1
Q
What is the endocrine system?
A
- 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)
2
Q
What are the similarities between the nervous and endocrine system?
A
- 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
3
Q
Describe lipids vs. water soluble hormones:
A
- 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
4
Q
Describe the negative feedback loops:
A
- 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)
5
Q
Describe tropic vs. non-tropic hormones:
A
- 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)
6
Q
Describe the hypothalamus:
A
- 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
7
Q
Describe the pituitary:
A
- 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
8
Q
Describe the posterior pituitary:
A
- 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
9
Q
Describe the antidiuretic hormone (ADH):
A
- 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
10
Q
Describe the anterior pituitary:
A
- 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
11
Q
Describe the human growth hormone (hGH):
A
- 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
12
Q
Describe the thyroid-stimulating hormone (TSH):
A
- Secreted from anterior pituitary
- Causes the thyroid gland to secrete thyroxine
- Operates on negative feedback loop
13
Q
Describe the adrenocorticotropic hormone (ACTH):
A
- 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
14
Q
Describe the thyroid:
A
- 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
15
Q
Describe thyroxine (T4):
A
- 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
16
Q
Describe the T4 negative feedback cycle:
A
- 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)
17
Q
Describe calcitonin:
A
- 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
18
Q
Describe the parathyroid glands:
A
- Four small glands attached to thyroid
- Produces and releases parathyroid hormone (PTH)
19
Q
Describe the parathyroid hormone (PTH):
A
- 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)
20
Q
Describe high blood calcium levels:
A
- Calcitonin hormone involved
- Secreted from thyroid
- Stimulates transfer of calcium from blood to bones
21
Q
Describe low blood calcium levels:
A
- PTH hormone involved
- Secreted fro parathyroid
- Stimulates bone breakdown
- Stimulates calcium absorption from urine
- Activates vitamin D
22
Q
Describe the adrenal glands:
A
- Located on top of kidneys
- Inner layer is adrenal medulla
- Outer layer is adrenal cortex
23
Q
Describe the adrenal medulla:
A
- Inner portion of adrenal glands
- Consider nervous tissue
- Involved in short term stress response
- Produces/secretes epinephrine and norepinephrine
24
Q
Describe epinephrine and norepinephrine:
A
- 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
25
Describe the adrenal cortex:
- 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
26
Describe cortisol:
- 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
27
Describe aldosterone:
- A mineralocorticoid
- Stimulates kidneys to increase absorption for sodium from urine
- Increases blood pressure
28
Describe the pancreas:
- 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)
29
Describe the islets of langerhan:
- Two types of cells:
- Beta cells - secrete insulin
- Decreases blood glucose levels
- Alpha cells - secrete glucagon
- Increases blood glucose
30
Describe insulin:
- 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)
31
Describe diabetes mellitus:
- 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
32
Describe glucagon:
- Secreted by alpha cells of pancreas
- Stimulates liver to convert glycogen back to glucose
33
Describe type 1 vs. type 2 diabetes:
- 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
34
Describe diabetes insipidus:
- Caused by lack of ADH
- Water isn’t reabsorbed from urine
- Results in increased urine volume, excessive thirst
- No change in blood sugar
Biology 30
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