Chapter 2 (Hormonal Communication) Flashcards
Communication of Cells
Essential for:
- Coordination of their diverse activities
- Maintain homeostasis
- Growth of cell
- Development of the body
Intracellular Control of Cellular Function
- Communication within cells of the body
eg. Synthesis of neurotransmitters. Need communication between RER, SER, ribosome
Intercellular (Extra) Control of Cellular Function
- Communication between the cells of the body
eg. Release of ACTH during stress causes release of cortisol.
Types of Intercellular Communication
Direct:
1. Gap Junction
Indirect chemical messengers:
- Paracrine
- Neurotransmitters secretion
- Hormonal secretion
- Neurohormone secretion
- Process
a. Specific cells of the body stimulate specific chemicals in the ECF
b. These chemicals possess ligand, which binds/interacts with receptors on target cell. This elicits a response.
Gap Junction
Direct Intercellular Communication
- Intimate way of communication
- Achieved through signaling molecules on the surface of the cells
eg. Phagocytes recognize and destroy bacteria and invaders.
eg. Antibodies “mark” bacteria as foreigner to destroy them
Paracrine
- Local chemical messenger exerts its effects on only the neighboring cells in an immediate environment
- Chemical messenger uses simple diffusion and acts at a short distance.
- Does not gain entry in the blood.
eg. The release of histamine causes vasodilation of the neighbouring blood vessel.
Neurotransmitters
- Short-range chemical messengers
- Diffuse across narrow spaces to act locally on adjoining target cells (another neuron, a muscle or a gland)
- Process:
Nerve cells - Neurotransmitters - ECF - affects adjoining target cells.
eg. Muscle, gland or neuron.
Hormonal Secretion
- Long-range chemical messengers
- Secreted into blood by endocrine glands in response to an appropriate signal
- Exerts effect on target cells some distance away from release site
eg. GH only bins to muscles and bones in the body - Process:
Stimuli - endocrine - hormone - blood - target gland - receptors - response.
Neurohormones
- Hormones released into blood by neurosecretory neurons.
- Distributed through blood to distant target cells.
Signal Transduction
The conversion of incoming signals (from extracellular chemical messengers) to target cells interior for its response.
Cell Response using Signal Transduction
The combination of extracellular chemical messengers with its membrane receptors triggers sequence of intracellular events for a particular cellular activity (transport, secretion, metabolism and contraction)
First Messengers
- Extracellular chemicals bind to receptors
- Open or close the specific channels to regulate the movement of particular ions in and out of cell.
- Transfer extracellular chemical messengers to the second messenger
Second Messenger
Triggers preprogrammed series of the biochemical events within a cell.
Cyclic AMP Second-Messenger Pathway
- Binding of extracellular messenger to receptor activates a G protein, the alpha subunit of which shuttles to and activate adenylyl cyclase.
- Adenylyl cyclase converts ATP to cAMP
- cAMP activates protein kinase A
- Protein kinase A phosphorylates inactive target proteins, activating it.
- Active target protein brings about desired change.
Function of cAMP
Activation of cAMP brings about:
- Modification of heart rate
- Formation of female sex hormones in the ovaries
- Breakdown of stored glucose in the liver
- Reception of a sweet taste by a taste bud
- Conservation of water during urine formation
Calcium Second -Messenger System
- Binding of an extracellular messenger to receptor activates a G protein, the alpha subunit of which shuttles to and activates phospholipase C
- Phospholipase C converts PIP2 to IP2 and DAG.
3a. IP3 mobilizes intracellular Ca2+
4a. Ca2+ activates calmoduin
5a. Ca2+ - calmoduliin complex activates a Ca2+ - calmodulin dependent protein kinase.
6a. CaM kinase phosphorylates inactive target protein, activating it.
7a. Active target protein brings about desired response.
3b. DAG activates protein kinase C
4b. Protein kinase C phosphorylates active target protein, activating it.
5b. Active target protein brings about desired response.
cGMP
- In a few cells, cyclic GMP serves as a second messenger in a system analogous to the cAMP system.
eg. The signal transduction pathway involved in vision.
Functions of Endocrine Glands
- Aldosterone regulates metabolism, H2O and electrolyte balance by acting on the kidneys.
