The endocrine system

Question 1

Water & fat-soluble hormones

Answer 1

Endocrine glands secrete hormones, circulating blood delivers to target tissues
* Most water‐soluble hormones made from chains of amino acids (peptides). Receptors usually on surface of cell. Binding causes a signalling cascade within cell. A common second messenger is cyclic AMP (cAMP), synthesized from ATP.
* Lipid‐soluble hormones (thyroxine and steroids) are transported in blood by being attached to transport proteins to make them soluble. These diffuse through lipid bilayer of plasma membrane and bind to their
receptors within target cells, often in cell nucleus.

Question 2

Water & fat-soluble hormones

Answer 2

Lipid based hormones
Steroids e.g., glucocorticoids, mineralocorticoids (adrenal gland)
Thyroid hormones
Peptide hormones
Adrenalin, noradrenalin (adrenal gland)
Insulin Glucagon

Question 3

Exocrine versus endocrine glands

Answer 3

Exocrine glands secrete their products into ducts that carry secretions into a body cavity, into lumen of an organ, or onto outer surface of body. Sweat glands and pancreatic enzyme producing glands are examples of exocrine glands.
* Endocrine glands secrete their products (hormones) into interstitial fluid, the fluid that surrounds tissue cells. The hormones diffuse into blood capillaries, and blood carries them throughout body

Question 4

Endocrine versus neural signalling Nervous System

Answer 4

Mediator molecules:Neurotransmitters released locally in response to nerve impulses
Site of mediator action:Close to site of release, at synapse; binds to receptors in postsynaptic membrane
Types of target cells:Muscle (smooth, cardiac, and skeletal) cells, gland cells, other neurons
Time to onset of action:Typically within milliseconds (thousandths of a second)
Duration of action:Generally briefer (milliseconds)

Question 5

Endocrine versus neural signalling Endocrine System

Answer 5

Mediator molecules:Hormones delivered to tissues throughout body by blood
Site of mediator action:Far from site of release (usually); binds to receptors on or in target cells
Types of target cells:Cells throughout body
Time to onset of action:Seconds to hours or days
Duration of action:Generally longer (seconds to days)

Question 6

Hypothalamus and pituitary gland

Answer 6

Hypothalamus and pituitary gland act as a unit
Posterior pituitary is an extension of nervous tissue down from brain Posterior pituitary has a “stand alone” blood supply.
Anterior pituitary supplied by blood that has already passed through capillaries in hypothalamus.
The hypothalamus releases peptides that stimulate or inhibit the hormones of anterior pituitary into these capillaries.
The blood then bathes anterior pituitary in a series of sinusoids, signalling anterior pituitary to increase or decrease secretion of hormones

Question 7

Hormones of Anterior pituitary

Answer 7

Growth hormone,
* Thyroid stimulating hormone
* Adrenocorticotrophin hormone
* Prolactin
* Follicle stimulating hormone * Luteinising hormone

Question 8

Negative feedback regulation of hormones by anterior lobe of pituitary gland

Answer 8

Hypothalamus senses amount of GH in blood, releases either GHRF or GHIF to bathe anterior pituitary to release more or less GH into blood

Question 9

Negative feedback regulation by anterior lobe of pituitary

Answer 9

TRH released by hypothalamus, causes anterior pituitary to release TSH, thyroid gland releases thyroxine
Thyroxine inhibits TRH release
CRH (corticotrophin releasing hormone) released from hypothalamus, causes anterior pituitary to release ACTH (adrenocorticotrophin releasing hormone) into bloodstream, causes cortisol from adrenal glands to be released.

Question 10

Hormones of anterior pituitary

Answer 10

growth hormone, thyroid stimulating hormone,adrenocorticotrophic hormone, prolactin, follicle stimulating hormone,Lutenising hormone,

Question 11

growth hormone,

Answer 11

regulates metabolism promotes tissue growth especially of bones and muscles.

Question 12

thyroid stimulating hormone,

Answer 12

stimulates growth and activity of thyroid gland and secretion of T3 and T4

Question 13

adrenocorticotrophic hormone

Answer 13

stimulates the adrenal cortex to secrete glucocorticoids

Question 14

prolactin,

Answer 14

stimulates growth of breast tissue and milk production

Question 15

follicle stimulating hormone

Answer 15

stimulates production of sperm in testes,stimulates secretion of oestrogen by the ovaries, maturation of ovarian follicles, ovulation.

