The Endocrine System

Question 1

1- what is homeostasis?

Answer 1

Maintenance of a dynamic equilibrium within the body
Regulating of variables so that internal states remain stable and relatively constant
Homeostatic mechanisms work to counteract internal changes to the body’s environment

Question 2

1- what does homeostasis failure lead to?

Answer 2

Disease

Question 3

1- name the four levels at which homeostasis mechanisms exist. Give examples

Answer 3

Cells (e.g. regulation of calcium concentration on intracellular level)
Tissues (e.g. apoptosis- balance between cell proliferation and cell death)
Organs (e.g. kidney regulates water and ion concentration in blood)
Organisms (e.g. constant body temp)

Question 4

1- what four things make up a control system?

Answer 4

1- stimulus
2- receptor- detects the stimuli (chemoreceptors, thermoreceptor, nocicereceotors, proprioceotors)
3- control centre- determines set point
4- effector- causes change (e.g. sweat glands, muscle, kidney)

Question 5

1- one example of a homeostasis control system is ‘body water homeostasis’, explain this

Answer 5

Total body water % is around 50% of total body mass in the average person
This needs to be maintained
Intercellular fluid needs to make up 2/3 of water
Extracellular fluid needs to make up 1/3 of water

Osmoreceptors and baroreceptors react accordingly to osmolality changes
Water-regulating hormone release
Kidneys react- to hormone stimulation and thirst activation

Question 6

2- define ‘hormone’

Answer 6

Chemicals signals
They are produced in endocrine glands or tissues
They travel in the bloodstream to cause an effect on other tissues

Question 7

2- what is the endocrine system?

Answer 7

A collection of glands located in different areas of the body that release hormones

Question 8

2- what other organs and tissues, apart from the endocrine glands, also release hormones?

Answer 8

Heart- ANP, BNP
Liver- IGF1
Stomach- ghrelin
Placenta- placental hormones
Adipose- leptin
Kidney- erythropoietin, renin

Question 9

2- identify as many if the major endocrine glands as you can

Answer 9

Hypothalamus
Pituitary gland
Pineal gland
Thyroid gland
Parathyroid gland
Thymus
Adrenal gland
Pancreas
Ovary
Testis

Question 10

2- name the four major mechanisms of communication used by hormones

Answer 10

Autocrine- hormone acts back on cell of origin
Paracrine- hormone carried short distance via interstitial fluid
Endocrine- hormone into bloodstream and carried to distant target cells
Neurocrine- hormone originates in neuron, travels down axon, released into blood, carried to distant target cells

Question 11

2- name and briefly explain the chemical classes of hormones

Answer 11

Peptide/polypeptide
-Largest group
-short chains of amino acids
-water soluble

Amines
-synthesised from aromatic amino acids
-adrenal medulla hormones- water soluble
-thyroid hormones- lipid soluble

Glycoproteins
-large protein molecules
-made of sub units
-carbohydrate side chain
-all water soluble

Steroids
-all derived from cholesterol
-tissues convert cholesterol into different hormones
All lipid soluble

Question 12

2- describe transportation of hormones

Answer 12

All hormones travel in blood
Blood travel is carried out in two different ways:
1- travel in blood in simple solution
2- most hormones bind to specific proteins (e,g, thyroid hormones bind to thyroxine-binding globulin protein)

Question 13

2- what are the three factors that determine hormone levels in blood?

Answer 13

Rate of production-
Synthesis and secretion

Rate of delivery-
Higher blood flow to specific organ means higher hormone delivery

Rate of degradation-
Metabolised and excreted

Question 14

2- what hormone does the hypothalamus release?

Answer 14

TRH
GHRH
CRH

Question 15

2- what hormone does the pituitary gland release?

Answer 15

LH
FSH
Prolactin
Oxytocin

Question 16

2- what hormone does the pineal gland release?

Answer 16

Melatonin

Question 17

2- what hormone does the thyroid gland release?

Answer 17

Thyroxine

Question 18

2- what hormone does the parathyroid gland release?

Answer 18

Parathyroid hormones

Question 19

2- what hormone does the thymus release?

Answer 19

Thymosin
Thymopoetin
Thymulin

Question 20

2- what hormone does the adrenal gland release?

Answer 20

Adrenaline

Question 21

2- what hormone does the pancreas release?

Answer 21

Insulin

Question 22

2- what hormone does the ovary release?

Answer 22

Oestrogen

Question 23

2- what hormone does the testis release?

Answer 23

Testosterone

Question 24

3- describe the concept of negative feedback

Answer 24

A way that the body responds in order to REVERSE the direction of change to maintain homeostasis
When conditions change from the set point, it works to return the conditions to this set point
Most common form of feedback

Question 25

3- describe the concept of positive feedback

Answer 25

Responds in a way to change/push the variable EVEN MORE IN DIRECTION OF CHANGE
Used when the stimulus is promoted, not unwanted
Used in times when we need rapid change
Quite rare

Question 26

3- give some examples of negative feedback

Answer 26

Body temperature regulation (sweating and shivering)
Blood sugar regulation (high- pancreas releases insulin, low- pancreas sleazes glucagon)
Metabolism (when hungry, metabolism slows down to conserve energy)

Question 27

3- give some examples of positive feedback

Answer 27

Childbirth (stretching continues using contractions to further promote labour)
Lactation (child feeding stimulates milk production to further promote breast feeding)

Question 28

4- what term describes the relationship between the hypothalamus and pituitary gland?

Answer 28

Hypothalamic pituitary axis

Question 29

4- outline what is meant by the hypothalamic pituitary axis

Answer 29

The hypothalamus and pituitary gland form a complex functional unit to serve as the major link between the ENDOCRINE and NERVOUS systems
Neuroendocrine mechanism
Mediates effects if stressors by regulating numerous physiological processes

Question 30

4- name some processes that are modulated by the hypothalamic pituitary axis

Answer 30

Lactation
Puberty
Body growth
Reproduction

Question 31

4- describe the function of the posterior pituitary gland

Answer 31

It is physically connected to the hypothalamus

Oxytocin and ADH secreted by hypothalamus, transported down nerve cell axons to the posterior pituitary, stored, released by posterior pituitary, into general blood circulation, acts on target cells and organs

Question 32

4- describe the function of the anterior pituitary gland

Answer 32

NEUROCRINE
Hormones are synthesised in hypothalamus,
Transported down axons,
Stored in median eminence,
Release into hypophyspheal system,
Target endocrine cells in anterior pituitary

ENDOCRINE
Anterior pituitary has endocrine cells,
They secrete different hormones into the bloodstream to act on distant targets

Question 33

4- what six type of hormones are produced by the hypothalamus? What do they have direct effect upon?

Answer 33

Six different tropic hormones are produced by the hypothalamus
Direct effect in the release of hormones from the anterior pituitary

Question 34

4- what two hormones are produced by the hypothalamus to have effect on the posterior pituitary gland and be released from here?

Answer 34

Oxytocin - milk and uterus contractions
Antidiuretic Hormone (ADH) - water volume regulation

Question 35

4- summarise the HPA in regards to its distinct neurocrine pathways

Answer 35

The hypothalamus has nerve cells which produce hormones, these hormones act via TWO neurocrine pathways

Posterior pituitary- direct effects on targets
Anterior pituitary- indirect effect on targets (hormones secreted into hypophyseal portal system, then they effect endocrine cells)