The EndocrineSystemChapter 15

Starr & McMillan, 11th ed

Objectives:1. Describe the regulatory functions of the endocrine system.2. Explain the actions of hormones & identify the differences between them.3. Analyze the structure of each endocrine gland, the hormone(s) they secrete, & the effects on target organs.4. Explain the negative feedback control as a regulator for hormone levels.5. Explain the hyposecretion & hypersecretion of the major endocrine glands.

Endocrine Glands

• Located throughout the body• Secrete hormones: –Chemical substances–Chemical “messengers”

• Ductless – hormones are secreted directly into bloodstream

• http://www.youtube.com/watch?v=ER49EweKwW8

The Endocrine System & Hormones

• Consists of glands that secrete chemicals called hormones

http://www.youtube.com/watch?v=TgNwxF3aQpE

• Hormones are chemical messengers, that are carried in bloodstream.–bind to target cells which are equipped with specific receptor molecules–& elicit in them a response.

Mechanisms of

hormone release

(a) Humoral: in response to changing levels of ions or nutrients in blood

(b) Neural: stimulation by nerves(c) Hormonal: stimulation received

from other hormones

Targets (Target Organs)

• The tissue or organ that the hormones influence.• Located either close or very

distant from the endocrine gland.• Hormones may have few or

many target organs.

• Hormones often interact with one another.

• Negative feedback mechanisms control secretion of hormones.

• Target cells may react differently to hormones at different times

• Environmental cues can affect release of hormones.

Factors Influencing Hormone Effects

Hormones

• Hormones often interact.– Opposing interaction– Synergistic interaction– Permissive interaction

Types of Hormones

• Steroid hormones

• Amine hormones

• Peptide hormones

• Protein hormones

Steroid hormones

•These are all derived from cholesterol.•Examples: testosterone, estrogen, progesterone, mineralocorticoids, glucocorticoids.•Crosses the plasma membrane• lipid-soluble

Peptide hormones• Amino acids/ modified amino acids/

peptide/glycoprotein or protein• The receptors are on the plasma

membrane• water-soluble• When hormone binds to receptor– Activates an enzyme to produce cyclic AMP

(cAMP)– This activates a specific enzyme in the cell,

which activates another………and so on– Known as an enzyme cascade

• Peptide hormones:– Each enzyme can be used over &

over again in every step of the cascade.

– So more & more reactions take place.– The binding of a single hormone

molecule can result in a 1000X response.

– Fact acting, as enzymes are already present in cells.

• Steroid hormones:– Act more slowly.– It takes more time to synthesize new

proteins.– Effects are longer lasting.

Protein Hormones:

• These are made of Amino Acids.• water-soluble• Protein hormones cannot cross

the plasma membrane!• Examples: Insulin, Hypothalamus

signaling hormones.

Control of Hormone Secretions

• Negative Feedback Control

• Biorhythms

• Control by the CNS

Negative Feedback AKA opposing interaction

• Hormones “oppose” each other’s actions• When one hormone is there to ↑

a body’s function, the antagonist hormone is there to ↓ it • Results: homeostasis• http://www.youtube.com/watch?v=TgNwxF3aQpE

Example• Pattern of Insulin Secretion–Glucose levels ↑ in blood (stimulus)–Pancreas secretes insulin–Insulin moves glucose into the cell.–Glucose levels in the blood ↓ (stimulus)–Pancreas stops secreting insulin.

• http://www.youtube.com/watch?v=OYH1deu7-4E

Biorhythms (Circadian Rhythm)

http://www.youtube.com/watch?v=UbQ0RxQu2gM

• Rhythmic alteration in the rate of secretion of the hormone.

example:• Female reproductive cycle

Biorhythms (Circadian Rhythm)

• A 24 hour rhythm.• Pattern repeats every 24 hrs.–Sleep

• Cortisol–Highest in the am–Lowest at midnight

Control by the CNS

• Activation of hypothalamus• Stimulation of sympathetic

nervous system

FUNCTIONS OF ENDOCRINE SYSTEM & ITS HORMONES

Endocrine & nervous system function in highly interconnected ways.

