Module 13 Flashcards
Define endocrine gland
A group of specialized cells that synthesize, store, and release hormones into the bloodstream to circulate to specific target cells with receptors for the hormone, which will either stimulate or inhibit activity of the cell
Define hormone
A chemical released by an endocrine gland that, when bound to a receptor, can stimulate or inhibit the activity of a cell
List the major organs in the endocrine system
Hypothalamus Pituitary gland Thyroid gland Parathyroid glands Adrenal glands Pancreas Gonads (ovaries or testes)
List the functions of the endocrine system
Maintenance of the internal environment
Adaptation to stress
Control of growth and metabolism
Control of reproduction
Identify 3 chemical subtypes of hormones
Derived from Tyrosine (amino acid)
Derived from proteins
Steroid hormones
Describe how hormones with different chemical makeups are carried in the blood
Protein hormones - hydrophilic, circulate freely in the blood, but cannot diffuse through cell membrane
Steroid and thyroid (tyrosine) hormones - hydrophobic, require a protein carrier to circulate in the blood, but diffuse freely through the cell membrane
Describe the basic features of hormones
Secreted into the blood in pulses by specific stimuli, in amounts that vary with strength of stimulus
Once secreted, are present in very small concentrations in the blood
Exert their effects by binding to receptors and regulating pre-existing reactions
Define a hormone receptor
A unique structure in or on a cell that interacts with a hormone in a particular way
Can be located on the membrane, in the cytoplasm, or in the nucleus
Describe receptors for hydrophilic hormones
Found on the cell membrane
When hormones attach, initiates a sequence of chemical reactions that will eventually alter activity in the cell
Three ways for the receptor to affect the cell: second messenger, tyrosine kinase, G-proteins
Describe how the second messenger system works
Hormone binds to receptor, causes G-protein on inside of membrane to produce a second messenger (first messenger is the hormone), normally cAMP, released into cytoplasm, rapidly alters proteins already in the cell, altered proteins trigger sequence of reactions to alter cell activity
Describe how tyrosine kinase works
Hormone/receptor complex activates tyrosine kinase on the inside surface of the membrane, and tyrosine kinase alters existing proteins that will then alter cell activity
Describe how G-proteins work
When hormone attaches to receptor, G-protein activates within the cell, can open adjacent ion channels
Describe how hormones are removed from blood
Same mechanism as other substances, metabolic destruction in the blood or by tissues (mainly liver and kidney), excretion by liver into bile, or excretion by kidneys into urine
Describe how hormone secretion is controlled
Negative feedback
Describe the location and general structure of the hypothalamus
Located at the base of the brain, above the pituitary gland and below the thalamus
Composed of many regions made of groups of nerve cell bodies (nuclei), several nuclei control the release of hormones from the pituitary gland
List the functions of the hypothalamus (what its hormones contribute to)
Homeostatic mechanisms (body temp, water balance, energy production), regulates some behavioural drives of thirst, hunger, and sexual behaviour
Performs these functions by receiving large amounts of info from the body, including metabolic, hormonal, temp, and neural info
List the hormones the hypothalamus releases
Prolactin Releasing Hormone (PRH) Prolactin Inhibiting Hormone (PIH) Thyrotropin Releasing Hormone (TRH) Corticotropin Releasing Hormone (CRH) Growth Hormone Releasing Hormone (GHRH) Growth Hormone Inhibiting Hormone (GHIH) Gonadotropin Releasing Hormone (GnRH)
Describe the structure of the pituitary gland
Two regions, anterior and posterior
Anterior is made of endocrine tissue
Posterior is made of neural tissue
Describe the function of the pituitary gland
Anterior receives hormones from the hypothalamic-hypophyseal portal system (releasing or inhibiting hormones to either stimulate or release pituitary hormones)
Posterior receives hormones from the hypothalamic-hypophyseal tract (neurohormones)