Question 16

Lutenising hormone,

Answer 16

stimulates secretion of testosterone by the testes,stimulates secretion of progesterone by the corpus luteum.

Question 17

Growth hormone (GH)pt2

Answer 17

In response to GH, cells in liver, skeletal muscles, cartilage, bones, and other tissues secrete secondary hormones called insulin-like growth factors (IGFs), which either enter bloodstream or act locally. IGFs stimulate protein synthesis, help maintain muscle and bone mass, and promote healing of injuries and tissue repair.
* The anterior pituitary releases GH in bursts that occur every few hours, especially during sleep.
* Blood glucose level is a major regulator of GHRH and GHIH secretion. Low blood glucose stimulates the hypothalamus to secrete GHRH (increasing GH). High blood glucose inhibits release of GHRH (and therefore GH)

Question 18

Negative feedback for ADH in posterior pituitary

Answer 18

ADH causes retention of water and brings osmolality down
Also restores blood pressure as ADH causes vasoconstriction
Same thing happens after salty meal
But if this was the only homeostatic mechanism

Question 19

Thyroid gland

Answer 19

Made up of microscopic spherical sacs called thyroid follicles. Walls of follicle comprise follicular cells, that produce two hormones: thyroxine, (T4, contains 4 I atoms) and triiodothyronine (T3, contains 3 I atoms).
* T3 and T4 known as thyroid hormones.
* Central cavity of thyroid follicles contain stored thyroid hormones.
* Most T4 converted to T3 as it enters cells. T3 more potent than T4.
* Smaller number of parafollicular cells lie between follicles . They produce the hormone calcitonin for Calcium and bone homeostasis

Question 20

Actions of Thyroid Hormones

Answer 20

Thyroid hormones increase basal metabolic rate (BMR), the rate of oxygen consumption under standard or basal conditions.
* Thyroid hormones play important role in maintenance of normal body temperature.
* Also stimulate protein synthesis, & body growth, especially growth of nervous systems in babies.

Question 21

Abnormalities of thyroid

Answer 21

Deficiency relatively common
* Congenital hypothyroidism, Need prompt diagnosis as can cause mental retardation. Babies screened routinely. Treated with thyroxine for life.
* Adult Hypothyroidism causes myxedema, oedema/swelling of facial tissues. Slow heart rate, low body temperature, cold sensitivity, dry hair and skin, lethargy, gain weight.
* Also caused by deficiency of iodine in diet. May cause enlarged thyroid gland (goiter) Too much thyroid hormones:
* XS thyroxine due to Graves disease, an autoimmune disorder. Antibodies mimic action of TSH, stimulating thyroid gland to grow & produce thyroxine. May get goiter and unusual swelling behind eyes causing them to protrude

Question 22

Calcitonin & parathyroid hormone (parathormone)

Answer 22

Calcitonin producing cells in thyroid
* Parathormone in parathyroid glands (behind thyroid gland)
* Act together to control calcium levels
* Calcitonin reduces blood calcium & stimulates bone cells to store calcium * Inhibit kidney reabsorption of calcium
* Parathormone does reverse
* Release calcium from bones
* Stimulates calcium reabsorption by kidneys

Question 23

Low blood calcium

Answer 23

Hypoparathyroidism
* Too little parathyroid hormone—causes reduced blood Ca2+, causes neurons and muscle fibres to depolarize and produce action potentials spontaneously.
* Leads to twitches, spasms, and tetany (maintained contraction) of skeletal muscle.

Question 24

Adrenal medulla

Answer 24

Produces adrenalin and noradrenalin
* Innervated by sympathetic nervous system * Short term flight or flight response
* Increase heart rate & blood pressure
* Increasing metabolic rate
* Dilates pupils

Question 25

Mineralocorticoids

Answer 25

Produced by adrenal cortex
* Main hormone aldosterone
* Not regulated by pituitary
* Important in water & electrolyte balance
* Stimulates sodium (and water reabsorption) by kidney * Stimulates loss of potassium by kidney

Question 26

Aldosterone-works in partnership with kidney

Answer 26

Works as part of the renin-angiotensin-aldosterone system involving kidney blood flow and hormone release
* If blood pressure low, blood volume low or sodium is low
* Kidneys release the enzyme renin into the blood.
* Renin converts the circulating protein angiotensin into angiotensin 1

Question 27

Glucocorticoids

Answer 27

Produced by adrenal cortex - Most important is cortisol.
* Control of cortisol levels via feedback loop involving pituitary.
* Released by adrenal glands at times of stress (internal or external).Infections, operations, emotional stress.
* Short term stress mediated by sympathetic nerves. Longer term via glucocorticoids
Cause metabolic changes for combating stress:
* Raised glucose: Liver converts amino acids to glucose.
* Protein breakdown in muscles to release extra amino acids for use elsewhere
* Breakdown of fat in fat cells to release fatty acids for use as energy source by other tissues * Anti‐inflammatory and immune suppression effects.

