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BIOL 1205 > Module 9 - Endocrine System > Flashcards

Module 9 - Endocrine System Flashcards

1
Q

What is the function of the endocrine system?

A

Mechanisms of cell to cell communication
-regulation of body activities and maintenance of homeostasis requires the communication between cells which occurs by:

  1. Direct contact
  2. Autocrine or paracrine communication
  3. Nervous (synaptic) communication
  4. Endocrine communication
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2
Q

How does direct communication work? Where?

A
  • exchange of ions and molecules between adjacent cells across gap junctions
  • occurs between 2 cells of the same type
  • highly specialized and rare
  • found in the heart
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3
Q

How does autocrine and paracrine communication work?

A

-involves chemical communication between cells of a single tissue
-local chemical factors released from one cell:
1. Bind to receptors on a neighbouring cell (paracrine action)
2. Bind to receptors on the cell of origin (autocrine action)
E.g histamine —> inflammation
Nitric acid —> vasodilation

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4
Q

How does nervous (synaptic) communication work?

A
  • involves the release of neurotransmitters at synapses
  • actions are limited to post-synaptic cells with specific receptors
  • communication occurs within seconds
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5
Q

How does endocrine communication work?

A
  • involves the release of hormones that are carried in the blood to distant and widespread target cells
  • slower acting than nervous communication, but effects may be prolonged
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6
Q

What is the endocrine system comprised of?

A
  • composed of glands and organs that synthesize and release hormones
  • endocrine glands are ductless glands
  • hormones are released into the interstitial space (between cells), then diffuse to nearby capillaries
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7
Q

What are the general functions of the endocrine system?

A

Hormones collectively act on VIRTUALLY ALL BODY CELLS to:

  1. Regulate tissue activity and processes involved in maintaining homeostasis (a stable internal environment)
  2. Control growth and development
  3. Contribute to the basic processes of reproduction (I.e sperm and egg production)
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8
Q

What are hormone characteristics?

A

ALL hormones share the following characteristics:

  1. They have specific rates and rhythms of secretion
  2. They affect only cells with appropriate receptors
  3. They operate within a feedback system
  4. Removal involves excretion by the kidneys or metabolism by the liver
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9
Q

What are the 2 classifications of hormones?

A

Hormones are grouped into two classes:

  1. Lipid-soluble hormones
    - I.e estrogen, testosterone, cortisol, aldosterone
  2. Water-soluble hormones
    - I.e insulin, glucagon, epinephrine, growth hormone
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10
Q

What are the functions of hormones?

A

General topics to be discussed:

  1. Hormone release
  2. Transport in the blood
  3. Mechanism of action (receptor binding)
  4. Effect on target cells
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11
Q

How does hormone release work?

A
  • hormones are released from endocrine cells
  • release depends on the body’s needs at a given time (specific stimuli) or natural rates/rhythms
  • hormones enter nearby capillaries and circulate until they reach their specific target cell that has the appropriate receptor
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12
Q

How does the regulation of hormone secretion work?

A

Hormone release is regulated by:

  1. Signals from the nervous system
    - I.e sympathetic neutrons stimulate epinephrine release from the adrenal gland
  2. Chemical changes in the blood
    - i.e changes in blood glucose regulate insulin release from the pancreas
  3. Other hormones
    - I.e ACTH release from the pituitary gland stimulates glucocorticoid release from the adrenal gland
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13
Q

How do hormones get transported?

A

lipid soluble hormones:

  • circulate bound to a carrier protein
  • these hormones are hydrophobic —> they don’t like watery environment of blood

Water soluble hormones:
-circulate freely in blood

Which would display longer lasting effects?

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14
Q

How does the mechanism of action of hormones work?

A
  • hormones bind to target cells that possess receptors that are specific for the hormone
  • difference cells may contain receptors for the same hormone but produce different effects
  • a single cell may contain >1 type of receptor

LIPID SOLUBLE HORMONES:
-bind to INTRACELLULAR receptors (in the nucleus or cytoplasm)

WATER SOLUBLE HORMONES:

  • bind to PLASMA MEMBRANE RECEPTORS
  • these hormones are hydrophilic —> they cannot diffuse through the lipid belayer of the cell membrane
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15
Q

What is the mechanism of action for lipid soluble hormones?

