Hormones and hormonal action Flashcards
Multicellular organisms depend on communication among cells for what 3 reasons
Regulation of metabolic processes
Control of cell growth and differentiation
Integration of normal physiological functions
what is a hormone
chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the body
hormones are carried via the blood circulation to target cells
they give specific changes in the metabolic behaviour of the target cell
what are some of the sites for hormone secretion
pineal gland, adrenal glands, pancreas, ovaries, testis etc
what does the pituitary gland regulate
regulates all other endocrine glands and releases growth hormone
what does the thyroid gland regulate
metabolism and body heat
what do the parathyroids regulate
use of calcium and phosphorus
what does the hypothalamus regulate
nervous and endocrine system
what does the adrenal gland regulate
response to emergency situations and salt balance
what does the pancreas regulate
blood glucose
what do the ovaries regulate
production of eggs and female characteristics
what does the testes regulate
production of sperm and male characteristics
what does the thymus regulate
immune system
what is the difference between nerve action and hormones
nerve action is quick and can be stopped quickly
hormone action is slower and lasts longer
what are the categories for hormone classification
Autocrine (act upon the secretory cell)
Paracrine (act on adjacent cells)
Endocrine (act on target cells at a distance)
what are autocrine hormones
hormones are released and act on the same cell that secreted them
what are paracrine hormones
act on adjacent cells, diffusing from the source to local target cell
what are endocrine hormones
travel from the source via the bloodstream to distant target cells
what are Eicosanoids
fatty acid derivatives
what is hydrophilic
proteins, peptide hormones and catecholamines and act through a second messenger system
what is lipophilic
steroids and thyroid hormones and activate genes on binding with receptors in the nucleus
what the structure of peptide hormones
Structure of one of the smallest peptide hormones – the tripeptide messenger thyrotropin releasing hormone (TRH).
The N-terminal glutamine is cyclized to pyro-glutamic acid, there is an amide on the C-terminus.
what are synthesised protein precursors known as
preprohormones
what is the prohormone is processed into
the active hormone and packaged into secretory vesicles.
Includes insulin and glucagon in this class.
what occurs in insulin biosynthesis
- preprohormone processing to the active form.
- The Preproinsulin is synthesised as a random coil on membrane associated ribosomes
- Disulphide bond formation occurs
- Connecting sequence (C-peptide) is cleaved out to leave the mature insulin molecule
where DOES INSULIN comes from
Insulin is produced in the beta-cells
of the islets of Langerhans in the
pancreas
where does insulin act
the liver, muscle and fat tissue
what does insulin do
causes cells to take up glucose from the blood, storing it in liver and muscle. Increases fat storage. It is an anabolic hormone.
what condition is associated with issues with insulin
diabetes
how does insulin effect carbohydrate metabolism
- Increases glucose uptake across cell membranes
- Increases rate of glycolysis in muscle + adipose tissue.
- Increases glycogen synthesis in muscle, adipose & liver.
- Decreases rate of glycogen breakdown in muscle & liver.
- Increases glucose oxidation in “Pentose Phosphate Pathway” in liver & adipose tissue.
what are feedback mechanisms
they give rapid information on the systems being regulated
what is direct negative feedback
where rate of hormone production/secretion is related to the blood concentration of metabolite e.g. insulin and blood glucose control.
Negative feedback means that when enough hormone is in the body, the body stops producing the hormone until it is needed again
what is the effect of insulin on lipid metabolism
- Inhibits rate of lipolysis (lipid breakdown) in adipose tissue
- Stimulates fatty acid (FA) and triacylglycerol
(TG) synthesis in adipose tissue & liver. - May decrease rate of FA oxidation in liver.
what is the effect of insulin on protein metabolism
- Increases transport of some amino acids
(aa’s) into muscle, adipose, liver & other cells. - Increases protein synthesis in muscle,
adipose & liver cells. - Decreases rate of protein breakdown in
muscle.
what does insulin encourage
protein synthesis
what is positive nitrogen balance in normal subjects called
anabolic hormone
what is the secretion of insulin stimulated by
amino acids, glucagon, GIT hormones and hyperglycaemia
what is the secretion of insulin inhibited by
adrenaline and fasting
what is the secretion of glucagon stimulated by
amino acids, fasting, hypoglycaemia
what is the secretion of glucagon inhibited by
insulin
what are steroid hormones
Steroid hormones are extracellular messengers derived from the gonads (ovary or testis), the adrenal cortex and the placenta in pregnancy.
