Endocrine System Quiz

• These study notes pertain to the endocrine system

Introduction

• Communication and coordination are key functions
• The nervous system uses neurotransmitters for this purpose
• The endocrine system uses hormones
• Hormones are chemical messengers moving through the bloodstream to target tissues and organs
• Tissues, glands, and cells are responsible for secreting hormones

Exocrine vs Endocrine Gland

• Exocrine glands secrete chemical substances through ducts to epithelial surfaces
• Endocrine glands secrete hormones directly into the bloodstream

Feedback Loops

• Negative feedback occurs when the response reverses the change detected
• Positive feedback happens when the response reinforces the change detected

Major Organs of the Endocrine System

• Pituitary gland is a major organ
• Adrenal gland is a major organ
• Thyroid gland is a major organ
• Parathyroid gland is a major organ
• Pancreas is a major organ
• Pineal gland is a major organ
• Thymus is a major organ
• Gonads are major organs

Secondary Organs of the Endocrine System

• Skin, heart, and gastrointestinal tract are secondary organs
• Kidneys and liver are secondary organs
• Placenta and adipose tissue are secondary organs

Pituitary Gland

• It sits in the sella turcica and connects to the hypothalamus via the infundibulum
• The posterior pituitary stores and secretes hormones originating from the hypothalamus, including Antidiuretic and Oxytocin
• The anterior pituitary is regulated by the hypothalamus
• It produces six other hormones

Posterior Pituitary: Antidiuretic Hormone (ADH)

• Originates in the supraoptic nuclei of the hypothalamus
• Carried by the hypothalamo-hypophyseal tract
• The target tissue is the kidney
• Action includes water retention by decreasing urine volume and raising blood pressure
• Production is stimulated by low blood pressure and certain drugs/substances
• Production is inhibited by alcohol
• Production is stimulated by nicotine, morphine, and barbiturates

Posterior Pituitary: Oxytocin

• It originates in the paraventricular nucleus of the hypothalamus
• Carried by the hypothalamo-hypophyseal tract
• The major target tissues are the uterus and breast
• Acts as an important chemical messenger in the brain

Oxytocin Regulation and Effect

• Release is triggered by stretch receptors in the uterus and cervix
• Infant nursing stimulates release
• Causes contraction of uterine muscles
• Responsible for the "letdown" reflex in lactation
• Plays a role in sexual arousal, orgasm, and affectionate behavior

Anterior Pituitary

• Made of glandular tissue
• Produces and secretes its own hormones
• Produces tropins and tropic hormones
• It is stimulated by the hypothalamus
• Regulatory hormones received through the hypothalamo-hypophyseal portal system

Anterior Pituitary Hormones

• Growth hormone (GH)
• Adrenocorticotropic hormone (ACTH)
• Thyroid stimulating hormone (TSH)
• Follicle stimulating hormone (FSH)
• Luteinizing hormone (LH)
• Prolactin (PRL)
• These are regulated by Hypothalamic hormones

Hypothalamic Releasing and Inhibiting Hormones

• Growth hormone-releasing hormone (GHRH)
• Corticotropin-releasing hormone (CRH)
• Thyrotropin-releasing hormone (TRH)
• Gonadotropin-releasing hormone (GnRH)
• Prolactin-inhibiting hormone (PIH)
• Somatostatin, also known as Growth hormone-inhibiting hormone (GHIH)

Anterior Pituitary Hormone: Growth Hormone (GH)

• Target tissue is all cells, but mostly in bone and skeletal muscle
• Comes from somatrope cells
• Increases cell size, cell division, muscle mass, and long bone growth

Growth Hormone Regulating Hormones

• Growth hormone-releasing hormone (GHRH) stimulates GH release
• This induces the liver to produce insulin growth stimulants and insulin-like growth factor (IGF-1)
• Somatostatin (or GHIH) inhibits GH and is produced when GH levels increase

Growth Hormone Abnormalities

• Decreased GH results in pituitary dwarfism
• Increased GH results in acromegaly.

