Flashcards in Homeostasis and the Endocrine System Deck (151):
What are the 4 characteristics of a control system?
Stimulus, Receptor, Control centre, Effector
What does a receptor do?
Give 4 examples of receptors
Give 2 examples of things chemoreceptors respond to?
What do proprioreceptors do?
Give awareness of position
What do nociceptors do?
Detects painful stimuli
How does the receptor communicate with the control centre?
By the afferent pathway
How does the nervous system communicate?
How does the endocrine system communicate?
Where is the control centre typically located?
In the brain, usually the hypothalamus
What does the control centre do?
How does the control centre communicate with the effector?
The efferent pathway
What does the effector do?
Give 3 examples of effectors
What usually happens once the effector has caused change?
In what direction does negative feedback act?
In direction opposing original stimulus
What does negative feedback do?
Responds in a way to reverse the direct change
What does positive feedback do?
Responds in a way as to change the variable even more in the direction of change
When is positive feedback used?
When rapid change is desirable
Give 3 examples of where positive feedback is used
- Blood clotting
- The Ferguson reflex during childbirth
Is the set point of a control centre constant or variable?
What rhythm does the body display?
Circadian (or diurnal)
What does the ‘biological clock’ in brain consist of?
Small group of neurones in suprachiasmatic nucleus
What does the biological clock respond to?
Cues from environment- Zietgeben
What cues from the environment keep the body on a 24h cycle?
Give an example of the manifestation of disruption of biological rhythms?
What causes jet lag?
Mismatch of the environmental cues and body clock when long haul flights cross time zones
How much body water does the average person have?
What does body water content vary between?
What are the 3 main compartments containing body water?
What is the osmotic pressure of the blood plasma monitored by?
Osmoreceptors in hypothalamus
What is osmolarity?
Number of osmoles per litre of solution
What is osmolality?
The number of osmoles per Kg of solution
What is an osmole?
The amount of substance that dissociates in solution to form one mole of osmotically active product
What is responsible for bodily fluid homeostasis?
Antidiuretic hormone (ADH)
Why is it important to keep osmolarity in set range?
Otherwise causes disruption to cells- can cause them to shrink or burst
What is it called when there is high blood osmolarity?
What must happen when the blood is hypertonic?
The body needs to conserve water
What are osmoreceptors in the hypothalamus technically detecting?
Tonicity, because across a membrane
What does hypertonicity lead to?
Why does hypertonicity cause thirst?
Because drinking reduces osmolarity, and so returns normal blood osmolarity
Is ADH synthesised by the posterior pituitary?
No, just secreted- synthesised in hypothalamus
Why does the body secrete more ADH when the blood is hypertonic?
Because it increases reabsorption of water from the urine into blood via collecting ducts in the kidney, leading to a return to normal blood osmolarity
What does the reabsorption of water from urine cause?
A smaller volume of concentrated urine
What does the body need to do when there is low blood osmolarity?
What detects low blood osmolarity?
Osmoreceptors in the hypothalamus
What happens in response to low blood osmolarity?
Posterior pathway secretes less ADH
What is the result of decreased secretion of ADH?
Decreased absorption of water from the urine into the blood from the collecting ducts of the kidney, leading to large volumes of dilute urine and a return to normal blood osmolarity
What does the endocrine system consist of?
A collection of glands located throughout the body
What are hormones?
Chemical signals produced in endocrine glands or tissues that travel in the bloodstream to cause an effect on other tissues
What are the major endocrine glands?
- Pituitary glands
- Pineal glands
- Thyroid glands
- Parathyroid glands
- Adrenal gland
What can release hormones other than endocrine glands?
Other organs and tissues
What other organs and tissues release important hormones?
What hormones does the heart produce?
What hormone does the liver produce?
What hormones does the stomach produce?
What hormones does the placenta produce?
What hormone does the adipose produce?
What hormones does the kidney produce?
What are the 4 mechanisms of communication via hormones?
How does autocrine communication work?
Hormone signal acts back on cell of origin
How does paracrine communication work?
