RAT #2

Question 1

Define receptor and ligand

Answer 1

Receptors are proteins that are embedded in the plasma membrane or inside the cell (cytosol or nucleus)
A ligand is a signal molecule that binds to the receptors on/in the cell which creates a change in the cells activity.

Changes may include:

• activation of an enzyme
• Opening/closing of an ion channel
• Changing gene expression

Question 2

Autocrine signal & example

Answer 2

Local communication
Chemical signal that acts on the cell that created it
“auto” = self
Ex: Growth - it may be noted that some hypothesis’ about cancer growth is due to an autocrine signal that won’t stop

Question 3

Explain how one signal can cause different effects in a target cell

Answer 3

The signal molecule (ligand) binds to a protein receptor. Then ligand-receptor binding activates the receptor. The receptor then initiates one or more intracellular molecules. Finally the last signal molecule creates a response by changing existing proteins or beginning the synthesis of new proteins.

Question 4

Define antagonistic control and explain how heart rate is controlled this way

Answer 4

When chemical signals have opposing effects they are said to be antagonistic. Ex: insulin decreases glucose in the blood but glucagon increase glucose in the blood. (therefore they are antagonistic)
Chemical signals from the sympathetic nervous system (EPI/NE) increase heart rate by chemical signals from the parasympathetic nervous system (Ach) decrease heart rate.

Question 5

Explain the relationship between the hypothalamus, the anterior pituitary and the posterior pituitary

Answer 5

x

Question 6

Explain what is meant by a tripartite axis for hormone control and release

Answer 6

Example - the stress axis. Tripartite means that the signaling pathway involved 3 different endocrine glands: the hypothalamus, the anterior pituitary gland, and the adrenal corte

Question 7

Paracrine signal & example

Answer 7

Signal binds with receptor on nearby cell - passes only through ISF
“para” - beside
Example: histamine, or neurotransmitters (Ach) at a synapse

Question 8

Endocrine signal & example

Answer 8

Hormones - chemicals that are secreted into the blood and distributed all over the body. However, only cells with the right receptors will respond to the signal.
ex: insulin, testosterone, estrogen

Question 9

Steroid hormone

Answer 9

-Fat soluble
-Need a protein carrier (in the blood) because they aren’t water soluble (steroid-binding globulins)
-Receptor located in cytosol or nucleus
-Steroids enter the cell by simple diffusion
-Steroids activate gene expression
-Once inside the cell, if not already in the nucleus the signal moves there and then binds with DNA to begin transcription which then ends in protein synthesis
-Response tends to be slow and enduring
Examples - estradiol, testosterone, progesterone, cortisol

Question 10

Non-steroid hormones

Answer 10

-Water soluble
-Travel dissolved in blood; may need a carrier protein to protect from enzymes
-Receptors located on plasma membrane; hormone does NOT enter the cell
-Transduction mechanisms:
1. Changes in ion permeability
2. Change in concentration of 2nd messengers inside the cell
3. Change in the amount of enzyme activity inside a cell
-Response tends to be fast (brief and enduring)
Examples - epinephrine, insulin, antidiuretic, oxytocin

Question 11

G-couped receptors

Answer 11

Large membrane spanning proteins. The types of ligands that bind to G-protein coupled receptors include: hormones, growth factors, olfactory molecules, visual pigments, and neurotransmitters.

When G-proteins are activated they:
-open an ion channel in the membrane or alter enzyme activity on the cytoplasmic side of the membrane

Question 12

Enzyme - coupled receptors

Answer 12

Ligand binding to a receptor-enzyme complex activates an intracellular enzyme.

Question 13

Ion-channel coupled receptors

Answer 13

Ligand binding open or closes the channel and alters the ion flow across the membrane.

Question 14

Agonist

Answer 14

A competing ligand that binds to a receptor and elicits a response.

Question 15

Antagonist

Answer 15

Competing ligands that bind to a receptor and DONT elicit a response. (blocking the primary ligand).