They are not stored for release after synthesis.
Five major categories – progestins, glucocorticoids,
mineralocorticoids, androgens and estrogens.
what occurs in steroid hormone synthesis
Cholesterol is converted first to pregnenolone by a 2 step process in the liver.
Pregnenolone is converted to progesterone by oxidation
when and where is cortisol is synthesised
it is synthesised in the adrenal cortex in response to signals from adrenocorticotropic hormone (ACTH)
when and where is cortisol is synthesised
it is synthesised in the adrenal cortex in response to signals from adrenocorticotropic hormone (ACTH)
what is cortisol
it is called the “fight or flight hormone” and is involved in response to stress and anxiety. It comes from the cortex and outer part of the adrenal gland and acts in multiple tissues
What are the two groups of hormones derived
from the amino acid tyrosine
- thyroid hormones (T4- thyroxine and T3- triiodothyronine)
- catecholamines
How are thyroid hormones made
by modifying tyrosine residues in the protein thyroglobulin.
How do thyroid hormones effect metabolism
- give a general increase in metabolism of carbs, fats and proteins
- increase oxygen consumption directly in heart, kidney and liver
how do thyroid hormones effect growth and development
help skeletal bone development and growth and maturation of CNS
What is thyroxine
it comes from the thyroid gland and acts in most cells of the body and controls the rate of metabolic processes
what is hypothyroidism
People may not produce enough thyroxine
what are amino acid derivatives known as
catecholamines
what are catecholamines
they are produced in the adrenal medulla and the most common are adrenaline and noradrenaline
how are catecholamines involved in the fight or flight response
they effect the heart by increasing heart rate and the force of contrition
they convert glycogen = glucose
they convert stored fat = free fatty acid
what is adrenaline
it comes from the Adrenal Gland and acts in the heart, blood vessels, eyes. It stimulates heart rate, increases blood pressure, dilates pupils and is released in high stress conditions or in excitement or fear. e.g loud noise can trigger its release
what processes does adrenaline increase
increase muscle and hepatic glycogenolysis, increase hepatic gluconeogenesis + glycolysis, increase lipolysis,
Increased glucagon and decreased insulin secretion
what are eicosanoids
a special class of hormones that act like hormones but are distinctive in their extreme metabolic lability.
Act primarily on cells close to those that secreted them
what do prostaglandins do
they stimulate the smooth muscle, regulate steroid biosynthesis, inhibit and stimulate platelet aggregation and give sensitisation to pain
where do hormones travel through
the blood
what can hormones influence
they only influence cells that have specific target receptors for the particular hormone
what are membrane receptors
they are embedded in the cell membrane and are often are G-protein coupled receptors with 7- transmembrane domains and respond to neurotransmitters, peptides and proteins.
what are intracellular receptors
they are in the cytoplasm or the nucleus and respond to steroids and thyroid hormones
what are the 2 hormone modes of action
- the use second messengers
- direct action on the activation of specific genes
what is involved in the use of second messengers
cAMP is a second messenger that mediates a cell-specific response.
An enzyme called phosphodiesterase breaks down cAMP, stops the signal.
what is involved in the use of second messengers
cAMP is a second messenger that mediates a cell-specific response.
An enzyme called phosphodiesterase breaks down cAMP, stops the signal.
what is involved in the direct action on the activation of specific genes
The hormone crosses the plasma membrane and
binds to specific receptor proteins in the cytoplasm. The receptor then moves to the nucleus where it interacts with
specific DNA sequences called hormone
responsive elements (HREs).
how can hormones be removed from the bloodstream after achieving the desired effect
it can be removed at target tissue, secreted to bile and excreted in the faeces, can enter the bloodstream and excreted by the kidneys. The kidneys can inactivate hormones and excrete amino acids directly into the urine
can steroid hormones be eliminated
they lack the ability to completely degrade
