Topic 7: Endocrinology Flashcards
What are hormones
chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body
What is the function of the endocrine system?
chemical signaling by hormones
What is the function of the nervous system?
a network of specialized cells–neurons– that transmit signals along dedicated pathways
Why are two criteria for cell signaling?
- type of secreting cell
- route taken by the signal in reaching its target
How do hormones reach their targets?
hormones secreted into extra cellular fluids by endocrine cells reach their targets via the bloodstream
What is the function of endocrine signaling (4)?
- maintains homeostasis
- mediates responses to stimuli
- regulates growth
- development
What are local regulators?
molecules that act over short distances, reaching target cells solely by diffusion
What is paracrine signaling?
the target cells lie near the secreting cells (i.e. growth factors)
What is autocrine signaling?
the target cell is also the secreting cell (i.e. cytokines)
What are synapses?
specialized junctions with target cells
What are neurotransmitters?
molecules that diffuse short distances and bind to receptors on target cells
What are neurohormones?
molecules that travel to target cells via the bloodstream
What are the three major classes of hormones?
- polypeptides
- steroids
- amines
What is the solubility of each of the three major classes of hormones?
- polypeptides are water-soluble
- amines are water-soluble
- steroid hormones and other largely nonpolar hormones are lipid-soluble
How do water soluble hormones move?
secreted by exocytosis, travel freely in the blood stream, and bind to cell-surface receptors
How do lipid-soluble hormones move?
diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells; they bind to receptors in the cytoplasm or nucleus of the target cells
What initiates from the binding of a hormone to its receptor?
a signal transduction pathway that can lead to changes in the cytoskeleton, enzyme activation or gene expression
What is epinephrine?
a hormone that has multiple effects in mediating the body’s response to short-term stress
What does epinephrine bind to?
receptors on the plasma membrane of liver cells
What happens when epinephrine binds to receptors?
triggers the release of messenger molecules that activate enzymes and result in the release of glucose in the bloodstream
What is usually the response to lipid-soluble hormones?
a change in gene expression
What happens when a steroid hormone binds to its cytosolic receptor?
a hormone-receptor complex forms that moves into the nucleus; the receptor part of the complex acts as transcriptional regulator of specific target genes
What are 5 characteristics of steroid hormones?
- lipid soluble, chemically derived from cholesterol
- enter target cells
- bind to intracellular receptor
- activate specific genes to produce specific proteins
- slower acting than nonsteorid hormones; minutes to hours
Why do steroid hormones act slowly?
they need to activate DNA and form new proteins
Why do steroid hormones last for a long time?
they activate DNA and form new proteins
What are 5 characteristics of nonsteroid hormones?
- water soluble
- bind to receptors on target cell membranes
- work through intermediate mechanisms to activate existing enzymes
- may involve a “second messenger” within the cell, such as cyclic AMP (cAMP)
- faster action than steroid hormones; seconds to minutes
Why do nonsteroid hormones act quickly?
they only need to change existing proteins
Why do nonsteroid hormones last for a short time?
they only change existing proteins
Can the same hormone have the same effects?
True
What are endocrine glands?
ductless organs that contain endocrine cells
What are examples of endocrine glands (4)?
- thyroid gland
- parathyroid gland
- testes
- ovaries
What are exocrine glands?
ducts to carry secreted substances on body surfaces or into body cavities
What is an example of exocrine glands?
salivary glands
What does the pineal gland release?
melatonin: participates in regulation of biological rhythms
What does the anterior pituitary gland release?
- follicle-stimulating hormone (FSH) and luteinizing hormone (LH): stimulate ovaries and testes
- thyroid-stimulating hormone (TSH): stimulates thyroid gland
- adrenocorticotropic hormone (ACTH): stimulates adrenal cortex
- prolactin: stimulates mammary gland cells
- growth hormone (GH): stimulate growth and metabolic functions
What does the posterior pituitary gland release?
- oxytocin: stimulates contraction of smooth muscle cells in uterus and mammary glands
- vasopressin (also called antidiuretic hormone, ADH): promotes retention of water by kidneys; influences social behavior and bonding
What does the thyroid gland release?
- thyroid hormone (T3 and T4): stimulates and maintains metabolic processes
- calcitonin: lowers blood calcium level
What do parathyroid glands release?
- parathyroid hormone (PTH): raises blood calcium level
What do adrenal medulla glands release?
epinephrine and norepinephrine: raise blood glucose level; increase metabolic activities: constrict certain blood vessels
What do adrenal cortex glands release?
- glucocorticoids: raise blood glucose level
- mineralocorticoids: promote reabsorption of Na+ and excretion of K+ in kidneys
What does the pancreas release?