- Cortisol induces adaptive changes to help the body cope with stressful situations
- Promotes growth and development (GH)
- Controls reproduction (FSH and LH)
- Regulates blood cell production (erythropoietin)
- Endocrine and ANS control and regulate both circulation, digestions and absorption of food in the GI)
Peptides and Protein Hormones
- Composed of specific amino acids arranged in chains of varying lengths.
- Hormones secreted by the following glands are peptides
1. Hypothalamus
2. Ant. and Pos. pituitary
3. Pancreas
4. Parathyroid
5. Gastrointestinal
6. Kidneys
7. Liver, thyroid, heart and thymus.
Synthesis of peptide hormones
- Preprohormone
a. RER - SER - Golgi Complex - Prohormone
- Active hormone
a. hormone - circulation 0 target.
Pre-proopiomelanocortin
POMC
- ACTH - adrenal gland - releases cortisol
- MSH - melanocytes - skin colour
- B-Endorphin - analgesic - pain relief.
Steroid Hormones
- Includes hormones secreted by adrenal cortex, gonads and placenta.
- Derivatives of cholesterol.
- Are not stored in cells once formed. They are released in blood immediately via lipid soluble pleural membrane.
- These hormones undergo interconversion in blood or other organs. eg, progesterone becomes cortisol
Steroidogenic Pathways
All steroid hormones are produced through a series of enzymatic reactions that modify cholesterol molecules, such as by varying the side groups attached to them.
eg. Testes have specific enzymes that allow them to changes cholesterol into testosterone.
Chemical Categories of Hormones
Cholesterol (precursor)
- Progesterone
- Aldosterone
- Cortisol - Dehydroepiandrosterone
- Testosterone
- Estradiol
Amines/catecholamines
- Derived from the amino acid tyrosine
- Includes the hormones secreted by thyroid and adrenal medulla (catecholamine)
- Enzymes synthesizing these hormones are not located in cell organelles
- Both amines are stored in cells until their secretion
Permissiveness
- One hormone must be present in adequate amount for the full exertion of another hormone’s effect
- One hormone enhances the responsiveness of other hormones on target glands.
eg. Thyroid hormone increases receptors for epinephrine
Synergism
- The actions of more than one hormone are complementary and their combined effect is greater than the sum of their separate effects.
eg. synergistic effects of FSH and testosterone on testes are required to maintain sperm production
Antagonsim
- One hormones causes the loss of another’s receptors reducing the effectiveness of the second hormone
eg. Progesterone inhibits the action of estrogen (reducing the receptors) on uterine muscles to prevent miscarriage during pregnancy
Hormone Secretion and Plasma Concentration of an Active Hormone
- Hormone’s rate of secretion into the blood by the endocrine glands.
- It’s extent to bind to plasma proteins
- It’s rate of removal from the blood by inactivation or excertion
- Availability and sensitivity of the target cells receptors for the hormone
Hormone Secretion by other Hormones (negative feedback)
- Fall in plasma thyroid hormones below a set point causes the pituitary gland to secrete TSH
- Thyroid hormone in turn inhibits its further secretion fo TSH by the anterior pituitary
Hormone Secretion by Neuronal Control (ANS)
- Neuroendocrine reflexes influence neural and hormonal components
- the neuroendocrine reflexes serve a sudden increase in hormone secretion in response to specific stimuli
- eg. secretion of cortisol by adrenal gland during stress responses
Diurnal Rhythm
Secretion of Cortisol
- Peaks when you first wake up
- Lowest when you go to sleep
Pituitary Gland
Adenohypophysis (Anterior) - ACTH - TSH - GH - PRL - LH & FSH Neurohypophysis (Posterior) - Vasopressin/ADH - Oxytocin
Facts
- hypothalamus controls the release of pituitary hormones
- secretion of each pituitary hormone is stimulated or inhibited by more than 7 hypophysiotropic hormones
Nervous and Endocrine Systems
Functionally interconnected
- some nerves release neurohormones which act as hormones
- nervous system directly or indirectly controls the secretion hormones
- many hormones act as neuromodulators
- hormones essential for brain development
- both systems influence the same target cells
Need to know
3 categories of the hormone, their target tissue, their function
What are the factors that control the plasma level of the hormone
Hormones of the anterior and posterior pitutiary
