The Endocrine System

AP Chapter 45

• The endocrine system, along with the nervous system, is responsible for coordinating our responses.

• The endocrine system is a slower system and the nervous system is a faster response.

Chemical signals

• Chemicals found in both systems and also as part of other signaling mechanisms bind to specific receptor proteins on or in target cells.

Secreted chemical signals include

– Hormones – produced by endocrine glands,

travel through the blood stream to target organs

ex – insulin, estrogen– Local regulators

(a) paracrine signals – act on neighboring cells, ex. – cytokines, interferon, prostaglandins

(b) autocrine signals – act on secreting cells itself, ex – cytokines

– Neurotransmitters - secreted by neurons at synapses

ex- serotonin, nitric oxide (NO)– Neurohormones – secreted by neurosecretory

cells, travel through the blood stream to target organs or synapses

ex- epinephrine– Pheromones – released into the environment;

between individuals

ex – insects marking trails,

mating, etc.

Fig. 45-2

Bloodvessel Response

Response

Response

Response

(a) Endocrine signaling

(b) Paracrine signaling

(c) Autocrine signaling

(d) Synaptic signaling

Neuron

Neurosecretorycell

(e) Neuroendocrine signaling

Bloodvessel

Synapse

Response

Chemical Classes of Hormones

• Three major classes of molecules function as hormones in vertebrates:– Polypeptides (proteins and peptides)– Amines derived from amino acids– Steroid hormones

Fig. 45-3

Water-soluble Lipid-soluble

Steroid:Cortisol

Polypeptide:Insulin

Amine:Epinephrine

Amine:Thyroxine

0.8 nm

• Lipid-soluble hormones (steroid hormones) pass easily through cell membranes, while water-soluble hormones (polypeptides and amines) do not

• The solubility of a hormone correlates with the location of receptors inside or on the surface of target cells

• Water-soluble hormones are secreted by exocytosis, travel freely in the bloodstream, and bind to cell-surface receptors

• Lipid-soluble hormones diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells

Fig. 45-5-1

NUCLEUS

Signalreceptor

(a) (b)

TARGETCELL

Signal receptor

Transportprotein

Water-solublehormone

Fat-solublehormone

Fig. 45-5-2

Signalreceptor

TARGETCELL

Signal receptor

Transportprotein

Water-solublehormone

Fat-solublehormone

Generegulation

Cytoplasmicresponse

Generegulation

Cytoplasmicresponse

OR

(a) NUCLEUS (b)

Multiple Effects of Hormones

• The same hormone may have different effects on target cells that have– Different receptors for the hormone– Different signal transduction pathways– Different proteins for carrying out the response

due to different transcription factors they activate

• A hormone can also have different effects in different species

Fig. 45-8-1

Glycogendeposits

receptor

Vesseldilates.

Epinephrine

(a) Liver cell

Epinephrine

receptor

Glycogenbreaks downand glucoseis released.

(b) Skeletal muscle blood vessel

Same receptors but differentintracellular proteins (not shown)

Fig. 45-8-2

Glycogendeposits

receptor

Vesseldilates.

Epinephrine

(a) Liver cell

Epinephrine

receptor

Glycogenbreaks downand glucoseis released.

(b) Skeletal muscle blood vessel

Same receptors but differentintracellular proteins (not shown)

Epinephrine

receptor

Different receptors

Epinephrine

receptor

Vesselconstricts.

(c) Intestinal blood vessel

Negative feedback and antagonistic hormone pairs are common features of the

endocrine system

• Hormones are assembled into regulatory pathways

• A negative feedback loop inhibits a response by reducing the initial stimulus

• Negative feedback regulates many hormonal pathways involved in homeostasis

Fig. 45-11Pathway Example

Stimulus Low pH induodenum

S cells of duodenumsecrete secretin ( )

Endocrinecell

Bloodvessel

PancreasTargetcells

Response Bicarbonate release

Neg

ativ

e fe

edb

ack

–

Insulin and Glucagon: Control of Blood Glucose – an example of antagonistic

hormone pairs

• The pancreas has clusters of endocrine cells called islets of Langerhans with alpha cells that produce glucagon and beta cells that produce insulin

• Insulin reduces blood glucose levels by– Promoting the cellular uptake of glucose– Slowing glycogen breakdown in the liver– Promoting fat storage

• Glucagon increases blood glucose levels by– Stimulating conversion of glycogen to glucose in

the liver– Stimulating breakdown of fat and protein into

glucose

– Remember: Glucagon – “Glucose ON!”

Fig. 45-12-2

Homeostasis:Blood glucose level

(about 90 mg/100 mL)

Insulin

Beta cells ofpancreasrelease insulininto the blood.

STIMULUS:Blood glucose level

rises.

Liver takesup glucoseand stores itas glycogen.

Blood glucoselevel declines.

Body cellstake up moreglucose.

Fig. 45-12-4

Homeostasis:Blood glucose level

(about 90 mg/100 mL)

Glucagon

STIMULUS:Blood glucose level

falls.

Alpha cells of pancreasrelease glucagon.

Liver breaksdown glycogenand releasesglucose.

Blood glucoselevel rises.

