Endocrine System

Question 1

Endocrine System Overview

Answer 1

• Second controlling system of the body
  o Nervous system is the fast-control system
• Uses chemical messengers (hormones) that are released into the blood
  o Collect information and stimulate effectors to respond
• Secretes hormones which are slow to react but effect is long-lasting

Question 2

Endocrine System Overview: Hormones Control Several Major Processes

Answer 2

o	Reproduction
o	Growth and development 
o	Mobilization of body defenses 
o	Maintenance of much of homeostasis
o	Regulation of carbohydrate, protein and fat metabolism
o	Water and electrolyte balance 
o	Energy balance 
o	Aid in the bodies response to stress

Question 3

The Chemistry of Hormones

Answer 3

Hormones are classified chemically as: 
o	Amino acid–based, which includes: 
	Proteins 
	Peptides
	Amines 
	Excludes those secreted by the adrenal cortex and the reproductive glands 

o Steroids (lipid hormones) — made from cholesterol

o Prostaglandins—made from highly active lipids that act as local hormones

Question 4

Hormone Action

Answer 4

Hormones affect only certain tissues or organs (target cells or target organs)
o Target cells must have specific protein receptors

• Hormone binding alters cellular activity

Typically, one or more of the following occurs:
o Change plasma membrane permeability or membrane potential by opening or closing ion channels
o Activate or inactivate enzymes
o Stimulate or inhibit cell division
o Promote or inhibit secretion of a product
o Turn on or turn off transcription of certain genes

Question 5

Hormone Action - Two Mechanisms

Answer 5

Direct gene activation
o Used by steroid hormones and thyroid hormone

Second-messenger system
o Used by protein and peptide hormones
o Can influence cell activity by binding to hormone receptors on the target cells

Question 6

Hormone Action: Direct Gene Activation

Answer 6

• Steroid hormones diffuse through the plasma membrane of target cells
• Once inside the cell, the hormone enters the nucleus
• Then, the hormone binds to a specific protein within the nucleus
• Hormone-receptor complex binds to specific sites on the cell’s DNA
• Certain genes are activated to transcribe messenger RNA
• mRNA is translated in the cytoplasm
• New proteins are synthesized

Question 7

Hormone Action: Second Messenger System

Answer 7

• Hormone (first messenger) binds to a membrane receptor protein
• Activated receptor sets off a series of reactions that activates an enzyme
• Enzyme catalyzes a reaction that produces a second-messenger molecule (such as cyclic AMP, known as cAMP)
• Oversees additional intracellular changes to promote a specific response in the target cell

Question 8

Hormonal Stimuli

Answer 8

• Most common category of stimulus
• Endocrine organs are activated by other hormones from other endocrine organs

Example:
o Hormones of the hypothalamus stimulate the anterior pituitary to secrete its hormones to influence the thyroid gland, adrenal cortex, gonads, pancreas and adrenal medulla
o After target tissue is stimulated –> hypothalamus and pituitary receive signals (hormones) that stop the hormones released –> ending chain of hormonal control

Question 9

Humoral Stimuli

Answer 9

Changing blood levels of certain ions and nutrients stimulate hormone release
o Humoral indicates various body fluids, such as blood and bile

Examples:
o Parathyroid hormone and calcitonin are produced in response to changing levels of blood calcium levels
 Blood calcium then rises –> ending release of parathyroid hormone
o Insulin is produced in response to changing levels of blood glucose levels

Question 10

Neural Stimuli

Answer 10

• Nerve fibers stimulate hormone release
• Most are under the control of the sympathetic nervous system

Examples:
o Sympathetic stimulation of the adrenal medulla to release epinephrine and norepinephrine during fight or flight response
 Effect
• Increased HR, BP, rate of respiration and blood flow to muscles
• Decreased blood flow to visceral organs and pupils are dilated

Question 11

Major Endocrine Organs

Answer 11

• Hypothalamus
• Pituitary gland
• Pineal gland
• Thyroid gland
• Parathyroid glands
• Thymus
• Adrenal glands
• Pancreas
• Gonads (testes and ovaries)

Question 12

The Major Endocrine Organs: Exocrine vs Endocrine

Answer 12

• Endocrine Glands –> internal secretion directly into the blood stream
• Exocrine Glands –> external secretion have ducts to carry secretions to body surface or other organs

Some glands have purely endocrine functions
o Anterior pituitary, thyroid, adrenals, parathyroids, sweat glands, salivary glands, lacrimal glands and pancreas glands

• 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)

Question 13

Hypothalamus

Answer 13

Collects information from body systems and integrate responses in systems to maintain homeostatic balance
o Regulates metabolism, heart rate, energy level, thirst, blood composition and pressure