Describe the functions of posterior pituitary hormones
ADH regulates water reabsorption in the kidney
Oxytocin regulates milk release from the breasts and causes contraction of the uterus during labour
List the anterior pituitary hormones and associated hypothalamus hormones
Thyroid stimulating hormone (TSH) in response to TRH stimulates thyroid to secrete thyroid hormones, also causes growth of the thyroid (hyperplasia)
Adrenocorticotropic hormone (ACTH) in response to CRH, stimulates adrenal glands to secrete cortisol
Growth hormone (GH) in response to GHRH or GHIH/somatostatin, GHRH is stronger
Luteinizing hormone (LH) and follicle stimulating hormone (FSH) in response to GnRH, acts on testes and ovaries
Prolactin (PRL) in response to PRH and PIH, PIH is stronger, stimulates breast milk production
Describe three ways the pituitary gland is regulated by negative feedback
Hypothalamus secretes H1, causes release of anterior pituitary H2, H2 can feed back to hypothalamus to decrease release of H1 (short loop feedback)
H2 can circulate to an endocrine gland to cause release of an H3, which can feed back to hypothalamus and pituitary to decrease release of H1 and H2 (long loop)
H3 can affect one or more target tissues, whose response can feed back to decrease release of H1 (ultra long loop)
Describe regulation of prolactin
Released from AP when PIH levels decrease, suckling causes decrease in PIH to cause secretion of prolactin, when suckling stops PIH levels increase, prolactin levels decrease (short loop)
Describe regulation of TSH
TRH (H) causes release of TSH (AP), stimulates thyroid gland to secrete T3 and T4, both feed back to H to decrease TRH release and AP to decrease TSH release (long loop)
Describe regulation of GH
GHRH (H) stimulates release of GH (AP) and GHIH (H) decreases it, GH feeds back to H to decrease GHRH release (short loop)
Describe regulation of ACTH
CRH (H) released into portal system, causes release of ACTH (AP), which stimulates adrenal glands to secrete cortisol, aldosterone and androgens, cortisol feeds back to both H and AP to decrease CRH and ACTH release (long loop)
Describe regulation of FSH and LH
GnRH (H) stimulates release of LH and FSH (AP), travel to gonads (testes or ovaries) to stimulate release of sex hormones, sex hormones feed back to H and AP to inhibit GnRH and LH/FSH (long loop)
Describe position of thyroid and general structure
Thyroid gland lies below larynx, consists of two lobes that almost completely surround trachea
Made of follicles (functional units of the gland), consisting of central region of colloid surrounded by epithelial cells, between follicles are parafollicular or C cells
Describe functions of the thyroid
First organ identified as a gland, produces T3 and T4, both contain iodine, responsible for regulating BMR
Made of tyrosine (hydrophobic, requires protein carrier but diffuse through cell membrane)
Follicular cells of thyroid produce the protein hormone calcitonin which causes decrease in Ca++ levels in the blood
Describe the production of T3 and T4
Produced inside follicles, combine iodine and tyrosine with a glycoprotein thyroglobulin
Epithelial cells absorb tyrosine, combine it with thyroglobulin (produced in the cells), absorb iodine from the diet, tyrosine-thyroglobulin complex secretes into colloid, 1-2 molecules of iodine attach to each
If 4 attach, T4, if 3 attach, T3
Describe secretion of T3 and T4
TSH from AP binds to receptor on membrane of epithelial cell, stimulates multiple reactions:
Traps and takes up iodine
Stimulates endocytosis of T3 and T4-thyroglobulin complex
Enzymatic removal of thyroglobulin from T3 and T4
Stimulates secretion of T3 and T4 into blood
Describe regulation of T3 and T4 secretion
T3 and T4 feed back to H and AP to inhibit TRH and TSH (long loop)
Describe the circulation of T3 and T4
90% of released thyroid hormones are T4, 10% is T3, both tyrosine based and hydrophobic
Even though mostly T4 secreted, much is converted to T3, which is more biologically active than T4
Describe the effects of T3 and T4 on the body
Hydrophobic, diffuse through cell membrane, receptors in nucleus of almost all cells, alter transcription of genes for many proteins and enzymes enhancing metabolic activity of the cells
