Flashcards in Endocrinology Deck (57):
What does the endocrine system contain?
Glands that are made up secretory cells that produce hormones. These hormones will be released when a specific stimulus is detected. The glands are not anatomically connected.
Definition of hormones:
- Chemical messengers
- Produced by endocrine glands or organs
- Released into the circulation by secretory cells
- Travel in circulation to the target organ/tissue
- They will influence cellular activity (in order maintain homeostasis)
What kind of hormones are water-soluble (so can't travel across membrane directly)?
Peptide and amine hormones
What hormones are lipid-soluble (so can diffuse across the membrane directly)?
Steroid hormones and some amine hormones
How are hormones regulated in the body?
Hormones are self-regulating!
(either via positive or negative feedback systems)
Hormone is released from a cell and binds to receptors on local cells to affect this cell function
Hormone binds to the receptor on the cell that produces this hormone and affects the cell function (from where it is produced)
What is the target for water-soluble hormones (peptide hormones and some amine hormones)?
Bind to the receptors of chemical-gated channels in the membrane of cells.
What is the target for lipid-soluble hormones (steroids and some amine hormones)?
Either cytoplasm receptors or nuclear receptors
Which hormones take longer for their effects to show?
Lipid-soluble hormones that target nuclear receptors. As these hormones will affect the transcription/translation process in order to affect protein synthesis.
What are the 9 endocrine glands?
1) Pineal gland
2) Pituitary gland
3) Thyroid gland
4) Parathyroid gland
6) Adrenal glands (above kidneys)
8) Testes (male)
9) Ovaries (female)
Compare the descriptions of the endocrine glands and exocrine glands:
Endocrine glands (aka as ductless glands) as these glands do not rely of ducts to transport the hormones they secrete - instead, they will secrete their hormones straight into the bloodstream.
Exocrine glands (aka duct glands) do rely on ducts for the transportation of the hormones they release.
Compare the transportation time between endocrine and exocrine glands?
Endocrine glands - slow
Exocrine glands - fast
Compare the response time between endocrine and exocrine glands?
Endocrine glands - Lasts longer (due to it being filtered in the kidney and being reabsorbed back into the blood stream)
Exocrine glands - Lasts for a shorter time (as not released into circulation so won't go through kidney filtration in order to be absorbed again)
What allows an organ to be classed as an endocrine organ?
If it has cells that contain endocrinocytes (hormone-producing cells)
Why aren't the endocrine organs classed as endocrine glands?
Because producing/secreting hormones is not their main function
What are the names of the 8 endocrine organs?
4) Part of the GI Tract
What hormone does the heart release and what is this hormones function?
The atrial myocytes release ANP when the baroreceptors in the atrial arch detect a high blood pressure. ANP acts on the kidney to affect the GFR, so that more sodium is excreted into the urine and water will follow. This lowers the blood pressure.
What hormone does the liver release and what is this hormones function?
Erythropoietin - stimulates the development of red blood cells from red bone marrow
What hormone does the stomach release and what is this hormones function?
In the gastric pit, enteroendocrine cells release Gastrin. Gastrin is responsible for stimulating the secretion of the gastric juice (both from the parietal and chief cells of the gastric pit).
What hormone do parts of the GI tract release and what is this hormone's function?
Motilin - stimulates the smooth muscle (inside the muscularis externa layer of the GI tract wall) in order to contract (for peristalsis)
What hormone does the duodenum release and what is this hormone's function?
Secretin - released when there is a low blood pH (stimulates the duct cells to release bicarbonate ions in order to increase the pH of the bolus)
CCK - released when fats and protein enter the duodenum (stimulates bile to enter the duodenum from the gall bladder)
What hormone doe the kidneys release and what is this hormone's function?
Renin (released when the blood pressure is low). Renin stimulates the adrenal glands to secrete aldosterone. Aldosterone targets the kidney to reabsorb sodum. Water follows and the blood pressure increases.
What hormone does the skin release and what is this hormone's function?
Calciol (inactive form of Vitamin D) and calcitriol (active form of Vitamin D). Calcitriol increases the calcium concentrations in the blood plasma.
What hormone does adipose tissue release and what is this hormone's function?
Leptin - stimulates the hypothalamus to suppress appetitie
What is the relationship between the hypothalamus and pituitary gland?
They act as a unit in order to regulate other endocrine glands. The hypothalamus will either stimulate or inhibit the release of hormones from the pituitary gland
Where is the pituitary gland situated?
In the hypophyseal fossa of the sphenoid bone.
How is the hypothalamus connected to the anterior pituitary gland?
By blood vessels. The blood vessels near the secretory cells in the anterior pituitary gland originate from the capillary network in the hypothalamus.
How do the hypothalamus and anterior pituitary gland work together to control hormone levels in the blood?
(through negative feedback systems)
1) The hypothalamus will detect a low concentration of a hormone in the network of blood cappillaries, surrounding the hypothalamus.
2) The hypothalamus releases a RELEASING hormone.
3) This hormone will travel in the blood vessels to reach the secretory cells of the anterior pituitary gland.
4) The releasing hormones stimulate the anterior pituatary gland to release a TROPHIC HORMONE.
5) The trophic hormone travels in the blood to its target organ/tissue.
6) The trophic hormone will stimulate this organ/tissue to release a hormone.
7) This hormone inhibits further releasing hormones to be released from the hypothalamus.
How is the hypothalamus connected to the posterior pituitary gland?
The cell bodies of the neurones present in the posterior pituitary gland will be situated either in:
1) The hypoventricular nucleus
2) The supraoptic nucleus.
The axon will then enter the posterior pituitary gland.
The bundle of axons in the posterior pituitary gland is called: HYPOTHALAMO - HYPOPHYSEAL TRACT
Which part of the pituitary gland directly controls the release of hormones from the endocrine organs? (e.g. hear, liver etc.)
