Homeostasis And Endocrine System

Question 1

What is the role of the control centre in a control system?

Answer 1

In a control system, the control centre is responsible for setting a limit for which a variable must be maintained within, and then sending signals to effector organs to maintain this.

Question 2

What is the afferent pathway?

Answer 2

This is the pathway from stimulus to control centre.

Question 3

In a control system, what is the name of the pathway from control centre to effector organ?

Answer 3

Efferent.

Question 4

What is a circadian rhythm?

Answer 4

This is the 24 hour pattern of a control system as its parameters vary with time.

Question 5

What nucleus is the biological clock in the brain?

Answer 5

Superachiasmalic

Question 6

Name the five zeitgebers which help to keep our biological clock:

Answer 6

Light, temp, social interaction, eating, exercise.

Question 7

Name the hormone which maintains the biological clock.

Answer 7

Melatonin.

Question 8

What are the three main compartments of water in the body?

Answer 8

Extracellular fluid, intracellular fluid, blood plasma.

Question 9

Where is osmotic pressure of the blood measured?

Answer 9

It is measured by osmoreceptors in the hypothalamus.

Question 10

What is the difference between osmolality and osmolarity?

Answer 10

The first is the number of moles in a litre of solution and the second is the number of moles in a kilo of solution.

Question 11

What hormone is used to control blood osmolarity and where does this act?

Answer 11

ADH. This is secreted by the pituitary and acts on the kidneys to increase or decrease reabsorption.

Question 12

How does the body respond if blood osmolarity is high?

Answer 12

If blood osmolarity is high this is detected by osmoreceptors in the hypothalamus. This sends a signal to the pituitary to secrete ADH which leads to increased reabsorption of water in the kidneys. Osmoreceptors also stimulate thirst.

Question 13

Explain why someone may have very dilute urine.

Answer 13

If someone has low blood osmolarity, then osmoreceptors in the hypothalamus will send a signal to the pituitary to decrease ADH secretion. This means that less water will be reabsorbed in the kidney and so urine is dilute.

Question 14

What is the endocrine system?

Answer 14

This is a collection of glands throughout the body which secrete hormones into the blood stream to effect other tissues.

Question 15

What is it called when a hormone signal acts upon the cell it was secreted from?

Answer 15

Autocrine

Question 16

What does paracrine mean?

Answer 16

Paracrine is when a hormone signal acts on a cell after traveling a short distance through interstitial fluid.

Question 17

What is neurocrine?

Answer 17

This is where a signal is carried down an axon into the bloodstream

Question 18

How are nervous signals conveyed?

Answer 18

Via axons and synapses.

Question 19

How does the speed of endocrine and nervous signals vary?

Answer 19

Endocrine signals are slow and nervous signals are fast.

Question 20

What are the four different types of hormones?

Answer 20

Polypeptide, amino acid derivatives, steroids and glycoproteins.

Question 21

Give examples of glycoprotein hormones.

Answer 21

LH, FSH, TSH. These are large, water soluble protein molecules with carbohydrate side chains.

Question 22

What type of hormone are Insulin, Glugacon and Growth Hormone?

Answer 22

These are polypeptide hormones. They are water soluble and made from short amino acid chains.

Question 23

Are amino acid derivatives hormones soluble?

Answer 23

Some are. They are all derived from tyrosine. Adrenaline and noradrenaline from the adrenal medulla are both water soluble, whilst thyroid hormones are lipid soluble.

Question 24

What is a steroid hormone derived from?

Answer 24

Cholestrol.

Question 25

Explain what a biologically active hormone is?

Answer 25

This is a hormone which is in its free (unbound) form in the blood and not bound to a carrier protein.

Question 26

State three useful properties of carrier proteins.

Answer 26

They increase hormone solubility in plasma, they increase half life and they allow a hormone reserve to be maintained.

Question 27

State what factors can affect hormone concentration in the blood.

Answer 27

Rate of hormone synthesis/secretion, rate of delivery and rate of degradation.

Question 28

Name the two water soluble hormone cell surface receptors.

Answer 28

G protein coupled receptor, tyrosine kinase.

Question 29

Explain the action at a G protein coupled receptor.

Answer 29

The alpha subunit dissociates which leads to activation of the effector protein and a second messenger leads to protein kinase activation. This phosphorylates the target protein and activates a cellular response.

Question 30

How does tyrosine kinase cause a cellular response?

Answer 30

Dimerisation followed by auto phosphorylation of specific tyrosines. Adapter proteins and the signalling complex are recruited leading to protein kinase activation. Phosphorylation of target protein activates cellular response.

Question 31

Where can lipid soluble hormones act?

Answer 31

Lipid soluble hormones can cross the plasma membrane so these act within the cell, either in the cytoplasm or in the nucleus.

Question 32

What happens when a lipid soluble hormone binds to a cytoplasmic receptor?

Answer 32

This forms a complex which enters the nucleus and binds to DNA.

Question 33

What do lipid soluble hormones bind to when they enter the nucleus?

Answer 33

They bind to pre bound receptor on DNA. This relieves the repression in transcription. Receptors are generally found in promoter regions for different genes.

Question 34

Which part of the pituitary gland is connected to the hypothalamus?

Answer 34

Posterior.

Question 35

What hormones are produced in the hypothalamus but then pass down neurones to the posterior pituitary?

Answer 35

Oxytocin (milk let down and uterus contractions)

Antidiuretic hormone. ADH responsible for osmotic balance.

Question 36

What is meant by the neurocrine function of the posterior pituitary?

Answer 36

Hormones synthesised in the hypothalamus pass down axons to the posterior pituitary where they are stored and then released to act on target tissues.

Question 37

How are cells of the anterior pituitary stimulated?

Answer 37

Neurocrine signals from the hypothalamus.

Question 38

What is the hypophyseal portal system?

Answer 38

This is a series of blood vessels which hormones produced in the hypothalamus pass through to stimulate the anterior pituitary.

Question 39

What type of hormone secretion occurs in the anterior pituitary?

Answer 39

Endocrine cells secrete hormones into the blood stream, but also Autocrine and paracrine secretion occurs which affects neighbouring cells.

Question 40

What is a tropic hormone?

Answer 40

These are produced in the hypothalamus and act on the anterior pituitary.

Question 41

What is the name of the hormone released from the hypothalamus to stimulate release of TSH from the pituitary?

Answer 41

TRH thyrotropin releasing hormone.

Question 42

What does Corticotropin releasing hormone (CRH) leads to release of from the pituitary? Where does this act?

Answer 42

ACTH which leads to secretion of cortisol from the adrenal gland.

Question 43

What is the name of the hormone which controls lactation of the mammary glands?

Answer 43

Prolactin, secreted by the pituitary. This is activated by PRH from hypothalamus and inhibited by PRIH.

Question 44

What two hormones secreted by the hypothalamus act on the pituitary to control growth hormone release?

Answer 44

GHRH, GHIH.

Question 45

What is the function of GnRH (Gonadotropin releasing hormone)?

Answer 45

This is released from the hypothalamus and acts on the pituitary to control release of FSH and LH.

Question 46

What are the two possible forms of communication in a control system?

Answer 46

Nervous or Endocrine.