Lecture 23: Endocrine 1

Question 0

Tell me about gap junctions

Answer 0

-Gap junctions link adjacent cells
-connections form channels that link the cytosol of adjacent cells
-connexion a form channels that link the cytosol of adjacent cells, allowing ions and small molecules to move between cells.
Slide 6

Question 1

What are the 2 types of intercellular communication

Answer 1

1st: direct communication via gap junctions
2nd: via an assortment of chemical messengers, and one of these form the basis of the endocrine system

Question 2

Chemical messengers

Answer 2

• secretory cell releases chemical messengers into ECF
• messenger bond to specific receptors on the ‘target’ cell
• blinding of messenger to receptor triggers a response in the target cell.

Question 3

There are 6 general classifications of chemical messengers.

What are they and how they work?

Answer 3

1. Paracrines- secreted by one cell and diffuse to nearby target cell. Distance travelled is quite short 
Eg histamine (released in damaged tissue and involved in inflammatory response)  and growth factors eg epidermal growth factor- stimulates cell division 

2. Autocrines: they bind to receptors (and exert their effects) on the same cell that secreted them. Often an autocrine also functions as a paracrines or other messenger eg growth factors
3. Cytokines: secreted by a cells of the immune system eg interleukins, released by white blood cells and involved in immune response
4. Neurotransmitters- released from neurons at the axon terminal; this form of communication sometimes called synaptic signalling (junction between 2 neurons) eg acetylcholine- involved on triggering contraction of skeletal muscle
5. Classic endocrine: secreted by one cell and travel to a remote target cell
6. Neurohormones: hormones secreted by neurons (neurons excretory cells) but which diffuse into the blood for transport to target cells eg vasopressin or ADH from pituitary gland

Question 4

What are the major features of the endocrine system?

Answer 4

• effects exerted at very low concentrations
• hormones bind f cell receptors on the target site and triggers a response
• same hormone can cause different responses in different types of cells.
• endocrine glands have a rick vascular and lymphatic drainage for rapid dispersal of hormones throughout body
• hormones control the long term physiological responses of an animal (homeostasis) eg growth, metabolism, reproduction
• they are also involved in some short term responses eg stress

Question 5

What are the mechanisms of hormone action

Answer 5

For hormones to exert their effect, they just bind to a specific receptor

• receptors a) bind Ligands (hormone) and then b) translate the messe of the signal ligand info a cellular response.
• target cell receptors are located outside the cell membrane, in the cytosol or in the nucleus
• Only lipophilic hormones can diffuse across cell membrane and bind to cytosolic or nuclear receptors
• lipophobic hormones bind to cell membrane receptor