Week 9 - Endocrine System Flashcards
What is the Endocrine System?
- second controlling system of the body
- – nervous system is the fast-control system
- uses chemical messengers (hormones) that are released into the blood
- endocrinology is the scientific study of hormones and endocrine organs
What major processes do hormones control?
- reproduction
- growth and development
- mobilization of body defenses
- maintenance of much of homeostasis
- regulation of metabolism
What cells produce hormones?
specialized cells
- cells secrete hormones into extracellular fluids
- blood transfers hormones to target sites
- these hormones regulate the activity of other cells
What is the Chemistry Classification of Hormones?
- amino acids-based, which includes:
- – proteins
- – peptides
- – amines
- steroids => made from cholesterol
- prostaglandins => made from highly active lipids that act as local hormones
What is the Hormone action?
- hormones affect only certain tissues or organs (target cells or target organs)
- target cells must have specific protein receptors
- hormone binding alters cellular activity
What is the stimuli for control of hormone release?
- hormone levels in the blood are maintained by NEGATIVE ( - ) feed feedback
- a stimulus or low hormone levels in the blood trigger the release of more hormone
- hormone release stops once an appropriate level in the blood is reached
What are the 3 major categories that the stimuli that activate endocrine glands fall into?
- hormonal
- humoral
- neural
What is Hormonal stimuli?
- most common category of stimulus
- endocrine organs are activated by other hormones
example of hormonal stimuli
hormones of the hypothalamus stimulate the anterior pituitary to secrete its hormones
what is humoral stimuli?
- changing blood levels of certain ions and nutrients stimulate hormone release
- – humoral indicates various body fluids (such as blood and bile)
example of humoral stimuli
- parathyroid hormone and calcitonin are produced in response to changing levels of blood calcium levels
- insulin is produced in response to changing levels of blood glucose levels
what is neural stimuli?
- nerve fibers stimulate hormone release
- most are under the control of the sympathetic nervous system
example of neural stimuli
sympathetic stimulation of the adrenal medulla to release epinephrine and norepinephrine
What are the major endocrine organs?
- hypothalamus
- pituitary gland
- pineal gland
- thyroid gland
- parathyroid glands
- thymus
- adrenal glands
- pancreas
- gonads (testes and ovaries)
Overview of the major endocrine organs
- some glands have purely endocrine functions
- – anterior pituitary, thyroid, adrenals, parathyroids
- endocrine glands are DUCTLESS glands
- hormones are released directly into blood or lymph
- other glands are mixed glands, with both endocrine and exocrine functions (pancreas, gonads)
What is the pituitary gland?
- pea-sized gland that hands by a stalk from the hypothalamus in the brain
- protected by the sella turcica of the sphenoid bone
- has two functional lobes
- often called the “master endocrine gland”
What are the pituitary gland’s 2 functional lobes?
- glandular tissue
2. nervous tissue
What is the hypothalamus?
- produces releasing hormones and inhibiting hormones
- – these hormones released into portal circulation, which connects hypothalamus to anterior pituitary
What are the two hormones that the hypothalamus makes?
- oxytocin hormone
- antidiuretic hormone (ADH)
- carried to posterior pituitary via neurosecretory cells for storage
What is the posterior pituitary?
- does not make the hormones it releases
- stores hormones made by the hypothalamus
What is oxytocin?
- stimulates contractions of the uterus during labor, sexual relations, and breastfeeding
- causes milk ejection (let-down reflex) in a breastfeeding woman
What is antidiuretic hormone (ADH)?
- inhibits urine production (diuresis) by promoting water reabsorption by the kidneys
- urine volume decreases = blood pressure increases
- in large amounts, causes constriction of arterioles, leading to increased blood pressure (the reason why ADH is known as “vasopressin”)
- alcohol inhibits ADH secretion
What are the 6 anterior pituitary hormones?
Two hormones affect NONendocrine targets
- growth hormone
- prolactin
Four are tropic hormones
- follicle-stimulating hormone
- luteinizing hormone
- thyrotropic hormone
- adrenocorticptropic hormone
describe the anterior pituitary hormones
- are proteins (or peptides)
- act through second-messenger systems
- are regulated by hormonal stimuli
- are regulated mostly by negative feedback
What are growth hormones (GH)?
- general metabolic hormone
- major affects are directed to growth of skeletal muscles and long bones
- plays a role in determining final body size
- causes amino acids to be built into proteins
- causes fats to be broken down for a source of energy
Function of Prolactin (PRL)
- stimulates and maintains milk production following childbirth
- function in males is unknown
What are Gonadotropic hormones?
regulate hormonal activity of the gonads
- follicle-stimulating hormone (FSH)
- – stimulates follicle development in ovaries
- – stimulates sperm development in testes
- luteinizing hormone (LH)
- – triggers ovulation of an egg in females
- – stimulates testosterone production in males
Function of Thyrotropic hormone (TH)
- aka thyroid-stimulating hormone (TSH)
- influences growth and activity of thyroid gland
Function of Adrenocorticotropic hormone (ACTH)
- regulates endocrine activity of the adrenal cortex
What is the pineal gland?
- hangs from the rood of the third ventricle of the brain
- secretes melatonin
- – believed to trigger the body’s sleep/wake cycle
- – believed to coordinate the hormones of fertility in humans and to inhibit the reproductive system until maturity occurs
What is the Thyroid gland?