The posterior pituitary gland
Where is the thyroid gland situated?
In front of the trachea. It is shaped in two lobes (one each side of the trachea). The two lobes of the thyroid gland are connected by ISTHMUS.
How many parathyroid glands for humans have?
Where are the parathyroid glands situated?
On the posterior side of the thyroid gland (within the gland)
What are the 2 types of cells in the thyroid gland?
1) Parafollicular cells
2) Follicular cells
What is the function of the parafollicular cells in the thyroid gland?
- They contain colloid
- Hormones produced by the thyroid gland are produced as THYROGLOBULIN 1st and then converted to the thyroid hormones (as they stay within the colloid of parafollicular cells)
What is the function of the follicular cells in the thyroid gland?
To secrete CALCITONIN
What type of hormones are the thyroid hormones?
What substance is required for the synthesis of thyroid hormones?
What are the 3 main sources of iodine?
1) Sea food
2) Vegetables (grown from iodine rich soil)
3) Table Salt
What are the 2 types of thyroid hormones and their description?
T3 - TRIIODOTHYRONINE (3 iodine ions) - 10% of the thyroid gland secretions
T4 - THYROXINE (4 iodine ions) - 90% of the thyroid gland secretions
What happens to thyroxine (T4) when it reaches its target cell?
It converts to T3.
Describe the regulation of the Thyroid Hormones:
(via a negative feedback mechanism)
1) 5 Stimulus: Exercise, Sleep, Stress, Malnutrition and low blood glucose level.
2) Hypothalamus releases THYROID RELEASING HORMONE.
3) This acts on the ANTERIOR PITUITARY GLAND to release THYROID STIMULATING HORMONES.
4) This acts on the thyroid gland - and the THYROGLOBULIN (contained within the colloid of parafollicular cells) converts to T3 and T4.
5) T3 and T4 act on the target organ.
6) T3 and T4 effects:
- Increases metabolic rate and heat production
- Regulates the metabolism of : Fat, Carbs and proteins
What causes goitre formation during hyperthyroidism?
Hyperthyroidism is caused by an autoimmune response. Whereby antibodies mimic TSH and so the thyroid gland is stimulated. Thyroglobulin is converted to T3 and T4. This causes the thyroid gland to grow.
What causes goitre formation during hypothyroidism?
Hypothyroidism is caused by an iodine deficiency. Therefore, T3 and T4 can't be synthesised. However, as there are low T3 and T4 in the blood - the hypothalamus will secrete TRH, which in turn causes the anterior pituitary gland to release TSH. The TSH stimulates the production of T3 and T4. The thyroid gland is stimulated, even though the hormones can't be produced. This causes the thyroid gland to grow.
What hormone is responsible for decreasing calcium plasma levels?
Calcitonin (secreted from the c-cells/follicular cells of the thyroid gland).
What are the 2 mechanisms for calcitonin in decreasing calcium plasma levels?
1) Inhibits OSTEOBLASTS (cells which break down bone in order for calcium to be released)
2) Inhibits the reabsorption of calcium into the blood steam at the kidney tubules - and so instead it is lost in the urine.
What hormone is responsible for increasing calcium plasma levels?
Parathyroid hormone (secreted from the 4 parathyroid glands)
What are the 3 mechanisms for calcitonin in decreasing calcium plasma levels?
1) Stimulates OSTEOBLASTS (cells which break down bone in order for calcium to be released)
2) Stimulates the reabsorption of calcium into the blood steam at the kidney tubules, so less is lost in the urine and more is taken up into the blood.
3) Stimulates the absorption of calcium into the circuation from the small intestine.
What substances are secreted from the adrenal medulla and adrenal cortex?
Adrenal Medulla - Adrenalin
Adrenal Cortex - Glucocorticoids (Cortisol, Cortisone, Corticosterone) Mineralcorticoids (e.g. Aldosterone) and sex hormones (mainly androgens - male hormones)
How does the nervous and endocrine system work together in order to respond to stress?
Sympathetic post-ganglionic neurones will release noradrenalin. Noradrenalin binds to the chemical-gated receptors in the adrenal medulla. The adrenal medulla releases adrenalin.
What are the main responses of adrenaline?
1) Increases heart rate
2) Increases blood pressure
3) Increases metabolic rate
4) Vasoconstriction of blood vessels supplying less vital organs (in order for more blood to be directed to more vital organs)
5) Dilates pupils
What stimulates the release of Glucocorticoids and Mineralcorticoids from the adrenal cortex?
1) The hypothalamus is stimulated by stress.
2) Hypothalamus release CRH (CORTICO-TROPHIN RELEASING HORMONE).
3) CRH acts on the anterior pituitary gland.
4) The anterior pituitary gland releases ACTH (ADRENOCORTICO-THROPHIN HORMONE).
5) ACTH acts on the adrenal medulla to release gluccocorticoids and mineralcorticoids.
What are the effects of mineralcorticoids?
(e.g. aldosterone) Increase the sodium reabsorbtion into the blood stream. Water follows. Increases blood pressure.
What are the 5 effects of gluccorticoids?
(cortisoil, cortisone, corticosterone)
1) Stimulates Gluconeogenesis - to increase glucose plasma levels
2) Stimulates lipolysis - to increase the breakdown of triglycerides (3 fatty acids and 1 glycerol)
3) Stimulates the breakdown of proteins into amino acids - in order to synthesise new proteins
4) Stimulates sodium to be reabsorbed in the kidneys - to increase sodium plasma levels.
5) Supresses the immune system.
What is the other stimulus for the release of gluccorticoids (other than stress)?
Circadian variations = any biological processes that have an oscilliation of 24 hours