Endocrine system Flashcards
What is homeostasis?
A state of relative constancy of the internal environment maintained by a negative feedback loop.
Who is considered the first person to study physiology?
Erasistratus
What did William Harvey demonstrate in physiology?
The heart pumps blood through a closed system of vessels.
What term did Walter Cannon coin in 1932?
Homeostasis
How do homeostatic mechanisms maintain physiological variables?
By comparing their values to a desired, or set point, value.
What role do receptors play in maintaining internal constancy?
They function as sensors that send information to an integrating center.
What is the integrating center?
A specific region in the brain or spinal cord, or a group of cells in an endocrine gland.
What is a negative feedback loop?
A process where changes from a normal range are compensated by reverse changes in effector activity.
True or False: Homeostasis is a completely static state.
False
What is meant by antagonistic effectors?
Control described as ‘push-pull’, where increasing activity of one effector is accompanied by decreasing activity of another.
How is normal body temperature maintained?
By antagonistic effectors such as sweating and shivering.
What is positive feedback?
A mechanism where the action of effectors amplifies changes that stimulated the effectors.
Moving it further away from its set point, rather tahn returning it to equilibrium (homeostasis)
What is the role of the nervous system in homeostasis?
It controls secretion of many endocrine glands and can affect the function of the nervous system.
What are target organs?
Specific organs that can respond to a particular hormone.
What is negative feedback inhibition?
A closed loop system where the secretion of a hormone is inhibited by its own effects.
Define endocrine glands.
Glands that secrete hormones into the blood without ducts.
What is a neurohormone?
A chemical messenger secreted by specialized neurons into the blood.
What types of hormones are derived from amino acids?
Amines
Fill in the blank: Hormones that are derived from cholesterol are called _______.
Steroids
What are glycoproteins?
Proteins bound to one or more carbohydrate groups.
How do lipophilic hormones enter target cells?
They can pass through the plasma membrane due to their lipid solubility.
What is the difference between prohormones and prehormones?
Prohormones are less active parent molecules, while prehormones are inactive until converted in target cells.
What is a synergistic effect?
When two or more hormones work together to produce a particular result.
What is desensitization?
A reduced response of target tissue to the same concentration of a hormone after repeated exposure.
What is the half-life of a hormone?
The time required for the plasma concentration of a hormone to be reduced by half.
Define priming effects.
Increased responsiveness of a target tissue to a subsequent exposure to a hormone.
What are orphan receptors?
Receptors for unknown hormone ligands.
Mechanism of steroid hormone activation includes which steps?
- Hormone dissociates from carrier proteins
- Binds to receptor
- Translocates to nucleus
- Binds to DNA
- Stimulates genetic transcription
- Produces new proteins
How does thyroid hormone activation differ from steroid hormone activation?
- T₄ dissociates from carrier
- Converted to T₃ in cytoplasm
- Uses binding proteins to enter nucleus
- Stimulates synthesis of new mRNA
What happens to T₄ in the cytoplasm of the target cell?
T₄ is converted into T₃ (triiodothyronine)
T₄ (thyroxine) is a prohormone that is converted into the active form T₃.
How do hormones that use second messengers enter target cells?
They bind to receptor proteins on the outer surface of the target cell membrane
These hormones cannot pass through the lipid barrier of the plasma membrane.
What are intracellular mediators called?
Second messengers
Which enzyme systems are involved in second messenger systems?
- Adenylate cyclase
- Phospholipase C
- Tyrosine kinase
What is cyclic AMP (cAMP)?
A second messenger and the first to be discovered
What is the role of adenylate cyclase in the cAMP second-messenger system?
Catalyzes the conversion of ATP to cyclic AMP (cAMP)
What does activated cAMP-dependent protein kinase do?
Transfers phosphate groups to (phosphorylates) other enzymes in the cytoplasm
What does the phospholipase C-Ca²⁺ second messenger system involve?
Conversion of phospholipids to inositol triphosphate (IP₃) and diacylglycerol
What does inositol triphosphate (IP₃) do in the phospholipase C pathway?
Diffuses to the endoplasmic reticulum to open Ca²⁺ channels
What does activated calmodulin do?
Activates protein kinase, which phosphorylates other enzyme proteins
What is the primary function of insulin?
Promotes glucose and amino acid transport, stimulates glycogen, fat, and protein synthesis
What is the pituitary gland also known as?
Hypophysis
What are the two lobes of the pituitary gland?
- Anterior lobe (adenohypophysis)
- Posterior lobe (neurohypophysis)
What is the primary function of trophic hormones?
Stimulate target organs to hypertrophy or atrophy based on concentration
What is the role of growth hormone (GH)?
