Endocrine system1. General data on endocrine glands

2. Morphofunctional characteristics

of the endocrine glands

a) Pituitary gland

b) Epiphysis

c) Thyroid gland

d) Parathyroid glands

e) Thymus

f) Adrenal glands

g) Pancreas

h) gonads

3. Organogenesis of the endocrine

system

Lecturer: PhD, professor Tamara

Hacina

Characteristics of the endocrine

system

•The endocrine system functions in the regulation

of body activities.

•It acts through chemical messengers called

hormones that influence growth, development,

metabolic activities.

•Its action is measured in minutes, hours, or weeks

& is more generalized than the action of the

nervous system.

The endocrine system• The endocrine system comprises a group of

ductless glands that secrete chemical messenger substances, called hormones, into the bloodstream.

• Hormones are responsible for the long-term regulation of many bodily functions.

• The endocrine system includes the pituitary, thyroid, parathyroid, thymus and adrenalglands, and the pancreas and gonads (ovaries and testes).

Common features of the endocrine

glands

• Superior blood-supply: fenestrated

capillaries,on at least one side

• Ductless glands

• Cells organized in “chunks”: blocks,

islands, plates, cords

• Epithelial in origin (an or two

exceptions)

• Polihedral cells with round nucleus

• Plentifull organelle content (indicates

synthesis)

• The endocrine system acts with nervous system to

coordinate the body's activities.

• Both systems enable cells to communicate with others by

using chemical messengers.

• The endocrine system uses chemical messengers

called hormones that are transported by the circulatory

system (blood). They act on target cells that may be

anywhere in the body.

• The endocrine system is slower than the nervous system

because hormones must travel through the circulatory

system to reach their target.

• Target cells have receptors that are specific to the

signaling molecules. The binding of hormones to the

receptors on or within the target cell produces a

response by the target cell.

HormonesHormones are:

chemical messengers

mostly proteins, amines

(small molecules derived

from amino acids) or

steroids

secreted by endocrine

glands (glands without

ducts)

carried in bloodstream

to target organs

change the way in which

cells function

target specific

Groups of hormones :

1. Amono acid derivatives:

epinephrine, norepinephrine,

thyroxine

2. Small peptides: encephalin,

vasopressin, TRH

3. Proteins: nerve growth factor,

insulin, parathormone, TSH, EGF

4. Steroids: cortisol, progesterone,

testosterone, estradial.

Chemical Classificaton of Hormones

• Steroid Hormones:

– Lipid soluble

– Diffuse through cell

membranes

– Endocrine organs

• Adrenal cortex

• Ovaries

• Testes

• Placenta

Receptors for steroid

hormones are found in

the cell’s cytoplasm or

in its nucleus

• Nonsteroid Hormones:

– Not lipid soluble

– Received by receptors

external to the cell

membrane

– Endocrine organs

• Thyroid gland

• Parathyroid gland

• Adrenal medulla

• Pituitary gland

• pancreas

Receptors for nonsteroid

hormones are located on the

cell membrane

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Mechanisms of

hormone

release

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

(b) Neural: stimulation by nerves

(c) Hormonal: stimulation received from other hormones

Hypothalamus

Pituitary gland (hypophysis)

Pineal body

The endocrine and

nervous systems are so

closely associated that

they are collectively

called the neuroendocrine

system.

The main control center is

the hypothalamus, also

known as the “master

switchboard”.

Suspended from the

hypothalamus by a stalk

is the pituitary gland.

The hypothalamus sends

messages to the pituitary

gland, in turn, releases

hormones that regulate

body functions.

The Pineal Gland

Pineal GlandThe pineal gland was called the "third eye" by ancient people. It was

thought to have mystical powers.

The pineal does contain a complete map of the visual field of the eyes,

and it plays several significant roles in human functioning.

It is the center for the production of the hormone melatonin.

It regulates daily body rhythms, most notably the day/night cycle,

prevents jet lag, is implicated in seasonal affective disorder, coordinates

fertility, and allows for deep restful sleep patterns.

The pineal gland or in its Latin and anatomical name "epiphysis

cerebri", is a tiny bean-size brain organ or "gland" which is connected

to the brain and nervous systems through a complex network of

bidirectional links.