Hypothalamus produces releasing hormones and inhibiting hormones
o These hormones are released into portal circulation, which connects hypothalamus to anterior pituitary

Hypothalamus also makes two hormones: oxytocin and antidiuretic hormone
o Carried to posterior pituitary via neurosecretory cells for storage

Question 14

Pituitary Gland

Answer 14

• Pea-sized gland that hangs by a stalk from the hypothalamus in the brain
• Protected by the sella turcica of the sphenoid bone

Has two functional lobes
o Anterior pituitary—glandular tissue
o Posterior pituitary—nervous tissue

• Often called the “master endocrine gland”

Question 15

Posterior Pituitary

Answer 15

• Does not make the hormones it releases –> not a true endocrine gland

Stores hormones made by the hypothalamus
o Two Hormones Released
 Oxytocin
 Antidiuretic hormone (ADH)

Question 16

Oxytocin

Answer 16

• Stimulates contractions of the uterus during labor, sexual relations, and breastfeeding
• Causes milk ejection (let-down reflex) in a breastfeeding woman

Question 17

Antidiuretic Hormone (ADH)

Answer 17

• 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)
• Increases blood volume –> because of increased reabsorption of fluid and sodium by the kidney –> contributing to higher blood pressure

Alcohol inhibits ADH secretion
o Resulting in increased urination, dehydration and dry mouth the morning after drinking
- Subject to humoral control
- Secreted when plasma levels decreases from hydration, profuse sweating during exercise, secreted when solid particles in the blood become more concentrated

Question 18

Six Anterior Pituitary Hormones

Answer 18

Two hormones affect nonendocrine targets
o Growth hormone
o Prolactin

Four are tropic hormones 
o	Follicle-stimulating hormone 
o	Luteinizing hormone 
o	Thyrotropic hormone 
o	Adrenocorticotropic hormone

Question 19

Anterior Pituitary Hormones

Answer 19

• Are proteins (or peptides)
• Act through second-messenger systems
• Are regulated by hormonal stimuli
• Are regulated mostly by negative feedback

Question 20

Growth Hormones

Answer 20

• General metabolic hormone
• Major effects 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
o GH is an anabolic hormone that induces protein synthesis and stimulates most target cells to grow and divide

• Causes fats to be broken down for a source of energy and spares glucose

Question 21

Prolactin

Answer 21

• Stimulates growth of mammary glands and maintains milk production following childbirth
• Function in males is unknown

Question 22

Gonadotropic Hormones

Answer 22

Regulate hormonal activity of the gonads

Follicle-stimulating hormone (FSH)
 Stimulates estrogen and egg development in ovaries
 Stimulates sperm development in testes

Luteinizing hormone (LH)
 Triggers ovulation of an egg in females
 Produces progesterone and estrogen in women
 Stimulates testosterone production in males
• By stimulating the interstitial cells

Question 23

Thyrotropic Hormone (Thyroid Stimulating Hormone)

Answer 23

• Influences growth and activity of the thyroid gland

- Stimulates the release of thyroxin and triiodothyronine

Question 24

Adrenocorticotropic Hormone (ACTH)

Answer 24

Regulates endocrine activity of the adrenal cortex

o Stimulates the release of steroid hormones

Question 25

Pineal Gland

Answer 25

Hangs from the roof of the third ventricle of the brain Secretes melatonin o Level releases rises and falls through day and night  Lowest is around noon o Believed to trigger the body’s sleep/wake cycle o Believed to coordinate the hormones of fertility in humans and to inhibit the reproductive system until maturity occurs

Question 26

Thyroid Gland

Answer 26

- Found at the base of the throat, inferior to the Adam’s apple - Consists of two lobes and a connecting isthmus - Follicles are hollow structures that store colloidal material Produces two hormones o Thyroid hormone o Calcitonin

Question 27

Thyroid Hormone

Answer 27

- Major metabolic hormone - Controls rate of oxidation of glucose to supply body heat and chemical energy - Needed for tissue growth, development and maturation ``` Composed of two active iodine-containing hormones (iodine is from dietary intake) o Thyroxine (T4 )—secreted by thyroid follicles o Triiodothyronine (T3 )—conversion of T4 at target tissues ```

Question 28

Calcitonin

Answer 28

- Maintains calcium homeostasis o Decreases blood calcium levels by causing calcium deposition on bone - Also reduces the absorption of calcium by the intestine and kidney - Within adulthood --> very little is released by the thyroid gland - Antagonistic to parathyroid hormone - Produced by parafollicular cells found between the follicles of the thyroid gland

