The Endocrine System Flashcards
intercellular communication
-preserves homeostasis
-mostly done through chemical messages
distant communication
is coordinated by endocrine and nervous systems
nervous system is fast
specific and short duration
endocrine system is slower
releases hormones into bloodstream that bind to target cells, long duration
nervous and endocrine systems comparison
-both rely on the release of chemicals that bind to specific receptors on target cells
-both share chemical messengers
-both are regulated by negative feedback mechanisms
-both coordinate and regulate activities of other cells, tissues, organs, and systems to maintain homeostasis
chemical messengers for nervous and endocrine systems
-Epinephrine (E) and norepinephrine (NE), hormones released from the adrenal medulla
-NE, a neurotransmitter when released in synapses
the endocrine system
-includes all endocrine cells and tissues
-cells are glandular and secretory
-secretions enter the ECF
-cytokines are local chemical messengers
-hormones are chemical messengers secreted into the blood and transported to target cells
peptide hormones
-largest group
-includes ADH, oxytocin, hypothalamic, pituitary, pancreatic hormones
lipids derivatives
-most derived from cholesterol
-steroid hormones released by reproductive organs and adrenal cortex
-for example, testosterone, estrogen
mechanisms of hormonal action
hormones alter operations of target cells
-changes identities, activities, locations, or quantities of structural proteins and enzymes
-sensitivity of target cell to hormones depends on specific receptors
-receptors are located either on plasma membrane or inside the cell
hormonal action at the plasma membrane
receptors on plasma membrane
-E, NE, and peptide hormones are not lipid soluble
-cannot diffuse through the plasma membrane
-must use a receptor on outside of membrane
-effect is not direct; they are first messengers that activate second messengers in the cytoplasm
-action is linked by G protein, an enzyme complex
cyclic-AMP second messenger system
cyclic AMP, or cAMP
-first messenger activates a G protein
-which activates enzyme adenylate cyclase
-which converts ATP to second messenger, cAMP
-which activates kinase enzymes inside cell
-which phosphorylates another molecule
-enzyme cascade
-produces amplification of signal
intracellular receptors
receptors inside cytoplasm or nucleus
-for thyroid and steroid hormones, lipid soluble
-forms hormone-receptor complex
-activates or inactivates specific genes
-alters rate of mRNA transcription
-changes structure or function of cell
hormone secretion and distribution
-rapidly enter blood and distributed throughout body
-freely circulating hormones are short-lived and inactivated when:
1. They diffuse to target cells and bind to receptors
2. They are absorbed and broken down in liver and kidney
3. They are broken down by enzymes in plasma or interstitial fluid
-hormones bound to transport proteins stay in circulation longer (steroid and thyroid hormones)
-each hormone has an equilibrium between bound and free forms
the hypothalamus and endocrine control
coordinating centers in hypothalamus regulate nervous and endocrine systems
the hypothalamus
- Acts as an endocrine gland, synthesizing ADH and oxytocin
- Secretes releasing and inhibiting regulatory hormones to control anterior pituitary secretions
- Contains ANS centers that control adrenal medullae through sympathetic innervation
the pituitary gland
-Also called the hypophysis
-Hangs from hypothalamus by infundibulum
-Anterior and posterior have very different structure
-Secretes nine hormones
-All are unique peptides or small proteins
-All use cAMP second messenger mechanism
the seven anterior lobe hormones
- Thyroid-stimulating hormone (TSH)
- Adrenocorticotropic hormone (ACTH)
- Follicle-stimulating hormone (FSH)
- Luteinizing hormone (LH)
- Prolactin (PRL) (milk production in mammary gland)
- Growth hormone (GH)
- Melanocyte-stimulating hormone (MSH) (triggers production of melanin)
Prolactin (PRL)
milk production in mammary gland
Melanocyte-stimulating hormone (MSH)
triggers production of melanin
thyroid-stimulating hormone also called thyrotropin
-Released in response to thyrotropin-releasing hormone (TRH) from hypothalamus
-Triggers release of thyroid hormones from thyroid glands
-Increases in thyroid hormones cause decrease in TRH and TSH secretion
adrenocorticotropic hormone also called corticotropin
-Stimulates secretion of steroid hormones, called glucocorticoids, from adrenal cortex
-Corticotropin-releasing hormone (CRH) from the hypothalamus triggers release of ACTH
-Increases in glucocorticoids feed back to inhibit ACTH and CRH secretion
the gonadotropins, or sex hormones, are triggered by
gonadotropin-releasing hormone (GnRH) from hypothalamus
Follicle-stimulating hormone (FSH)
-promotes follicle (and egg) development females
-promotes sperm production in males
luteinizing hormone (LH)
-induces ovulation and secretion of progestins in females
stimulates production of androgens such as testosterone in males
growth hormone