The "pineal master gland" acts as a true "director of the hormonal

orchestra" in the course of growth, puberty, fertility and aging.

The Pineal Gland• At the end of a short stalk on the roof of the diencephalon

• Pinealocytes with dense calcium particles

• Can be seen on x-ray (because of Ca++)

• Melatonin helps regulate the cardium rhythm

– The biological clock of the diurnal (night/day) rhythm

– Complicated feedback via retina’s visual input

Why is the Hypothalamus so

Important?• Secretes

regulatory

homones

– RH

– RIH

• "Directs"

pituitary

Hypothalamus (general)

• Connection to pituitary:

– Neuronal to POSTERIOR

PITUITARY

– Endocrine to ANTERIOR

PITUITARY

• RH = Pituitary

releasing hormones

• RIH = Pituitary

release inhibiting

hormones

Neurosecretory Cells

1. Specialized neurons

– Synthesize and

secrete hormones

2. Extend from

HYPOTHALAMUS

to POSTERIOR

PITUITARY

Neurosecretory cells in Hypothalamus

• Nuclei synthesize and

secrete hormones

• Neuronal connection to

POSTERIOR pituitary

• Antidiuretic Hormone

(ADH), Oxytocin

Posterior Pituitary Hormones• Manufactured in

Hypothalamus, released from Post. Pit.

• Oxytocin

– Target = smooth ms. Uterus and Breast (&brain)

– Function = labor and delivery, milk ejection,(pair bonding)

• ADH (Vasopressin AVP)

– Target = kidneys

– Function = water reabsorption

Pituitary

Gland

The pituitary gland, which is located in the center of the skull, just

behind the bridge of the nose, is about the size of a pea.

It is an important link between the nervous system and the

endocrine system and releases many hormones which affect growth,

sexual development, metabolism and the system of reproduction.

The "hypothalamus" is a tiny cluster of brain cells just above the

pituitary gland, which transmits messages from the body to the

brain.

The pituitary gland has two distinct parts, the anterior and the

posterior lobes, each of which releases different hormones which

affect bone growth and regulate activity in other glands.

This gland was once believed to be the main controlling gland of the

body, but we now know that, it is subservient to a master gland

called the hypothalamus, which is the needed link between the

pituitary gland and the brain.

This "master gland" is really a way station between the body and

the brain and sorts out messages going to and from the brain.

It responds to the body through the pituitary gland, which is

suspended just below it.

It sometimes replies by nerve impulses and sometimes with needed

hormones. The pituitary gland then makes hormones of its own in

answer to the body's needs.

Pituitary gland

MASTER GLAND

• Anterior and

posterior portions

• Posterior

connected to

hypothalamus by

infundibulum

• Anterior

connected via

blood stream

The pituitary gland is:• a pea-sized structure located at the base of the

brain.

• an extension of the hypothalamus.

• consists of an anterior lobe and a posterior lobe.

• produces hormones that control other glands and

many body functions.

Releasing hormones

(factors) of hypothalamus

Secreted like neurotransmitters from neuronal axons into capillaries and veins to anterior pituitary (adenohypophysis)

TRH (thyroid releasing hormone) -turns on TSH

CRH (corticotropin releasing hormone)- turns on ACTH

GnRH (gonadotropin releasing hormone) - turns on FSH and LH

PRF (prolactin releasing hormone) -turns on PR

GHRH (growth hormone releasing hormone) - turns on GH

Inhibiting hormones of hypothalmus

PIF (prolactin inhibiting factor) -----turns off PRL

GH (growth hormone) inhibiting hormone ---turns off GH

The hypothalamus controls secretion

of hormones which in their turn control

the secretion of hormones by the thyroid

gland, the adrenal cortex and gonads:

in this way the brain controls these

endocrine glands

Pituitary______(hypophysis)

Hypothalamus____

From the

posterior

pituitary

(neuro-

hypophysis)

• ADH (antidiuretic hormone or vasopressin) stimulates the kidneys to

reclaim more water from the urine, raises blood pressure.

• Oxytocin prompts contraction of smooth muscle in reproductive tracts,

in females initiating labor and ejection of milk from breasts.