Question 28

Insufficient adrenal cortex hormones

Answer 28

Failure of adrenal gland causes loss of glucocorticoids and aldosterone. Called Addison’s disease.
* Symptoms include weight loss, hypoglycemia, and muscular weakness. Low aldosterone causes raised potassium and low sodium in blood; low blood pressure; dehydration.

Question 29

Pancreas

Answer 29

Has both endocrine & exocrine functions.
* Endocrine part comprises clusters of cells called pancreatic islets or islets of Langerhans.
* Islet cells, comprise alpha cells that make glucagon and beta cells that make insulin.
* Normal blood glucose 3.5-8mmol/L

Question 30

Insulin/glucagon actions

Answer 30

When glucagon is raised, glucose released from liver glycogen & amino acids are metabolised into glucose

Question 31

Diabetes Mellitus

Answer 31

Diabetes mellitus is when pancreas does not produce sufficient insulin or body cells do not use insulin properly.
An action of insulin is to move blood glucose into muscle and liver. So insulin deficiency has abnormal high blood glucose levels
Two types of diabetes.
Type 1 diabetes is an autoimmune disease. Insulin levels low because immune system has destroyed pancreatic beta cells. Previously called juvenile onset. Treatment insulin injections.

Question 32

Diabetes Mellitus pt2

Answer 32

Type 2 diabetes (noninsulin-dependent or adult‐onset diabetes) usually occurs in later life
May be treated with medicines that stimulate extra insulin release by pancreas.
The bodies cells become more resistant to actions of insulin. Therefore, insulin usually present in blood but blood glucose remains too high.
Type 2 diabetes increased risk if positive family history, being overweight, and inactivity. Treatments include lifestyle changes (diet and exercise), drugs that improve cell sensitivity to glucose or stimulate pancreas to produce more insulin, or insulin injections.

Question 33

Diabetes Mellitus pt3

Answer 33

Signs and symptoms of diabetes include thirst, frequent urination (because glucose passing into urine, drawing water along with it) , increased hunger, fatigue, slow healing sores, frequent infections, and ketone bodies in the urine.
* As the bodies cells can’t use glucose (because no insulin or because they are less responsive), cells break down fats into fatty acids and glycerol. Fatty acids metabolised into ketone bodies. Build up of ketones causes blood pH to fall (more acidic). Keto- acidosis.
* Long‐term complications develop gradually. Risks reduced by good control of blood glucose levels. Cardiovascular disease. Increased risk of heart attack, stroke, coronary artery disease.
-Kidney damage. Due to damage to blood vessels in kidneys (nephropathy)
-Eye damage. Blood vessel damage in the eyes (retinopathy) can affect vision.
-Nerve damage. Damage to blood vessels that supply nerves (neuropathy) can cause numbness, tingling, burning, affects fingers and toes. Loss of sensation increases risk of foot damage.

Question 34

Hormones Produced by Other Organs and Tissues
That Contain Endocrine Cells

Answer 34

Thymus
Thymosin
Gastrointestinal Tract
Gastrin
Cholecystokinin (CCK)
Kidney
Erythropoietin (EPO)
Heart
Atrial natriuretic peptide (ANP)
Adipose Tissue
Leptin

Question 35

Thymosin

Answer 35

Promotes the maturation of T cells

Question 36

Gastrin

Answer 36

Promotes secretion of gastric acid

Question 37

Cholecystokinin (CCK)

Answer 37

Stimulates secretion of pancreatic juice& bile from the gallbladder, and satiety

Question 38

Erythropoietin (EPO)

Answer 38

Increases red blood cell production

Question 39

Atrial natriuretic peptide (ANP)

Answer 39

Decreases blood pressure

Question 40

Leptin

Answer 40

Suppresses appetite