T3 and T4 are responsible for regulating body’s BMR, and responsible for proper development of the nervous system in the fetus, help maintain alertness, responsiveness, and emotional state
Define basal metabolic rate (BMR)
The amount of O2 and energy the body is using at rest, or the least amount of energy a person will use
Describe the results of an increase in thyroid hormones
Increased body temperature Increased cardiac output Increased ventilation Increased food intake Increased breakdown of energy stores (carbs, fats, proteins)
Describe goiter
Disease resulting in enlargement of thyroid gland, caused by insufficient iodine in diet or too much TRH/TSH being produced
Hypothalamic tumour can cause excess TRH or TSH secretion, causing uncontrollable thyroid growth
Without iodine in blood, thyroid unable to produce T3 and T4, and in absence of these, no negative feedback, so TRH and TSH continue being secreted
Describe causes of hypothyroidism
Before or after birth and during childhood, insufficient amounts of thyroid hormones result in cretinism (dwarfism and mental retardation), can be prevented with thyroid hormone treatments
Can be caused by lack of thyroid gland, inability of gland to produce T3 or T4 due to genetic defect, or lack of iodine in diet
Describe symptoms of hypothyroidism
Low BMR Sensitive to cold temperatures Weight gain due to decreased fat breakdown and increased fat storage Low blood pressure/weak pulse Slow reflexes, apathy, lethargy Depression Easily fatigued
Describe hyperthyroidism and symptoms
Excess thyroid hormone secretion
High BMR Sensitive to warm temperatures Weight loss due to increased fat breakdown and decreased fat storage Rapid heart rate Hyperactive or "nervous" activity
Describe calcitonin and its effect on the body
A protein hormone secreted by parafollicular/C cells, which make up 0.1% of thyroid gland
Calcitonin helps regulate blood Ca++ levels, secreted when levels rise above normal
Decreases activity of osteoclasts (responsible for enzymatically breaking down bone into Ca++ that is released into blood
Calcitonin also stimulates secretion of Ca++ into urine
Works with parathyroid hormone (PTH)
Describe the parathyroid glands
Located on posterior side of thyroid, 4 of them, small, secrete PTH
Describe parathyroid hormone and its effects
Secreted when blood calcium levels are low, acting antagonistically to calcitonin
Increases number and activity of osteoclasts, releasing calcium into blood
Decreases excretion of calcium in urine by reabsorbing it from filtrate
Without PTH, kidney would continually excrete Ca++, depleting bones and extracellular fluid of Ca++
Describe the location and structure of adrenal glands
One resting on top of each kidney, made of neural and glandular tissue
Inner medulla is neural tissue under control of SYN
Outer cortex is endocrine under control of PSYN
Cortex has 3 layers: outer zona glomerulosa, middle zona fasciculata, inner zona reticularis, each secreting different hormone
Describe the function of each adrenal gland region and the hormone it secretes
All cortex hormones are steroid hormones (hydrophobic)
Outer zona glomerulosa secretes aldosterone (mineralocorticoid, regulates mineral and fluid volume by kidneys)
Middle zona fasciculata secretes the glucocorticoid hormone cortisol (helps in glucose metabolism)
Inner zona reticularis secretes small amounts of androgens (sex steroids)
Medulla secretes epinephrine/adrenaline
Describe the release and effects of epinephrine
Released from medulla when stimulated by SYN, increases heart rate and force of contraction, and increases blood flow to heart and skeletal muscle
Describe the release and effects of aldosterone
Secreted in response to Ang II, low Na+ levels and high K+ levels in blood, and ACTH
Stimulates reabsorption of Na+ in nephrons
List the types of stress that increase cortisol production and secretion
Stress: Physical (extreme hot or cold) Physiological (pain, loss of blood, low blood sugar) Emotional (fear or anxiety) Social (personal conflicts)
Describe how stress stimulates production and secretion of cortisol
Stress stimulates H to secrete CRH, causes AP to secrete ACTH, stimulates adrenal glands to produce cortisol
