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54 Cards in this Set
- Front
- Back
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What is a hormone?
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a substance secreted by cells in one part of the body that passes to another part where it is effective, in very small concentrations, in regulating the growth or activity of the cells
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Hormones reach their target organ usually complexed to these.
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Plasma proteins
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Describe neurosecretion
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Neurohormones are produced by neurons and secreted at the nerve endings to be released into special capillary networks near the target organ
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Which hormones have a local effect?
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Tissue hormones include kinins, prostaglandins, angiotensin II and hormones of the GIT.
They can be autocrine signaling, which bind to the same cell that secreted the hormone, or paracrine signaling, which target tissues which are close by. |
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Most hormones fall into these two groups based on chemical structure.
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Amine-Peptide hormones [polypeptides/amino compounds]
Steroid hormones [fatty acid/cholesterol derivatives] |
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Name several steroid hormones
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Cortisol and oestradiol are cholesterol derivatives
Prostaglandin is a fatty acid derivative |
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Name several amine-peptide hormones
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Oxytocin
ADH |
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What are the three general effects a hormone can have on the target cell
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1. Change the rate of enzyme/protein synthesis
2. Change the rate of metabolic pathways 3. Changing the cell membrane permeability |
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State the two major mechanisms of hormone action and which type of hormone usually employs this mechanism.
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Activation of the cyclic-AMP system occurs with amine-peptide hormones
Activation of the genes to produce specific proteins occurs with steroid/thyroid hormones |
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Describe hormonal activation of the cyclic-AMP system
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1. Hormone targets a membrane receptor which is linked to a G protein
2. The G protein activates adenylyl cyclase which converts ATP to cyclic-AMP 3. Cyclic-AMP activates specific protein kinases 4. Kinases will phosphorylate proteins thereby affecting the cell's metabolism, membrane or gene activity |
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Describe the hormonal mechanism of gene activation via a receptor protein.
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1. A lipid soluble hormone passes freely into the cell where a it complexes to a protein receptor in the cytoplasm or karyoplasm.
2. The complexed hormone acts as a transcription factor which activates/represses mRNA transcription. Note that this mechanism takes between 45 minutes to several hours. |
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Structure which connects the pituitary to the hypothalamus
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Infundibular stalk
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The pituitary is embryologically derived from two origins. Name them.
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Infundibulum - a downgrowth of the hypothalamus
Adenohypophysis - an inpushing of the mouth ectoderm called Rathke's pouch |
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As the pituitary develops, the infundibulum gives rise to an area called this.
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Neurohypophysis (posterior lobe)
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Name the two parts of the neurohypophysis
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Pars nervosa
Median eminence |
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Name the three parts of the adenohypophysis
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Pars tuberalis - surrounds the infundibular neck
Pars intermedia - adjacent to the pars nervosa Pars distalis - outermost layer making up the bulk of the anterior lobe |
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Where is the residual cleft found?
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Between the pars intermedia and the pars distalis
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How many hormones are secreted by the adenohypophysis? Name them
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7 hormones which have releasing/inhibitory factors. The releasing function is dominant except for prolactin.
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What is a trophic hormone? Name them
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Trophic hormones have another endocrine gland as the target organ.
The four are TSH, ACTH, FSH, LH |
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Describe the hypothalamic-hypophyseal portal system.
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1. The hypothalamus releases neurohormones (hypothalamic releasing/inhibitory hormones) into the median eminence.
2. Neurohormones are transfered via a special portal system to the pars distalis |
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What are the two blood supplies to the adenohypophysis and their appropriate percentages?
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85% from the hypothalamic-hypophyseal portal system
15% from the superior hypophyseal artery |
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Of the three parts of the adenohypophysis, which is the main source of trophic hormones?
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Pars distalis with its five different cell types
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What is the function of TSH?
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Also known as thyrotrophin, it stimulates growth in the size and number of thyroid follicular cells, stimulates hormonal release of the thyroid and enhances thyroid-hormone uptake by muscle cells
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What is the structure of TSH?
What is the plasma half-life? What controls its release? |
TSH is a glycoprotein with a plasma half-life of 35-55 mins.
It's release is under control of thyrotrophic releasing hormone TRH secreted by the hypothalamus |
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Where is TSH secreted from?
In what pattern is it secreted? |
TSH is secreted from the pars distalis in a pulsatile manner with a peak activity at night
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What is the function of ACTH?
Where is it secreted from? |
Secreted from the pars distalis, adrenocorticotrophic hormone targets the adrenal cortex of the adrenal gland to stimulate growth and release of adrenal cortical hormones.
It will also be secreted within seconds upon any stress to the body |
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What is the structure of ACTH?
What is the plasma half-life? What controls its release? When is it secreted? |
ACTH is a peptide with a plasma half-life of 5-10 mins.
It's release is under control of hypothalamic corticotrophin releasing hormone CRH It is secreted in a pulsatile manner with a diurnal rhythm peaking in early morning It's also secreted in response to the stress reaction |
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What is the function of FSH?
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In females, FSH stimulates growth of follicles and oestrogen secretion by follicular cells
In males, FSH stimulates growth of the germinal epithelium in the seminiferous tubules targeting the sertoli cells |
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What controls the secretion of FSH?