Anterior Pituitary: Adrenocorticotropic Hormone (ACTH)

• Originates from corticotrope cells
• Target tissue is the adrenal cortex
• Causes production of glucocorticoids

Adrenocorticotropic Hormone: Regulating Hormones

• Corticotropin-releasing hormone (CRH) regulates ACTH hormone
• Rising glucocorticoid levels inhibit the pituitary by decreasing CRH

Anterior Pituitary: Thyroid Stimulating Hormone (TSH)

• Originates from thyrotrope cells
• Target tissue is the thyroid
• Increases production and release of thyroid hormone

Thyroid Stimulating Hormone (TSH): Regulating Hormone

• Production is regulated by thyrotropin-releasing hormone (TRH)
• Elevated thyroid hormone levels inhibit TRH production by the hypothalamus
• Elevated thyroid hormone levels inhibit TSH production by the anterior pituitary gland

Anterior Pituitary: Gonadotropins

• Follicle-stimulating hormone (FSH) stimulates gamete production
• Luteinizing hormone (LH) stimulates hormone production
• Originates from gonadotrope cells
• Target tissue is ovaries/testis

Gonadotropins: Regulating Hormones

• Production is regulated by gonadotropin-releasing hormone (GnRH)
• The hypothalamus produces it in response to gonadal hormones

Anterior Pituitary: Prolactin

• Originates from lactotropes
• Target tissue is the breasts
• Stimulates milk production

Prolactin: Regulating Hormones

• Regulated by thyrotropin-releasing hormone (TRH)
• Regulated by prolactin-inhibiting hormone (PIH)
• Possibly regulated by prolactin-releasing hormone (PRH)

Prolactin Regulation in Females

• Prolactin (PRL) levels rise when prolactin-inhibiting hormone (PIH) levels decrease with a fall in estrogen
• Rise prior to menstruation, towards the end of pregnancy, and when stimulated with infant nursing

The Adrenal (Suprarenal) Gland

• It sits on the kidney
• It is enclosed by a fibrous capsule and a fat pad
• It is structurally and functionally two glands
• The components are the Adrenal Cortex and Adrenal Medulla

Adrenal Gland: Adrenal Cortex

• Produces corticosteroids that consist of three layers: Zona glomerulosa, zona fasciculata, and zona reticularis
• Zona glomerulosa produces mineralocorticoids like aldosterone
• Zona fasciculata produces glucocorticoids and androgens like cortisol and sex hormones
• Zona reticularis produces glucocorticoids and gonadocorticoids like cortisol and sex hormones

Mineralocorticoid: Aldosterone

• Targets the kidneys
• Reduces sodium secretion in the kidney, causing water retention
• Enhances sodium reabsorption in urine, sweat, and the gut
• Raises blood pressure
• Regulation to be covered in chapter 23

Glucocorticoids: Cortisol

• Target tissue is most body cells
• Regulates metabolism and helps adapt to stress and repair tissues
• Has an anti-inflammatory effect
• Stimulates gluconeogenesis promoting glucose formation from fat and protein
• Enhances epinephrine's vasoconstrictive effects

Cortisol Regulation

• Corticotropin-releasing hormone (CRH) is produced by the hypothalamus
• Adrenocorticotropic hormone (ACTH) is released from the pituitary in response to CRH
• ACTH stimulates the adrenal gland to produce cortisol
• Elevated cortisol levels inhibit the release of both CRH and ACTH

Cortisol Abnormalities

• Elevated cortisol results in Cushing's Syndrome
• Depressed is Addison's

Gonadocorticoids: Effect and Regulation

• Contribute to the onset of puberty
• Responsible for sex drive
• Cause changes in metabolism
• Regulated by Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH)

Adrenal Gland: Adrenal Medulla

• Part of the autonomic nervous system
• Produces hormones such as catecholamines (epinephrine, norepinephrine, dopamine - in trace amounts) which act as both neurotransmitters and hormones

Adrenal Medulla: Catecholamines

• Originates from chromaffin cells (modified postganglionic neurons)
• The target tissue affects nearly all tissue

Catecholamines: Effects and Regulation

• Effects are part of flight or fight
• Elevates heart rate and blood pressure
• Pupils dilate
• Blood shunted to brain
• Regulation is by sympathetic control

Endocrine System: Thyroid Gland

• Largest of the pure endocrine glands
• Located in the anterior neck
• Structure is butterfly shaped with two lobes and an isthmus

Thyroid Gland: Micro Structure

• Composed of hollow spherical follicles
• Follicular cells are cuboidal or squamous epithelial cells forming walls that produce thyroid hormone
• Thyroid hormone examples are thyroxine (T4) and triiodothyronine (T3)
• Parafollicular cells (C cells) are also present

Thyroid Gland: Thyroid Hormone

• Origin is follicular cells
• Target cells include all cells except spleen, testis, uterus, thyroid gland and adult brain

Thyroid Hormone: Effect

• It causes a calorigenic effect, resulting it an increase in metabolism
• It increases alertness/reflexes, respiratory rate, heart rate, and appetite
• Also increases the breakdown of carbs, fats, and proteins, and GH
• Required for fetal development

