Endocrine System

Question 1

Define Homeostasis

Answer 1

Maintenance of constant internal environment in response to changing conditions in: Internal + External enviro.

Feedback mechanism: Response to stimulus alters internal conditions and may become new stimulus

Question 2

What is an exocrine gland? Give an example.

Answer 2

Gland that secretes its products into ducts that empty either onto:

• the body surface
• the spaces between organs
• a body cavity

Example: Oil sebaceous gland –> Secretes oil into ducts that lead to body surface.

Question 3

What is an endocrine gland? Give an example.

Answer 3

Gland lacking a duct that secrete hormones that move from the cell to a fluid outside the cells where they diffuse into the blood.

Example: Thyroid gland

Question 4

What do we call the cell that responds to a particular hormone? Why do these cells repond and others do not?

Answer 4

Target cell.

Because target cells bear receptors to respond to the hormone.

Question 5

What type of activities does the endocrine system control and why?

Answer 5

Metabolic rate, maturation, growth, reproduction.

Hormone molecule can dramatically alter a target cell’s metabolism by turning on the production of a number of enzymes

Tiny amount of a hormone can control activities of enormous numbers of target cells in multiple organs.

Question 6

What is the hypothalamus, where is it found and what are its functions?

Answer 6

Hypothalamus is a neuroendocrine organ (belongs to both nervous and endocrine systems)

Location: It is found in the brain, inferior to the thalamus.

Functions: Controlling pituitary, homeostasis.

Question 7

Describe feedback mechanisms and explain why positive feedback is less common.

Answer 7

Feedback mechanisms are hormonal regulation mechanisms.
They occur when the response to a stimulus has an effect on the original stimulus.

Negative feedback: Diminishes initial stimulus
Positive feedback: Enhances initial stimulus

Positive feedback less common because most changes to a steady (equilibrium) state pose a threat and enhancing them would make the situation worse. (e.g., milk sucking)

Question 8

Give some examples of functions of hormones.

Answer 8

• Coordination and control of whole-body activity
• Regulation of glandular secretion
• Regulation of reproductive system
• Regulation of contractions for smooth (viscera) and cardiac (heart) muscle fibers
• Influence on immune system activity
• Control of growth and development
• Establishment of circadian rhythms

Question 9

Give some examples of effects caused by hormones.

Answer 9

• Alter plasma membrane permeability or membrane potential by opening or closing ion channels
• Stimulate protein synthesis (e.g. enzymes)
• Activate or inactivate enzymes
• Induce secretory activity
• Stimulate mitosis

Question 10

Describe the two major types of hormones and give some examples of each.

Answer 10

Water-soluble hormone (cell surface receptors): Generate second messengers which alter activity of other molecules (enzymes) within the cell.

e.g.: Insulin, GH, Adrenalin, Prolactin

Lipid-soluble hormone (intracellular receptors): Attach to DNA and activate certain genes (protein synthesis)

e.g.: Steroid hormones (only secreted by adrenal cortex and gonads)

Question 11

Describe the effect of steroid hormones (i.e. where is the receptor located and what happens when the hormone binds to the receptor).

Answer 11

Receptor in cytoplasm or nucleus. Attaches to DNA and activate certain genes (prot. synthesis)

Question 12

Describe the effect of water soluble hormones (i.e. where is the receptor located and what happens when the hormone binds to the receptor).

Answer 12

Binds to receptor on plasma membrane of target cell because cannot cross it.

Sets off series of reactions activating enzyme that catalyzes reaction and produces 2nd messenger molecule.

Question 13

What are the three main stimuli to control hormone release, give an example of each.

Answer 13

Hormonal (MOST COMMON)l: Hypothalamic-pituitary-thyroid relationship to secrete T3&T4 by thyroid

Humoral: Parathyroid hormone and calcitonin produced in response to changing levels of blood calcium levels.

Insulin produced in response to changing levels of blood glucose

Neural: Release of norepinephrine and epinephrine by adrneal medulla

Question 14

Describe the relationship between the pituitary gland and the hypothalamus.

Answer 14

Pituitary attached to the hypothalamus by a short stalk (posterior lobe).

Lies immediately beneath hypothalamus in a depression of the base of the skull.

Question 15

Describe the morphology of the pituitary gland (i.e. anterior and posterior lobes).

Answer 15

Anterior lobe:
Classical gland composed mostly of cells that secrete protein (water-soluble) hormones.

Posterior lobe:
Not an organ –> extension of hypothalamus. Forms the stalk that suspends anterior gland from the hypothalamus.

composed of axons of hypothalamic neurons which extend downward as a large bundle behind anterior pituitary.

Question 16

What are the two hormones that the neurosecretory cells of the posterior pituitary secrete and describe the function of each.

Answer 16

Oxytocin: Activates uterine muscles for contractions during childbirth, causes mammary glands to eject milk during nursing.

– Regulated by positive feedback mechanisms –

Acts on brain tissue, might induce trust and bonding between sexual partners since produced during orgasm.

Antidiuretic hormone (ADH): Causes more water to be reabsorbed back into the blood. Maintains water content constant.

– Negative feedback kicking in when water content falls in blood –

Question 17

What is the difference between a tropic and non-tropic hormone?

Answer 17

A tropic hormone activates the synthesis and release of hormones from endocrine glands such as the thyroid, the adrenal, and the sex gland

…whereas a non-tropic hormone’s target is a non-endocrine gland.

Question 18

Describe the negative feedback control over the pituitary hormones, include the role of the hypothalamus. Give an example using thyroid hormones.