Promotes movement of amino acids into cells and incorporation into proteins
What does thyroid-stimulating hormone (TSH) do?
Stimulates the thyroid gland to produce and secrete T₄ and T₃
What stimulates the secretion of adrenocorticotropic hormone (ACTH)?
Stimulates the adrenal cortex to secrete glucocorticoids
What does follicle-stimulating hormone (FSH) stimulate?
- Growth of ovarian follicles in females
- Production of sperm in testes in males
What does luteinizing hormone (LH) stimulate in females?
Stimulates ovulation and conversion of the ovulated follicle into an endocrine structure
What is the function of prolactin (PRL)?
Stimulates milk production by mammary glands after birth
What are the two hormones stored and released by the posterior pituitary?
- Antidiuretic hormone (ADH)
- Oxytocin
What does ADH do?
Stimulates water retention in the kidneys
How is the release of ADH and oxytocin controlled?
By neuroendocrine reflex
What stimulates ADH secretion?
Osmoreceptor neurons in response to a rise in plasma osmolality
What inhibits ADH secretion?
Sensory input from stretch receptors in the left atrium of the heart
What is the function of releasing and inhibiting hormones from the hypothalamus?
Regulate the secretion of anterior pituitary hormones
What is the hypothalamo-hypophyseal portal system?
The vascular link between the hypothalamus and the anterior pituitary
What does thyrotropin-releasing hormone (TRH) stimulate?
Secretion of TSH
What is the feedback control of the anterior pituitary primarily based on?
Negative feedback inhibition from target gland hormones
What is the primary function of the adrenal glands?
Secretion of hormones that regulate metabolism, immune response, and stress
What are the two parts of the adrenal glands?
- Adrenal cortex
- Adrenal medulla
What does the adrenal cortex secrete?
Corticosteroids, or corticoids
What are the three functional categories of corticosteroids?
- Mineralocorticoids
- Glucocorticoids
- Adrenal androgens
What is the most potent mineralocorticoid?
Aldosterone
What is cortisol’s primary role?
Regulates metabolism of glucose and other organic molecules during stress
What ratio do epinephrine and norepinephrine get secreted in?
4:1
What is the effect duration of hormones from the adrenal medulla compared to the sympathetic nervous system?
10 times longer
What does the thyroid gland secrete?
Thyroxine
What stimulates the secretion of thyroxine?
Thyroid-stimulating hormone (TSH) from the anterior pituitary
What is the role of calcitonin?
Regulates calcium levels in the blood
What are the thyroid follicles?
Spherical hollow sacs that contain follicular cells synthesizing the thyroid hormone thyroxine.
The interior of the follicles contains colloid, a protein-rich fluid.
What hormone do parafollicular cells secrete?
Calcitonin (or thyrocalcitonin).
Calcitonin inhibits the activity of osteoclasts and stimulates urinary excretion of Ca²⁺.
What is the first step in thyroid hormone production?
Accumulation of iodine (I¯) from the blood into the colloid.
Iodine is oxidized and attached to tyrosine in thyroglobulin.
What does MIT stand for in thyroid hormone synthesis?
Monoiodotyrosine.
Produced when one iodine is attached to tyrosine.
What does DIT stand for in thyroid hormone synthesis?
Diiodotyrosine.
Produced when two iodines are attached to tyrosine.
What is formed when two DIT molecules couple?
Tetraiodothyronine (T₄), or thyroxine.
What is formed when one MIT and one DIT couple?
Triiodothyronine (T₃).
What hormone stimulates the secretion of T₃ and T₄?
TSH (Thyroid-Stimulating Hormone).
What are the primary effects of thyroid hormones?
- Promote protein synthesis
- Mature the nervous system
- Increase the rate of cellular respiration in most tissues.
What is the prevalence of thyroid cancer?
More common in women than in men with a very good cure rate.
What type of thyroid cancer accounts for 85% of cases?
Papillary thyroid carcinoma.
What is endemic goiter?
Abnormal growth of the thyroid gland due to iodine deficiency.
What condition results from inadequate secretion of thyroid hormones?
Hypothyroidism.
What are common symptoms of hypothyroidism?
- Abnormally low basal metabolic rate
- Weight gain
- Lethargy.
What severe condition can result from hypothyroidism?
Myxedema.
What can hypothyroidism during the first trimester to 6 months after birth lead to?
Cretinism.
What hormone does the anterior pituitary secrete that stimulates growth?
Growth hormone (somatotropin).
What inhibits the secretion of growth hormone?
Somatostatin.
What stimulates the secretion of growth hormone?
Growth hormone-releasing hormone (GHRH).
When is growth hormone primarily secreted?
At night, following a circadian pattern.
What are insulin-like growth factors (IGFs)?
