Chapter 5: The Endocrine System Flashcards
1
Q
What is the endocrine system?
A
a system made up of glands which release hormones into the bloodstream, which relay chemical messages throughout the body to regulate behaviour and physiology
2
Q
What are hormones?
A
- signalling molecules that are secreted directly into the bloodstream and travel to a distant target tissue
- the hormones bind to receptors on the target tissue to induce a change in gene expression or cellular functioning
3
Q
Hormones can be classified by chemical structure as: (3)
A
- peptides
- steroids
- amino acid derivatives
4
Q
Explain 6 features of peptide hormones.
A
- composed of amino acids; derived from larger precursor proteins that are cleaved during post translational modification
- polar; cannot pass through the cell membrane
- they are first messengers which bind to extracellular receptors to trigger a second messenger
- each step of the signalling cascade can demonstrate amplification of the signal
- rapid onset but short lived
- water soluble; travel freely in the bloodstream (do not require carriers)
5
Q
What is a signalling cascade?
A
the connection between the hormone at the surface and the effect brought about by the second messengers within the cell
6
Q
Name 3 common second messengers.
A
cAMP (cyclic adenosine monophosphate)
IP3 (inositol triphosphate)
calcium
7
Q
Explain 7 features of steroid hormones.
A
- derived from cholesterol
- produced by the gonads and adrenal cortex
- minimally polar; can pass through the plasma membrane
- bind to and promote a conformational change of intracellular or intranuclear receptors
- the hormone-receptor complex binds to DNA, affecting the transcription of a particular gene
- slow onset but long-lived
- require a specific protein carrier; cannot dissolve in the bloodstream
8
Q
A common form of steroid hormone-receptor complex conformational change is:
A
dimerization: two receptor-hormone complexes pair
9
Q
Explain 3 features of amino acid-derivative hormones?
A
- they are made of 1-2 amino acids with a few modifications
- ex. the addition of iodine to tyrosine
- less common than peptide and steroid hormones
- common examples: epinephrine, norepinephrine, triiodothyronine, thyroxine
10
Q
What are the catecholamines?
A
epinephrine and norepinephrine
bind to G protein-coupled receptors
11
Q
Do thyroid hormones bind intracellularly or extracellularly?
A
intracellularly
12
Q
Hormones can be classified by their target tissue as either:
A
direct hormones or tropic hormones
13
Q
Direct vs tropic hormones
A
direct hormones: secreted into the bloodstream and travel to target tissues where they have direct effects
tropic hormones: cause secretion of another hormone (an intermediary) that then travels to the target tissue to cause an effect; usually originate in the brain and anterior pituitary gland
14
Q
List the 8 endocrine organs/glands covered in this chapter.
A
- hypothalamus
- anterior and posterior pituitary
- thyroid
- parathyroid glands
- adrenal cortex
- adrenal medulla
- gonads (testes and ovaries)
- pineal gland
note: some other organs serve important endocrine roles but arena considered endocrine organs because hormone production is not their main function
15
Q
The hypothalamus is the bridge between which 2 systems?
A
the endocrine and nervous system
16
Q
Where is the hypothalamus located?
A
in the forebrain, directly above the pituitary gland and below the thalamus
17
Q
What is the role of the hypothalamus?
A
regulates the pituitary gland through tropic hormones
controls the pituitary gland through paracrine release of hormones into a portal system that directly connect the two organs
receives input from many sources
18
Q
Provide 3 examples of input received by the hypothalamus.
A
- the suprachiasmatic nucleus receives light input from the retinae to control sleep-wake cycles
- increases in blood osmolarity
- appetite and satiety regulation
19
Q
Describe the negative feedback mechanism of the hypothalamus. (2 notes)
A
- negative feedback occurs when a hormone (or product) later in the pathway inhibits hormones (or enzymes) earlier in the pathway
- this type of feedback maintains homeostasis and prevents wasted energy by restricting production of substances that are already present in sufficient quantities
20
Q
The hypothalamus is highly linked with which gland?
A
the pituitary gland
(there are unique interactions between the anterior and posterior components)
21
Q
Describe the interactions between the hypothalamus and the anterior pituitary gland.
