Endocrine 1 Flashcards
Glands defn
Epithelial tissue derivatives specialised for secreting.
Epithelial tissue defn
Functional grouping of cells specialised in the exchange of material between the cell and it’s environment, lines and covers various body surfaces and cavities and forms secretory glands.
Secretion defn
Release from a cell in response to appropriate stimulation of specific products that have been produced by the cell.
Two major communication systems
– nervous system
– endocrine system
Name 4 types of chemical messengers
1) Autocrine / Paracrine
2) Neurotransmitter
3) Neurohormones
4) Hormones
What are neurohormones and distribution?
- hormones released into blood by neurosecretory neurons
* distributed through blood to distant target cells
What are hormones?
- long-range messengers
* secreted into blood by endocrine glands in response to appropriate signal and act on distant target cells
What are Autocrine / Paracrine and effect
- local chemical messengers
* exert effect on neighbouring cells (paracrine) or on same cell (autocrine)
What are neurotransmitters?
- short-range chemical messengers
* diffuse across narrow space (synapse) to act on adjoining target cell (another neuron, a muscle, or a gland)
Autocrine meaning
Can act on itself
Paracrine meaning
Can act on another cell close-by
What are neurotransmitters released from?
Synaptic vesicles
What does a neurotransmitter bind?
A receptor
What does receptor activation cause?
Stimulates the cells
Where do neurotransmitters diffuse?
Across synapse between two cells
Release of neurohormones
Released from synaptic vesicles by neuron
Where are neurohormones released into?
The blood
Where are hormones released from?
Released from endocrine gland into blood
Where are hormones transported?
In blood
What do a hormones target cell express?
Specific receptors
Structure of the nervous system
Wired system of neurons
Structure of the endocrine system
Wireless system of glands
Chemical messenger in nervous system
Neurotransmitter
Chemical messenger in endocrine system
Hormones
Target site (length) in nervous system
Very close
Target site (length) in endocrine system
Far away
Distance of action of nervous system
Across synaptic cleft
Distance of endocrine of nervous system
Carried by blood
Speed of response of nervous system
milliseconds
Speed of response of endocrine system
mins to hours
Duration of action of nervous system
milliseconds
Duration of action of endocrine system
mins to days
Major function of nervous system
fast precise responses
Major function of endocrine system
long duration responses
NB - differences between hormones and neurotransmitters travel
Neural messages can only travel along existing nerve tracts; hormonal messages can travel in the circulatory system; thus any cell receiving blood is potentially able to receive a message.
NB - Differences between Hormones and Neurotransmitters
Neural messages are digital, all-or-none events that have rapid onset and offset; neural signals can take place in milliseconds; plus, electrical signal can travel along myelinated axons at speeds up to 100 meters per sec! Hormonal messages are analog, graded events that can take seconds, minutes or hours to occur.
What does interaction of a hormone with its receptor lead to?
A genomic response whereby the hormone activates genes that regulate protein synthesis (e.g., up-regulation: synthesis of a receptor for that hormone).
What are cell with receptors for the hormone called?
Target cells
What do hormones affect?
Cell morphology and size (including development of muscle and neuronal cells), and affect cell death (apoptosis) throughout the nervous system.
Hormonal Effects (understand)
• Sufficient number of receptors must be available for hormonal effects to occur.
• Popular belief that individual differences in behavior reflects differences in hormone concentrations. For example, it is assumed that roosters that crow frequently have more testosterone than roosters that seldom crow (or that aggressive men have higher T).
• Not necessarily true! – Individual differences in behavior can reflect hormone concentrations, pattern of hormone release, numbers and location of hormone receptors, and the efficiency of those receptors in affecting gene
transcription.
• Hormones rarely change the function of a cell; rather, they alter the rate of normal cellular function.
– Thus, hormones affect cell morphology and size (including development of muscle and neuronal cells), and affect cell death (apoptosis) throughout the nervous system.
• Although hormones obviously affect behavior, it is also true that behavior can influence hormonal levels and hormonal effects.
What are the two hormone catagories based on solubility?
– Hydrophilic (lipophobic, water soluble)
– Lipophilic (hydrophobic, water insoluble)
What are the two hydrophilic hormones?
- Peptide hormones
2. Catecholamines
What are the two lipophilic hormones?
- Thyroid hormone
4. Steroid hormones
What are the four types of hormones?
- Peptide hormones
- Catecholamines
- Thyroid hormone
- Steroid hormones
Structure of peptide
Amino acids
Solubility of peptide
hydrophilic
lipophobic
Receptors of peptide (location)
on cell surface
Place of peptide synthesis
In endoplasmic reticulum
Storage of peptide
Granules
Secretion of peptide
Exocytosis of granules
Blood transport of peptide
Free hormone
Hormones of peptide, x 9
hypothalamic, pituitary, pineal, pancreas, parathyroid, GIT, kidney, liver, heart
Structure of catecholamine
Tyrosine derivative
Solubility of catecholamine
- Hydrophilic
- Lipophobic
Structure of Thyroid hormone
Iodinated tyrosine derivative
Solubility of thyroid
- Lipophilic
- Hydrophobic
(location) Receptors of catecholamine
On cell surface
Place of catecholamine synthesis
In cytosol
Storage place of catecholamine
Granules
Secretion of catecholamine
Exocytosis of granules
Blood transport of catecholamine
Plasma bound
Hormone of catecholamine synthesis and storage in ….
