Lecture 14- Animal hormones Flashcards
What are hormones?
Chemical signals secreted by the cells of the endocrine system into the extracellular fluid
What are endocrine cells?
Cells that secrete hormones
What are target cells?
Cells that have receptors for the hormones secreted by the endocrine system.
What hormones act at a distance?
Circulating hormones
How do circulating hormones enter the system?
Hormones are secreted into the extracellular fluid and can diffuse into the blood
What are the three types of hormone?
Circulating hormones
Paracrine hormones
Autocrine hormones
What cells do paracrine hormones effect?
Cells near the site of release
What cells do autocrine hormones effect?
The cells that released the hormone
Why do paracrine hormones only effect cells near the site of release?
They are released in tiny quantities
Rapidly inactivated by enzymes
Taken up efficiently by local cells
Give an example of a paracrine hormone.
Histamine- a mediator of inflammation
What do autocrine functions do?
Provide negative feedback to control rates of secretion
Give an example of endocrine cells that exist as single, isolated cells within a tissue.
Hormones of the digestive tract are secreted by cells in the stomach and small intestine walls
What is the name given to aggregations of endocrine cells?
Endocrine glands
What are exocrine glands?
Glands that have ducts that carry their product to the surface of the skin or a body passageway that leads out of the body (sweat glands and salivary glands respectively)
When did chemical communication arise?
Early in evolution
Give examples of organisms that use chemical communication.
Plants, sponges, protists.
What do hormones control in arthropods?
Molting and metamorphosis
What are the three chemical groups hormones can be divided into?
- Peptides/polypeptides
- Steroid hormones
- Amine hormones
To what chemical group does the majority of hormones belong to?
Peptides/polypeptides
Give an example of peptide/polypeptide hormones.
Insulin
What are the chemical properties of peptide or polypeptide hormones?
Water soluble, easily transported in blood
Cannot pass lipid rich cell membranes
How do peptide or polypeptide hormones pass cell membranes?
They are packed in vesicles in the cells that make them and released by exocytosis
What are the chemical properties of steroid hormones?
Lipid soluble
Give an example of steroid hormones.
Testosterone and estrogen- derivatives of cholestrol
How are steroid hormones transported?
They are bound to carrier proteins in order to be transported to target cells
What are amine hormones?
Mostly derivatives of the amino acid tyrosine- some are lipid soluble some are water soluble.
Where are hormone receptors found?
The cell surface or cell interior
Where are the receptors for lipid soluble hormones?
Inside the cell interior in the cytoplasm or nucleus
Where are the hormone receptors for water-soluble hormones?
Receptors are large glycoproteins with three domains
What are the three domains of glycoprotein receptor molecules?
- Binding domain (projects outside plasma membrane)
- Transmembrane domain (anchors receptor to membrane)
- Cytoplasmic domain (extends into cytoplasm)
How do most steroids act on a cell?
Altering gene-expression in the cell
How does the cytoplasmic domain initiate the target cells response?
Activates protein kinase or phosphatases which activate or inactivate enzymes in the cytoplasm
Can also alter gene expression
What does the nature of a response to a hormone depend on?
The responding cell and its receptor- one hormone can trigger different responses.
Give an example of a hormone that can cause different responses on different cells.
Epinephrine which triggers fight-or-flight response
What responses does epinephrine cause?
- Heart- stronger and faster
- Constriction of blood vessels in digestive tract (more blood for muscles)
- Less blood flow to skin and kidneys
- Suppresses immune system
- Breaks down glycogen in the liver- a source of energy
What does the pituitary gland do?
Connect nervous and endocrine functions
Where is the pituitary gland found?
A depression at the bottom of the skill, over the back of the roof of the mouth
What is the pituitary gland attached to?
The hypothalamus
What are the two parts of the pituitary gland?
The anterior pituitary and the posterior pituitary
Why are there two parts to the pituitary gland?
They have different functions and developmental origins
What two hormones does the posterior pituitary secrete?
Antidiuretic hormone (ADH) and oxytocin
ADH and oxytocin are considered….
Neurohormones
Why is ADH and oxytocin considered neurohormones?
These hormones are synthesised in neurons in the hypothalamus
What is the main action of ADH in mammals and birds?
To increase the amount of water conserved by the kidneys
When is ADH secreted?
When blood pressure falls or blood becomes too salty
What does oxytocin do?
Stimulates uterine contractions before birth
Stimulates milk flow
Promotes bonding
What hormones does the anterior pituitary secrete?
-Tropic hormones
-Growth hormones
-Prolactin
-Enkephalins and endorphins
(peptide and protein hormones)
What do tropic hormones do?