A
- hormones are released from the hypothalamus into the hypophyseal portal system/bloodstream
- these hormones travel down the pituitary stalk and bind to receptors in the anterior pituitary which stimulates the release of other hormones
22
Q
What is the hypophyseal portal system?
A
a blood vessel system that directly connects the hypothalamus with the anterior pituitary
23
Q
What is an alternate term for “pituitary”?
A
“hypophysis”
24
Q
Which hormone is release by the anterior pituitary in response to the release of GnRH by the hypothalamus?
A
note: GnRH: Gonadotropin-releasing hormone
follicle-stimulating hormone (FSH)
luteinizing hormone (LH)
25
Which hormone is released by the anterior pituitary in response to the release of **GHRH** by the hypothalamus?
*note: GHRH: growth hromone-releasing hormone*
## Footnote
**growth hormone (GH)**
26
Which hormone is released by the anterior pituitary in response to the release of **TRH** by the hypothalamus?
*note: TRH: thyroid-releasing hormone*
## Footnote
**thyroid-stimulating hormone (TSH)**
27
Which hormone is released by the anterior pituitary in response to the release of **CRF** by the hypothalamus?
*note: CRF: corticotropin-releasing factor*
## Footnote
**adrenocorticotropic hormone (ACTH)**
28
What is the affect of **PIF** release by the hypothalamus?
*PIF: prolactin-inhibiting factor (dopamine)*
## Footnote
**causes a decreases in prolactin secretion by the anterior pituitary**
29
What is an axis? Provide 2 examples.
a three-organ system
hypothalamic-pituitary-adrenal axis
hypothalamic-pituitary-ovarian axis
30
Describe the interactions between the hypothalamus and the posterior pituitary.
* neurons in the hypothalamus send their axons down the pituitary stalk directly into the posterior pituitary
* oxytocin and antidiuretic hormone are synthesized in the hypothalamus and then travel down the pituitary stalk into the posterior pituitary
* the posterior pituitary then releases oxytocin and antidiuretic hormone in the bloodstream
31
Which 2 hormones are released into the bloodstream by the anterior pituitary and what are their effects?
**oxytocin**
* stimulates uterine contractions during labor and milk letdown during lactation
**antidiuretic hormone (ADH or vasopressin)**
* increases reabsorption of water in the kidney collecting ducts
* secreted due to increase plasma osmolarity (high solute concentration in the blood)
32
What are the 7 different products synthesized and secreted by the anterior pituitary?
* mnemonic: **FLAT PEG**
* **F**SH
* **L**H
* **A**CTH
* **T**SH
* * **P**rolactin
* **E**ndorphins
* **G**rowth Hormone
*note: FLAT (tropic hormones) PEG (direct hormones)*
33
How do tropic hormones work?
cause the release of another hormone at the organ level
34
Which gland releases **follicle-stimulating hormone (FSH)** and what is its effect?
* a tropic hormone released by the **anterior pituitary**
* promotes the _development of ovarian follicles_ in females and spermatogenesis in males
35
Which gland releases **luteinizing hormone (LH)** and what is its effect?
* a tropic hormone released by the **anterior pituitary**
* promotes _ovulation_ in females and _testosterone production_ in males
36
Which gland releases **adrenocorticotropic hormone (ACTH)** and what is its effect?
* a tropic hormone released by the **anterior pituitary**
* promotes synthesis and release of _glucocorticoids_ from the adrenal cortex
37
Which gland releases **thyroid-stimulating hormone (TSH)** and what is its effect?
* a tropic hormone released by the **anterior pituitary**
* promotes synthesis and release of _triiodothyronine and thyroxine_ from the thyroid
38
Which gland releases **prolactin** and what is its effect?
* a direct hormone released by the **anterior pituitary**
* promotes _milk production_ in the mammary glands
* the release of dopamine by the hypothalamus decreases its secretion
* dopamine levels drop after birth allowing lactation to begin
39
Which gland releases **endorphins** and what is its effect?
* a direct hormone released by the **anterior pituitary**
* decrease perception of pain
* can cause euphoria
40
Which gland releases **growth hormone (GH)** and what is its effect?
