Endocrine System Flashcards
Define Homeostasis
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
What is an exocrine gland? Give an example.
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.
What is an endocrine gland? Give an example.
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
What do we call the cell that responds to a particular hormone? Why do these cells repond and others do not?
Target cell.
Because target cells bear receptors to respond to the hormone.
What type of activities does the endocrine system control and why?
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.
What is the hypothalamus, where is it found and what are its functions?
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.
Describe feedback mechanisms and explain why positive feedback is less common.
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)
Give some examples of functions of hormones.
- 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
Give some examples of effects caused by hormones.
- 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
Describe the two major types of hormones and give some examples of each.
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)
Describe the effect of steroid hormones (i.e. where is the receptor located and what happens when the hormone binds to the receptor).
Receptor in cytoplasm or nucleus. Attaches to DNA and activate certain genes (prot. synthesis)
Describe the effect of water soluble hormones (i.e. where is the receptor located and what happens when the hormone binds to the receptor).
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.
What are the three main stimuli to control hormone release, give an example of each.
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
Describe the relationship between the pituitary gland and the hypothalamus.
Pituitary attached to the hypothalamus by a short stalk (posterior lobe).
Lies immediately beneath hypothalamus in a depression of the base of the skull.
Describe the morphology of the pituitary gland (i.e. anterior and posterior lobes).
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.
What are the two hormones that the neurosecretory cells of the posterior pituitary secrete and describe the function of each.
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 –
What is the difference between a tropic and non-tropic hormone?
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.
Describe the negative feedback control over the pituitary hormones, include the role of the hypothalamus. Give an example using thyroid hormones.
- Thyroid-releasing hormone is secreted by hypothalamic neurons
- receptors on thyrotrophs in the anterior pituitary and stimulates secretion of TSH.
- 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.
- When blood concentrations of thyroid hormones increase above a certain threshold, TRH-secreting neurons in the hypothalamus are inhibited and stop secreting TRH
What are the functions of growth hormone?
Controls development and growth as well as metabolic activities such as use of body fat and protein synthesis.
What happens if growth hormone levels are high in childhood, low in childhood, or high in adulthood?
Low in childhood: Dwarfism
High in childhood: Gigantism
High in adulthood: Acromegaly (overgrowth of bone in areas still responsive to GH effects)
Which cells have receptors for thyroid hormone? What are some of the functions of thyroid hormone?
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.
What happens if thyroid hormone levels are high in adulthood, or low in adulthood?
High in adulthood: Hyperthyroidism (High bp, high T°, HR, irritability)
Low in adulthood: Hypothyroidism (weight gain, memory loss, lethargy)
What is goiter, what causes it?
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.
The parathyroid hormones control homeostasis of what ion? Why is this ion important?
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
