Endocrine System Study Guide Flashcards

A comprehensive set of vocabulary flashcards based on the Endocrine System lecture objectives, covering hormone definitions, control mechanisms, and the roles of specific glands.

Hormone

A chemical messenger produced by endocrine glands that is transported in the blood to target cells to control and integrate body functions.

Endocrine gland

A ductless gland that produces and secretes hormones directly into the bloodstream.

Target cell

A specific cell equipped with receptors that allow it to respond to the presence of a particular hormone.

Neural stimulus

A type of control for hormone production and secretion where nerve fibers stimulate the release of hormones.

Humoral stimulus

A type of stimulus where hormone secretion is controlled by changing blood levels of certain ions and nutrients.

Hormonal stimulus

A control mechanism where the release of a hormone is triggered by another hormone produced by a different endocrine gland.

Negative feedback

A regulatory mechanism in which the output of a system inhibits the process that led to its release, maintaining homeostasis.

Positive feedback

A feedback mechanism that tends to magnify a process or increase its output, such as in the control of specific hormone releases.

Hypophyseal portal system

A specialized network of blood vessels that allows for the rapid transport of releasing and inhibiting hormones from the hypothalamus to the anterior pituitary.

Releasing hormone

A category of hormones released by the hypothalamus that stimulate the anterior pituitary to secrete its specific hormones.

Inhibiting hormone

A category of hormones released by the hypothalamus that stop the anterior pituitary from secreting specific hormones.

Growth hormone (GH)

A hormone produced by the anterior pituitary that regulates the growth and development of various tissues throughout the body

Thyroid-stimulating hormone (TSH)

An anterior pituitary hormone that stimulates the thyroid gland to produce and release thyroid hormones (T4 & T3)

regulates Metabolism

Luteinizing hormone (LH)

A pituitary hormone that plays a critical role in reproductive function and the regulation of gonadal activity

Follicle stimulating hormone (FSH)

An anterior pituitary hormone that aids in the development of reproductive cells and the regulation of the ovaries and testes.

stimulates follicle development (female) & sperm production (male)

Prolactin

A hormone produced by the anterior pituitary gland that primarily targets mammary tissue to stimulate milk production.

Adrenocorticotropic hormone (ACTH)

A hormone secreted by the anterior pituitary that stimulates the adrenal gland to release glucocorticoids

Oxytocin

A hormone produced by the hypothalamus and stored in the posterior pituitary that is involved in uterine contractions and milk ejection.

ADH (aka vasopressin)

A hormone produced by the hypothalamus and released by the posterior pituitary that helps the body conserve water by acting on the kidneys.

$T_3$ (tri-iodothyrine) and $T_4$ (thyroxine)

The primary hormones produced by the thyroid gland that regulate the body's metabolic rate and energy balance.

Calcitonin

A hormone produced by the thyroid gland that plays a role in calcium homeostasis by potentially lowering blood calcium levels.

Parathyroid hormone (PTH)

A hormone that is the primary regulator of blood calcium levels and increases osteoclast activity, which erodes bone matrix

Glucocorticoids (cortisol)

Hormones produced by the adrenal gland (specifically the cortex) that help the body manage long-term stress and regulate glucose metabolism.

Mineralocorticoids (aldosterone)

Hormones produced by the adrenal gland that regulate salt and water balance in the body, primarily targeting the kidneys.

Epinephrine and Norepinephrine

Hormones produced by the adrenal gland (medulla) that facilitate the body's 'fight or flight' response to acute stress.

Testosterone

A hormone produced by the testis that is responsible for male reproductive development and characteristic traits.

Estrogen and Progesterone

Hormones produced by the ovary that regulate the female reproductive cycle and development.

Insulin

A hormone produced by the pancreas that lowers blood glucose levels by facilitating the uptake of glucose into cells.

targets most body tissues

Glucagon

A hormone produced by the pancreas that raises blood glucose levels by stimulating the liver to release stored glucose.

targets mainly the liver

Melatonin

A hormone secreted by the pineal gland that is involved in the regulation of sleep-wake cycles.

Thymosins

Hormones produced by the thymus gland that are essential for the development and differentiation of T-lymphocytes.

Function of the endocrine system

responsible for producing hormones that regulate various body functions, including metabolism, growth and development, tissue function, sexual function, reproduction, sleep, and mood.

also maintains homeostasis

Hormone secretion and circulation

Hormones → secreted by endocrine glands → enter bloodstream → target specific cells → regulate physiological processes.