Diabetes Mellitus

• Diabetes mellitus is perhaps the best-known endocrine disorder

• It is caused by a deficiency of insulin or a decreased response to insulin in target tissues

• It is marked by elevated blood glucose levels

• Type I diabetes mellitus (insulin-dependent) is an autoimmune disorder in which the immune system destroys pancreatic beta cells

• Type II diabetes mellitus (non-insulin-dependent) involves insulin deficiency or reduced response of target cells due to change in insulin receptors

Fig. 45-10Major endocrine glands:

Adrenalglands

Hypothalamus

Pineal gland

Pituitary gland

Thyroid gland

Parathyroid glands

Pancreas

Kidney

Ovaries

Testes

Organs containingendocrine cells:

Thymus

Heart

Liver

Stomach

Kidney

Smallintestine

Coordination of Endocrine and Nervous Systems in Vertebrates

• The hypothalamus receives information from the nervous system and initiates responses through the endocrine system

• Attached to the hypothalamus is the pituitary gland composed of the posterior pituitary and anterior pituitary

• The posterior pituitary stores and secretes hormones that are made in the hypothalamus

• The anterior pituitary makes and releases hormones under regulation of the hypothalamus

Fig. 45-14

Spinal cord

Posteriorpituitary

Cerebellum

Pinealgland

Anteriorpituitary

Hypothalamus

Pituitarygland

Hypothalamus

Thalamus

Cerebrum

Hypothalamus

• The hypothalamus secretes two hormones which are stored in the posterior pituitary.

1) oxytocin – induces uterine contractions during birth and milk production

2) ADH – which decreases urine volume

Fig. 45-15

Posteriorpituitary

Anteriorpituitary

Neurosecretorycells of thehypothalamus

Hypothalamus

Axon

HORMONE OxytocinADH

Kidney tubulesTARGET Mammary glands,uterine muscles

The anterior pituitary gland secretes releasing hormones and inhibiting

hormones.

• TSH – thyroid stimulating

• FSH and LH – stimulates gonads

• ACTH - stimulates adrenal cortex

• Prolactin – milk production

• MSH – stimulates production of melanocytes (skin pigments)

• GH – growth hormone

Fig. 45-17

Hypothalamicreleasing andinhibitinghormones

Neurosecretory cellsof the hypothalamus

HORMONE

TARGET

Posterior pituitary

Portal vessels

Endocrine cells ofthe anterior pituitary

Pituitary hormones

Tropic effects only:FSHLHTSHACTH

Nontropic effects only:ProlactinMSH

Nontropic and tropic effects:GH

Testes orovaries

Thyroid

FSH and LH TSH

Adrenalcortex

Mammaryglands

ACTH Prolactin MSH GH

Melanocytes Liver, bones,other tissues

Tropic Hormones

• A tropic hormone regulates the function of endocrine cells or glands

• The four strictly tropic hormones are– Thyroid-stimulating hormone (TSH) – Follicle-stimulating hormone (FSH)– Luteinizing hormone (LH)– Adrenocorticotropic hormone (ACTH)

Thyroid Gland

• T3 and T4, regulates metabolism (needs dietary iodine to function properly – goiter)

• Calcitonin – lowers calcium in blood – deposition in bones and secretion into kidney filtrate

Parathyroid Gland

• PTH parathormone – raises calcium levels in blood – from bones and reuptake in kidneys

Fig. 45-20-2

PTH

Parathyroid gland(behind thyroid)

STIMULUS:Falling blood

Ca2+ level

Homeostasis:Blood Ca2+ level

(about 10 mg/100 mL)

Blood Ca2+ level rises.

Stimulates Ca2+

uptake in kidneys

Stimulates Ca2+ release from bones

Increases Ca2+ uptake in intestines

Activevitamin D

Adrenal medulla

• Epinephrine (adrenaline) – raises metabolic rate, “fight or flight”

• Norepinephrine (noradrenaline) controls blood pressure

Adrenal cortex

• Glucocorticoids – glucose from noncarb sources, such as muscles

• Mineralocorticoids (aldosterone) – induces kidneys to reabsorb water and salts

• Both of these deal with long-term stress

Fig. 45-21c

(b) Long-term stress response

Effects ofmineralocorticoids:

Effects ofglucocorticoids:

1. Retention of sodium ions and water by kidneys

2. Increased blood volume and blood pressure

2. Possible suppression of immune system

1. Proteins and fats broken down and converted to glucose, leading to increased blood glucose

Adrenalgland

Kidney

Adrenal cortex

Testes

• Androgens (testosterone) – gender, male secondary sex characteristics

Ovaries

• Estrogen – maintenance of female reproductive system and development of secondary female characteristics

• Progesterone – prepares uterus for child

Pineal Gland

• Melatonin – biological clock

Hormonal pathways work with the hypothalamus and anterior pituitary to

coordinate responses

• Ex – in the gonads

• GnRH (hypothalamus) affects FSH and LH (anterior pituitary) which affects estrogens and androgens (ovaries/testes)

Which endocrine gland?

• Too little of my hormone and you will feel tired and sluggish and probably gain weight.

THYROID

A malfunction in this gland can result in a giant.

Anterior Pituitary

This gland prepares me for an emergency situation by increasing my heartrate.

AdrenalGlands

This gland is also used in the digestive system. It also comes into play when I eat lots of M and M’s!

PANCREAS

This gland is called the “master gland” because it secretes nine hormones many of which control other endocrine glands by feedback control.

PituitaryGland

If this gland is not working properly, diabetes can result.

Pancreas

• If this gland is not working properly, your nerves and muscles will not function properly either due to calcium deficiency.

ParathyroidGland

• These glands do not function properly in chromosomal mutations such as in Turner’s and Klinefelter’s syndrome.

Gonads

This gland makes me wake up in the morning and ready to go!

Pineal Gland