- found at the base of the throat
- inferior to the Adam’s apple
- consist of two lobes and a connecting isthmus
- follicles are hollow structures that store colloidal material
What are the two hormones that the thyroid gland produces?
- thyroid hormone
2. calcitonin
What is the thyroid hormone?
- major metabolic hormone
- controls rate of oxidation of glucose to supply body heat and chemical energy
- needed for tissue growth and development
What are the two active iodine-containing hormones that the thyroid hormone is composed of?
- Thyroxine (T4)
secreted by thyroid follicles - Triiodothyronine (T3)
conversion of T4 at target tissues
What is calcitonin?
- decreases blood calcium levels by causing calcium deposition on bone
- antagonistic to parathyroid hormone
- produced by pararfollicular cells found between the follicles
What are parathyroid glands?
- tiny masses on the posterior of the thyroid
- secrete parathyroid hormone (PTH)
- – most important regulator of calcium ion (Ca^2+) homeostasis of the blood
- – stimulates osteoclasts to remove calcium from bone
- – hypercalcemic hormone (increases blood calcium levels)
- – stimulate the kidneys and intestine to absorb more calcium
describe the thymus
- located in the upper thorax
- posterior to the sternum
- largest in infants and children
- decreases in size throughout adulthood
- produces a hormone called “thymosin”
What is thymosin hormone?
- matures some types of white blood cells
- important in developing the immune system
where are the adrenal glands?
sit on top of the kidneys
What are the two regions of the adrenal gland?
- adrenal cortex (outer glandular region has three layers that produce corticosteroids)
- mineralocorticoids are secreted by outermost layer
- glucocorticoids are secreted by middle layer
- sex hormones are secreted by innermost layer - adrenal medulla (inner neural tissue region)
What is the mineralocorticoids hormone of the adrenal cortex?
- produced in outer adrenal cortex
- regulate mineral (salt) content in blood, particularly sodium and potassium ions
- regulate water and electrolyte balance
- target organ is the kidney
what is the release of aldosterone stimulated by?
- humoral factors (fewer sodium ions or too many potassium ions in the blood)
- hormonal stimulation (ACTH)
- renin and angiotensin II in response to a drop in blood pressure
Aldosterone production is inhibited by atrial natriuretic peptide (ANP), a hormone produced by the heart when the blood pressure is too high
What is the glucocorticoids?
(including cortisone and cortisol)
- produced by middle layer of adrenal cortex
- promote normal cell metabolism
- help resist long-term stressors by increasing blood glucose levels (hyperglycemic hormone)
- anti-inflammatory properties
- released in response to increased blood levels of ACTH
what are sex hormones?
- produced in the inner layer of the adrenal cortex
- small amounts are made throughout life
- most of the hormones produced are androgens (male sex hormones), but some estrogens (female sex hormones) are also formed
what is the adrenal medulla?
- produces two similar hormones (catecholamines)
- these hormones prepare the body to deal with short-term stress (fight-or-flight) by:
- – increasing heart rate, blood pressure, blood glucose levels
- – dilating small passageways of lungs
what are the two similar hormones that the adrenal medulla produces?
- epinephrine (adrenaline)
2. norepinephrine (noradrenaline)
describe the pancreas?
- located in the abdomen, close to stomach
- mixed gland, with both endocrine and exocrine function
what hormones does the pancreatic islets (islets of Langerhans) produce?
- insulin — produced by beta cells
- glucagon — produced by alpha cells
these hormones are antagonists that maintain blood sugar homeostasis
describe insulin
- released when blood glucose levels are high
- increases the rate of glucose uptake and metabolism by body cells
- effects are hypoglycemic
describe glucagon
- released when blood glucose levels are low
- stimulates the liver to release glucose to blood, thus increasing blood glucose levels
what are gonads?
- produce sex cells
- produce sex hormones
describe ovaries
- female gonads located in the pelvic cavity
- produce eggs
what are the two groups of steroid hormones produced by the ovaries?
- estrogens
2. progesterone
describe testes
- male gonads suspended outside the pelvic cavity
- produce sperm
- produce androgens (ie, testosterone)
describe estrogens
- stimulate the development of secondary female characteristics
- mature the female reproductive organs
with progestrerone, estrogens also:
- promote breast development
- regulate menstrual cycle
describe progesteron
- acts with estrogen to bring about the menstrual cycle
- helps in the implantation of an embryo in the uterus
- helps prepare breasts for lactation
describe testes
- produce several androgens
- testosterone is the most important androgen
- – responsible for adult male secondary sex characteristics
- – promotes growth and maturation of male reproductive system
- – required for sperm cell production
what are the other hormone-producing tissues and organs?
(organs that are generally nonendocrine in function also secrete hormones)
- stomach
- small intestine
- kidneys
- heart
what are the developmental aspects of the endocrine system?
- without a disease, the efficiency of the endocrine system is high until old age
- decreasing function of female ovaries at menopause leads to symptoms (osteoporosis, increased change of heart disease, and possible mood changes)
- efficiency of all endocrine glands gradually decreases with aging, which leads to generalized increase in incidence of:
- – diabetes mellitus
- – immune system depression
- – lower metabolic rate
- – cancer rates in some areas