Question 29

Parathyroid Glands

Answer 29

Tiny masses on the posterior of the thyroid Secrete parathyroid hormone (PTH) in response to low blood calcium levels o Most important regulator of calcium ion (Ca2+) homeostasis of the blood o Stimulates osteoclasts to remove calcium from bone  Moves calcium from bone to blood o Hypercalcemic hormone (increases blood calcium levels) o Stimulates the kidneys and intestine to absorb more calcium  With aid of Vitamin D in digestion  Stimulating kidney resorption of calcium from urine and excreting phosphorus

Question 30

Thymus

Answer 30

- Located in the upper thorax, posterior to the sternum - Largest in infants and children - Decreases in size throughout adulthood Produces a hormone called thymosin o Matures some types of white blood cells (e.g., T-cells) o Important in developing the immune system

Question 31

Adrenal Glands

Answer 31

Sit on top of the kidneys Two regions o Adrenal cortex (functions as a gland)  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  Part of the nervous system • Stimulated by the sympathetic branch of the ANS

Question 32

Hormones of the Adrenal Cortex: Mineralcorticoids

Answer 32

o Produced in outer adrenal cortex o Regulate mineral (salt) content in blood, particularly sodium and potassium ions o Regulate water and electrolyte balance o Regulation to changes in blood pressure and plasma levels o Target organ is the kidney o Controlled by the anterior pituitary

Question 33

Hormones of the Adrenal Cortex: Mineralcorticoids (Release of Aldosterone)

Answer 33

 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 • Renin triggers a series of reactions that trigger the release of angiotensin II • Angiotensin II is a potent stimulator for aldosterone release  Aldosterone production is inhibited by atrial natriuretic peptide (ANP), a hormone produced by the heart when blood pressure is too high • Reduces blood volume and blood pressure  Under the influence of aldosterone, when sodium and water are reabsorbed by kidneys plasma volume increases --> raising blood pressure

Question 34

Hormones of the Adrenal Cortex: Glucocorticoids (e.g., cortisone and cortisol)

Answer 34

o Produced by middle layer of adrenal cortex o Promote normal cell metabolism o Help resist long-term stressors by increasing blood glucose levels (hyperglycemic hormone) Anti-inflammatory properties  Decreasing edema  Inhibit pain by inhibiting pain causing prostaglandin o Released in response to increased blood levels of ACTH o Maintain blood glucose levels by converting fats and amino acids into glucose --> through process of glucogenesis  Ensure brain and NS have constant supply of glucose --> only fuel source

Question 35

Hormones of the Adrenal Cortex: Sex Hormones

Answer 35

o Produced in the inner layer of the adrenal cortex o Small amounts are made throughout life o Most of the hormones produced are androgens (male sex hormones), but some estrogens (female sex hormones) are also formed

Question 36

Adrenal Medulla

Answer 36

``` Produces two similar hormones (catecholamines) o Epinephrine (adrenaline) o Norepinephrine (noradrenaline) ``` These hormones prepare the body to deal with short term stress (“fight or flight”) by: o Increasing heart rate, blood pressure, blood glucose levels o Increases in metabolic rate and glucose production by liver make more energy available for the potential brush with danger o Dilating small passageways of lungs

Question 37

Catecholamines

Answer 37

Hormones released into blood in times of physical or emotional stress o Bodies response is called an ‘adrenaline rush’ Prepare body for short term stressful situations and cause the so-called alarm stage of stress response

Question 38

Glucocorticoids

Answer 38

Produced by cortex and are important when coping with prolonged or continuing stress  E.g., dealing with death of family member or having major operation Operate primarily in resistance stage of stress response  If successful --> problem will be resolved without lasting damage  If continues --> adrenal cortex may burn out --> potentially fatal

Question 39

Pancreatic Islets

Answer 39

Pancreas o Located in the abdomen, close to stomach o Mixed gland, with both endocrine and exocrine functions  Endocrine – secreting hormones controlling blood glucose  Exocrine – excretes digestive enzymes ``` The pancreatic islets (islets of Langerhans) produce hormones o Insulin—produced by beta cells  Decrease blood glucose levels o Glucagon—produced by alpha cells  Increase blood glucose levels ``` These hormones are antagonists that maintain blood sugar homeostasis

Question 40

Insulin

Answer 40

o Released when blood glucose levels are high o Increases the rate of glucose uptake and metabolism by body cells o Stimulates liver to convert glucose into glycogen or fat o Effects are hypoglycaemic o Provides life sustaining energy  Only hormone capable of getting glucose into the body cells

Question 41

Glucagon

Answer 41

o Released when blood glucose levels are low o Stimulates the liver to release glucose to blood, through the breakdown of glycogen  Thus increasing blood glucose levels

Question 42

Gonads: Ovaries

Answer 42

o Female gonads located in the pelvic cavity o Produce eggs o Produce two groups of steroid hormones  Estrogens  Progesterone

Question 43

Gonads: Testes

Answer 43

o Male gonads suspended outside the pelvic cavity o Produce sperm o Produce androgens, such as testosterone o 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 o Released when stimulated by LH from the anterior pituitary

Question 44

Gonads: Estrogen and Progesterone

Answer 44

Oestrogens o Stimulate the development of secondary female characteristics o Mature the female reproductive organs o Regulates menstrual cycle and promotes breast development Progesterone o Acts with oestrogen to bring about the menstrual cycle o Helps in the implantation of an embryo in the uterus o Helps prepare breasts for lactation With progesterone, oestrogens also: o Promote breast development o Regulate menstrual cycle

Question 45

Other Hormone Producing Tissues and Organs

Answer 45