Adrenal medulla
Receptor location of thyroid
inside cell
Place of synthesis of thyroid hormones
organelles
Storage of thyroid hormone
Colloid
Secretion of thyroid hormone
Endocytosis of colloid
Blood transport of thyroid hormone
Plasma bound
Name a thyroid hormone x 1
Thyroid follicular
Structure of steroids
Cholesterol derivative
Solubility of steroids
- Lipophilic
- Hydrophobic
Receptor location of steroids
Inside cell
Synthesis location of steroids
Intracell
Storage of steroid as..
Lipid droplets
Secretion of steroids by..
Diffusion
Blood transport of steroids
Plasma bound
Steroid hormones x 2
- Adrenal cortex gonads
- Vit D
What are steroid hormones derived from?
Cholesterol
Synthesis of steroids
Cholesterol pathway
2 types of receptors
- surface receptors
* nuclear receptors
Surface receptors binding
– bind peptides & catecholamines
– at cell membrane
Nuclear receptors binding
– bind thyroid & steroid hormones
– inside the cell
What do extracellular chemical hormone bind to?
Surface receptor
What does receptor activation alter in surface receptors?
– channel function
– second-messenger systems
How can all cells be exposed to hormones? (surface receptors)
Circulation
What do steroid receptors bind?
Steroid hormone
What does the hormone-receptor complex become?
A transcription factor (alters gene transcription)
What does each steroid receptor bind?
A unique DNA sequence (response element within an enhancer region)
What does steroid binding alter?
The rate of transcription
Surface receptor domains
- ligand binding domain (LBD)
- 7 transmembrane domains (TMDs)
- G-protein coupled
Mechanism of surface receptor
- peptide hormone binds to receptors on the surface of the cell
- activates G-protein
- induces intracellular signals
Give 6 neuropeptide examples
- Prolactin
- Adrenocorticotrophic hormone (ACTH)
- Antidiuretic hormone (vasopressin)
- Oxytocin
- Insulin
- Somatostatin
Nuclear receptor domains
- Hormone/Ligand binding domain (LBD)
- DNA binding domain binds steroid response element (SRE).
- Nuclear Localization Signal (NLS) covered by heat shock proteins (HSP)
Nuclear receptor mechanism
- binding of hormone induces detachment of HSP; uncovers NLS
- receptor + hormone enters nucleus
- acts as a transcription factor
Nuclear receptors x 5 examples
Estrogen, Glucocorticoid (Cortisol),
Mineralocorticoid (Aldosterone), Progesterone,
Androgen (Testosterone)
How can one hormone influence the activity of another hormone?
By regulation of its receptor
Why might target cell be unresponsive?
Due to lack of receptors (physiological, genetic, disease)
3 types of receptor regulation
Permissiveness
Synergism
Antagonism
Permissiveness
One hormone is required for another hormone to work
Synergism
– actions of several hormones are complimentary
– combined effect is greater than sum of separate effects
Antagonism
– one hormone inhibits another hormone’s receptors
– reduces effectiveness of second hormone
What are endocrine glands derived from?
Epithelial tissue
What are endocrine glands composed of?
Clumps of secretory cells
What are endocrine glands surrounded by?
capillaries
fenestrated
Do endocrine glands have a duct system?
no!
Do exocrine glands have ducts
Yes
Primary endocrine organs
– discrete organs
– main function is endocrine hormone release
– pituitary, thyroid, parathyroid, adrenal and pineal glands
Secondary endocrine organs
– dispersed in organs
– have other major functions
– heart, kidney, liver, etc.
What is the study of endocrine regulation?
Neuro-Endocrinology
What is neuro-endocrinology?
The study of how the brain regulates Pituitary hormone secretion
What do neuroendocrine cells release?
Neurohormones
Where are neuroendocrine cells found?
- adrenal medulla
- thyroid
- Pancreas / islet of Langerhans
- pituitary cells
- renin-secreting cells
- gastro-intestinal tract
- lower respiratory tract
What is endocrine gland secretion triggered by?
- hormones
- neurotransmitters
- metabolic factors
What are two types of feedback loops
- long-loop
- short-loop
What can feeedback be?
- excitatory
- inhibitory
Diagram of hypothalamus short and long loop negative feedback
Example of positive and negative feedback
Positive Feedback -
e.g. Hormone 3 activates Gland 2
Negative Feedback -
e.g. Hormone 3 inhibits Gland 1
What do trophic hormones regulate?
secretion other of hormones (either releasing or inhibitory)
Example of a trophic hormone
Thyroid-stimulating hormone (TSH)
Where is TSH secreted from?
Anterior pituitary
What does TSH stimulate?
Thyroid hormone secretion from thyroid gland
What does TSH maintain?
Maintains structural integrity of thyroid gland
TSH basic pathway
Disease of endocrine system
- Hyposecretion
- Hypersecretion
Cause of primary hyposecretion
• due to abnormality within gland • causes – genetic – dietary (eg lack of iodine) – chemical or toxic – immunologic (autoimmune diseases) – cancer – surgery (removal / Iatrogenic) – idiopathic (unknown)
Cause of secondary hyposecretion
Deficiency of tropic hormone
Cause of hypersecretion
– tumours continuously secrete hormone
– immune factors
Cause of primary hypersecretion
Too much hormone secreted due to abnormality within gland
Cause of secondary hypersecretion
Excessive stimulation of gland causes oversecretion