A
  • binding to intracellular receptors alters gene expression and the synthesis of proteins
  • new proteins alter cell activity
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16
Q

What is the mechanism of action for water soluble hormones?

A
  • the hormone is called the first messenger
  • receptor binding activates a second messenger system that relays the message inside the cell
  • this activates intracellular proteins to alter cell activity or permeability

Generally, hormone binding acts to modify cellular activities by:

  1. Altering membrane permeability
  2. Activating or inactivating key enzymes
  3. Changing genetic activity (protein synthesis)
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17
Q

What is the importance of the hypothalamus?

A

It is the link between the nervous system and the endocrine system.
One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland

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18
Q

What are the endocrine functions of the hypothalamus?

A
  1. Releases regulatory hormones that act on endocrine cells of the anterior pituitary (regulating the release of other hormones)
  2. Produces antidiuretic hormone and oxytocin that are stored in neutron terminals of the posterior pituitary
  3. Contains sympathetic motor neurone that act on the adrenal gland (epinephrine and norepinephrine release)
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19
Q

What is the pituitary gland?

A
  • attached to the hypothalamus by a stalk called the infundibulum
  • located within the hypophyseal fossa of the skull
  • divided into the anterior and posterior pituitary glands
  • the pituitary gland is often called the “master gland” because many of its hormones control other parts of the endocrine system
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20
Q

What is the anterior pituitary?

A
  • release of anterior pituitary hormones is regulated by the release of regulatory hormones from the hypothalamus
  • anterior pituitary hormones include:
    1. Growth hormone (hGH)
    2. Thyroid stimulating hormone (TSH)
    3. Adrenocorticotropic hormone (ACTH)
    4. Gonadotropic hormones (LH and FSH)
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21
Q

What are hypothalmic neurons? hypophyseal portal system?

A

regulatory hormones called releasing hormones are released from neuron terminals into capillaries located in the infundibulum

hypophyseal portal system: carries hormones from capillaries of the infundibulum to capillaries of the anterior pituitary

anterior pituitary contains target endocrine cells

anterior pituitary hormones released into the circulation

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22
Q

What does growth hormone do? What are some disorders of growth hormone secretion?

A

hGH Growth hormone:

  • stimulates body growth
  • targets LIVER, SKELETAL MUSCLES and BONE TISSUE

hyposecretion during adulthood:
simmonds disease
main symptoms: weakness, loss of muscle mass

hypersecretion during adulthood:
acromegaly
main symptoms: thickening of bones and other tissues

hyposecretion during childhood:
pituitary dwarfism
main symptom: long-bone growth retardation

hypersecretion during childhood:
gigantism
main symptom: excessive long bone growth

23
Q

what does thyroid stimulating hormone (TSH) do?

A

stimulates the synthesis and secretion of thyroid hormone from the thyroid gland

24
Q

what does adrenocorticotropic hormone (ACTH) do?

A

-controls the production and secretion of glucocorticoids by the adrenal gland

25
Q

What are the 2 hormones that act on the ovaries and testes? what do they do?

A

follicle stimulating hormone (FSH)
-controls the development and production of oocytes (female) and sperm (male)

luteinizing hormone (LH) 
-stimulates (1) ovulation, (2) the secretion of progesterone and estrogens which prepare the uterus for implantation, and (3) testosterone production
26
Q

What does prolactin (PRL) do?

A

-initiates milk secretion from the mammary glands

27
Q

what does melanocyte-stimulating hormone (MSH) do?

A

-unknown role in humans –> administration causes darkening of the skin

28
Q

How does regulation of the hypothalamus and pituitary hormones work?

A
  • regulated by negative feedback mechanisms

- target hormone levels rise –> bind to receptors on the hypothalamus and pituitary –> inhibit hormone release

29
Q

What is the posterior pituitary?

