Chapter 7 - The Endocrine Glands Flashcards
The thyroid gland consists of ____ lobes of endocrine tissue
2
What are the major thyroid secretory cells?
follicular cells
What is the functional unit of the thyroid gland?
a follicle
What is a follicle?
-follicular cells arranged in hollow spheres
-the lumen is filled with colloid
What is the purpose of the colloid?
it serves as an extracellular storage site for thyroid hormone (TH)
Thyroglobulin (Tg)
-a large protein molecule
-the chief constituent of the colloid
What are the two iodine containing hormones produced by follicular cells?
-Thyroxine (aka T4 or tetraiodothyronine)
-Tri-iodothyronine (T3)
What are the iodine-containing hormones derived from?
amino acid tyrosine
____% of the hormone secreted is T4 and the other 10% is T3
90
Together T3 and T4 make ____
thyroid hormone
Where are C cells housed?
between the follicles in the interstitial space
What do C cells secrete?
calcitonin (calci-bone-in)
What are the two basic ingredients of TH?
iodine and tyrosine
How is tyrosine obtained?
synthesized by the body (housed in Tg)
How is iodine obtained?
dietary intake
Where does TH synthesis occur?
on thyroglobulin molecules within the colloid
How is Tg (+ tyrosine) exported into follicular cells colloid?
exocytosis
How is iodine brought into colloid?
iodine pump
Where does iodine attach to tyrosine?
in the colloid
Where is TH stored until they are split off and secreted?
in the colloid
Enough TH is stored to supply the body for how long?
several months
T3 and T4 are stored bound to _____
thyroglobulin
How are T3 and T4 ‘freed’?
-follicular cells phagocytize a piece of colloid to break the Tg molecule down
-T3 and T4 diffuse across plasma membrane into the blood
How many iodine molecules does T3 contain?
3
How many iodine molecules does T4 contain?
4
What type of hormone is TH?
amine
How many tyrosines are attached to TH?
2
Is TH lipophilic or hydrophilic?
lipophilic
How does TH transport in the blood?
bound to plasma proteins
What plasma protein transports TH
thyroxine-binding globulin
What is the major biologically active form of TH? Why?
-even though the majority of TH released is in T4 form, target cells at the liver and kidney take off one of the iodine molecules and convert it to T3
-T3 is 4x stronger than T4
How many cells in the body have receptors for TH in their nuclei?
almost all of them
What does TH do to cells?
-alters gene transcription and protein synthesis (how cells make new proteins)
What are the 3 major actions of TH?
- metabolic rate and heat production
- sympathomimetic (mimic SNS)
- growth and CNS development
TH is the main determinant of B_______ M_______ R_____
basal metabolic rate
Basal Metabolic Rate
the number of calories you burn as your body performs basic life-sustaining functions
TH has what action on BMR?
-it is calorigenic, meaning it produces heat
How does TH generate heat?
-it stimulates the Na+/K+ ATPase pump and generates heat through glycolysis
Does TH directly alter heart rate?
no
What does sympathomimetic mean?
-sympathetic mimic
-TH has the ability to mimic the effects of the sympathetic nervous system (fight or flight)
TH has a permissive action on _______.
catecholamines (epinephrine)
How does TH mimic the sympathetic NS?
-it increases target cell responsiveness to epinephrine by increasing B-adrenoceptors on the heart
What is the sympathomimetic effect of TH?
increases heart rate and force of contraction
What is a by-product of TH’s sympathomimetic effect?
heat production
TH promotes normal development of the nervous system by…
-stimulating GH release and ISF production
-enhances their effects on growth
What can an absence of T3 and T4 during fetal life lead to?
congenital hypothyroidism (cretinism)
What is an example of something that leads to congenital hypothyroidism?
lack of iodine in pregnant mother
What hormone stimulates the thyroid gland to make and release TH?
Thyroid stimulating hormone (TSH)
What can an absence of TSH lead to?
thyroid gland atrophy
What can an excess of TSH lead to?
-thyroid gland hypertrophy (size of cells) and hyperplasia (amount of cells)
-leads to Goiter (enlarged thyroid gland)
TH secretion is regulated by a ______ -feedback system
negative
What hormone is released by the hypothalamus to stimulate TSH secretion?
thyroid-releasing hormone (TRH)
What causes hypothyroidism?
-Primary: thyroid gland failure
-Secondary: TRH or TSH deficiency
-inadequate iodine supply
What is myxedema?
-a term used for hypothyroidism in adults
What causes the edema seen in hypothyroidism?
accumulation of mucopolysaccharides under the skin
Symptoms of Hypothyroidism
-increased sensitivity to cold (calorigenic)
-weight gain (calorigenic)
-fatigue
-slow, weak pulse
-impaired mental function
How is hypothyroidism treated?
-replacement hormone therapy
-dietary idodine
Grave’s Disease
-an autoimmune disease that causes by hyperthyroidism
-causes exophthalmos (wide eyes)
What does the body produce in hyperthyroidism?
