WEEK 2 :ENDOCRINE SYSTEM AND HOMEOSTASIS Flashcards
What is endocrinology?
Endocrinology is the study of hormones and endocrine glands and organs
State the functions of the endocrine system.
*Regulate organic metabolism and H2O and electrolyte balance
*Induce adaptive changes to help body cope with stressful situations.
*Promote smooth, sequential growth and development
*Control reproduction
*Regulate red blood cell production.
*Along with autonomic nervous system, they control and integrate both circulation and the digestion and absorption of food.
What is a hormone?
A hormone is a chemical messenger that travels from one endocrine gland or organ in your body to another part of your body through your blood
What are tropic hormones?
Tropic hormones are a group of hormones that stimulate other endocrine glands to produce their particular hormones.
They are all produced from the anterior pituitary gland.
Examples of tropic hormones
GH, TSH, LH, ACTH, FSH, MSH
Describe the relation between the hypothalamus and the pituitary gland.
*The hypothalamus is a structure found in the diencephalon of the brain.
*Hypothalamus has both neural and endocrine functions.
*It is connected to the pituitary gland by the infundibulum
State the two tracts that the hypothalamus use to communicate with the anterior and posterior pituitary gland respectively.
1.Hypothalamic hypophyseal portal tract
2.Hypothalamohypophyseal tract.
What are the functions of the hypothalamo-hypophyseal tract?
i) transports oxytocin and ADH to the neurohypophysis
ii) it also allows hypothalamus hormones to go directly into the pituitary without first entering the systemic circulation.
What are hypophysiotropic hormones?
*Acting on or stimulating the hypophysis
*Are hormones produced by the endocrine cells in the hypothalamus. They are released to the corresponding capillary bed—the median eminence—and transported directly to the anterior pituitary via the hypophyseal portal vessels.
*They regulate the release of hormones from the Adenohypophysis by either INHIBITING or RELEASING.
State the 7 hypophysiotropic hormones
*GHIH (Somatostatin)
*GHRH
*Prolactin inhibiting hormone (Dopamine)
*Prolacting releasing hormone
*Thyrotropin releasing hormone
*Corticotropin releasing hormone
*Gonadotropin releasing hormone
2for GH, 2 for Prolactin
corticotropin, gonadotropin and thyrotropin are all releasing hormones
Name the hormone that is also known as somatostatin
GHIH
Growth hormone inhibiting hormone
Name the hormone that is also known as dopamine
Prolactin inhibiting hormone
Describe ways of controlling hormone secretion
*Negative feedback
*neuroendocrine reflexes; using nervous system regulation
e.g epinephrine secretion is controlled by sympathetic stimulation
*Circadian rythmn
Outline the 3 components of the hormone hierarchy of command
*Hypophysiotropic hormones
*Anterior Pituitary hormones
*Target cell hormone
What influences the secretion of hypophysiotropic hormones?
*Stress
*Mood
*Chemical substances that reach the brain
What are the factors that influence the plasma concentration of a hormone?
*hormone secretion
*Rate of reaction
*mode of transport
*Excretion
State the causes of hyposecretion by an endocrine gland
*immunity
*diet
*toxic chemicals
*Genetic
*Diseases
*Iatrogenic (physician induced)
*Reason not known
What are the likely causes of hypersecretion by an endocrine gland?
*Tumor
*substance abuse
*immunologic factors ( TSI in hyperthyroidism)
State the main two types of hormones
hydrophilic and lipophilic
Differentiate between hydrophilic and lipophilic hormones.
H:dissolve in blood for transport
L:Transported bound to plasma proteins
H:They act via second messenger pathway.They alter the activity of pre-existing protein (enzymes) within the target cell to produce their physiological response
L: They activate genes on binding with receptors inside the cell thus bringing about information of new proteins in the target cell that carry out the desired response
State the types of hydrophilic hormones
*Peptide hormones: made of chains of amino acids
e.g insulin, glucagon, parathyroid hormone
from the adrenal medulla
INDOLEAMINES: Derived from amino `````acids tryptophan
e.g melatonin (from the pineal gland)
State the types of lipophilic hormones
STEROID HORMONES; Derived from cholestrol
From adrenal cortex and the reproductive endocrine glands
THYROID HORMONES: Derived from the iodinated deriavatives of tyrosine.