Answer 18

1. Thyroid-releasing hormone is secreted by hypothalamic neurons
2. receptors on thyrotrophs in the anterior pituitary and stimulates secretion of TSH.
3. TSH binds to receptors on epithelial cells in the thyroid gland, stimulating synthesis and secretion of thyroid hormones, which affect all cells in the body.
4. When blood concentrations of thyroid hormones increase above a certain threshold, TRH-secreting neurons in the hypothalamus are inhibited and stop secreting TRH

Question 19

What are the functions of growth hormone?

Answer 19

Controls development and growth as well as metabolic activities such as use of body fat and protein synthesis.

Question 20

What happens if growth hormone levels are high in childhood, low in childhood, or high in adulthood?

Answer 20

Low in childhood: Dwarfism
High in childhood: Gigantism
High in adulthood: Acromegaly (overgrowth of bone in areas still responsive to GH effects)

Question 21

Which cells have receptors for thyroid hormone? What are some of the functions of thyroid hormone?

Answer 21

Nearly all cells have receptors for thyroid hormone.

Functions: Regulates body’s metabolic rate and production of heat. Maintains homeostasis by affecting blood pressure, heart rate, muscle tone, digestion, nerve function, and reproductive functions.

Question 22

What happens if thyroid hormone levels are high in adulthood, or low in adulthood?

Answer 22

High in adulthood: Hyperthyroidism (High bp, high T°, HR, irritability)

Low in adulthood: Hypothyroidism (weight gain, memory loss, lethargy)

Question 23

What is goiter, what causes it?

Answer 23

Enlargement of the thyroid gland due to insufficient iodine in the diet.

Lack of thyroid hormone causes neg feedback to be more defective. –> Hypo and ant. pituitary still secrete TRH and TSH causing the enlargment.

Question 24

The parathyroid hormones control homeostasis of what ion? Why is this ion important?

Answer 24

A constant concentration of 10mg/100ml of calcium is necessary to maintain: 
proper nerve function 
proper muscle function
blood clotting mechanisms
transport of molecules across membranes

Question 25

Describe what happens when blood Ca++ levels are too low or too high.

Answer 25

Ca++ lvl too low: Parathyroid releases PTH –> calcium released by bones, reabsorbed by kidneys, and absorbed in intestines.

Ca++ lvl too high: Thyroid gland releases CT, and calcium is taken up by the bones.

Question 26

What is the principal physiological action of prolactin?

Answer 26

Initiate and sustain lactation, stimulating mammary gland growth and milk production.

Question 27

What are the gonadotropins and what are their functions

Answer 27

FSH (Follicle Stimulating Hormone): stimulates gametogenesis in both males and females.
Women –> Stimulates estrogen secretion.

Men –> Stimulates spermatogenesis

LH (Luteinizing Hormone): Causes ovulation and progesterone secretion. In males it stimulates interstitial cells in testes to secrete testosterone.

Question 28

How do oral contraceptives function?

Answer 28

The oral pills contain progestin combined with an estrogen. Prevents ovulation (Not enough LH) by thining the uterine lining and thickening the cervical mucus.

Question 29

What are the corticosteroid hormones and where are they synthesized?

Answer 29

Steroid hormones synthesized in the adrenal glands

Question 30

Briefly describe the functions of the gonadocorticoids, the mineralcorticoids, and the glucocorticoids.

Answer 30

Gonadocorticoids (androgens and estrogens): androgens influence sex drive and converte to estrogens after menopause for women.

Mineralcorticoids: Regulating concentrations of minerals (particularly Na and K) in extracellular fluids.

regulating plasma levels of Na and K –> Aldosterone

Glucocorticoids (cortisol and cortisone): Glucose regulation and protein metabolism, important to deal with stress.

Question 31

Describe the secretory cells of the adrenal medulla, which hormones do they synthesize?

Answer 31

Specialized sympathetic postganglionic nerve cells that secrete hormones into the circulatory system.

Synthesizes epinephrine and norepinephrine.

Question 32

Describe the effects of these hormones

Answer 32

Epinephrine: Increases blood glucose levels and increase basal metabolic rate.

EP and NEP: Increase rate and strength of heartbeat, and dilate and constrict blood vessels which increases blood supply to parts of the body.

Question 33

What is Diabetes mellitus?

Answer 33

Inability to produce insuline or inability to use insulin.

Insulin reduces glucose levels in blood. Without it, blood glucose levels rise dramatically and glucose spills in urine. Water flows out of the body in urine and leads to dehydration.

Without insuline, break down of fats and proteins to find energy. –> Body weight declines.

Ketones = metabolites that breakdown fat, acidic and accumulation in blood can lead to acidosis –> coma and death. ;[

Question 34

What are the three “Poly’s” of Diabetes Mellitus?

Answer 34

Polyuria: Excessive urination resulting from excess water lost in urine.

Polydipsia: Excessive thirst (followed by drinking copious amounts of water) resulting from water loss

Polyphagia: Extreme hunger and eating due to the inability to use carbohydrates as an energy souce and the loss of fats and proteins from the body b/c of their use as energy source.

Question 35

Describe Type 1 and Type 2 Diabetes.

Answer 35

Type 1 Diabetes: Insulin dependent diabetes mellitus (IDDM) –> need insulin injections.

Insulin not produce b/c person’s immune system destroys pancreatic beta cells.

3 polys obvious with onset of symptoms and aid in diagnosis

Type 2 Diabetes: Non-insulin-dependent diabetes mellitus (NIDDM)

Pancreas produces and secretes insulin normally but target cells less sensitive to insulin

Much more common than type 1 DM

Clinical symptoms milder than type 1

High glucose levels controlled by diet, exercise, and weight loss.