* a direct hormone released by the **anterior pituitary**
* promotes _growth of bone and muscle_
* prevents glucose uptake in non-growing tissues to raise overall blood-glucose concentrations, allowing muscle and bone to use it
* stimulated by GHRH from the hypothalamus
41
What area of the bone does bone growth originate in?
**epiphyseal plates**
seal shut during puberty
42
Describe acromegaly.
a medical condition resulting …. finish later
43
Posterior Pituitary
contains the nerve terminals of neurons with cell bodies in the hypothalamus
receives and stores 2 hormones produced by the hypothalamus: ADH and oxytocin
44
When is antidiuretic hormone (ADH) secreted?
secreted in response to low blood volume (sensed by baroreceptors) or increased blood osmolarity (sensed by osmoreceptors)
45
What are the effects of antidiuretic hormone (ADH)
* causes the kidneys to release less water, decreasing the amount of urine produced
* increases the reabsorption of water in the kidney collecting duct = increases blood volume = higher blood pressure = decreased blood osmolarity
46
When is oxytocin secreted?
* secreted during childbirth
* secretion may also be stimulated by suckling
47
What is the effect of oxytocin?
* allows for coordinated contraction of uterine smooth muscle
* promotes milk ejection
* may be involved in bonding behaviour
48
Explain the feedback loop of oxytocin.
a positive feedback loop: the release of oxytocin promotes uterine contraction, which promotes more oxytocin releases, which promotes stronger uterine contractions, etc.
the definitive endpoint of this loop is delivery of the infant
49
Which hormone is the thyroid controlled by?
the thyroid-stimulating hormone from the anterior pituitary
50
Where is the thyroid located?
at the base of the neck in front of the trachea
51
What are the 2 major functions of the thyroid and how are these effects mediated?
setting basal metabolic rate (by releasing T3 and T4 thyroid hormones)
calcium homeostasis (controlled by calcitonin)
52
What are the 3 key products of the thyroid?
triiodothyronine (T3) - a thyroid hormone
thyroxine (T4) - a thyroid hormone
calcitonin
53
How and where are T3 and T4 produced?
by the _addition of iodine atoms to tyrosine_ within the _follicular cells_ of the thyroid
* T3 has 3 iodine atoms attached to tyrosine*
* T4 has 4 iodine atoms attached to tyrosine*
54
What are the effects of T3 and T4?
increase cellular respiration
increase basal metabolic rate
alto the utilization of glucose and fatty acids
required for proper neurological and physical development in children
**edit slide**
55
What is hypothyroidism and how does it result?
characterized by lethargy, decreased body temperature, slowed respiratory and heart rate, cold intolerance, weight gain
results from iodine deficiency or inflammation of the thyroid causing thyroid hormones to be secreted in insufficient amounts or not at all
56
What is hyperthyroidism and how does it result?
excess thyroid hormones
may results from a tumor or thyroid overstimulation
characterized by heightened activity levels, increased body temperature, increased respiratory and heart rate, heat intolerance, weight loss
57
Which cells within the thyroid produce calcitonin?
parafollicular (C) cells
58
What is the effect of calcitonin?
decreases plasma/blood calcium levels in 3 ways:
* promoting calcium excretion from the kidneys
* decreasing calcium absorption from the gut
* promoting calcium storage in the bone
59
What stimulates calcitonin secretion by C-cells?
high levels of calcium in the blood
60
Where are the parathyroid glands located and what do they resemble?
they are 4 small pea-sized structures that sit on the posterior surface of the thyroid
61
What do the parathyroid glands do?
releases parathyroid hormone (PTH), which increases blood calcium concentration
62
Parathyroid hormone is an antagonistic hormone to which molecule?
**calcitonin** (decreases blood calcium levels)
*(parathyroid hormone increases blood calcium levels)*
63
Explain how parathyroid hormone (PTH) increases blood calcium concentration.
* decreases calcium excretion by the kidney
* increases calcium absorption in the gut (by activating vitamin D)
* increases bone resorption to free up calcium
64
Explain how parathyroid hormone (PTH) affects phosphorus homeostasis.