http://www.youtube.com/watch?v=0_yGqRz4Qts

• Help to regulate growth• Assist in use of foods to produce energy• Meet demands of infection, trauma &

stress• Fluid & electrolyte balance• Reproduction

Endocrine Glands

• Hypothalamus• Pituitary (anterior & posterior)• Thymus• Thyroid• Parathyroids

• Pancreas• Adrenal medulla• Adrenal cortex• Ovaries • Testes • Pineal

The Hypothalamus & Pituitary Gland

• Hypothalamus–Monitors internal organs &

conditions r/t their functioning–Secretory neurons that extend into

the pituitary

• Pituitary gland–Posterior lobe stores hormones–Anterior lobe secretes hormones

Hypothalamus

• Regulates the internal environment through the autonomic system.

• Heart beat, body temperature, water balance.

• Controls the glandular secretions of the pitutary gland.

• Connected to the pitutary gland by a stalk-like structure (hypothalamic-hypophyseal portal system)

• Corticotropin-releasing hormone (CRH)• Gonadotropin-releasing hormone (GnRH)• Growth hormone-releasing hormone

(GHRH) or growth hormone-inhibiting hormone (GHIH) (also known as somatostain)

• Prolactin-releasing hormone (PRH) or prolactin-inhibiting hormone (PIH) (also known as dopamine)

• Thyrotropin releasing hormone (TRH):

• Released to anterior pituitary

The Hypothalamus

Hypothalamus

• Antidiuretic hormone (ADH) also known as Vasopressin

• Oxytocin Stored in Posterior pituitary gland.

Pituitary Gland http://www.youtube.com/watch?v=ZfDXSKhNS4I

Posterior pituitaryOxytocin • Target organs = uterus &

mammary glands (breasts)• Stimulates muscles in uterus to

contract (labor) to expel the fetus

• Stimulates mammary glands to release & secrete milk• Positive feedback

• “Cuddle hormone”

Posterior Pituitary Lobe

ADH (antidiuretic hormone, vasopressin). –Target cells in the kidneys –promotes water reabsorptionConserves water; urine output ↓’s

Released in response to concentrated plasma (blood volume ↓’s,= dehydration)

Negative feedback

kidney nephrons mammary

glands

muscles in uterus

wall

ADH oxytocin

Fig. 15.3, p. 274

a Secretory neurons in the hypothalamus synthesize ADH or oxytocin.

b The ADH or Oxytocin moves downward inside the axons of the secretory neurons and accumulates in the axon endings.

c Action potentials trigger the release of these hormones, which enter blood capillaries in the posterior lobe of the pituitary.

d The hormone molecules move into the general circulation.

6 Anterior Pituitary Hormones

–ACTH: corticotropin–TSH: thyrotropin–Gonadotropins:–FSH: follicle-stimulating hormone–LH: luteinizing hormone

–PRL: prolactin–GH: growth hormone (somatotropin)

Remember

• PRO Prolacin• ATHletes ACTH• Got Gonadotropins (FSH,LH)• To TSH• GROW Growth Hormone

Anterior Pituitary Gland

–Corticotropin (ACTH–adrenocorticotropic) stimulates the adrenal cortex to secrete 3 steroid hormones (ie. cortisol)• Secretion of ACTH is ↑ by corticotropin

releasing hormone (CRH) from the hypothalmus which is produced during stressful situations or hypoglycemia

↑stress→Hypothalamus→CRH→Pituitary→ACTH

Anterior Pituitary Gland

Thyrotropin (Thyroid-stimulating hormone TSH) stimulates normal growth of the thyroid gland• Secretion is stimulated by thyrotropin releasing hormone (TRH) from the hypothalmus when metabolic rate (energy production) ↓

Metabolic rate↓→Hypothalamus→TRH→Pituitary→TSH

Anterior Pituitary Gland

Follicle-stimulating hormone (FSH) women: Ovarian follicle development

& egg production. men: Initiates sperm production in

testes• Stimulated by hypothalmus which produces

Gonadotropin releasing hormone (GnRH)