-thyroid-stimulating immunoglobulins (TSI)
-mimic TSH
What are the 3 causes of hyperthyroidism?
-Grave’s disease
-excess TRH or TSH secretion
-thyroid tumour
Hypothyroidism causes increased plasma TSH levels, except when…
the cause is hypothalamic or anterior pituitary failure
Hyperthyroidism causes decreased plasma TSH levels, except when…
the cause is excess hypothalamic or anterior pituitary secretion
What are the symptoms of hyperthyroidism?
-heat intolerance
-weight loss
-muscle weakness
-increased apetite
-increased SNS activity (heart rate, anxiety)
How is hyperthyroidism treated?
-surgical removal of part of they over secreting thyroid
-radioactive iodine administration
-antithyroid drugs
Where are the adrenal glands located?
above each kidney
What encloses the adrenal glands?
a capsule of fat
The adrenal cortex is the ______ portion.
outer
What type of hormones does the adrenal cortex secrete?
steroid hormones
The adrenal medulla is the _____ portion.
inner
What type of hormones does the adrenal medulla secrete?
catecholamines (norepinephrine and epinephrine)
What are the 3 layers/zones of the adrenal cortex from outward in?
-zona glomerulosa
-zona fasciculata
-zona reticularis
What does the zona glomerulosa secrete?
aldosterone (mineralcorticoids)
What does the zona fasciculata secrete?
mainly cortisol some DHEA
What does the zona reticularis secrete?
mainly DHEA some cortisol
Which adrenal cortex zone is the largest?
the middle zone - zona fasciculata
What are the 3 categories of adrenal steroids?
-mineralocorticoids
-glucocorticoids
-sex hormones
Mineralcorticoids
-mainly aldosterone
-influences Na+ and K+ balance
Glucocorticoids
-mainly cortisol
-role in glucose, protein, lipid metabolism
Sex Hormones
-identical or similar to those produced by gonads
-DHEA is the most abundant
Dehydroepiandrosterone (DHEA)
-male ‘sex’ hormone
The adrenal cortex hormones are ______ based and hydro ____.
cholesterol based; hydrophobic
How are steroid hormones carried in the blood?
bound to plasma proteins
Which plasma protein does cortisol bind to?
corticosteroid-binding globulin
Which plasma protein do aldosterone and DHEA bind to?
albumin
Where does aldosterone act?
on distal and collecting tubules of the kidney
What controls the secretion of aldosterone?
the renin-angiotensin-aldosterone system
RAAS increases aldosterone secretion when… and results in…
-when Na+ reduction is detection with a fall in blood pressure
-directly stimulated by rise in plasma K+ concentration
-results in Na+ reabsorption, water follows to increase blood pressure
Aldosterone is __________ of anterior pituitary control.
independent
What can cause aldosterone hypersecretion?
-adrenal tumour made of aldosterone-secreting cells
-Conn’s syndrome (primary)
-high RAAS activity (secondary)
What are the symptoms of aldosterone hypersecretion?
-high blood pressure
-less urine volume
-highly concentrated urine
What is another name for glucocorticoids?
corticosteroids
What do steroid hormones do?
glucose, protein, fat metabolism
What is the most abundant steroid hormone?
cortisol
What are the 4 functions of cortisol?
-hepatic glucogenesis
-increases plasma glucose
-stimulates protein degradation
-facilitates lipolysis
Hepatic Glucogenesis
-conversion of non-carbohydrate sources (ie. amino acids) into carbohydrates in the liver
-cortisol increases this process by up to 10x
When is glucogenesis by cortisol important?
maintaining glucose levels between meals
How does cortisol increase plasma glucose?
-by inhibiting glucose uptake by tissues (not the brain)
Why does cortisol contribute to protein degradation?
-uses the proteins in muscles to get amino acids to make glucose
-why we have muscle breakdown when stressed
What is lipolysis?
-splitting of adipocytes from triglycerides to increase fatty acids in the blood
How does lipolysis contribute to stress adaptation?
the fatty acids are used as alternative fuel while glucose is being used for the brain
Cortisol has a characteristic dinural rhythm, what does this mean?
-its secretion is cyclical, more is secreted in the morning and less at night
What are the hormones involved in the cortisol negative-feedback loop?
-hypothalamic CRH
-anterior pituitary ACTH
What hormone requires the permissive action of cortisol?
catecholamines (epinephrine)
What does cortisol allow epinephrine to do?
-permit induction of vasoconstriction
What do cortisol and epinephrine do during stressful situations?
-induce vasoconstriction to prevent circulatory shock
Cushing’s Syndrome
-caused by cortisol hypersecretion when adrenal cortex is overstimulated by CRH and ACTH
What are other causes of cortisol hypersecretion?
-adrenal tumour secreting cortisol (ACTH independent)
-ACTH secreting tumours
Symptoms of Cushing’s Syndrome
-hyperglycaemia (diabetes mellitus levels)
-fat redistribution (buffalo hump and mood face)
-muscle weakness
-osteoporosis
-immunosuppression
-hypertension
-stratia line on skin caused by protein breakdown
-red cheeks
How is Cushing’s Syndrome treated?