* promoting resorption of phosphate from bone
* reduces reabsorption of phosphate in the kidney (promote its excretion in the urine)
* vitamin D promotes absorption of phosphate from the gut
*note: these effects on phosphate concentration somewhat cancel each other*
65
Explain the feedback loop of PTH.
undergoes feedback inhibition
as blood calcium levels rise, PTH secretion is decreased
66
List 4 important functions of calcium.
* bone structure and strength
* release of neurotransmitters from neurons
* regulation of muscle contraction
* clotting of blood (calcium is a cofactor)
67
Where are the adrenal glands located?
on top of the kidneys
*(adrenal translates to ‘next to the kidney’)*
68
Each adrenal gland consists of which 2 structures?
a cortex and medulla which are each responsible for the secretion of different hormones
69
What does the adrenal **cortex** secrete?
corticosteroids
70
What are the 3 functional classes of corticosteroids?
glucocorticoids
mineralocorticoids
cortical sex hormones
71
Which gland secretes glucocorticoids and what do they regulate?
corticosteroids are secreted by the adrenal cortex that regulate **glucose levels**
also affect protein metabolism
72
Name and describe 2 common glucocorticoids.
**cortisol and cortisone**
* _raise_ blood glucose by increasing gluconeogenesis and decreasing protein synthesis
* can decrease inflammation and immunologic responses
* cortisol is a stress hormone released times of physical/emotional stress to allow the body to react quickly if needed
73
Glucocorticoid release is under the control of which hormone?
adrenocorticotropic hormone (ACTH)
74
How is the release of glucocorticoid controlled?
corticotropin-releasing factor (CRF) from the hypothalamus promotes release of **adrenocorticotropic hormone (ACTH)** from the anterior pituitary, which promotes release of glucocorticoids from the adrenal cortex
75
What is the function of mineralocorticoids?
used in salt and water homeostasis
most profound effects are on the kidney
76
Name one noteworthy mineralocorticoid and its function.
**aldosterone**
* increases sodium reabsorption in the distal convoluted tubule and collecting duct of the nephron
* water follows the sodium cations into the bloodstream, increasing blood volume and pressure (plasma osmolarity doesn't change)
* decreases the reabsorption of potassium and hydrogen ions the same segments of the nephron, promoting their excretion in the urine
* primarily under the control of the renin-angiotensin-aldosterone system
77
Which system is aldosterone primarily under the control of? Explain this system.
renin-angiotensin-aldosterone system
decreased blood pressure causes the juxtaglomerular cells of the kidney to secrete renin,
**finish later**
78
What are the cortical sex hormones in males and females?
androgens (males) and estrogens (females)
79
Differentiate androgens and estrogens.
androgens (the male cortical sex hormones)
* males secrete large quantities in the testes so adrenal testosterone plays a small role in male physiology
estrogens (the female cortical sex hormones)
* sensitive to disorders of cortical sex hormone production
80
Which structure is located within the adrenal cortex?
the adrenal medulla
81
What is the adrenal medulla responsible for?
the production of the sympathetic hormones **epinephrine** and **norepinephrine**
82
What type of hormones are epinephrine and norepinephrine?
**amino acid-derivative** hormones that belong to the _catecholamines_ class of molecules
83
What is the general function of epinephrine and norepinephrine?
they affect a wide variety of systems, with all of their effects centered on the **fight-or-flight** response
84
epinephrine
* increase the breakdown of glycogen to glucose in liver and muscle
* increase metabolic rate
both
* increase heart rate
* dilate the bronchi
* alter blood flow to supply the systems used in a sympathetic response
vasoconstriction decreases blood flow to the gut, kidneys, and skin
85
The stress response involves both _____ and \_\_\_\_\_. Explain the difference in their stress responses.
**cortisol:** long-term (slow) stress responses
**epinephrine:** short-term (fast) stress responses
*note: cortisol increases the synthesis of catecholamines (including epinephrine)*
86
What is the purpose of the pancreas?
it produces hormones that regulate **glucose homeostasis**
87
Label the structure of the pancreas.
