Chapter 16 Part A Flashcards
What is the primary function of the endocrine system?
To coordinate and integrate activity of body cells via hormones.
What is endocrinology?
The study of hormones and endocrine organs.
What are the main functions controlled by the endocrine system?
- Reproduction
- Growth and development
- Maintenance of electrolyte, water, and nutrient balance of blood
- Regulation of cellular metabolism and energy balance
- Mobilization of body defenses
What is the difference between exocrine and endocrine glands?
Exocrine glands produce nonhormonal substances and have ducts; endocrine glands produce hormones and lack ducts.
Name some major endocrine glands.
- Pituitary gland
- Thyroid gland
- Parathyroid glands
- Adrenal glands
- Pineal gland
What role does the hypothalamus play in the endocrine system?
It is considered a neuroendocrine organ.
What are the two main classes of hormones?
- Amino acid–based hormones
- Steroids
What are autocrines and paracrines?
- Autocrines: Chemicals that exert effects on the same cells that secrete them
- Paracrines: Locally acting chemicals that affect cells other than those that secrete them
What is the role of target cells in hormone action?
Target cells are tissues with receptors for a specific hormone that are affected by the hormone.
How do water-soluble hormones act on target cells?
They act on plasma membrane receptors and use G protein second messengers.
How do lipid-soluble hormones act on target cells?
They act on intracellular receptors that directly activate genes.
What is the cyclic AMP (cAMP) signaling mechanism?
A hormone binds to a receptor, activating a G protein that activates adenylate cyclase, converting ATP to cAMP, which then activates protein kinases.
What is the role of calcium ions in hormone signaling?
Calcium ions act as a second messenger that alters enzyme activity and channels.
True or False: Calcium ions can bind to regulatory proteins to amplify cellular response.
True.
What initiates the release of hormones in the endocrine system?
Hormone release is triggered by endocrine gland stimuli, nervous system modulation, and negative feedback systems.
What is the function of humoral stimuli in hormone release?
Changing blood levels of ions and nutrients directly stimulate secretion of hormones.
Fill in the blank: The three types of endocrine gland stimuli are _______ stimuli, _______ stimuli, and _______ stimuli.
humoral, neural, hormonal.
What is a humoral stimulus?
Hormone release caused by altered levels of certain critical ions or nutrients.
Example: Declining blood Ca2+ concentration stimulates parathyroid glands to secrete PTH.
What triggers the secretion of parathyroid hormone (PTH)?
Low concentration of Ca2+ in capillary blood.
What is a neural stimulus?
Hormone release caused by neural input.
How do sympathetic nervous system fibers affect hormone release?
They stimulate adrenal medulla to secrete catecholamines.
What is a hormonal stimulus?
Hormone release caused by another hormone (a tropic hormone).
What role do hypothalamic hormones play in the endocrine system?
They stimulate the release of most anterior pituitary hormones.
What is the feedback loop involving hypothalamic, pituitary, and target endocrine organs?
Hypothalamic hormones stimulate anterior pituitary hormones, which in turn stimulate target organs to secrete hormones.
What are the three factors that determine target cell activation?
- Blood levels of hormone
- Relative number of receptors on/in target cell
- Affinity of binding between receptor and hormone
What is up-regulation in hormone signaling?
Target cells form more receptors in response to low hormone levels.
What is down-regulation in hormone signaling?
Target cells lose receptors in response to high hormone levels.
What is the half-life of a hormone?
Time required for the level of hormone in blood to decrease by half.
What factors influence the concentration of circulating hormones?
- Rate of release
- Speed at which it is inactivated and removed from the body
How can hormones be removed from blood?
- Degrading enzymes
- Kidneys
- Liver
What are the typical response times for hormones?
Ranges from immediate responses to those that take hours to days.
What is permissiveness in hormone interaction?
One hormone cannot exert its effects without another hormone being present.
What is synergism in hormone interaction?
More than one hormone produces the same effects on a target cell, causing amplification.
What is antagonism in hormone interaction?
One or more hormones oppose the action of another hormone.
What is the function of the hypothalamus in relation to the pituitary gland?
It controls the release of hormones from the pituitary gland.
What are the two major lobes of the pituitary gland?
- Posterior pituitary
- Anterior pituitary
What type of tissue makes up the posterior pituitary?
