Endocrine System Flashcards
What is the endocrine system
The collection of glands and secretory tissues whose function is to regulate multiple organs in the body
What are the 2 functions of the endocrine system
- Respond to fluctuations within the internal environment to maintain homeostasis
- Meet growth and reproductive needs of organism
Why do animals have endocrine system instead of paracrine
Acts via hormones and blood stream because the target cells are too distant to be reached by diffusion
Autocrine signalling
cell releases the signal to which it itself responds to
How does the endocrine system work
Migrate substance into circulatory system which allow substances to travel throughout the body, and be released from the circulatory system to cells throughout the body
How do paracrine signals work
Diffuses into the interstitial fluid and elicits its response in the neighboring cells (gradient of signal, the further the fell is away from the source the less it will see)
Where are hormones produced
endocrine cells
What are endocrine cells
Ductless organs excrete outside the cell, into interstitial fluid where it then diffuses into the circulatory system
Why do endocrine glands have lots of capillaries
Dense network of capillaries in endocrine glands to quickly take up hormones and spread them throughout the body
How many endocrine glands do we have and what are they
9 overall, 8 per sex
- Pineal
- Hypothalamus
- Pituitary gland (master regulator)
- Thyroid Gland
- Parathyroid Gland
- Adrenal Glands
- Pancreas
- Ovaries
-Testes
What are hormones
Chemical signals that are secreted into the circulatory system and communicate regulatory messages throughout the body.
(Long-distance regulators in the body)
What do protozoans use as communication signals
Use secreted chemicals called pheromones (or gamones) for mating purposes
Why do protozoans need pheromones
communicate to undergo sexual reproduction
Protozoans
unicellular eukaryotes
metazoans
multicellular animals
What happened with the development of multicellularity
metazoans established short distance paracrine signalling
Limitations of paracrine signalling and the effect of this
limited to a distance of about 10 cells (limited to simple animals)
What version of endocrine system do phyla with lower physiological and anatomical complexity have
Neural systems but not an endocrine or circulatory system because they have lower physiological/anatomical complexity
Where does paracrine signalling occur in the neural system
At the end of axons, in the synapse
Where are chemical signals released in the neuron
By the synapse, at the end of the axon
Why not ONLY use the nervous system to communicate over long distances
Does not suffice due to dilution effect
2 advantages of endocrine system in addition to a neural system
A) blood vessels are designed to reach every cell in the body (because every cell in the body needs oxygen, nutrients, excretion)
B) Hormones are more suited for long-term effects (minutes to years) - whereas nerves work on more immediate responses
Why does the endocrine system require the circulatory system
Allow long-distance dispersal of chemical signals to alll the cells in the body
How did endocrine glands form
Hormone-producing cells accumulated together into glands
Function of endocrine glands
Allowed secretion of large amounts of hormones into capillary beds for dispersion around the body.
First endocrine glands
Neurohemal organ
What organisms has neurohemal organs
Mollucs and earthworms
What is the neurohemal organ
Neurons bundled together
Summary of the evolution of endocrine glands/system
Summary
1) Started with single cells organisms that used only pheromones
2) As we became multicellular, we used paracrine signalling (cell to surrounding cells and neural synapses)
3) As multicellular organisms became bigger, and circulatory systems developed, endocrine signalling was born
4) Accumulation of hormone-secreting cells into glands (“endocrine glands”) containing capillary beds
3 classes of hormones
Polypeptide hormones, Steroids, Amines
Polypetide hormones
- Chains of Amino acids
- Range from 3 amino acids to about 200 amino acids (size of a protein)
Why are polypeptide hormones ideal
Hormones usually work with a receptor - use the key and lock mechanism - Polypeptide has the greatest range of shapes
Steroids
Based on basic backbone of cholesterol
Amines
Built of single amino acids or single amino acids hooked together to another
What amines are water soluble
Polypeptides and epinephrine
What hormones are fat soluble
All cholesterol and other amines are fat-soluble
How do water soluble hormones work
- Water soluble hormones cannot freely cross the cell membrane.
- To be released, they have to be bundled in vesicles and released during an active process. - Once excreted, they can freely dissolve into and out of capillaries. However, they need a receptor to get into target cells.
- Once they bind to the receptor, it elicits a downstream effect that changes a cell to respond to the release of that hormone
How do fat-soluble hormones work
- Fat-soluble hormones cannot be retained in the cell that produces it.
- They immediately cross the lipid membrane however they are not very soluble in interstitial fluid and blood vessels.
- Must be carried around by a carrier protein - they can diffuse into all cells (even those that aren’t target cells) but only certain cells will have a receptor for that certain steroid.
- The cells with the certain receptor bind the steroid and eliciting a response.
Epinephrine hormone different effects on different cells
In liver cells - the release of glucose (increase glucose levels)
In smooth muscle cells in blood vessels that supply blood to muscles - relaxation (increased flow)
In smooth muscle cells in blood vessels that supply blood to intestines - contracts (decrease flow)
Connection between neural and endocrine system
Hypothalamus
Location of hypothalamus
situated at the base of the brain, connected to the anterior pituitary
How does hypothalamus mechanism work
Hormones produced inside hypothalamus, travel down the axons, and are released at the synapses into the capillary bed. Then they travel to pituitary gland which may release hormones - which then travel further around the whole body
The main role of endocrine system
Maintain internal homeostasis
Negative feedback loop
Inhibits a response by reducing the initial stimulus, preventing excessive pathway activity
How does negative feedback loop work in duodenum
- When chyme is passed into duodenum, it comes with a lot of acidity.
- Responder cells (S cells) measure PH. If it gets very acidic they cause the secretion of a hormone which travels around the body, eventually hitting the target cells in the pancreas.
- The pancreas responds by producing bicarbonate (pancrease is an exocrine gland) which dumps bicarbonate into duodenum to remove low pH, remove stimulus, so S cells no longer produce secretin.