Hormone signal carried to adjacent cell over a short distance via interstitial fluid
How does endocrine communication work?
Hormone signal released into bloodstream carried to distant target cells
How does neurocrine communication work?
Hormone originates in neurone, and after transport down axon, released into bloodstream and carried to distant target cells
Where is neurocrine communication important?
In hypothalamic pituitary axis
What features to endocrine and nervous system have in common?
- Both neurones and endocrine cells are capable of secreting
- Both neurones and endocrine cells can be depolarised
- Some molecules act on both neurotransmitters and hormones
- The mechanism of action requires interaction with specific receptors in the target cells
What do neurones secrete?
Why can both neurones and endocrine cells be depolarised?
They are both excitable cells with a resting membrane potential
What do the endocrine and nervous systems work in parallel to do?
What are the differences between endocrine and nervous systems?
- The signal for the endocrine system is hormones, whereas for the nervous system it is neurotransmitters and action potentials
- The signals for the endocrine system are chemical in nature, whereas they are both chemical and electrical for the nervous system
- Signals from the endocrine system are conveyed in the bloodstream, whereas the nervous signals are conveyed by synapses and axons
- Endocrine signals are slow, whereas nervous signals are fast
What groups are hormones classified into?
Which is the largest group of hormones?
What do peptide/polypeptide hormones consist of?
Short chains of amino acids
Give 3 examples of peptide/polypeptide hormones
- Growth hormones
Are peptide/polypeptide hormones water or lipid soluble?
All water soluble
What are amino acids derivatives synthesised form?
Amino acids (tyrosine)
Give 3 examples of amine hormones
- Thyroid hormones
Are amine hormones water or lipid soluble?
- Adrenal medulla hormones water soluble
- Thyroid hormones lipid soluble
Are do glycoprotein hormones consist of?
Large protein molecules, that tend to be glycosylated. Often made up of sub-units
What is meant by glycosylated?
They have a carbohydrate side chain
Give 3 examples of glycoprotein hormones
- Lutenizing hormone
- Follicle stimulating hormone
- Thyroid stimulating hormone
Are glycoproteins water or lipid soluble?
What are steroid hormones derived from?
Where are steroid hormones produced?
Give 3 examples of steroid hormones
Are steroid hormones water or lipid soluble?
How are hormones transported?
- Some hormones in the blood in simple solution
- Most hormones bind to (usually) proteins
Give two examples of hormones that can travel in the blood in simple solution
What feature must a hormone have to be able to travel in the blood in simple solution?
What group of hormones bind to proteins to travel in the blood in particular?
Give an example of a hormone that binds to a specific protein for transport?
Thyroid hormones bind to thyroxine-binding globulin
What exists between bound and free forms of hormone in plasma?
What form of a hormone is biologically active?
Only the free form
Give the equilibrium between bound and free forms of a hormone
Free hormone + binding protein ↔ bound hormone
What are the roles of carrier proteins?
What 3 main factors determine hormone levels in the blood?
- Rate of production
- Rate of delivery
- Rate of degradation
What is the most highly regulated aspect of hormonal control?
Rate of production
What does rate of production of hormone consist of?
What would result in a higher rate of delivery of hormone?
Increased blood flow to a particular organ
What is meant by rate of degradation of hormones?
The rate at which its metabolised and excreted from body
At what concentrations do hormones circulate in the blood?
What do hormones do to exert their effects?
Bind to specific receptors
Why are hormone receptors needed?
For specificity, as the blood stream bathes all cells
What do endocrine cells do?
Synthesise and release hormone into the bloodstream
What happens to hormones in the blood stream?
It’s carried to distant target tissue
What happens in a non-target cell?
There is no receptor for hormones, so no response to hormone
What happens in a target cell?
It has expressed the specific receptor for hormone, and so there is a specific cellular response to hormone
What do water soluble hormones bind to?
Cell surface receptors
Why do water soluble hormones bind to cell surface receptors?
As they can’t cross the plasma membrane
Give an example of a G protein coupled receptor
What is the mechanism of action for a G protein coupled receptor?
