Endocrine system

Question 1

What is the endocrine system?

Answer 1

• A system of glands that secrete chemical messengers called hormones into the bloodstream
• Messages carried by hormones travel slower than those carried by nerve impulses (bloodstream is slower than nervous system)

Question 2

What are the similarities between the nervous and endocrine system?

Answer 2

• Some nervous tissues (eg. hypothalamus, pituitary, adrenal glands) secrete hormones
• Some chemical function as neurotransmitters and hormones
• Both systems include positive and negative feedback loops
• Often work hand in hand

Question 3

Describe lipids vs. water soluble hormones:

Answer 3

• Hormones lipid based are lipid - soluble
  
  • Can diffuse through cell membrane easily
  • Inside cell bind to receptors and often affect genes
• Hormones that are protein based are water - soluble
  
  • Cannot diffuse across membrane
  • Bind to receptor on surface which sends message to inside of cell

Question 4

Describe the negative feedback loops:

Answer 4

• Need some way to “turn off” hormone production
• Negative feedback - some way of stopping hormone release once certain level of hormone is reached or after desired effect eg. ADH
• Also sometimes positive feedback loops to increase amount of hormone produced eg. during birth (oxytocin)

Question 5

Describe tropic vs. non-tropic hormones:

Answer 5

• Tropic - have endocrine glands as targets (eg. thyroid stimulating hormone (TSH —> thyroid)
• Non - tropic - do not have endocrine glands as targets (eg. insulin —-> muscle, liver, fat cells)

Question 6

Describe the hypothalamus:

Answer 6

• Located at the base of the brain (a component of the brain)
  -Secretes hypothalamic releasing and inhibiting hormones
• Produces ADH and oxytocin
• Regulates anterior pituitary
• Hormones travel down stalk to pituitary glands
• Also uses natural impulses to communicate with pituitary

Question 7

Describe the pituitary:

Answer 7

• Located at the base of the brain (below hypothalamus)
• Secretes hGH, TSH, ACTH, FSH, LH and PRL hormones
• pituitary is divided into two lobes, posterior (smaller lobe) and anterior

Question 8

Describe the posterior pituitary:

Answer 8

• Part of the nervous system
• Does not make any hormones
• Oxytocin and ADH travel to pituitary via nerve portal
• Posterior pituitary stores and releases these hormones

Question 9

Describe the antidiuretic hormone (ADH):

Answer 9

• Secretes from posterior pituitary
• Acts on collecting duct of kidney to increase water reabsorption
• Control based on osmotic pressure (quantity of salt vs. water) of body fluids
• If fluid is too concentrated, hypothalamus signals posterior pituitary to release ADH
• If fluid is to dilute, hypothalamus signals posterior pituitary to decrease ADH

Question 10

Describe the anterior pituitary:

Answer 10

• Produces and releases hGH, prolactin (PRL), TSH, ACTH, follicle stimulating hormone (FSH), leutenizing hormone (LH)
• Blood vessel/nerve portal carries hormones from hypothalamus (releasing or inhibiting) - either stimulate or inhibit hormone release from anterior pituitary

Question 11

Describe the human growth hormone (hGH):

Answer 11

• Secreted from anterior pituitary
• Stimulates growth and metabolism either directly or indirectly
• Stimulates liver to release growth factors
• Effects include:
  
  • Protein synthesis and cell division
  • Breakdown and release of stored fats
  • Results in growth of muscles, connective tissue and at the plates of long bones

Question 12

Describe the thyroid-stimulating hormone (TSH):

Answer 12

• Secreted from anterior pituitary
• Causes the thyroid gland to secrete thyroxine
• Operates on negative feedback loop

Question 13

Describe the adrenocorticotropic hormone (ACTH):

Answer 13

• Secreted from anterior pituitary
• When body senses danger, hypothalamus signals release of ACTH by the way of a releasing hormone
• ACTH stimulates cortisol release from adrenal cortex

Question 14

Describe the thyroid:

Answer 14

• Located around trachea just below larynx
• Produces T3, thyroxine (T4) and calcitonin
• Iodine is needed to make T3 and T4
• Stimulated by TSH from anterior pituitary

Question 15

Describe thyroxine (T4):

Answer 15

• Produced and released in the thyroid
• Increases metabolism of CHOs, fats and proteins
• Increases rate of cellular respiration of individual cells (especially those of the heart, skeletal muscles, liver and kidney)
• Influences organ and tissue development in children

Question 16

Describe the T4 negative feedback cycle:

Answer 16

• TSH stimulates thyroid to produce T4
• Elevated levels of T4 signal pituitary to stop producing TSH (both indirectly through hypothalamus and directly)
• If T4 does not get produced (sometimes due to lack of iodine) TSH continues to stimulate thyroid (results in goiter)

