Endocrine system Flashcards
What is the endocrine system? function
This is a network of glands that produce and release hormones
They help control important body functions
Along with the bodies ability to change calories into energy it also influences other things such as:
Bone growth
Heart beat
Tissue growth
Fertility
Development of disease and a host of hormone-related disorders
The endocrine feedback system
This helps to control the balance of hormones within the bloodstream
The feedback system will detect when there is too much or too little of a certain hormone and signal to the correct gland to solve the problem
If the feedback system has difficulty correcting the hormone balance this is known as a hormone imbalance
Whats exocrine gland?
Secretes substances
Released through ducts
Secreted outside of the body or into the GI tract
Whats endocrine gland?
Releases hormones
Ductless glands
Directly released into the bloodstream
A hormone imbalance can be caused by what?
A hormone imbalance can be caused by a number of reasons:
A problem with the feedback system
Disease
Genetic disorder
Infection
Injury
Tumor
Failure of a gland to stimulate another gland
Most tumors or nodules are noncancerous, usually do not spread,
A tumor or nodule may interfere with the gland’s hormone production.
What is a hormone?
-Chemical signals released into the bloodstream
-Transported to target tissues
-Coordinate the activity of the cell
-Effective in small amounts
this will vary depending on the physiological change that has been detected, which hormone it is and which organ will be activated to respond to this change.
Hormone classification water soluble (hydrophilic) - peptides/amines overview
Polypeptide or protein chains, or amines
Manufactured on rough endoplasmic reticulum before packaging into golgi bodies prior to release – BULK TRANSPORT
Often secreted as pro-hormones
Examples EPO, ACTH, FSH
Water-soluble hormones (all amino acid-based hormones except thyroid hormone) exert their effects through an intracellular second messenger that is activated when a hormone binds to a membrane receptor.
Hormone-Target Interaction - Individual hormones only affect certain target cells, receptor molecules are present on specific organs
Hormone classification lipid soluble (lipophilic) - steroids overview
Principally derived from steroids
Could be cholesterol based
Penetrate through the cell membrane
Examples testosterone, oestrogen, cortisone
Passive transport
Chemical Classification Of Hormones:
Peptide and Protein:
Peptide and protein hormones are short and long chains of amino acids respectively
Majority of peptide hormones are secreted by: Hypothalamus, Anterior and posterior pituitary, Pancreas
Amines:
Derived from tyrosine, Hormones secreted by: Thyroid gland, Adrenal medulla (catecholamines- adrenalin & noradrenalin)
Steroids Natural lipids derived from cholesterol, Hormones of adrenal cortex, gonads and most placental hormones
Synthesis, Storage, Secretion
Peptide Hormones
Synthesized using the classical protein synthesis pathways, Synthesized as inactive prohormones which are finally activated to the active hormone
Golgi complex concentrates final product into vesicles stored in the cytoplasm, Upon the correct stimulus, vesicle fuse with the plasma membrane and release their contents by exocytosis
Steroid Hormones
Most material derived from LDL, Requires series of enzymatic reactions. Steroid hormones are “NOT STORED” after formation. Once synthesized, they diffuse through plasma membrane and enter blood. Only cholesterol (steroid hormone precursor) is stored within cells Therefore, rate of secretion of steroid hormones is controlled by rate of steroid hormone synthesis. Steroid hormones can be modified once released into the blood into a more potent form
Transport
Peptide hormones are simply dissolved in the blood, Steroid hormones reversibly bound to plasma proteins e.g. Albumin binds any hormone, However, some plasma proteins only bind specific hormones (e.g. testosterone binding protein), Only unbound version of steroid hormone is biologically active, Once the hormone has interacted with its target, it is rapidly inactivated, Chemical properties of a hormone dictate method of artificial administration, e.g. Steroid hormones cannot be destroyed by digestive enzymes, therefore administered orally
Intracellular Actions of Hormones
See Pre slides for Endocrine for this information.