Target cell

A specific cell that is equipped with receptors, allowing it to respond to the presence of a particular hormone.

Signaling mechanism (Nervous System)

Electrical stimulus

Signaling Mechanism (Endocrine System)

Chemical

Chemical substance released (Nervous System)

Neurotransmitters released

Chemical substance released (Endocrine System)

Hormones released

Response Time of Nervous System (NS)

fast, allows for rapid communication

Response time of Endocrine System (ES)

slower

Cessation of response (Nervous System)

stops quickly when stimulus stops, allows for immediate feedback

Cessation of response (Endocrine System)

slower to stop

Steroid Hormone

synthesized from cholesterol, lipid-soluble in nature, allowing them to easily cross cellular membranes.

function of steroid hormones

bind to specific intracellular receptors and modulate gene expression and various cellular processes.

Peptide and Protein Hormones

composed of chains of amino acids, are hydrophilic (water soluble), preventing them from easily crossing cell membranes.

function of Peptide and Protein Hormones

bind to receptors on the plasma membrane of target cells, initiating a signaling cascade that leads to a cellular response.

The 3 steroid glands

adrenal cortex, testes, and ovaries

types of stimulus for hormone secretion

Humoral, neural and hormonal

Hemochromatosis

hereditary condition characterized by excessive accumulation of iron in the body, leading to iron overload.

can cause damage to various organs, including the liver, heart, and pancreas, and may result in conditions such as cirrhosis, diabetes, and heart disease if not managed properly.

Catecholamines

epinephrine + norepinephrine + dopamine

plays critical role in body’s response to stress

Pheochromocytoma

A tumor of the adrenal medulla that produces hormones, notably cranking out epinephrine, norepinephrine, and sometimes dopamine.

can increase heart rate, elevate blood pressure, and heightened stress response

Medulla of Adrenal Gland

The storage site for epinephrine and norepinephrine, which are crucial for the body's 'fight or flight' response.

Release of T3 and T4 from Thyroid Gland

stimulated by the release of hormones from both the hypothalamus and the pituitary gland, orchestrating the regulation of metabolism and energy balance in the body.

Negative Feedback Loop

This signaling is inhibited when the levels of hormones T3 (tri-iodothyronine) and T4 (thyroxine) become elevated, which generates negative feedback signals to the pituitary gland and hypothalamus, ultimately maintaining homeostasis.

Positive feedback loop ex.

amplifies the system output; during childbirth where the secretion of oxytocin intensifies uterine contractions, leading to further release of oxytocin until delivery is achieved.

Pituitary gland

consists of an anterior and posterior lobe

Hypothalamus-Pituitary Complex

The hypothalamus connects to the pituitary gland via the stalk-like infundibulum, allowing it to control the release of hormones from the pituitary gland and regulate various body functions.

Anterior Pituitary Gland

also known as adenohypophysis, is the ventral part of the pituitary gland responsible for producing hormones that regulate growth, metabolism, and other vital bodily functions.

Hypothalamus

produces separate hormones that stimulate or inhibit hormone production by the anterior pituitary.

hormones secreted by anterior pituitary

Growth Hormone (GH), Thyroid-Stimulating Hormone (TSH), Luteinizing Hormone (LH), Follicle Stimulating Hormone (FSH), Prolactin, Adrenocorticotropic Hormone (ACTH), Melanocyte-Stimulating Hormone (MSH)

Posterior Pituitary Gland

responsible for storing and releasing hormones made by the hypothalamus, such as oxytocin or ADH

Neurosecretory Cells

Specialized neurons that produce and secrete hormones, specifically in the hypothalamus, and transport them to the posterior pituitary gland for storage and release into the bloodstream.

Thyroid Gland

An endocrine gland located in the neck that produces hormones such as $T_3$ (tri-iodothyronine), $T_4$ (thyroxine) and calcitonin plays crucial roles in regulating the body's metabolic rate and energy balance.

Isthmus

A narrow bridge of thyroid tissue that connects the two lobes of the thyroid gland, located anterior to the trachea and typically overlying the second and third tracheal rings.