Question 17

Describe calcitonin:

Answer 17

• Produced and secreted by thyroid
• Stimulates CA2+ (calcium) uptake by bones from blood when blood calcium levels get to high
• Minor role in calcium regulation in humans

Question 18

Describe the parathyroid glands:

Answer 18

• Four small glands attached to thyroid
• Produces and releases parathyroid hormone (PTH)

Question 19

Describe the parathyroid hormone (PTH):

Answer 19

• Produced and secreted by parathyroid glands
• Responds to low blood calcium levels
• Breaks down bones
• Stimulates kidneys to reabsorb calcium from urine
• Activates vitamin D (stimulates absorption of calcium from food)

Question 20

Describe high blood calcium levels:

Answer 20

• Calcitonin hormone involved
• Secreted from thyroid
• Stimulates transfer of calcium from blood to bones

Question 21

Describe low blood calcium levels:

Answer 21

• PTH hormone involved
• Secreted fro parathyroid
• Stimulates bone breakdown
• Stimulates calcium absorption from urine
• Activates vitamin D

Question 22

Describe the adrenal glands:

Answer 22

• Located on top of kidneys
• Inner layer is adrenal medulla
• Outer layer is adrenal cortex

Question 23

Describe the adrenal medulla:

Answer 23

• Inner portion of adrenal glands
• Consider nervous tissue
• Involved in short term stress response
• Produces/secretes epinephrine and norepinephrine

Question 24

Describe epinephrine and norepinephrine:

Answer 24

• Release signal directly (by neurons) from hypothalamus
• Prepare body for fight or flight response by:
  
  • Increasing metabolism
  • Increase breathing rate
  • Increase heart rate
  • Increase blood flow to heart and muscles
  • Pupil dilatation
• Acts quickly because it is stimulated by the nervous system
• Because they are hormones, effects last longer than nervous stimulation
• Remember norepinephrine is also a neurotransmitter

Question 25

Describe the adrenal cortex:

Answer 25

• Outer portion of adrenal gland
• Produces and secretes the following (involved in the long-term stress response):
  
  • Glucocorticoids (increase blood sugar)
  • Mineralcorticoids (increase blood pressure)
  • Gonadocorticoids (supplement hormones produced by gonads)
  • All of the above are made from cholesterol

Question 26

Describe cortisol:

Answer 26

• A glucocorticoid
• Release stimulated by ACTH (from pituitary)
• Longer-lasting then epinephrine
• Natural anti-inflammatory
• raises blood glucose levels
  
  • Promotes breakdown of muscle
  • Protein converted to glucose by liver
  • Prompts breakdown of fat cells

Question 27

Describe aldosterone:

Answer 27

• A mineralocorticoid
• Stimulates kidneys to increase absorption for sodium from urine
• Increases blood pressure

Question 28

Describe the pancreas:

Answer 28

• Located below stomach
• Attached to small intestine by duct
• Exocrine functions - secretes digestive enzymes
• Endocrine functions – performed by islets of Langerhans (clusters of endocrine cells in the pancreas)

Question 29

Describe the islets of langerhan:

Answer 29

• Two types of cells:
  
  • Beta cells - secrete insulin
    
    • Decreases blood glucose levels
  • Alpha cells - secrete glucagon
    
    • Increases blood glucose

Question 30

Describe insulin:

Answer 30

• Secreted by beta calls of pancreas
• Decreases blood glucose levels
• Acts on receptors of target cells - makes them more permeable to glucose (especially muscle and liver cells)

Question 31

Describe diabetes mellitus:

Answer 31

• Body does not respond to insulin or produce enough insulin
• Blood sugar levels are significantly higher
• Cells starve - results in fatigue
• Body breaks down fats and proteins in attempt to get energy
• Large volumes of glucose-rich urine produced
• Complications include blindness, kidney failure, nerve damage and gangrene
• Alpha cells may also be degenerate

Question 32

Describe glucagon:

Answer 32

• Secreted by alpha cells of pancreas
• Stimulates liver to convert glycogen back to glucose

Question 33

Describe type 1 vs. type 2 diabetes:

Answer 33

• Type 1 - immune system destroys beta cells, insulin is not produced
  
  • Also called insulin dependent
  • Usually diagnosed in childhood
• Type 2 - Insulin receptors on cells stop responding to insulin
  
  • Adult - onset
  • 90% of diabetes
  • Can result in type 1

Question 34

Describe diabetes insipidus:

Answer 34

• Caused by lack of ADH
• Water isn’t reabsorbed from urine
• Results in increased urine volume, excessive thirst
• No change in blood sugar