Neural tissue.
What hormones are secreted by the posterior pituitary?
- Oxytocin
- Antidiuretic hormone (ADH)
What is the primary capillary plexus?
A network of capillaries in the hypophyseal portal system connected to the hypothalamus.
What hormones does the anterior pituitary secrete in response to hypothalamic stimulation?
- Growth hormone (GH)
- Thyroid-stimulating hormone (TSH)
- Adrenocorticotropic hormone (ACTH)
- Follicle-stimulating hormone (FSH)
- Luteinizing hormone (LH)
- Prolactin (PRL)
What is the role of oxytocin during childbirth?
It is a strong stimulant of uterine contractions.
What triggers the secretion of antidiuretic hormone (ADH)?
High solute concentrations in the blood.
What condition results from ADH deficiency?
Diabetes insipidus.
What is the syndrome of inappropriate ADH secretion (SIADH)?
Retention of fluid, headache, and disorientation.
What is the function of osmoreceptors in the hypothalamus?
They monitor solute concentrations in the blood.
What is vasopressin another name for?
Antidiuretic hormone (ADH) when in high concentrations.
What is diabetes insipidus?
ADH deficiency due to damage to hypothalamus or posterior pituitary
Must keep well hydrated
What are the symptoms of the syndrome of inappropriate ADH secretion (SIADH)?
Retention of fluid, headache, disorientation
Treatment includes fluid restriction and blood sodium level monitoring
How many hormones are secreted by the anterior pituitary?
Six hormones
All are peptide hormones
Which hormone is not a tropic hormone among anterior pituitary hormones?
Growth hormone (GH)
All but GH activate target cells via cAMP second-messenger system
What does growth hormone (GH) do?
Has direct actions on metabolism and indirect growth-promoting actions
Also called somatotropin
What are the direct actions of growth hormone (GH) on metabolism?
Glucose-sparing actions, triggers liver to break down glycogen into glucose, increases blood levels of fatty acids, encourages protein synthesis
GH decreases the rate of cellular glucose uptake and metabolism
What are insulin-like growth factors (IGFs)?
Produced by liver, skeletal muscle, and bone under stimulation from GH; stimulate cellular uptake of nutrients, formation of collagen, and deposition of bone matrix
Major targets of GH are bone and skeletal muscle
What regulates the secretion of growth hormone (GH)?
Hypothalamic hormones on somatotropic cells
GHRH stimulates GH release; GHIH inhibits release
What triggers the release of growth hormone-releasing hormone (GHRH)?
Low blood GH or glucose, or high amino acid levels
Ghrelin also stimulates GH release
What is the effect of hypersecretion of GH in children?
Gigantism
Can reach heights of 8 feet
What is the effect of hypersecretion of GH in adults?
Acromegaly
Results in overgrowth of hands, feet, and face
What is the effect of hyposecretion of GH in children?
Pituitary dwarfism
May reach a height of only 4 feet
What is thyroid-stimulating hormone (TSH) also called?
Thyrotropin
Produced by thyrotropic cells
What triggers the release of TSH?
Thyrotropin-releasing hormone (TRH) from hypothalamus
Inhibited by rising blood levels of thyroid hormones
What is adrenocorticotropic hormone (ACTH) also called?
Corticotropin
Secreted by corticotropic cells
What does ACTH stimulate?
Adrenal cortex to release corticosteroids
Triggered by hypothalamic corticotropin-releasing hormone (CRH)
What are gonadotropins?
Follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
Secreted by gonadotropic cells of anterior pituitary
What is the role of FSH?
Stimulates production of gametes (egg or sperm)
In females, LH helps mature follicles of egg
What is the role of LH in males?
Stimulates production of testosterone
LH promotes production of gonadal hormones
What regulates the release of gonadotropins?
Gonadotropin-releasing hormone (GnRH)
Suppressed by gonadal hormones
What is prolactin (PRL) primarily responsible for?
Stimulates milk production in females
Role in males is not well understood
What inhibits prolactin release?
Prolactin-inhibiting hormone (PIH), which is dopamine
Decreased levels lead to lactation
What is hyperprolactinemia?
Most frequent abnormality of anterior pituitary tumors
Clinical signs include inappropriate lactation, lack of menses, infertility in females, and impotence in males