Follicular Cells

Cells that line the thyroid follicles and are responsible for synthesizing and secreting T3 (tri-iodothyronine) and T4 (thyroxine)

Parafollicular Cells (C Cells)

Located between thyroid follicles, secretes calcitonin

Effects of T3 and T4

Stimulate basal metabolic rate and heat production

Effects of Calcitonin

Reduces blood Ca²⁺ levels

Stimulates Ca²⁺ bone deposition

thyroid hormones

T3 (tri-iodothyronine), T4 (thyroxine), and calcitonin

Goiter

A pronounced enlargement of the thyroid gland, which can arise from a variety of factors including a deficiency in iodine, autoimmune disorders, or the presence of nodules.

may result in neck swelling, difficulty in swallowing, or alterations in hormone levels.

Parathyroid Glands

Small glands situated on the posterior surface of the thyroid gland that secrete PTH. Typically, four are present.

Effects of PTH (Parathyroid hormone)

increases blood Ca2+ levels

increases osteoclast activity which erodes bone matrix

Calcium Homeostasis

the balanced regulation of calcium levels in the body, primarily involving the interactions between parathyroid hormone (PTH), calcitonin, and vitamin D to maintain stable blood calcium levels and ensure adequate supply for physiological functions.

Adrenal Glands

responsible for producing a variety of hormones, including cortisol, aldosterone, epinephrine, and norepinephrine, which play key roles in regulating metabolism, immune response, and stress adaptation.

Adrenal cortex

secretes aldosterone and cortisol

Adrenal medulla

secretes epinephrine and norepinephrine

Effects of mineralocorticoid (aldosterone)

Increases renal reabsorption of Na⁺ 

Increased blood Na⁺ levels

Water conservation by kidneys Decreases blood K⁺ levels

Effects of Glucocorticoid (cortisol)

increase blood glucose levels

Effects of epinepehrine and norepinephrine

stimulate fight or flight response

Pancreas

glandular organ located behind the stomach that has both endocrine and exocrine functions. produces hormones insulin and glucagon that regulate blood glucose levels, while also secreting digestive enzymes into the small intestine.

Pancreatic Exocrine Function

involves the acinar cells secreting digestive enzymes, which are transported into the small intestine by the pancreatic duct.

Pancreatic Endocrine Function

involves the secretion of insulin by beta cells and glucagon by alpha cells within the pancreatic islets.

Insulin and glucagon

regulates the rate of glucose metabolism in the body.

Effects of Glucagon

Increases blood glucose levels

Effects of Insulin

Decreases blood glucose levels

Homeostasis of Blood Glucose

Insulin decreases blood glucose levels by facilitating cellular uptake, while glucagon increases blood glucose levels by promoting the release of stored glucose. This balance is vital for energy supply and metabolic processes in the body.

Gonads

receives stimulation from anterior pituitary gland

responsible for producing gametes (sperm in males and eggs in females) and secreting sex hormones such as testosterone and estrogen.

Function of Gonads (both genders)

play a crucial role in reproduction and the development of secondary sexual characteristics.

Inhibin

Inhibits secretion of FSH; plays a role in the regulation of reproductive function and maintaining homeostasis of hormone levels.

Pineal Gland

A small endocrine gland located in the brain that produces melatonin, which helps regulate sleep-wake cycles.

Secretion of Melatonin

influences the body’s circadian rhythms, the dark-light fluctuations that affect not only sleepiness and wakefulness, but also appetite and body temperature.

How does melatonin production respond to light and darkness?

increases in the dark, causing drowsiness. In light, blood levels of melatonin fall, promoting wakefulness.

Thymus Gland

An endocrine gland located in the upper chest that produces thymosins

Mode of Action of Peptide Hormones: Second Messenger cAMP

bind to receptors on the plasma membrane of target cells, initiating a signaling cascade that often involves the production of cyclic AMP (cAMP) as a second messenger, which amplifies the hormone's effects and leads to a cellular response.

Mode of Action of Steroid Hormones: Direct Gene Activation

exert their effects by directly entering target cells, binding to specific intracellular receptors, and then activating gene expression, which leads to the production of proteins that alter cellular function.

Adenylate Cyclase

An enzyme that catalyzes the conversion of ATP to cyclic AMP (cAMP)

function of Adenylate Cyclase

plays a key role in the signaling pathways of peptide hormones and modulating various physiological responses in the cell.

cAMP & Calcium

the most common second messengers that activate protein kinases, leading to various cellular responses and facilitating communication within and between cells.