88
What are **islets of Langerhans** and their 3 distinct cell types?
small clusters of hormone-producing cells throughout the pancreas
alpha cells, beta cells, and delta cells
89
What hormone does each of the 3 islet of Langerhans cells secrete?
alpha cells: secretes glucagon
beta cells: secretes insulin
delta cells: secretes somatostatin
90
Exocrine vs endocrine
**exocrine glands**
secrete substances into a ductal system to an epithelial surface
**endocrine glands**
secrete products directly into the bloodstream
91
How is glucagon produced?
by alpha-cells
92
What is the function of glucagon and how does it do this?
raises blood glucose levels by:
* stimulating protein and fat degradation
* glycogenolysis (conversion of glycogen to glucoses)
* gluconeogenesis (production of new glucose)
93
When is glucagon released and inhibited?
glucagon is secreted when blood glucose levels run low (during times of fasting)
*(mnemonic: gluca**_gon_** levels are high when glucose is _gone_)*
glucagon release is inhibited when blood glucose concentrations are high
94
What is the function of insulin?
* lowers blood glucose levels (secreted when blood glucose levels are high)
* induces muscle and liver cells to take up glucose and store it as glycogen for later use
* stimulates anabolic processes such as fat and protein synthesis
95
What is hypoglycemia characterized by?
low blood glucose concentration
96
What is diabetes mellitus and what is it characterized by?
characterized **hyperglycemia** (high blood glucose concentration)
can result from underproduction, insufficient secretion, or insensitivity to insulin
97
Name and describe the 2 types of diabetes mellitus.
**Type I (insulin-dependent)**
* caused by autoimmune destruction of the pancreas beta-cells
* individuals produce little to no insulin
* requires regular insulin injections to prevent hyperglycemia
**Type II (non-insulin-dependent)**
* results from receptor-level resistance to the effects of insulin
* partially inherited and partially due to environmental factors (diet)
* oral pharmaceuticals can be used to help the body use the insulin in produces
* require insulin only when their bodies can no longer control glucose levels
98
What is somatostatin and what stimulates its secretion? Which other glad is it also produced by and for what function?
* an inhibitor of both insulin and glucagon secretion
* high blood glucose and amino acid concentrations stimulate its secretion
* also produced by the hypothalamus where it functions to decrease growth hormone secretion
99
What are the gonads?
produce hormones involved in development and maintenance of the reproductive systems and secondary sex characteristics
100
What are the male gonads and what do they secrete?
the testes secrete testosterone in response to stimulation by gonadotropins
101
What is the effect of testosterone?
causes sexual differentiation of the male during gestation
promotes development and maintenance of secondary sex characteristics in males (ex. axillary and pubic hair, deepening of the voice, muscle growth)
102
What are the female gonads and what do they secrete?
the ovaries secrete estrogen and progesterone in response to gonadotropins
103
What is the effect of estrogen and progesterone?
estrogen:
* involved in development of the female reproductive system during gestation
* promotes the development and maintenance of secondary sex characteristics in females (ex. axillary and pubic hair, breast growth, body fat redistribution)
both
* govern the mestrual cycle and pregnancy
104
Which hormone does the pineal gland secrete?
melatonin
105
What is the function of melatonin?
involved in circadian rhythms
melatonin blood levels are partially responsible for tiredness
106
The pineal gland receives progectyion directly from the \_\_\_\_\_\_. Explain the implications of this.
**retina**
it is not involve in vision
rather, it is hypothesized that the pineal gland responds to decreased light intensity by releasing melatonin
107
Which hormone is released by the kidney and what is its purpose?
**erythropoietin**
stimulates erythrocyte (red blood cell) production in the bone marrow
secreted in response to low blood oxygen levels
108
Which hormones are released by the stomach and intestines?
secretin, gastrin, and cholecystokinin
109
Which hormone is released by the heart and what is its purpose?
**atrial natriuretic peptide (ANP)**
promotes excretion of sodium and water via the urine
lowers blood volume/pressure
110
Which hormone is released by the thymus and what is its purpose?
**thymosin**
stimulates T-cell development and differentiation
*(note: the thymus is located behind the sternum and atrophies by adulthood, dropping thymosin levels)*
