General Physiology Lesson 12

Define hormone.

Chemical substances used by the neuroendocrine system to exert regulatory control over target cells.

What is an endocrine gland?

Organized tissues (e.g., adrenal gland, pituitary gland) or isolated cells/tissues that release hormones into the bloodstream.

Define neurosecretory tissue.

Hormone secreting cells that are stimulated by neural input (e.g., the adrenal medulla).

Define tropic hormone.

Hormones, such as those released by the anterior pituitary gland, that stimulate the release of other hormones.

Define Antidiuretic hormone (ADH).

A hormone released by the posterior pituitary gland (also known as vasopressin) that limits the production of urine and causes water retention in the kidneys and vasoconstriction.

Define oxytocin.

A hormone released by the posterior pituitary gland involved in contraction of the uterus during birth, lactation, and bonding.

Define releasing hormones.

Neurohormones released by the hypothalamus that stimulate the release of anterior pituitary hormones.

Define inhibiting hormones.

Neurohormones released by the hypothalamus that inhibit the release of anterior pituitary hormones.

Define endocrine axis.

A sequence of endocrine control, often involving the hypothalamus, pituitary, and a target gland.

Define antagonism (in hormonal regulation).

A hormonal relationship where one hormone opposes the effect of another (e.g., glucagon and epinephrine are insulin antagonists).

Define synergism (in hormonal regulation).

A hormonal relationship where two hormones work together to produce a combined effect (e.g., glucagon and epinephrine are synergistic to each other).

Define corticotropin releasing hormone (CRH).

A releasing hormone involved in the regulation of the stress response (HPA axis).

Define adrenocorticotropic hormone (ACTH).

A hormone released by the anterior pituitary that stimulates the adrenal cortex to release corticosteroids (e.g., glucocorticoids).

Define glucocorticoids.

Corticosteroids (e.g., cortisol) released by the adrenal cortex.

Define aldosterone.

A hormone that stimulates the kidney to retain Na+, which also leads to fluid retention.

Define insulin.

A peptide hormone secreted by pancreatic beta cells that promotes storage and uptake of nutrients into cells, acting to decrease blood glucose.

Define glucagon.

A peptide hormone secreted by pancreatic alpha cells that promotes glucose release from the liver.

Define diabetes mellitus.

A condition when the body doesn't produce enough insulin or recognize the insulin.

What is neural transmission characterized as?

Fast addressed signals.

What is endocrine transmission characterized as?

Slow, broadcast signaling.

What is paracrine transmission characterized as?

Local diffusion signaling.

What are pheromones?

Chemical signaling between conspecific organisms.

What regulates blood hormone levels?

Balancing synthesis and degradation rates.

Which control system (nervous or endocrine) typically directs communication at more specific targets?

Nervous system communication is directed at more specific targets.

Which system typically sends signals that are longer lasting?

Endocrine system signals are longer lasting.

Which system's signals usually travel a farther distance between the secretory and receiver cells?

The Endocrine system.

How does a hormone signal reach only the correct target tissue when released into the bloodstream?

The hormones will only bind to those cells that are expressing that hormone's receptor.

What determines the magnitude of a hormone's effect?

Both the abundance of the hormone and the abundance of the receptor.

What stimulates Epithelial (nonneural) endocrine cells to secrete hormones?

They are usually stimulated by other hormones (e.g., adrenal cortex).

What stimulates Neurosecretory cells to secrete hormones?

They are stimulated by neural input (e.g., adrenal medulla).

What are the three major classes of hormones?

Steroid hormones, Peptide hormones, and Amines.

What is the chemical derivative of Steroid hormones?

Cholesterol derivatives.

Are Steroid hormones water soluble or lipid soluble?

Lipid soluble.

Where are Steroid hormones secreted from?

Gonads and adrenal cortex

Where are the target receptors for Steroid hormones located?

Intracellularly.

How are Steroid hormones handled regarding storage?

They are synthesized as needed, not stored.

What is the chemical nature of Peptide hormones?

Peptide chains.

Are Peptide hormones water soluble or lipid soluble?

Water soluble.

How are Peptide hormones stored and released?

Stored in secretory granules and released by exocytosis (vesicle fusion).

Where are the target receptors for Peptide hormones located?

Extracellularly.

What ion is likely the molecule that causes the release of stored peptide hormones via exocytosis?

Ca2+.

What are Amine hormones derivatives of?

Tyrosine (e.g., catecholamines) and tryptophan (e.g., melatonin).

Name two glands or organs that secrete Amine hormones.

Adrenal medulla and thyroid.

What is the "master gland" located at the base of the hypothalamus?

The pituitary gland.

What are the two main parts of the pituitary gland?

The posterior pituitary (neurohypophysis) and the anterior pituitary (adenohypophysis).

What are the main functions of the posterior pituitary?

Water retention, birth muscle contraction, and lactation.

How is the posterior pituitary controlled?

By neural control from the hypothalamus via neural synapses.

What is the function of ADH (vasopressin) in the posterior pituitary?

Water retention in the kidneys and vasoconstriction.

What is the function of oxytocin in the posterior pituitary?

Contraction of the uterus during birth, lactation, and bonding.

What is the function of growth hormone (GH)?

Influences growth and metabolism of bone and muscle (a non-glandotropic hormone).

What is the function of adrenocorticotropic hormone (ACTH)?

Stimulates the adrenal cortex to release corticosteroids (e.g., glucocorticoids).

What is the function of thyroid stimulating hormone (TSH)?

Stimulates the thyroid to release thyroxins.