- Dissociation of G protein sub-unit
- Activation of effector protein
- Formation of second messenger
- Activation of protein kinase
- Phosphorylation of target proteins
- Cellular response
Give an example of a tyrosine kinase receptor
An insulin receptor
What is the mechanism of action for a tyrosine kinase?
- Autophosphorylation of specific tyrosines
- Recruitment of adaptor proteins and signalling complexes
- Activation of protein kinase
- Phosphorylation of target proteins
- Cellular response
Where does dimerisation not occur in a tyrosine kinase?
In an insulin receptor
Why does dimerisation not occur in an insulin receptor?
It is already dimerised
What do lipid soluble hormones bind to?
Why can lipid soluble hormones bind to intracellular receptors?
Because they are able to diffuse across plasma membrane
How does a type I lipid soluble hormone interact with its target cell?
Cytoplasmic receptor binds hormone, and receptor-hormone complex enters nucleus and binds DNA
How does a type II lipid soluble hormone interact with it’s target cell?
Hormone enters nucleus and binds to a pre-bound receptor DNA. Binding relieves repression of gene transmission
Where does a receptor bind to a DNA molecule?
To a specific sequence called a hormone response element (HRE) in the promoter region of specific genes
What is the effect of hormonal binding to DNA?
It affects the mRNA, and therefore the new protein, which induces a cellular response
What mediates the effect of a lipid soluble hormone?
The expression of new protein
Do lipid soluble hormones promote or repress gene transcription rate?
Can do either
What is the hypothalamic pituitary axis?
A complex functional unit formed by the hypothalamus and the pituitary gland that serves as the major link between the endocrine and nervous systems
Where does the pituitary gland sit?
Beneath the hypothalamus, in a sock of bone called the sella turcia
Give 8 processes that the hypothalamus and pituitary gland module
- Body growth
- Adrenal gland function
- Water homeostasis
- Milk secretion
- Thyroid gland function
What does the pituitary gland consist of?
- Anterior pituitary gland (adenohypophysis)
- Posterior pituitary gland (neurohypophysis)
How are the anterior and posterior pituitary gland distinct from one another?
- Different embryological origins
- Distinct functions
Is the pituitary gland physically connected to the hypothalamus?
Yes, the posterior pituitary gland is
How is the posterior pituitary gland connected to the hypothalamus?
The hypothalamus drops down through the infundibulum to form the posterior pituitary
What is the neurocrine function of the posterior pituitary?
- Oxytocin and ADH hormone are produced by neurones in the hypothalamus
- These hormones are transported down nerve cell axons to the posterior pathway
- The hormones are stored and released from the posterior pituitary into the general circulation to act on distinct targets
How are hormones synthesised in the hypothalamus transported to the anterior pituitary?
They are transported down axons
What happens to hormones once they are in the anterior pituitary?
They are stored in median eminence before release into hypophyseal portal system
What is the neurocrine function of anterior pituitary hormones?
The hormones stimulate or inhibit target endocrine cells in the anterior pituitary gland
What is the endocrine function of the anterior pituitary hormones?
The endocrine cells of the anterior pituitary secrete a variety of hormones into the bloodstream to act on distant target cells
What is the autocrine and paracrine function of the anterior pituitary hormones?
The hormones also affect neighbouring cells
In summary, what pathways do the hormones produced by nerve cells in the hypothalamus act?
What hormones are produced in the hypothalamus for release from the posterior pathway?
What does oxytocin do?
What does ADH do?
Regulates body water volume
How many trophic hormones are there produced in the hypothalamus?
What do trophic hormones do?
Have direct effects on release of anterior pituitary hormone
What are the 7 trophic hormones produced in hypothalamus?
Give 6 hormones produced by the anterior pituitary
What does TSH do?
Controls secretion of thyroid hormone from the thyroid gland
What does AOTH do?
Controls secretion of hormones from adrenal cortex
What does LH do?
Controls ovulation and secretion of sex hormones
What does FSH do?
Controls development of eggs and sperm
What does PRL do?
Controls mammary gland development and milk secretion
What does GH do?
Controls growth, and energy metabolism, and stimulates IGFs