Anterior Pituitary GlandLuteinizing hormone (LH) also acts on

the ovary to release an egg.women: ovulation, rupture of ovarian

follicle to become corpus luteum, & ↑ secretion of progesterone by corpus luteum & secretion of sex hormones

men: ↑ secretion of testosterone by the interstitial cells of the testes & causes secretion of sex hormones (interstitial cell-stimulating hormone (ICSH))

– Regulated by GnRH from hypothalmus

Anterior Pituitary Gland

Prolactin (PRL) acts on the mammary glands to develop & stimulate & sustain milk production after childbirth

• 1st estrogen & progesterone (secreted by placenta) act on the mammary glands

• After delivery of baby, prolactin secretion ↑ & milk is produced

• Nursing will keep levels high

Anterior Pituitary Gland

Somatotropin (STH), growth hormone (GH), acts on body cells in general to promote growth (↑ rate of cell division).

• Promotes– skeletal & muscle growth– Controls the rate at which amino acids enters

cells thus the rate at which protein synthesis

Remember

• Tropic hormones are aimed at & control other glands • Usually end in tropin or tropic(adrenocorticotropic hormone)

Melanocyte stimulating hormone (MSH)

Causes a rapid ↑ in the formation of melanin or pigment granules in specialized skin cells.

Intermediate lobe of the Pituitary gland

• Problems with control mechanisms can result in skewed hormone signals.– Endocrine glands in general

only release small quantities of hormones & control the frequency of release to make sure there isn’t too much or too little hormone.

Factors That Influence Hormone Effects

Hormones as Long-Term Controllers

• Hormones typically regulate activities that occur over an extended period

• Involved in slower body ∆’s including:–Growth–Sexual maturation

Thymus gland

Secretes Thymosins• Plays role in immune system• Target:–WBC’s (T-lymphocytes)

• Action:–Maturation of the WBC’s

Thymus Gland

• Thymosin: Lymphocytes from bone marrow pass through this to form T-lymphocytes; maturation of T-cells (peptide)• Immune system

Thyroid hormone (TH):–Thyroxine (T4)–Triiodothyronine (T3)

• Requires iodine (from dietary sources)• Regulates metabolism of carbohydrates,

proteins, & fats• Necessary for normal maturation of

nervous system & for normal growth & development

Hypothalmus →TRH→pituitary→Thyroid→TSH(T3,T4)

The Thyroid Gland

An example of a feedback loop

• A certain item in the blood decreases

• A certain area of the brain senses this decrease

• A certain hormone is released

• This hormone stimulates the release of another hormone

• This other hormone stimulates the release of the hormone which was sensed to be decreased in the first place, causing it to be increased to desired level

• Thyroxine (T4)

• Hypothalamus

• TRH from the hypothalamus

• TSH from anterior pituitary

• Thyroxine from the thyroid

generic

particular example: thyroid hormone

CALCITONIN

• Stimulated when blood calcium levels are ↑

Regulates plasma levels of calcium by:• ↓ blood calcium by stimulating bone-

making activity (osteoblastic) which drives calcium from blood into bone &/or Inhibits osteoclast activity in bones

• Inhibits Ca2+ absorption by the intestines • ↑ excretion of calcium in urine• Antagonist to PTH

Produces Parathyroid hormone (PTH)•Main Calcium Regulator

3 target organs:1. bone2. digestive tract (intestines)3. kidneys

Calcitonin & PTH work together to maintain normal blood calcium levels. Antagonistic action

Parathyroid glands

PTH & Calcitonin

Blood calcium levels drop:PTH → ↑ Ca+ (↑ release from bones to

blood) →Stimulates kidneys to reabsorb Ca from urine & ↑ absorption of Ca in GI tract with help of Vitamin D. Phosphate ↓

Blood calcium levels raise:Calcitonin → ↓ Ca+ (causes bones to

absorb) Phosphate ↑

PTH & Calcitonin

• Negative feedback mechanism:• Blood calcium levels control the

secretion of calcitonin & PTH • High blood Ca levels stimulate

secretion of calcitonin & inhibit secretion of PTH

• Low blood Ca levels inhibit secretion of calcitonin & stimulate secretion of PTH

• http://www.youtube.com/watch?v=F9iBEN51D-8

Adrenal Glands

–Adrenal cortex

–Adrenal medulla

Kidney

Adrenal Cortex

• Affected by adrenocorticotropic hormone (ACTH).