Polypeptides that mediate some actions of growth hormone.
What is the primary function of IGF-1?
Stimulate cell division and growth in cartilage.
What effect does growth hormone have on metabolism?
It has both anabolic and catabolic effects.
What condition can excessive secretion of growth hormone cause in children?
Gigantism.
What is acromegaly?
A condition in adults caused by excessive growth hormone secretion, leading to bone deformities.
What is dwarfism caused by?
Inadequate secretion of growth hormone during the growing years.
What regulates calcium and phosphate balance?
Parathyroid hormone, 1,25-dihydroxyvitamin D₃, and calcitonin.
What is bone deposition?
The process of osteoblasts secreting an organic mixture that hardens with hydroxyapatite.
What is the role of parathyroid hormone (PTH)?
Raises blood Ca²⁺ concentration.
What does calcitonin do?
Inhibits osteoclast activity and lowers Ca²⁺ concentration.
What is the primary action of lactation hormones?
Stimulate milk production and ejection.
What hormone is vital for milk production after childbirth?
Prolactin.
What inhibits prolactin secretion?
Prolactin-inhibiting hormone (PIH), also known as dopamine.
What stimulates the secretion of prolactin during pregnancy?
High levels of estrogen.
What is the milk-ejection reflex?
Occurs due to oxytocin stimulating contraction of myoepithelial cells.
What nutrients are found in breast milk?
- Proteins (casein and lactalbumin)
- Lipids
- Carbohydrates (primarily lactose)
- Vitamins (A, D, E)
- Minerals (calcium, iron, zinc, selenium).
What effect can the mother’s anxiety have on breastfeeding?
It can suppress the milk-ejection reflex.
What reflex can be suppressed by adrenergic effects during breastfeeding?
The milk-ejection reflex
This reflex may be inhibited if the mother experiences anxiety while breastfeeding.
What are the primary nutrients found in breast milk?
- Proteins (casein and lactalbumin)
- Lipids
- Carbohydrates (primarily lactose)
- B vitamins
- Vitamins A, D, and E
- Calcium
- Iron
- Zinc
- Selenium
Breast milk also contains biologically active molecules like immunoglobulin A (IgA).
What type of antibodies provide immune protection to infants during the first 3-12 months after birth?
Immunoglobulin G (IgG)
These antibodies cross the placenta from the mother to the fetus.
What is colostrum and what does it contain?
Colostrum is the first milk produced and contains * IgA antibodies * Cytokines * Lymphocytes * Other constituents that promote active immunity development in babies
It provides a high amount of IgA antibodies.
How does breastfeeding affect ovulation in mothers?
Breastfeeding inhibits the secretion of gonadotropins from the anterior pituitary, thereby inhibiting ovulation
This occurs through reflex inhibition of GnRH secretion.
What is the significance of genetic diversity in sexual reproduction?
Genetic diversity ensures that some members of a population will survive changes in the environment over evolutionary time.
What process forms gametes in the gonads?
Meiosis
This process involves reduction division, halving the chromosome number from 46 to 23.
What results from the fusion of a sperm cell and ovum?
Restoration of the original chromosome number of 46 in the zygote.
What are the two types of chromosomes inherited by a zygote?
- Autosomal chromosomes (first 22 pairs)
- Sex chromosomes (23rd pair)
In females, these are two X chromosomes; in males, one X and one Y chromosome.
What is the function of the SRY gene?
Codes for testis-determining factor (TDF), promoting the conversion of embryonic gonads to testes.
What hormone do Leydig cells secrete?
Testosterone
Testosterone is crucial for male sex organ development and spermatogenesis.
What are the male accessory sex organs derived from?
Wolffian (mesonephric) ducts.
What hormone causes regression of the Müllerian ducts?
Anti-Müllerian hormone (AMH)
This hormone is secreted by Sertoli cells.
What is the condition called where both ovarian and testicular tissue is present?
Hermaphroditism
This condition is extremely rare.
What is pseudohermaphroditism?
A condition where individuals have either testes or ovaries but not both, often with improper development of accessory organs or external genitalia.
What is the most common cause of pseudohermaphroditism in females?
Congenital adrenal hyperplasia.
What is the most common cause of pseudohermaphroditism in males?
Testicular feminization syndrome.
What happens to the inactive X chromosome in females?
It forms a clump of heterochromatin, known as a Barr Body.
What is genomic imprinting?
A process where certain genes are shielded from the removal of epigenetic changes.
What are palindromes in the context of the Y chromosome?
Regions of DNA bases that read the same from either direction, enabling gene conversions.
What is the chromosomal sex of a zygote determined by?
The fertilizing cell.
What are the functional units of the ovaries called?
Ovarian follicles.
