The endocrine system (1) Flashcards
Week 5
What is the endocrine system’s role and what does it do?
- Acts with the nervous system to coordinate and integrate body activities
- Influences metabolic activities via hormones transported in the blood
What is the meaning of endocrinology?
The study of hormones and endocrine organs
What does the endocrine system control and integrate? (5)
- Reproduction
- Growth and development
3.Maintenance of electrolyte, water, and nutrient balance of blood - regulation of cellular metabolism and energy balance
- Mobilisation of body defences
What is hormone (and what does it do)
A chemical messenger secreted by ductless glands directly into the blood stream to have an effect elsewhere in the body at its target issue
What are neurotransmitters and what do they do? (+ example)
Released by axon terminals into synaptic junctions and act locally to control nerve cell functions
~ Acetylcholine, epinephrine
What do endocrine hormones do? (+ example)
Release into the blood and affect target cells at another location in the body
~ Thyroid hormones, growth hormone, estrogen, insulin.
What do neuroendocrine hormones do?
Secreted by neurons into the blood and affect target cells at another location.
What do paracrines do? (+ examples)
Secreted by cells into the ECF and affect neighbouring target cells.
~ Somatostatin, histamine, eicosanoids
What do autocrines do? (+ examples)
Secreted by cells into the ECF and affect the function of the same cells that produced them
~ Eicosanoids (prostaglandins, thromboxanes)
What are cytokines what do they do?
Peptides that are secreted into the ECF and can function as paracrines, autocrines or endocrine hormones.
What are exocrine glands and what do they do?
-Ducts carry secretion to a surface or organ cavity
-Extracellular effects (food digestion)
-GIT
What are endocrine glands and what do they do?
-No ducts
-Intracellular effects, alter target cell metabolism
Examples of glands
- Pineal gland (side of head)
2.Thyroid gland (throat)
3.Ovary/ testis
What are the two main classes of hormones and what do they include?
- Amino acid-based hormones (amino acid derivatives, peptides and proteins)
- Steroids (synthesized from cholesterol, gonadal and adrenocortical hormones)
What are target cells?
Tissues with receptors for a specific hormone
Examples of water-soluble hormones and what do they act on?
-All amino acid-based hormone except thyroid hormones
1. Act on plasma membrane receptors
2.Act via G protein second messengers
Major difference between water and lipid soluble hormones
Water soluble CANNOT enter cell, lipid soluble CAN
Examples of liquid-soluble hormones and what do they act on?
- Steroid and thyroid horones
-Act on intracellular receptors that directly activate genes
Which hormones exert effects through second-messenger systems?
Amino acid-based hormones (except thyroid hormone)
What are the two main second-messenger systems?
- Cyclic AMP
- PIP2- calcium
Go through the steps of the cyclic AMP second messenger system (6)
1.Hormone binds to the receptor within the cell membrane (1st messenger)
2. Receptor activates G protein (Gs)
3. G protein activates adenylate cyclase
4. Adenylate cyclase converts ATP to cAMP (2nd messenger)
5. cAMP activates protein kinases
6. The active protein kinases triggers responses of target cells (activates enzymes, stimulates cellular secretion, opens ion channel etc.)
Which effector enzyme does hormone-activated G protein activate?
Phospholipase C
Which two messengers does activated phospholipase C split membrane phospholipid PIP2 into?
- Diacylglycerol (DAG)
- Inositol trisphosphate (IP3)
What do Diacylglycerol and Inositol trisphosphate do?
- Activates protein kinases
- Causes Ca2+ release from intracellular storage sites
How do calcium ions act as another second messenger?
Ca2+ alters enzyme activity and channels, or binds to regulatory protein calmodulin
What does calcium-bound calmodulin do?
Activates enzymes that amplify cellular response
Steps undertaken by intracellular receptors and direct gene activation (hormones) (5)
- The steroid hormone (lipid-soluble hormones and thyroid diffusing into target cells) diffuses through the plasma membrane and binds an intracellular receptor
- The receptor-hormone complex enters the nucleus
- The receptor-hormone complex binds to a specific DNA region
- Binding initiates transcription of the gene to mRNA
- The mRNA directs protein synthesis.
What does negative feedback prevent?
Overactivity of hormone systems
What can surges of hormones occur with? (+ example)
Positive feedback , e.g. oxytocin
What are the three stimuli that endocrine hormones are stimulated to synthesize and release hormones in response to?
- Humoral stimuli
- Neural stimuli
- Hormonal stimuli
What are humoral stimuli (+ example)
-Changing blood levels of ions and nutrients directly stimulate secretion of hormones
e.g. Ca2+ in blood:
Declining blood Ca2+ concentration stimulates parathyroid glands to secrete PTH (parathyroid hormone), PTH causes Ca2+ conc to rise = stimulu s removed
What happens during a neural stimuli and example of one.
- Nerve fibers stimulate hormone release
-Sympathetic nervous system fibers stimulate adrenal medulla to secrete catecholamines
Hormonal stimulus and example.
-Hormones stimulate other endocrine organs to release their hormones
- e.g. Hypothalamic hormones stimulate release of most anterior pituitary hormones then anterior pituitary hormones stimulate targets to secrete more hormones.
What three factors does target cell activation depend on?
- Blood levels of hormone
- Relative number of receptors on/in target cell
- Affinity (strength) of binding between receptor and hormone
What is up-regulation (target cell specificity)
Target cells form more receptors in response to low hormone levels
What is down-regulation and its importance to target cells.
When target cells lose receptors in response to high hormone levels
-Desensitize the target cells to prevent them from overreacting to persistently high levels of hormone.
All hormones circulate in the blood freely without carriers except?
Steroid an thyroid hormones which are attached to plasma proteins.
What does the concentration of circulating hormones reflect? (2)
- Rate of release
- Speed at which it is inactivated and removed from body
How can hormones be removed from the body? (3)
- Degrading enzymes
- Kidneys
- Liver
Definition of Half-life
Time required for level of hormone in blood to decrease by half
(can vary from half a minute to a week)