A
  • contains axon terminals from neurons of the hypothalamus

- hypothalamic neurons synthesize hormones and store them in secretory vesicles within these axon terminals

30
Q

What is oxytocin? (posterior pituitary hormone)

A
  • acts on uterine smooth muscles to stimulate contractions during delivery
  • acts on the breasts to stimulate the ejection of milk
31
Q

What is antidiuretic hormone (ADH)?

A
  • release is regulated by blood osmotic pressure (detected by receptors located in the hypothalamus)
  • stimulates (1) water reabsorption by the kidneys and (2) constriction of blood vessels
32
Q

What is the thyroid gland?

A
  • located below the larynx

- formed by two lobes on either side of the trachea (butterfly shaped)

33
Q

What are follicular cells? what are parafollicular cells?

A

follicular cells:
-secrete thyroid hormones:
thyroxine (T4) and triiodothyronine (T3)
-T3 and T4 are partially composed of iodine
-stored in central cavity

parafollicular cells secrete calcitonin

34
Q

What are the functions of the thyroid hormone?

A
  • most body cells have receptors for T3 or T4 (intracellular)
  • receptor binding alters the expression of genes involved in energy utilization
  • -> increases basal metabolic rate (the rate of oxygen consumption at rest)
  • ->increases ATP production and use, which in turn increases body temperature (heat given off)

stimulates growth (particular nervous and skeletal systems of growing children)

35
Q

How are thyroid hormone levels regulated?

A
  • release is stimulated by: (1) low thyroid hormone levels and (2) conditions that increase ATP demand (i.e. cold)
  • regulated by negative feedback mechanisms involving thyroid hormones, the anterior pituitary and the hypothalamus
36
Q

What is goiter?

A
  • enlargement of thyroid gland
  • occurs when thyroid hormone synthesis is impaired (i.e iodine deficiency)
  • high levels of TSH from the pituitary gland stimulate the thyroid gland, causing it to grow in compensation
37
Q

What are parathyroid glands?

A
  • small, round glands that produce parathyroid hormone

- present in pairs on the posterior surface of the 2 lobes of the thyroid gland

38
Q

What is parathyroid hormone?

A

-released in response to low blood Ca2+ levels
-acts on bone and kidneys to increase blood Ca2+
levels
–> stimulates osteoclasts
–> increases active vitamin D synthesis (which stimulates intestinal Ca2+ absorption)
–> decreases Ca2+ excretion by kidneys

39
Q

What is calcitonin?

A

released by parafollicular cells in response to elevated blood Ca2+ levels

  • acts on bone and kidneys to decrease blood Ca2+
  • ->inhibits osteoclast activity
  • -> increases Ca2+ excretion by kidneys
40
Q

What is the pancreas?

A
  • flattened organ located in the curve of the duodenum
  • contains both exocrine and endocrine function
  1. acinar cells (exocrine cells)
    - comprise 99% of pancreatic cells
    - secrete digestive enzymes into the pancreatic duct –> duodenum
2. pancreatic islets (endocrine cells) 
comprise of 1% of pancreatic cells (~2 mill islets)
2 key cell types: 
-alpha cells (secrete glucagon)
-beta cells (secrete insulin)

hormones involved in energy storage and utilization

41
Q

what is insulin?

A
  • released from beta cells in response to elevated blood glucose levels (i.e following a meal)
  • acts mainly on muscle, liver and adipose tissue
  • -> decreases blood glucose levels:
  • facilitates the uptake of glucose into cells
  • stimulates the storage of glucose as glycogen

–> stimulates the uptake of amino acids in muscle and storage as proteins

–> stimulates fat storage in adipose tissue

42
Q

What is glucagon?

A
  • released from alpha cells in response to lowered blood glucose levels (i.e between meals)
  • acts primarily on liver cells (also muscle and adipose tissue)
  • -> increases blood glucose levels
  • stimulates the breakdown of glycogen
  • stimulates the formation of glucose from amino acids

–> stimulates the breakdown of triglycerides in adipose tissue

43
Q

How does the regulation of insulin and glucagon levels work?