What are the functions of FSH (follicle stimulating hormone) and LH (lutenizing hormone)?

They stimulate the gonads to release estrogens and testosterone.

How is the anterior pituitary controlled by the hypothalamus?

Via neurohormones (releasing and inhibiting hormones) released through the hypothalamo-hypophysial portal system.

What controls the release of tropic hormones from the anterior pituitary?

Neurohormonal control from the hypothalamus via the portal system.

What sequence of hormones makes up the HPA axis release pathway, starting from the hypothalamus?

Corticotropin-releasing hormone (CRH) > Adrenocortiotropin hormone (ACTH) > Corticosterone (or Cortisol/Glucocorticoids).

What mechanism regulates the HPA axis?

Negative feedback.

What two systems work together to mediate the mammalian stress response ("fight or flight")?

The HPA axis and the sympathetic nervous system.

What is the value of vasoconstriction during the stress response?

To increase blood pressure.

What happens to insulin activity during the stress response?

It decreases (insulin is inhibited by epinephrine).

What is the value of decreased insulin activity during the stress response?

To increase available blood glucose for immediate use by any tissue.

Why are complex fuels (like proteins and lipids) broken down during the stress response?

To break them down into glucose, a fast fuel, prioritizing immediate payoff.

What potentially harmful result can chronic stress lead to?

Chronic fluid retention leading to chronic high blood pressure.

ADH (vasopressin) stimulates the kidney to retain fluid by doing what to the urine?

Concentrating the urine.

How does ADH cause water reabsorption in the kidney?

By stimulating membrane aquaporin channels, allowing water to diffuse back into the bloodstream by osmosis.

Aldosterone stimulates the kidney to conserve which ion?

Na+.

What hormonal system regulates blood pressure and water balance by conserving sodium ions?

The renin-angiotension-aldosterone system.

When is renin secreted?

When blood pressure is low, leading to the secretion of aldosterone.

When blood pressure is low, leading to the secretion of aldosterone.

It increases Na+-K+ pump activity to conserve Na+.

How does the action of aldosterone reinforce the action of ADH?

Aldosterone keeps the concentration gradient of water pointing toward the bloodstream (by conserving Na+).

What cells secrete insulin?

Pancreatic beta cells.

What cells secrete glucagon?

Pancreatic alpha cells.

What is insulin's primary effect on blood glucose levels?

Insulin acts to decrease blood glucose levels.

What is glucagon's primary effect on blood glucose levels?

It promotes glucose release from the liver, thereby increasing blood glucose levels.

Insulin and glucagon are antagonists; which hormone is synergistic with glucagon?

Epinephrine.

When should insulin levels be the highest?

Right after a meal.

What state inside the pancreatic beta cells most likely stimulates insulin release?

High ATP levels (Beta cells measure blood glucose via respiration).

How do beta cells release insulin?

From vesicles via the action of voltage-gated Ca2+ channels.

What change in ion conductance would most likely stimulate insulin release from beta cells?

Blocking K+ channels.

What metabolic process does insulin stimulate?

Glucose uptake and glycogen/fatty acid synthesis.

What is Type I Diabetes mellitus characterized by?

The body does not produce insulin, usually caused by autoimmune attack on the pancreas beta cells, with a strong genetic component.

What is Type II Diabetes mellitus characterized by?

The body produces insulin but the body becomes resistant to insulin, with a strong environmental component.

Why are the effects of Type II diabetes unlikely to be aided effectively by insulin injections alone?

Because the body is already resistant to the insulin.

What type of hormone is cortisol, and what does it promote in the liver?

A steroid hormone secreted by the adrenal cortex that promotes gluconeogenesis (increased blood glucose).

What type of hormone is epinephrine, and where is it secreted from?

A catecholamine secreted by the adrenal medulla.

Epinephrine promotes gluconeogenesis in the liver and is synergistic with which other hormone?

Cortisol.

Which hormone inhibits insulin?

Epinephrine.

Which ion conductance increases in the post-synaptic membrane often match an inhibitory synapse (like C)?

Chloride (C).

What combination of inhibitory synapses (C and B) would be least likely to generate an action potential?

Simultaneous activation of both inhibitory synapses (C + B).

In Rough-skinned newts, what immediate effect does injecting corticosterone have on mating males?

It quickly inhibits clasping behavior.

How does corticosterone exert its effect on newt behavior?

It acts upon brain cells to produce a paracrine inhibitor of the cells that control the clasping motor response.

Which hormone plays a role in bonding and monogamy in female prairie voles?

Oxytocin.

Which hormone plays a role in monogamy and aggression in male prairie voles?

ADH (vasopressin).

What behavioral change occurs in prairie voles a day after mating?

They become monogamous and the male becomes aggressive towards other males near his female.

How does insulin suppression relate to behavior in eusocial ants?

Low insulin levels suppress reproduction and induce the shift to caretaking behavior when ants are exposed to larvae.

What happens when ant adults are injected with insulin?

Their ovaries reactivate, even if larvae are still present.

How does the geography cone snail (C. geographus) use insulin?

It releases fish insulin into the water to slow its prey down.

Which genetic complex has been linked to influencing body odor and mate preference in humans?

Variations in the major histocompatibility gene complex (MHC).

People consistently preferred the scents of T-shirts worn by individuals whose MHC immune genes differed significantly from their own, suggesting a role in what?

Mating behaviors in humans.

What hormones are responsible for the main functions of the posterior pituitary (water retention, birth muscle contraction, and lactation)?

ADH and Oxytocin.