Two divisions:

• Anterior pituitary(adenohypophysis)

• Posterior pituitary(neurohypophysis)

Sits in hypophyseal fossa: depression in sella turcica

of sphenoid bone

Pituitary secretes 9 hormones

The Pituitary

1. TSH

2. ACTH

3. FSH

4. LH

5. GH

6. PRL

7. MSH

8. ADH (antidiuretic hormone), or vasopressin

9. Oxytocin

_________________________________________________________________

The first four are “tropic”

hormones, they regulate the

function of other hormones________

The pituitary gland

ANTERIOR

LOBE

POSTERIOR

LOBE

Thyroid stimulating

hormone

Adrenocorticotropic

hormone

Gonadotropic

hormones (FSH &

LH)

Growth hormone

Prolactin

Antidiuretic

hormone

Oxytocin

Anterior pituitary gland

Gland Principle hormones Action

Anterior

pituitary

Thyroid stimulating hormone

(TSH)

Regulates thyroid gland

Adrenocortico tropic hormone

(ACTH)

Regulates adrenal cortex

Gonadotropic hormones

Follicle stimulating

hormone (FSH)

Luteinising hormone (LH)

Regulates gonads

Growth hormone (GH) Regulates growth in children

Prolactin Regulates milk production

Posterior pituitary gland

Gland Principle

hormones

Action

Posterior pituitary

gland

Antidiuretic hormone

(ADH)

Regulates water

reabsorption from

kidneys

Oxytocin Allows milk

letdown/suckling reflex

Initiates labor

Maternal behaviour

Hypersecretion of pituitary gland

Hyposecretion of the pituitary gland

Simmonds disease, also known as anterior

pituitary hypofunction, is lack secretion of

pituitary hormones, lesions of pituitary or

hypothalamus involve the endocrine function in

pituitary gland. when the pituitary had

destroyed, may produce the performance of

endocrine gland hypofunction, the mainly

involvement of the gland is sex gland, thyroid

and adrenal cortex.

Thyroid GlandThe thyroid gland is shaped like a butterfly

and usually weighs less than one ounce.

The thyroid cartilage covers the larynx and

produces the prominence on the neck known

as the "Adam's Apple".

The thyroid gland controls the rate at which

the body produces energy from nutrients.

If the body does not get enough iodine, the

thyroid gland cannot produce a proper

amount of hormones for this conversion

process.

The result can be a goiter, an enlargement of

the thyroid gland.

In some parts of the world, iodine is so

scarce that most of the population have

goiters.

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• Thyroid is composed of spherical follicles

– Follicle cells: produce thyroglobulin, the precursor of

thryoid hormone (thyroxin)

– Colloid lumen is of thyroglobulin

– Parafollicular “C” cells: produce calcitonin

Action of

thyroid

hormons

Hypersecretion of the

thyroid glands at adults

Exophthalmos of

Grave’s disease

Enlarged thyroid

(goiter) from

iodine deficiency

1. Cretinism (in infancy) – dwarfs, retarded

- hypothyroidism

2. Myxedema (in adults) – swelling, slowness

- hypothyroidism

3. Regular Goiter – too little iodine yields

pituitary response

4. Toxic Goiter – TSH overproduction

Malfunctions of Thyroid gland

Hyposecretion of the

thyroid gland at

adults

Hyposecretion of the thyroid gland in childhood

Hyposecretion of the thyroid gland

Parathyroid Glands• There are four

parathyroid glands, which are located behind the thyroid.

• The sole purpose of the gland is to regulate the calcium level in our bodies within a very narrow range in which our muscular and nervous systems can function properly.

Functions of

thyroid &

parathyroid

hormons

Thyroid & parathyroid glands

Gland Principle

hormones

Action

Thyroid Thyroxine Stimulates

metabolism/releases

glucose

Calcitonin Lowers blood calcium

Parathyroid Parathyroid hormone Raises calcium levels

Cronical

hypopara-

thyroidism

Adrenal

Gland

53

Adrenal (suprarenal) glands(“suprarenal” means on top of the kidney)

• Each is really two endocrine glands

– Adrenal cortex (outer)

– Adrenal medulla (inner)

• Unrelated chemicals but all help with extreme situations

Adrenal glandGland Principle

hormones

Action

Adrenal cortex Mineralocorticoids e.g.

aldosterone

Sodium metabolism

Glucocorticoids e.g.

cortisol

Stress response/glucose

metabolism

Gonadocorticoids e.g.