• Which in turn stimulates the production of steroids:–Mineralocorticoids (salts)– Glucocorticoids (sugars)– Gonadocorticoids (sex)

The Adrenal Cortex• Mineralocorticoids–Most abundant hormone: aldosterone–Acts on the distal tubules of the kidneys–Adjust concentration of mineral salts,

e.g., K+ & Na+, in the extracellular fluid

• In a fetus & early puberty–Adrenal cortex produces large amounts

of sex hormones

Mineralocorticoids

• Aldosterone–Chief Mineralocorticoids–Regulates blood volume & BP–Target: Kidneys–Action: ↑’s reabsorption of Na⁺ by kidneys, ↑’s excretion of K⁺

Adrenal Glands & Stress Responses

• Glucocorticoids, e.g., cortisol– Raises blood glucose levels– “Glucose sparing” in skeletal muscles– Promotes breakdown of fats– Gluconeogensis in the liver– Hypoglycemia: ↓ glucose – Reduce inflammation– Long term use of glucocorticoids; side effects

Cortisol

• Dampens uptake of glucose from blood,

• Stimulates breakdown of fats for energy

• Conserves glucose for use by brain• Anti-inflammatory effect – blocks

effects of histamine & prevents excess tissue damage

• Secreted during stressful situations

Regulation of blood pressure & volume

When sodium ions levels are high- so a high blood volume a glucocorticord (cortisol) makes the heart release atrial natriuretic hormone (ANH)

Kidneys excrete sodium ions & water follows. Volume & pressure return to normal.When sodium ions levels are low- a low blood volume makes kidneys secrete renin (ENZYME)

Adrenal cortex secretes a mineralocorticoid (Aldosterone), which makes the kidneys reabsorb sodium ions & thus water. Volume & pressure return to normal.http://www.youtube.com/watch?v=tANEMMGoy9k

Anterior Pituitary Gland → → ACTH→

→ Adrenal Cortex→→Glucocorticoid hormone

Cortisol

Gonadocorticoids

Sex Hormones- small amounts of both male & female sex hormones.

Male androgens: testosterone Female: estrogens

Adrenal Medulla

• IS UNDER NERVOUS CONTROL• This produces: – Epinephrine (adrenaline)–Norepinephrine (nor-adrenaline)

» Both modified amino acids

• Heart rate & blood pressure up• Blood glucose levels rise• Muscles become energized• The effects are short-termhttp://www.youtube.com/watch?v=0_yGqRz4Qts

Adrenal Medulla

• Catecholamines (Fight or Flight)–Epinephrine (Adrenalin)•↑ heart rate & force of contraction•Dilates bronchioles, slows peristalsis• Causes vasodilation in skeletal muscles•↑ use of fats for energy•↑ conversion of glycogen to glucose

–Norepinephrine• Causes vasoconstriction in skin, viscera, & skeletal muscles (raises BP)

Adrenal Glands & Stress Responses

Long-Term Stress Can Damage Health• Stress ↑ amt of adrenal hormones• Psychosocial stressors• Negative stressors can contribute to:–HTN & related cardiovascular disease–Suppressed immune system

• Stress reducers: social connections & physical exercise

Pancreas

• Long, slender organ• Lies transversely

across the abdomen from the curve of the duodenum to the spleen (LUQ)

• Secretes hormones:– Insulin– Glucagon– Somatostatin

Pancreas

• Exocrine & endocrine functions• Pancreatic islet: (islets of langerhans)–Alpha cells•Glucagon: raises glucose levels in blood

