocrine

• the epithelial cells are arranges as clumps of cells
• these release their hormones between the cell
• the hormones then diffuse into the bloodstream

Paracrine

• similar to endocrine, but when hormone released, it does not diffuse away; instead, it act locally
• e.g.: neurocells diffuse from synapse and bind to the dendrites of another cell

Autocrine
- hormone released comes back to join the receptor on the cell, stopping it from producing more of the same hormone

Question 6

List all the main glands of the endocrine system

Answer 6

Pineal gland

• sleep patterns
• releases melatonin and seratonin

Hypothalamus

• neuroendocrine junction
• regulates endocrine systems

Pituitary gland
- regulates hormones

Thymus
- matures T-cells and lymphocytes

Pancreas
- both endocrine and exocrine

Thyroid gland
- controls metabolic pathways

Adrenal gland
- secretes adrenaline and steroids

Parathyroid glands

Ovary and Testis

Question 7

Describe how the hormones in the blood work

Answer 7

Low concentration;

Steroid and thyroid hormones are transported by specific carrier/binding proteins because they are hydrophobic and insoluble in blood

• this improves their solubility
• increases half life since you don’t filter out the proteins
• provides a reserve in the blood

Question 8

When are hormones biologically active?

Answer 8

When they are free

Protein-bound hormones are inactive

Question 9

Where are the protein receptors for hormones found?

Answer 9

Cell-membrane receptors: peptides, glycoproteins, catecholamines (adrenalin, dopamine, noradrenalin)

Intracellular receptors in the nucleus: steroid and thryoid hormones
The hormones can diffuse through the nuclear membrane because they like lipids - they will bind onto the receptor of the nucleus and alter the transcription of genes

Question 10

Where does the anterior pituitary develops from?

Answer 10

The epithelium of the mouth

Question 11

Where does the posterior pituitary develops from?

Answer 11

Downgrowth of the hypothalamus; consist of nerve fibres

Question 12

Function of the neuronal-endocrine junction

Answer 12

Controls neurosecretory cells in the hypothalamus, controlling the secretions from the anterior and posterior pituitary

Ultimately, it combines the nervous system and endocrine system

Question 13

What is the Endocrine Axes/Cascade?

Answer 13

The hormones of one endocrine gland targets another endocrine gland - therefore, production of one type of hormone influences the production of another type of hormone
e.g.: the hypothalamus secretes hormones that control the secretion and releas of pituitary hormones;
pituitary hormones then control the production of thyroid hormones, gonads etc

Question 14

What is the function of the Hypothalamus?

Answer 14

• Sends neural hormones to the anterior pituitary and controls the release of its hormones via releasing hormones
• Secretes hormone that are stored and released by the posterior pituitary gland (eg oxytocin and ADH - neuralsecretory hormones - made in Hypothalamus, transferred to p.p.g.)

Question 15

Structure and function of the anterior pituitary gland

Answer 15

Also called ADENOHYPOPHYSIS

It consists of clumps of epithelial cells, secreting 6 hormones

Question 16

What are the 6 hormones the anterior pituitary gland secretes?

Answer 16

1. Growth Hormone (GH)
2. Thyroid stimulating hormone (TSH)
3. Adrenocorticotropic hormone (ACTH)
4. Follicle stimulating hormons (FSH)
5. Luteinising hormone (LH)
6. Prolactin (milk production)

Question 17

Which of the anterior pituitary gland’s 6 hormones regulate other endocrine hormones?

Answer 17

TSH, ACTH, FSH, LH

Question 18

What hormones are controlled by hypothalamic secretory factors, and which are inhibited by them?

Answer 18

Controlled: GH, TSH, ACTH, FSH, LH

Inhibited: Prolactin

Question 19

Structure and function of the posterior pituitary gland

Answer 19

Also called NEUROHYPOPHYSIS
Consists of neural tissue - extensions of axons from the hypothalamus
Stores hormones which are secreted by the neurosecretory cells in the hypothalamus, and transported by the neuronal axons
Two hormones released are:
- ADH (vasopressin) - prevents you losing water from the kidneys; causes constriction of smooth muscle around arteries, increasing BP
- Oxytocin - constriction of uterus, helps during birth giving; constricts alveoli of lungs

Question 20

What is the concept of negative feedback?

Answer 20

The final product of a cascade acts to inhibit a hormone higher up in the cascade (e.g.: negative feedback inhibition of GnRH by gonadal steroid)

Question 21

What is the name of the tumour found in the pituitary gland, and what does it result in?

Answer 21

Pituitary Adenoma - causes over-secretion of hormones, compressing on and killing the pituitary gland

Question 22

What is the condition of having excess growth hormone referred to as?

Answer 22

Acromegaly

Question 23

What is the position of the thyroid gland?

Answer 23

Anterior to the trachea

Question 24

What did the thyroid gland develop from?

Answer 24

It is a downgrowth of the epithelium of the tongue

Question 25

What is the foramen caecum?

Answer 25

Pit left behind by the thyroid gland, at the back of the tongue

Question 26

Describe the microscopic structure of thyroid

Answer 26

The thyroid epithelial/follicular cells are arranged as thyroid follicles - these are filled with colloid/thyroglobulin

Question 27

What hormones do follicular cells secrete? | Where are they stored?

Answer 27

Tri-iodothyronine (T3) and Thyroxine (T4) - requires iodine | These are stored in colloid/thyroglobulin

Question 28

What is the function of Thyroxine?

Answer 28

Regulates: - energy use - rate of metabolism - protein production - growth and development - regulates sensitivity of cells to other hormones

Question 29

Function of Parafollicular (aka C) cells

Answer 29

They produce Calcitonin which regulates Calcium homeostasis - stimulates osteoblasts

Question 30

How many parathyroid glands do we have? | What is their location?

Answer 30

Two pairs, aka 4 | Posterior aspect of the thyroid

Question 31

What hormones do parathyroid glands secrete and what is their function?

Answer 31

Parathyroid hormones - regulates calcium homeostasis - stimulates osteoclasts to breakdown bone matrix and increase blood calcium levels

Question 32

Describe the structure of the adrenal glands?

Answer 32

Cortex - produces steroid hormones; has three layers of epithelial cells: - Zona glomerulosa - mineralocorticoids e.g.: aldosterone (- conserve sodium, increase water retention) - Zona fasciculata - glucocorticoids e.g.: cortisol (- increase blood sugar) - Zona reticularis - sex steroids e.g.: androgens (- activity of sex organs) Medulla - forms from neural crest cells/NEUROECTODERM Contains chromaffin cells that produce cathecolamines: - Epinephrine - Norepinephrine - Dopamine Has a direct connection with the SNS (controlling the fight or flight response)

Question 33

What is Cushing's syndrome?

Answer 33

A collection of symptoms that develop as the result of very high levels of a hormone called CORTISOL in the body

Question 34

Describe the endocrine and exocrine nature of the pancreas

Answer 34

Exocrine - pancreatic acini cell - synthesises, stores and secrete digestive enzymes; e.g.: amylase, lipase Disorder: pancreatitis ``` Endocrine - islets of Langerhans - produce hormones like: - Alpha cells - glucagon - Beta cells - insulin Disorder: diabetes mellitus ```

Question 35

What hormone does the GI tract produce?

Answer 35

Gastrin

Question 36

What hormone do the kidneys produce?

Answer 36

Renin

Question 37

What hormones do the gonads produce?

Answer 37

Testosterone or Oestrogen