Hormones

Napoleon Cybulski – discovererof adrenaline”, 1895)

Ernest Starling – introducedthe term ’hormone’ (1905), discovered secretin

Hormon (gr. hormao)

Types of intercellular communication

• Autocrine

• Paracrine

• Endocrine

• Synapses

• Slot connections (nexus)

Systems of Internal Communication

– the nervous system

– the endocrine system

Systems of Internal Communication

• The nervous system conveys high-speed electrical

signals along specialized cells called neurons.

• The endocrine system, made up of endocrine glands,

secretes hormones that coordinate slower but longer-

acting responses to stimuli.

Hormones

• A hormone is a chemical signal that is secreted into the

circulatory system and communicates regulatory

messages within the body.

• Hormones may reach all parts of the body, but only

certain types of cells, target cells, are equipped to

respond.

Hormones

Advantages of using chemical messengers:

– Chemical molecules can spread to all tissues through the blood.

– Chemical signals can persist longer than electrical ones.

– Many different kinds of chemicals can act as hormones; different

hormones can target different tissues.

Hormone Action

• Secretion into the bloodstream by specialized cells

arranged in glands

• A specific biological effect occurs when hormone

combines with a receptor on the target cell

• Within 1 min after the secretion, hormon is throughout

the whole body

Glands

• Many hormones are secreted by ductless endocrine glands.

– Obtain raw materials from and secrete hormones directly into the bloodstream

• Exocrine glands have ducts for discharging secretions onto a free surface.– Sweat glands, salivary glands, enzyme-secreting glands in the

digestive tract

Hormone action

• All hormones act on cells by way of their ‘receptors’.

• Each hormone has its own receptor to which it binds,

matching rather like a lock and key. This is why

hormones circulating throughout the body in the blood

may leave capillaries to enter the extracellular fluid of

many tissues, but act only on those cells which possess

the appropriate receptor.

The role of receptors in hormone action

Hormone classification

• Peptide hormones

• Amino acid-derived hormones (thyroid hormones,

biogenic amines)

• Cholesterol-derived hormones (adrenal hormones)

• Fat-soluble hormones

• Water-soluble hormones

• Proteins and peptides cannot enter the cell and therefore

they act via cell membrane receptors, producing their

effects by ‘second messengers’, which are activated in

the cell as soon as the hormone binds to the receptor.

Thus peptide hormones can produce quite rapid

responses.

• Steroid and thyroid hormones, by contrast, can enter the

cell and bind to intracellular receptors, producing their

effects by stimulating the production of new proteins.

There is therefore a relatively long lag period before the

response to these hormones is seen.

Function of Receptor

• pick up signals which cell is interested in

• intensify the weak signals

• translate the language of hormones into language

understandable to cell

The impact of the lipophilic properties on

hormones actionWater-soluble

hormone

Fat-soluble

hormone

secondary

messenger

Effects of hormones action

• metabolic changes in a cell (eg. increase of glucose

uptake in response to insulin)

• stimulation of cell division (eg. growth hormone)

• changes gene expression (stimulation or inhibition

production of specific protein products)

Mechanism of hormone action

PROTEIN

PRODUCT

A hormone-receptor

complex can be

transcription factor of

particular genes

Membrane-Bound Receptors• Many hormones are too

large, or too polar, to pass through plasma membranes.

– Bind to transmembrane proteins that act as receptor sites on target cell membranes.

• Hormone is first messenger.

• Causes activation of a second messenger in the cytoplasm.

– Ca2+

– cAMP

– triphosphate (IP3) and diacylglycerol (DAG)

Nuclear Receptors

• Steroid hormones are lipid soluble molecules that bind to hormone receptors in the cytoplasm of the target cell.

– Site of activity is the nucleus.

• Steroids are manufactured from cholesterol.

• Estrogen, progesterone, testosterone, cortisol.

Nuclear Receptors

• Thyroid hormones

also act through

nuclear receptors.

– Binds to

transmembrane

protein that uses

ATP to move it into

the cell.

Control Pathways and Feedback Loops

• A common feature of control pathways is a feedback loop connecting the response to the initial stimulus.

• Negative feedbackregulates many hormonal pathways involved in homeostasis.

The hypothalamic–pituitary–

adrenal axis (HPA axis or

HTPA axis), also known as

the limbic–hypothalamic–

pituitary–adrenal axis (LHPA

axis), is a complex set of direct

influences and feedback

interactions among three

endocrine glands: the

hypothalamus, the pituitary

gland (a pea-shaped structure

located below the

hypothalamus), and the

adrenal (also called

"suprarenal") glands (small,

conical organs on top of the

kidneys).

• The hypothalamus regulates the

neuroendocrine system, maintaining

homeostasis in the body.

– The hypothalamus can use motor

nerves to send short-lived electrical

messages or hormones to send

chemical messages with a longer

duration.

The hypothalamus

Oxytocin and vasopressin – produced by the hypothalamus

and stored and secreted into the bloodstream from the

posterior pituitary gland

Releasing hormones (factors) or liberins

Inhibiting hormones (factors) or statins

The Chain of Command

• The hypothalamus produces different

“releasing”/”inhibiting” hormones that

travel to the pituitary gland.