A
  1. negative feedback of GLUCOSE (not hormones) on pancreatic islets
    - hypoglycemia –> stimulates glucagon release
    - hyperglycemia –> stimulates insulin release
  2. nervous regulation
    - stimulation of parasympathetic nervous system (i.e during eating and digestion) –> release of insulin –> store nutrients for later use
    - stimulation of the sympathetic nervous system (i.e during exercise) –> release of glucagon –> releases nutrients in times of increased demand
44
Q

What are the mechanisms of diabetes mellitus?

A

type 1 diabetes: insufficient insulin

type 2 diabetes: insulin resistance

insulin stimulates fat and muscle glut-4 glucose transporters to be expressed into far and muscle cell membranes allowing glucose to enter the cells

45
Q

What are the two acute complications of DM?

A
  1. hypoglycemia
    - typically a side effect of excess insulin given relative to the amount of glucose in the blood stream = “insulin shock/reaction”
    - much more dangerous complication than hyperglycemia
    - brain requires glucose as main energy source
    - cold, clammy skin, sweating, tremor, tachycardia, palpitations, dizziness, confusion, seizures, coma –> death if untreated
    - requires immediate replacement of glucose or other monosaccharides orally (e.g fruit juice), I.V. if reduced consciousness or glucagon IM
  2. diabetic ketoacidosis (DKA)
    build up of ketones in the blood due to an inability of cells to utilize glucose, either through insufficient insulin, insulin resistance, or both
    -with insulin deficiency (more so with Type 1) lipolysis is enhanced, more fatty acids are delivered to the liver leading to the production of more ketones than can be used in the body
    -build up of ketones in blood –> metabolic acidosis
    -ketones detected on breath (fruity smell), in urine (ketonuria) in blood
    -hyperventilation to correct pH, lethargy, dizziness, nausea, CNS depression –> coma
    -treatment as appropriate for the type of diabetes
46
Q

What are the adrenal glands?

A

two glands, each present on the top of the kidneys

divided into to regions:

  1. outer cortex
  2. inner medulla
47
Q

What is the adrenal cortex?

A

divided into three zones:

  1. outer zone (mineralocorticoids)
  2. middle zone (glucocorticoids)
  3. inner zone (androgens)
48
Q

what are mineralcorticoids?

A

i. e aldosterone
- released in response to the activation of the renin-angiotensin pathway
- activated when blood volume and pressure decrease
- acts on kidneys
- ->increases Na+ and water retention

49
Q

what are glucocorticoids?

A

i. e cortisol
- release is regulated by negative feedback mechanisms involving hypothalmic hormones and ACTH (anterior pituitary)
- release in response to stress

50
Q

What are the functions of cortisol (and other glucocorticoids)?

A
  • protein breakdown (muscle)
  • glucose formation (from amino acids)
  • triglyceride (fat) breakdown
  • anti-inflammatory effects
  • immune suppression
51
Q

What does excess glucocorticoid do?

A
  • cushing’s syndrome
  • breakdown of muscle proteins and redistribution of body fats –> moon face, spindly arms
  • hyperglycemia
  • decreased resistance to infection
52
Q

What is the adrenal medulla?

A

-regulated by sympathetic neurons from the hypothalamus
-secretes epinephrine and norepinephrine
-activated in stressful situations (i.e exercise)
-contribute to flight or fight response:
increase in heart and respiratory rates
changes in circulation (vasodilation)
mobilization of energy stores
increased sweat gland secretion

53
Q

What are ovaries?

A
  • paired oval bodies located in the pelvic cavity
  • produce the sex hormones, estrogen, and progesterone

function in:

  • development of female sexual characteristics
  • menstrual cycle
  • pregnancy
  • lactation
54
Q

what are testes?

A
  • located external to the body of the male in a sac called the scrotum
  • produce the sex hormone, testosterone

function:
- the development of male sexual characteristics and normal reproductive functions

BIOL 1205 (9 decks)

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