-surgical removal of the pituitary tumour
-adrenalectomy
Does the adrenal gland only secrete sex hormones relative to biological sex?
No, it secretes both male and female sex hormones in both sexes
What is the only adrenal sex hormone that has biological importance?
DHEA
Which pituitary hormone drives DHEA?
ACTH (not FSH or LH)
What overpowers DHEA in males?
testicular testosterone
What does DHEA do in females?
-pubic and axillary hair growth
-pubertal growth spurt
-development and maintenance of sex drive
What is adrenogenital syndrome?
hypersecretion of adrenal androgen
Symptoms of adrenogenital syndrome in adult females:
-male like body hair (hirsutism)
-deep voice
-muscular arms and legs
-smaller breasts
-possible menstruation caseation
Why does excess DHEA production occur?
-malfunctioning adrenal gland doesn’t make cortisol in response to ACTH due to absent enzymes
-DHEA production increases
How do gonads respond to increased DHEA production?
-inhibition of gonadotropins
-no sex hormone or gamete production (sterile)
How is adrenogenital syndrome treated?
glucocorticoid therapy
What are the symptoms of adrenogenital syndrome in newborn females?
male-type external genitalia
What are the symptoms of adrenogenital syndrome in prepubertal males?
-precocious pseudo-puberty (facial hair but no sperm)
Does adrenogenital syndrome have an effect on adult males?
no
The adrenal medulla is a modified part of which nervous system?
sympathetic nervous system
How does the adrenal medulla respond?
releasing their chemical transmitter into circulation
What is the primary stimulus of the adrenal medulla?
stress
What does the adrenal medulla release?
catecholamines - 80% epinephrine and 20% norepinephrine
How do catecholamine activities differ?
depending on the adrenergic receptor type
What is another name for epinephrine?
adrenaline
What does epinephrine do?
-reinforce the SNS fight or flight response
-increases heart rate
-increases blood glucose and fatty acids
-inhibits insulin secretion
Where are catecholamines stored?
chromaffin granules
How does epinephrine inhibit insulin secretion?
by increasing glucagon secretion
Stress Definition
a generalized, nonspecific response to any factor that overwhelms the body’s ability to maintain homeostasis
Stressor Definition
any stimulus that brings about the stress response
Generalized Stress Response
-↓ insulin secretion
-↑ glucagon secretion
-elevated blood glucose and fatty acids
How are blood volume and blood pressure maintained?
-increased RAAS activity
-increased vasopressin secretion
Metabolism Definition
all the chemical reactions that occur within the cells of the body
Anabolsim
build up or synthesis of larger organic macromolecules from small organic subunits
Do anabolic reactions require ATP?
usually
What do anabolic reactions result in?
-manufacture of needed cell materials
-storage of excess nutrients
Catabolism
breakdown or degradation of large, energy rich organic molecules within cells
What are the 2 levels of catabolic breakdown?
- hydrolysis of large molecules into subunits
- oxidation of subunits to yield ATP energy
What are the most important hormones in regulating fuel metabolism?
insulin and glucagon
What are the endocrine cells in the pancreas called?
Islets of Langerhans
What occurs at Beta cells?
insulin synthesis and secretion
What do alpha cells produce?
glucagon
What do delta cells do?
somatostatin synthesis
What are the least common islet cells?
PP cells
What do PP cells secrete?
pancreatic polypeptide
Is insulin an anabolic or catabolic hormone?
anabolic
What is the major insulin stimulus?
blood glucose
When is insulin secretion increased?
during absorptive state
Insulin promotes the cellular uptake of g_____, f___ a____, and a_____ a____
glucose, fatty acids, amino acids
What does insulin turn glucose into?
glycogen
What does insulin turn fatty acids into?
triglycerides
What does insulin turn amino acids into?
proteins
What factors increase blood glucose?
-GI tract glucose absorption
-hepatic glucose production (glycogenesis of stored glucose, glucogenesis)
What factors decrease blood glucose?
-glucose transport into cells for energy production or storage (as glycogen or triglycerides)
-urinary glucose excretion
Insulin _____ blood glucose
decreases
Insulin ____ blood fatty acids
decreases
Insulin ______ blood amino acids
decreases
Insulin ______ protein synthesis
increases
Insulin _______ fuel storage
increases
What is the most common endocrine disorder?
diabetes mellitus
_______ blood glucose levels is the prominent feature of diabetes mellitus.
elevated
What is type I diabetes?
lack of insulin secretion to store glucose
What is the occurrence of type I diabetes?
10%
What is type II diabetes
characterized by normal insulin secretion but reduced sensitivity of insulins target cells (insulin resistance)
What is the occurrence of type II diabetes?
90% (more common)
What is a classic sign of diabetes mellitus?
-polyuria (large urine production)
-glucose in urine, water stays with glucose (osmotic diuresis)