``` Other organs that are generally non-endocrine in function also secrete hormones o Stomach o Small intestine o Kidneys o Heart ```

Question 46

Placenta

Answer 46

o Produces hormones that maintain pregnancy o Some hormones play a part in the delivery of the baby o Produces human chorionic gonadotropin (hCG) in addition to estrogen, progesterone, and other hormones  Initially produced by the developing embryo --> then continued to be produced by fetal part of placenta  Stimulates ovaries to continue producing oestrogen and progesterone • Ensures uterine lining is not degraded as menstrual bleeding occurs  In third month of pregnancy --> produces estrogen and progesterone • Ovaries become inactive for remainder of pregnancy o Human placental lactogen (hPL) prepares the breasts for lactation  Works alongside estrogen and progesterone o Relaxin relaxes pelvic ligaments and pubic symphysis for childbirth  Eases birth passage o Respiratory, excretory and nutrition delivery systems for the fetus

Question 47

Endocrine Disorders and Diseases

Answer 47

- Major disorders of the pituitary gland include acromegaly dwarfism and diabetes insipidus - Major disorders of the thyroid gland are hyperthyroidism and hypothyroidism - Parathyroid gland disorders affect calcium levels in the blood

Question 48

Diabetes Mellitus

Answer 48

Diabetes mellitus results from the inability of the pancreas to produce sufficient amounts of insulin to regulate blood glucose levels Type I  Autoimmune disorder  Immune cells attack insulin secreting beta cells in the pancreas • Causes insulin production to decrease or stop altogether Type II  Pancreas secretes insulin, but bodies receptors are downregulated • Called insulin resistance • Insulin resistant receptors wont intake insulin  blood glucose levels increase

Question 49

Overactive and Inactive Pituitary Gland

Answer 49

Overactive pituitary gland secretes excessive amounts of a particular hormone o Most common --> hypersecretion of GH --> results in gigantism  Can result in diabetes Inactive pituitary gland secretes inadequate amounts of a particular hormone o Hypo --> can lead to dwarfism and hypothyroidism  Dwarfism only affects height and size • Mental capability is normal

Question 50

Antidiuretic Hormone: Hyposecretion

Answer 50

Hyposecretion of an antidiuretic hormone from posterior pituitary gland o Cause diabetes insipidus  Excessive thirst

Question 51

Hyperthyroidism: Over-active and Under-active

Answer 51

Hyperthyroidism (over-active thyroid) o Characterised by a visibly enlarged thyroid gland  Called a goiter  Caused by insufficient levels of iodine --> necessary for production of TH o Can lead to increased HR, body temperature, hyperactivity, weight loss, diarrhea and difficulty concentration Hypothyroidism (under-active thyroid) o Caused by thyroiditis --> result of inflammation which damages thyroid cells o Symptoms  Fatigue, pale, dry skin, thin hair, brittle fingernails, increased sensitivity to cold, constipation and weight gain

Question 52

Hyper and Hyposecretion of the Parathyroid Hormone

Answer 52

Hypersecretion of parathyroid hormone o Causes too much calcium in blood --> hypercalcemia  Leads to increased calcium absorption by kidneys, brittle bones, decreased HR, fatigue, depression Hyposecretion of parathyroid hormone o Leads to low blood calcium levels --> sustained muscle contractions

Question 53

Adrenal Gland: Tumour Glands

Answer 53

Can cause an adrenal cortex disorder  Can also be caused by irregular secretion of hormones from other glands acting on adrenal cortex  Pushing Syndrome • Disorder caused by hypersecretion of cortisol • Associated with symptoms such as a rounded moon shaped face, weight gain, high blood glucose, high BP, osteoporosis, difficulty concentrating, facial hair in women

Question 54

Hyposecretion of Adrenal Cortex Hormones

Answer 54

Can cause Adison’s Disease |  Can cause muscle atrophy, a bronze skin tone and kidney damage