Chemical Classification Of Hormones:
Peptide and Protein:
Peptide and protein hormones are short and long chains of amino acids respectively
Majority of peptide hormones are secreted by: Hypothalamus, Anterior and posterior pituitary, Pancreas
Amines:
Derived from tyrosine, Hormones secreted by: Thyroid gland, Adrenal medulla (catecholamines- adrenalin & noradrenalin)
Steroids Natural lipids derived from cholesterol, Hormones of adrenal cortex, gonads and most placental hormones
Synthesis, Storage, Secretion
Peptide Hormones
Synthesized using the classical protein synthesis pathways, Synthesized as inactive prohormones which are finally activated to the active hormone
Golgi complex concentrates final product into vesicles stored in the cytoplasm, Upon the correct stimulus, vesicle fuse with the plasma membrane and release their contents by exocytosis
Steroid Hormones
Most material derived from LDL, Requires series of enzymatic reactions. Steroid hormones are “NOT STORED” after formation. Once synthesized, they diffuse through plasma membrane and enter blood. Only cholesterol (steroid hormone precursor) is stored within cells Therefore, rate of secretion of steroid hormones is controlled by rate of steroid hormone synthesis. Steroid hormones can be modified once released into the blood into a more potent form
Transport
Peptide hormones are simply dissolved in the blood, Steroid hormones reversibly bound to plasma proteins e.g. Albumin binds any hormone, However, some plasma proteins only bind specific hormones (e.g. testosterone binding protein), Only unbound version of steroid hormone is biologically active, Once the hormone has interacted with its target, it is rapidly inactivated, Chemical properties of a hormone dictate method of artificial administration, e.g. Steroid hormones cannot be destroyed by digestive enzymes, therefore administered orally
Intracellular Actions of Hormones
See Pre slides for Endocrine for this information.
Examples of Endo? and structure
Thymus thyroid pancreas adrenals
Ductless
Vascularity
intracellular vacuoles or granules that store their hormones.
Examples of exo? and structure
salivary glands, sweat glands and glands within the gastrointestinal tract.
Exocrine Glands
less vascular and
have ducts or a hollow lumen
Pituitary gland is the control centre – controls several other glands
Hypothalamus collects information and secretes hormones – hypothalamus + pituitary gland work together = hypothalamic-pituitary axis
Back to the abdomen!
Hypothalamus overview
Situated in the brain
A collecting centre for information
Regulation of hormone secretion
Forms part of the hypothalamic-pituitary axis
The hypothalamus is the master of the endocrine system.
It is situated in the brain at the base of the optic chiasm (posterior to the orbits, where the optic nerves partially cross)
It acts as a collecting centre for information about with the internal environment of the body and uses much of this information to regulate the secretion of the hormones produced by the pituitary gland.
And you can see the hypothalamus is actually attached to the pituitary gland via a stalk-like structure.
With the pituitary gland it forms part of the hypothalamic-pituitary axis – which we will briefly look at in a minute
Pituitary gland overview
‘Master’ gland
Also known as the hypophysis
Pea-sized structure made up of 2 lobes
Situated in a bony hollow beneath the base of the brain
It releases hormones produced by the hypothalamus which either inhibit or stimulate other organs to release their hormones.
The gland consists of two parts (often called lobes), each of which has different functions which you can look into if you wish.
It is usually about the size of a pea and is situated in a bony hollow beneath the base of the brain. This bony hollow is called the sella turcica or the pituitary fossa.
Pituitary fossa & Sella turcica, what is it on x-rays
This is an important feature for radiographers – we check there is no rotation of this on lateral skull x-rays and on a lateral cervical spine x-ray also. This can be enlarged or eroded which may indicate certain pathologies.
Adrenal glands: where are they what hormone do they release
Adrenal glands: two glands that are positioned on top of the kidneys and release the hormone cortisol, also adrenalin and noradrenalin
Ovaries: what hormones, function
Ovaries: release eggs and produce sex hormones
Islet cells in the pancreas: function
Islet cells in the pancreas: control the release of insulin and glucagon
Parathyroid gland: where are they and their role
Parathyroid gland: 4 glands in the neck that play a role in the development of bone
Pineal gland: where is it and hormone
Pineal gland: near the center of the brain linked to sleep patterns releases Melatonin during low light
Testes, what hormones and function
Testes: produce sperm and sex hormones
Thymus gland: where is it and function
Thymus gland: in the upper chest and develops the immune system early in life releases thymosin
Thyroid gland: where is it and function
Thyroid gland: the butterfly shaped gland found in the front of the neck and this controls metabolism, releases two hormones Tri-iodothyronine (T3) and Thyroxin (T4)
What does insulin do?
What does insulin do?
cells of the pancreas secrete insulin when blood glucose levels rise above 6 mmol/litre
Promotes entry of glucose into target cells (liver cells, adipose cells, muscle cells)
Promotes conversion of glucose to glycogen in the liver
Promotes fat storage
Glycogen is a stored form of glucose. It is a large multi-branched polymer of glucose which is accumulated in response to insulin and broken down into glucose in response to glucagon.
Glycogen is mainly stored in the liver and the muscles and provides the body with a readily available source of energy if blood glucose levels decrease.