Control other endocrine glands
What do growth hormones do?
Promote growth in a variety of tissues by stimulating cells to take up amino acids and stimulating the liver to produce growth factors.
What does prolactin hormones do?
Stimulates breast development
The production and secretion of milk
Controlling endocrine functions in the testes
What are endorphins and enkephalins?
Opiates- act as neurotransmitters that control pain
What is the anterior pituitary gland controlled by?
Hypothalamic hormones
How does the hypothalamus control the anterior pituitary gland?
- Nerve endings secrete neurohormones
- Portal blood vessels connect the anterior pituitary and the hypothalamus
- Neurohormones activate or inhibit release of hormones
How does the hypothalamus control the posterior pituitary?
- Hypothalamus produces neurohormones
- Neurohormones are released by nerve endings that extend into the posterior pituitary
What does the hormone thyroxine do?
Controls metabolism by elevating metabolic rate of cells and tissues
Where is thyroxine produced?
Follicles in the thyroid gland
What other hormone does the thyroid gland produce?
Triidothyronine (a version of throxine with only three atoms of iodine)
How is sensitivity to thyroid hormones controlled?
T4 is converted to the more active form T3 by enzyme action
What is a goiter?
An enlarged thyroid gland resulting from thyroid disfunction (hypo/hyperthyroidism)
Where is the adrenal gland found?
Above each kidney
What is the anatomy of the adrenal gland?
A gland inside a gland
What is the core of the adrenal gland called?
The adrenal medulla
What does the adrenal medulla produce?
Epinephrine, norepinephrine (adrenaline and noradrenaline)
What surrounds the adrenal medulla?
The adrenal cortex
What does the adrenal cortex produce?
Steroid hormones
What are epinephrine and norepinephrine examples of?
Amine hormones
What two types of receptors do epinephrine and norepinephrine bind to?
alpha adrenergic and beta adrenergic receptors
Which of the receptors do epinephrine and norepinephrine act on?
Epinephrine- both
Norepinephrine- mostly alpha adrenergic receptors
What drug acts on these receptors?
beta blockers
How do beta blockers work?
Block beta-adrenergic receptors to reduce fight or flight responses to epinephrine without disrupting regulatory functions of norepinephrine
The adrenal cortex use cholesterol to produce what?
Three classes of steroid hormones, collectively called corticosteroids
What are the three corticosteroids produced in the adrenal cortex?
Glucocorticoids
Mineralocorticoids
Sex steroids
What do glucocorticoids do?
Influence blood glucose concentrations as well as other aspects of fat, protein and carbohydrate metabolsim.
What do mineralocorticoids do?
Influcence the ionic balance in extracellular fluid
What do sex steroids do?
sexual development, sex drive, anabolism
What is the main mineralocorticoid?
Aldosterone
What does aldosterone do?
Makes kidneys conserve sodium and excrete potassium
What is the main glucocorticoid?
Cortisol
What does cortisol do?
Mediates the bodies response to stress- blocks immune system.
What are the three aspects to studying hormones?
- Detect, identify and measure the hormone
- Identify the receptors
- Understand the signal transduction pathways in different tissues
What techniques are used to measure hormone concentration?
Immunoassay techniques
What is the half-life of a hormone?
The time required for one half of the hormone molecules to be depleted.
How does an immunoassay work?
- Saturating amount of labelled hormone binds to antibodies
- Add different known quantities of unlabeled hormone to different test tubes to displace labeled hormone
- Wash out unbound hormone and measure amount of bound hormone
How do different hormones mediate the actions of a single hormone?
One hormone may bind to different receptors
How can receptors be identified?
Affinity chromatography
Genomic analysis
How is the abundance of hormone receptors regulated?
Negative feedback
What types of negative feedback can occur to change the abundance of hormone receptors?
Downregulation
Upregulation
Explain downregulation.
Continuous high levels of hormone decreases number of receptors (type II diabetes mellitus)
Explain upregulation.
When hormone secretion is suppressed, receptors increase.
Explain how type II diabetes mellitus develops.
Downregulation of insulin receptors
Possibly due to overstimulation of pancreatic release of insulin by excessive carbohydrate intake
Explain how beta blockers can result in upregulation.
Beta receptors are blocked over time, more receptors are produced.
Why is there a diverse action of hormones in cells if hormones are cell and tissue specific?
Hormones can act through different signal transduction pathways- they can elicit different responses within the same cell
What does it mean if a signal transduction pathway is a cascade?
Each step amplifies the response-one molecule binding to a receptor might result in many molecules of the final product
Give an example of a cascade.
Live cells in a response to epinephrine
