Chapter 45

Hormones and the Endocrine System

Tissue Communication

• Extracellular animals have multiple levels of tissue organization.

• Communication is essential to maintain homeostasis.• Endotherms vs ectotherms

• Bioregulators are used.

The thermostat function of the hypothalamus and feedback mechanisms in human thermoregulation

Chemical Signals

• Used for tissue communication• Secreted chemical signals include

– Local regulators (travel short distances via diffusion)– Neurotransmitters (nervous or endocrine

communication)– Hormones (secreted into bloodstream, travel long

distances)– Neurohormones (nerves that secrete hormones)

Types of Cellular Action

• __________ – impacting yourself. • __________– impacting your neighbors.• __________– impacting the next nerve in

sequence. Short distance, quick communication.• __________– chemical secreted into blood stream.

Impacts distant targets, longer lasting communication.

• __________– neurons secrete hormones into bloodstream.

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

Integration of Systems

• Hormones impact the body through interrelationships of the __________ system and the __________ system.

• The endocrine system secretes hormones that coordinate __________ , but longer-acting responses including reproduction, development, energy metabolism, growth, and behavior.

• The nervous system conveys __________ electrical signals along specialized cells called neurons; these signals regulate other cells.

• NOTE: Some neurons can secrete hormones…

Neurotransmitters

• Neurons (nerve cells) contact target cells at __________ .• At synapses, neurons secrete chemical signals called

__________ that diffuse a short distance to bind to receptors on the target cell.

• Neurotransmitters play a role in sensation, memory, cognition, and movement.

• Many neurotransmitters can also serve as __________ .– Example: Epinephrine (__________ ) during ‘fight or flight’

response

Neuron

Synapse

Response

The Body’s Long-Distance Regulators

• Animal __________ are chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body.

• Hormones mediate responses to environmental stimuli and regulate growth, development, and reproduction.

• Stimuli can include:– Change in __________

– Another __________

– __________ impulses– __________ cues

Neurohormones

• Nerves that secrete hormones into the __________ .

• Have long-lasting effects at distant targets.

• Can store hormones (weird)

• Examples: hypothalamic hormones, oxytocin, anti-diuretic hormone

Neurosecretorycell

ResponseBloodvessel

How Hormones Work…• Three part system:

– 1. Hormone is secreted

– 2. Travels to distant targets via bloodstream

– 3. Bind at specific target cells and cause a specific response

• Endocrine glands are: – Ductless glands, secretory

cells

– Well vascularized

– Range in size from individual cells to entire organs

• Secretion can be turned off or amplified via feedback loops

Feedback Mechanisms: Negative

• The goal is to get back to the ‘norm’.

• Something in the body needs to be amended hormone secreted from endocrine tissue travels to target tissue target response deals with situation, levels rise, etc. and shuts down further hormone secretion from endocrine tissue.

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.

Feedback Mechanisms: Positive

• The goal is to bring about ‘change’

• Endocrine tissue secretes hormone hormone impacts target tissue, elicits response causes greater production of original endocrine tissue

Fig. 45-16

Suckling

Pathway

Stimulus

Hypothalamus/posterior pituitary

Po

siti

ve

feed

bac

k

Example

Sensoryneuron

Neurosecretorycell

Bloodvessel

Posterior pituitarysecretes oxytocin ( )

Targetcells

Response

Smooth muscle inbreasts

Milk release

+

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

A few hormones…

and a few more…

Let’s simplify a bit…Chemical Classes of Hormones

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

Protein (or peptide) Hormones

• Made from proteins (hydrophilic)• 2 categories:

– Monoamines-made from one amino acid (lots of neurotransmitters, such as epinephrine)

– Polypeptides-made from multiple amino acids. Examples: Growth Hormone, Insulin

• Bind to membrane-bound receptors, use intracellular second messengers for response

• Can bring about a quick response• Secreted from:

– Pituitary– Pancreas– Parathyroid

Steroid Hormones

• Made from lipids• All are derived from cholesterol• Made within:

a. Gonads (testosterone, estrogen)b. Adrenals (cortisol, aldosterone)c. Brain (???)

• Bind to intracellular receptors• Influence gene formation• Impacts:

– Metabolism– Gamete formation– Stress response– Growth– Sex characteristics– Behavior

Coordination of Endocrine and Nervous Systems in Vertebrates

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

• It turns neural input into hormonal output through neurohormone secretions.

• Examples:• Gonadotropin releasing hormone (GnRH)

• Thyrotropin releasing hormone (TRH)

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

• Together, these structures regulate lots of hormonal processes.

Fig. 45-14

Spinal cord

Posteriorpituitary

Cerebellum

Pinealgland

Anteriorpituitary

Hypothalamus

Pituitarygland

Hypothalamus

Thalamus

Cerebrum

• The anterior pituitary makes and releases peptide hormones into the bloodstream under regulation of the hypothalamus.

• The anterior pituitary releases a new hormone in response to having received one by the hypothalamus.• These hormones impact a variety of targets.• Examples:

• Follicle stimulating hormone (FSH)• Luteinizing hormone (LH)• Adrenocorticotropic hormone (ACTH)

Anterior Pituitary

Posterior Pituitary Hormones• The posterior pituitary stores and secretes hormones that are made in the hypothalamus. These are neurohormones.

• Two hormones released from the posterior pituitary act directly on nonendocrine tissues.– Oxytocin (OT) induces uterine contractions and the release of milk– Antidiuretic hormone (ADH) enhances water reabsorption in the kidneys

Fig. 45-15

Posteriorpituitary

Anteriorpituitary

Neurosecretorycells of thehypothalamus

Hypothalamus

Axon

HORMONE OxytocinADH

Kidney tubulesTARGET Mammary glands,uterine muscles

Endocrine Gland What it does…Pineal gland Serves as biological clockThyroid Regulates metabolismParathyroid Calcium regulationAdrenals Stress coping, ion regulationPancreas (certain cells) Glucose regulationGonads Gamete formation, behavior

Plus many, many, many more…..

Some examples:

A practical application:Diabetes mellitus

• Diabetes mellitus is perhaps the best-known endocrine disorder.

• It is caused by a deficiency of insulin (Type I) or a decreased response to insulin in target tissues (Type II).

– Type I = usually genetic

– Type II = lifestyle induced, some genetic influence

• It is marked by elevated blood glucose levels.

– Used to be assessed through urine tasting (yuck!)

Insulin and Glucagon: Control of Blood Glucose

• Diabetes results in the inability to effectively regulate glucose levels.

• Insulin and glucagon are antagonistic hormones that help maintain glucose homeostasis.

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

Target Tissues for Insulin and Glucagon

• 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

Fig. 45-12-5

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.

STIMULUS:Blood glucose level

rises.

Beta cells ofpancreasrelease insulininto the blood.

Liver takesup glucoseand stores itas glycogen.

Blood glucoselevel declines.

Body cellstake up moreglucose.

Insulin

Other Applications:

Gamete Production

Secondary Sex Characteristics

Birth Control

Aggression