• Each releasing/ inhibiting hormone

stimulates or inhibites the pituitary to

release a corresponding hormone which

travels to an endocrine gland and causes

it to start producing a particular endocrine

hormone.

Liberins/statins

Hypothalamic releasing

hormone

Effect on pituitary

Corticotropin releasing hormone

(CRH)

Stimulates ACTH secretion

Thyrotropin releasing hormone

(TRH)

Stimulates TSH and Prolactin

secretion

Growth hormone releasing

hormone (GHRH)

Stimulates GH secretion

Somatostatin Inhibits GH (and other

hormone) secretion

Gonadotropin releasing

hormone (GnRH) a.k.a LHRH

Stimulates LH and FSH

secretion

Prolactin releasing hormone

(PRH)

Stimulates PRL secretion

Prolactin inhibiting hormone

(dopamine)

Inhibits PRL secretion

Hypothalamus

Anterior pituitary Posterior pituitary

Thyrotropin

ACTH

Somatotropin

LH

FSH

Prolactin

Vasopressin

Oxytocin

Thyroid

Adrenal

CortexAdrenal

MedullaPancreas Ovary Testis

Muscles

liver Tissues

Liver,

muscles

Estradiol TestosteroneInsulin,

glucagon,

somatostatin

T3, T4Cortisol

aldosterone

Mammary

glands

Reproductive

organs

Epinephrine

Releasing

hormones

Nervous

The Pituitary

• The pituitary gland

is located below the

hypothalamus.

• Nine major hormones

are produced here.

• These hormones act

primarily to influence

other endocrine

glands.

Pituitary

Pro-opiomelanocortin (POMC) hormones

Follicle stimulating hormone (FSH)

Luteinizing hormone (LH)

Somatotropin (GH)

Prolactin (PRL)

Thyrotropin (TRH)

Liberins/Statins

Vasopressin (ADH)

Oxytocin

Peptide hormones

The Pituitary

• The posterior lobe of the pituitary regulates water

conservation, milk letdown, and uterine contraction in

women.

• The anterior lobe regulates the other endocrine glands.

The Anterior Pituitary

• Thyroid stimulating hormone (TSH) – stimulates the thyroid gland to produce thyroxine which stimulates oxidative respiration.

• Luteinizing hormone (LH) plays an important role in the menstrual cycle. It also stimulates the production of testosterone in males.

The Anterior Pituitary

• Follicle-stimulating hormone (FSH) – plays an important role in the menstrual cycle. In males, it causes the testes to produce a hormone that regulates sperm production.

• Adrenocorticotropic hormone (ACTH) –stimulates the adrenal gland to produce steroid hormones. Some regulate glucose production, others balance sodium & potassium in the blood.

The Anterior Pituitary

• Growth hormone (GH) – stimulates the growth of

muscle and bone.

• Prolactin – stimulates milk production.

The Posterior Pituitary

• Antidiuretic hormone (ADH) regulates the kidney’s retention of water.

• Oxytocin initiates uterine contraction during childbirth and milk release in mothers.

• These hormones are actually synthesized in the hypothalamus and stored in the posterior pituitary.

Biological Clocks

• The pineal gland is

located in the brain

of most vertebrates.

– Evolved from a light

sensitive “third eye”.

– Primitive fish &

some reptiles still

have a third eye.

Biological Clocks

• In other vertebrates it functions as an endocrine gland secreting melatonin.

• Melatonin controls color change in amphibians & reptiles.

• Release of melatonin is controlled by light/dark cycles.

• The primary functions of melatonin appear to be modulation of sleep patterns in both circadian and seasonal cycles– Circadian rhythms – 24 hours long.

The thyroid gland

- The thyroid gland produces three hormones in response to TSH release by

thyrotroph cells of the anterior pituitary:

1) Triiodothyronine (T3) - made in follicle

2) Thyroxine (T4) - made in follicle

T3 and T4 are dependent on iodine for synthesis

T4 is the more prevalent in humans (98% of circulating iodinated thyroid hormone)

T3 and T4 regulate body growth and metabolism, and are important in development and

maturation of the brain and nervous system

3) Calcitonin - made by C cells

- decreases blood calcium levels and blood phosphate levels (by helping them get

deposited in bone, and by stimulating excretion of them by kidneys)

The Thyroid

• The hypothalamus

and anterior pituitary

control the secretion

of thyroid hormones

through two negative

feedback loops.

• TRH- thyrotropin-releasing

hormone

• TSH - thyroid-stimulating hormone

• Triiodothyronine (T3)

• Thyroxine (T4)

thyrotropin-releasing hormonethyrotropin-releasing hormone

The Thyroid• The thyroid hormones

play crucial roles in

stimulating

metabolism and

influencing

development and

maturation.