–Beta cells http://www.youtube.com/watch?v=kIPYVV4aThM

• Insulin: lowers glucose levels in blood

–Delta cells•Somatostatin: inhibits secretion of insulin and glucagon

PANCREAS

• INSULIN• http://www.youtube.com/watch?v=eDm9hEOn8zc

• GLUCAGON

(PIG- pancreas secretes insulin & glucagon)Antagonistic action

INSULIN

• Helps regulate blood glucose levels• Stimulated by hyperglycemia• Insulin enable cells to use glucose for

immediate energy• Excess glucose stored in liver & muscles

as glycogen• ↓ blood glucose • Enables cells to take in fatty acids &

amino acids for synthesis of lipids & proteins

GLUCAGON

• Helps regulate blood glucose levels• Stimulus is low blood glucose• Stimulates the liver to ∆ glycogen to

glucose • ↑ blood glucose• ↑ the use of fats & excess amino

acids for energy production• Makes all types of food available for

energy production

Diabetes

Type I: insulin-dependant diabetes – Pancreas is not producing insulin – Thought to be brought on by an

environmental agent (virus) – destroy pancreatic islets

• Type II: noninsulin-dependant diabetes– Pancreas producing insulin– Liver and muscles cells don’t respond– Thought to be caused by being

inactive/obese

Diabetes

• Type II symptoms often overlooked. One estimate suggests 7 million Americans have Type II diabetes without knowing it.

• It is estimated that a further 9 million Americans have Type I diabetes.

Long term complications of diabetes

• Blindness• Kidney disease• Heart disease• Stroke• Reduced circulation–Gangerene in arms & legs

•Estrogens

•Progesterone

•Inhibin

Ovaries

Estrogen

• Secreted by ovaries• Stimulated by FSH from anterior

pituitary • Promotes maturation of ovum in

ovarian follicle & stimulates growth of blood vessels in endometrial lining of uterus

• Causes development of female secondary sex characteristics

Progesterone

• Secreted by corpus luteum• Stimulated by LH from

anterior pituitary gland• Promotes storage of glycogen

& growth of blood vessels in endometrium (may become placenta)

Inhibin

• Secreted by the ovaries • Acts primarily to inhibit the

secretion of follicle-stimulating hormone by the anterior pituitary gland

• negative feedback

Testes• Testosterone (steroid

hormone)• Inhibin

Testosterone

• Stimulus for secretion is LH from anterior pituitary• Promotes maturation of sperm

at puberty• Stimulates development of

male secondary sex characteristics

• http://www.youtube.com/watch?v=djqqao2Uebo

Inhibin

• Secreted by testes• Stimulus for secretion is ↑’ed

testosterone • Interaction of inhibin, testosterone,

& the anterior pituitary hormones maintains spermatogenesis at a constant rate

The Pineal Gland

–Located in the brain–Produces the hormone melatonin

primarily at night– Influences sleep/wake cycles–Biological clock•Monitors day length• Influenced by melatonin

• SAD: seasonal affective disorder–Symptoms & treatments

– Seasonal affective disorder (SAD) affects persons during the winter and may result from an out-of-sync biological clock; melatonin makes it worse; exposure to intense light helps.

– Melatonin helps regulate seasonal reproductive cycles in other mammals

– Melatonin levels may potentially be linked to the onset of puberty.

The Pineal Gland

The Heart

• Heart–Atrial natriuetic peptide (ANP)• Inhibits reabsorption of Na+ in the kidneys when blood pressure is high

•Gastrin: Produces an acid for dissolving & digesting some foods.

•Secretin: causes the pancreas to send out digestive juices that are rich in bicarbonate

•CCK: causes the pancreas to produce the enzymes of pancreatic juice, & causes the gallbladder to empty

•Ghrelin: stimulates the appetite

•Peptide YY: Inhibits the appetite

GI Hormones

Hormones from other tissues

• Leptin– Protein hormone produced by fat tissue– Sends a signal to the hypothalamus that

you have had enough to eat.– Obese people have a genetic mutation

which makes either • Inactive leptin• No receptor cells in the hypothalamus

Connections: The Endocrine System in Homeostasis

http://www.youtube.com/watch?v=jkioZCDHT_E

• Skeletal system

• Muscular system

• Cardiovascular system & blood

• Immunity & lymphatic system

Connections: The Endocrine System in Homeostasis

• Digestive system

• Urinary system

• Nervous system

• Reproductive system