BIOM 3200 Chapter Notes - Chapter 3: Luteinizing Hormone, Enzyme Inhibitor, Pineal Gland
19 Dec 2016
School
Department
Course
Professor
ENDOCRINE!
Homeostasis and Feedback Control!
Homeostasis: a state of relative consistency of the internal environment maintained by •
feedback loops!
Changes in the body are monitored by sensors which send information to an ◦
integrating centre, allowing the integrating centre to deter changes from a set point
Integrating Centre: particular region of the brain or spinal cord, but it can also be a ◦
group of cells in the endocrine gland. Can receive informations from a variety of
sensors!
Effectors are generally muscles of glands that increase or decrease in action in ◦
order to counteract the deviations from the set point and defend homeostasis. Can
be thought of as "defending" the set points against deviations!
Negative Feedback Loop: when the activity of the effectors is influenced by the effects •
they produce, and because this regulation is in a negative or reverse direction (inversely
related)!
Continuous and ongoing, never static - hormones are always circulating, they just ◦
differ in concentration depending on the information the sensors provide !
Changes from the normal range in either direction are compensated for by reverse ◦
changes in effector activity!
Constant state of dynamic constancy in which conditions are stabilized above and ◦
below the set point (average alum within the normal range of measurement!
Antagonistic Effectors: increasing activity of an effector is accompanied by decreasing •
activity of an antagonistic effector!
Example: body temperature is maintained at 37C, by experiencing the antagonistic ◦
effects of sweating, shivering and other mechanisms!
"push-pull"!◦
Majority of effectors are antagonistic !◦
Quantitative Measurements: in order to study physiological mechanisms, scientists •
must measure specific values and mathematically determine values such as normal
range, averages and deviations from the average.!
For example - blood glucose levels and the relationship with insulin in relation to time ◦
before and after an injection.!
Positive Feedback: the action of the effectors amplifies those changes that stimulate the •
effectors !
Less common than negative feed back loops!◦
For example - blood clotting occurs as a result of sequential activation of clotting ◦
factors (positive feedback), while the completion of clotting and removal of clotting
agents is negative feedback !
When estrogen is secreted by the ovaries, stimulating the ovaries to secrete LH ◦
(Luteinizing hormone) which triggers ovulation!
Contraction of the uterus during childbirth as oxytocin secretion is increased, while ◦
leads to increased contractions !
Neural and Endocrine Regulation •
Intrinsic: or "built into" the organs being regulated (such as molecules produced in ◦
the blood vessels that cause dilation or constriction) !
Extrinsic: regulation of an organ by the nervous and endocrine system !◦
Nervous: controls the secretion of many endocrine glands and some hormones ‣
in turn affect the function of the nervous system !
Endocrine: regulating and integrating body processes and homeostasis !‣
Hormones: chemical regulators hat carry hormones to all the organs in the body!◦
Target Organs: only specific organs can respond to specific hormones !◦
Nerve fibres innervate the organs that they regulate - when stimulated these fibres ◦
produce electrochemical nerve impulses that are conducted from the origin of the
fibre to its terminals in the target organ innervated by the fibre!
Example - Blood pressure influences the activity of sensory neutrons form the blood ◦
pressure receptors (sensors); a rise in pressure increases the firing rate, and a fall in
pressure decreases the firing rate of nerve impulses, when a person stands up from
a lying down position, the blood pressure momentarily falls. The resulting decreased
firing rate of the heart (effector) to increase the heart rate, helping to raise the blood
pressure (negative feedback loop)!
Feedback Control of Hormone Secretion •
Hormones are secreted in response to specific chemical stimuli !◦
A rise in plasma glucose levels stimulates insulin secretion from structures in the ‣
pancreas known as the pancreatic islets!
The secretion of a hormone can be inhibited by its own effects, in a negative ◦
feedback manner!
A rise in blood pressure causes a secretion of insulin, while a lowering of blood ‣
glucose caused by insulins actions inhibits further insulin secretion !
This is known as negative feedback inhibition ‣
Blood glucose is extremely important therefore there are multiple antagonistic agents ◦
used to keep it within homeostatic range: insulin secretion to decrease tissues from
taking too much glucose form the blood, glucagon (antagonistic to insulin) stimulates
the process of the liver to break down glycogen in order to produce more glucose!
!
Endocrine Glands and Hormones!
Endocrine Glands: lack ducts that are present in exocrine glands, secrete hormones into •
the blood that is carried to target cells that contain specific receptor proteins !
Pancreas functions as both an exocrine and endocrine system !◦
Neurohormone: specialized hormones in the hypothalamus secrete chemical ◦
messengers into the blood rather than into a narrow synaptic cleft!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
Chemical Classification of Hormones •
1. Amines: derived from tyrosine and tryptophan, include hormones secreted by the ◦
adrenal medulla, thyroid and pineal glands!
2. Polypeptides and Proteins: if a polypeptide chain is larger than 100 AA it can be ◦
called a protein, antidiuretic hormone is only 8AA is too small to be a protein, insulin
blurs the line because it is composed of two polypeptide chains derived from a
single, larger molecule!
3. Glycoproteins: protein bound to one or more carbohydrate groups. Examples are ◦
follicle stimulating hormone (FSH) and Luteinizing hormone (LH)!
4. Steroids: derived from cholesterol after an enzyme cleaves off the side chain ◦
attached to the five carbon D ring. Includes testosterone, estradiol, progesterone and
cortisol!
Note: progesterone is a common precursor of all other steroid hormones and ‣
that testosterone is a precursor of estradiol-17B, the major estrogen secreted by
the follicles of the ovaries!
Lipophilic Hormones: non polar ◦
hormones that are soluable in lipids!
Cannot pass through plasma ‣
membranes!
Include steroid hormones and ‣
thyroid hormones !
Steroid hormones are secreted by 2 ◦
endocrine glands: adrenal (secretes
corticosteroids - cortisol and aldosterone
& small amounts of sex steroids) and
gonads (secrete sex steroids)!
Thyroid hormones are composed of 2 ◦
derivatives of the AA tyrosine bonded
together.!
T3 and T4 are steroid like (small, ‣
non polar)!
Polar water soluble hormones include polypeptides, glycoproteins, and the ◦
catecholamine hormones secreted by the adrenal medulla, epinephrine and
norepinephrine !
Catecholamines are too polar to pass through the phospholipid portion of the ‣
plasma membrane!
Melatonin secreted by the pineal gland is derived from tryptophan (non polar) ‣
therefore it can be effective as a pill as it can pass through the membrane !
Prohormones and Prehormones •
Prohormone: a long polypeptide that is cut and spliced to make a hormone!◦
Insulin is a product of proinsulin within the beta cells of the islets of Langerhans ‣
of the pancreae
Prehormone: the precursor of prehormones !◦
In some cases the pro hormone itself is derived from an even larger precursor ‣
molecule, for example preproinsulin
Sometimes the molecules secreted by the endocrine system is inactive in the target ◦
Document Summary
Homeostasis: a state of relative consistency of the internal environment maintained by feedback loops. Changes in the body are monitored by sensors which send information to an integrating centre, allowing the integrating centre to deter changes from a set point. Integrating centre: particular region of the brain or spinal cord, but it can also be a group of cells in the endocrine gland. Can receive informations from a variety of sensors. E ectors are generally muscles of glands that increase or decrease in action in order to counteract the deviations from the set point and defend homeostasis. Can be thought of as defending the set points against deviations. Negative feedback loop: when the activity of the e ectors is in uenced by the e ects they produce, and because this regulation is in a negative or reverse direction (inversely related)