Thyroid hormones

T4

T3

TSH

Thyroid hormones

T4

T3 ↓TSH

↑T3

↑T4

Graves-Basedow disease

Thyroid hormones

T4

T3 ↑TSH

↓T3

↓T4

TSH

Hashimoto disease

The Parathyroids

• The parathyroid glands are

four small glands attached

to the thyroid.

• The hormone they produce

is parathyroid hormone

(PTH) which regulates the

level of calcium in the blood.

– Essential that calcium is

kept within narrow limits

for muscle contraction,

including the heart.

Calcium Homeostasis

• Two antagonistic

hormones,

parathyroid

hormone (PTH) and

calcitonin, play the

major role in calcium

(Ca2+) homeostasis in

mammals.

Calcium Homeostasis

• Calcitonin, secreted by the thyroid gland,

stimulates Ca2+ deposition in the bones and

secretion by the kidneys, thus lowering blood

Ca2+ levels.

• PTH, secreted by the parathyroid glands, has

the opposite effects on the bones and kidneys,

and raises Ca2+ levels.

– Also has an indirect effect, stimulating the kidneys to

produce activate vitamin D, which promotes intestinal

uptake of Ca2+ from food.

The Adrenals

• Mammals have an adrenal gland above each kidney.

– Adrenal medulla is the inner core which produces

adrenaline (epinephrine) and norepinephrine.

– Adrenal cortex is the outer shell that produces the

steroid hormones cortisol and aldosterone.

The adrenal glandsAdrenal medulla (catecholamines):

• epinephrine & norepinephrine - increase basal

metabolic rate (blood glucose and pressure)

Adrenal cortex (corticoids):

• glucocorticoids (corticosterone, cortisol,

hydrocortisone) – inhibit incorporation of amino

acids into protein muscles, stimulate formation

and storage of glycogen, help maintain normal

blood sugar level

• mineralocorticoids (aldosterone,

deoxycorticosterone) – regulate metabolism of

Na+ and K+

• sex hormones (especially androstenedione) –

regulate facial and body hair

Adrenal Medulla

• The adrenal medulla releases adrenalin (epinephrine)

and norepinephrine in times of stress.

– Identical to the effects of the sympathetic nervous system, but

longer lasting.

• Accelerated heartbeat, increased blood pressure, higher levels of

blood sugar and increased blood flow to heart and lungs.

Adrenal Cortex

• The adrenal cortex produces the steroid hormone

cortisol (hydrocortisone).

– Reduces inflammation.

• Synthetic derivatives such as prednisone are used as anti-

inflammatory agents.

– Stimulates carbohydrate metabolism.

Adrenal Cortex

• The adrenal cortex also produces aldosterone.

• Aldosterone acts in the kidney to promote the uptake of sodium & other salts from the urine.– These salts are important in nerve conduction.

• Aldosterone and PTH are the only two hormones essential for survival.

The Pancreas

• The pancreas is located

behind the stomach and

is connected to the small

intestine by a small tube.

• It secretes digestive

enzymes into the

digestive tract (exocrine

function).

• Endocrine function –

production of insulin

and glucagon.

The endocrine cells of the pancreas

exist in islets of tissue that are

surrounded by exocrine cells.

1. Islets of Langerhans

• Alpha cells:

- glucagon - raises blood glucose levels

• Beta cells:

- insulin - lowers blood glucose levels

2. Other cells (delta cells) of the

pancreas produce somatostatin, SS,

SOM) – lowers secretion of insulin

and glucagon

The pancreas

insulin:

- stimulates uptake of glucose (and amino acids) by muscle

and liver cells

- inhibits production of glucose in liver (gluconeogenesis,

glycogenolysis)

- stimulates incorporation of fatty acids in fats

- stimulates protein synthesis in muscle and liver

glucagon:

- stimulates production of glucose in liver (gluconeogenesis,

glycogenolysis)

- stimulates lipolysis (breakdown of fats to free fatty acids +

glycerol)

Note: glucagon and insulin work in opposition,

and their combined effects control blood glucose

Prevents hypoglycemia

Prevents hyperglycemia

Diabetes

• Diabetes mellitus, perhaps the best-known endocrine

disorder, is caused by a deficiency of insulin or a

decreased response to insulin in target tissues.

– Marked by elevated blood glucose levels.

Diabetes

• Type I diabetes mellitus (insulin-dependent

diabetes) is an autoimmune disorder in which

the immune system destroys the beta cells of

the pancreas.

• Type II diabetes mellitus (non-insulin-dependent

diabetes) is characterized either by a deficiency

of insulin or, more commonly, by reduced

responsiveness of target cells due to some

change in insulin receptors.

The gonads

Steroid hormones: precursor is cholesterol

• Testes:

Androgens (testosterone, dihydrotestosterone) – stimulate development and

maintenance of male primary and secondary sexual characteristics and

behavior

• Ovaries:

Estrogens (estradiol, estrone, etc) - stimulate development and maintenance

of female secondary sexual characteristics and behavior

Progestins (progesterone) - stimulate female secondary sexual

characteristics and behavior, maintain pregnancy

Thank you for your

attention!!!