Communications
between cells
Cells releasing Signaling molecules:Hormones, Factors and
Neurotransmitters released by
specific cells and Acting by:
- Endocrine signaling
- Paracarine signaling
- Autocrine signaling
Blood
vessel
Response
(a) Endocrine signaling
Response
(b) Paracrine signaling
Response
(c) Autocrine signaling
Endocrine
GLANDS are
releasing
Hormones
Exocrine
(Glands with Duct
system)
Endocrine
vs
(Ductless glands)
and their
release
5
Fig. 11-1
Endocrine Organs
• Purely endocrine organs
–
–
–
–
–
Pituitary gland
Pineal gland
Thyroid gland
Parathyroid glands
Adrenal glands:
• Cortex
• Medulla
• Endocrine cells in other organs
–
–
–
–
–
–
Pancreas
Thymus
Gonads
Hypothalamus
Kidney
GI system
6
Table 45.1a
Table 45.1b
General characteristics of
Endocrine signaling
• System of ductless glands that secrete
hormones
– Hormones are “messenger molecules”
– Released into blood from endocrine
structures
– Act on distant target cells
– Target cells respond to hormones for which
they have specific receptors
– The effects on target cells are dependent on
the induced responses.
– Hormones are just molecular triggers
Hormonal Receptors
• The ability of a cell to respond to a hormone
depends upon the presence of receptors for
that hormone:
on (over plasma membrane)=Extracellular
Receptors
in (Inside) the target cell. (Intracellular
Receptors).
SECRETORY
CELL
Lipidsoluble
hormone
Watersoluble
hormone
VIA
BLOOD
Transport
protein
Signal receptor
TARGET
CELL
Cytoplasmic
response
OR
Gene
regulation
Signal
receptor
Cytoplasmic
response
NUCLEUS
(a)
(b)
Gene
regulation
General Control of Hormones
•
•
•
•
•
•
•
•
- Metabolism
- Growth and development
- Red cell production
- Reproduction
- Adaptive changes like stress responses
- Fluid-electrolyte balance
- Acid-base balance
- Energy balance
Effectiveness of a hormone
• Depends on:
- Plasma Concentration:
- Responsiveness of Target Cells.
Effectiveness of a hormone
• Depends on:
- Plasma Concentration depends on:
-Rate of secretion: control mechanisms:
- Negative feed back
- Neuro-Endocrine reflexes
- Diurnal (Circadian) rhythm of secretion
-Transport in plasma
-Peripheral conversion
-Inactivation
-Excretion
Effectiveness of a hormone
• Depends on:
- Responsiveness of Target Cells.
- Depends on the Number of receptors:
- An increase in the number of
receptors for a hormone is called upregulation.
- A decrease in the number of
receptors for a hormone is called downregulation.
- Concentration of other hormones:
Effectiveness of a hormone
- Concentration of other hormones:
- Permissiveness:
Example: Thyroid hormones increases number of receptors
for epinephrine over target cells
- Antagonistic actions by other hormones:
Example: Progesterone and estrogen effects over uterine
smooth cells. (Progesterone reducing estrogen receptors)
- Synergistic actions:
Example FSH and Testosterone which are both needed to
maintain sperm production by testis.
Permissive Actions of Hormones
20
Fig. 11-9
Pituitary Gland
The Hypothalamus and Pituitary Gland
23
Fig. 11-13
Summary of Posterior Pituitary
Hormones
• The posterior pituitary does not synthesize any
hormones; it only secretes them.
• Oxytocin is involved in the milk ejection reflex of
nursing mothers and emotional bonding.
• Antidiuretic hormone (Vasopressin) is involved in
regulation of:
- Water balance and osmolarity.
- Blood Pressure
26
Anterior Pituitary Gland
Hormones
Anterior Pituitary Hormones and the Hypothalamus
29
Fig. 11-17
31
Fig. 11-15
Anterior Pituitary Hormones and the Hypothalamus
32
Fig. 11-17