- insulin: lowers blood glucose level
- glucagon: raises blood glucose level
What do ovaries release?
- estrogens: stimulate uterine lining growth; promote development and maintenance of female secondary sex characteristics
- progestins: promote uterine lining growth
What do testes release?
androgens: support sperm formation; promote development and maintenance of male secondary sex characteristics
What happens in a simple endocrine pathway?
- hormones are assembled into regulatory pathways
- hormones released from an endocrine cell, travel through the blood stream, and interact with specific receptors within a target cell to cause a physiological response
What is an example of simple endocrine signaling?
- the release of acidic contents of the stomach into the duodenum stimulate endocrine cells there to secrete secretin
- this causes target cells in the pancreas, a gland behind to stomach, to raise the pH in the duodenum
What happens in a simple neuroendocrine pathway?
- the stimulus is received by a sensory neuron, which stimulates a neurosecretory cell
- the neurosecretory cell secretes a neurohormone, which enters the bloodstream and travels to target cells
What is an example of simple neuroendocrine pathway?
- the suckling of an infant stimulates signals in the nervous system that reach the hypothalamus
- nerve impulses from the hypothalamus trigger the release of oxytocin, from the posterior pituitary gland
- this causes the mammary glands to secrete milk
What is a negative feedback loop?
inhibits a response by reducing the initial stimulus, thus preventing excessive pathway activity
What is an example of a negative feedback loop?
bicarbonate release raises pH of duodenum
What is a positive feedback loop?
reinforces a stimulus to produce an even greater response
What is an example of a positive feedback loop?
oxytocin causes the release of milk, causing greater suckling by offspring, which stimulates the release of more oxytocin
What is the function of the hypothalamus?
receives information from the nervous system and initiates responses through the endocrine system
What is the pituitary gland?
- attached to the hypothalamus
- composed of the posterior pituitary and anterior pituitary
What is the posterior pituitary?
stores and secretes hormones that are made in the hypothalamus
What is the anterior pituitary?
makes and releases hormones under the regulation of the hypothalamus
What synthesizes the two posterior pituitary hormones?
the neurosecretory cells of the hypothalamus
What is the function of antidiuretic hormone (ADH)?
regulates water reabsorption
What is the function of oxytocin?
regulates milk secretion by the mammary glands
How is hormone production in the anterior pituitary controlled?
the releasing hormones and inhibiting hormones secreted by the hypothalamus
What is an example of production and release of anterior pituitary hormones?
prolactin-releasing hormone from the hypothalamus stimulates the anterior pituitary to secrete prolactin (PRL), which has a role in milk production
What is the function of thyroid stimulating hormones (TSH)?
anterior pituitary hormone that stimulates the growth of thyroid gland and secretion of thyroid hormone
What is the function of adrenocorticotropic hormone (ACTH)?
anterior pituitary hormones that stimulates the growth of the adrenal cortex and secretion of the steroid hormone cortisol–increases blood glucose in response to stress
What is the function prolactin (PRL)?
anterior pituitary hormones in women that stimulates growth of the mammary glands in the breasts and the production of milk. Its function in men is not well understood
What is growth hormone (GH)?
anterior pituitary hormone that causes generalized body growth
What is luteinizing hormone (LH) and Follicle stimulating hormone (FSH)?
anterior pituitary hormone called the gonadotropins because they control the secretion of sex hormones by the gonads, the testes and ovaries
How does thyroid hormone regulate functions?
- if thyroid hormone levels drop in the blood, the hypothalamus secretes thyrotropin-releasing hormone (TRH) causing the anterior pituitary to secrete thyroid-stimulating hormone (TSH)
- TSH stimulates the release of thyroid hormone by the thyroid gland
How is the thyroid gland regulated?
regulated by thyroid-stimulating hormone (TSH) from the anterior pituitary gland
What does the thyroid gland secrete?
two structurally similar hormones, T3 and T4
What is the function of T3 and T4?
- hormones are involved in basal metabolic rate (BMR) and help determine how quickly and efficiently energy is used by the body
- important for cellular conversion of glucose to ATP
What is hypothyroidism?
- the thyroid secretes too little T3 and T4
- in children, congenital hypothyroidism lead to mental retardation and stunted bone growth
- in adults, the thyroid fails to secrete enough hormones, causing slow heart rate, low body temperature, muscular weakness, general tiredness, and tendency to gain weight
What is hyperthyroidism?
- the oversecretion of thyroid hormones
- graves disease: BMR can be 60 to 100 percent above normal, fluid builds up behind the eyes, causing them to “pop”
What is goiter?