also called human growth hormone (hGH) and somatotropin
-stimulates cell growth and replication of all cells, but especially skeletal muscle and chondrocytes
the two posterior lobe hormones
hormones diffuse down axons of hypothalamic neurons that extends into posterior lobe, then into capillaries
1. antidiuretic hormones (ADH)
2. oxytocin (OXT)
antidiuretic hormone also called vasopressin
-stimulated by increase in ECF osmolarity or decrease in blood volume and pressure
-primary target is kidney to decrease water loss
-triggers vasoconstriction to increase blood pressure
oxytocin
-in women stimulates contraction of uterine muscles during labor and delivery
-also stimulates contraction of cells surrounding milk secretory cells in mammary glands
-appears to play unclear role in sexual arousal
the thyroid gland
-found anterior to trachea and inferior to thyroid cartilage
-has two lobes connected by narrow isthmus
-contains many spherical thyroid follicles
-defined by simple cuboidal epithelium
-filled with viscous colloid with many proteins and thyroid hormones moleclues
the thyroid follicles
-follicular cells make thyroid hormones that are then stored in colloid
-TSH causes release of thyroid hormones
-majority are transported by plasma proteins
-dervied from amino acid tyrosine, and iodine
-thyroxine (T4 or tetraiodothyronine) has four atoms of iodine
-triiodothyronine (T3) has three iodine and is more potent
the effects of thyroid hormones
-activate nearly every cell in body
-increase rate of ATP production in mitochondria
-activate genes coding for enzyme synthesis
-enzymes increase rate of metabolism
-calorigenic effect is when cell uses more energy, measured in calories, and heat is produced
the c cells of the thyroid gland also called parafollicular cells, are found between follicles
produce calcitonin (CT)
-stimulated by increases in plasma Ca2+
-inhibits osteoclasts in bone
-stimulates calcium excretion by kidneys
-essential for normal bone growth in children and last trimester of pregnancy
calcium imbalances
hypercalcemia and hypocalemia
hypercalcemia causes
-decreased sodium permeability of excitable membranes
-results in less responsive muscles and nerves
hypocalcemia causes
-increased sodium permeability
-highly excitable, spasmodic muscles and nerves
-parathyroid glands prevent hypocalcemia
the parathyroid glands
-paired, small glands embedded in posterior surface of thyroid
-chief cells produce parathyroid hormone (PTH)
chief cells produce parathyroid hormone (PTH)
-stimulated by decrease in plasma Ca2+
-activates osteoclasts in bone
-reduces calcium excretion by kidney
-stimulates kidney to secrete calcitriol, which increases Ca2+ absorption in digestive tract
the adrenal gland also called the suprarenal gland
-yellow, pyramid-shaped
-sits on superior border of each kidney
-two portions
1. Adrenal cortex
-outer part
2. Adrenal medulla
-inner part
the adrenal cortex
-contains high levels of cholesterol and fatty acids
-produces more than 24 steroid hormones called corticosteroids
corticosteroids
-are essential for metabolic functions
-transported in plasma bound to proteins
-three zones of cortex produce three types
1. Mineralcorticoids
2. Glucocorticoids
3. Androgens
mineralocorticoids also called MCs
-produced by outer zone
-affect electrolyte balance in body fluids
-aldosterone - major MC
aldosterone - major MC
-secreted in response to low plasma Na=, low BP, high plasma K+, or presence of angiotensin II
-triggers reabsorption of sodium ions in kidney, sweat glands, salivary glands, and pancreas
-secondarily triggers water reabsorption through osmosis
glucocorticoids also called GCs
-produced mostly by middle zone
-affect glucose metabolism
-most important are cortisol, corticosterone, and cortisone
most important are cortisol, corticosterone, and cortisone
-secreted in response to ACTH
-increase rates of glycolysis and glycogenesis, resulting in increase in blood glucose levels
-also act as anti-inflammatory
androgens
-produced by inner zones in both males and females
-some converted to estrogens in plasma
-in normal amounts do not affect sexual characteristics
-function remains unclear
the adrenal medulla
-highly vascular, containing cells similar to sympathetic ganglia
-innervated by preganglionic sympathetic fibers
-epinephrine (E, or adrenaline) is 80 percent
-norepinephrine (NE, or noradrenaline) is 20 percent
-triggers metabolic changes to increase availability of energy molecules
-supports and prolongs overall sympathetic response
the pineal gland
-located on posterior portion of roof of third ventricle
-contains neurons, glial cells, and secretory cells that produce melatonin
-rate of secretion affected by light and day–night cycles
-may influence timing of sexual maturation
-plays role in maintaining circadian rhythms (day–night cycles)
-linked to pineal or parietal eye in some organisms (fish, amphibians, reptiles)
the endocrine pancreas
-pancreas lies between stomach and proximal small intestine
-contains both exocrine and endocrine cells
-endocrine cells located in pancreatic islets