Question 16

Examples and chemical nature of steroids

Answer 16

• Lipophilic (hydrophobic) “water hating, lipid loving)
• derived from cholesterol
• Glucocorticoids (cortisol)
• Testosterone
• Progesterone
• Estradiol

Question 17

Examples and chemical nature of non steroids

Answer 17

• Lipophobic “water loving, lipid hating”

- Proteins - insulin, oxytocin, ADH (antidiuretic hormone)

Question 18

Steroid transport in the blood

Answer 18

Steroids are not soluble in the blood, which means that they have to be transported via a protein created by the liver

Question 19

Steroid transport in the blood

Answer 19

Steroids are not soluble in the blood, which means that they have to be transported via a carrier protein created by the liver

Question 20

Non steroid transport

Answer 20

These signals dissolve in the plasma of the blood for transport. However some require a carrier protein in order to be protected from enzymatic degradation

Question 21

Location of steroid receptor

Answer 21

Steroid receptors are inside the cell cytosol or the nucleus.
Hormones cross the plasma membrane by simple diffusion

Question 22

Location of non steroid receptor

Answer 22

Non steroid receptors are located on the cells membrane. These hormones DO NOT enter the cell.

Question 23

Transduction mechanism of steroids

Answer 23

The hormone-receptor complex moves into the nucleus (if it was not there already) and binds with DNA to activate transcription.

Question 24

Transduction mechanisms of non steroids

Answer 24

1. A change in the permeability of the membrane to ions
2. A change in the concentration of 2nd messengers inside the cell ex cAMP
3. A change in the amount of enzyme activity inside the cell

Question 25

Temporal patterns of response steroids

Answer 25

Slow and enduring - it can take up to 90 mins to activate gene expression but the effect can last up to several days

Question 26

Temporal patterns of response non steroids

Answer 26

Brief and dramatic (ex the adrenaline surge of a panic attack)
These signals need to be constantly secreted because their half lives are very short

Question 27

ADH source

Answer 27

Posterior pituitary gland

Question 28

Oxytocin source

Answer 28

Posterior pituitary gland

Question 29

Stimulus for secretion of ADH

Answer 29

• decreased blood pressure

- increased osmolarity (“saltiness”) of the cerebrospinal fluid

Question 30

Stimulus for secretion of oxytocin

Answer 30

-neural reflex initiated by mechanical stimulation of the nipples

Question 31

Target of hormone (location of receptors) ADH

Answer 31

Kidney - water conservation
Peripheral vascular circular smooth muscle - causes blood vessels to squeeze blood from the periphery into the heart brain loop

Question 32

Target of hormone (location of receptors) oxytocin

Answer 32

Increased contraction of myoepithelial cells in the mammary glands
(Prolactin from the APG is responsible for milk production)

Question 33

Transduction mechanism of ADH

Answer 33

ADH-receptor on the surface of the target cell; ADH is a protein (can’t diffuse across the membrane)

Question 34

Transduction mechanism of Oxytocin

Answer 34

Oxytocin - receptors on the surface of the target cells

Question 35

Functional response of tissues ADH

Answer 35

Increased blood pressure and less urine formed

Question 36

Functional response of tissues oxytocin

Answer 36

Milk “let down” reflex

Question 37

Tonic control

Answer 37

Control that blood vessels are under. There are not two different signals to cause contraction/relaxation.

When EPI/NE binds with the alpha adrenergic receptor the blood vessel contracts. For the vessel to relax, stimulation by EPI/NE has to be reduced.

Question 38

The stress axis

Answer 38

Stress causes the hypothalamus to release CRH (corticotropin releasing hormone) which travels to receptors in the anterior pituitary gland which causes it to release ACTH (adreno-corticotropic hormone) which travels to receptors in the adrenal cortex which stimulates it to release cortisol, which then affects the immune system cells, liver cells, muscles, and adipose tissue.

*Cortisol causes catabolism of stored fuel molecules

Question 39

How is the stress axis an example of negative feedback?

Answer 39

Because cortisol binds with receptors in the hypothalamus and anterior pituitary gland to suppress release of CRH and ACTH

Question 40

Posterior pituitary hormones

Answer 40

Antidiuretic hormone (vasopressin) and oxytocin