Thyroid Hormone: Regulation

• Thyrotropin-releasing hormone (TRH) and thyroid stimulating hormone (TSH) regulate thyroid hormone

Regulation: Thyrotropin-Releasing Hormone

• TRH overcomes the negative feedback loop in conditions requiring increased body energy needs
• Examples of conditions are pregnancy and prolonged cold

Regulation: Thyroid Stimulating Hormone

• TSH rises in response to declining T4 levels
• It is suppressed by rising T4 levels, somatostatin, rising levels of glucocorticoids, and sex hormones

Thyroid Hormone: Abnormalities

• Enlarged thyroid gland is known as goiter
• Decreased thyroid hormone can result in hypothyroidism and congenital iodine deficiency syndrome
• Increased levels results in hyperthyroidism and Grave's disease

Thyroid Gland: Calcitonin

• Originates from parafollicular cells or C cells
• Target tissue is bone, mostly important in childhood

Calcitonin: Effect

• It responds to high blood calcium levels
• Inhibits osteoclast activity, decreasing bone resorption and calcium release
• Stimulates the uptake of calcium into the bone matrix

Calcitonin: Regulation

• Release is stimulated by excessive blood levels of calcium.
• Inhibited release via dropping levels of calcium

Endocrine System: Parathyroid Gland

• Are tiny glands imbedded in the thyroid, usually four, but may be up to eight
• This is the gland that produces parathyroid hormone (PTH)

Parathyroid Gland: Parathyroid Hormone

• Origin is chief cells
• Target tissues are skeletal, kidney, and intestine

Parathyroid Hormone: Effect

• It stimulates osteoclasts to release ionic calcium and phosphates into the blood
• Inhibits osteoblasts
• Enhances reabsorption of calcium in the kidney
• Increases absorption of calcium in the intestine

Parathyroid Hormone: Abnormalities

• Increased parathyroid hormone results in hyperparathyroidism

Endocrine System: Pancreas

• It is located behind the stomach
• It is a mixed gland, with endocrine and exocrine functions
• It is made up of acinar cells and pancreatic islets

Pancreas: Hormones

• The pancreatic hormones are insulin and glucagon
• Insulin is anabolic which converts smaller molecules into larger ones. Glucose becomes Glycogen and Amino acids become Proteins
• Glucagon is catabolic by breaking down larger molecules into their subunits and reverses all functions of insulin

Pancreas: Insulin

• Origin is beta cells of the pancreatic islets
• The main effect is that it removes glucose from the blood, uses it for immediate energy and then converts it to fat for storage
• The target tissue for insulin is muscle and fat
• This excludes the liver, the kidney, and the brain

Insulin: Effects

• lowers blood glucose levels and enhances membrane transport of glucose into body cells
• inhibits breakdown of glycogen to glucose (action of glucagon)
• Prevents conversion of fats and amino acids into glucose

Insulin: Regulation

• Insulin is stimulated by elevated blood sugar levels, rising levels of amino acids and fatty acids and acetylcholine released by parasympathetic nerves
• Inhibited by dropping serum glucose and by somatostatin (GHIH)

Insulin: Abnormalities

• Diabetes Mellitus (DM) can be Type I (IDDM) which is an autoimmune disease or it can be Type II (NIDDM) which is reduced sensitivity to insulin
• The opposite would be Too much Insulin producing Hypoglycemia

Pancreas: Glucagon

• Origin is alpha cells of pancreatic islets
• Target its the liver

Glucagon: Effects

• Raises blood glucose levels
• Causes breakdown of Glycogen to Glucose (Glycogenolysis)
• Performs Synthesis of glucose (Gluconeogenesis)
• Causes Release of glucose from the liver

Glucagon: Regulation

• Released in response to failing glucose levels
• Stimulated by sympathetic activity and rising amino acids
• Insulin antagonizes effects
• Inhibited by rising blood sugar and somatostatin (GHIH)

Endocrine System: Pineal Gland

• Tiny pine-cone shaped gland in the epithalamus
• Produces melatonin

Pineal Gland: Melatonin

• The origin is pinealocytes
• Target tissue is suprachiasmatic nuclei

Melatonin: Effect and Regulation

• Regulates sleep cycles causing drowsiness and regulating the circadian rhythm
• It is light responsive
• The peak level is at night
• Lowest level at noon

Test your knowledge of the endocrine system with these questions. Topics include hormone regulation, glands, and functions. Review key concepts of endocrine system.