- the overproduction of TSH results in an enlarged thyroid
- can often be prevented by simply adding iodine to the diet
What causes hypothyroidism?
- primary failure of thyroid gland
- secondary to hypothalamic or anterior pituitary failure
- lack of dietary iodine
What causes hyperthyroidism?
- abnormal presence of thyroid stimulating antibody (TSI) (Graves’ disease)
- secondary to excess hypothalamic or anterior pituitary secretion
- hypersecreting thyroid tumor
What is the plasma concentration of abnormal presence of thyroid stimulating antibody (TSI) (Graves’ disease)?
- increased T3 and T4
- decreased TSH or TRH
- goiter
What is the plasma concentration of secondary to excess hypothalamic or anterior pituitary secretion?
- increased T3 and T4
- increase TSH or TRH
- present goiter
What is the plasma concentration of thyroid tumor?
- increased T3 and T4
- decreased TSH or TRH
- no goiter
What is the plasma concentration of primary failure of thyroid gland?
- decreased T3 and T4
- increased TSH and TRH
- present goiter
What is the plasma concentration of secondary to hypothalamic or anterior pituitary failure?
- decreased T3 and T4
- decreased TSH and TRH
- no goiter
What is the plasma concentration of lack of dietary iodine?
- decrease T3 and T4
- increased TSH and TRH
- present goiter
What secretes the growth hormone?
secreted by the anterior pituitary gland and has tropic and nontropic effects
What is the function of growth hormone?
- promotes growth directly and has diverse metabolic effects
- stimulates production of growth factors
- excess can cause gigantism, while lack can cause dwarfism
What is acromegaly?
the secretion of excess growth hormone after the bones have stopped growing, when further increase in height is impossible
What are the two antagonistic hormones that regulate the homeostasis of calcium (Ca2+) in the blood of mammals?
- parathyroid hormone (PTH)
- calcitonin
What releases parathyroid hormones?
parathyroid glands
What is the function of the parathyroid hormone?
- increases the level of blood Ca2+
- releases Ca2+ from bone and stimulates reabsorption of Ca2 in the kidneys
- indirect effect: stimulates the kidneys to activate vitamin D, which promotes intestinal update of Ca2+ from food
What releases calcitonin?
thyroid glands
What is the function of calcitonin?
- decreases the level of blood Ca2+
- stimulates Ca2+ deposition in boned
- inhibits Ca2+ uptake by the kidney
What do each adrenal gland consist of?
- adrenal medulla (inner portion)
- adrenal cortex (outer portion)
What is the structure of the adrenal gland?
- mineralocorticoids
- glucocorticoids
- sex steroids
- cortex
- medulla
What is the function of the mineralocorticoids?
produces aldosterone: Na+ and water reabsorption, increased blood volume and blood pressure
What is the function of the glucocorticoids?
produces cortisol: gluconeogenesis, anti-inflammatory
What is the function of sex steroids?
- produces androgens in men
- produces estrogens and progestins in women
What is the function of the medulla?
- controlled by sympathetic nerves
- secretes epinephrine
What are the effects of epinephrine and norepinephrine?
- glycogen broken down to glucose; increased blood glucose
- increased blood pressure
- increase breathing rate
- increased metabolic rate
- change in blood flow patterns, leading to increased alertness and decreased digestive, excretory, and reproductive system activity
What are the effects of mineralocorticoids?
- retention of sodium ions and water by kidneys
- increased blood volume and blood pressure
What are the effects of glucocorticoids?
- proteins and fats broken down and converted to glucose, leading to increased blood glucose
- partial suppression of immune system
What regulates glucose?
insulin and homeostasis regulate the breakdown of glycogen into glucose
What is Type 1 diabetes?
an autoimmune disorder in which the immune system destroys the beta cells of the pancreas
What is Type 2 diabetes?
- characterized by a failure of target cells to respond normally to insulin
- excess body weight and lack of exercise significantly increase the risk of type 2 diabetes
- generally appears after age 40, but may develop earlier in younger people who are sedentary
What is the function of the pancreas?
secrete glucagon and insulin
What is the function of pancreatic hormones?
involved in regulating blood glucose levels
What do endocrine cells in islets of Langerhans within the pancreas secrete?
- alpha cells: secrete glucagon
- beta cells: secrete insulin
What is the function of glucagon?
- raises blood sugar
- causes breakdown of glycogen to glucose in liver
What is the function of insulin?
- lowers blood sugar
- promotes uptake of sugar by cells in liver, muscle, and adipose tissue
- promotes conversion of glucose into glycogen