testosterone

Secondary sexual

characteristics

Adrenal medulla Adrenaline

(epinephrine) Fight or flight response

Noradrenaline

(norepinephrine)

Microscopic structure of adrenal gland

Adrenal GlandAdrenal cortex

Secretes lipid-based steroid

hormones, called

“corticosteroids”

MINERALOCORTICOIDS

Aldosterone is the main one

GLUCOCORTICOIDS

Cortisol (hydrocortisone)

is the main one

Adrenal medulla

Secretes epinephrine and

norepinephrine

Aldosterone, the main

mineralocorticoid

• Secreted by adrenal cortex in response to a decline in either blood volume or blood pressure (e.g. severe hemorrhage)

– Is terminal hormone in renin-angiotensin mechanism

• Prompts distal and collecting tubules in kidney to reabsorb more sodium

– Water passively follows

– Blood volume thus increases

Cortisol, the most important glucocorticoid

• It is essential for life

• Helps the body deal with stressful situations within minutes

– Physical: trauma, surgery, exercise

– Psychological: anxiety, depression, crowding

– Physiological: fasting, hypoglycemia, fever, infection

• Regulates or supports a variety of important cardiovascular,

metabolic, immunologic, and homeostatic functions including

water balance

People with adrenal insufficiency: these stresses can cause

hypotension, shock and death: must give glucocorticoids, eg for

surgery or if have infection, etc.

Adrenal medulla

• Part of autonomic nervous system

• Spherical chromaffin cells are modified postganglionic sympathetic neurons

– Secrete epinephrine and norepinephrine

– Amine hormones

– Fight, flight, fright

• Vesicles store the hormones

Pathology of

Adrenal gland

Cushing’s syndrome:

Usually caused by an

ACTH-secreting

pituitary tumor, rarely

by tumor of adrenal

cortex, iatrogenic

Addison’s

disease

Hyposecretion

(under

secretion) of

adrenal cortex

Usually involves

cortisol and

aldosterone: low

blood glucose

and sodium,

severe

dehydration,

fatigue, loss of

appetite,

abdominal pain

Note the

generalised skin

pigmentation but

ispecially the

deposition in the

palmer skin, nails

& gums.

The pancreas

• Endocrine tissue in the pancreas (the islets of Langerhans) secrete hormones that regulate the blood sugar level.

Ilets of

Langerhans

Pancreas

Pancreas • The Pancreas has

two main

functions:

• to produce

pancreatic

endocrine

hormones, which

help regulate

many aspects of

our metabolism,

and

• to produce

pancreatic

digestive enzymes.

Located slightly behind the stomach

• Insulin: reduces blood glucose

– Facilitates glucose transport into the

cells

– Promotes glycogenesis

– Inhibits gluconeogenesis

• Glucagon: increases blood glucose

• When low plasma

glucose levels occur, the

catecholamines are

released to accelerate

lypolysis.

• Triglycerides are

reduced to free fatty

acids by lipase which is

activated by:

– Cortisol

– Epinephrine

– Norepinephrine

– Growth Hormone

• Glucose must not only be

delivered to the cells, it

must also be taken up by

them. That job relies on

insulin.

• Exercise may enhance

insulin’s binding to

receptors on the muscle

fiber.

• Up-regulation (receptors)

occurs with insulin after 4

weeks of exercise to

increase its sensitivity

(diabetic importance).

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The PancreasExocrine and endocrine

cells

• Acinar cells (forming

most of the pancreas)

– Exocrine function

– Secrete digestive

enzymes

• Islet cells (of

Langerhans)

– Endocrine function

ThymusThe thymus is a gland that forms part of the immune

system.

It is situated in the upper part of the chest, behind the

breastbone, and is made up of two lobes that join in front

of the trachea.

Each lobe is made of lymphoid tissue, consisting of tightly

packed white blood cells and fat.

The thymus enlarges from about the 12th week of

gestation until puberty, when it begins to shrink.

Its function is to transform lymphocytes (white blood cells

developed in the bone marrow) into T-cells (cells developed

in the thymus).

These cells are then transported to various lymph glands,

where they play an important part in fighting infections

and disease.

Swelling of lymph glands and fever are a signal that

immune cells are multiplying to fight off invaders of the

body: bacteria, fungi, viruses or parasites.

