2: Endocrine system and receptors

Question 1

The endocrine system consists of ___.

Answer 1

glands

Question 2

Do endocrine glands have ducts?

Answer 2

No - release hormones into bloodstream

Question 3

Parietal cells and G cells in the stomach have ___ so they are examples of exocrine cells.

Answer 3

ducts

Question 4

How do hormones have specific actions i.e why don’t they react with all receptors on all cells?

Answer 4

Hormones have distinct structures

Receptors are specific to each hormone

Receptors are found in different distributions on different cells

Question 5

The tissues or cells on which a hormone acts are called ___ tissues / cells.

Answer 5

target tissues / cells

Question 6

What are the three categories of hormone?

Answer 6

Modified amino acids (hormones derived from tyrosine and tyramine)

Steroid hormones (derived from cholesterol)

Peptide hormones (from proteins)

Question 7

What are some examples of modified amino acid hormones?

Answer 7

Adrenaline

Thyroid hormones

Question 8

What are some examples of steroid hormones?

Answer 8

Cortisol

Progesterone

Testosterone

Question 9

What are some examples of peptide hormones?

Answer 9

Insulin

ACTH

ADH

Oxytocin

Question 10

What types of hormone are derived from:

a) tyrosine and tyramine
b) cholesterol
c) protein?

Answer 10

a) Modified amino acid hormones

b) Steroid hormones

c) Peptide hormones

Question 11

What type of hormones are:

a) ADH
b) thyroid hormones
c) testosterone?

Answer 11

a) Peptide

b) Modified amino acid

c) Steroid

Question 12

What is autocrine signalling?

Answer 12

Hormone causes response in the same cell

Question 13

What is paracrine signalling?

Answer 13

Hormone exits cell and causes response in adjacent cells

Question 14

What is endocrine signalling?

Answer 14

Hormone exits cell, enters bloodstream and causes response in distant cells

Question 15

In what types of signalling do hormones:

a) enter the bloodstream and cause a response in distant cells
b) cause a response in the same cell it was made in
c) cause a response in adjacent cells?

Answer 15

a) Endocrine

b) Autocrine

c) Paracrine

Question 16

Hormones act in (very low / very high) concentrations to cause a response in target cells.

Answer 16

very low concentrations

measured in mmol/L

Question 17

Specific hormones affect (one / more than one) target cell.

Target cells are regulated by (only one / more than one) hormone.

Answer 17

Specific hormones affect several different cell types

Target cells are regulated by loads of different hormones

Question 18

Binding of a ligand to a receptor to cause a cellular response (i.e carrying a signal through the cell membrane) is called ___ ___.

Answer 18

signal transduction

Question 19

Seeing as hormones are present in tiny concentrations, what process often occurs when hormones bind to receptors?

Answer 19

Amplification

to increase the number of responses to a single hormone molecule

Question 20

Where are hormones deactivated?

Answer 20

Where they bound to the receptor

OR

The liver

Question 21

Several different hormones can work together to regulate a physiological factor like blood glucose concentration.

What is this process called?

Answer 21

Complementary / cooperative action

Question 22

What are two processes regulated by complementary action of hormones?

Answer 22

Increase in blood glucose conc. during exercise - adrenaline, cortisol and glucagon working together

Normal growth - growth hormone, insulin, IGF-1 and sex steroids working together

Question 23

What is antagonistic action of hormones?

Answer 23

Hormones have the opposite effect and work against each other

e.g insulin and glucagon - insulin decreases blood glucose conc., glucagon increases it

Question 24

Amino acid based proteins like adrenaline are more commonly known as ___ hormones.

Answer 24

amine hormones

Question 25

Amine hormones are synthesised (within / outwith) cells, stored in ___ and then released in response to activation of a receptor by ligand.

Answer 25

**synthesised within cells** stored in **vesicles**

Question 26

By what process are vesicles containing amines released from a cell?

Answer 26

**Exocytosis**

Question 27

What ion is required for exocytosis of vesicles from cells?

Answer 27

**Ca**²⁺

Question 28

Amines are **(hydrophilic / hydrophobic)**, which means they can flow freely in the blood.

Answer 28

**hydrophilic** (remember that thyroid hormones are hydrophobic and therefore lumped in with steroids)

Question 29

Why are amine hormones always ready to be secreted from cells?

Answer 29

**Cells have big reserves of them**

Question 30

Peptide hormones are cleaved off longer ___ proteins before they are stored in vesicles and released by exocytosis.

Answer 30

**precursor proteins**

Question 31

Are peptide hormones hydrophilic or hydrophobic?

Answer 31

**Hydrophilic** so they freely float in the blood as well

Question 32

From which precursor molecule are all steroid hormones produced?

Answer 32

**Cholesterol**

Question 33

What is the intermediate molecule between cholesterol and **all** steroid hormones?

Answer 33

**Pregnenolone**

Question 34

Are steroid hormones stored in vesicles?

