lecture 25 - homeostasis & hormones

Question 1

What are the 3 steps of the homeostatic mechanism?

Answer 1

Receptors detect change, control centre compares to set point and signals to effectors, effectors (organs/tissues) respond with localised or wide spread effects.

Question 2

Why might a value for a characteristic be abnormal for an individual, even though it is inside the normal population range?

Answer 2

The population reference range is wider than the normal fluctuations found within an individual, because it contains the extremes of individuals within the population.

Question 3

What are the differences between the neural and endocrine control systems?

Answer 3

Neural: fast, short lasting and highly targeted, Endocrine: slow, long lasting, targeted via specific receptors.

Question 4

What are the major endocrine organs (studied in HUBS191)?

Answer 4

Hypothalamus, pituitary gland, adrenal gland, thyroid gland, pancreas, parathyroid glands.

Question 5

What are some key physiological variables held in homeostasis by hormones?

Answer 5

Blood sugar concentration, growth & repair, basal metabolic rate, blood calcium concentration

Question 6

What are hormone receptors?

Answer 6

Proteins found inside or in the plasma membrane of target cells that can bind to specific hormones.

Question 7

What are water-soluble hormones typically made up of?

Answer 7

Peptides or catecholamines (e.g. adrenaline and noradrenaline)

Question 8

What proportion of water-soluble hormones are peptides?

Answer 8

75%

Question 9

What kind of receptors do water soluble hormones bind to?

Answer 9

Receptors on the surface of cells (within the cell membrane)

Question 10

How are water-soluble hormones transported around the body?

Answer 10

Via the bloodstream, where they are dissolved into the blood.

Question 11

Are water-soluble hormones stored?

Answer 11

Yes - stored until required, then released by exocytosis.

Question 12

What is the process of cellular response to water-soluble hormone receptor activation?

Answer 12

Hormone binds to cell surface receptor, G protein is activated and activates or deactivates second messenger pathways that result in a cellular response.

Question 13

What levels are controlled by water soluble hormones in a cell?

Answer 13

cAMP and Ca2+

Question 14

What are key examples of lipid-soluble hormones?

Answer 14

Steroids, thyroid hormones

Question 15

What are lipid soluble steroid hormones synthesised from?

Answer 15

Made when required (generally not stored) from cholesterol.

Question 16

How do lipid-soluble hormones travel around the body?

Answer 16

In the bloodstream, bound to carrier proteins as they are insoluble in water.

Question 17

Where are lipid-soluble hormone receptors found?

Answer 17

In the cytoplasm or nucleus of target cells.

Question 18

How do lipid-soluble hormones enter target cells?

Answer 18

They arrive at the cell, dissociate from their carrier protein and diffuse across the phospholipid cell membrane.

Question 19

What do lipid-soluble hormones receptor complexes act as?

Answer 19

Transcription factors, that bind to DNA to activate target genes.

Question 20

When target genes are activated by lipid-soluble hormone receptor complexes, what is produced?

Answer 20

transcription makes mRNA that can then be translated for protein synthesis.

Question 21

How do lipid-soluble hormones lead to cellular responses?

Answer 21

The receptors facilitate gene activation, transcription and mRNA production, and then translation to produce proteins that have cellular effects.

Question 22

Are the cellular effects of lipid-soluble hormones rapid or slow?

Answer 22

Slow - can take hours of days to synthesise proteins within the cell.

Question 23

What is the most common mechanism for maintaining hormone levels in the body?

Answer 23

Negative feedback

Question 24

How does negative feedback maintain hormone levels?

Answer 24

When the stimulus is removed and the change has been restored to normal, a feedback loop inhibits further release of the hormone.

Question 25

What is positive feedback in terms of hormone levels?

Answer 25

Amplification of a change, by releasing more and more hormones until the desired outcome is released, rather than trying to revert the body to the set point.

Question 26

What are blood hormone concentrations dependent on ?

Answer 26

Rate of hormone secretion, and rate of removal from the blood.

Question 27

How is removal of hormones from the blood regulated?

Answer 27

By enzymes or target cells

Question 28

What is the pancreas?

Answer 28

An organ, posterior to the stomach, which acts as an endocrine and exocrine gland

Question 29

In what way does the pancreas act as an exocrine gland?

Answer 29

Secretes digestive enzymes into the digestive tract, which is technically considered to be outside the body

Question 30

What part of the pancreas acts as an endocrine gland?

Answer 30

The pancreatic islets

Question 31

What proportion of the mass of the pancreas are taken up by pancreatic islets?

Answer 31

approx. 1%

Question 32

What are the hormones secreted by the pancreas?

Answer 32

Insulin and glucagon

Question 33

What cells secrete insulin?

Answer 33

Beta cells

Question 34

What cells secrete glucagon?

Answer 34

Alpha cells

Question 35

What is the role of the pancreatic hormones?

Answer 35

To regulate blood sugar levels

Question 36

What are the 2 metabolic states that the body is in, in terms of blood sugar concentration?

Answer 36

Fed and fasting states

Question 37

What is the fed state?

Answer 37

There is cellular uptake of nutrients & anabolic metabolism.

Question 38

What is anabolism?

Answer 38

Growth and building - synthesis of glycogen, protein and fat. Storing of energy

Question 39

What is the fasting state?

Answer 39

Mobilisation of nutrients and catabolic metabolism

Question 40

What is catabolism?

Answer 40

When the body breaks down food for energy - breakdown of glycogen, protein and fat

Question 41

What are the key target cells of insulin?

Answer 41

Muscle and adipose tissue cells, liver cells

Question 42

What stimulus causes the secretion of insulin?

Answer 42

Increasing blood glucose levels.

Question 43

What is the effect of insulin on liver cells?

Answer 43

Stimulates the liver to convert and store glucose as glycogen (glycogenesis). Fat is also synthesised.

Question 44

What is the effect of insulin on muscle and adipose tissue cells?

Answer 44

Increased glucose uptake/breakdown/cell respiration - fat is synthesised in adipose tissue. Increased amino acid uptake. Glycogen and protein synthesis in muscle.

Question 45

What is the primary function of glucagon?

Answer 45

To increase fuel release in response to low blood glucose concentration.

Question 46

What occurs in the liver in response to the release of glucagon?

Answer 46

Increased breakdown of glycogen to glucose (glycogenolysis), increased glucose synthesis (glucogenesis), increased ketone synthesis, increased breakdown of fat

Question 47

What is glycogenolysis?

Answer 47

The breakdown of glycogen into glucose by the liver

Question 48

What is gluconeogenesis?

Answer 48

The synthesis of glucose from non-carbohydrate sources

Question 49

What types of hormones are modified amino acids?

Answer 49

Catecholamines and thyroid hormones

Question 50

What types of hormones are able to be stored ready for release?

Answer 50

All water soluble (catecholamines and peptides) and modified amino acids (which includes catecholamines and thyroid hormones)

Question 51

What are steroid hormones?

Answer 51

Modified forms of cholesterol

Question 52

What is the difference between catecholamines in the nervous and endocrine system?

Answer 52

Catecholamines (e.g. epinephrine and norepinephrine) are used as synaptic neurotransmitters in the nervous system, but are transported via blood in the endocrine system. Some target cells can receive catecholamine signals via both systems.

Question 53

What tissues does glucagon act on?

Answer 53

Primarily the liver, but also adipose tissue.

Question 54

What is the overall effect of insulin on target cells throughout the body?

Answer 54

Increases their uptake of glucose.