Tema 5

Question 1

types of cell communication

Answer 1

Direct communication: Closed and GAP junctions
Communication by contact: surface markers
Communication by molecules: emission and reception of diffusible chemical signals

Question 2

Direct communication - closed junctions

Answer 2

Closed unions
-they hold cells together + give tissue stability // don’t allow substance passage

1. tight junctions
2. desmosomes + hemidesmosomes
3. adherent zones
4. focal adhesions

Question 3

Direct communication - open junctions

Answer 3

GAP junctions -
*allow passage of ions and small molecules (important in chemical synapse)

Formed by connexons (proteins) that assemble themselves as a channel allowing direct contact between the cytoplasms.
Each connexion is form of 6 connexins (subunits)

They are adjustable; change their diameter
-changes in osmolarity
-increase of h+ or intracellular Ca2+
-in repsonse to hormones (glucagon in liver)

Question 4

Communication by contact

Answer 4

cells exchange information through surface markers (membrane proteins), which are attached to the outer surface of their membrane

when markers of different cells compliment each other they create a permanent or temporary union

• Las células de adhesión e interinas
  -participan en la formación de tejidos y en la migración celular

Question 5

Communication by molecules

Answer 5

cells produce and release CHEMICAL MESSENGERS that diffuse through the extracellular fluid and interact with SPECIFIC RECEPTORS

Protein receptors trigger different responses

Question 6

chemical messengers

Answer 6

The duration of the action of a chemical messenger is very limited: effective inactivation mechanisms

Messengers are very diverse and they can exercise very different actions on different parts of the body /adrenaline is a hormone + neurotransmitter)

Question 7

chemical messengers - classification

Answer 7

SIZE
- from a few daltons (nitric oxide) to several thousands (growth hormone)

SOLUBILITY
-water soluble: amines, a.a, peptides
-liposouble: prostaglandins, steroid hormones

AVAILABILITY
-produced on demand: nitric oxide
-stores in vesicles: neurotransmitters

Question 8

chemical messengers - topographic classification

Answer 8

AUTOCRINE: receptor is in the same cell that secretes the messenger
PARACRINE: receptor is located in adjacent cells to the secretory cell
NEUROCRINE-SYNAPTIC: it combines the transmission of an electrical signal with the release of a neurotransmitter - it acts in a autocine or paracrine way
ENDOCRINE: hormone is released in blood and goes to large cells
NEUROENDOCRINE: messenger is released as a neurotransmitter but it travels as a hormone to its receptor in the target cell

Question 9

TYPES OF RECEPTORS

Answer 9

Proteins located on the surface or inside of the cell

-membrane receptors: bound to channel, enzyme-linked, association to G-protein
-intracellular receptors: cytosolic (class I), nuclear (class II)

Question 10

RECEPTORS - CHARACTERISTICS I

Answer 10

Affinity and reversibility:
-ligand-receptor binding has a high affinity + reversible
-affinity is inversely proportional to the con of the ligand (low conc, more affinity), allowing them to act even in low conc

Concentration:
-amount of receptors in cells increases or decreases in response to different stimuli
-when the conc of neurotransmitters decreases, the amount of receptors increases

Ligand specificity:
-only a given mediator/messenger binds to a receptor
-COMPLEMENTARY

Question 11

RECEPTORS - CHARACTERISTICS II

Answer 11

Tissue specificity:
-only the cells with the specific receptor will respond to the messenger, even all the cells are exposed to the messenger
-ACTH in the cortex

Cellular location:
-membrane receptors: hydrosoluble hormones that don’t cross the membrane
-intracellular receptors: liposoluble hormones that cross the membrane easily

Signal transduction mechanisms: generally only membrane receptors have them