Slide 3a

Question 1

What are 4 methods of cell to cell communication and what they are.

Answer 1

1. Gap junctions: direct cytoplasmic transfer from - one cell to the next

• large molecules cannot pass through
• only way electrical signal can pass cell to cell
  2. Contact-dependent signals: molecules on membrane surface bind to surface molecules
• includes CAMs (cell adhesion molecules), integrins transfer signals in both directions
• requires membranes on both cells to interact

3. chemicals that diffuse: via extracellular fluid to act on cells close by
4. long-distance communication: combo of chemical signals via blood or endocrine glands
   - only target cell receptors respond

Question 2

Which protein do gap junctions form from?

Answer 2

It forms from membrane spanning protein: connexions.

Question 3

When do we have contact dependent signals?

Answer 3

occurs in immune system and during growth

Question 4

Name the 2 types of signals and the difference between them.

Answer 4

1. autocrine signal: acts on the same cell that secreted

2. Paracrine: acts on the cell adjacent to it

Question 5

Describe cytokines.

Answer 5

Cytokines: act as oth local and long distance signals

• synthesized and secreted by nucleated cells (not specialized cells)
• control cell development, differentiation and immune responses
• broader spectrum of target cells than hormones
• made on demand (not stored)

Question 6

What are the general features of signal pathways?

Answer 6

• followed by paracrine or autocrine molecules and hormones
• depends on the presence of target receptors
• have a ligand (signal molecule that brings info to target cell)
• ligand-receptor binding activates receptor
• receptor activates one or more signals in the cell
• last signal initiates the synthesis as target protein or modification of existing as the response

Question 7

Where are receptors located?

1. ligand/receptor binding is dependent on whether it is…
2. … can diffuse through the PL bilayer binding to … receptors

Answer 7

On the cell membrane or in the cell.

1. lipophobic or lipophilic
2. lipophilic can diffuse through binding to cytosol or nucleus receptor

Question 8

Compare the speed of lipophobic and lipophilic ligands.

Answer 8

Lipophilic: slower, diffuse directly in
Lipophobic: rapid, bind to extra cellular receptor

Question 9

What is a biological signal transduction?

Answer 9

converts chemical signals to cellular responses

Question 10

What doe second messengers do?

Answer 10

1. alter gating of ion channels
2. increase intracellular calcium (to bind to protein to change their function like in contraction)
3. change enzyme activity like using kinases/phosphorylases

Question 11

What does the tyrosine kinase receptor pathway do?

Answer 11

Its ligand binds to it and activates it on the cytoplasmic side where it phosphorylates a protein using ATP (hydrolysis)

Question 12

Explain what GPCRs do.

Answer 12

They use G proteins and bind to nucleotide guanosine. These G coupled protein receptors are membrane spanning and cross the PL bilayer 7 times.
Once they are activated: open ion channels in membranes and alter enzyme activity on cytoplasmic side of membrane

Question 13

Give an example of GPCR.

Answer 13

Adenylyl cyclases- cAMP
Signal molecule binds to GPCR which binds to adenylyl cyclase which converts ATP to cAMP (a second messenger). cAMP activates PKA which phosphorylates proteins and initiates cell response.

PLC system
Signal molecule binds to GPCR which binds to PL-C. This will take a phospholipid from membrane and turn it to DAG + IP3. IP3 diffuses into cytoplasm binds to ligand gated calcium channels which releases calcium from its stores in the ER. DAG stays in the membrane and activates PKC where it phosphorylates proteins. Both give the cellular response.

Question 14

Describe a receptor-channel.

Answer 14

If a ligand binds to a channel receptor, it will have the most rapid response which either opens or closes the gate.
eg. ion channel can change the sodium, potassium or chlorine permeability if an ECsignal binds to it. This changes the electrical signal causing a response from voltage-sensitive proteins.

Question 15

Why are calcium ions versatile messengers?

Answer 15

It can enter the cell through voltage gated, channel, ligand or mechanically gated channels.

Question 16

What is the difference agonist and antagonist ligand?

Answer 16

1. primary ligan: activates a receptor
2. agonist: also activates receptor (only)
   - > both initiate a response
3. antagonist: blocks receptor activity, there is no response.

Question 17

What is the purpose of the endocrine and nervous system?

Answer 17

They both function to achieve and maintain homeostasis.
Both systems working as one is the neuroendocrine system.
Communication, integration and control
Neurons: can release neurotransmitters and neurohormones (hormones created and produced by neuroendocrine gland) into blood.

Question 18

Make general distinctions between nervous and the endocrine system.

Answer 18

Nervous system:
-nerve cell terminates on specific target cell (wired for specific transmission to a target)
-neurotransmitters are rapid and short lived
-neurons stimulate muscle and glands across a synapse only
Endocrine system:
-wireless (endocrine glands are not linked to their target cells.)
- endocrine chemical messengers are secreted into blood and delivered to distant target sites.
-hormones are slow and longer lasting
-hormones diffuse in blood and can access most tissues and cells

Question 19

How is neural specificity achieved?