endocrine cells located in pancreatic islets also called islets of Langerhans, contain:
-alpha cells that secrete hormone glucagon
-beta cells that secrete hormone insulin
pancreatic regulation of blood glucose
-increases in blood glucose levels (BGL) activate beta cells to release more insulin
-decreases in blood glucose levels activate alpha cells to release more glucagon
-secretion of hormones is independent of direct neural stimulus
-indirectly affected by ANS activity and any hormones that also influences BGL
-for example, cortisol and thyroid hormones
increases in blood glucose levels (BGL) activate beta cells to release more insulin
-stimulates glucose uptake by cells
-result is lower BGL
decreases in blood glucose levels activate alpha cells to release more glucagon
mobilizes energy reserves
-glycogen in liver and muscles broken down to glucose
-adipose tissue releases fatty acids
-proteins broken down to convert to glucose in the liver
-result is higher BGL
diabetes mellitus
either hyposecretion of insulin or decreased sensitivity of insulin receptors
diabetes mellitus symptoms
hyperglycemia, glycosuria, polyuria, and polydipsia
what are the two forms of diabetes mellitus
type I and type II
type I – insulin-dependent diabetes mellitus
-pancreas does not produce insulin
-immune cells destroy the pancreatic islets
type II –non-insulin-dependent diabetes mellitus
-normal or elevated amounts of insulin are present in the blood
-receptors on the cells do not respond to insulin
the intestines
-secrets local hormones that coordinate digestive activities
-major control over rate of digestive processes
-can be influenced by ANS
the kidneys has
calcitriol, erythropoietin, renin
calcitriol
stimulated by PTH, derived from vitamin D3, increases absorption of calcium and phosphate ions from gut
erythropoietin
stimulated by kidney hypoxia, causes RBC production
renin
an enzyme that triggers hormonal chain reaction to increase BP, blood volume
the heart
atrial natriuretic peptide (ANP)
-promotes loss of sodium, and therefore water
-inhibits renin release
-results in decrease n BP and blood volume
the thymus is located
deep to sternum in mediastinum
the thymus
very active in early childhood, atrophies in adults
secretes thymosins
-aid in development and maintenance of immune defenses
the gonads: the testes
-in males, interstitial cells produce androgens
-most important is testosterone
testosterone
-promotes sperm production
-maintains secretory glands of reproductive tract
-determines secondary sex characteristics
-stimulates protein synthesis
-sperm production effect balanced by inhibin
the gonads: the ovaries
-in females, the ova are surrounded by follicles
-FSH triggers follicular cells to produce: estrogens and inhibin
-once follicles releases ovum (ovulation) the corpus luteum is formed from follicular cells
-releases progesterone
-all gonadal hormones regulated by hormones of the anterior pituitary
estrogens
support maturation of ova and growth of uterine lining
inhibin
provides negative feedback to FSH
releases progesterone
-accelerates fertilized egg movement through uterine tube
-prepares uterus for arrival of developing embryo
adipose tissue - produces leptin
-provided negative feedback control of appetite
-binds to neurons in hypothalamus to trigger satiation (fullness) and suppression of appetite
-must be present for normal GnRH and gonadotropin synthesis
-low body fate can result in late puberty and cessation of menstrual cycles
-increase in body fat can increase fertility
hormonal interactions
ECF contains hormones that may have the same target, resulting in four possiblities
-antagonistic, synergistic, permissive, and intefrative effects
hormonal interactions
ECF contains hormones that may have the same target, resulting in four possiblities
-antagonistic, synergistic, permissive, and integrative effects
antagonistic effects
opposing receptors
synergistic effects
net result of two is greater that the sum of their individual effects
permissive effects
need for one hormones to be present for another to work
integrative effects
coordinate diverse activities
six key hormones required for normal growth
GH, thyroid hormones, insulin, PTH, calcitriol(,) same at PTH, reproductive hormones
GH
-undersecretion causes dwarfism
-oversecretion causes gigantism
thyroid hormones
required for normal nervous system development
insulin
required for energy supply to growing cells
PTH
promotes calcium availability for normal bone growth
calcitriol, same as PTH
lack of PTH and calcitriol can result in rickets
reproductive hormones
can affect activity of osteoblasts and influence secondary sex characteristic development
stress is triggered by
-physical injury or disease
-emotional responses: anxiety or depression
-environmental conditions: extreme cold or heat
-metabolic conditions: acute starvation
stress triggers
-the general adaptation syndrome (GAS)
-also called the stress response
hormones and aging
-usually most hormones remain the same throughout adulthood
-exceptions are the reproductive hormones
-changes to target organ receptors more likely to occur through reduced sensitivity