T3 and T4
from the thyroid gland
Name the hormone released by the pineal gland.
melatonin
What are the functions of melatonin?
keeping the body’ s circadian rhythms in general synchrony with the light dark cycle
What is a target cell?
A cell that has receptors for the hormone released
What happens if the internal environment is not synchronized with the external environment (light-dark cycle)?
Experiences a jet lag: A temporary sleep disorder usually caused by travelling in different time zones
How does melatonin keep the body’s circadian rhythms in synchrony with the light-dark cycle?
Melanopsin, a protein found in the special type of retinal ganglion cell is a light receptor molecule that keeps the body in tune with external time.
The majority of the retinal ganglion cells receive input from the rod and cone photoreceptors.
The axons of theses ganglion cells form optic nerve that carries information to the visual cortex in the occipital lobe.
The melanopsin-containing, illuminating -detecting retinal ganglion cells cue the pineal gland about the presence or absence of light by sending their signals along the retino-hypothalamic tract. to the SCN. The SCN relays the messages regarding light status to the pineal gland.
NOTE:
*Melatonin is a dark hormone. it’s release increases 10-fold during darkness and then falls to low levels during the day.
*These fluctuations in melatonin secretion in turn help maintain the body’s biological rhythms with the external light-dark cycle.
What can cause abnormal cell responsiveness?
*lack of receptors
*competitive inhibitors
State the other functions of melatonin apart from keeping the biological clock synchronized with the external environment.
*Promotes sleep
*Inhibits hormones that promote reproductive activity
* is an effective antioxidant , a defense tool against free radicals biological damaging
Enhances immunity , reverse some of the age related shrinkage of the thymus
Name the master biological clock that serves as the pacemaker for body circadian rhythms.
Suprachiasmatic nucleus (SCN)
How does the SCN synchronize the circadian rhythms with the environmental cues?
The SCN resets daily to ensure that biological rhythms are synchronized with the activity levels driven by the surrounding environment. It works with the pineal gland and its hormonal product melatonin to synchronize the various circadian rhythms with the 24-hr. day-night cycle.
It has clock proteins.
Name the anatomical positions of the 2 clusters of nerve cell bodies of the suprachiasmatic nucleus.
in the hypothalamus above the optic chiasm
at a point where the nerve fibers from the eye cross the opposite half of the brain
State the 2 main causes of endocrine disorders
hyposecretion
hypersecretion
abnormal target cell responsiveness
What are the functions of the clock proteins?
Produced by genes within the nucleus of SCN neurons in the cytosol surrounding the nucleus. Upon accumulation, they will fill up the SCN and block it inhibiting their own production. After being used up by the SCN the cycle repeats itself. Each cycle takes about a day.
- The fluctuating levels of clock proteins bring about cyclic changes in neural output from the SCN, that in return leading to cyclic changes in effector organs throughout the day
What is primary hypersecretion?
Too much hormone is secreted due to abnormality within the gland
What is secondary hypersecretion?
Excessive stimulation from outside the gland causes oversecretion
What is primary hyposecretion?
Too little hormone is secreted due to abnormality within the gland
What is secondary hyposecretion?
Gland is normal but too little hormone is secreted due to deficiency of it’s tropic hormone
State the 2 types of receptors found in the surface of the target cells
*Receptors for water soluble hormones ( hydrophilic)
*Receptors for lipid soluble hormones
Which receptors are found in the surface of target cells on the plasma membrane?
receptors for water soluble hormones
Which receptors are found in the nucleus of target cells?
receptors for lipid soluble hormones
WHY?
Because they can diffuse through the lipid bilayer of plasma membrane
Define down-regulation and up-regulation
Down-regulation: decrease in the number of receptors which decreases the sensitivity to that hormone
Up-regulation: the increase in the number of receptors which cause the cell to be sensitive to a particular hormone
How are hormones classified?
Chemical nature: peptides, amines, steroid, protein, glycoprotein, eicosanoids
mechanism of action: lipophilic, hydrophilic
* effects: reproductive hormones
*stimulation of other endocrine glands: tropic, non tropic