Answer 34

**No** Secreted as soon as they are synthesised from cholesterol \> pregnenolone

Question 35

Steroids are **(hydrophilic / hydrophobic)**. How are they transported in the blood?

Answer 35

**hydrophobic** transported by carrier proteins

Question 36

The receptors responsible for activating steroid synthesis are found **(within / on the membrane)** of cells.

Answer 36

**within** Amine and peptide synthesis receptors are found on the cell membrane

Question 37

Steroid hormones are ___ when bound to carrier proteins and ___ when freely floating around. ## Footnote **(active / inactive)**

Answer 37

**inactive when bound** **active when free**

Question 38

Which proteins are **hydrophobic** and require carrier proteins to transport them in the bloodstream?

Answer 38

**Steroid hormones** Thyroid hormones (like thyroxine and triiodothyronine) - the other amine proteins are all hydrophilic and flow freely

Question 39

\_\_\_ proteins increase the amount of **hydrophobic** protein which can be transported in the blood.

Answer 39

**Carrier proteins**

Question 40

Carrier proteins also extend the ___ \_\_\_ of hormones i.e their duration of action.

Answer 40

**half-life**

Question 41

Which classes of hormone are a) soluble b) insouble in the blood?

Answer 41

**a) Amines, peptides** **b) Steroids** and thyroid hormones (which are amines)

Question 42

Name three **specific** carrier proteins for steroids and thyroid hormones.

Answer 42

**Cortisol-binding globulin (CBG)** **Thyroxine-binding globulin (TBG)** **Sex steroid-binding globulin (SSBG)**

Question 43

Name two **general** carrier proteins for steroids and thyroid hormones.

Answer 43

**Albumin** **Transthyretin**

Question 44

Carrier proteins act as a **reservoir** for hormones. What does this mean?

Answer 44

There is both **bound** and **free** hormone in the blood (existing in equilibrium with each other) When free hormone diffuses out of the bloodstream into cells, bound hormone is freed to replace it, **keeping blood hormone concentration the same**

Question 45

Carrier proteins act as a **buffer** for hormones. What does this mean?

Answer 45

If a lot of hormone is suddenly secreted, free carrier proteins are available to bind them ("mopping up the excess") So free blood hormone concentration doesn't suddenly rise

Question 46

The secretion of many hormones is controlled by what feedback mechanism?

Answer 46

**Negative feedback** e.g the presence of cortisol inhibits its own secretion by inhibiting glands all the way up the chain

Question 47

Negative feedback loops can be **short** or **long**. What does this mean?

Answer 47

**Short** - negative feedback to a gland "one up the chain" - see diagram **Long** - negative feedback to glands "at the top of the chain"

Question 48

The rate of ___ of a hormone is the primary determinant of its plasma concentration.

Answer 48

**rate of secretion**

Question 49

Apart from negative feedback via the endocrine system, what other body system influences levels of hormone secretion by endocrine glands?

Answer 49

**Nervous system** e.g **stress** increases secretion of hormones by the hypothalamus, leading to cortisol secretion

Question 50

The secretion of some hormones changes througout the day. What is this called?

Answer 50

**Diurnal variation**

Question 51

A hormone whose secretion is affected by diurnal variation is **cortisol**. When is the secretion of cortisol at its highest and lowest? So what is likely responsible for the diurnal variation?

Answer 51

**Highest during the day** (late morning) **Lowest at night** So **sunlight** is the likely factor

Question 52

Where is most hormone a) metabolised b) excreted?

Answer 52

**Liver** **Kidneys**

Question 53

The plasma concentration of hormone depends on the rates of ___ and \_\_\_.

Answer 53

**secretion** **elimination**

Question 54

The plasma concentration of hormone is equal to the rate of **\_\_\_** - the rate of \_\_\_.

Answer 54

**Rate of secretion - rate of elimination**

Question 55

Different hormones have **(the same / different)** rates of secretion and elimination.

Answer 55

**different rates**

Question 56

In which two places are hormone receptors found?

Answer 56

**On the cell membrane** **Within the cell** (either in the cytoplasm or nucleus)

Question 57

What specific types of hormone receptor are found on the cell membrane?

Answer 57

**G-protein coupled receptors** **Receptors associated with tyrosine kinase**

Question 58

Ligands for cell surface hormone receptors are **(hydrophilic / hydrophobic)**.

Answer 58

**hydrophilic**

Question 59

Ligands for intracellular hormone receptors are **(hydrophilic / hydrophobic)**.

Answer 59

**hydrophobic** remember they're associated with steroids which are fatty and hydrophobic

Question 60

revise g protein signalling

Question 61

receptor tyrosine kinases when insulin binds, beta subunits **autophosphorylate** each other (why they're called tyrosine kinases) THEN tyrosine phosphorylation of a protein which produces the cellular effect

Question 62

revise nuclear receptors (resp - asthma)