Gonads Female ovariesMale testes

Gland Principle hormones Action

Male gonads

The testes

Testosterone Male secondary sexual

characteristics

Female gonads

The ovaries

Oestrogen

(estrogen)

Progesterone

• Female secondary sexual

characteristics

• Development of the

endometrium

• Maintenance of endometrium

Testes

The scrotum is a sac that hangs under the penis and holds the testes.

It is divided internally into two halves by a membrane; each half containing a testis.

It has an outer layer of thin, wrinkled skin over a layer of tissue which contains muscle.

The testicle lies inside the scrotum and produces as many as 12 trillion sperm in a male's

lifetime, about 400 million of which are ejaculated in one average intercourse.

Each sperm takes about seventy-two days to mature and its maturity is overseen by a

complex interaction of hormones.

The scrotum has a built-in thermostat, which keeps the sperm at the correct temperature.

It may be surprising that the

testicles should lie in such a

vulnerable place, outside the body,

but it is too hot inside.

The sperm production needs a

temperature which is three to five

degrees below body temperature.

If it becomes too cool on the

outside, the scrotum will contract

to bring the testes closer the body

for warmth.

Ovaries

The

ovaries

produce a

female

hormone,

called

estrogen,

and store

female sex

cells, or

“ova.”

The Gonads (testes and ovaries) main source of the steroid sex hormones

• Testes– Interstitial cells secrete androgens

– Primary androgen is testosterone

• Maintains secondary sex characteristics

• Helps promote sperm formation

• Ovaries– Androgens secreted by thecal folliculi

• Directly converted to estrogens by follicular granulosa cells

– Granulosa cells also produce progesterone

– Corpus luteum also secretes estrogen and progesterone

Functions of

the gonads

Regulation of the ovarian

and menstrual cycles

• The ovarian cycle (the monthly sequence of changes that take place in the ovaries) is regulated by the pituitary hormones follicle stimulating hormone(FSH) and luteinising hormone (LH).

• The menstrual cycle (the monthly sequence of changes that take place in the uterus) is regulated by the ovarian hormones estrogen and progesterone.

• Both cycles are regulated by complex feedback processes.

Hormonal action on the female reproductive organs

Progesterone Luteinising

hormone (LH)

Estrogen Follicle

stimulating

hormone (FSH)

Ovarian hormone

(corpus luteum)

Target –

endometrium

Role –

maintenance of

endometrium

Predominant in

second part of

cycle

Anterior pituitary

hormone

Target – corpus

luteum

Roles – ovulation,

maintenance

of corpus

luteum

Predominant in

second part of

cycle

Ovarian hormone

(ovarian follicle)

Target –

endometrium

Role – repair of

endometrium after

menstruation

Predominant in

first part of cycle

Anterior pituitary

hormone

Target – ovarian

follicle

Role –

maturation of

ovarian

follicle

Predominant in

first part of

cycle

Hormonal control of ovarian/menstrual cycle

85

Endocrine cells in various organs continued

• The heart: atrial natriuretic peptide (ANP)

– Stimulates kidney to secrete more salt

– Thereby decreases excess blood volume, high BP and high blood sodium concentration

• GI tract & derivatives: Diffuse neuroendocrine system (DNES)

• The placenta secretes steroid and protein hormones

– Estrogens, progesterone

– CRH

– HCG

• The kidneys

– Juxtaglomerular cells secrete renin

• Renin indirectly signals adrenal cortex to secrete aldosterone

– Erythropoietin: signals bone marrow to increase RBC production

• The skin

– Modified cholesterol with uv exposure becomes Vitamin D precursor

– Vitamin D necessary for calcium metabolism: signals intestine to absorb CA++

Pathology• Pituitary

– Gigantism –too much GH in childhood

– Acromegaly – too much GH in adulthood

– Pituitary dwarfs – too little GH in childhood

– Diabetes insipidus - too much ADH

• Pancreas– Diabetes mellitus – one type of insulin (not enough)

• Thyroid– Hyperthyroidism, commonest is Grave’s disease (autoimmune)

– Hypothyroidism• In childhood leads to cretinism

• Endemic goiter from insufficient iodine in diet

• Adult hypothyroidism (myxedema): autoimmune

The end