Describe how cortisol has its effects on the cell
Hydrophobic, carried in blood attached to proteins, releases from proteins to diffuse through cell membrane and attach to receptors in the cytoplasm, then translocates into nucleus where it will alter cell activity
Describe the rhythmic blood concentration of cortisol
Varies due to the body’s circadian rhythm, low most of the day and evening, increases between 2-4am and peaks just before waking
Describe how cortisol is involved in glucose metabolism
A glucocorticoid, protects against low blood glucose levels (hypoglycemia), is catabolic (causes breakdown of complex molecules to be used for energy)
Will cause breakdown of metabolic substrates like carbs to glucose, proteins to amino acids, fat to fatty acids and glycerol
Describe how cortisol effects different tissues
Liver: increases gluconeogenesis (producing glucose molecules from non-carbs like fats and amino acids)
Skeletal muscle: decreases protein synthesis and glucose uptake, increases breakdown of proteins
Adipose tissue: decreases fat synthesis, increases lipolysis (breakdown of fat except in abdomen and cheeks)
Describe Cushing’s Syndrome and its symptoms
Disease of the adrenal glands, causes excess secretion of cortisol
Wasting of muscles Thin skin Poor wound healing Fat deposits in cheeks and abdomen Depression
Describe location and structure of the pancreas
Parallel and beneath the stomach
Contains endocrine tissue (secretes hormones) and exocrine tissue (secretes chemicals)
Endocrine portion consists of 1-2 million pancreatic islets, three kinds: alpha (25%) beta (60%) and delta (10%)
Exocrine portion consists of pancreatic acinar cells and ducts
Describe insulin and its function
Protein hormone secreted by beta cells
Causes cells to rapidly take up, store, and use glucose, decreasing blood glucose levels
Secreted when blood glucose levels increase, even small increases in blood glucose cause large amounts of insulin release
All cells respond, but liver, muscle and adipose tissue respond best
Describe glucagon and its function
Works in opposition to insulin
Protein hormone secreted by alpha cells
Increases blood glucose concentrations, secreted when blood glucose levels decreases and when amino acid levels in the blood rise
Stimulates liver where it causes glycogenolysis (breakdown of glycogen) and gluconeogenesis (formation of new glucose)
Secreted during long, exhaustive exercise, up to 4-5x normal amount
Describe somatostatin and its function
Somatostatin is also GHIH
Protein hormone secreted by delta cells
Secreted when blood glucose levels rise, when amino acid levels in the blood increase, and when there is an increase in blood born fats (all related to food ingestion)
Primary function is to reduce secretion of both insulin and glucagon
Describe blood glucose regulation
Normal: 80-90mg/mL blood
Hour after meal, can rise to 120-140mg/mL blood, but once all carbs absorbed, levels return to normal with help of insulin
During starvation, glucagon stimulates gluconeogenesis to maintain 80-90mg/mL blood
Define diabetes mellitus
A disease involving either the inability of the pancreas to produce insulin or the inability of the target cells to react to insulin in the blood
Briefly describe type I diabetes
Insulin-dependent diabetes
Involves damage of beta cells leading to lack of insulin production
Occurs around 14 (juveniles)
Immune system attacks and destroys beta cells
Without insulin produced, blood glucose levels can reach 300-1200mg/mL blood
Body must rely on fats and amino acids as fuel instead of glucose
Briefly describe type II diabetes
Most common, 80-90% of cases
Onset often after 40 (adult)
Insulin has little effect on body cells, as if resistant to insulin
Causes insulin to flood system, depleting beta cells, causing decreased insulin release in later stages of the disease
Most patients are obese and can be controlled through diet
List symptoms of diabetes
Type I diabetes: Increased glucose in urine Increased dehydration Damage to blood vessels Severe metabolic acidosis Depletion of protein stores
Type II diabetes: (later stages)
Increased glucose in urine
Increased dehydration
Damage to blood vessels