What is the structure and plasma half-life? |
Sex hormone levels (testosterone/oestrogen) trigger the release of hypothalamic gonadotrophin releasing hormone GRH
FSH is a glycoprotein with a plasma-halflife of 60 min. |
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What is the function of LH
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Luteinizing hormone maintains the interstitial tissue of the testes/ovaries even when the gametogenic tissue is inactive
In males, it is also known as interstitial cell stimulating hormone ICSH and stimulates the growth of the Leydig cells and the secretion of testosterone In females it causes luteinization of the ovarian follicle after ovulation to form the corpus luteum. It also controls the final step in ovulation based on oestrogen levels |
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What are the two gonadotrophins? What controls their release?
What is the structure and plasma half-life of both? |
FSH & LH secretion is controlled by hypothalamic gonadotrophin releasing hormone GRH
Both gonadotrophins are glycoproteins with plasma half-lives of 60 min. |
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What is the function of prolactin?
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In females, prolactin is responsible for milk production in the mammary gland
In males, it increases the LH receptors of the Leydig cells |
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What controls the release of prolactin?
What is unique about the feedback mechanism? |
Once the mammary gland has been primed with gonadotrophins and sex hormones of pregnancy, tactile stimulation of the nipple stimulates hypothalamic thyrotrophic releasing hormone TRH secretion which stimulates prolactin production.
Dopamine is the prolactin release inhibitory hormone and is part of a positive feedback mechanism |
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doler
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to ache, to pain, to hurt, to cause grief, to cause regret
endoloriser |
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What is the function of STH?
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Somatotrophic (growth) hormone controls the growth and metabolism of an individual
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What controls the release of STH?
What is the pattern of secretion? What is the structure and plasma half-life of STH? |
STH is under control of hypothalamic growth hormone releasing hormone GHRH. It shows diurnal variation peaking during sleep. It is a polypeptide with a plasma half-life of 30 minutes.
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How does STH control the growth of an individual?
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STH stimulates the production of somatomedins in the liver which are insulin-like growth factors I and II. These somatomedins promote growth in various tissues.
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What are several [3] disorders associated with STH?
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Dwarfing caused by lack/absence of STH in children
Giantism caused by excessive amounts in children Acromegaly caused by excessive amounts in adults |
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How does STH control the metabolism of an individual?
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Through stimulation of amino acid transport and protein synthesis.
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Name the hormone(s) secreted from the pars intermedia.
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Melanocyte stimulating hormone MSH
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What is the function of MSH?
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MSH affects the production and dispersion of melanin granules in melanocytes
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What is the structure and plasma half-life of MSH?
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MSH is a class of peptide hormones with a plasma half-life of 120 min
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The pars nervosa of the neurohypophysis is under control of this structure.
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The hypothalamic neurons extend into the pars nervosa of the posterior lobe and release neurohormones
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Hormones of the neurohypophysis are produced in the _____ and stored and secreted from the ______.
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Both hormones are produced in the supraoptic and paraventricular nuclei and stored in the pars nervosa.
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The structure and half-life of both hormones of the neurohypophysis are...
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Both are nonapeptides with plasma half-lives of 2-4 mins
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Name the two hormones of the neurohypophysis?
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Oxytocin & Antidiuretic Hormone ADH
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What is the function of oxytocin?
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Oxytocin is responsible for the ejection of milk from the mammary gland as well as the contraction of uterine smooth muscle.
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Describe the feedback system of oxytocin.
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Tactile stimulation of the nipple stimulates the hypothalamus.
The thalamus then activates oxytocin neurons in the supraoptic and paraventricular nuclei. This releases oxytocin from the pars nervosa which is carried to the mammary gland Upon reaching the mammary gland, oxytocin causes myoepithelial cells of the milk duct to contract thus ejecting milk |
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Describe the relationship between labor and oxytocin.
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Oxytocin causes contraction of uterine smooth muscle.
Synthetic oxytocin is used in induced labor though natural labor occurs without a rise in oxytocin levels |
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What is the function(s) of ADH?
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Antidiuretic hormone or vasopressin regulates the volume of body fluids (v2 receptors) and regulates blood pressure (v1 receptors).
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How does ADH regulate the volume of body fluids?
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Release of ADH causes the collecting ducts and distal convoluted tubules of the kidney to become more permeable to water.
Increased ADH decreased urine flow (antidiuresis) |
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How does ADH change the water permeability in the kidneys?
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ADH acts on v2 receptors on the basal side of the tubule epithelial cells. Activation causes aquaporin proteins to move to the apical membrane to increase water re-uptake.
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Describe the feedback mechanism of ADH.
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Increased sodium levels detected by osmoreceptors triggers the supraoptic and paraventricular nuclei. This causes a nerve impulse to travel down to the pars nervosa which releases ADH
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Discuss diabetes insipidus
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A deficiency of ADH causes a failure to reabsorb water in the kidney thus leading to diuresis.
The cause is usually pituitary or hypothalamic injury. Treatment is administration of an ADH analogue through nasal spray or injection. |