Answer 19

• due to anatomic proximity between nerve cell and target cells
• unlike endocrine system: it does not rely on message and cell having the right receptor
• the muscle selected to move depends on the neuron that releases the ACh since all motor neurons have ACh receptors
• sharply contrasts endocrine system

Question 20

Describe main features of the endocrine system.

Answer 20

• ductless
• made of glandular epithelium (manufacture and secrete hormones)
• endocrine glands: secrete hormones
• exocrine glands secrete products
• glands are widely scattered throughout the body
• some are made of neurosecretary tissue: modified neurons that secrete chemical messengers which diffuse into blood stream rather than across a synapse (adrenal medulla)

Question 21

What is the major function of the hypothalamus?

Answer 21

• “master gland”
• receives input and acts accordingly
• controls the release of anterior pituitary hormones via releasing and inhibiting factors

Question 22

What are the 6 secreted anterior pituitary hormones?

Answer 22

1. TSH: t3/t4 - brain development, metabolism and reproduction
2. ACTH: stimulates cortisol secretion from adrenal cortex
3. GH: growth hormone - growth and metabolic effect
4. FSH & LH: follicle stimulating hormone & luteinizing hormone - ovulations, gonads, leydig cells to stimulate testosterone, androgen binding protein expression by sertoli cells
5. PRL: prolactin - milk synthesis from mammary glands
6. MSH: melanocyte stimulating hormone

Question 23

What hormones at released from the posterior pituitary?

Answer 23

It mainly stores hormones but does release 2 hormones into veins.

1. vasopressin - ADH acts on kidneys
2. Oxytocin: milk let downt and uterine contraction

Question 24

What is the function of the pineal gland?

Answer 24

produces melatonin - controls biological rhythm (circadian)

Question 25

What is the function of the thyroid gland?

Answer 25

produces t3 and t4, calcitonin to decrease plasma controls on how fast body burns energy and makes protein (metabolism regulator)

Question 26

What is the function of the adrenal cortex?

Answer 26

mineralocorticoids (aldosterone: actos on kidney for sodium retention for ultimate water retention), corticosteroids (cortisol: increase BP, blood sugar, reduces immune responses) and androgens (DHEA)

Question 27

What is the function of the adrenal medulla?

Answer 27

norepinephrine and epinephrine for stess adaptation

Question 28

What is the function of the pancreas?

Answer 28

insulin, glucagon, somatostatin (inhibit gastric secretion) (nutrient levels and utilization)

Question 29

What is the function of the gonads?

Answer 29

produces testosterone (testes), estrogen and progesterone (ovaries)

Question 30

What causes goiters?

Answer 30

• lack of iodine which essential for thyroxine production

- thyroid hormone deficiency can lead to cretinism in children (stunted physical and mental growth)

Question 31

What is grave’s disease?

Answer 31

• common form of hyperthyroidism
• immune system protein mimics TSH (autoimmune disease)
• so the there is a constant stimulation of TSH effect that causes more thyroid hormone to be produced

Question 32

How can hormones be classified?

Answer 32

1. hydrophilic (peptide hormones eg epinephrine)
2. lipophilic (steroids from cholesterol and thyroid hormone as an exception) from iodinated tyrosine amino acid derivative.
3. tropic hormones: target other endocrine glands to stimulate their growth or secretion of hormones
4. sex hormones: target reproductive tissues eg: ACTH targets adrenal cortex
5. anabolic hormones: stimulate anabolism (to build in target cells eg. testosterone stimulates protein synthesis and build up cellular tissue in muscles especially

Question 33

What does the solubility of hormones determine?

Answer 33

1. the way of transport in blood
2. mechanism by which it exerts effect signals
3. how hormone is processed in endocrine cell

Question 34

What are the way of hormone transport in the blood?

Answer 34

1. hydrophilic: dissolve in plasma
   bind to receptor on the surface of target cell
2. lipophilic: boud reversible to plasma proteins like albumin
   effects are produce by altering intracell proteins
   they can pass through target cell membrane and bind to receptors inside the target cell

Question 35

What is the mechanism by which hormone synthesize, store and secrete?

Answer 35

hydrophilic: made on ribosome of ER, in the Golgi-converted to prohormone and then active hormones. they are packaged in secretory vesicles by Golgi complex. They are released by endocrine cells via exocytosis.

Lipophilic - cholesterol is a common precursor for all steroid hormone except thyroid hormone.
They use enzymatic steps to modify it into a hormone. Cholesterol (precursor is stored but the hormone is not as it is metabolized by liver or excreted in urine.)
EXCEPT: thyroid amine hormone which are made from tyrosine = stored until secreted.

Question 36

How to go from preprohormone to secreted hormone?

Answer 36

mRNA binds on ribosome into peptide chain called preporhormone. THe chain is directed into ER lumen via signal sequence, . The ER chops it into an inactive prohormone packaged into vesicle to the Golgi where enzymes chop prohormones into one or more active peptide with additional fragments. It is goes in a secretory vesicle out of cell via exocytosis and moves into circulations across the ECF.